University:
Kentucky State University
Course:
BIO 301 | Human Anatomy
Academic year:

2022
Views:

271

Pages:

50
Author:

palangresq3v

Learning Objectives At the end of the lecture, the student should be able to: • Discuss the gross anatomy of large intestine. • Enlist the characteristic features of large intestine. • Identify the positions of the appendix. • Describe the blood supply of the large intestine. • Understand clinical correlations related to the large intestine. Large Intestine • The large intestine extends from the distal end of the ileum to the anus. Length: ~ 1.5 m Dr. Refat AboGhazleh Parts: o Cecum with appendix o Ascending, transverse, descending, and sigmoid colon. o Rectum o Anal canal Function: Is the absorption of water and electrolytes and the storage of undigested material to be expelled as feces. Parts of Large Intestine 1. Cecum 6 2. Appendix 3. Ascending colon 4 4. Right colic flexure / hepatic flexure 5. Transverse colon 6. Left colic flexure / splenic flexure 7. Descending colon 8. Sigmoid colon 9. Rectum 10. Anal canal 5 3 7 1 8 2 9 10 Features of Large Intestine 1. Teniae coli 2. Haustra of colon 3. Omental appendices Features of Large Intestine (Cont.) Teniae coli § Thickened bands of smooth muscle representing most of the longitudinal coat. § Begin at the base of the appendix as the thick longitudinal layer of the appendix splits to form three bands. § The teniae run the length of the large intestine. § Teniae coli terminate by merging with each other again at the rectosigmoid junction, forming longitudinal muscle layer around rectum. § The teniae coli are not present on the appendix or rectum. Three teniae coli: 1. 2. 3. Mesocolic tenia: To which the transverse and sigmoid mesocolons attach. Omental tenia: to which the omental appendices attach. Free tenia: Neither mesocolons nor omental appendices are attached. Features of Large Intestine (Cont.) Haustra: § Sacculation of the wall of the colon between the teniae. § The teniae are shorter than the intestine, the colon becomes sacculated between the teniae, forming the haustra. Omental appendices: Small, fatty-like projections Parts of Large Intestine o The pouch-like cecum, the widest part of the large intestine, is completely intraperitoneal and movable. o Ascending colon is narrower than the cecum and is retroperitoneal. o Transverse colon. o Descending colon occupies a retroperitoneal position. o Sigmoid colon, characterized by its S-shaped loop, usually has a long mesentery, therefore, has considerable freedom of movement, especially its middle part. Parts of Large Intestine Cecum • Blind ended pouch situated in the right iliac fossa, RLQ. • It completely covered with peritoneum. • It has considerable amount of mobility, although it does not have a mesentery. Dr. Refat AboGhazleh Ileocecal valve • Consists of two horizontal folds of mucous membrane that project around the orifice of the ileum. • The valve plays little or no part in the prevention of reflux of cecal contents into the ileum. The orifice is usually closed by tonic contraction, by ileal papilla on the cecal side, preventing reflux from the cecum into the ileum. Relations of Cecum: Anterior: - Anterior Abdominal wall. - Part of greater omentum. - Coils of small intestine. Posterior: • Psoas and iliacus muscle. • Lateral cutaneous nerve of thigh, femoral nerve, and genitofemoral nerves. • Rt Ext iliac artery & Rt gonadal vessels. Blood Supply of the Cecum Arteries: Anterior and posterior cecal arteries from ileocolic artery, the terminal branch of the superior mesenteric artery (SMA). Veins: Corresponding to the arteries and drain into the superior mesenteric vein. Lymph Drainage The lymph vessels pass through several mesenteric nodes and finally reach the superior mesenteric nodes. The appendix • • Ø Ø Is a narrow muscular tube, has a short triangular mesentery (mesoappendix). It is completely covered by peritoneum. Lies in the right iliac fossa. Appendix arises from the posteromedial aspect of the cecum, just 2cm below ileocecal junction. - Appendix is variable in length (usually about 7 to 10 cm). - Contains numerous lymphoid tissue in its walls. The appendix The base of the appendix lies deep to a point that is one third of the way along the oblique line joining the right ASIS (anterior superior iliac spine) to the umbilicus (McBurney’s point). Following positions of the Tip of the appendix: ■ Retrocecal or retrocolic position: posterior to the cecum or the lower ascending colon. ■ Suspended over the pelvic brim in a pelvic or descending position. ■ Subcecal location: below the cecum. ■ Pre-ileal position: anterior to the terminal ileum, possibly contacting the body wall. ■ Postileal position: posterior to the terminal ileum. The first and second positions are the most common sites. Acute Appendicitis Is a common inflammation of the appendix, often caused by bacterial infection. Initially, diffuse pain is felt in the periumbilical region. However, as the appendix becomes more inflamed and irritates the parietal peritoneum, the pain becomes well localized to the right lower quadrant (tenderness to palpation). Surgical resection is the treatment of choice to prevent more serious lifethreatening complications (abscesses and peritonitis). Pain of Appendicitis Visceral pain in the appendix is produced by distention of its lumen, and stretching the visceral peritoneum. The afferent pain fibers enter the spinal cord at the level of the 10th thoracic segment, and a vague referred pain is felt in the region of the umbilicus. Later, the pain shifts to where the inflamed appendix irritates the parietal peritoneum. Here the pain is precise, severe, and localized. Blood supply of the appendix: The appendicular artery, a branch of the ileocolic artery, supplies the appendix. Venous drainage from the cecum and appendix flow through a tributary of the SMV, the ileocolic vein. Lymph Drainage The lymph vessels drain into lymph nodes lying along the course of the colic blood vessels and ultimately reach the superior mesenteric nodes. Cecal folds of peritoneum Ascending Colon • Lies in the right lower quadrant. • Peritoneum covers the front and the sides of the ascending colon. Relations of Ascending Colon Anterior: • Anterior Abd. Wall • Greater omentum • Coils of small intestine Posterior: • Iliacus, iliac crest, quadratus lumborum, lower pole of Rt kidney, iliohypogastric and ilioinguinal nerve. Blood supply of ascending colon - Ileocolic and right colic artery (branches of superior mesenteric artery) Veins: The veins correspond to the arteries and drain into the superior mesenteric vein. 26 v Lymph Drainage: The lymph vessels drain into lymph nodes lying along the course of the colic blood vessels and ultimately reach the superior mesenteric nodes. v Nerve Supply: Sympathetic and parasympathetic (vagus) nerves from the superior mesenteric plexus supply this area of the colon. Transverse Colon • The transverse colon is the longest, and most mobile part of the large intestine, usually occupying the umbilical region. • The mesentery of the transverse colon (transverse mesocolon) loops down, often inferior to the level of the iliac crests. The root of the transverse mesocolon lies along the inferior border of the pancreas. Transverse colon crosses the abdomen from the right colic flexure to the left colic flexure, where it turns inferiorly to become the descending colon. The right colic flexure (hepatic flexure) lies deep to the 9th and 10th ribs and is overlapped by the inferior part of the liver. The left colic flexure (splenic flexure) is usually more superior, more acute, and less mobile than the right colic flexure. It lies anterior to the inferior part of the left kidney and attaches to the diaphragm through the phrenicocolic ligament. Relations of transverse colon Anterior: Greater Omentum and Anterior Abdominal Wall (umbilical and hypogastric regions). Posterior: 2nd part of duodenum, head of pancreas, and coils of jejunum and ileum Blood supply of transverse colon o Proximal two third of transverse colon are supplied by middle colic artery, which is a branch of superior mesenteric artery. o Distal third of transverse colon are supplied by left colic artery, which is a branch of Inferior mesenteric artery. Veins :The veins correspond to the arteries and drain into the superior and inferior mesenteric veins. 34 Lymph Drainage of transverse colon: The proximal two thirds drain into the colic nodes and then into the superior mesenteric nodes. The distal third drains into the colic nodes and then into the inferior mesenteric nodes. Descending colon • Lies in the left upper and lower quadrants. • Extended from left colic flexure to the pelvic brim, where it becomes continuous with sigmoid colon. • Peritoneum covers the front and the sides of the descending colon. Relations of descending colon Anterior: - Anterior Abd. Wall. - Greater omentum - Coils of small intestine Posterior: Iliacus, iliac crest, Lt psoas, quadratus lumborum, lateral boarder of Lt kidney, iliohypogastric and ilioinguinal nerve, femoral nerve and lateral cutaneous nerve of the thigh. Blood supply of descending colon Left colic and sigmoid branch of inferior mesenteric artery and vein. Sigmoid Colon The final segment of the colon (the sigmoid colon) begins above the pelvic inlet and extends to the level of vertebra SIII, where it is continuous with the rectum. This S-shaped structure is quite mobile except at its beginning, where it continues from the descending colon, and at its end, where it continues as the rectum. Between these points, it is suspended by the sigmoid mesocolon. Relations of Sigmoid Colon Laterally: • left external iliac vessels • obturator nerve • ovary or vas deferens • lateral pelvic wall Posteriorly: • left external and internal iliac • gonadal vessels • Ureter • piriformis • Sacral plexus Anteroinferiorly: • bladder in males, or the uterus and bladder in females The sigmoid mesocolon is an inverted, Vshaped peritoneal fold that attaches the sigmoid colon to the abdominal wall. The apex of the V is near the division of the left common iliac artery into its internal and external branches, that crossed by ureter. The left limb of the descending V along the medial border of the left psoas major muscle right limb descending into the pelvis to end at the level of vertebra SIII. The sigmoid and superior rectal vessels, along with the nerves and lymphatics associated with the sigmoid colon, pass through this peritoneal fold. Arterial Supply of Large Intestine Venous Drainage Venous drainage of the spleen, pancreas, gallbladder, and abdominal part of the gastrointestinal tract, except for the inferior part of the rectum, is through the portal system of veins, which deliver blood from these structures to the liver. Portal vein • The portal vein is the final common pathway for the transport of venous blood from the spleen, pancreas, gallbladder, and abdominal part of the gastrointestinal tract. • The SMV ends posterior to the neck of the pancreas, where it unites with the splenic vein to form the portal vein. Remember that Inferior mesenteric vein joins the splenic vein. Tributaries to the portal vein include: ■ Right and left gastric veins draining the lesser curvature of the stomach and abdominal esophagus, ■ Cystic veins from the gallbladder, and ■ Para-umbilical veins, which are associated with the obliterated umbilical vein and connect to veins on the anterior abdominal wall. Superior mesenteric vein It drains blood from the small intestine, cecum, ascending colon, and transverse colon. Inferior mesenteric vein It drains blood from the rectum, sigmoid colon, descending colon, and splenic flexure Caput medusae Portal Vein Obstruction In severe cases of portal obstruction, the veins of the anterior abdominal wall (normally caval tributaries) that anastomose with the paraumbilical veins (normally portal tributaries) may become varicose and look somewhat like small snakes radiating under the skin around the umbilicus. This condition is referred to as caput medusae, a character in Greek mythology. Colostomy In many circumstances it is performed to protect the distal large bowel after surgery. A further indication would include large bowel obstruction with imminent perforation wherein a colostomy allows decompression of the bowel and its contents. An end colostomy is necessary when the patient has undergone a surgical resection of the rectum and anus (typically for cancer). Dr. Refat AboGhazleh Colonoscopy The interior of the colon can be observed and photographed in a procedure called colonoscopy or coloscopy, using a long, flexible fiberoptic endoscope (colonoscope) inserted into the colon through the anus and rectum.

Anatomy of Large Intestine

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