Respiratory System and Thoracic Cavity PDF

Respiratory system and thoracic cavity By Dr. Maher Finjan  General arrangement of the thoracic cavity In a cross section through the chest you will find that the thoracic cavity contains principally two pleural cavities. The pleural cavity on each side is almost completely fill...

Respiratory system and thoracic cavity By Dr. Maher Finjan  General arrangement of the thoracic cavity In a cross section through the chest you will find that the thoracic cavity contains principally two pleural cavities. The pleural cavity on each side is almost completely filled by a lung, leaving the cavity as a potential space containing a thin film of fluid (pleural fluid). The lungs are separated from each other by the structures in the mediastinum The hilum of the lung, is where the structures which enter and leave the lung form the root of the lung. the aorta lies in contact with the vertebral bodies slightly to the left of the midline. The esophagus lies anterior to the aorta. The trachea lies anterior to oesophagus. The posterior border of the lung is rounded because it is shaped by the ribs. The anterior border is sharp because it fits in between the heart and the chest. From the front, therefore, part of the heart is in contact with the chest wall but part of it is overlaid by lung tissue. The mediastinum forms a complete septum across the chest from front to back. The thoracic cage is composed of 1-12 thoracic vertebrae 2-12 pairs of ribs 3-sternum. The thoracic cage shape and boundaries: It is conical in shape, It is flattened antero-posteriorly. The thoracic cavity extend from superior to inferior thoracic apertures. Superior thoracic aperture bounded by T1 vertebra, first rib and manubrium. Inferior thoracic aperture is bounded by attachment of diaphragm. It is important that you do not think of the thoracic cage as a separate entity but remember that Upper limb muscles largely cover the thoracic wall Pectoralis major Pectoralis minor Serratus anterior Because the diaphragm extends superiorly, the ribs enclose abdominal viscera such as the liver and spleen. as well as thoracic viscera such as the heart and lungs. Thus, when ribs break (fracture) they may injure both thoracic and abdominal viscera Function of thoracic cage: 1-The chest wall provides a protective shield for both thoracic and abdominal viscera. 2-The articulations of the ribs, sternum, and vertebral column are important for respiration.  ribs Most individuals have 12 pairs of ribs however not true uncommonly an extra rib may costal cartilages articulate directly with the sternum be present. rib 1-7 false costal cartilages do not articulate directly with the sternum rib 8-12 articulate indirectly with the sternum rib 8-10 floating do not articulate with the sternum rib 11 &12 Typical rib (3-10): 1-head 2-neck 3-tubercle 4-and a shaft Atypical ribs: 1st rib 2nd rib 11th rib 12th rib  Typical rib long, thin, flat, curved, and slightly twisted bones. Head of typical rib: is the posterior end of the rib is wedge- shaped carries two articular facets. The neck: located between the head and tubercle. The tubercle: is at the junction of the neck and shaft. carries a smooth articular facet and a rough non-articular part. The smooth facet is for articulation (costo-transverse joint)with the numerically corresponding transverse process of a thoracic vertebra Shaft: Is lateral to the tubercle primarily it is directed posteriorly then it bends sharply anteriorly. The angle: The point of greatest change in curvature. becomes more and more medial as one ascends on the first rib the angle and tubercle correspond. The angle of a rib is its weakest part where it tends to break (fracture).  Typical ribs (3-10): Have external and internal surfaces superior and inferior borders. The inferior border is sharp and extends inferior to the costal groove on the internal surface of the shaft so that it protects the intercostal neurovascular bundle located in the costal groove  Atypical ribs The first rib: is the broadest and most curved rib. its head carries a single facet for articulation with the body of T1 vertebra. The shaft has inner and outer borders. The shaft has superior and inferior surfaces The superior surface of first rib carries a prominent scalene tubercle on its inner border for the insertion of scalenus anterior muscle. The subclavian vein crosses anterior to scalene tubercle, while the subclavian artery and the inferior trunk of the brachial plexus pass posterior to it  Cervical rib may articulate with the transverse process of C7 vertebra May be symptomless or may cause neurovascular symptoms in the upper limb due to stretching or compression related to structures on the superior surface of the first rib The second rib: Is longer than the first rib is characterized by the presence of a tuberosity for the attachment of serratus anterior muscle The 11th & 12th ribs: are short and carry a single 12 facet on the head for articulation with the body of the numerically corresponding vertebral body. 11 have neither neck nor tubercle. in other words, they do not articulate with transverse processes of vertebrae. The 11th rib has a slight angle and a shallow costal groove, the 12th rib has neither Costal cartilages: The anterior end of each rib is attached to a costal cartilage at a costochondral junction (joint). Costal cartilages are made of hyaline cartilage provide elasticity to the thoracic cage allow mobility of the ribs calcify after the age of about 55 years, this reduces elasticity of the rib cage and produces shadows on an x- ray. increase in length from the 1st to the 7th then gradually become shorter.  Costal margin: The inferior edges of the 7th-10th costal cartilages form the costal margin.  Sternochondral joints: The first costal cartilage articulates with the manubrium of the sternum by a primary cartilaginous joint The 2nd - 7th costal cartilages articulate with the body of the sternum by synovial joints The sternum (breastbone): is a flat bone. It consists of the manubrium sterni, body and the xiphoid process. The manubrium is almost quadrilateral. Has a palpable notch on its superior surface called the suprasternal or jugular notch. On each side of the jugular notch there is an articular facet for articulation with the medial end of the clavicle (clavicular notch) Sternoclavicular joint: the articulation is by a synovial joint. Costal facet: At the lateral margin of the manubrium there is a facet for the articulation with the first costal cartilage, the articulation is by a primary cartilaginous joint Manubrio-sternal joint: The inferior border of the manubrium articulates with the body of the sternum by a secondary cartilaginous joint. Bony union (synostosis) may take place between the body of the sternum and the manubrium after the age of 40 years Manubrio-sternal joint: Since there is a slight angulation between the manubrium and the body of the sternum, the region of the joint is called the sternal angle (of Louis). Sternal angle Is palpable as a raised horizontal ridge in the midline of the chest making it an important bony landmark located at about 5cm inferior to the jugular notch. Sternal angle is here that the second costal cartilage joins the sternum, It is the starting place where the physician counts the ribs to use them as landmarks. Counting ribs: The first rib is difficult to palpate because it lies deep to the clavicle. An intercostal space is located inferior to the rib of a corresponding number. Ribs may be counted posteriorly This is difficult and inaccurate, However, the inferior angle of the scapula is at the level of the 7th rib and is a good guide to the 7th intercostal space. The sternal angle also lies in the horizontal plane that passes trough the lower border of T4 vertebra. The body of the sternum is shorter in the female than in the male. Xiphoid process: Is small, thin, and variable in shape. It is located at the infrasternal angle, which is located at the diverging costal margins. The xiphoid process is made of cartilage that calcifies later in life and appears as a dense shadow on x-ray of the chest in older adults. The sternum is often used to obtain a specimen of red bone marrow in the investigations of various blood diseases by sternal puncture, using a wide bore needle. Features of thoracic vertebrae: Costal facets, vertebral canal, body, processes. Costal facets: The presence of the costal facet on the cervical thoracic body of the thoracic lumbar vertebra distinguishes it from vertebrae of other regions in the vertebral column. A thoracic vertebra has costal facets on the body and transverse processes. except T11 and T12, which has no costal facets on their transverse processes. Vertebral canal: The vertebral canal of a thoracic vertebra Cervical: Large & triangular Lumbar: Small & triangular is circular. Vertebral body: The body of a thoracic vertebra is heart-shaped. Transversly elongated Lumbar: Kidney-shaped Spinous process: The spinous processes of thoracic vertebrae are long and tapered They vary in their obliquity. In vertebrae of the middle of the series (T5-T8), the spinous processes are almost vertical. However, since the thoracic spines run downwards are joined by thick supraspinous ligaments are covered by fairly thick skin they are not easy to examine individually. Spine levels: The spine of T2 lies against the superior angle of the scapula, The spine of T3 lies against the spine of the scapula, The spine of T7 lies against the inferior angle of the scapula. Articulations: Thoracic vertebrae articulate with each other by means of a secondary cartilaginous joint between the bodies. Thoracic vertebrae also articulate with each other by means of a plane synovial joint on each side between superior and inferior articular processes Intervertebral foramen: When two adjacent vertebrae are articulated, an intervertebral foramen is formed bounded above and below by the pedicles, A spinal nerve emerges from the foramen. In the thoracic region T1 spinal nerve emerges between the 1st and 2nd thoracic vertebra and T12 spinal nerve between the 12th thoracic vertebra and the 1st lumbar vertebra. Muscles of the thoracic wall: In addition to the muscles of the thorax proper, many muscles are attached to the ribs including muscles of the back, abdominal muscles, the diaphragm, and pectoral muscles. Muscles of the thorax proper: Serratus posterior, levator costarum, and intercostal muscles. Serratus posterior: flat muscles extend from spinous processes of vertebrae to ribs. There is a serratus posterior superior and inferior. both serratus posterior superior and inferior are supplied by intercostal nerves (anterior primary rami of spinal nerves) Levator costarum: are 12 pairs of fan-shaped (triangular) muscles extend from transverse processes of vertebrae to insert into the rib below. they elevate the rib as the name indicates. They are supplied by posterior rami of spinal nerves Intercostal muscles: There are three layers of muscles in both the thoracic and the abdominal walls. Internal oblique External intercostal Internal oblique External oblique Innermost intercostal Transverse abdominis External intercostal: forms the most superficial layer, Its fibers are directed downwards and forward. Its fibers has the same direction of external oblique muscle of the abdomen. It extends from the inferior border of the rib above to the superior border of the rib below. The external intercostal muscle extends from the rib tubercle behind to the costochondral junction in front. Anteriorly the external intercostal muscle is replaced by an aponeurosis (thin flat tendon), the anterior (external) intercostal membrane. Internal intercostal: forms the intermediate layer Its fibers are directed downwards and backwards. Its fibers have the same direction of the internal oblique muscle of the. the fibers of the internal intercostal are therefore at right angles to those of the external intercostal. Extends from the costal groove of the rib above to the upper border of the rib below. The internal intercostal extends from the side of the sternum in front to the angles of the ribs behind. The internal intercostal muscle is replaced by an aponeurosis, the posterior (internal) intercostal membrane. Innermost intercostal: Forms the deepest layer, Its fibers have the same direction of that of internal intercostal muscle layer. It corresponds to the transversus abdominis muscle of the anterior abdominal wall. Extends between internal surfaces of adjacent. The innermost intercostal fibers cover the middle 2/4th of the intercostal spaces. Subcostalis & transversus thoracis: Lie in a deeper plane than the innermost intercostal their fibers cross more than one intercostal space. The Subcostalis slips: are located near the angles of the ribs mainly in the lower intercostal spaces, Their fibers run parallel with those of the innermost intercostal. Transversus thoracis: Is also called sternocostalis since its fibers extend from the lower 1/3rd of the posterior surface of the sternum and the costal cartilages of the lower true ribs to the internal surfaces of the upper costal cartilages. Its fibers have different obliquity, the lower fibers are horizontal and become continuous with the transversus abdominis muscle, hence the name transversus thoracis. Nerve supply: intercostal nerves. The neurovascular plane lies between the internal intercostal and innermost intercostal. Subcostalis Diaphragm: it is a thin musculotendinous structure that fills the inferior thoracic aperture and separate abdominal cavity from thoracic cavity. Attachments of diaphragm: 1- xiphoid process of sternum. 2- costal margin of thoracic wall. 3- ends of the ribs 11, 12. 3-vertebrae of lumber region. Structures passing through the diaphragm: 1-inferior vena cava T8. 2-oesophagus T10. 3-vagus nerves passing through diaphragm with oesophagus. 4-Aorta T12. 5- thoracic duct passing behind diaphragm with aorta. 6-Azygous and hemiazygous also pass behind aortic hiatus. Blood supply of diaphragm: 1- from above: pericardiacophrenic and musculophrenic arteries branches of internal thoracic artery. 2-from below: inferior phrenic arteries right and left from abdominal aorta. Nerve supply: phrenic nerves right and left ( C3-C5). Endothoracic fascia: The innermost intercostal, subcostales, and transversus thoracis separate the intercostal neurovascular bundle from the layer of fascia external to the pleura called the endothoracic fascia Tapping of pleural fluid: Commonly the needle is passed in the mid-axillary line at the 8th intercostal space (Do not introduce the needle below the 9th intercostal space; the diaphragm may be pierced and abdominal viscera endangered). The needle thus pierces the following structures from without inwards: skin, superficial fascia, serratus anterior, external intercostal, internal intercostal, innermost intercostal, endothoracic fascia, and parietal pleura. The needle should be inserted close to the upper border of the rib to avoid damage of the intercostal neurovascular bundle, which is close to the lower border of the rib. Intercostal Nerves: The neurovascular intercostal bundle is arranged in the following order from above downwards: intercostal vein, artery, and nerve (i.e. VAN). In the thorax, the neurovascular bundle is located near the lower border of the corresponding rib sheltered by the costal groove. Intercostal nerves: These are the anterior primary rami (ramus = branch L.) of the first 11 thoracic spinal nerves. subcostal nerve: The anterior ramus of the 12th thoracic spinal nerve runs at the lower border of the twelfth rib. The first six intercostal nerves are distributed within their intercostal spaces, The 7th to 11th intercostal nerves and the subcostal nerve leave the anterior end of the intercostal space to enter the anterior abdominal wall, which they also supply. e.g. the 10th intercostal nerve reaches the level of the umbilicus. Branches of intercostal nerves: 1-Lateral cutaneous branch 2-Anterior cutaneous branch 3-Collateral branch 4-Muscular (motor) branches 5-Sensory branches 6-Rami communicantes. 1-Lateral cutaneous branch: reaches the skin near the mid- axillary line and divides into anterior and posterior branches. 2-Anterior cutaneous branch: reaches the skin near the midline and divides into medial and lateral branches 3-Collateral branch: runs inferior to the main nerve near the upper border of the rib below 4-Muscular (motor) branches : given off by the main nerve and its collateral 5-Sensory branches: to the pleura and to the peritoneum in the case of the 7th-11th intercostal nerves 6-Rami communicantes: connect the intercostal nerve to a ganglion of the sympathetic trunk Referred pain: Since the lower five intercostal nerves share in the nerve supply of the anterior abdominal wall (sensory and motor). pathology (such as tuberculosis) of for example T9 vertebral body affecting the spinal nerve arising through the intervertebral foramen would give rise to abdominal pain. pain is referred to the longest fibers of spinal nerves involved. The T9 spinal nerve has its cutaneous branches in the anterior abdominal wall. It is here that referred pain from the back may be felt. Subluxation of the interchondral joints of the lower thoracic region following trauma may trap the intercostal nerve as it crosses the costal margin along its way to the anterior abdominal wall. This may cause stimulation of the intercostal nerve and contraction of its myotome causing contraction of the anterior abdominal muscles and the patient might present with abdominal symptoms Sympathetic trunk: This is a nerve trunk beaded by ganglia. It extends the whole length of the trunk on each side of the midline from the base of the skull to the tip of the coccyx. Developmentally, there is the same number of ganglia as there are spinal nerves but many of them fuse. In the thoracic region, there are usually 10-12 ganglia Sympathetic ganglion: A ganglion is a collection of nerve cells surrounded by connective tissue. The nerve fibers that reach the ganglion are called preganglionic. Preganglionic fibers synapse with the ganglion cells whose fibers are thus called postganglionic. Each intercostal nerve is connected to a ganglion of the sympathetic trunk by two rami. A white ramus (white since it is myelinated), which carries preganglionic sympathetic fibers to the sympathetic trunk. A gray ramus (unmyelinated), which carries postganglionic sympathetic fibers from the sympathetic trunk. Postganglionic fibers are distributed to sweat glands and smooth muscles of the skin, viscera and blood vessels. The 1st intercostal nerve: divides into a large superior and a small inferior part The superior part joins the brachial plexus (the nerve plexus that supplies the upper limb) The inferior part is thus left small and has neither anterior nor lateral cutaneous branches; in other words, it does not reach the skin of the thorax. The skin of the thorax above the level of the sternal angle is supplied by C4. The skin of the thorax below the level of the sternal angle is supplied by intercostal nerves starting from T2. The nerves from C5-T1 form the brachial plexus and are distributed to the upper limb. The lateral cutaneous branch of the 2nd intercostal nerve joins the brachial plexus and supplies the skin of the axilla and the upper medial side of the arm (brachium). The lateral cutaneous branch of the 2nd intercostal nerve is called the intercostobrachial nerve. 1-Costocervical trunk: Arises from the posterior aspect of the third part subclavian artery and divides into a branch that supplies the back of the neck (ascending cervical) and the superior intercostal artery (hence the name costocervical). Superior intercostal artery crosses the neck of the first rib to supply the upper 2-3 intercostal spaces. 2-Internal thoracic artery: arises from the lower border of the subclavian artery and travels down into the thorax. Descends vertically behind the costal cartilages. The internal thoracic artery ends in the 6th intercostal space by dividing into two terminal branches: superior epigastric and musculophrenic arteries. Branches of the internal thoracic artery: a-Superior epigastric artery b- Musculophrenic artery c-anterior intercostal arteries d-perforating arteries e-pericardiophrenic artery f-mediastinal arteries a-Superior epigastric artery: Descends almost vertically and enters the anterior abdominal wall which it supplies. b-Musculophrenic artery: Runs along the costal margin. It supplies the diaphragm and the lower intercostal spaces by anterior intercostal arteries c-anterior intercostal arteries of the upper six spaces. d-perforating arteries: accompany the anterior cutaneous branches of the corresponding intercostal nerves. Are large and important in the female since they provide for the blood supply of the breast; hence, the internal thoracic artery is also called the internal mammary artery e-pericardiophrenic artery: Accompanies the phrenic nerve and supplies the pericardium f-mediastinal arteries: Supplied to the contents of the anterior mediastinum e.g. the thymus gland A portion of the internal thoracic artery is now frequently used to increase the blood supply of the heart in coronary artery bypass grafting (CABG) Intercostal arteries: Each intercostal space has a large single posterior intercostal artery and two small anterior intercostal arteries. In each space the anterior and posterior intercostal arteries anastomose with each other A-Posterior intercostal arteries: The posterior intercostal arteries of the first two spaces are branches of the superior intercostal artery (a branch of the costo-cervical trunk, a branch of the subclavian artery). The posterior intercostal arteries of the lower nine spaces are branches of the descending thoracic aorta, so as the subcostal artery. Because the aorta lies on the left side of the posterior thoracic wall, the lower nine intercostal arteries are longer than their counterparts on the left B-Anterior intercostal arteries: The anterior intercostal arteries of the upper six spaces are branches of the internal thoracic artery The anterior intercostal arteries of the lower intercostal spaces are branches of the musculophrenic artery. The lower two spaces have posterior intercostal arteries only. Each intercostal artery supplies muscles, skin, and parietal pleura. In the region of the breast, in the female, the branches are particularly large In one type of a congenital condition called coarctation of the aorta, the aorta is narrowed beyond the origin of the left subclavian artery Since the anterior intercostal arteries link with the posterior intercostal arteries, blood is conveyed to the descending thoracic aorta beyond the narrowing  Intercostal veins the left and right posterior intercostal veins drain towards the posterior mediastinum into the azygos and hemiazygos veins respectively. The anterior intercostal veins drain into the internal thoracic vein Pleural cavity: The pleural cavity on each side is almost completely filled by a lung, leaving a the cavity as a potential space containing a thin film of fluid (pleural fluid). The pleura is a thin membrane of fibrous tissue surfaced by a single layer of flat cells to make it slippery. The pleura is in two layers, the visceral pleura which covers the outer surface of the lung and is continuous at the hilum with the parietal pleura that lines the thoracic cavity on each side of the mediastinum. Unlike the parietal pleura, the visceral pleura dips into the lung fissures; therefore, in the fissures, the visceral pleura of adjacent lobes lie in contact with each other. Parts of parietal pleura: The parietal pleura, though a continuous sheet, is given different names according to the parts it covers. It is therefore divided into costal, mediastinal, diaphragmatic, and cervical pleura At the root of the lung, the mediastinal pleura passes laterally forming a sleeve that encloses the structures at the lung root. Inferior to the lung root the sleeve of the mediastinal pleura is too big for the contained structures forming a double layer called the pulmonary ligament. The function of the pulmonary ligament is to provide a dead space into which the lung root descends with descent of the diaphragm. More important is that pulmonary veins (contained in the lung root) can expand during periods of increased venous return from the lungs as in exercise (remember that the pulmonary veins carry oxygenated blood from the lungs to the heart). The cervical pleura or the cupola of the pleura extends through the superior thoracic aperture into the root of the neck. Its summit is 2-4 cm superior to the medial 1/3rd of the clavicle. The cervical pleura does not extend superior to the neck of the first rib because the first rib slopes inferiorly. Extension of the lung and pleura into the root of the neck make them liable to be injured in wounds of the neck. Surface projection of the pleura: Think of even numbers. The cervical pleura extends into the neck 2-4cm above the medial third of the clavicle. From this point, the pleura passes behind the sternoclavicular joint reaching the midline at the level of the 2nd costal cartilage. From here, the two pleural cavities are in contact as far as the 4th cartilage, here the right pleura continues vertically down to the level of the 6th costal cartilage. The left pleura arches laterally at the level of the 4th costal cartilage and descends lateral to the border of the sternum down to the level of the 6th costal cartilage. At the level of the 6th costal cartilage the pleura on both sides pass around the chest wall crossing the 8th rib at the mid-clavicular line. The pleura on both sides pass around the chest wall crossing the 10th rib at the mid-axillary line. The pleura on both sides pass around the chest wall crossing the 12th rib at the back. The lung markings correspond to those of the pleura above but are two ribs higher in the lower part of the thorax. Pleural reflections: The previously-mentioned lines are called lines of pleural reflection. The sternal pleural reflection is where the costal pleura is continuous with the mediastinal pleura posterior to the sternum. The costal pleural reflection is where the costal pleura is continuous with the diaphragmatic pleura near the costal margin. The vertebral reflection lies posteriorly along the lateral side of the bodies of thoracic vertebrae. The mediastino-diaphragmatic reflection connects the inferior ends of the sternal and vertebral reflections. Pleural recesses: The sites where parietal pleura comes into contact with parietal pleura are called pleural recesses. During full inspiration, the lung expands and fill the pleural cavity; but during quiet inspiration there are three sites where the lung does not fully occupy the pleural cavities. The pleural recesses are only occupied by lung tissue during full inspiration, they are the right and left costo-diaphragmatic recesses(Radiologists call this region the costophrenic angle, Excess fluid in the pleural cavity will cause an opacity which obliterates this angle). and the costo- mediastinal recess (Lies at the anterior ends of the 4th and 5th intercostal spaces and during full inspiration it becomes occupied by the lingula of the left lung) The pleura descends inferior to the costal margin in three regions 1- the right infrasternal angle 2 & 3:The right and left costovertebral angles. These regions should be remembered by the surgeon when making incisions through the anterior abdominal wall so that the incision should not enter the pleural sac since this results in pneumothorax. This is especially important for the costo-vertebral angles Which are located behind the upper pole of the kidney and are liable to be opened while incising for nephrectomy (removal of the kidney) Nerve supply of pleura: The nerve supply of the visceral pleura as in the lung is autonomic through nerves that accompany the bronchial arteries, these are vasomotor. The visceral pleura is thus insensitive to ordinary stimuli as pain and touch. The parietal pleura as part of the chest wall is supplied by somatic nerves namely intercostal and phrenic nerves. The collateral branches of intercostal nerves segmentally supply the costal pleura and the peripheral part of the diaphragmatic pleura. The central part of the diaphragmatic pleura and the mediastinal pleura are supplied by the phrenic nerves. The parietal pleura is thus sensitive to pain. Referred pain: Irritation of the costal and peripheral part of the diaphragmatic pleura by disease causes local pain and referred pain i.e. pain referred or seems to be arising frown regions supplied by the same intercostal nerves that supply the pleura. Thus pain is referred to the chest and abdominal walls, both are supplied by intercostal nerves. Irritation of the mediastinal or central part of the diaphragmatic pleura supplied by the phrenic nerve is referred to the tip of the shoulder where the dermatome there is that of C4 since the root value of the phrenic nerve is C3, 4, and 5 mainly C4 (therefore pain is referred to the dermatome whose root value is the same as that of the phrenic nerve. A root value of a nerve is the spinal cord segment from which it is derived) Irritation of the parietal peritoneum below the diaphragm (which is also supplied by the phrenic nerve) is also referred to the tip of the shoulder Blood supply of pleura: The visceral pleura derives its arterial supply from bronchial arteries that supply lung tissue with oxygenated blood. The bronchial arteries are branches of the thoracic aorta. The blood supply of the parietal pleura is derived from that supplying the chest wall namely internal thoracic, intercostal, and musculophrenic arteries pleural cavity: The pleural cavity is a potential space containing a thin film of pleural fluid. The pressure inside the cavity is slightly below atmospheric. The pressure inside the lung is more or less atmospheric. Pneumothorax: If the chest wall is penetrated following for example a stab wound or the visceral pleura is punctured usually as a result of rupture of bullae on the surface of the lung, air enters the pleural cavity so that its pressure becoming the same as that inside the lung; since the lungs are more elastic, the lungs tend to collapse. The clinician can recognize mediastinal deviation by feeling the position of the trachea at the root of the neck where the trachea can normally be felt most anteriorly in the midline at the jugular notch. Pleural effusion (hydrothorax): The presence of excess fluid in the pleural cavity. The fluid tends to gravitate towards the costomediastinal recesses, thus, it obliterates the costophrenic angle. Accumulation of more fluid, like in pneumothorax, tends to collapse the lung and displace the mediastinum to the other side. Lungs: Each lung has the shape of a half cone. The right lung usually has three lobes, the left only two. In the adult, the lung is gray and its surface is mottled especially in people living in industrial areas and in smokers. In the child, the lung is pink Oblique fissure: In each lung an oblique fissure extends from the surface to the hilum (i.e. a deep fissure) and divides the organ into separate upper and lower lobes Horizontal fissure: On the right lung a horizontal fissure passes from the anterior margin into the oblique fissure to separate a wedge-shaped middle lobe from the upper lobe. There is no middle lobe in the left lung but there is a tongue-like projection of the upper lobe at the cardiac notch, which corresponds to the right middle lobe and is called the lingula. The cardiac notch is produced on the superior lobe of the left lung owing to the bulging of the heart. Right/ left lung differences: 1-The relation of the medial surfaces. 2-The cardiac notch. 3- The number of lobes. 4-The right lung is larger than the left. 5-The base of the lung (diaphragmatic surface) is more concave on the right than that on the left, this is produced by the underlying liver thus making the right lung shorter than the left Surfaces and borders: Each lung has an apex, three surfaces, and three borders. The apex extends into the root of the neck. Surfaces: 1-Costal surface: Convex, Shows impressions of the ribs in the embalmed cadavers. 2-Medial surface: a-vertebral part: occupies the paravertebral gutter on each side of the thoracic part of the vertebral column. b- mediastinal part: fits against the mediastinum contents and contains the root of the lungs. 3-Diaphragmatic surface (or the base since it is opposite the apex; remember that the lung is a half cone). Borders of the lung: 1-anterior border: Is thin and sharp, Apart from the cardiac notch of the left side, it corresponds more or less to the anterior border of the pleura. 2-posterior border: Thick and rounded. 3-inferior border: Surrounds the base of the lung. Is thin and sharp when it extends into the costodiaphragmatic recess. Is blunt where it divides the diaphragmatic from the mediastinal surfaces. Tracheo-broncheal tree: The trachea is flexible tube extend through mediastinum anterior to oesophagus and inferior to larynx. The anterior and lateral wall of trachea supported by cartilaginous rings about 15-20 rings these rings made the tube rigid and open. The posterior part of tube lined by trachealis muscle. it divides into right and left main (principal) bronchi at the level of the manubriosternal joint (lower border of T4 vertebra). The most inferior part of tracheal cartilages separates internally the two main bronchi at their origin and forms internal ridge called carina. the right main bronchus is 2.5cm long and enters the lung at the level of the body of T5. the left main bronchus is 5cm long and enters the lung at the level of T6. Right bronchus: Since the trachea deviates slightly to the right in the lower part of its course, the right bronchus is shorter and more in line with the trachea than the left. It is also wider than the left. Note that the right main bronchus is larger than the left due to the fact that the right lung is larger than the left (60%:40%). Since the right bronchus is more in line with the trachea than the left and since it is shorter and wider than the left, inhaled foreign bodies are more likely to be found in the right lung than the left. Lobar bronchi: Each main bronchus is divided symmetrically into lobar bronchi. The right main bronchus as it approaches the hilum, gives off an upper lobe bronchus (outside the hilum) and then divides into a middle and lower lobe bronchus (within the hilum). On the left side, the middle lobe bronchus is replaced by the lingular bronchus. Segmental bronchi: Each lobar bronchus divides into segmental bronchi. Each segmental bronchus supplies one bronchopulmonary segment of the lung. Within each segment there is further branching of the bronchi. The bronchopulmonary segments are roughly pyramidal in shape. Their apices towards the hilum, their bases on the surface of the lung. Bronchopulmonary segments have the same names and number as the segmental bronchi. Each bronchopulmonary segment has its own artery and vein. The vessels accompany the bronchi and their subdivisions The arteries are a 1-branches of the pulmonary vein from the heart to alveoli only for respiration and 2- bronchial arteries from aorta (usually one on the right and two on the left) to the bronchi and lung tissue only for nutrition The veins are 1-a tributary of the pulmonary artery then to the left atrium of the heart. 2-The bronchial veins drain into the azygos vein on the right and the accessory hemiazygos on the left. There is no anastomosis between bronchial and pulmonary arteries Clinical points: Pneumonia: Disease of the lung (tumor or abscess) may be limited to one segment before spreading to another. Pulmonary embolism: A blood clot obstructs the flow of blood through a branch of the pulmonary artery resulting in destruction (infarction) of a lung segment or lobe Pulmonary angiogram demonstrating a large perfusion defect in the right lower lobe Lobectomy: The affected segment may be surgically removed (resected) without disrupting surrounding lung tissue. Atelectasis: Each segment is surrounded by connective tissue that prevents air from passing between segments. Air in a bronchopulmonary segment whose segmental bronchus is obstructed will be absorbed by the blood. This causes segmental atelectasis (collapse) of the tissue in the affected segment