SELF ASSESSMENT HIGH YIELD ANATOMY (ABDOMEN) HTMS .

ABDOMEN

Anterior Abdominal Wall

I. Abdomen

II. Muscles of the Anterior Abdominal Wall

III. Fasciae and Ligaments of the Anterior Abdominal Wall

IV. Inguinal Region

V. Spermatic Cord, Scrotum, and Testis

VI. Inner Surface of the Anterior Abdominal Wall

VII. Nerves of the Anterior Abdominal Wall

VIII. Lymphatic Drainage of the Anterior Abdominal Wall

IX. Blood Vessels of the Anterior Abdominal Wall

Peritoneum and Peritoneal Cavity

I. Peritoneum

II. Peritoneal Reflections

III. Peritoneal Cavity

Gastrointestinal (GI) Viscera

I. Esophagus (Abdominal Portion)

II. Stomach

III. Small Intestine

IV. Large Intestine

V. Accessory Organs of the Digestive System

VI. Spleen

VII. Development of Digestive System

VIII. Celiac and Mesenteric Arteries

IX. Hepatic Portal Venous System

Retroperitoneal Viscera, Diaphragm, and Posterior Abdominal Wall

I. Kidney, Ureter, and Suprarenal Gland

II. Development of Kidney, Urinary Bladder, and Suprarenal Gland

III. Posterior Abdominal Blood Vessels and Lymphatics

IV. Nerves of the Posterior Abdominal Wall

V. The Diaphragm and Its Openings

VI. Muscles of the Posterior Abdominal Wall

High-Yield Topics

·       The inguinal triangle is bounded by the lateral edge of the rectus abdominis (linea semilunaris), the inferior epigastric vessels, and the inguinal ligament. The superficial inguinal ring is in the aponeurosis of the external abdominal oblique muscle and lies just lateral to the pubic tubercle. The deep inguinal ring lies in the transversalis fascia, just lateral to the inferior epigastric vessels.

·       The inguinal canal transmits the spermatic cord or the round ligament of the uterus and the genital branch of the genitofemoral nerve.

·       The spermatic cord contains the ductus deferens, testicular, cremasteric, and deferential arteries; pampiniform plexus of testicular veins; genital branch of the genitofemoral and cremasteric nerves; the testicular sympathetic plexus; and lymph vessels. The spermatic cord is covered by the external spermatic fascia derived from the aponeurosis of the external oblique abdominal muscle, the cremasteric fascia (cremaster muscle and fascia) derived from the internal oblique abdominal muscle, and the internal spermatic fascia derived from the transversalis fascia.

·       Inguinal hernia arises when a portion of intestine protrudes through a weak spot in the inguinal canal or in the inguinal triangle. It occurs superior to the inguinal ligament and lateral to the pubic tubercle. In a reducible hernia, the contents of the hernial sac can be returned to their normal position. Incarcerated hernia is an irreducible hernia where the hernial sac is entrapped or stuck in the groin. Strangulated hernia is an irreducible hernia in which the intestine becomes tightly trapped or twisted; thus, the circulation is arrested, and gangrene (death of tissue) occurs unless relief is prompt.

·       Indirect inguinal hernia passes through the deep inguinal ring, inguinal canal, and superficial inguinal ring and descends into the scrotum. Indirect hernias lie lateral to the inferior epigastric vessels, are congenital (present at birth), derived from persistence of the processus vaginalis, and covered by the peritoneum and the coverings of the spermatic cord.

·       Direct inguinal hernia occurs in the inguinal triangle directly through the abdominal wall muscles (posterior wall of the inguinal canal), lateral to the edge of the conjoint tendon (falx inguinalis), and rarely descends into the scrotum. Located medial to the inferior epigastric vessels, the hernia protrudes forward to (but rarely through) the superficial inguinal ring. It is acquired (develops after birth) and has a sac formed by peritoneum and occasionally transversalis fascia.

·       Cremasteric reflex is a drawing up of the testis by contraction of the cremaster muscle when the skin on the upper medial side of the thigh is stroked. The efferent limb of the reflex arc is the genital branch of the genitofemoral nerve; the afferent limb is a femoral branch of the genitofemoral nerve and also of the ilioinguinal nerve.

·       Peritonitis is inflammation and infection of the peritoneum. Common causes include leakage of feces from a burst appendix, a penetrating wound to the abdomen, a perforating ulcer that leaks stomach contents into the peritoneal cavity (lesser sac), or poor sterile technique during abdominal surgery.

·       Paracentesis (abdominal tap) is a procedure in which a needle is inserted 1 to 2 in. through the abdominal wall into the peritoneal cavity to obtain a sample or drain fluid while the patient’s body is elevated at a 45-degree angle. The puncture site is midline at approximately 2 cm below the umbilicus or lateral to McBurney point, avoiding the inferior epigastric vessels.

·        Epigastric hernia is a protrusion of extraperitoneal fat or a small piece of greater omentum through a defect in the linea alba above the umbilicus and may contain a small portion of intestine.

·       The median umbilical fold or ligament contains the fibrous remnant of the obliterated urachus, the medial umbilical fold contains the fibrous remnant of the obliterated umbilical artery, and the lateral umbilical fold contains the inferior epigastric vessels.

·       The lesser omentum contains the right and left gastric vessels, and its right free margin contains the proper hepatic artery, bile duct, and portal vein, forming the anterior wall of the epiploic foramen.

·       The greater omentum contains the right and left gastroepiploic vessels. The mesentery proper contains the superior mesenteric vessels and branches and tributaries. The transverse mesocolon contains the middle colic vessels. The sigmoid mesocolon contains the sigmoid vessels, and the mesoappendix contains the appendicular vessels.

·       The lienogastric (gastrosplenic) ligament contains the short gastric and left gastroepiploic vessels, and the lienorenal (splenorenal) ligament contains the splenic vessels and tail of the pancreas.

·       The free margin of the falciform ligament contains the ligamentum teres hepatis, which is the fibrous remnant of the left umbilical vein, and the paraumbilical vein, which connects the left branch of the portal vein with the subcutaneous veins in the region of the umbilicus.

·       Retroperitoneal structures include the duodenum (second, third, and fourth parts), pancreas except a small portion of its tail, ascending colon, descending colon, kidney, ureter, suprarenal gland, renal and suprarenal vessels, gonadal vessels, abdominal aorta, IVC, and so forth.

·       Umbilical hernia may occur due to failure of the midgut to return to the abdomen early in fetal life, and it occurs as a protrusion of intestines and other organs through a defect in the abdominal wall at the umbilicus. The hernia is covered by subcutaneous tissue and skin, is not usually treated surgically, but it closes spontaneously. In contrast, an omphalocele is a persistence of the herniation of abdominal contents that remain outside the abdominal cavity, are covered only by the amniotic membrane, and thus immediate surgical repair is required. Gastroschisis is a protrusion of intestines and other organs through a defect in the abdominal wall on the right side of the umbilicus without involving the umbilical cord.

·       Gastroesophageal reflux disease (GERD) is caused by a lower esophageal sphincter dysfunction (relaxation or weakness) and hiatal hernia, causing reflux of stomach contents. Symptoms include heartburn or acid indigestion, painful swallowing, burping, and feeling of fullness in the chest.

·        Hiatal or esophageal hernia is a herniation of a part of the stomach through the esophageal hiatus into the thoracic cavity. The hernia is caused by an abnormally large esophageal hiatus by a relaxed and weakened lower esophageal sphincter, or by an increased pressure in the abdomen, resulting from coughing, vomiting, straining, and constipation.

·       The stomach is divided into the cardia, fundus, body, pyloric antrum, and pyloric canal. The rugae are longitudinal folds of mucous membrane and form the gastric canals along the lesser curvature that direct fluids toward the pylorus.

·       The stomach produces mucus, hydrochloric acid (which destroys many organisms in food and drink), pepsin (which converts proteins to polypeptides), and gastrin (which is produced in its pyloric antrum and stimulates gastric acid secretion).

·       Peptic ulcer is erosion in the lining of the stomach or duodenum. It is commonly caused by an infection with Helicobacter pylori, but is also caused by stress, acid, and pepsin. It occurs most commonly in the pyloric region of the stomach (gastric ulcer) or the first part of the duodenum (duodenal ulcer). Symptoms of peptic ulcer are epigastric pain (burning, cramping, or aching), abdominal indigestion, nausea, vomiting, loss of appetite, weight loss, and fatigue. Gastric ulcers may perforate into the lesser sac and erode the pancreas and the splenic artery, causing fatal hemorrhage. Duodenal ulcers may erode the pancreas or the gastroduodenal artery, and are three times more common than gastric ulcers.

·       The duodenum is a C-shaped small intestine surrounding the head of the pancreas and is retroperitoneal except for the beginning of the first part. Its descending (second) part contains the junction of the foregut and midgut, where the bile duct and main pancreatic ducts open at the greater papilla. The duodenojejunal junction is fixed in position by the suspensory ligament of Treitz, a surgical landmark.

·       The jejunum constitutes the proximal two-fifths of the small intestine. It has tall, closely packed plicae circulares, is emptier, larger in diameter, and thicker walled than the ileum. The ileum is longer than the jejunum, and its mesentery contains more prominent arterial arcades and shorter vasa recta. Its lower part contains Peyer patches (aggregations of lymphoid tissue).

·       Small bowel obstruction is caused by postoperative adhesions, tumors, Crohn disease, hernias, peritonitis, gallstones, volvulus, congenital malrotation, stricture, and intussusception. Strangulated obstructions occluding the arterial supply are surgical emergencies causing death, if untreated. Sign and symptoms include colicky abdominal pain, cramping, nausea and vomiting, constipation, dizziness, abdominal distention, and high-pitched bowel sounds.

·       Inflammatory bowel disease includes Crohn disease and ulcerative colitis. Crohn disease usually occurs in the ileum (ileitis or enteritis), but may occur in any part of the digestive tract. Symptoms include diarrhea, rectal bleeding, anemia, weight loss, and fever. Ulcerative colitis involves the colon and the rectum, causing ulcers in the lining (mucosa) of the organs. Patients with prolonged ulcerative colitis are at increased risk for developing colon cancer.

·       Celiac disease is an immune reaction to eating gluten (protein of wheat, barley, and rye). Gluten ingestion triggers an immune response resulting in inflammation that damages the lining of the small intestine. Celiac disease causes malabsorption of nutrients, constipation, diarrhea, vitamin and mineral deficiencies, fatigue, and weight loss.

·       Meckel diverticulum is an outpouching (fingerlike pouch) of the ileum, derived from an unobliterated vitelline duct, located 2 ft proximal to the ileocecal junction on the antimesenteric side. It is approximately 2 in. long, occurs in approximately 2% of the population, may contain two types of ectopic tissues (gastric and pancreatic), presents in the first two decades of life (more often in the first 2 years), and is found two times as frequently in boys as in girls.

·       The large intestine consists of the cecum, appendix, colon, rectum, and anal canal and functions to convert the liquid contents of the ileum into semisolid feces by absorbing water and electrolytes such as sodium and potassium.

·       The colon includes the ascending and descending colons, which are retroperitoneal, and transverse and sigmoid colons, which are surrounded by peritoneum. The ascending and transverse colons are supplied by the superior mesenteric artery and the vagus nerve; the descending and sigmoid colons are supplied by the inferior mesenteric artery and the pelvic splanchnic nerves. The colons are characterized by presence of teniae coli, sacculations or haustra, and epiploic appendages.

·       The appendix has large aggregations of lymphoid tissue, and its base lies deep to McBurney point. Maximum tenderness in acute appendicitis occurs at the point which is located one-third the distance along a line connecting the right anterior–superior iliac spine and the umbilicus.

·       Diverticulitis is inflammation of diverticula (external evaginations) of the intestinal wall, commonly found in the colon, especially the sigmoid colon, developing as a result of high pressure within the colon. Symptoms are abdominal pain usually in the left lower abdomen, chills, fever, nausea, and constipation.

·       Sigmoid volvulus is a twisting of the sigmoid colon around its mesentery creating a colonic obstruction. Volvulus can cause intestinal ischemia that may progress to infarction, necrosis, peritonitis, and abdominal distension. Symptoms include vomiting, abdominal pain, constipation, bloody diarrhea, and hematemesis.

·       Megacolon (Hirschsprung disease) is caused by the absence of enteric ganglia (cell bodies of parasympathetic postganglionic fibers) in the lower part of the colon, which leads to dilation of the colon proximal to the inactive segment. It is of congenital origin, results from failure of neural crest cells to migrate and form the myenteric plexus, and is usually diagnosed during infancy and childhood. Symptoms are constipation or diarrhea, abdominal distention, vomiting, and a lack of appetite.

·       The liver is the largest visceral organ and plays an important role in bile production and secretion, detoxification, storage of carbohydrate as glycogen, protein synthesis, production of heparin and bile pigments from breakdown of hemoglobin, and storage of vitamins, iron, and copper.

·       The liver is divided, based on hepatic drainage and blood supply, into the right and left lobe by the fossae for the gallbladder and the IVC. On the visceral surface of the liver, there is an H-shaped group of fissures, including fissures for the ligamentum teres hepatis, the ligamentum venosum, gallbladder, and the IVC. The porta hepatis is a transverse fissure between the quadrate and caudate lobes that transmits the hepatic ducts, hepatic arteries, branches of the portal vein, hepatic nerves, and lymphatic vessels.

·       The liver contains the portal triad, which consists of (a) branches of the hepatic artery bringing oxygen and nutrients to the liver, (b) branches of the portal vein bringing nutrient-rich and oxygen poor blood to the liver, and (c) hepatic ducts that carry bile in the opposite direction of the blood flow. Bile emulsifies fat in the digestive system.

·       Liver cirrhosis is a disease in which liver cells are progressively destroyed and replaced by fatty and fibrous tissue that surrounds the intrahepatic blood vessels and biliary radicles, thus impeding the circulation of blood through the liver. Causes include chronic alcohol abuse (alcoholism); hepatitis B, C, and D; and ingestion of poisons. Liver cirrhosis may cause portal hypertension, resulting in esophageal varices (dilated veins in the lower part of the esophagus), hemorrhoids (dilated veins around the anal canal), caput medusa (dilated veins around the umbilicus), spider nevi or spider angioma (small, red, spiderlike arterioles in the cheeks, neck, and shoulder), ascites (accumulation of fluid in the peritoneal cavity), edema in the legs (lower albumin levels lead to decreased oncotic pressure and increased fluid into tissues surrounding blood vessels), jaundice (yellow eyes or skin resulting from bile duct disease failing to remove bilirubin), splenomegaly (enlarged spleen resulting from venous congestion causing sequestered blood cells that lead to thrombocytopenia, a low platelet count, and easy bruising), palmar erythema (persistent redness of the palms), and pectoral alopecia (loss of hair).

·       The gallbladder with its fundus, body, and neck (that contains Hartmann pouch and joins the cystic duct) lies on the visceral surface of the liver and has a capacity of 30 to 50 mL. It receives bile, concentrates it (by absorbing water and salts), stores it, and releases it. It receives blood from the cystic artery arising from the right hepatic artery within the cystohepatic triangle (of Calot), which is formed by the visceral surface of the liver, the cystic duct, and the common hepatic duct.

·       Gallstones (choleliths or cholelithiasis) are formed by solidification of bile constituents and composed chiefly of cholesterol crystals, usually mixed with bile pigments and calcium. Bile crystallizes and forms sand, gravel, and finally stones. Gallstones present commonly in fat, fertile (multiparous) females who are older than forty (40) years (4-F/5-F individuals).

·       Cholecystitis is an inflammation of the gallbladder, caused by obstruction of the cystic duct by gallstones. Symptoms are pain in the upper right quadrant and the epigastric region, fever, nausea, and vomiting. The pain may radiate to the back or right shoulder region.

·       Bile flows from the liver through the right and left hepatic ducts, which unite to form the common hepatic duct. This is joined by the cystic duct to form the bile duct. The bile duct descends behind the first part of the duodenum and runs through the head of the pancreas and joins the main pancreatic duct to form the hepatopancreatic duct, which enters the second part of the duodenum at the greater papilla.

·       The pancreas is a retroperitoneal organ except for a small portion of its tail, which lies in the lienorenal (splenorenal) ligament. It is divided into the head, neck, body, and tail. The head lies within the C-shaped concavity of the duodenum, and its lower portion projects to the left behind the superior mesenteric vessels as the uncinate process. The tail projects toward the hilum of the spleen. The pancreas is both an exocrine gland, which produces digestive enzymes, and an endocrine gland, which secretes insulin, glucagon, and somatostatin.

·       Pancreatitis is an inflammation of the pancreas commonly caused by gallstones or alcohol abuse. Symptoms include upper abdominal pain (which may be severe and constant and may reach to the back), nausea, vomiting, weight loss, fatty stools, mild jaundice, diabetes, low blood pressure, heart failure, and kidney failure.

·       Pancreatic cancer frequently causes severe back pain, has the potential to invade into the adjacent organs, and is extremely difficult to treat. Surgical resection called a pancreaticoduodenectomy or Whipple procedure may extend life. Cancer of the pancreatic head often compresses and obstructs the bile duct, causing obstructive jaundice. Cancer of the pancreatic neck and body may cause portal or IVC obstruction because the pancreas overlies these large veins.

·       Diabetes mellitus is characterized by hyperglycemia caused by an inadequate production of insulin or inadequate action of insulin on body tissues. There are two types of diabetes: type I diabetes (also known as insulin-dependent diabetes), in which the pancreas (β cells) produces an insufficient amount of insulin, and type II diabetes, which results from insulin resistance of target tissues. Diabetes causes diabetic retinopathy, neuropathy, kidney failure, heart disease, stroke, and limb disease. It has symptoms of polyuria (excessive secretion of urine), polydipsia (thirst), weight loss, tiredness, infections of urinary tract, and blurring of vision.

·       Annular pancreas occurs when the ventral and dorsal pancreatic buds form a ring around the duodenum, thereby obstructing it.

·       The spleen is a large vascular lymphatic organ that develops in the dorsal mesogastrium. It is supported by the lienogastric (splenogastric) and lienorenal (splenorenal) ligaments.

·       The spleen contains white pulp, which consists of diffuse and nodular lymphoid tissue and provides the immune function, and red pulp, which consists of venous sinusoids and splenic cords. It is hematopoietic in early life, and later destroys and removes aged (or worn-out) red blood cells.

·       The spleen filters blood (lymph nodes filter the lymph), stores blood and platelets, produces lymphocytes and antibodies, and is involved in body defense against foreign particles (removal of blood-borne antigens as its immune function).

·       The spleen metabolizes hemoglobin into (a) globin (protein part), which is hydrolyzed to amino acids that are reused for protein synthesis; (b) iron, which is released from heme and transported to the bone marrow where it is reused in erythropoiesis; and (c) iron-free heme, which is metabolized to bilirubin in the liver and excreted in the bile.

·       Splenomegaly is caused by venous congestion resulting from thrombosis of the splenic vein or portal hypertension, causing sequestering of blood cells, leading to thrombocytopenia (a low platelet count) and easy bruising.

·       Rupture of the spleen occurs frequently by fractured ribs or severe blows to the left hypochondrium and causes profuse bleeding. The ruptured spleen is difficult to repair; consequently, splenectomy is performed to prevent the person from bleeding to death.

·       Lymphoma is a cancer of lymphoid tissue. Hodgkin’s lymphoma is a malignancy characterized by painless, progressive enlargement of the lymph nodes, spleen, and other lymphoid tissue, accompanied by night sweats, fever, and weight loss.

·       Superior mesenteric artery obstruction is caused by a thrombus, an embolus, atherosclerosis, an aortic aneurysm, a tumor in the uncinate process of the pancreas, compression by the third part of the duodenum, or surgical scar tissue. The obstruction leads to small and large intestinal ischemia, resulting in necrosis of all or part of the involved intestinal segment.

·       The portal vein is formed by the union of the splenic vein and the superior mesenteric vein and receives the right and left gastric vein. The inferior mesenteric vein joins the splenic vein or the superior mesenteric vein or the junction of these veins. The portal vein carries deoxygenated blood containing nutrients and toxins and carries three times as much blood as the hepatic artery.

·       The important portal–caval (systemic) anastomoses occur between (a) the left gastric vein and the esophageal vein of the azygos vein; (b) the superior rectal vein and the middle and inferior rectal veins; (c) the paraumbilical veins and radicles of the epigastric (superficial and inferior) veins; and (d) the retrocolic veins and twigs of the renal, suprarenal, and gonadal veins.

·       Portal hypertension results from liver cirrhosis or thrombosis in the portal vein, forming esophageal varices, caput medusae, and hemorrhoids. It can be treated by diverting blood from the portal to the caval system using a portacaval shunt achieved by creating a communication between the portal vein and the IVC as they lie close together below the liver, or by the splenorenal (Warren) shunt accomplished by anastomosing the splenic vein to the left renal vein. Portal Budd–Chiari or Chiari syndrome is an occlusion of the hepatic veins and results in high pressure in the veins, causing hepatomegaly, upper right abdominal pain, ascites, mild jaundice, and eventually portal hypertension and liver failure.

·       The kidney is retroperitoneal in position and extends from T12 to L3, with the right kidney a little lower than the left. It is invested by a fibrous renal capsule and is surrounded by the renal fascia that divides the fat into two regions. The perirenal fat lies between the renal capsule and renal fascia, and the pararenal fat lies external to the renal fascia.

·       The kidney consists of the medulla and cortex, containing 1 to 2 million nephrons, which are the anatomic and functional units. Each nephron consists of a renal corpuscle, a proximal convoluted tubule, Henle loop, and a distal convoluted tubule. The renal corpuscle consists of a glomerulus (tuft of capillaries), surrounded by a glomerular capsule, which is the invaginated blind end of the nephron.

·       The kidney produces and excretes urine (by which metabolic waste products are eliminated), maintains electrolyte (ionic) balance and pH, and produces renin and erythropoietin. The cortex contains renal corpuscles and proximal and distal convoluted tubules.

·       The medulla consists of 8 to 12 renal pyramids, which contain straight tubules (Henle loops) and collecting tubules. The apex of the renal pyramid, the renal papilla, fits into the cup-shaped minor calyx on which the collecting tubules open.

·       The minor calyces receive urine from the collecting tubules and empty into two or three major calyces, which in turn empty into the renal pelvis.

·       The right renal artery arises from the abdominal aorta, is longer and a little lower than the left, and passes posterior to the IVC; the left artery passes posterior to the left renal vein.

·       The ureter is a muscular tube that extends from the kidney to the urinary bladder. It may be obstructed by renal calculi (kidney stones) where it joins the renal pelvis (ureteropelvic junction), where it crosses the pelvic brim over the distal end of the common iliac artery, or where it enters the wall of the urinary bladder (ureterovesicul junction).

·       Pelvic kidney is an ectopic kidney that occurs when kidneys fail to ascend and thus remain in the pelvis. Two pelvic kidneys may fuse to form a solid lobed organ called a cake (rosette) kidney.

·       Horseshoe kidney develops as a result of fusion of the lower poles of two kidneys and may obstruct the urinary tract by its impingement on the ureters.

·       Nephroptosis is a downward displacement of the kidney, dropped kidney, or floating kidney caused by loss of supporting perirenal fascia. It may cause intermittent ureteric obstruction or kinking of a renal artery, resulting in hydronephrosis.

·       Polycystic kidney disease is a genetic disorder characterized by numerous cysts filled with fluid in the kidney. The cysts can slowly replace much of normal kidney tissues, reducing kidney function and leading to kidney failure.

·       Kidney stone (renal calculus or nephrolith) is composed of calcium oxalate or calcium phosphate, urea, uric acid, or cystine. Crystals and subsequently stones are formed in the urine and collected in calyces of the kidney or in the ureter.

·       Obstruction of the ureter occurs by renal calculi or kidney stones and result in hydroureter and hydronephrosis.

·       Hydronephrosis is a fluid-filled enlargement of the renal pelvis and calyces as a result of obstruction of the ureter.

·       The suprarenal (adrenal) gland is a retroperitoneal organ lying on the superomedial aspect of the kidney and is surrounded by a capsule and renal fascia.

·       Its cortex is essential to life and produces steroid hormones. The medulla is derived from embryonic neural crest cells, receives preganglionic sympathetic nerve fibers directly, and secretes epinephrine and norepinephrine.

·       The gland receives arteries from three sources: the superior suprarenal artery from the inferior phrenic artery, the middle suprarenal from the abdominal aorta, and the inferior suprarenal artery from the renal artery. It drains via the suprarenal vein, which empties into the IVC on the right and the renal vein on the left.

·       Addison’s disease is a disorder caused by an adrenocortical insufficiency (insufficient production of cortisol and, in some cases, aldosterone) caused by autoimmune destruction of the suprarenal cortex or tuberculosis. Disorders of the suprarenal cortex also include an excess production of glucocorticoids (Cushing syndrome) or aldosterone (Conn syndrome) or by androgens (hirsutism).

·       The suprarenal and gonadal veins drain into the IVC on the right and the renal vein on the left. The azygos vein is connected to the IVC, while the hemiazygos vein is connected to the left renal vein.

·       The cisterna chyli is the lower dilated end of the thoracic duct and lies just to the right and posterior to the aorta, usually between two crura of the diaphragm. It is formed by the intestinal and lumbar lymph trunks.

·       The diaphragm arises from the xiphoid process, lower six costal cartilages, and medial and lateral lumbocostal arches and vertebrae, and inserts into the central tendon. It is the principal muscle of inspiration and receives somatic motor fibers solely from the phrenic nerve. Its central part receives sensory fibers from the phrenic nerve, whereas the peripheral part receives sensory fibers from the intercostal nerves.

·       It has (a) the vena caval hiatus, which lies in the central tendon at the level of T8 and transmits the IVC and the right phrenic nerve; (b) the esophageal hiatus, which lies in the muscular part of the diaphragm at the level of T10 and transmits the esophagus and vagus nerves; and (c) the aortic hiatus, which lies between the two crura at the level of T12 and transmits the aorta, thoracic duct, azygos vein, and sometimes greater splanchnic nerve.