By Y. Shawn. Salisbury State University.
It lies behind the free border of tinue downwards to form the posterior two layers of the greater omen- the lesser omentum and its contained structures buy perindopril toronto, below the caudate pro- tum 4mg perindopril overnight delivery, which hangs down over the coils of the small intestine purchase 2 mg perindopril with mastercard. They then cess of the liver, in front of the inferior vena cava and above the ﬁrst turn back on themselves to form the anterior two layers of the omentum part of the duodenum. The four layers of • The subphrenic spaces are part of the greater sac that lies between the the omentum are fused and impregnated with fat. There are right and left plays an important role in limiting the spread of infection in the peri- spaces, separated by the falciform ligament. It thus forms the shows a central ridge from the apex of the bladder to the umbilicus pro- posterior wall of the omental bursa. Two medial umbilical ligaments converge to the • From the diaphragm and anterior abdominal wall it is reﬂected onto umbilicus from the pelvis. They represent the obliterated umbilical the liver to form its ‘mesentery’ in the form of the two layers of the fal- arteries of the fetus. It represents the obliterated left folds back on itself to form the sharp edge of the left triangular liga- umbilical vein. The peritoneum 37 15 The upper gastrointestinal tract I Cardiac notch Lesser curvature Fundus Angular incisure Pyloric sphincter Body Duodenum Greater curvature Pyloric antrum Fig. The stomach is outlined but the shape is by no means constant 38 Abdomen and pelvis The embryonic gut is divided into foregut, midgut and hindgut, sup- verse colon. The anterior and posterior vagal trunks descend along the plied, respectively, by the coeliac, superior mesenteric and inferior lesser curve as the anterior and posterior nerves of Latarjet from which mesenteric arteries. The latter includes a supply The midgut extends down to two-thirds of the way along the transverse to the acid-secreting partathe body. It largely develops outside the abdomen until this congenital ‘umbilical hernia’ is reduced during the 8th–10th week of gestation. It is • The lower third of the oesophagus is a site of porto-systemic venous considered in four parts: anastomosis. The sphinc- • The pyloric sphincter controls the release of stomach contents into ter of Oddi guards this common opening. The sphincter is composed of a thickened layer of circu- pancreatic duct (of Santorini) opens into the duodenum a small lar smooth muscle which acts as an anatomical, as well as physiolo- distance above the papilla. The junction of the pylorus and duodenum can be seen • Third part (10 cm)athis part is crossed anteriorly by the root of externally as a constriction with an overlying veinathe prepyloric vein the mesentery and superior mesenteric vessels. The cardiac sphincter acts to prevent reﬂux of peritoneal fold stretching from the junction to the right crus of stomach contents into the oesophagus. The discrete anatomical sphincter at the cardia; however, multiple factors terminal part of the inferior mesenteric vein lies adjacent to the contribute towards its mechanism. The superior artery arises from the coeliac axis compression of the short segment of intra-abdominal oesophagus by in- and the inferior from the superior mesenteric artery. The body are denervated thus not compromising the motor supply to the coeliac branch of the posterior vagus passes to the coeliac ganglion stomach and hence bypassing the need for a drainage procedure (e. A large internal surface area throughout the towards the right iliac region on the posterior abdominal wall. The small and ileal branches arise which divide and re-anastomose within the intestine is suspended from the posterior abdominal wall by its mesen- mesentery to produce arcades. End-artery vessels arise from the tery which contains the superior mesenteric vessels, lymphatics and auto- arcades to supply the gut wall. The origin of the mesentery measures approximately 15 sists of few arcades and little terminal branching whereas the vessels to cm and passes from the duodenojejunal ﬂexure to the right sacro-iliac the ileum form numerous arcades and much terminal branching of end- joint. No sharp distinction occurs between the jejunum and ileum; however, certain characteristics help distinguish between them: Small bowel obstruction (Fig. Loops of jejunum tend to occupy the umbilical region adhesions and herniae are the most frequent causes. In the pelvic position the appendix may be close to the ovary in the female Longitudinal muscle Circular muscle Rectum Levator ani Obturator internus Fat of ischiorectal fossa Sphincter Deep Submucosa ani Superficial Sphincter ani internus externus Subcutaneous Pudendal canal Adductor muscles Inferior rectal vesels and nerve Fig. It commences in front of ascending, transverse, descending and sigmoid colon have similar the 3rd sacral vertebra as a continuation of the sigmoid colon and fol- characteristic features. The teniae coli fan out over the rec- course from the base of the appendix (and form a useful way of locating tum to form anterior and posterior bands. These sacculations are visible • Peritoneum covers the upper two-thirds of the rectum anteriorly but not only at operation but also radiographically. In the female it is reﬂected forwards onto ray, the colon, which appears radiotranslucent because of the gas within, the uterus forming the recto-uterine pouch (pouch of Douglas). They are adherent to the posterior The anorectal junction is slung by the puborectalis component of lev- abdominal wall and covered only anteriorly by peritoneum. This is the site where the The appendix varies enormously in length but in adults it is approxim- proctodeum (ectoderm) meets endoderm. The base of the appendix arises from the postero- tion is reﬂected by the following characteristics of the anal canal: medial aspect of the caecum; however, the lie of the appendix itself is • The epithelium of the upper half of the anal canal is columnar.
The pulmonary artery provides deoxygenated blood to the capillaries that form respiratory membranes with the alveoli purchase perindopril 4mg with mastercard, and the pulmonary veins return newly oxygenated blood to the heart for further transport throughout the body order 4 mg perindopril. The lungs are innervated by the parasympathetic and sympathetic nervous systems cheap 2 mg perindopril fast delivery, which coordinate the bronchodilation and bronchoconstriction of the airways. The lungs are enclosed by the pleura, a membrane that is composed of visceral and parietal pleural layers. The mesothelial cells of the pleural membrane create pleural fluid, which serves as both a lubricant (to reduce friction during breathing) and as an adhesive to adhere the lungs to the thoracic wall (to facilitate movement of the lungs during ventilation). The force exerted by gases within the alveoli is called intra-alveolar (intrapulmonary) pressure, whereas the force exerted by gases in the pleural cavity is called intrapleural pressure. Air flows when a pressure gradient is created, from a space of higher pressure to a space of lower pressure. A gas is at lower pressure in a larger volume because the gas molecules have more space to in which to move. The same quantity of gas in a smaller volume results in gas molecules crowding together, producing increased pressure. The surface tension of the alveoli also influences pressure, as it opposes the expansion of the alveoli. However, pulmonary surfactant helps to reduce the surface tension so that the alveoli do not collapse during expiration. Pulmonary ventilation consists of the process of inspiration (or inhalation), where air enters the lungs, and expiration (or exhalation), where air leaves the lungs. During inspiration, the diaphragm and external intercostal muscles contract, causing the rib cage to expand and move outward, and expanding the thoracic cavity and lung volume. This creates a lower pressure within the lung than that of the atmosphere, causing air to be drawn into the lungs. The air pressure within the lungs increases to above the pressure of the atmosphere, causing air to be forced out of the lungs. However, during forced exhalation, the internal intercostals and abdominal muscles may be involved in forcing air out of the lungs. Respiratory volume describes the amount of air in a given space within the lungs, or which can be moved by the lung, and is dependent on a variety of factors. Tidal volume refers to the amount of air that enters the lungs during quiet breathing, whereas inspiratory reserve volume is the amount of air that enters the lungs when a person inhales past the tidal volume. Expiratory reserve volume is the extra amount of air that can leave with forceful expiration, following tidal expiration. Residual volume is the amount of air that is left in the lungs after expelling the expiratory reserve volume. Anatomical dead space refers to the air within the respiratory structures that never participates in gas exchange, because it does not reach functional alveoli. Respiratory rate is the number of breaths taken per minute, which may change during certain diseases or conditions. Both respiratory rate and depth are controlled by the respiratory centers of the brain, which are stimulated by factors such as chemical and pH changes in the blood. These changes are sensed by central chemoreceptors, which are located in the brain, and peripheral chemoreceptors, which are located in the aortic arch and carotid arteries. A rise in carbon dioxide or a decline in oxygen levels in the blood stimulates an increase in respiratory rate and depth. Dalton’s law states that each specific gas in a mixture of gases exerts force (its partial pressure) independently of the other gases in the mixture. Henry’s law states that the amount of a specific gas that dissolves in a liquid is a function of its partial pressure. The greater the partial pressure of a gas, the more of that gas will dissolve in a liquid, as the gas moves toward equilibrium. Gas molecules move down a pressure gradient; in other words, gas moves from a region of high pressure to a region of low pressure. The partial pressure of oxygen is high in the alveoli and low in the blood of the pulmonary capillaries. In contrast, the partial pressure of carbon dioxide is high in the pulmonary capillaries and low in the alveoli. Ventilation is the process that moves air into and out of the alveoli, and perfusion affects the flow of blood in the capillaries. Both are important in gas exchange, as ventilation must be sufficient to create a high partial pressure of oxygen in the alveoli. If ventilation is insufficient and the partial pressure of oxygen drops in the alveolar air, the capillary is constricted and blood flow is redirected to alveoli with sufficient ventilation.