(BQ) Part 2 book High-Yield gross anatomy presents the following contents: Sigmoid colon, rectum and anal canal; spleen; kidney, ureter, bladder and urethra; suprarenal (adrenal) glands; female reproductive system; male reproductive system, pelvis, perineum, upper limb, lower limb.
CHAPTER 12 Sigmoid Colon, Rectum, and Anal Canal I Sigmoid Colon (Figure 12-1) A General Features ● ● The sigmoid colon is a segment of the large intestine which lies between the descending colon and rectum The sigmoid colon begins at vertebral level S1 (i.e., the sacral promontory or pelvic inlet) and ends at vertebral level S3 (i.e., the rectosigmoid junction) S1 TC M SC S3 PC Rectosigmoid junction RA RV B TF R PR AMP Anorectal junction perineal flexure (90°) U Pectinate line L T Figure 12-1 Sagittal view of the male pelvis The sigmoid colon (SC) extends from vertebral level S1 to S3 suspended by the sigmoid mesocolon (M) and ends at the rectosigmoid junction (dotted line) The rectum (R) and ampulla of the rectum (AMP) are shown along with the transverse rectal folds (TF) (Houston valves) The rectum ends at the anorectal junction (dotted line) at the tip of the coccyx where the puborectalis muscle (PR) maintains a perineal flexure of 90 degrees The anal canal is divided into the upper anal canal (U) and lower anal canal (L) by the pectinate line TC, teniae coli; RV, rectovesical pouch; B, urinary bladder; T, testes; PC, peritoneal cavity; RA, rectus abdominis muscle 129 130 ● ● ● ● ● Chapter 12 At the rectosigmoid junction, the teniae coli which are longitudinal bands of smooth muscle characteristic of the large intestine spread out to form a circumferentially continuous layer of longitudinal smooth muscle of the rectum and the appendices epiploicae are discontinued The sigmoid colon is highly variable in both position and shape Since the segmental contractions in the rectum are more active than in the sigmoid colon, fecal mass tends to accumulate in the sigmoid colon The sigmoid colon is suspended by the sigmoid mesocolon (i.e., intraperitoneal) The left ureter and left common iliac artery lie at the apex of the sigmoid mesocolon B Arterial Supply ● The arterial supply of the sigmoid colon is from the sigmoid arteries (abdominal aorta → inferior mesenteric artery → sigmoid arteries) C Venous Drainage ● The venous drainage of the sigmoid colon is to the sigmoid veins (sigmoid veins → inferior mesenteric vein → portal vein → hepatic sinusoids → central veins → hepatic veins → inferior vena cava) D Innervation. See Chapter 11 VIII E Clinical Considerations Colonic aganglionosis (Hirschsprung disease) (Figure 12-2) is caused by the arrest of the caudal migration of neural crest cells The hallmark is the absence of ganglionic cells in the myenteric and submucosal plexuses most commonly in the sigmoid colon and rectum resulting in a narrow segment of colon (i.e., the colon fails to relax) Although the ganglionic cells are absent, there is a proliferation of hypertrophied nerve fiber bundles The most characteristic functional finding is the failure of internal anal sphincter to relax following rectal distention (i.e., abnormal rectoanal reflex) Mutations of the rearranged during transfection (RET) protooncogene (chromosome 10q.11.2) have been asso- ciated with Hirschsprung disease Clinical findings include a distended abdomen, inability to pass meconium, gushing of fecal material upon a rectal digital examination, fecal retention, and a loss of peristalsis in the colon segment distal to the normal innervated colon The barium radiograph shows a narrowed rectum and a classic transition zone (arrows) The upper segment (*) of normal colon is distended with fecal material The distal segment (**) of the colon is narrow and is the portion of colon where the myenteric plexus of ganglion cells is absent * ** Figure 12-2 Hirschsprung disease Sigmoid Colon, Rectum, and Anal Canal 131 Diverticulosis (Figure 12-3) is the presence of diverticula (abnormal pouches or sacs) most commonly found in the sigmoid colon in patients >60 years of age It is associated with a low-fiber, modern Western world diet Perforation and/or inflammation of the diverticula results in diverticulitis Clinical findings include pain in left lumbar region, palpable inflammatory mass in left lumbar region, fever, leukocytosis, ileus, and peritonitis The postevacuation barium radiograph shows numerous small outpouchings or diverticula (arrows) from the colonic lumen These diverticula are filled with barium and fecal material Note the hernia (H) on the right Figure 12-3 Diverticulosis Flexible sigmoidoscopy permits examination of the sigmoid colon and rectum During sigmoidoscopy, the large intestine may be punctured if the angle at the rectosigmoid junction is not negotiated properly At the rectosigmoid junction, the sigmoid colon bends in an anterior direction and to the left During sigmoidoscopy, the transverse rectal folds (Houston valves) must be negotiated also Colostomy The sigmoid colon is often used in a colostomy due to the mobility rendered by the sigmoid mesocolon (mesentery) An ostomy is an intestinal diversion that brings out a portion of the GI tract through the rectus abdominis muscle A colostomy may ablate the pelvic nerve plexus which results in loss of ejaculation, loss of erection, urinary bladder retention, and decreased peristalsis in remaining colon II Rectum A General Features ● ● ● ● ● The rectum is a segment of the large intestine which lies between the sigmoid colon and the anal canal The rectum begins at vertebral level S3 and ends at the tip of the coccyx (i.e., the anorectal junction) where the puborectalis muscle forms a U-shaped sling causing an 80-degree perineal flexure The ampulla of the rectum is a dilated portion of the rectum that lies just above the pelvic diaphragm The rectum is normally empty or nearly so of fecal mass When mass movement contractions occur in the sigmoid colon, fecal mass moves into the rectum When the fecal mass distends the rectum to >25% of its capacity, a reflexive relaxation of the internal anal sphincter and a reflexive contraction of the external anal sphincter occurs (called the retrosphincteric reflex) This generates the urge to defecate The rectum contains three transverse rectal folds (Houston valves) formed by the mucosa, submucosa, and inner circular layer of smooth muscle that permanently extend into the lumen of the rectum to support the fecal mass B Arterial Supply. The arterial supply of the rectum is from the following ● ● Superior rectal artery (abdominal aorta → inferior mesenteric artery → superior rectal artery) Middle rectal artery (abdominal aorta → common iliac artery → internal iliac artery → middle rectal artery) ● Inferior rectal artery (abdominal aorta → common iliac artery → internal iliac artery → internal pudendal artery → inferior rectal artery) C Venous Drainage. The venous drainage of the rectum is to the following ● Superior rectal vein (superior rectal vein → inferior mesenteric vein → portal vein → hepatic ● ● Middle rectal vein (middle rectal vein → internal iliac vein → common iliac vein → inferior vena cava) Inferior rectal vein (inferior rectal vein → internal pudendal vein → internal iliac vein → common sinusoids → central veins → hepatic veins → inferior vena cava) iliac vein → inferior vena cava) D Innervation. See Chapter 11 VIII 132 Chapter 12 E Clinical Consideration. Rectal prolapse is the protrusion of the full thickness of the rectum through the anus (should be distinguished from mucosal prolapse which is the protrusion of only the rectal mucosa through the anus) Clinical findings include bowel protruding through anus, bleeding, anal pain, mucous discharge, and anal incontinence caused by stretching of the internal and external anal sphincters or stretch injury to the pudendal nerve III Anal Canal (Figure 12-4) A General Features. The entire anal canal is ≈4 cm long which extends from the rectum at the anorectal junction to the surface of the body at the anus The anal canal is divided into the upper anal canal and lower anal canal by the pectinate line Upper Anal Canal ● The upper anal canal extends from the anorectal junction (perineal flexure) to the pectinate line ● The mucosa of the upper anal canal is thrown into longitudinal folds called the anal columns (of Morgagni) The base of the anal columns defines the pectinate line ● At the base of the anal columns are folds of tissue called the anal valves Behind the anal valves are small, blind pouches called the anal sinuses into which anal glands open ● The upper anal canal is predominately surrounded by the internal anal sphincter which is a continuation of smooth muscle from the rectum with involuntary control via autonomic innervation Lower Anal Canal ● The lower anal canal extends from the pectinate line to the anal verge (the point at which perianal skin begins) ● The lower anal canal is predominately surrounded by external anal sphincter which is striated muscle under voluntary control via the pudendal nerve B Arterial Supply ● ● ● The arterial supply of the upper anal canal is from the superior rectal artery (abdominal aorta → inferior mesenteric artery → superior rectal artery) The arterial supply of the lower anal canal is from the inferior rectal artery (abdominal aorta → common iliac artery → internal iliac artery → internal pudendal artery → inferior rectal artery) The middle rectal artery (abdominal aorta → common iliac artery → internal iliac artery → middle rectal artery) forms an anastomosis with the superior and inferior rectal arteries C Venous Drainage ● ● The venous drainage of the upper anal canal is to the superior rectal vein (superior rectal vein → inferior mesenteric vein → portal vein → hepatic sinusoids → central veins → hepatic veins → inferior vena cava) The venous drainage of the lower anal canal is to the inferior rectal vein (inferior rectal vein → internal pudendal vein → internal iliac vein → common iliac vein → inferior vena cava) D Innervation ● ● The innervation of the upper anal canal is via the autonomic nervous system (parasympathetic and sympathetic nervous systems) such that the internal anal sphincter is under autonomic, nonvoluntary control and sensation is limited to stretch sensation See Chapter 11 VIII The innervation of the lower anal canal is via the somatic nervous system by the pudendal nerve such that the external anal sphincter is under voluntary control and sensation is expanded to pain, temperature, and touch E Clinical Considerations Internal hemorrhoids are varicosities of the superior rectal veins They are located above the pectinate line and are covered by rectal mucosa Clinical findings include bleeding, mucus discharge, prolapse, pruritus, and painless External hemorrhoids are varicosities of the inferior rectal veins They are located below the pectinate line near the anal verge and are covered by skin Clinical findings include bleeding, swelling, and pain Sigmoid Colon, Rectum, and Anal Canal 133 PR AMP Upper AC PL IS Lower ES AV Feature Upper Anal Canal Lower Anal Canal Arterial supply Superior rectal artery (branch of inferior mesenteric artery) Inferior rectal artery (branch of internal pudendal artery) Venous drainage Superior rectal vein → inferior mesenteric vein → hepatic portal system Inferior rectal vein → internal pudendal vein → internal iliac vein → IVC Lymphatic drainage Deep nodes Superficial inguinal nodes Innervation Motor: Autonomic innervation of internal anal sphincter (smooth muscle) Sensory: Stretch sensation; no pain sensation Motor: Somatic innervation (pudendal nerve) of external anal sphincter (striated muscle) Sensory: Pain, temperature, touch sensation Embryologic derivation Endoderm (hindgut) Ectoderm (proctodeum) Epithelium Simple columnar Stratified squamous non-keratinized Tumors Palpable enlarged superficial nodes will NOT be found Patients NOT complain of pain Palpable enlarged superficial nodes will be found Patients complain of pain Hemorrhoids Internal hemorrhoids (varicosities of superior rectal veins) Covered by rectal mucosa Patients NOT complain of pain External hemorrhoids (varicosities of inferior rectal veins) Covered by skin Patients complain of pain Figure 12-4 Diagram of the anal canal Note the following structures AC, anal columns; AV, anal verge; PL, pectinate line; IS, internal anal sphincter; ES, external anal sphincter; AMP, ampulla of the rectum; PR, puborectalis muscle IV Defecation Reflex. Sensory impulses from pressure-sensitive receptors within the ampulla of the rectum travel to sacral spinal cord levels when feces are present Motor impulses travel with the pelvic splanchnic nerves (parasympathetics; S2 to S4) which increase peristalsis and relax the internal anal sphincter If the external anal sphincter and puborectalis muscle are also relaxed, defecation takes place with the help of contraction of the anterior abdominal wall muscles and closure of the glottis If the external anal sphincter and puborectalis muscle are voluntary contracted via the pudendal nerve, defecation is delayed and the feces move back into the sigmoid colon for storage The hypogastric plexus and lumbar splanchnic nerves (sympathetics) decrease peristalsis and maintain tone of the internal anal sphincter 134 V Chapter 12 Radiology A Anteroposterior (AP) Barium Radiograph (Figure 12-5A) B Lateral Barium Radiograph (Figure 12-5B) A SC R AMP B SC R AMP PF Figure 12-5 Radiology A: AP barium radiograph shows the sigmoid colon (SC), rectum (R), and ampulla of the rectum (AMP) B: A lateral barium radiograph shows the sigmoid colon (SC), rectosigmoid junction (dotted line), rectum (R), ampulla of the rectum (AMP), and perineal flexure (PF) CHAPTER 13 Spleen I ● ● ● ● ● ● II ● ● ● III ● ● ● ● General Features (Figure 13-1) The spleen is located in the left hypochondriac region anterior to the 9th, 10th, and 11th ribs which puts the spleen in jeopardy in the case of rib fractures The spleen does not extend below the costal margin and therefore is not palpable unless splenomegaly is present The spleen is attached to the stomach by the gastrosplenic ligament which contains the short gastric arteries and veins and the left gastroepiploic artery and vein The spleen is attached to the kidney by the splenorenal ligament which contains the five terminal branches of the splenic artery, tributaries of the splenic vein, and the tail of the pancreas Accessory spleens occur in 20% of the population and are commonly located near the hilum, tail of the pancreas, or within the gastrosplenic ligament The functions of the spleen include removal of old or abnormal red blood cells (RBCs), removal of inclusion bodies from RBCs [e.g., Howell-Jolly bodies (nuclear remnants), Pappenheimer bodies (iron granules), Heinz bodies (denatured hemoglobin)], removal of poorly opsonized pathogens, IgM production by plasma cells, storage of platelets, and protection from infection Arterial Supply The arterial supply is from the splenic artery (the largest branch of the celiac trunk) which gives off the following branches: Dorsal pancreatic artery, great pancreatic artery, caudal pancreatic arteries, short gastric arteries, left gastroepiploic artery, and ends with about five terminal branches The five terminal branches of the splenic artery supply individual segments of the spleen with no anastomosis between them (i.e., end arteries) so that obstruction or ligation of any terminal branch will result in splenic infarction (i.e., the spleen is very prone to infarction) Splenic artery aneurysms show a particularly high incidence of rupture in pregnant women such that these aneurysms should be resected in women of childbearing age Venous Drainage The venous drainage is to the splenic vein via tributaries The splenic vein joins the superior mesenteric vein to form the portal vein The inferior mesenteric vein usually joins the splenic vein Splenic vein thrombosis is most commonly associated with pancreatitis and shows the following clinical signs: Gastric varices and upper gastrointestinal bleeding 135 136 Chapter 13 A Dorsal pancreatic artery Aorta Celiac artery Splenic artery Common hepatic artery Gastroduodenal artery Right gastroomental artery Greater pancreatic artery Inferior pancreaticoduodenal artery (dividing into anterior and posterior branches) Anterior and posterior superior pancreaticoduodenal arteries stric area Ga rea Renal a Hilum Co lic ar e Splenorenal ligament • Terminal branches of splenic artery • Tributaries of splenic vein • Tail of pancreas Superior mesenteric artery Gastrosplenic ligament • Short gastric arteries and veins • Left gastroepiploic artery and vein B Posterior extremity (medial end) Uncinate process of pancreas (posterior to superior mesenteric artery) a Borders of spleen Anterior extremity Inferior border Superior border Figure 13-1 Spleen A: Diagram of arterial [v4]supply of the spleen The splenic artery is the largest branch of the celiac trunk B: Diagram of visceral surface (inferomedial view) of the spleen The gastrosplenic ligament and splenorenal ligament are shown along with the structures they contain Note the association of the tail of the pancreas and the spleen IV Clinical Considerations A Splenectomy is the surgical removal of the spleen Nearby anatomical structures may be injured during a splenectomy which include the gastric wall (stomach) if the short gastric arteries are compromised, tail of pancreas if the caudal pancreatic arteries are compromised or during manipulation of the splenorenal ligament, and left kidney during manipulation of the splenorenal ligament The most common complication of a splenectomy is atelectasis of the left lower lobe of the lung Spleen 137 Thrombocytosis (i.e., increased number of platelets within the blood) is common postoperatively such that anticoagulation therapy may be necessary to prevent spontaneous thrombosis Abnormal RBCs with bizarre shapes, some of which contain Howell-Jolly bodies (nuclear remnants), are found in the blood postoperatively B Splenic Vein Thrombosis most commonly is associated with pancreatitis and is one of the causes of splenomegaly Clinical signs include gastric varices and upper gastrointestinal bleeding C Splenomegaly. The causes of splenomegaly include autoimmune disease (e.g., systemic lupus erythematosus, rheumatoid arthritis), infectious disease (e.g., mononucleosis, visceral leishmaniasis), infiltrative disease (e.g., lysosomal storage disease, leukemias), extramedullary hematopoiesis (e.g., myeloproliferative diseases like myelofibrosis and myeloid metaplasia), and vascular congestion (portal hypertension in cirrhosis) In the United States, myeloproliferative disease and lymphoid malignancies (e.g., chronic lymphocytic leukemia) are the most common causes of massive splenomegaly D Splenic Infarct (Figure 13-2) An infarction is a process by which coagulating necrosis develops in an area distal to the occlusion of an end artery The necrotic tissue or zone is called an infarct The CT scan shows multiple wedge-shaped areas of diminished contrast enhancement in the spleen representing multiple areas of embolic infarction (arrows) Figure 13-2 Splenic infarction V Radiology (Figure 13-2) A CT Scan at the Level of the Liver and Spleen (Figure 13-3) Air in stomach Left hepatic lobe Right hepatic lobe Barium in stomach Celiac artery Inferior vena cava Aorta Right and left adrenal glands Spleen Left kidney Right kidney Figure 13-3 CT scan at the level of the liver and spleen CHAPTER 14 Kidney, Ureter, Bladder, and Urethra I ● ● General Features (Figure 14-1) The kidneys are retroperitoneal organs that lie on the ventral surface of the quadratus lumborum muscle and lateral to the psoas muscle and vertebral column The kidneys are directly covered by a fibrous capsule called the renal capsule (or true capsule) which can be readily stripped from the surface of the kidney except in some pathologic conditions where it is strongly adherent due to scarring A Superior pole Medial margin Renal hilum Lateral margin Renal artery Renal vein Renal pelvis Anterior surface Ureter Inferior pole B Renal cortex Renal papilla Minor calyx Calyces Major calyx Renal pelvis Ureter Renal columns Renal pyramids Figure 14-1 External and internal anatomy of the kidney A: This figure (anterior view) shows the external anatomy of the right kidney B: This figure (anterior view, coronal section) shows the internal anatomy of the kidney 138 ... sphincter 134 V Chapter 12 Radiology A Anteroposterior (AP) Barium Radiograph (Figure 12- 5A) B Lateral Barium Radiograph (Figure 12- 5B) A SC R AMP B SC R AMP PF Figure 12- 5 Radiology A: AP barium... relay pain sensation from the kidney to T 12- L2 spinal cord segments within the CNS ● The pain associated with kidney pathology may be referred over the T 12- L2 dermatomes (i.e., lum● bar region, inguinal... and internal anatomy of the kidney A: This figure (anterior view) shows the external anatomy of the right kidney B: This figure (anterior view, coronal section) shows the internal anatomy of the