Adonlce Khoury, PharmD, BCPS

• Clinical Assistant Professor
• College of Pharmacy
• University of Florida
• U F Health Shands Hospital
• Clinical Pharmacy Specialist
• Gainesville, Florida

Trachea Right common Es ophagus Right internal carotid artery jugular vein Left common carotid artery Right s ubclavian artery Right s ubclavian vein Right brachiocephalic vein Left internal jugular vein Left s ubclavian artery Thymus Lying immediately posterior to the manubrium of the sternum mood disorder other dis lexapro 20 mg free shipping, the thymus depression definition quotes best buy lexapro, asymmetrical and bilobed depression memory loss order lexapro from india, is the most anterior component of the superior mediastinum anxiety nos dsm code buy lexapro 10mg online. The upper extent of the thymus can reach into the neck as high as the thyroid gland and a lower portion typically extends into the anterior mediastinum over the pericardial sac depression disease definition buy lexapro 10mg with amex. Involved in the early development of the immune system anxiety uncontrollable shaking purchase lexapro 5 mg on line, the thymus is a large structure in the child, begins to atrophy after puberty, and shows considerable size variation in the adult. In the elderly adult, it is barely identi able Left s ubclavian vein Left brachiocephalic vein Right pulmonary Arch of aorta artery Left pulmonary artery Left main bronchus Superior vena cava Pulmonary trunk Thoracic aorta Right main bronchus Es ophagus As cending aorta 116. It crosses to the right, moving in a slightly inferior direction, and joins with the right brachiocephalic vein to form the superior vena cava posterior to the lower edge of the right rst costal cartilage close to the right sternal border. Venous tributaries include the vertebral, rst posterior intercostal, left superior intercostal, inferior thyroid, and internal thoracic veins. Clinical app Left brachiocephalic vein the left brachiocephalic vein crosses the midline posterior to the manubrium in the adult. In infants and children, the left brachiocephalic vein rises above the superior border of the manubrium and therefore is less protected. The lower half of the superior vena cava is within the pericardial sac and contained in the middle mediastinum. The superior vena cava receives the azygos vein immediately before entering the pericardial sac and may also receive pericardial and mediastinal veins. Left superior intercostal vein the left superior intercostal vein receives the second, third, and sometimes the fourth left posterior intercostal veins, usually the left bronchial veins, and sometimes the left pericardiacophrenic vein. It passes over the left side of the aortic arch, lateral to the left vagus nerve and medial to the left phrenic nerve, before entering the left brachiocephalic vein. Inferiorly, it may connect with the accessory hemiazygos vein (superior hemiazygos vein). Clinical app Venous access for central and dialysis lines Large systemic veins are used to establish central venous access for administering large amounts of uid, drugs, and blood. Most of these lines (small bore tubes) are introduced through venous puncture into the axillary, subclavian, or internal jugular veins. The lines are then passed through the main veins of the superior mediastinum, with the tips of the lines usually residing in the distal portion of the superior vena cava or in the right atrium. Arch of aorta and its branches the thoracic portion of the aorta can be divided into ascending aorta, arch of aorta, and thoracic (descending) aorta. Three branches arise from the superior border of the arch of the aorta and, at their origins, all three are crossed anteriorly by the left brachiocephalic vein. Clinical app Using the superior vena cava to access the inferior vena cava Because the superior and inferior vena cava are oriented along the same vertical axis, a guidewire, catheter, or line can be passed from the superior vena cava through the right atrium and into the inferior vena cava. The rst branch Beginning on the right, the rst branch of the arch of aorta is the brachiocephalic trunk. It is the largest of the three branches and, at its point of origin behind the manubrium of sternum, is slightly anterior to the other two branches. The vessel closes soon after birth and forms the ligamentous connection observed in the adult. The arteries mainly supply the right side of the head and neck and the right upper limb, respectively. Occasionally, the brachiocephalic trunk has a small branch, the thyroid ima artery, which contributes to the vascular supply of the thyroid gland. Clinical app Coarctation of the aorta Coarctation of the aorta is a congenital abnormality in which the aortic lumen is constricted just distal to the origin of the left subclavian artery. At this point, the aorta becomes signi cantly narrowed and the blood supply to the lower limbs and abdomen is diminished. Over time, collateral vessels develop around the chest wall and abdomen to supply the lower body. The coarctation also affects the heart, which has to pump the blood at higher pressure to maintain peripheral perfusion. The second branch the second branch of the arch of aorta is the left common carotid artery. It arises from the arch immediately to the left and slightly posterior to the brachiocephalic trunk and ascends through the superior mediastinum along the left side of the trachea. The third branch the third branch of the arch of the aorta is the left subclavian artery. It arises from the arch of aorta immediately to the left of, and slightly posterior to , the left common carotid artery and ascends through the superior mediastinum along the left side of the trachea. Clinical app Traumatic injury to the aorta the aorta has three xed points of attachment: the aortic valve, the ligamentum arteriosum, and the point of entry behind the crura of the diaphragm. The rest of the aorta is relatively free from attachment to other structures of the mediastinum and is less likely to be injured. Ligamentum arteriosum the ligamentum arteriosum is also in the superior mediastinum and is important in embryonic circulation, when it is a patent vessel (the ductus arteriosus). Posterior to it is the esophagus, which is immediately anterior to the vertebral column. Signi cant mobility exists in the vertical positioning of these structures as they pass through the superior mediastinum. As the trachea and esophagus pass through the superior mediastinum, they are crossed laterally by the azygos vein on the right side and the arch of aorta on the left side. As they pass through the thorax, they provide parasympathetic innervation to the thoracic viscera and carry visceral afferents from the thoracic viscera. Visceral afferents in the vagus nerves relay information to the central nervous system about normal physiological processes and re ex activities. Clinical app Aortic dissection In certain conditions, such as in severe arteriovascular disease, the wall of the aorta can split longitudinally, creating a false channel, which may or may not rejoin into the true lumen distally. This aortic dissection occurs between the intima and media anywhere along its length. In the abdomen the visceral vessels may be disrupted, producing ischemia to the gut or kidneys. Right vagus nerve the right vagus nerve enters the superior mediastinum between the right brachiocephalic vein and the brachiocephalic trunk. Es ophagus Trachea Rig ht vag us ne rve Azygos vein Bronchus Es ophagus Brachiocephalic trunk Right brachiocephalic vein Left brachiocephalic vein Superior vena cava Rig ht phre nic ne rve Clinical app Abnormal origin of great vessels Great vessels occasionally have an abnormal origin, including: a common origin of the brachiocephalic trunk and the left common carotid artery, the left vertebral artery originating from the aortic arch, and the right subclavian artery originating from the distal portion of the aortic arch and passing behind the esophagus to supply the right arm-as a result, the great vessels form a vascular ring around the trachea and the esophagus, which can potentially produce dif culty swallowing. As it passes through the superior mediastinum, branches are given off to the esophagus, cardiac plexus, and pulmonary plexus. As they pass through the thorax, they provide innervation through somatic afferent bers to the mediastinal pleura, brous pericardium, and parietal layer of the serous pericardium. Left vagus nerve the left vagus nerve enters the superior mediastinum posterior to the left brachiocephalic vein between the left common carotid and left subclavian arteries. It passes into the superior mediastinum just deep to the mediastinal part of the parietal pleura and crosses the left side of the arch of aorta. It descends in a posterior direction and passes posterior to the root of the left lung to reach the esophagus in the posterior mediastinum. As the left vagus nerve passes through the superior mediastinum, branches go to the esophagus, cardiac plexus, and pulmonary plexus. The left vagus nerve also gives rise to the left recurrent laryngeal nerve, which arises at the inferior margin of the arch of aorta just lateral to the ligamentum arteriosum. The left recurrent laryngeal nerve passes inferior to the arch of aorta before ascending on its medial surface. Entering a groove between the trachea and esophagus, the left recurrent laryngeal nerve continues superiorly to enter the neck and terminate in the larynx. Right phrenic nerve the right phrenic nerve enters the superior mediastinum lateral to the right vagus nerve, and lateral and slightly posterior to the beginning of the right brachiocephalic vein. It continues inferiorly along the right side of this vein and the superior vena cava. On entering the middle mediastinum, the right phrenic nerve descends along the right side of the pericardial sac, within the brous pericardium, anterior to the root of the right lung. The pericardiacophrenic vessels accompany it through most of its course in the thorax. It leaves the thorax by passing through the diaphragm with the inferior vena cava. Left phrenic nerve the left phrenic nerve enters the superior mediastinum in a position similar to the path taken by the right phrenic nerve. It lies lateral to the left vagus nerve and lateral and slightly posterior to the beginning of the left brachiocephalic vein. Es ophagus Le ft re c urre nt laryng e al ne rve Left s ubclavian artery Phrenic nerves the phrenic nerves arise in the cervical region from the third, fourth, and fth cervical spinal cord segments. On each side, the internal jugular and subclavian veins join to form the brachiocephalic veins behind the sternal ends of the clavicles near the sternoclavicular joints. The left brachiocephalic vein crosses from left to right behind the manubrium of sternum. The brachiocephalic veins unite to form the superior vena cava behind the lower border of the costal cartilage of the right rst rib. Right common carotid artery Trachea Right internal jugular vein Right s ubclavian artery Right s ubclavian vein Right brachiocephalic vein Superior vena cava Es ophagus Left common carotid artery Left internal jugular vein Left s ubclavian artery Left s ubclavian vein Left brachiocephalic vein Arch of aorta Left pulmonary artery Left main bronchus Pulmonary trunk Thoracic aorta Right pulmonary artery Right main bronchus Es ophagus As cending aorta and the aorta, a region known clinically as the aortopulmonary window and may be compressed in any patient with a pathological mass in this region. Lymph node enlargement, often associated with the spread of lung cancer, is a common condition that may produce compression. Chest radiography is therefore usually carried out for all patients whose symptoms include a hoarse voice. More superiorly, the right vagus nerve gives off the right recurrent laryngeal nerve, which "hooks" around the right subclavian artery at the superior sulcus of the right lung. Thoracic duct in the superior mediastinum the thoracic duct, the major lymphatic vessel in the body, passes through the posterior portion of the superior mediastinum. Posterior mediastinum the posterior mediastinum is posterior to the pericardial sac and diaphragm and anterior to the bodies of the mid and lower thoracic vertebrae. Laterally, it is bordered by the mediastinal part of parietal pleura on either side. Major structures in the posterior mediastinum include the: esophagus and its associated nerve plexus, thoracic aorta and its branches, azygos system of veins, thoracic duct and associated lymph nodes, sympathetic trunks, and thoracic splanchnic nerves. Clinical app the vagus nerves, recurrent laryngeal nerves, and hoarseness the left recurrent laryngeal nerve is a branch of the left vagus nerve. It passes between the pulmonary artery Esophagus the esophagus is a muscular tube passing between the pharynx in the neck and the stomach in the abdomen. As it approaches the diaphragm, it moves anteriorly and to the left, crossing from the right side of the thoracic aorta to a position anterior to it. The esophagus has a slight anterior-to-posterior curvature that parallels the thoracic portion of the vertebral column, and is secured superiorly in the neck by its attachment to the pharynx and inferiorly in the thorax by its attachment to the diaphragm. Clinical app Esophagus constrictions the esophagus is a exible, muscular tube that can be compressed or narrowed by surrounding structures at four locations. An ingested corrosive substance would move more slowly through a narrowed region, causing more damage at this site than elsewhere along the esophagus. Relationships to important structures in the posterior mediastinum In the posterior mediastinum, the right side of the esophagus is covered by the mediastinal part of the parietal pleura. Posterior to the esophagus, the thoracic duct is on the right side inferiorly, but crosses to the left more superiorly. Anterior to the esophagus, below the level of the tracheal bifurcation, are the right pulmonary artery and the left main bronchus. The esophagus then passes immediately posteriorly to the left atrium, separated from it only by pericardium. Structures other than the thoracic duct posterior to the esophagus include portions of the hemiazygos veins, the right posterior intercostal vessels, and, near the diaphragm, the thoracic aorta. 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. Arterial supply and venous and lymphatic drainage Es ophagus Left vagus nerve Right vagus nerve Innervation Innervation of the esophagus, in general, is complex. Striated muscle bers in the superior portion of the esophagus originate from the branchial arches and are innervated by branchial efferents from the vagus nerves. Smooth muscle bers are innervated by components of the parasympathetic part of the autonomic division of the peripheral nervous system, visceral efferents from the vagus nerves. These are preganglionic bers that synapse in the myenteric and submucosal plexuses of the enteric nervous system in the esophageal wall. Sensory innervation of the esophagus involves visceral afferent bers originating in the vagus nerves, sympathetic trunks, and splanchnic nerves. The visceral afferents from the vagus nerves are involved in relaying information back to the central nervous system about normal physiological processes and re ex activities. The visceral afferents that pass through the sympathetic trunks and the splanchnic nerves are the primary participants in detection of esophageal pain and transmission of this information to various levels of the central nervous system. Ante rio r vag al trunk Es o phag e al ple xus Stomach Po s the rio r vag al trunk. Clinical app Esophageal cancer When patients present with esophageal cancer, it is important to note which portion of the esophagus contains the tumor, because tumor location determines the sites to which the disease will spread. Esophageal cancer spreads quickly to lymphatics, draining to lymph nodes in the neck and around the celiac artery in the abdomen.

It has been postulated that this subset of T cells may initiate immune responses to microbes at epithelia anxiety xanax dosage buy lexapro on line, before the recruitment and activation of antigenspecific T cells depression symptoms nausea purchase generic lexapro line. It is not known if this is the case in other inflammatory disorders or what the cells are recognizing or how much they are contributing to the development of the disease depression symptoms in adolescence purchase lexapro with amex. However anxiety 20 weeks pregnant cheap lexapro 20 mg visa, the roles of these cells in protective immunity or disease in humans are unclear depression definition by psychologist discount lexapro 5 mg. Given their abundance in the liver anxiety 27 weeks pregnant generic lexapro 5 mg without prescription, it is possible that they represent a second important barrier to gut flora that have breached the intestinal epithelial barrier and entered the blood, since blood draining the gut first enters the liver through the portal circulation. Each subset produces cytokines that increase its own development and inhibit the development of the other subsets, thus leading to increasing polarization of the response. Activated macrophages kill phagocytosed microbes ingested into phagolysosomes by the actions of reactive oxygen and nitrogen species and enzymes (called classical macrophage activation). Th17 cells may also be important in mediating tissue damage in autoimmune diseases. These cells produce cytokines and may contribute to host defense and inflammatory diseases. It is mediated by T lymphocytes and can be transferred from immunized to naive individuals by T cells and not by antibodies. Mechanisms underlying helper T-cell plasticity: implications for immune-mediated disease. Th17 cell pathway in human immunity: lessons from genetics and therapeutic interventions. A brief history of T(H)17, the first major revision in the T(H)1/T(H)2 hypothesis of T cell-mediated tissue damage. Interleukin-4- and interleukin13-mediated alternatively activated macrophages: roles in homeostasis and disease. The viruses cannot be destroyed if the infected cells are not phagocytes with intrinsic lysosomal microbicidal mechanisms. Even in phagocytes, if the viruses are in the cytosol, they are inaccessible to these killing mechanisms. In these situations, the only way to eradicate the established infection is to kill the infected cell, crippling the ability of the virus to survive and replicate. The same mechanism is used to eliminate phagocytes containing ingested bacteria that escape from phagosomes into the cytosol and are no longer susceptible to the killing activity of the phagocytes. Two transcription factors that are required for this program of new gene expression are T-bet (which we discussed in relationship to Th1 differentiation in Chapter 10) and eomesodermin, which is structurally related to T-bet. As we discussed in Chapter 6, the immune system deals with this problem by the process of cross-presentation. The requirement for helper cells varies according to the type of antigen exposure. These cytokines may be produced by different dendritic cell populations during the innate immune response to viral and some bacterial infections. The term exhaustion has been used to imply that the effector response starts but is shut down (unlike in tolerance, when lymphocytes fail to develop into effector cells). This phenomenon of exhaustion was first described in a chronic viral infection in mice and was implicated in the prolonged persistence of the virus. The cells also express transcription factors associated with effector and memory cells, including T-bet and eomesodermin, but they remain functionally inactive. The phenomenon of T cell exhaustion may have evolved to attenuate the tissue-damaging consequences of chronic infection. The granules also contain a sulfated proteoglycan, serglycin, which serves to hold granzymes and perforin in the granules in an inactive state. The main function of perforin is to facilitate delivery of the granzymes into the cytosol of the target cell. Perforin can polymerize and form aqueous pores in the target cell membrane, but these pores may not be of sufficient size to allow granzymes to enter. Perforin may then act on the endosomal membrane to facilitate the release of the granzymes into the target cell cytosol. Once in the cytosol, the granzymes cleave various substrates, including caspases, and initiate apoptotic death of the cell. For example, granzyme B cleaves and activates caspase-3 as well as the Bcl-2 family member Bid, which triggers the mitochondrial pathway of apoptosis. The granzymes are delivered into the cytoplasm of the target cells by a perforin-dependent mechanism, and they induce apoptosis. This interaction also results in activation of caspases and apoptosis of Fas-expressing targets. This is particularly important in two types of situations when cells cannot destroy microbes that infect them. First, most viruses live and replicate in cells that lack the phagosome/lysosome machinery for destroying microbes (such as hepatitis viruses in liver cells). Second, even in phagocytes, some microbes escape from vesicles and live in the cytosol, where microbicidal mechanisms are ineffective because these mechanisms are largely restricted to vesicles (to protect the host cells from damage). Bacteria such as Mycobacterium tuberculosis and Listeria monocytogenes are examples of microbes that escape from vesicles and enter the cytosol of infected cells. These viruses are not highly cytopathic, but the host senses and reacts against the infectious microbe and is not able to distinguish microbes that are intrinsically harmful or relatively harmless (see Chapter 19). The severe and prolonged macrophage activation underlies the manifestations of the disease, including enlargement of the spleen caused by increased numbers of activated macrophages ("lymphohistiocytosis") which phagocytose and destroy normal red blood cells ("hemophagocytosis"). Perforin facilitates granzyme entry into the cytoplasm of target cells, and granzymes initiate the process of apoptosis. The mechanisms by which antibodies eliminate microbes are described in Chapter 13. Humoral immune responses are initiated by specific B cell recognition of antigen in secondary lymphoid organs. Antigen binds to membrane immunoglobulin M (IgM) and IgD on mature, naive B cells, generating signals required for their proliferation and differentiation into plasma cells. The antibody that is eventually secreted by the plasma cell has essentially the same specificity as the original antibody that served as the antigen receptor on the surface of the naive B cell. A single B cell may, within a week, give rise to as many as 5000 antibody-secreting cells, which collectively produce more than 1012 antibody molecules per day. Antibody responses are T-dependent or T-independent, depending on the nature of the antigen and the involvement of helper T cells. The responses to protein antigens require T cell help, so these antigens are called T-dependent. The term helper T lymphocyte came from the realization that T cells stimulate, or help, B lymphocytes to produce antibodies. In Tdependent responses some activated B cells begin to produce antibodies other than IgM; this process is called heavy chain isotype (class) switching. As the response develops, activated B cells produce antibodies that bind to antigens with increasing affinity, and these B cells progressively dominate the response; this process is called affinity maturation. In addition to isotype switching and affinity maturation, helper T cells stimulate the production of long-lived plasma cells and the generation of memory B cells. Multivalent antigens with repeating determinants, such as polysaccharides, can activate B cells without T cell help. The activation of B cells is initiated by specific recognition of antigens by the surface Ig receptors of the cells. Antigen and other stimuli, including helper T cells, stimulate the proliferation and differentiation of the specific B cell clone. Progeny of the clone may differentiate into plasma cells that produce IgM or other Ig isotypes. T-dependent Protein antigen Helper T cell Isotype-switched, high-affinity antibodies; memory B cells, long-lived plasma cells IgG Follicular B cells IgM IgE Mainly IgM, low-affinity antibodies; short-lived plasma cells IgA T-independent IgM Polysaccharide antigen B-1 cells, marginal zone B cells IgM Other signals. T-dependent antibody responses to protein antigens mainly involve follicular B cells. T-independent responses to multivalent antigens are mediated mainly by marginal zone B cells in the spleen and B-1 cells in mucosal sites. In a primary immune response, naive B cells are stimulated by antigen, become activated, and differentiate into antibody-secreting cells that produce antibodies specific for the eliciting antigen. A secondary immune response is elicited when the same antigen stimulates memory B cells, leading to production of greater quantities of specific antibody than are produced in the primary response. Note that the characteristics of secondary antibody responses summarized in the table are typical of T-dependent antibody responses to protein antigens. Primary responses result from the activation of previously unstimulated naive B cells, whereas secondary responses are due to the stimulation of expanded clones of memory B cells. Therefore, the secondary response develops more rapidly than does the primary response, and larger amounts of antibodies are produced in the secondary response. Furthermore, because the memory cells have already undergone isotype switching and affinity maturation, there is more IgG and other isotypes compared to IgM, and the affinity of the antibody is higher in secondary responses. Distinct subsets of B cells respond preferentially to different types of antigens. Follicular B cells in peripheral lymphoid organs primarily make antibody responses to protein antigens, and these B cell responses require collaboration with helper T cells. Marginal zone B cells in the spleen and other lymphoid tissues and B-1 cells in mucosal tissues and the peritoneum recognize multivalent antigens, such as blood-borne polysaccharides, and mount primarily T-independent antibody responses. Some marginal zone B cells participate in T-dependent responses, and some follicular B cells may make T-independent responses. With this background, we proceed to a discussion of B cell activation, starting with the interaction of antigen with B cells. We will then describe the role of helper T cells in B cell responses to protein antigens and the mechanisms of isotype switching and affinity maturation. The antigens then initiate the process of B cell activation, often working in concert with other signals that are generated during innate immune responses triggered by microbes or by adjuvants in vaccines. Antigens that elicit antibody responses may vary in size and composition (they may be small, soluble, large, or particulate) and may be free or bound to antibodies. Soluble antigens, generally smaller than 70 kD, may then reach the B cell zone through conduits that extend between the subcapsular sinus and the underlying follicles. Many antigens that enter the node through afferent lymphatic vessels are not captured by subcapsular sinus macrophages and are too large to enter the conduits. It has been suggested that these antigens may be captured in the medullary region by a subset of resident dendritic cells and transported into follicles, where they can activate B cells. These dendritic cells are not well defined, and how they are instructed to travel to the follicle is unclear. Natural antibodies may contribute to the formation of immune complexes and the presentation of some antigens during primary immune responses. Polysaccharide antigens can be captured by macrophages in the marginal zone of splenic lymphoid follicles and displayed or transferred to B cells in this area. In all of these cases, the antigen that is presented to B cells is generally in its intact, native conformation and is not processed by antigen-presenting cells. Small antigens are delivered to B cells in follicles through afferent lymphatics and via conduits, and larger antigens by subcapsular sinus macrophages or by dendritic cells in the medulla. Antigen Recognition and Antigen-Induced B Cell Activation 255 antigens recognized by B and T lymphocytes (see Chapter 6). Although the presentation of antigen to B cells by subcapsular sinus macrophages, macrophages in the splenic marginal zone, and by medullary dendritic cells has been described in experimental models, how these cells prevent the proteins antigens they capture from being engulfed and degraded remains unclear. First, binding of antigen to the receptor delivers biochemical signals to the B cells that initiate the process of activation. As discussed later, signaling is more robust with multivalent T-independent antigens than with T-dependent protein antigens. Second, the receptor internalizes the bound antigen into endosomal vesicles, and if the antigen is a protein, it is processed into peptides that may be presented on the B cell surface for recognition by helper T cells. This antigen-presenting function of B cells will be considered later in the context of T-dependent B cell activation. Although antigen recognition can initiate B cell responses, by itself it is usually inadequate to stimulate significant B cell proliferation and differentiation, even for T-independent antigens. Complement activation typically occurs in response to microbes that activate this system in the absence of antibodies by the alternative and lectin pathways, and in the presence of antibodies by the classical pathway (see Chapters 4 and 13). In all of these situations, complement fragments are generated that bind to the microbes. Some nonmicrobial polysaccharides also activate complement by the alternative or lectin pathway, and this is one reason that such antigens are able to induce antibody responses without T cell help. These pattern recognition receptors provide signals that enhance or cooperate with those from the B cell receptor complex during B cell activation. In addition, the activation of myeloid cells through pattern recognition receptors can promote B cell activation indirectly in two ways. Most T-independent antigens, such as polysaccharides, contain multiple identical epitopes on each molecule. Such multivalent antigens can effectively cross-link many B cell antigen receptors and initiate responses even though they are not recognized by helper T lymphocytes. In contrast, many naturally occurring globular protein antigens possess only one copy of each epitope per molecule. These weak signals may be sufficient to keep the B cells alive, induce changes in chemokine receptor expression, and promote antigen endocytosis (Table 12. Some protein antigens may be displayed as multivalent arrays on the surfaces of microbes or cells, or they may be multivalent because they are in aggregates. After specific B cells recognize antigens, the subsequent steps in humoral immune responses are very different in T-dependent and T-independent responses. We will next describe the activation of B cells by protein antigens and helper T cells.

The angle formed by the pubic arch can be approximated by the angle between the thumb and index nger for women and the angle between the index nger and middle nger for men anxiety relief techniques discount 10mg lexapro, as shown in the insets bipolar depression or major depression discount lexapro 5 mg without a prescription. Sa cro-iliac joint Margin of ala Promontory Clinical app Pelvic fracture the pelvis can be viewed as a series of anatomical rings bipolar depression 7 months lexapro 20mg without a prescription. The major bony pelvic ring consists of parts of the sacrum bipolar depression dsm code purchase lexapro 10 mg without a prescription, ilium depression exhaustion purchase lexapro from india, and pubis rumination depression definition buy lexapro without prescription, which forms the pelvic inlet. The greater and lesser sciatic foraminae, formed by the greater and lesser sciatic notches and the sacrospinous and sacrotuberous ligaments form the four bro-osseous rings. It is not possible to break one side of a bony ring without breaking the other side of the ring, which in clinical terms means that if a fracture is demonstrated on one side, a second fracture should always be suspected. Pubic tub ercle Pubic s ymphys is Pubic cres t Pecten Arcuate pubis line Linea terminalis. The smaller of the two, the sacrospinous ligament, is triangular, with its apex attached to the ischial spine and its base attached to the related margins of the sacrum and the coccyx. The sacrotuberous ligament is also triangular and is super cial to the sacrospinous ligament. Its base has a broad attachment that extends from the posterior superior iliac spine of the pelvic bone, along the dorsal aspect and the lateral margin of the sacrum, and onto the dorsolateral surface of the coccyx. Laterally, the apex of the ligament is attached to the medial margin of the ischial tuberosity. These ligaments stabilize the sacrum on the pelvic bones by resisting the upward tilting of the inferior aspect of the sacrum. They also convert the greater and lesser sciatic notches of the pelvic bone into foramina. The greater sciatic foramen lies superior to the sacrospinous ligament and the ischial spine. The lesser sciatic foramen lies inferior to the ischial spine and sacrospinous ligament between the sacrospinous and sacrotuberous ligaments. These muscles originate in the pelvic cavity but attach peripherally to the femur (Table 5. Apertures in the pelvic w all Passing through the foramen below the piriformis are the inferior gluteal nerves and vessels, the sciatic nerve, the pudendal nerve, the internal pudendal vessels, the posterior femoral cutaneous nerves, and the nerves to the obturator internus and quadratus femoris muscles. Each lateral pelvic wall has three major apertures through which structures pass between the pelvic cavity and other regions. Obturator canal At the top of the obturator foramen is the obturator canal, which is bordered by the obturator membrane, the associated obturator muscles, and the superior pubic ramus. The obturator nerve and vessels pass from the pelvic cavity to the thigh through this canal. Greater sciatic foramen the greater sciatic foramen is a major route of communication between the pelvic cavity and the lower limb. It is formed by the greater sciatic notch in the pelvic bone, the sacrotuberous and the sacrospinous ligaments, and the spine of the ischium. The piriformis muscle passes through the greater sciatic foramen, dividing it into two parts. The superior gluteal nerves and vessels pass through the foramen above the piriformis. Lesser sciatic foramen the lesser sciatic foramen is formed by the lesser sciatic notch of the pelvic bone, the ischial spine, the sacrospinous ligament, and the sacrotuberous ligament. The tendon of the obturator internus muscle passes through this foramen to enter the gluteal region of the lower limb. Because the lesser sciatic foramen is positioned below the attachment of the pelvic oor, it acts as a route of communication between the perineum and the gluteal region. The pudendal nerve and internal pudendal vessels pass between the pelvic cavity (above the pelvic oor) and the perineum (below the pelvic oor), by rst passing out of the pelvic cavity through the greater sciatic foramen, then looping around the ischial spine and sacrospinous ligament to pass through the lesser sciatic foramen to enter the perineum. Pelvic outlet the pelvic outlet is diamond shaped, with the anterior part of the diamond de ned predominantly by bone and the posterior part mainly by ligaments. In the midline anteriorly, the boundary of the pelvic outlet is the pubic symphysis. Reinforces the external anal sphincter and, in women, functions as a vaginal sphincter Contributes to the formation of the pelvic oor, which supports the pelvic viscera; pulls the coccyx forward after defecation Coccygeus Branches from the anterior rami of S3 and S4 Pubic s ymphys is Pubic arch Body of pubis the area enclosed by the boundaries of the pelvic outlet and below the pelvic oor is the perineum. Pelvic oor the pelvic oor is formed by the pelvic diaphragm and, in the anterior midline, the perineal membrane and the muscles in the deep perineal pouch. The pelvic diaphragm is formed by the levator ani and the coccygeus muscles from both sides. Extending laterally and posteriorly, the boundary on each side is the inferior border of the body of the pubis, the inferior ramus of the pubis, the ramus of the ischium, and the ischial tuberosity. From the ischial tuberosities, the boundaries continue posteriorly and medially along the sacrotuberous ligament on both sides to the coccyx. Terminal parts of the urinary and gastrointestinal tracts and the vagina pass through the pelvic outlet. Shaped like a bowl or funnel and attached superiorly to the pelvic walls, it consists of the levator ani and the coccygeus muscles (Table 5. Thus: the greater sciatic foramen is situated above the level of the pelvic oor and is a route of communication between the pelvic cavity and the gluteal region of the lower limb; and the lesser sciatic foramen is situated below the pelvic oor, providing a route of communication between the gluteal region of the lower limb and the perineum. These measurements include: the sagittal inlet (between the promontory and the top of the pubic symphysis); the maximum transverse diameter of the inlet; the bispinous outlet (the distance between ischial spines); and the sagittal outlet (the distance between the tip of the coccyx and the inferior margin of the pubic symphysis). Levator ani the two levator ani muscles originate from each side of the pelvic wall, course medially and inferiorly, and join together in the midline. The attachment to the pelvic wall follows the circular contour of the wall and includes. At the midline, the muscles blend together posterior to the vagina in women and around the anal aperture in both sexes. Posterior to the anal aperture, the muscles come together as a ligament or raphe called the anococcygeal ligament (anococcygeal body) and attaches to the coccyx. Anteriorly, the muscles are separated by a U-shaped defect or gap termed the urogenital hiatus. The margins of this hiatus merge with the walls of the associated viscera and with muscles in the deep perineal pouch below. The hiatus allows the urethra (in both men and women), and the vagina (in women), to pass through the pelvic diaphragm. The levator ani muscles are divided into at least three collections of muscle bers, based on site of origin and relationship to viscera in the midline: the pubococcygeus, the puborectalis, and the iliococcygeus muscles. The pubococcygeus originates from the body of the pubis and courses posteriorly to attach along the midline as far back as the coccyx. This part of the muscle is further subdivided on the basis of association with structures in the midline into the puboprostaticus (levator prostatae), the pubovaginalis, and the puboanalis muscles. A second major collection of muscle bers, the puborectalis portion of the levator ani muscles, originates, in association with the pubococcygeus muscle, from the pubis and passes inferiorly on each side to form a sling around the terminal part of the gastrointestinal tract. This muscular sling maintains an angle or exure, called the perineal exure, at the anorectal junction. This angle functions as part of the mechanism that keeps the end of the gastrointestinal system closed. This part of the muscle originates from the fascia that covers the obturator internus muscle. It joins the same muscle on the other side in the midline to form a ligament or raphe that extends from the anal aperture to the coccyx. The levator ani muscles help support the pelvic viscera and maintain closure of the rectum and vagina. Clinical app Defecation At the beginning of defecation, closure of the larynx stabilizes the diaphragm and intra-abdominal pressure is increased by contraction of abdominal wall muscles. As defecation proceeds, the puborectalis muscle surrounding the anorectal junction relaxes, which straightens the anorectal angle. Both the internal and the external anal sphincters also relax to allow feces to move through the anal canal. The fatty tissue of the ischio-anal fossa allows for changes in the position and size of the anal canal and 217 Pelvis and Perineum anus during defecation. During evacuation, the anorectal junction moves down and back and the pelvic oor usually descends slightly. During defecation, the circular muscles of the rectal wall undergo a wave of contraction to push feces toward the anus. As feces emerge from the anus, the longitudinal muscles of the rectum and levator ani bring the anal canal back up, the feces are expelled, and the anus and rectum return to their normal positions. The perineal membrane and deep perineal pouch the perineal membrane is a thick fascial, triangular structure attached to the bony framework of the pubic arch. Anteriorly, there is a small gap between the membrane and the inferior pubic ligament (a ligament associated with the pubic symphysis). The perineal membrane is related above to a thin space called the deep perineal pouch (deep perineal space). The deep perineal pouch is open above and is not separated from more superior structures by a distinct layer of fascia. The parts of perineal membrane and structures in the deep perineal pouch, enclosed by the urogenital hiatus above, therefore contribute to the pelvic oor and support elements of the urogenital system in the pelvic cavity, even though the perineal membrane and deep perineal pouch are usually considered parts of the perineum. The perineal membrane and adjacent pubic arch provide attachment for the roots of the external genitalia and the muscles associated with them. The urethra penetrates vertically through a circular hiatus in the perineal membrane as it passes from the pelvic cavity, above, to the perineum, below. In women, the vagina also passes through a hiatus in the perineal membrane just posterior to the urethral hiatus. Within the deep perineal pouch, a sheet of skeletal muscle functions as a sphincter, mainly for the urethra, and as a stabilizer of the posterior edge of the perineal membrane (Table 5. Anteriorly, a group of muscle bers surround the urethra and collectively form the external urethral sphincter. Two additional groups of muscle bers are associated with the urethra and vagina in women. One group forms the sphincter urethrovaginalis, which surrounds the urethra and vagina as a unit. The second group forms the compressor urethrae, on each side, which originate from the ischiopubic rami and meet anterior to the urethra. Together with the external urethral sphincter, the sphincter urethrovaginalis and compressor urethrae facilitate closing of the urethra. In both men and women, a deep transverse perineal muscle on each side parallels the free margin of the perineal membrane and joins with its partner at the midline. These muscles are thought to stabilize the position of the perineal body, which is a midline structure along the posterior edge of the perineal membrane. Perineal body the perineal body is an ill-de ned but important connective tissue structure into which muscles of the pelvic oor and the perineum attach. It is positioned in the midline along the posterior border of the perineal Table 5. The posterior end of the urogenital hiatus in the levator ani muscles is also connected to it. The deep transverse perineal muscles intersect at the perineal body; in women, the sphincter urethrovaginalis also attaches to the perineal body. Other muscles that connect to the perineal body include the external anal sphincter, the super cial transverse perineal muscles, and the bulbospongiosus muscles of the perineum. Op ening for vagina Opening for urethra External urethral s phincter Dee p trans vers e perineal mus cles Clinical app Episiotomy During childbirth the perineal body may be stretched and torn. Traditionally it was felt that if a perineal tear is likely, the obstetrician may proceed with an episiotomy. This is a procedure in which an incision is made in the perineal body to allow the head of the fetus to pass through the vagina. The maternal bene ts of this procedure have been thought to be less trauma to the perineum and decreased pelvic oor dysfunction. However, more recent evidence suggests that an episiotomy should not be performed routinely. Review of data has failed to show a decrease in pelvic oor damage with routine use of episiotomies. A Sphincter urethrovaginalis Compres s or urethrae Dee p perine al p ouc h Perineal memb rane Op ening for urethra External urethral s phincter Dee p tra ns vers e perineal mus cles B Perineal memb ra ne De ep pe rine al pouch. The viscera are arranged in the midline, from front to back; the neurovascular supply is through branches that pass medially from vessels and nerves associated with the pelvic walls. Gastrointestinal system Pelvic parts of the gastrointestinal system consist mainly of the rectum and the anal canal, although the terminal part of the sigmoid colon is also in the pelvic cavity. The rectum, the most posterior element of the pelvic viscera, is immediately anterior to , and follows the concave contour of the sacrum. The anorectal junction is pulled forward (perineal exure) by the action of the puborectalis part of the levator ani muscle, so the anal canal moves in a posterior direction as it passes inferiorly through the pelvic oor. In addition to conforming to the general curvature of the sacrum in the anteroposterior plane, the rectum has three lateral curvatures; the upper and lower curvatures to the right and the middle curvature to the left. Finally, unlike the colon, the rectum lacks distinct taeniae coli muscles, omental appendices, and sacculations (haustra of the colon). Sigmoid colon Rectum Rec tal ampulla Puborectalis mus cle Anal canal External anal s phincter A Rectum Levator ani Iliococcygeus Puborectalis Anal column Anal s inus Anal valve Internal anal s phincter (s mooth mus cle) Pectinate line Anocutaneous line ("white") Deep Superficial Subcutaneous External anal s phincter (s keletal mus cle) B Anal pecten Anal aperture 220. The anal mucosa can be palpated for abnormal masses, and in women, the posterior wall of the vagina and the cervix can be palpated.

They are divided into celiac bipolar depression 6 weeks cheap lexapro 5 mg with visa, superior mesenteric depression mentality definition discount lexapro 10 mg visa, and inferior mesenteric nodes depression bible verses cheap 20mg lexapro amex, and receive lymph from the organs supplied by the similarly named arteries anxiety bible verses buy line lexapro. Finally mood disorder related to general medical condition discount generic lexapro canada, the lateral aortic or lumbar nodes form the right and left lumbar trunks depression symptoms holden caulfield cheap 5mg lexapro fast delivery, whereas the pre-aortic nodes form the intestinal trunk. These trunks come together and form a con uence that, at times, appears as a saccular dilation (the cisterna chyli). The pre-aortic lymph node group drains lymph from the embryological midline structures, such as the liver, bowel, and pancreas. The para-aortic lymph node group (the lateral aortic or lumbar nodes), on either side of the aorta, drain lymph from bilateral structures, such as the kidneys and adrenal glands. Organs embryologically derived from the posterior abdominal wall also drain lymph to these nodes. These organs include the ovaries and the testes (importantly, the testes do not drain lymph to the inguinal regions). Massively enlarged lymph nodes are a feature of lymphoma, and smaller lymph node enlargement is observed in the presence of infection and metastatic malignant spread of disease. The surgical approach to retroperitoneal lymph node resection involves a lateral paramedian incision in the midclavicular line. The three layers of the anterolateral abdominal wall (external oblique, internal oblique, and transversus abdominis) are opened and the transversalis fascia is divided. Instead of entering the parietal peritoneum, which is standard procedure for most intra-abdominal surgical operations, the surgeon gently pushes the parietal peritoneum toward the midline, which moves the intra-abdominal contents and allows a clear view of the retroperitoneal structures. On the left, the para-aortic lymph node group (lateral aortic or lumbar nodes) are easily demonstrated with a clear view of the abdominal aorta and kidney. On the right the inferior vena cava is demonstrated, which has to be retracted to access to the right para-aortic lymph node chain (lateral aortic or lumbar nodes). The procedure of the retroperitoneal lymph node dissection is extremely well tolerated and lacks the problems of entering the peritoneal cavity. Unfortunately, the complication of a vertical incision in the midclavicular line is to divide the segmental nerve supply to the rectus abdominis muscle. This produces muscle atrophy and asymmetrical proportions to the anterior abdominal wall. Sympathetic trunks and splanchnic nerves the sympathetic trunks pass through the posterior abdominal region anterolateral to the lumbar vertebral bodies, before continuing across the sacral promontory and into the pelvic cavity. These represent collections of neuronal cell bodies-primarily postganglionic neuronal cell bodies-which are located outside the central nervous system. There are usually four ganglia along the sympathetic trunks in the posterior abdominal (lumbar) region. Also associated with the sympathetic trunks in the posterior abdominal region are the lumbar splanchnic nerves. These components of the nervous system pass from the sympathetic trunks to the plexus of nerves and ganglia associated with the abdominal aorta. Usually two to four lumbar splanchnic nerves carry preganglionic sympathetic bers and visceral afferent bers. Abdominal prevertebral plexus and ganglia the abdominal prevertebral plexus is a network of nerve bers surrounding the abdominal aorta. It extends from the aortic hiatus of the diaphragm to the bifurcation of the aorta into the right and left common iliac arteries. Continuing inferiorly, the plexus of nerve bers extending from just below the superior mesenteric artery to the aortic bifurcation is the abdominal aortic plexus. At the bifurcation of the abdominal aorta, the abdominal prevertebral plexus continues inferiorly as the superior hypogastric plexus. Throughout its length, the abdominal prevertebral plexus is a conduit for: preganglionic sympathetic and visceral afferent bers from the thoracic and lumbar splanchnic nerves. Associated with the abdominal prevertebral plexus are clumps of nervous tissue (the prevertebral ganglia), which are collections of postganglionic sympathetic neuronal cell bodies in recognizable aggregations along the abdominal prevertebral plexus; they are usually named after the nearest branch of the abdominal aorta. They are therefore referred to as celiac, superior mesenteric, aorticorenal, and inferior mesenteric ganglia. These structures, along with the abdominal prevertebral plexus, play a critical role in the innervation of the abdominal viscera. Nervous system in the posterior abdominal region Several important components of the nervous system are in the posterior abdominal region. These include the sympathetic trunks and associated splanchnic nerves, the plexus of nerves and ganglia associated with the abdominal aorta, and the lumbar plexus of nerves. Pos terior root Anterior root Es ophagus Vagus nerve Aorta Celiac ganglion Preganglionic paras ympathetic Enteric neuron Gray ramus communicans Pos terior and anterior rami White ramus communicans Sympathetic ganglion and trunk Greater s planchnic nerve Vis ceral afferent Vis ceral afferent Preganglionic s ympathetic Pos tganglionic s ympathetic 202. Lumbar plexus the lumbar plexus is formed by the anterior rami of nerves L1 to L3, and most of the anterior ramus of L4 (Table 4. Branches of the lumbar plexus include the iliohypogastric, ilio-inguinal, genitofemoral, lateral cutaneous nerve of thigh (lateral femoral cutaneous), femoral, and obturator nerves. The lumbar plexus forms in the substance of the psoas major muscle anterior to its attachment to the transverse processes of the lumbar vertebrae. Therefore, relative to the psoas major muscle, the various branches emerge either: anterior-genitofemoral nerve, medial-obturator nerve, or lateral-iliohypogastric, ilio-inguinal, and femoral nerves, and the lateral cutaneous nerve of the thigh. T12 L1 Iliohypogas tric nerve Ilio-inguinal nerve Genitofemoral nerve L3 Lateral cutaneous nerve of thigh L4 To iliacus mus cle Femoral nerve Obturator nerve To lumbos acral trunk L2 Iliohypogastric and ilio-inguinal nerves (L1) the iliohypogastric and ilio-inguinal nerves arise as a single trunk from the anterior ramus of nerve L1. Either before or soon after emerging from the lateral border of the psoas major muscle, this single trunk divides into the iliohypogastric and the ilio-inguinal nerves. It pierces the transversus abdominis muscle and continues anteriorly around the body between the transversus abdominis and internal oblique muscles. Above the iliac crest, a lateral cutaneous branch pierces the internal and external oblique muscles to supply the posterolateral gluteal skin. The remaining part of the iliohypogastric nerve (the anterior cutaneous branch) continues in an anterior direction, piercing the internal oblique just medial to the anterior superior iliac spine as it continues in an obliquely downward and medial direction. Becoming cutaneous, just above the super cial inguinal ring, after piercing the aponeurosis of the external oblique, it distributes to the skin in the pubic region. Ilio-inguinal nerve the ilio-inguinal nerve is smaller than, and inferior to , the iliohypogastric nerve as it crosses the quadratus lumborum muscle. Its course is more oblique than that of the iliohypogastric nerve, and it usually crosses part of the iliacus muscle on its way to the iliac crest. Near the anterior end of the iliac crest, it pierces the transversus abdominis muscle, and then pierces the internal oblique muscle and enters the inguinal canal. The ilio-inguinal nerve emerges through the super cial inguinal ring, along with the spermatic cord, and provides cutaneous innervation to the upper medial thigh, the root of the penis, and the anterior surface of the scrotum in men, or the mons pubis and labium majus in women. Genitofemoral nerve (L1 and L2) the genitofemoral nerve arises from the anterior rami of the nerves L1 and L2. It passes downward in the substance of the psoas major muscle until it emerges on the anterior surface of psoas major. It then descends on the surface of the muscle, in a retroperitoneal position, Subcos tal nerve Iliohypogas tric nerve Ilio-inguinal nerve Lateral cutaneous nerve of thigh Subcos tal nerve (T12) Ps oas major mus cle Iliohypogas tric nerve (L1) Ilio-inguinal nerve (L1) Genitofemoral nerve (L1,L2) Iliacus mus cle Femoral nerve Genitofemoral nerve Obturator nerve Lateral cutaneous nerve of thigh (L2,L3) Femoral nerve (L2 to L4) Obturator nerve (L2 to L4) Lumbos acral trunks (L4,L5) 204. The genital branch continues downward and enters the inguinal canal through the deep inguinal ring. It continues through the canal and: In men, innervates the cremasteric muscle and terminates on the skin in the upper anterior part of the scrotum; and In women, accompanies the round ligament of the uterus and terminates on the skin of the mons pubis and labium majus. The femoral branch descends on the lateral side of the external iliac artery and passes posterior to the inguinal ligament, entering the femoral sheath lateral to the femoral artery. It pierces the anterior layer of the femoral sheath and the fascia lata to supply the skin of the upper anterior thigh. The lateral cutaneous nerve of thigh supplies the skin on the anterior and lateral thigh to the level of the knee. Obturator nerve (L2 to L4) Lateral cutaneous nerve of thigh (L2 and L3) the lateral cutaneous nerve of thigh arises from the anterior rami of nerves L2 and L3. It emerges from the lateral border of the psoas major muscle, passing obliquely downward across the iliacus muscle toward the anterior superior iliac spine. It descends in the psoas major muscle, emerging from its medial side near the pelvic brim. The obturator nerve continues posterior to the common iliac vessels, passes across the lateral wall of the pelvic cavity, and enters the obturator canal, through which the obturator nerve gains access to the medial compartment of the thigh. In the area of the obturator canal, the obturator nerve divides into anterior and posterior branches. On entering the medial compartment of the thigh, the two branches are separated by the obturator externus and adductor brevis muscles. Throughout their course through the medial compartment, these two branches supply: articular branches to the hip joint, muscular branches to obturator externus, pectineus, adductor longus, gracilis, adductor brevis, and adductor magnus muscles, cutaneous branches to the medial aspect of the thigh, and 205 Abdomen in association with the saphenous nerve, cutaneous branches to the medial aspect of the upper part of the leg, and articular branches to the knee joint. Femoral nerve (L2 to L4) the femoral nerve arises from the anterior rami of nerves L2 to L4. It descends through the substance of the psoas major muscle, emerging from the lower lateral border of the psoas major. Continuing its descent, the femoral nerve lies between the lateral border of the psoas major and the anterior surface of the iliacus muscle. It is deep to the iliacus fascia and lateral to the femoral artery as it passes posterior to the inguinal ligament and enters the anterior compartment of the thigh. Muscular branches innervate the iliacus, pectineus, sartorius, rectus femoris, vastus medialis, vastus intermedius, and vastus lateralis muscles. The true pelvis (lesser pelvis) is related to the inferior parts of the pelvic bones, sacrum, and coccyx, and has an inlet and an outlet. This cavity is continuous superiorly with the abdominal cavity and contains and supports elements of the urinary, gastrointestinal, and reproductive systems. The perineum contains and supports the external genitalia and external openings of the genitourinary and gastrointestinal systems. Pelvic bone the pelvic bone is irregular in shape and has two major parts separated by an oblique line on the medial surface of the bone. The pelvic bone below this line represents the lateral wall of the true pelvis, which contains the pelvic cavity. The linea terminalis is the lower two-thirds of this line and contributes to the margin of the pelvic inlet. The lateral surface of the pelvic bone has a large articular socket, the acetabulum, which together with the head of the femur, forms the hip joint. Inferior to the acetabulum is the large obturator foramen, most of which is closed by a at connective tissue membrane, the obturator membrane. A small obturator canal remains open superiorly between the membrane and adjacent bone, providing a route of communication between the lower limb and the pelvic cavity. The posterior margin of the bone is marked by two notches separated by the ischial spine. The irregular anterior margin of the pelvic bone is marked by the anterior superior iliac spine, the anterior inferior iliac spine, and the pubic tubercle. Components of the pelvic bone Each pelvic bone is formed by three elements: the ilium, pubis, and ischium. At birth, these bones are connected by cartilage in the area of the acetabulum; later, Ilium Of the three components of the pelvic bone, the ilium is the most superior in position. The ilium is separated into upper and lower parts by a ridge on the medial surface. Posteriorly, the ridge is sharp and lies immediately superior to the surface of the bone that articulates with the sacrum. This sacral surface has a large L-shaped facet for articulating with the sacrum and an expanded, posterior roughened area for the attachment of the strong ligaments that support the sacro-iliac joint. Anteriorly, the ridge separating the upper and lower parts of the ilium is rounded and termed the arcuate line. The portion of the ilium lying inferiorly to the arcuate line is the pelvic part of the ilium and contributes to the wall of the lesser or true pelvis. The upper part of the ilium expands to form a at, fanshaped "wing," which provides bony support for the lower abdomen, or false pelvis. This part of the ilium provides attachment for muscles functionally associated with the lower limb. The external (gluteal surface) of the wing is marked by lines and roughenings and is related to the gluteal region of the lower limb. The entire superior margin of the ilium is thickened to form a prominent crest (the iliac crest), which is the site of attachment for muscles and fascia of the abdomen, back, and lower limb and terminates anteriorly as the Iliac cres t Tuberculum of iliac cres t Gluteal s urface Anterior s uperior iliac s pine Ilium Is c hium P ubis. A prominent tubercle, tuberculum of iliac crest, projects laterally near the anterior end of the crest; the posterior end of the crest thickens to form the iliac tuberosity. This structure serves as the point of attachment for the rectus femoris muscle of the anterior compartment of the thigh and the iliofemoral ligament associated with the hip joint. The superior pubic ramus projects posterolaterally from the body and joins with the ilium and ischium at its base, which is positioned toward the acetabulum. The sharp superior margin of this triangular surface is termed the pecten pubis (pectineal line), which forms part of the linea terminalis of the pelvic bone and the pelvic inlet. Anteriorly, this line is continuous with the pubic crest, which also is part of the linea terminalis and pelvic inlet. The superior pubic ramus is marked on its inferior surface by the obturator groove, which forms the upper margin of the obturator canal. The inferior ramus projects laterally and inferiorly to join with the ramus of the ischium. It has: a large body that projects superiorly to join with the ilium and the superior ramus of the pubis; and a ramus that projects anteriorly to join with the inferior ramus of the pubis.

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