Respiratory System Midterms PDF

MIDTERMS Respiratory System By : Marc Anthony Cueto MD Learning Objectives 1.To identify the different organs of respiration. 2.To locate in detail structure and landmarks of the different organs of respiration 3.To understand how the mechanism of breathing and gas exchange in the lungs wor...

MIDTERMS Respiratory System By : Marc Anthony Cueto MD Learning Objectives 1.To identify the different organs of respiration. 2.To locate in detail structure and landmarks of the different organs of respiration 3.To understand how the mechanism of breathing and gas exchange in the lungs work. 4.To relate the function of the system to clinical aspect. Respiratory System When the respiratory system is mentioned, people generally think of breathing, but breathing is only one of the activities of the respiratory system. The body cells need a continuous supply of oxygen for the metabolic processes that are necessary to maintain life. The respiratory system works with the circulatory system to provide this oxygen and to remove the waste products of metabolism. It also helps to regulate pH of the blood.  Respiration Respiration is the sequence of events that results in the exchange of oxygen and carbon dioxide between the atmosphere and the body cells. Every 3 to 5 seconds, nerve impulses stimulate the breathing process, or ventilation, which moves air through a series of passages into and out of the lungs. After this, there is an exchange of gases between the lungs and the blood. This is called external respiration. The blood transports the gases to and from the tissue cells. The exchange of gases between the blood and tissue cells is internal respiration. Finally, the cells utilize the oxygen for their specific activities: this is called cellular metabolism, or cellular respiration. Together, these activities constitute respiration. Organs of the Respiratory System Upper Lower 1.Nose 1.Trachea 2.Pharynx 2.Bronchus 3.Larynx 3.Lungs Upper Respiratory Tract Nose The nose consists of the external nose and the nasal cavity. The nasal septum divides both of these into right and left halves. External Nose The external nose consists of the surface and skeletal structures that result in the outward appearance of the nose and contribute to its numerous functions. The root is the region of the nose located between the eyebrows. The bridge is the part of the nose that connects the root to the rest of the nose. The dorsum nasi is the length of the nose. The apex is the tip of the nose. On either side of the apex, the nostrils are formed by the alae (singular = ala). An ala is a cartilaginous structure that forms the lateral side of each naris (plural = nares), or nostril opening. The philtrum is the concave surface that connects the apex of the nose to the upper lip.  Nares The nares are oval apertures on the inferior aspect of the external nose and are the anterior openings of the nasal cavities. They are held open by the surrounding alar cartilages and septal cartilage, and by the inferior nasal spine and adjacent margins of the maxillae. Although the nares are continuously open, they can be widened further by the action of the related muscles of facial expression (nasalis, depressor septi nasi, and levator labii superioris alaeque nasi muscles  Choanae The choanae are the oval-shaped openings between the nasal cavities and the nasopharynx. Unlike the nares, which have flexible borders of cartilage and soft tissues, the choanae are rigid openings completely surrounded by bone, and their margins are formed: inferiorly by the posterior border of the horizontal plate of the palatine bone, laterally by the posterior margin of the medial plate of the pterygoid process, and medially by the posterior border of the vomer. The roof of the choanae is formed: anteriorly by the ala of the vomer and the vaginal process of the medial plate of the pterygoid process, and posteriorly by the body of the sphenoid bone. Nasal Cavity The two nasal cavities are the uppermost parts of the respiratory tract and contain the olfactory receptors. They are elongated wedge-shaped spaces with a large inferior base and a narrow superior apex and are held open by a skeletal framework consisting mainly of bone and cartilage. The smaller anterior regions of the cavities are enclosed by the external nose, whereas the larger posterior regions are more central within the skull. The anterior apertures of the nasal cavities are the nares, which open onto the inferior surface of the nose. The posterior apertures are the choanae, which open into the nasopharynx. The nasal cavities are separated: from each other by a midline nasal septum, from the oral cavity below by the hard palate, and from the cranial cavity above by parts of the frontal, ethmoid, and sphenoid bones. Lateral to the nasal cavities are the orbits. Each nasal cavity has a floor, roof, medial wall, and lateral wall  Nasal Cavity Each nasal cavity consists of three general regions— the nasal vestibule, the respiratory region, and the olfactory region (Fig. 8.232): The nasal vestibule is a small dilated space just internal to the naris that is lined by skin and contains hair follicles. The respiratory region is the largest part of the nasal cavity, has a rich neurovascular supply, and is lined by respiratory epithelium composed mainly of ciliated and mucous cells. The olfactory region is small, is at the apex of each nasal cavity, is lined by olfactory epithelium, and contains the olfactory receptors. In addition to housing receptors for the sense of smell (olfaction), the nasal cavities adjust the temperature and humidity of respired air by the action of a rich blood supply, and trap and remove particulate matter from the airway by filtering the air through hair in the vestibule and by capturing foreign material in abundant mucus. The mucus normally is moved posteriorly by cilia on epithelial cells in the nasal cavities and is swallowed.  Nasal Cavity : Skeletal Framework Bones that contribute to the skeletal framework of the nasal cavities include: the unpaired ethmoid, sphenoid, frontal, and vomer bones, and the paired nasal, maxillary, palatine, and lacrimal bones and inferior conchae.  Nasal Cavity The nasal septum is formed by : 1. anteriorly by a portion of the septal cartilage (the flexible portion you can touch with your fingers) and 2. posteriorly by the perpendicular plate of the ethmoid bone (a cranial bone located just posterior to the nasal bones) and the 3. thin vomer bones (whose name refers to its plough shape). 4. Crest of the maxillary bone 5. Crest of the Palatine bone  Nasal Cavity : Lateral Wall The lateral wall is characterized by three curved shelves of bone (conchae), which are one above the other and project medially and inferiorly across the nasal cavity. The medial, anterior, and posterior margins of the conchae are free. The conchae divide each nasal cavity into four air channels : an inferior nasal meatus between the inferior concha and the nasal floor, a middle nasal meatus between the inferior and middle concha, a superior nasal meatus between the middle and superior concha, and a spheno-ethmoidal recess between the superior concha and the nasal roof. These conchae increase the surface area of contact between tissues of the lateral wall and the respired air.  Nasal Cavity : Medial Wall The medial wall of each nasal cavity is the mucosa-covered surface of the thin nasal septum, which is oriented vertically in the median sagittal plane and separates the right and left nasal cavities from each other. The nasal septum consists of: the septal nasal cartilage anteriorly, posteriorly, mainly the vomer and the perpendicular plate of the ethmoid bone, small contributions by the nasal bones where they meet in the midline, and the nasal spine of the frontal bone, and contributions by the nasal crests of the maxillary and palatine bones, rostrum of the sphenoid bone, and the incisor crest of the maxilla.  Nasal Cavity : Floor The floor of each nasal cavity is smooth, concave, and much wider than the roof. It consists of: soft tissues of the external nose, and the upper surface of the palatine process of the maxilla and the horizontal plate of the palatine bone, which together form the hard palate.  Nasal Cavity : Roof The roof of the nasal cavity is narrow and is highest in central regions where it is formed by the cribriform plate of the ethmoid bone. Anterior to the cribriform plate the roof slopes inferiorly to the nares and is formed by: the nasal spine of the frontal bone and the nasal bones, and the lateral processes of the septal cartilage and major alar cartilages of the external nose. Posteriorly, the roof of each cavity slopes inferiorly to the choana and is formed by: the anterior surface of the sphenoid bone, the ala of the vomer and adjacent sphenoidal process of the palatine bone, and the vaginal process of the medial plate of the pterygoid process.  Nasal Cavity : Innervation and Blood Supply Innervation of the nasal cavities is by three cranial nerves: Olfaction is carried by the olfactory nerve [I]. General sensation is carried by the trigeminal nerve [V], the anterior region by the ophthalmic nerve [V1], and the posterior region by the maxillary nerve [V2]. All glands are innervated by parasympathetic fibers in the facial nerve [VII] (greater petrosal nerve), which join branches of the maxillary nerve [V2] in the pterygopalatine fossa. Blood supply to the nasal cavities is by: terminal branches of the maxillary and facial arteries, which originate from the external carotid artery, and ethmoidal branches of the ophthalmic artery, which originates from the internal carotid artery. Muscles of the External Nose (Nasal Group)  Nasalis The largest and best developed of the muscles of the nasal group is the nasalis, which is active when the nares are flared. It consists of a transverse part (the compressor naris) and an alar part (the dilator naris): The transverse part of the nasalis compresses the nares – it originates from the maxilla and its fibers pass upward and medially to insert, along with fibers from the same muscle on the opposite side, into an aponeurosis across the dorsum of the nose. The alar part of the nasalis draws the alar cartilages downward and laterally, so opening the nares-it originates from the maxilla, below and medial to the transverse part, and inserts into the alar cartilage.  Nasalis ORIGIN : Transverse part : Maxilla just lateral to the nose Alar part : Maxilla over the lateral incisor INSERTION : Transverse part : Aponeurosis across dorsum of the nose with muscle fibers from the other side Alar part : Alar cartilage of the nose INNERVATION : Zygomatic and buccal branches of the Facial nerve (CN VII)  Nasalis ACTION : Tranverse part : compresses nasal aperture Alar part : Draws cartilage downward and laterally, opening nostril  Procerus The procerus is a small muscle superficial to the nasal bone and is active when an individual frowns. It arises from the nasal bone and the upper part of the lateral nasal cartilage and inserts into the skin over the lower part of the forehead between the eyebrows. It may be continuous with the frontal belly of the occipitofrontalis muscle of the scalp. The procerus draws the medial border of the eyebrows downward to produce transverse wrinkles over the bridge of the nose. The name procerus literally means prince (in Latin). This muscle is so-named because contraction of this muscle creates the facial expression of superiority that a prince would make.  Procerus ORIGIN : Nasal bone and upper part of the lateral nasal cartilage INSERTION : Skin of lower forehead between the eyebrows INNERVATION : Temporal and zygomatic branches of facial nerve Procerus ACTION : Draws down medial angle of eyebrows, producing transverse wrinkles over the bridge of the nose  Depressor septi nasi The final muscle in the nasal group is the depressor septi nasi, another muscle that assists in the widening of the nares. Its fibers arise from the maxilla above the central incisor tooth and ascend to insert into the lower part of the nasal septum. Pulls the nose inferiorly, so assisting the alar part of the nasalis in opening the nares.  Depressor septi nasi ORIGIN : Maxilla above middle incisor INSERTION : Mobile part of the nasal septum INNERVATION : Zygomatic and buccal branches of facial nerve  Depressor septi nasi ACTION : Depressor septi pulls the columella, the tip of the nose and the nasal septum downwards. It tenses the nasal septum at the start of nasal inspiration, and, with the alar part of nasalis, widens the nasal aperture as well as causing the nose to ‘dip’ when some people smile.  Levator labii superioris alaeque nasi Medial to the levator labii superioris Arises from the maxilla next to the nose Inserts into both the alar cartilage of the nose and skin of the upper lip It may assist in flaring the nares  Levator labii superioris alaeque nasi ORIGIN: Frontal process of maxilla INSERTION: Alar cartilage of nose and upper lip INNERVATION: Zygomatic and buccal branches of facial nerve  Levator labii superioris alaeque nasi ACTION: Raises upper lip and opens nostril Pharynx  Pharynx The pharynx is a musculofascial half-cylinder that links the oral and nasal cavities in the head to the larynx and esophagus in the neck. It is a common pathway for air and food. It is attached above to the base of the skull and is continuous below, approximately at the level of vertebra CVI, with the top of the esophagus. The walls of the pharynx are attached anteriorly to the margins of the nasal cavities, oral cavity, and larynx.  Pharynx Based on these anterior relationships the pharynx is subdivided into three regions, the nasopharynx, oropharynx, and laryngopharynx: the posterior apertures (choanae) of the nasal cavities open into the nasopharynx; the posterior opening of the oral cavity (oropharyngeal isthmus) opens into the oropharynx; the superior aperture of the larynx (laryngeal inlet) opens into the laryngopharynx.  Pharynx In addition to these openings, the pharyngeal cavity is related anteriorly to the posterior one-third of the tongue and to the posterior aspect of the larynx. The pharyngotympanic tubes open into the lateral walls of the nasopharynx. Lingual, pharyngeal, and palatine tonsils are on the deep surface of the pharyngeal walls. The pharynx is separated from the posteriorly positioned vertebral column by a thin retropharyngeal space containing loose connective tissue.  Pharynx Although the soft palate is generally considered as part of the roof of the oral cavity, it is also related to the pharynx. The soft palate is attached to the posterior margin of the hard palate and is a type of "flutter valve" that can: swing up (elevate) to close the pharyngeal isthmus, and seal off the nasopharynx from the oropharynx; swing down (depress) to close the oropharyngeal isthmus and seal off the oral cavity from the oropharynx. The pharyngeal wall is formed by skeletal muscles and by fascia. Gaps between the muscles are reinforced by the fascia and provide routes for structures to pass through the wall. Muscles of the Pharyngeal wall The muscles of the pharynx are organized into two groups based on the orientation of muscle fibers : The constrictor muscles have fibers oriented in a circular direction relative to the pharyngeal wall, The longitudinal muscles have fibers oriented vertically.  Constrictor muscles The three constrictor muscles on each side are major contributors to the structure of the pharyngeal wall and their names indicate their position-superior, middle, and inferior constrictor muscles. Posteriorly, the muscles from each side are joined together by the pharyngeal raphe. Anteriorly, these muscles attach to bones and ligaments related to the lateral margins of the nasal and oral cavities and the larynx.  Constrictor muscles They overlap each other in a fashion resembling the walls of three flower pots stacked one on the other. The inferior constrictors overlap the lower margins of the middle constrictors and, in the same way, the middle constrictors overlap the superior constrictors. Collectively, the muscles constrict or narrow the pharyngeal cavity. When the constrictor muscles contract sequentially from top to bottom, as in swallowing, they move a bolus of food through the pharynx and into the esophagus. All of the constrictors are innervated by the pharyngeal branch of the vagus nerve [X].  Longitudinal muscles of the Pharynx The three longitudinal muscles of the pharyngeal wall are named according to their origins : stylopharyngeus from the styloid process of the temporal bone, salpingopharyngeus from the cartilaginous part of the pharyngotympanic tube (salpinx is Greek for "tube"), and palatopharyngeus from the soft palate. From their sites of origin, these muscles descend and attach into the pharyngeal wall. The longitudinal muscles elevate the pharyngeal wall, or during swallowing, pull the pharyngeal wall up and over a bolus of food being moved through the pharynx and into the esophagus.  Fascia of the Pharyngeal wall The pharyngeal fascia is separated into two layers, which sandwich the pharyngeal muscles between them: a thin layer (buccopharyngeal fascia) coats the outside of the muscular part of the wall and is a component of the pretracheal layer of cervical fascia; a much thicker layer (pharyngobasilar fascia) lines the inner surface. The fascia reinforces the pharyngeal wall where muscle is deficient. This is particularly evident above the level of the superior constrictor where the pharyngeal wall is formed almost entirely of fascia. This part of the wall is reinforced externally by muscles of the soft palate (tensor and levator veli palatini).  Nasopharynx This lies above the soft palate and behind the nasal cavities. In the submucosa of the roof is a collection of lymphoid tissue called the pharyngeal tonsil sometimes referred to as the Adenoids (when enlarged). The pharyngeal isthmus is the opening in the floor between the soft palate and the posterior pharyngeal wall. On the lateral wall is the opening of the auditory tube, the elevated ridge of which is called the tubal elevation also referred to as the Torus tubarius. The pharyngeal recess is a depression in the pharyngeal wall behind the tubal elevation. The salpingopharyngeal fold is a vertical fold of mucous membrane covering the salpingopharyngeus muscle.  Oropharynx The oropharynx is posterior to the oral cavity, inferior to the level of the soft palate, and superior to the upper margin of the epiglottis. The palatoglossal folds (arches), one on each side, that cover the palatoglossal muscles, mark the boundary between the oral cavity and the oropharynx. The arched opening between the two folds is the oropharyngeal isthmus. Just posterior and medial to these folds are another pair of folds (arches), the palatopharyngeal folds, one on each side, that overlie the palatopharyngeus muscles. The anterior wall of the oropharynx inferior to the oropharyngeal isthmus is formed by the upper part of the posterior one-third or pharyngeal part of the tongue. Large collections of lymphoid tissue (the lingual tonsil) are in the mucosa covering this part of the tongue.  Oropharynx The palatine tonsils are on the lateral walls of the oropharynx. On each side, there is a large ovoid collection of lymphoid tissue in the mucosa lining the superior constrictor muscle and between the palatoglossal and palatopharyngeal arches. The palatine tonsils are visible through the oral cavity just posterior to the palatoglossal folds. When holding liquid or solids in the oral cavity : the oropharyngeal isthmus is closed by depression of the soft palate, elevation of the back of the tongue, and movement toward the midline of the palatoglossal and palatopharyngeal folds.  Oropharynx This allows a person to breathe while chewing or manipulating material in the oral cavity. On swallowing : the oropharyngeal isthmus is opened, the palate is elevated, the laryngeal cavity is closed, and the food or liquid is directed into the esophagus. A person cannot breathe and swallow at the same time because the airway is closed at two sites, the pharyngeal isthmus and the larynx.  Laryngopharynx The laryngopharynx extends from the superior margin of the epiglottis to the top of the esophagus at the level of vertebra CVI. The laryngeal inlet opens into the anterior wall of the laryngopharynx. Inferior to the laryngeal inlet, the anterior wall consists of the posterior aspect of the larynx. The cavity of the laryngopharynx is related anteriorly to a pair of mucosal pouches (valleculae), one on each side of the midline, between the base of the tongue and epiglottis. The valleculae are depressions formed between a midline mucosal fold and two lateral folds that connect the tongue to the epiglottis. There is another pair of mucosal recesses (piriform fossae) between the central part of the larynx and the more lateral lamina of the thyroid cartilage. The piriform fossae form channels that direct solids and liquids from the oral cavity around the raised laryngeal inlet and into the esophagus.  Vessels of the Pharynx : Arteries Arteries that supply upper parts of the pharynx include: the ascending pharyngeal artery; the ascending palatine and tonsillar branches of the facial artery; and numerous branches of the maxillary and the lingual arteries. All these vessels are from the external carotid artery. Arteries that supply the lower parts of the pharynx include pharyngeal branches from the inferior thyroid artery, which originates from the thyrocervical trunk of the subclavian artery. The major blood supply to the palatine tonsil is from the tonsillar branch of the facial artery, which penetrates the superior constrictor muscle. Vessels of the Pharynx : Veins Veins of the pharynx form a plexus, which drains superiorly into the pterygoid plexus in the infratemporal fossa, and inferiorly into the facial and internal jugular veins.  Lymphatics of the Pharynx Lymphatic vessels from the pharynx drain into the deep cervical nodes and include retropharyngeal (between nasopharynx and vertebral column), paratracheal, and infrahyoid nodes. The palatine tonsils drain through the pharyngeal wall into the jugulodigastric nodes in the region where the facial vein drains into the internal jugular vein (and inferior to the posterior belly of the digastric muscle).  Nerve supply of the Pharynx Motor and most sensory innervation (except for the nasal region) of the pharynx is mainly through branches of the vagus [X] and glossopharyngeal [IX] nerves, which form a plexus in the outer fascia of the pharyngeal wall. The pharyngeal plexus is formed by: the pharyngeal branch of the vagus nerve [X]; branches from the external laryngeal nerve from the superior laryngeal branch of the vagus nerve [X]; and pharyngeal branches of the glossopharyngeal nerve [IX].  Nerve supply of the Pharynx The pharyngeal branch of the vagus nerve [X] originates from the upper part of its inferior ganglion above the origin of the superior laryngeal nerve and is the major motor nerve of the pharynx, in addition to carrying sensory information from the laryngopharynx. All muscles of the pharynx are innervated by the vagus nerve [X] mainly through the pharyngeal plexus, except for the stylopharyngeus, which is innervated directly by a branch of the glossopharyngeal nerve [IX].  Nerve supply of the Pharynx Each subdivision of the pharynx has a different sensory innervation: the nasopharynx is innervated by a pharyngeal branch of the maxillary nerve [V2] that originates in the pterygopalatine fossa and passes through the palatovaginal canal in the sphenoid bone to reach the roof of the pharynx; the oropharynx is innervated by the glossopharyngeal nerve [IX] via the pharyngeal plexus; the laryngopharynx is innervated by the vagus nerve [X] via the pharyngeal plexus. Larynx  Larynx The larynx is a complex hollow structure located in the anterior midline region of the neck. It is anterior to the esophagus and at the level of the third to the sixth cervical vertebrae in its normal position. It consists of a cartilaginous skeleton connected by membranes, ligaments and associated muscles that suspend it from surrounding structures. It sits just above the trachea and is continuous with the oropharynx (the portion of the throat posterior to the oral cavity) above.  Larynx The larynx conducts air into the lower respiratory tract and closes off the airway especially during swallowing to prevent aspiration of food. It is commonly referred to as the “voice box” or the “organ of phonation” as it houses the structure responsible for sound production. It is quite mobile in the neck and can be seen and felt moving upward and forward during swallowing, closing off the trachea and opening the esophagus.  Larynx : Cartilaginous framework and ligaments The larynx is composed of three large unpaired cartilages (cricoid, thyroid, and epiglottis) and three paired smaller cartilages (arytenoid, corniculate, and cuneiform), making a total of nine individual cartilages. The thyroid cartilage is the largest of the laryngeal cartilages and is composed of hyaline cartilage. It forms the anterior and lateral portions of the larynx and has no posterior component. The broad flat right and left halves (laminae) of the cartilage fuse anteriorly in the midline to form a V-shaped anterior projection called the laryngeal prominence (commonly called the “Adam’s apple”). The Adam’s apple is typically more prominent in males after puberty. This is due to the influence of the hormone testosterone, which stimulates the overall growth of the larynx resulting in a deeper voice with time.  Larynx : Cartilaginous framework and ligaments The cricoid cartilage is a much smaller signet ring-shaped hyaline cartilage located directly below the thyroid cartilage. It forms the inferior aspect of the larynx and is connected to the trachea inferiorly. It is the only complete ring of cartilage that encircles the airway. The cricoid cartilage has a narrow anterior arch (band portion) and a wider posterior lamina (signet portion) with a midline ridge that serves as a surface of attachment for the esophagus.  Larynx : Cartilaginous framework and ligaments Located on the superolateral aspects of the wider posterior cricoid cartilage lamina are the paired pyramidal- shaped arytenoid cartilages. Each cartilage has a superior apex, an anterior vocal process and a large lateral muscular process. Attached to the apices of the arytenoid cartilage are the small, paired and conical- shaped corniculate cartilages.  Larynx : Cartilaginous framework and ligaments The last unpaired cartilage, the epiglottis, is a large leaf- shaped elastic cartilage that is covered by mucous membrane. It is attached by its stalk to the inner aspect of the angle formed by the laminae of the thyroid cartilage via the thyroepiglottic ligament in the midline. The epiglottis is also attached to the hyoid bone by the hyoepiglottic ligament which extends from the anterosuperior surface of the epiglottis to the body of the hyoid bone. The epiglottis projects superiorly into the pharynx, with its upper margin just behind the root of the tongue. As its name suggests (epi = above, glottis = mouth of windpipe), it sits above the laryngeal opening (inlet). During swallowing, as the larynx moves up and forwards, the epiglottis swings downward to close off the laryngeal inlet, and thus prevents materials from entering the airway.  Larynx : Cartilaginous framework and ligaments A thin layer of connective tissue, the quadrangular membrane extends between the lateral borders of the epiglottis and the anterolateral margins of the arytenoid cartilage. Its free lower edge is thickened and forms the vestibular ligament. This ligament is enclosed by a fold of mucous membrane to form the vestibular fold (false vocal cord) which extends from the thyroid cartilage to the arytenoid cartilage.  Laryngeal cavity The laryngeal cavity is divided into three regions: Vestibule: between the laryngeal inlet and the vestibular folds Middle part: between the vestibular folds above and vocal folds below Infraglottic cavity: between the vocal fold and the trachea  Cavity of the Larynx The vocal apparatus of the larynx is called the glottis and consists of two vocal folds (true vocal cords) and the rima glottidis. Each mucous membrane-covered vocal fold contains a vocal ligament that extends from the inner surface of the thyroid cartilage to the vocal process of the corresponding arytenoid cartilage. Running parallel to each vocal ligament is the vocalis muscle which is responsible for adjusting the tension of the vocal folds. The vocal folds are the “true” structures that produce sound as air passes over them, whereas the vestibular folds (false vocal cords) have no role in sound production but protect the vocal cords.  Rima vestibuli and Rima glottidis When viewed from above, there is a triangular opening (the rima vestibuli) between the two adjacent vestibular folds at the entrance to the middle chamber of the laryngeal cavity. The apex of the opening is anterior and its base is formed by the posterior wall of the laryngeal cavity. Inferior to the vestibular folds, the vocal folds (true vocal cords) and adjacent mucosa-covered parts of the arytenoid cartilages form the lateral walls of a similar, but narrower triangular opening (the rima glottidis between the two adjacent vocal folds). This opening separates the middle chamber above from the infraglottic cavity below. The base of this triangular opening is formed by the fold of mucosa (interarytenoid fold) at the bottom of the interarytenoid notch. Both the rima glottidis and the rima vestibuli can be opened and closed by movement of the arytenoid cartilages and associated fibro-elastic membranes. Laryngeal joints : Cricothyroid joints The joints between the inferior horns of the thyroid cartilage and the cricoid cartilage, and between the cricoid cartilage and arytenoid cartilages are synovial. Each is surrounded by a capsule and is reinforced by associated ligaments. The cricothyroid joints enable the thyroid cartilage to move forward and tilt downward on the cricoid cartilage. Because the vocal ligaments pass between the posterior aspect of the thyroid angle and the arytenoid cartilages sit on the lamina of cricoid cartilage, forward movement and downward rotation of the thyroid cartilage on the cricoid cartilage effectively lengthens and puts tension on the vocal ligaments.  Laryngeal joints : Cricoarytenoid joints The crico-arytenoid joints between articular facets on the superolateral surfaces of the cricoid cartilage and the bases of the arytenoid cartilages enable the arytenoid cartilages to slide away or toward each other and to rotate so that the vocal processes pivot either toward or away from the midline. These movements abduct and adduct the vocal ligaments.  Muscles There are two groups of muscles that are associated with the larynx, the extrinsic and intrinsic muscles. The extrinsic laryngeal muscles move the larynx as a whole. They consist of the suprahyoid muscles that elevate the hyoid bone and the larynx during swallowing and vocalization, and the infrahyoid muscles that depress the hyoid bone and the larynx. The small intrinsic laryngeal muscles are responsible for moving various components of the larynx. They modify the length and tension of the vocal cords as well as the shape of the rima glottidis during breathing, swallowing and vocalization.  Functions of the larynx The larynx is an elaborate sphincter for the lower respiratory tract and provides a mechanism for producing sounds. Adjustments of the size of the central cavity of the larynx result from changes in the dimensions of the rima glottidis, the rima vestibuli, the vestibule, and the laryngeal inlet. These changes result from muscle actions and laryngeal mechanics. Respiration During quiet respiration, the laryngeal inlet, vestibule, rima vestibuli, and rima glottidis are open. The arytenoid cartilages are abducted and the rima glottidis is triangular shaped. During forced inspiration, the arytenoid cartilages are rotated laterally, mainly by the action of the posterior crico-arytenoid muscles. As a result, the vocal folds are abducted, and the rima glottidis widens into a rhomboid shape, which effectively increases the diameter of the laryngeal airway.  Phonation When phonating, the arytenoid cartilages and vocal folds are adducted and air is forced through the closed rima glottidis. This action causes the vocal folds to vibrate against each other and produce sounds, which can then be modified by the upper parts of the airway and oral cavity. Tension in the vocal folds can be adjusted by the vocalis and cricothyroid muscles.  Effort closure Effort closure of the larynx occurs when air is retained in the thoracic cavity to stabilize the trunk, for example during heavy lifting, or as part of the mechanism for increasing intra-abdominal pressure. During effort closure, the rima glottidis is completely closed, as is the rima vestibuli and lower parts of the vestibule. The result is to completely and forcefully shut the airway.  Swallowing During swallowing, the rima glottidis, the rima vestibuli, and vestibule are closed and the laryngeal inlet is narrowed. In addition, the larynx moves up and forward. This action causes the epiglottis to swing downward toward the arytenoid cartilages and to effectively narrow or close the laryngeal inlet. The up and forward movement of the larynx also opens the esophagus, which is attached to the posterior aspect of the lamina of cricoid cartilage. All these actions together prevent solids and liquids from entry into the airway and facilitate their movement through the piriform fossae into the esophagus.  Blood supply and lymphatic drainage The arterial supply of the larynx is by the superior and inferior laryngeal arteries which are branches of the thyroid arteries. The larynx is drained by corresponding veins, namely the superior and inferior laryngeal veins. The lymphatic vessels above the vocal folds drain into the superior deep cervical lymph nodes whereas those below the vocal folds drain first to nodes around the trachea (pretracheal and paratracheal nodes) and subsequently into the inferior deep cervical lymph nodes.  Innervation The right and left superior and inferior laryngeal nerves which are branches of the vagus nerve, the tenth cranial nerve (CN X), provide motor and sensory innervation to the larynx. Each superior laryngeal nerve divides into the internal and external laryngeal nerves. The internal laryngeal nerve accompanies the superior laryngeal artery through the thyrohyoid membrane and provides the sensory and autonomic innervation of the laryngeal cavity to the level of the vocal cords. The smaller external laryngeal nerve provides motor innervation to the cricothyroid muscle. The recurrent laryngeal nerves which are ascending branches of the vagus nerves continue toward the larynx as the right and left inferior laryngeal nerves. They provide motor innervation to all the intrinsic muscles of the larynx except the cricothyroid muscles and sensory innervation to the laryngeal cavity below the vocal cords. Lower Respiratory Tract  Trachea The trachea (windpipe) extends from the larynx toward the lungs. The trachea is formed by 16 to 20 stacked, C-shaped pieces of hyaline cartilage that are connected by dense connective tissue. The trachealis muscle and elastic connective tissue together form the fibroelastic membrane, a flexible membrane that closes the posterior surface of the trachea, connecting the C-shaped cartilages. The fibroelastic membrane allows the trachea to stretch and expand slightly during inhalation and exhalation, whereas the rings of cartilage provide structural support and prevent the trachea from collapsing. In addition, the trachealis muscle can be contracted to force air through the trachea during exhalation. The trachea is lined with pseudostratified ciliated columnar epithelium, which is continuous with the larynx. The esophagus borders the trachea posteriorly. Trachea  Bronchial Tree The trachea branches into the right and left primary bronchi at the carina. These bronchi are also lined by pseudostratified ciliated columnar epithelium containing mucus-producing goblet cells. The carina is a raised structure that contains specialized nervous tissue that induces violent coughing if a foreign body, such as food, is present. Rings of cartilage, similar to those of the trachea, support the structure of the bronchi and prevent their collapse. The primary bronchi enter the lungs at the hilum, a concave region where blood vessels, lymphatic vessels, and nerves also enter the lungs.  Bronchus Right Principal The right principal (main) bronchus is wider, shorter, and more vertical than the left principal bronchus. Before entering the hilum of the right lung, it gives off the superior lobar bronchus. On entering the hilum, it divides into a middle and an inferior lobar bronchus. Left Principal The left principal (main) bronchus is narrower, longer, and more horizontal than the right principal bronchus. It passes to the left below the arch of the aorta and in front of the esophagus. On entering the hilum of the left lung, it divides into a superior and an inferior lobar bronchus.  Bronchial Tree Once inside the lungs, each main bronchus further divides into lobar bronchi. The right lung has three lobar bronchi (one for each lobe), while the left lung has two lobar bronchi (one for each of its lobes). The lobar bronchi divide into smaller branches called segmental bronchi, each supplying a specific bronchopulmonary segment of the lung. The segmental bronchi branch into even smaller passages called bronchioles. Unlike the bronchi, bronchioles do not have cartilage and are composed mainly of smooth muscle. The bronchioles continue to divide into terminal bronchioles, which are the smallest conducting airways that do not participate in gas exchange.  Bronchial Tree Terminal bronchioles further divide into respiratory bronchioles, which have small outpouchings where gas exchange begins. These lead into alveolar ducts. The respiratory bronchioles open into alveolar ducts, which are passageways lined with numerous alveoli. The alveolar ducts end in clusters of alveoli. These tiny, balloon-like sacs are the primary site of gas exchange, where oxygen is absorbed into the bloodstream and carbon dioxide is expelled.  Lungs The two lungs are organs of respiration and lie on either side of the mediastinum surrounded by the right and left pleural cavities. Air enters and leaves the lungs via main bronchi, which are branches of the trachea. The pulmonary arteries deliver deoxygenated blood to the lungs from the right ventricle of the heart. Oxygenated blood returns to the left atrium via the pulmonary veins. The right lung is normally a little larger than the left lung because the middle mediastinum, containing the heart, bulges more to the left than to the right. Each lung has a half-cone shape, with a base, apex, two surfaces, and three borders.  Lungs The base sits on the diaphragm. The apex projects above rib I and into the root of the neck. The two surfaces—the costal surface lies immediately adjacent to the ribs and intercostal spaces of the thoracic wall. The mediastinal surface lies against the mediastinum anteriorly and the vertebral column posteriorly and contains the comma-shaped hilum of the lung, through which structures enter and leave. The three borders—the inferior border of the lung is sharp and separates the base from the costal surface. The anterior and posterior borders separate the costal surface from the medial surface. Unlike the anterior and inferior borders, which are sharp, the posterior border is smooth and rounded.  Lungs : Root and Hilum The root of each lung is a short tubular collection of structures that together attach the lung to structures in the mediastinum. It is covered by a sleeve of mediastinal pleura that reflects onto the surface of the lung as visceral pleura. The region outlined by this pleural reflection on the medial surface of the lung is the hilum, where structures enter and leave. A thin blade-like fold of pleura projects inferiorly from the root of the lung and extends from the hilum to the mediastinum. This structure is the pulmonary ligament. It may stabilize the position of the inferior lobe and may also accommodate the down-and-up translocation of structures in the root during breathing. In the mediastinum, the vagus nerves pass immediately posterior to the roots of the lungs, while the phrenic nerves pass immediately anterior to them.  Lungs : Root and Hilum Within each root and located in the hilum are: a pulmonary artery, two pulmonary veins, a main bronchus, bronchial vessels, nerves, and lymphatics. Generally, the pulmonary artery is superior at the hilum, the pulmonary veins are inferior, and the bronchi are somewhat posterior in position. On the right side, the lobar bronchus to the superior lobe branches from the main bronchus in the root, unlike on the left where it branches within the lung itself, and is superior to the pulmonary artery.  Right Lung The right lung has three lobes and two fissures. Normally, the lobes are freely movable against each other because they are separated, almost to the hilum, by invaginations of visceral pleura. These invaginations form the fissures: The oblique fissure separates the inferior lobe (lower lobe) from the superior lobe and the middle lobe of the right lung. The horizontal fissure separates the superior lobe (upper lobe) from the middle lobe.  Right Lung The medial surface of the right lung lies adjacent to a number of important structures in the mediastinum and the root of the neck. These include the: heart, inferior vena cava, superior vena cava, azygos vein, and esophagus. The right subclavian artery and vein arch over and are related to the superior lobe of the right lung as they pass over the dome of the cervical pleura and into the axilla.  Left Lung The left lung is smaller than the right lung and has two lobes separated by an oblique fissure. The oblique fissure of the left lung is slightly more oblique than the corresponding fissure of the right lung. From the anterior border of the lower part of the superior lobe a tongue-like extension (the lingula of the left lung) projects over the heart bulge.  Left Lung The medial surface of the left lung lies adjacent to a number of important structures in the mediastinum and root of the neck. These include the: heart, aortic arch, thoracic aorta, and esophagus.  Lungs : Vasculature The lungs are supplied with deoxygenated blood by the paired pulmonary arteries. Once the blood has received oxygenation, it leaves the lungs via four pulmonary veins (two for each lung). The bronchi, lung roots, visceral pleura and supporting lung tissues require an extra nutritive blood supply. This is delivered by the bronchial arteries, which arise from the descending aorta. The bronchial veins provide venous drainage. The right bronchial vein drains into the azygos vein, whilst the left drains into the accessory hemiazygos vein.  Lungs : Pleura Each lung is enclosed within a cavity that is surrounded by the pleura. The pleura (plural = pleurae) is a serous membrane that surrounds the lung. The right and left pleurae, which enclose the right and left lungs, respectively, are separated by the mediastinum. The pleurae consist of two layers. The visceral pleura is the layer that is superficial to the lungs, and extends into and lines the lung fissures. In contrast, the parietal pleura is the outer layer that connects to the thoracic wall, the mediastinum, and the diaphragm. The visceral and parietal pleurae connect to each other at the hilum. The pleural cavity is the space between the visceral and parietal layers.  Lungs : Pleura The pleurae perform two major functions: They produce pleural fluid and create cavities that separate the major organs. Pleural fluid is secreted by mesothelial cells from both pleural layers and acts to lubricate their surfaces. This lubrication reduces friction between the two layers to prevent trauma during breathing, and creates surface tension that helps maintain the position of the lungs against the thoracic wall. This adhesive characteristic of the pleural fluid causes the lungs to enlarge when the thoracic wall expands during ventilation, allowing the lungs to fill with air. The pleurae also create a division between major organs that prevents interference due to the movement of the organs, while preventing the spread of infection.  Lungs : Innervation Structures of the lung and the visceral pleura are supplied by visceral afferents and efferents distributed through the anterior pulmonary plexus and posterior pulmonary plexus. These interconnected plexuses lie anteriorly and posteriorly to the tracheal bifurcation and main bronchi. The anterior plexus is much smaller than the posterior plexus. Branches of these plexuses, which ultimately originate from the sympathetic trunks and vagus nerves, are distributed along branches of the airway and vessels. Visceral efferents from: the vagus nerves constrict the bronchioles; the sympathetic system dilates the bronchioles. Respiratory System The air contains potentially harmful particles and gases. Particles, such as dust and soot, mold, fungi, bacteria, and viruses deposit on airway and alveolar surfaces. Fortunately, the respiratory system has defense mechanisms to clean and protect itself.  Respiratory System One of the respiratory system's defense mechanisms involves tiny, muscular, hair-like projections (cilia) on the cells that line the airways. Particles and pathogens that are trapped on this mucus layer are coughed out or moved to the mouth and swallowed – cough reflex. Because of the requirements of gas exchange, alveoli are not protected by mucus and cilia. Instead, the body has another defense system. Mobile cells on the alveolar surface called phagocytes seek out deposited particles, bind to them, ingest them, kill any that are living, and digest them. The phagocytes in alveoli of the lungs are called alveolar macrophages. Cough Reflex Lower Respiratory Tract Disorders Bronchial Asthma  Bronchial Asthma Asthma is a disease of diffuse airway inflammation caused by a variety of triggering stimuli resulting in partially or completely reversible bronchoconstriction. Asthma involves Bronchoconstriction Airway edema and inflammation Airway hyperreactivity Airway remodeling Risk factors of Bronchial Asthma Endogenous factors Environmental factors Genetic predisposition Indoor allergens Atopy Outdoor allergens Airway hyperresponsiveness Occupational sensitizers Gender Passive smoking Ethnicity Respiratory infections Obesity Diet Early viral infection Drugs (Paracetamol)  Triggers of Bronchial Asthma Allergens Upper respiratory tract viral infections Exercise and hyperventilation Cold air Sulfur dioxide and irritant gases Drugs (β blockers, aspirin) Stress Irritants (household sprays, paint fumes)  Bronchial Asthma Symptoms and signs include dyspnea, chest tightness, cough, and wheezing. Patients with mild asthma are typically asymptomatic between exacerbations. Patients with more severe disease and those with exacerbations experience dyspnea, chest tightness, audible wheezing, and coughing. Coughing may be the only symptom in some patients (cough-variant asthma). Symptoms can follow a circadian rhythm and worsen during sleep, often around 4 AM. Many patients with more severe disease waken during the night (nocturnal asthma). Acute Severe Asthma (Status Asthmaticus) Acute severe asthma is an acute exacerbation of asthma that does not respond to standard treatments of bronchodilators (inhalers) and corticosteroids. Signs of a more severe disease include wheezing, pulsus paradoxus (ie, a fall of systolic BP > 10 mm Hg during inspiration), tachypnea, tachycardia, and visible efforts to breathe (use of neck and suprasternal [accessory] muscles, upright posture, pursed lips, inability to speak). Patients with a severe exacerbation and impending respiratory failure typically have some combination of altered consciousness, cyanosis, pulsus paradoxus > 15 mm Hg, SaO 2 < 90%, Pa CO 2 > 45 mm Hg, or hyperinflation. Rarely, pneumothorax or pneumomediastinum is seen on chest x-ray.  Bronchial Asthma Diagnosis is based on history and physical examination and is confirmed with pulmonary function tests. Treatment involves controlling triggering factors and drug therapy, most commonly with inhaled β 2 -agonists and inhaled corticosteroids. Prognosis is good with treatment. Pneumonia  Pneumonia Pneumonia is acute inflammation of the lungs caused by infection. It is classed as “primary” if it occurs in a previously healthy individual and is usually lobar; Or “secondary” to some other disorder such as a previous viral respiratory infection, aspiration of foreign material, lung disease, or depressed immunity or aspiration of oral bacteria.  Pneumonia It causes cough, fever, rapid respiration, breathlessness, chest pain, dyspnea and shivering. Complications can include lung abscess or empyema. Diagnosis is suspected on the basis of clinical presentation and infiltrate seen on chest x-ray. When there is high clinical suspicion of pneumonia and the chest x-ray does not reveal an infiltrate, doing CT or repeating the chest x-ray in 24 to 48 h is recommended. Treatment is with empirically chosen antibiotics.  Community Acquired Pneumonia Community-acquired pneumonia develops in people with limited or no contact with medical institutions or settings. The most commonly identified pathogens are Streptococcus pneumoniae,Haemophilus influenzae, atypical bacteria (ie, Chlamydia pneumoniae, Mycoplasma pneumoniae, Legionella sp), and viruses. Symptoms and signs are fever, cough, sputum production, pleuritic chest pain, dyspnea, tachypnea, and tachycardia. Diagnosis is based on clinical presentation and chest x-ray. Treatment is with empirically chosen antibiotics.  Hospital Acquired Pneumonia Hospital-acquired pneumonia (HAP) develops at least 48 h after hospital admission. The most common pathogens are gram-negative bacilli and Staphylococcus aureus; antibiotic-resistant organisms are an important concern. Symptoms and signs include malaise, fever, chills, rigor, cough, dyspnea, and chest paina, but in ventilated patients, pneumonia usually manifests as worsening oxygenation and increased tracheal secretions. Diagnosis is suspected on the basis of clinical presentation and chest x-ray and is confirmed by blood culture or bronchoscopic sampling of the lower respiratory tract. Treatment is with antibiotics. Overall prognosis is poor, due in part to comorbidities. Pulmonary Tuberculosis  Pulmonary Tuberculosis Tuberculosis (TB) is a chronic, progressive infection, often with a period of latency following initial infection. TB most commonly affects the lungs. TB properly refers only to disease caused by Mycobacterium tuberculosis (for which humans are the main reservoir). TB results almost exclusively from inhalation of airborne particles (droplet nuclei) containing M. tuberculosis. They disperse primarily through coughing, singing, and other forced respiratory maneuvers by people who have active pulmonary TB and whose sputum contains a significant number of organisms (typically enough to render the smear positive). People with pulmonary cavitary lesions are especially infectious because of the high number of bacteria contained within a lesion.  Pulmonary Tuberculosis In active pulmonary TB, even moderate or severe disease, patients may have no symptoms, except “not feeling well,” anorexia, fatigue, and weight loss, which develop gradually over several weeks, or they may have more specific symptoms. Cough is most common. At first, it may be minimally productive of yellow or green sputum, usually when awakening in the morning, but cough may become more productive as the disease progresses. Hemoptysis occurs only with cavitary TB (due to granulomatous damage to vessels but sometimes due to fungal growth in a cavity). Low-grade fever is common but not invariable. Drenching night sweats are a classic symptom but are neither common in nor specific for TB. Dyspnea may result from lung parenchymal damage, spontaneous pneumothorax, or pleural TB with effusion.  Pulmonary Tuberculosis TB can be diagnosed by Chest X-ray and AFB sputum smear (3x)/GeneXpert and culture Skin testing or Purified Protein Derivative (PPD) test Treatment is with multiple antimicrobial drugs given for at least 6 mo. (HRZE-S) / TB-DOTS (Directly Observed Treatment) Isoniazid Rifampicin Pyrazinamide Ethambutol Streptomycin - injectable form Lung Cancer  Lung Cancer Lung carcinoma is the leading cause of cancer-related death worldwide. About 85% of cases are related to cigarette smoking. Cigarette smoking is the most important cause of lung cancer, accounting for about 85% of cases. The risk of cancer differs by age, smoking intensity, and smoking duration; the risk of cancer declines after smoking cessation, but it never returns to baseline. About 15 to 20% of people who develop lung cancer have never smoked or have smoked minimally.  Lung Cancer Lung cancer is classified into 2 major categories: Small cell lung cancer (SCLC), about 15% of cases Non–small cell lung cancer (NSCLC), about 85% of cases SCLC is highly aggressive and almost always occurs in smokers. It is rapidly growing, and roughly 80% of patients have metastatic disease at the time of diagnosis. The clinical behavior of NSCLC is more variable and depends on histologic type, but about 40% of patients will have metastatic disease outside of the chest at the time of diagnosis.  Lung Cancer Symptoms can include cough, chest discomfort or pain, weight loss, and, less commonly, hemoptysis; however, many patients present with metastatic disease without any clinical symptoms. The diagnosis is typically made by chest x-ray or CT and confirmed by biopsy. Depending on the stage of the disease, treatment includes surgery, chemotherapy, radiation therapy, or a combination. For the past several decades, the prognosis for a lung cancer patient was poor, with only 15% of patients surviving > 5 yr from the time of diagnosis. For patients with stage IV (metastatic) disease, the 5-yr overall survival rate was < 1%. Thank You ! Digestive System By : Marc Anthony Cueto MD Learning Objectives 1. Identify the detailed structure and landmarks of organs of digestion. 2. Provide an understanding on the organs of digestion. 3. Describe the mechanism of digestion from mastication down to removal of waste. Digestive System The digestive system has three main functions relating to food : digestion of food , absorption of nutrients from food , and elimination of solid food waste. Digestion is the process of breaking down food into components the body can absorb. It consists of two types of processes: mechanical digestion and chemical digestion. Mechanical digestion is the physical breakdown of chunks of food into smaller pieces. This type of digestion takes place mainly in the mouth and stomach. Chemical digestion is the chemical breakdown (bonds are broken) of large, complex food molecules into smaller, simpler nutrient molecules that can be absorbed by body fluids (blood or lymph). This type of digestion begins in the mouth and continues in the stomach but occurs mainly in the small intestine. Digestive System After food is digested, the resulting nutrients are absorbed. Absorption is the process in which substances pass into the bloodstream or lymph system to circulate throughout the body. The absorption of nutrients occurs mainly in the small intestine. Any remaining matter from food that is not digested and absorbed passes out of the body through the anus in the process of elimination. Digestive System 2 divisions of the digestive system: 1.alimentary canal – organs through which food passes: mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus 2.accessory organs – structures that aid in digestion: teeth, salivary glands, liver, gallbladder, and pancreas Abdomen Abdomen Oral Cavity Oral Cavity The oral cavity represents the first part of the digestive tube. Its primary function is to serve as the entrance of the alimentary tract and to initiate the digestive process by salivation and propulsion of the alimentary bolus into the pharynx. It also serves as a secondary respiratory conduit, a site of sound modification for the production of speech, and a chemosensory organ. The mobility of the lips is also critical to speech production, whistling, singing, the playing of wind and brass musical instruments, expectoration, and human behavioral communication (eg, kissing, smiling, pouting, baring of teeth). Even minor disruptions in the function of the oral cavity can seriously jeopardize an individual’s quality of life. Oral Cavity The oral cavity is inferior to the nasal cavity. It has a roof and floor and lateral walls, opens onto the face through the oral fissure, and is continuous with the cavity of the pharynx at the oropharyngeal isthmus. The roof of the oral cavity consists of the hard and soft palate. The floor is formed mainly of soft tissues, which include a muscular diaphragm and the tongue. The lateral walls also referred to as the cheeks are muscular and merge anteriorly with the lips surrounding the oral fissure (anterior opening of the oral cavity) The posterior aperture of the oral cavity is the oropharyngeal isthmus, which opens into the oral part of the pharynx. Oral Cavity The oral cavity is separated into two regions by the upper and lower dental arches consisting of the teeth and the alveolar bone that supports them: The outer oral vestibule, which is horseshoe shaped, is between the dental arches and the deep surfaces of the cheeks and lips-the oral fissure opens into it and can be opened and closed by muscles of facial expression, and by movement of the lower jaw. The inner oral cavity proper is enclosed by the dental arches. Oral Cavity The degree of separation between the upper and lower arches is established by elevating and depressing the lower jaw or mandible at the temporomandibular joint. The oropharyngeal isthmus at the back of the oral cavity proper can be opened and closed by surrounding soft tissues, which include the soft palate and tongue. Tongue The tongue is a muscular structure that forms part of the floor of the oral cavity and part of the anterior wall of the oropharynx. Its anterior part is in the oral cavity and is somewhat triangular in shape with a blunt apex of tongue. The apex is directed anteriorly and sits immediately behind the incisor teeth. The root of tongue is attached to the mandible and the hyoid bone. The superior surface of the oral or anterior two-thirds of the tongue is oriented in the horizontal plane. Tongue The pharyngeal surface or posterior one-third of the tongue curves inferiorly and becomes oriented more in the vertical plane. The oral and pharyngeal surfaces are separated by a V-shaped terminal sulcus of tongue. This terminal sulcus forms the inferior margin of the oropharyngeal isthmus between the oral and pharyngeal cavities. At the apex of the V-shaped sulcus is a small depression (the foramen cecum of tongue), which marks the site in the embryo where the epithelium invaginated to form the thyroid gland. Tongue In some people a thyroglossal duct persists and connects the foramen cecum on the tongue with the thyroid gland in the neck. The thyroglossal duct is an embryological anatomical structure forming an open connection between the initial area of development of the thyroid gland and its final position. It is located exactly mid-line, between the anterior 2/3 and posterior 1/3 of the tongue. The thyroid gland starts developing in the oropharynx in the fetus and descends to its final position taking a path through the tongue, hyoid bone and neck muscles. The connection between its original position and its final position is the thyroglossal duct. This duct normally atrophies and closes off as the foramen cecum before birth but can remain open in some people. Thyroglossal duct cyst A thyroglossal cyst is a fibrous cyst that forms from a persistent thyroglossal duct. Thyroglossal cysts can be defined as an irregular neck mass or a lump which had developed from cells and tissues left over after the formation of the thyroid gland during developmental stages. Papillae The superior surface of the oral part of the tongue is covered by hundreds of papillae : filiform papillae are small cone-shaped projections of the mucosa that end in one or more points; fungiform papillae are rounder in shape and larger than the filiform papillae, and tend to be concentrated along the margins of the tongue; the largest of the papillae are the vallate papillae, which are blunt-ended cylindrical papillae invaginations in the tongue's surface-there are only about 8 to 12 vallate papillae in a single V shaped line immediately anterior to the terminal sulcus of tongue; foliate papillae are linear folds of mucosa on the sides of the tongue near the terminal sulcus of tongue. The papillae in general increase the area of contact between the surface of the tongue and the contents of the oral cavity. All except the filiform papillae have taste buds on their surfaces. Inferior surface of the tongue The undersurface of the oral part of the tongue lacks papillae, but does have a number of linear mucosal folds. A single median fold (the frenulum of tongue) is continuous with the mucosa covering the floor of the oral cavity, and overlies the lower margin of a midline sagittal septum, which internally separates the right and left sides of the tongue. On each side of the frenulum is a lingual vein, and lateral to each vein is a rough fimbriated fold. Pharyngeal surface The mucosa covering the pharyngeal surface of the tongue is irregular in contour because of the many small nodules of lymphoid tissue in the submucosa. These nodules are collectively the lingual tonsil. There are no papillae on the pharyngeal surface. Muscles of the tongue The bulk of the tongue is composed of muscle. The tongue is completely divided into a left and right half by a median sagittal septum composed of connective tissue. This means that all muscles of the tongue are paired. There are intrinsic and extrinsic lingual muscles. Except for the palatoglossus, which is innervated by the vagus nerve [X], all muscles of the tongue are innervated by the hypoglossal nerve [XII]. Intrinsic muscles of the tongue The intrinsic muscles of the tongue originate and insert within the substance of the tongue. They are divided into superior longitudinal, inferior longitudinal, transverse, and vertical muscles, and they alter the shape of the tongue by: lengthening and shortening it; curling and uncurling its apex and edges; and flattening and rounding its surface. Working in pairs or one side at a time the intrinsic muscles of the tongue contribute to precision movements of the tongue required for speech, eating, and swallowing. Extrinsic muscles of the tongue Extrinsic muscles of the tongue originate from structures outside the tongue and insert into the tongue. There are four major extrinsic muscles on each side, the genioglossus, hyoglossus, styloglossus, and palatoglossus. These muscles protrude, retract, depress, and elevate the tongue. Oral fissure and lips The oral fissure is the slit-like opening between the lips that connects the oral vestibule to the outside. It can be opened and closed, and altered in shape by the movements of the muscles of facial expression associated with the lips and surrounding regions, and by movements of the lower jaw (mandible). The lips are entirely composed of soft tissues. They are lined internally by oral mucosa and covered externally by skin. Externally, there is an area of transition from the thicker skin that covers the face to the thinner skin that overlies the margins of the lips and continues as oral mucosa onto the deep surfaces of the lips. Oral fissure and lips Blood vessels are closer to the surface in areas where the skin is thin and as a consequence there is a vermilion border that covers the margins of the lips. The vermilion border is the normally sharp demarcation between the lip (red colored) and the adjacent normal skin. It represents the change in the epidermis from highly keratinized external skin to less keratinized internal skin. It has no sebaceous glands, sweat glands, or hair. The upper lip has a shallow vertical groove on its external surface (the philtrum) sandwiched between two elevated ridges of skin. The philtrum and ridges are formed embryologically by fusion of the medial nasal processes. On the inner surface of both lips, a fold of mucosa (the median labial frenulum) connects the lip to the adjacent gum. The lips enclose the orbicularis oris muscle, neurovascular tissues, and labial glands. The small pea-shaped labial glands are between the muscle tissue and the oral mucosa and open into the oral vestibule. Oral fissure and lips A number of muscles of facial expression control the shape and size of the oral fissure. The most important of these is the orbicularis oris muscle, which encircles the orifice and acts as a sphincter. A number of other muscles of facial expression blend into the orbicularis oris or other tissues of the lips and open or adjust the contours of the oral fissure. These include buccinator, levator labii superioris, zygomaticus major and minor, levator anguli oris, depressor labii inferioris, depressor anguli oris, and platysma. Oropharyngeal isthmus The oropharyngeal isthmus is the opening between the oral cavity and the oropharynx. It is formed: laterally by the palatoglossal arches; superiorly by the soft palate; and and inferiorly by the sulcus terminalis of the tongue that divides the oral surface of the tongue (anterior two-thirds) from the pharyngeal surface (posterior one-third). The oropharyngeal isthmus can be closed by elevation of the posterior aspect of the tongue, depression of the palate, and medial movement of the palatoglossal arches toward the midline. Medial movement of the palatopharyngeal arches medial and posterior to the palatoglossal arches is also involved in closing the oropharyngeal isthmus. By closing the oropharyngeal isthmus, food or liquid can be held in the oral cavity while breathing. Teeth and gingivae The teeth are attached to sockets (alveoli) in two elevated arches of bone on the mandible below and the maxillae above (alveolar arches). If the teeth are removed, the alveolar bone is resorbed and the arches disappear. The gingivae (gums) are specialized regions of the oral mucosa that surround the teeth and cover adjacent regions of the alveolar bone. The different types of teeth are distinguished on the basis of morphology, position, and function. Teeth and gingivae In adults, there are 32 teeth, 16 in the upper jaw and 16 in the lower jaw. On each side in both maxillary and mandibular arches are two incisor, one canine, two premolar, and three molar teeth. the incisor teeth are the "front teeth" and have one root and a chisel-shaped crown, which "cuts"; the canine teeth are posterior to the incisors, are the longest teeth, have a crown with a single pointed cusp, and "grasp"; the premolar teeth (bicuspids) have a crown with two pointed cusps, one on the buccal (cheek) side of the tooth and the other on the lingual (tongue) or palatal (palate) side, generally have one root (but the upper first premolar next to the canine may have two), and "grind"; the molar teeth are behind the premolar teeth, have three roots and crowns with three to five cusps, and "grind." Teeth and gingivae Two successive sets of teeth develop in humans, deciduous teeth ("baby" teeth) and permanent teeth ("adult" teeth). The deciduous teeth emerge from the gingivae at between six months and two years of age. Permanent teeth begin to emerge and replace the deciduous teeth at around age six years, and can continue to emerge into adulthood. The 20 deciduous teeth consist of two incisor, one canine, and two molar teeth on each side of the upper and lower jaws. These teeth are replaced by the incisor, canine, and premolar teeth of the permanent teeth. The permanent molar teeth erupt posterior to the deciduous molars and require the jaws to elongate forward to accommodate them. Esophagus Esophagus The esophagus is a muscular tube passing between the pharynx in the neck and the stomach in the abdomen. It begins at the inferior border of the cricoid cartilage, opposite vertebra CVI, and ends at the cardiac opening of the stomach, opposite vertebra TXI. The esophagus descends on the anterior aspect of the bodies of the vertebrae, generally in a midline position as it moves through the thorax. As it approaches the diaphragm, it moves anteriorly and to the left, crossing from the right side of the thoracic aorta to eventually assume a position anterior to it. It then passes through the esophageal hiatus, an opening in the muscular part of the diaphragm, at vertebral level TX.  Esophagus The esophagus is a flexible, muscular tube that can be compressed or narrowed by surrounding structures at four locations : the junction of the esophagus with the pharynx in the neck; in the superior mediastinum where the esophagus is crossed by the arch of the aorta; in the posterior mediastinum where the esophagus is compressed by the left main bronchus; in the posterior mediastinum at the esophageal hiatus in the diaphragm. These constrictions have important clinical consequences. For example, a swallowed object is most likely to lodge at a constricted area. An ingested corrosive substance would move more slowly through a narrowed region, causing more damage at this site than elsewhere along the esophagus. Also, constrictions present problems during the passage of medical instruments.  Esophagus The upper esophageal sphincter, which is continuous with the inferior pharyngeal constrictor, controls the movement of food from the pharynx into the esophagus. Esophagus is unique, unlike any other organ in the body, it is made up of partly skeletal and partly smooth muscles. Upper part is entirely skeletal (2–4 cm), the middle, a mixture of skeletal and smooth muscle, and the lower part, 11 cm or so in length is entirely smooth. Rhythmic waves of peristalsis, which begin in the upper esophagus, propel the bolus of food toward the stomach. Meanwhile, secretions from the esophageal mucosa lubricate the esophagus and food. Food passes from the esophagus into the stomach at the lower esophageal sphincter (also called the gastroesophageal or cardiac sphincter). Esophagus Recall that sphincters are muscles that surround tubes and serve as valves, closing the tube when the sphincters contract and opening it when they relax. The lower esophageal sphincter relaxes to let food pass into the stomach, and then contracts to prevent stomach acids from backing up into the esophagus. Surrounding this sphincter is the muscular diaphragm, which helps close off the sphincter when no food is being swallowed. When the lower esophageal sphincter does not completely close, the stomach’s contents can reflux (that is, back up into the esophagus), causing heartburn or gastroesophageal reflux disease (GERD). Arterial supply and venous and lymphatic drainage of the Esophagus The arterial supply and venous drainage of the esophagus in the posterior mediastinum involve many vessels. Esophageal arteries arise from the thoracic aorta, bronchial arteries, and ascending branches of the left gastric artery in the abdomen. Venous drainage involves small vessels returning to the azygos vein, hemiazygos vein, and esophageal branches to the left gastric vein in the abdomen. Lymphatic drainage of the esophagus in the posterior mediastinum returns to posterior mediastinal and left gastric nodes. Innervation of the Esophagus Innervation of the esophagus, in general, is complex. Esophageal branches arise from the vagus nerves and sympathetic trunks. Peritoneum The digestive organs within the abdominal cavity are held in place by the peritoneum, a broad serous membranous sac made up of squamous epithelial tissue surrounded by connective tissue. It is composed of two different regions: the parietal peritoneum, which lines the abdominal wall, and the visceral peritoneum, which envelopes the abdominal organs. The peritoneal cavity is the space bounded by the visceral and parietal peritoneal surfaces. A few milliliters of watery fluid act as a lubricant to minimize friction between the serosal surfaces of the peritoneum. Stomach  Stomach The stomach is a J-shaped dilated portion of the alimentary tract situated in the epigastric, umbilical and left hypochondriac regions of the abdominal cavity. The stomach is continuous with the oesophagus at the cardiac sphincter and with the duodenum at the pyloric sphincter. It has two curvatures. The lesser curvature is short, lies on the posterior surface of the stomach and is the downwards continuation of the posterior wall of the esophagus. Just before the pyloric sphincter, it curves upwards to complete the J shape. Where the esophagus joins the stomach the anterior region angles acutely upwards, curves downwards forming the greater curvature then slightly upwards towards the pyloric sphincter. Stomach The stomach is divided into four regions: the cardia, which surrounds the opening of the esophagus into the stomach; the fundus of the stomach, which is the area above the level of the cardial orifice; the body of the stomach, which is the largest region of the stomach; and the pyloric part, which is divided into the pyloric antrum and pyloric canal and is the distal end of the stomach.  Stomach The most distal portion of the pyloric part of the stomach is the pylorus. It is marked on the surface of the organ by the pyloric constriction and contains a thickened ring of gastric circular muscle, the pyloric sphincter, that surrounds the distal opening of the stomach, the pyloric orifice. The pyloric orifice is just to the right of midline in a plane that passes through the lower border of vertebra LI (the transpyloric plane). Stomach Other features of the stomach include: the greater curvature, which is a point of attachment for the gastrosplenic ligament and the greater omentum; the lesser curvature, which is a point of attachment for the lesser omentum; the cardial notch, which is the superior angle created when the esophagus enters the stomach; and the angular incisure, which is a bend on the lesser curvature.  Greater Omentum The greater omentum is a large, apron-like, peritoneal fold that attaches to the greater curvature of the stomach and the first part of the duodenum. It drapes inferiorly over the transverse colon and the coils of the jejunum and ileum. Turning posteriorly, it ascends to associate with, and become adherent to, the peritoneum on the superior surface of the transverse colon and the anterior layer of the transverse mesocolon before arriving at the posterior abdominal wall. Usually a thin membrane, the greater omentum always contains an accumulation of fat, which may become substantial in some individuals. Greater Omentum The greater omentum prevents the parietal and visceral peritoneum of the abdominal cavity from adhering to each other. For example, it prevents the parietal peritoneum lining the anterior abdominal wall from sticking to the visceral peritoneum of the ileum. It is very mobile, and moves around the abdomen with rhythmic, peristaltic motion of the intestines. It can also adhere to an inflamed organ, such as the appendix, to protect the healthy organs in the abdomen. Because of this, the greater omentum is sometimes referred to as the ‘policeman of the abdomen’. Lesser Omentum The other two-layered peritoneal omentum is the lesser omentum. It extends from the lesser curvature of the stomach and the first part of the duodenum to the inferior surface of the liver. Stomach : Functions Temporary storage allowing time for the digestive enzymes, pepsins, to act. Chemical digestion — pepsins convert proteins to polypeptides. Mechanical breakdown — the three smooth muscle layers enable the stomach to act as a churn, gastric juice is added and the contents are liquefied to chime. Performs limited absorption of water, alcohol and some lipid-soluble drugs Non-specific defense against microbes — provided by hydrochloric acid in gastric juice. Preparation of iron for absorption further along the track — the acid environment of the stomach solubilizes iron salts, which is required before iron can be absorbed Production of intrinsic factor needed for absorption of vitamin B12 in the terminal ileum Regulation of the passage of gastric contents into the duodenum. When the chyme is sufficiently acidified and liquefied, the pyloric antrum forces small jets of gastric contents through the pyloric sphincter into the duodenum. Small Intestine The small intestine is the longest part of the gastrointestinal tract and extends from the pyloric orifice of the stomach to the ileocecal fold. This hollow tube, which is approximately 6 to 7 m long with a narrowing diameter from beginning to end, consists of the duodenum, the jejunum, and the ileum. Small Intestine The small intestine comprises three main sections continuous with each other: 1.The duodenum: It is about 25 cm long and curves around the head of the pancreas. Secretions from the gall bladder and pancreas are released into the duodenum through a common structure, the hepatopancreatic ampulla, and the opening into the duodenum is guarded by the hepatopancreatic sphincter (of Oddi). 2.The jejunum: It is the middle section of the small intestine and is about 2 meters long. 3.The ileum, or terminal section, is about 3 meters long and ends at the ileocaecal valve, which controls the flow of material from the ileum to the caecum, the first part of the large intestine, and prevents regurgitation. Small Intestine : Duodenum The first part of the small intestine is the duodenum. This C-shaped structure, adjacent to the head of the pancreas, is 20 to 25 cm long and is above the level of the umbilicus; its lumen is the widest of the small intestine. It is retroperitoneal except for its beginning, which is connected to the liver by the hepatoduodenal ligament, a part of the lesser omentum. Small Intestine : Duodenum The duodenum is divided into four parts : The superior part (first part) extends from the pyloric orifice of the stomach to the neck of the gallbladder, is just to the right of the body of vertebra LI, and passes anteriorly to the bile duct, gastroduodenal artery, portal vein, and inferior vena cava. Clinically, the beginning of this part of the duodenum is referred to as the ampulla or duodenal cap, and most duodenal ulcers occur in this part of the duodenum. Small Intestine : Duodenum The descending part (second part) of the duodenum is just to the right of midline and extends from the neck of the gallbladder to the lower border of vertebra LIII. Its anterior surface is crossed by the transverse colon, posterior to it is the right kidney, and medial to it is the head of the pancreas. This part of the duodenum contains the major duodenal papilla, which is the common entrance for the bile and pancreatic ducts, and the minor duodenal papilla, which is the entrance for the accessory pancreatic duct.  Small Intestine : Duodenum The inferior part (third part) of the duodenum is the longest section, crossing the inferior vena cava, the aorta, and the vertebral column. It is crossed anteriorly by the superior mesenteric artery and vein. The ascending part of the duodenum passes upward on, or to the left of, the aorta to approximately the upper border of vertebra LII and terminates at the duodenojejunal flexure. This duodenojejunal flexure is surrounded by a fold of peritoneum containing muscle fibers called the suspensory muscle (ligament) of duodenum (ligament of Treitz). Contracts to help the contents of the intestines move along. Helps anchor the duodenum (first part of the small intestine, just after the stomach). Is an important landmark in human anatomy, especially for surgeons. It forms the boundary between the upper GI tract to the lower GI tract and helps define what classifies as an upper or lower gastrointestinal bleed. Upper GI vs Lower GI tract The upper digestive tract includes the esophagus (the tube that connects the mouth to the stomach), the stomach, and the duodenum (the first part of the small intestine). The lower gastrointestinal tract or lower GI includes most of the small intestine, the large intestine, and the anus. Small Intestine : Jejunum The jejunum and ileum make up the last two sections of the small intestine. The jejunum represents the proximal two-fifths. It is mostly in the left upper quadrant of the abdomen and is larger in diameter and has a thicker wall than the ileum. Additionally, the inner mucosal lining of the jejunum is characterized by numerous prominent folds that circle the lumen (plicae circulares). Small Intestine : Ileum The ileum makes up the distal three-fifths of the small intestine and is mostly in the right lower quadrant. Compared to the jejunum, the ileum has thinner walls, fewer and less prominent mucosal folds (plicae circulares), shorter vasa recta, more mesenteric fat, and more arterial arcades. The ileum opens into the large intestine, where the cecum and ascending colon join together. Jejunum vs Ileum Large Intestine/Colon It is about 1.5 meters long, beginning at the caecum in the right iliac fossa and terminating at the rectum and anal canal deep in the pelvis. The general characteristics of most of the large intestine are: its large internal diameter compared to that of the small intestine; peritoneal-covered accumulations of fat (the omental appendices) are associated with the colon; the segregation of longitudinal muscle in its walls into three narrow bands (the taeniae coli), which are primarily observed in the cecum and colon and less visible in the rectum; and the sacculations of the colon (the haustra of the colon). Large Intestine/Colon The colon is divided into the caecum, ascending colon, transverse colon, descending colon, sigmoid colon rectum, and anal canal. The caecum/cecum This is the first part of the colon. It is a dilated region which has a blind end inferiorly and is continuous with the ascending colon superiorly. Just below the junction of the two, the ileocaecal valve opens from the ileum. The vermiform appendix is a fine tube, closed at one end, which leads from the caecum. It is usually about 13 cm long and has the same structure as the walls of the colon but contains more lymphoid tissue. The surface projection of the base of the appendix is at the junction of the lateral and middle one-third of a line from the anterior superior iliac spine to the umbilicus (McBurney’s point). People with appendicular problems may describe pain near this location.  Large Intestine/Colon The ascending colon The colon begins as the ascending colon, a retroperitoneal structure which ascends superiorly from the cecum. When it meets the right lobe of the liver, it turns 90 degrees to move horizontally. This turn is known as the right colic flexure (or hepatic flexure), and marks the start of the transverse colon. The transverse colon This is a loop of the colon which extends across the abdominal cavity in front of the duodenum and the stomach to the area of the spleen where it forms the splenic flexure and curves acutely downwards to become the descending colon. The descending colon This passes down the left side of the abdominal cavity then curves towards the midline. After it enters the true pelvis it is known as the sigmoid colon. The sigmoid colon This part describes an S-shaped curve in the pelvis then continues downwards to become the rectum. Rectum/Anal Canal It is a slightly dilated section of the colon about 13 cm long. It leads from the sigmoid colon and terminates in the anal canal. The anal canal is a short passage about 3.8 cm long in the adult and leads from the rectum to the exterior. Two sphincter muscles control the anus; the internal sphincter, consisting of smooth muscle fibers, is under the control of the autonomic nervous system and the external sphincter, formed by skeletal muscle, is under voluntary control. Colon, Rectum and Anal Canal : Functions Absorption The contents of the ileum which pass through the ileocaecal valve into the caecum are fluid, even though some water has been absorbed in the small intestine. In the large intestine absorption of water continues until the familiar semisolid consistency of feces is achieved. Mineral salts, vitamins, and some drugs are also absorbed into the blood capillaries from the large intestine. Microbial activity The large intestine is heavily colonized by certain types of bacteria, which synthesize vitamin K and folic acid. They include Escherichia coli, Enterobacter aerogenes, Streptococcus faecalis and Clostridium perfringens (welchii). Defecation Usually, the rectum is empty, but when a mass movement forces the contents of the sigmoid colon into the rectum the nerve endings in its walls are stimulated by a stretch. Defaecation involves involuntary contraction of the muscle of the rectum and relaxation of the internal anal sphincter. Contraction of the abdominal muscles and lowering of the diaphragm increase the intra-abdominal pressure (Valsalva’s maneuver) and so assist the process of defecation. Small Intestine vs Large Intestine EXTERNAL DIFFERENCES The small intestine is more mobile (except for the duodenum), whereas the ascending and the descending parts of the colon are fixed. The small intestine has a mesentery (except for the duodenum), whereas the large intestine is retroperitoneal (except for the transverse colon and sigmoid colon). The diameter of the full small intestine is smaller than that of the full large intestine. In the small intestine, the longitudinal muscle forms a continuous layer around the gut, whereas in the large intestine (except for the appendix, rectum, and anal canal), the longitudinal muscle forms three bands (the teniae coli). The small intestine has no fatty tags attached to its wall, whereas the large intestine has the appendices epiploicae. The wall of the small intestine is smooth, whereas the wall of the large intestine is sacculated. Small Intestine vs Large Intestine INTERNAL DIFFERENCES The mucous membrane of the small intestine has permanent folds ( the plicae circulares), whereas the large intestine does not. The mucous membrane of the small intestine has Peyer’s patches, whereas the large intestine has solitary lymph follicles. The mucous membrane of the small intestine has villi, whereas the large intestine does not. Mesenteries Mesenteries are peritoneal folds that attach viscera to the posterior abdominal wall. They allow some movement and provide a conduit for vessels, nerves, and lymphatics to reach the viscera and include: the mesentery—associated with parts of the small intestine, the transverse mesocolon—associated with the transverse colon, and the sigmoid mesocolon—associated with the sigmoid colon. All of these are derivatives of the dorsal mesentery. Mesentery The mesentery is a large, fan-shaped, double-layered fold of peritoneum that connects the jejunum and ileum to the posterior abdominal wall. Its superior attachment is at the duodenojejunal junction, just to the left of the upper lumbar part of the vertebral column. In the fat between the two peritoneal layers of the mesentery are the arteries, veins, nerves, and lymphatics that supply the jejunum and ileum. Transverse Mesocolon The transverse mesocolon is a fold of peritoneum that connects the transverse colon to the posterior abdominal wall. Its two layers of peritoneum leave the posterior abdominal wall across the anterior surface of the head and body of the pancreas and pass outward to surround the transverse colon. Between its layers are the arteries, veins, nerves, and lymphatics related to the transverse colon. Sigmoid Mesocolon The sigmoid mesocolon is an inverted, V-shaped peritoneal fold that attaches the sigmoid colon to the abdominal wall The Digestive Process 1. The start of the process - the mouth: The digestive process begins in the mouth. Food is partly broken down by the process of chewing and by the chemical action of salivary enzymes (these enzymes are produced by the salivary glands and break down starches into smaller molecules). A mouthful takes 30-60 seconds. 2. On the way to the stomach: the esophagus After being chewed and swallowed, the food enters the esophagus. The esophagus is a long tube that runs from the mouth to the stomach. It uses rhythmic, wave-like muscle movements (called peristalsis) to force food from the throat into the stomach. This muscle movement gives us the ability to eat or drink even when we're upside-down. For a medium-sized bolus, it takes about 5–8 seconds to reach the stomach. The Digestive Process 3. In the stomach The stomach is a large, sack-like organ that churns the food and bathes it in a very strong acid (gastric acid). Food in the stomach that is partly digested and mixed with stomach acids is called chyme. Emptying the stomach takes 2–6 hours. 4. In the small intestine After being in the stomach, food enters the duodenum, the first part of the small intestine. It then enters the jejunum and then the ileum (the final part of the small intestine). In the small intestine, bile (produced in the liver and stored in the gall bladder), pancreatic enzymes, and other digestive enzymes produced by the inner wall of the small intestine help in the breakdown of food. It takes 3–5 hours from entry to the duodenum to exit from the ileum. The Digestive Process 5. In the large intestine – After passing through the small intestine, food passes into the large intestine. In the large intestine, some of the water and electrolytes (chemicals like sodium) are removed from the food. Many microbes (bacteria like Bacteroides, Lactobacillus acidophilus, Escherichia coli, and Klebsiella) in the large intestine help in the digestion process. The first part of the large intestine is called the cecum (the appendix is connected to the cecum). Food then travels upward in the ascending colon. The food travels across the abdomen in the transverse colon, goes back down the other side of the body in the descending colon, and then through the sigmoid colon. Residence time in the colon ranges from 4–72 hours, with a normal Accesory Organs of the Digestive System Salivary glands Salivary glands are glands that open or secrete into the oral cavity. Most are small glands in the submucosa or mucosa of the oral epithelium lining the tongue, palate, cheeks, and lips, and open into the oral cavity directly or via small ducts. In addition to these small glands are much larger glands, which include the paired parotid, submandibular, and sublingual glands. Parotid gland The parotid gland on each side is entirely outside the boundaries of the oral cavity in a shallow triangular-shaped trench formed by: the sternocleidomastoid muscle behind; the ramus of mandible in front; and superiorly, the base of the trench is formed by the external acoustic meatus and the posterior aspect of the zygomatic arch. Parotid gland The gland normally extends anteriorly over the masseter muscle, and inferiorly over the posterior belly of the digastric muscle. The parotid duct or Stensen’s duct passes anteriorly across the external surface of the masseter muscle and then turns medially to penetrate the buccinator muscle of the cheek and open into the oral cavity adjacent to the crown of the second upper molar tooth.  Submandibular gland The elongate submandibular glands are smaller than the parotid glands, but larger than the sublingual glands. Each is hook shaped : the larger arm of the hook is directed forward in the horizontal plane below the mylohyoid muscle and is therefore outside the boundaries of the oral cavity-this larger superficial part of the gland is directly against a shallow impression on the medial side of the mandible (submandibular fossa) inferior to the mylohyoid line; the smaller arm of the hook (or deep part) of the gland loops around the posterior margin of the mylohyoid muscle to enter and lie within the floor of the oral cavity where it is lateral to the root of the tongue on the lateral surface of the hyoglossus muscle. Submandibular gland The submandibular duct or Wharton’s duct emerges from the medial side of the deep part of the gland in the oral cavity and passes forward to open on the summit of a small sublingual caruncle (papilla) beside the base of frenulum of the tongue. The lingual nerve loops under the submandibular duct, crossing first the lateral side and then the medial side of the duct, as the nerve descends anteromedially through the floor of the oral cavity and then ascends into the tongue. Sublingual glands The sublingual glands are the smallest of the three major paired salivary glands. Each is almond shaped and is immediately lateral to the submandibular duct and associated lingual nerve in the floor of the oral cavity. Each sublingual gland lies directly against the medial surface of the mandible where it forms a shallow groove (sublingual fossa) superior to the anterior one-third of the mylohyoid line. The sublingual gland drains into the oral cavity via numerous small ducts (minor sublingual ducts or Ducts of Rivinus), which open onto the crest of the sublingual fold. Occasionally, the more anterior part of the gland is drained by a duct (major sublingual duct or Bartholin’s duct) that opens together with the submandibular duct on the sublingual caruncle.  Pancreas The pancreas lies mostly posterior to the stomach. It extends across the posterior abdominal wall from the duodenum, on the right, to the spleen, on the left. The pancreas is (secondarily) retroperitoneal except for a small part of its tail and consists of a head, uncinate process, neck, body, and tail. The head of the pancreas lies within the C-shaped