Digestive System Part I PDF

Lecture 1 Digestive system The digestive (alimentary) system – Lat. systema digestorium – is a complex of organs whose function consist in mechanical and chemical treatment of food, absorption of the treated nutrients, and excretion of undigested remnants of the food. The human digest...

Lecture 1 Digestive system The digestive (alimentary) system – Lat. systema digestorium – is a complex of organs whose function consist in mechanical and chemical treatment of food, absorption of the treated nutrients, and excretion of undigested remnants of the food. The human digestive system consists of the gastrointestinal tract and also the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). The gastrointestinal tract (digestive tract, alimentary canal) include the next part: Oral cavity Pharynx Esophagus Stomach Small intestine Large intestine  Oral cavity The oral cavity or mouth (lat. cavitas oris) is initial part of gastrointestinal tract. It lies inferior to the nasal cavities, and has a roof, floor, and lateral walls. It opens onto the face through the oral fissure and is continuous posteriorly with the cavity of the pharynx at the oropharyngeal isthmus. The oral cavity subdivided into two main parts: the outer oral vestibule (lat. vestibulum oris) is between the dental arches and the deep surface of the cheeks and lips. The inner oral cavity proper (lat. cavitas oris propria), which is enclosed by the dental arches, located behind the dental arches.  Oral cavity Walls of oral cavity: Superior wall or roof of the oral cavity is the palate. The palate consist of two part – hard palate (lat. palatinum durum) and soft palate (lat. palatinum molle). Inferior wall or floor of the oral cavity is the diaphragm of the mouth (lat. diaphragma oris) and the tongue. Diaphragm of the mouth include mylohyoid and geniohyoid muscles. Lateral walls are named the cheeks (lat. buccae).  Oral cavity The oral cavity has multiple functions: It is the inlet for the digestive system involved with the initial processing of food, which is aided by secretion from salivary glands. It manipulates sounds produced by the larynx an one outcome of this is speech. It can be used for breathing because it opens into the pharynx, Which is a common pathway for food and air.  Tongue The tongue is a muscular organ in the mouth of most vertebrates that manipulates food for mastication, and is used in the act of swallowing. A major function of the tongue is the enabling of speech. It is of importance in the digestive system and is the primary organ of taste in the gustatory system. The tongue's upper surface (dorsum) is covered by taste buds housed in numerous lingual papillae. The tongue also serves as a natural means of cleaning the teeth.  Tongue Papillae of the tongue filifirm papillae fungiform papillae vallate papillae foliate papillae  Tongue Muscles of the tongue The eight muscles of the human tongue are classified as either intrinsic or extrinsic. The four intrinsic muscles act to change the shape of the tongue, and are not attached to any bone. The four extrinsic muscles act to change the position of the tongue, and are anchored to bone.  Tongue Extrinsic muscles of the tongue The four extrinsic muscles originate from bone and extend to the tongue. They are the genioglossus, the hyoglossus (often including the chondroglossus) the styloglossus, and the palatoglossus. Their main functions are altering the tongue's position allowing for protrusion, retraction, and side-to-side movement.  Tongue Extrinsic muscles of the tongue The genioglossus arises from the mandible and protrudes the tongue. It is also known as the tongue's "safety muscle" since it is the only muscle that propels the tongue forward. The hyoglossus arises from the hyoid bone and retracts and depresses the tongue. The chondroglossus is often included with this muscle. The styloglossus arises from the styloid process of the temporal bone and draws the sides of the tongue up to create a trough for swallowing. The palatoglossus arises from the palatine aponeurosis, and depresses the soft palate, moves the palatoglossal fold towards the midline, and elevates the back of the tongue during swallowing.  Tongue Intrinsic muscles of the tongue Four paired intrinsic muscles of the tongue originate and insert within the tongue, running along its length. They are the superior longitudinal muscle, the inferior longitudinal muscle, the vertical muscle, and the transverse muscle. These muscles alter the shape of the tongue by lengthening and shortening it, curling and uncurling its apex and edges as in tongue rolling, and flattening and rounding its surface. This provides shape and helps facilitate speech, swallowing, and eating.  Tongue Intrinsic muscles of the tongue The superior longitudinal muscle runs along the upper surface of the tongue under the mucous membrane, and elevates, assists in retraction of, or deviates the tip of the tongue. It originates near the epiglottis, at the hyoid bone, from the median fibrous septum. The inferior longitudinal muscle lines the sides of the tongue, and is joined to the styloglossus muscle. The vertical muscle is located in the middle of the tongue, and joins the superior and inferior longitudinal muscles. The transverse muscle divides the tongue at the middle, and is attached to the mucous membranes that run along the sides.  Salivary glands The salivary glands are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands (parotid, submandibular, and sublingual) as well as hundreds of minor salivary glands. Salivary glands can be classified as serous, mucous or seromucous (mixed). In serous secretions, the main type of protein secreted is ptyalin(alpha-amylase), an enzyme that breaks down starch into maltose and glucose, whereas in mucous secretions, the main protein secreted is mucin which acts as a lubricant. Salivary glands  Waldeyer's – Pirogov’s tonsillar ring Waldeyer's – Pirogov’s tonsillar ring (pharyngeal lymphoid ring or Waldeyer's lymphatic ring) is a ringed arrangement of lymphoid tissue in the pharynx. Waldeyer's ring surrounds the naso- and oropharynx, with some of its tonsillar tissue located above and some below the soft palate (and to the back of the mouth cavity). The ring consists of the (from top to bottom): pharyngeal tonsils (or "adenoids"), are located on the roof of the nasopharynx, under the sphenoid bone. tubal tonsil on each side, where each auditory tube opens into the nasopharynx palatine tonsils (commonly called "the tonsils"), are located in the oropharynx group of lingual tonsils are located on the back part of the tongue  Pharynx The pharynx is a musculofascial half-cylinder that links the oral and nasal cavities in the head to the larynx and esophagus in neck. The pharyngeal cavity is a common pathway for air and food.  Pharynx The pharyngeal muscles are a group of muscles that form the pharynx, determining the shape of its lumen, and affecting its sound properties as the primary resonating cavity posterior to the oral cavity.The pharyngeal muscles contracts pushing the food into the esophagus. There are two muscular layers of the pharynx: the outer circular layer and the inner longitudinal layer. The outer circular layer includes: Inferior constrictor muscle Middle constrictor muscle Superior constrictor muscle During swallowing, these muscles constrict to propel bolus downwards (an involuntary process). The inner longitudinal layer includes: Stylopharyngeus muscle Salpingopharyngeus muscle Palatopharyngeus muscle During swallowing, these muscles act to shorten and widen the pharynx.  Classification of the organs The organs are divided into tubular and parenchymatous organs. The parenchymatous organs consist of two parts: parenchyma and stroma. The parenchyma is formed from specific elements, that assure the function of organs The stroma has a connective tissue origin sustain the parenchyma and leads the vessels and nerves. Common structure of tubular organs The wall of the tubular organs consists of few layers: The mucous coat The submucous layer The serous coat or adventitious coat