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Anatomy of the large intestine

Anatomy of the large intestine

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Anatomy of the large intestine

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  1. LARGEINTESTINE By Dr Nassar Ayoub

  2. LARGEINTESTINE • The large intestine extends from the cecum to the anus. It is divided into the cecum, appendix, ascending colon, transverse colon, descending colon and sigmoid colon. • The rectum and anal canal are considered in the sections on the pelvis and perineum. • The primary function of the large intestine is the absorption of water and electrolytes and the storage of undigested material until it can be expelled from the body as feces.

  3. CECUM (cont.) • Location and Description • The cecum is that part of the large intestine that lies below the level of the junction of the ileum with the large intestine. • It is a blind-ended pouch that is situated in the right iliac fossa. It is about 2.5 in. (6 cm) long and is completely covered with peritoneum. • It possesses a considerable amount of mobility, although it does not have a mesentery. Attached to its posteromedial surface is the appendix.

  4. CECUM (cont.) .As in the colon, the longitudinal muscle is restricted to three flat bands, the teniae coli, which converge on the base of the appendix and provide for it a complete longitudinal muscle coat . The cecum is often distended with gas and can then be palpated through the anterior abdominal wall in the living patient.

  5. CECUM (cont.) The terminal part of the ileum enters the large intestine at the junction of the cecum with the ascending colon. The opening is provided with two folds, or lips, which form the so-called ileocecal valve (see below). The appendix communicates with the cavity of the cecum through an opening located below and behind the ileocecal opening.

  6. CECUM (cont.)RELATIONS ■■ Anteriorly: Coils of small intestine, sometimes part of the greater omentum, and the anterior abdominal wall in the right iliac region ■■ Posteriorly: The psoas and the iliacus muscles, the femoral nerve, and the lateral cutaneous nerve of the thigh. The appendix is commonly found behind the cecum. ■■ Medially: The appendix arises from the cecum on its medial side.

  7. BLOOD SUPPLY & LYMPH DRAINAGE &NERVE SUPPLY of cecum • Arteries Anterior and posterior cecal arteries form the ileocolic artery, a branch of the superior mesenteric artery • Veins The veins correspond to the arteries and drain into the • superior mesenteric vein.

  8. CECUM (cont.) • Lymph Drainage • The lymph vessels pass through several mesenteric nodes and finally reach the superior mesenteric nodes. • Nerve Supply • Branches from the sympathetic and parasympathetic (vagus) nerves form the superior mesenteric plexus.

  9. ILEOCECALVALVE • The circular muscle of the lower end of the ileum (called the ileocecal sphincte that controls the flow of contents from the ileum into the colon. • The smooth muscle tone is reflexly increased when the cecum is distended.

  10. APPENDIX • Location and Description • The appendix is a narrow, muscular tube containing a large amount of lymphoid tissue. • It varies in length from 3 to 5 in. (8 to 13 cm). • The base is attached to the posteromedial surface of the cecum about 1 in. (2.5 cm) below the ileocecal junction. • The remainder of the appendix is free. • It has a complete peritoneal covering, which is attached to the mesentery of the small intestine by a short mesentery of its own, the mesoappendix.

  11. APPENDIX The mesoappendix contains the appendicular vessels and nerves. The appendix lies in the right iliac fossa, and in relation to the anterior abdominal wall its base is situated one third of the way up the line joining the right anterior superior iliac spine to the umbilicus (McBurney’s point). Inside the abdomen, the base of the appendix is easily found by identifying the teniae coli of the cecum and tracing them to the base of the appendix, where they converge to form a continuous longitudinal muscle coat.

  12. POSITION OF THEAPPENDIX • Common Positions of the Tip of the Appendix The tip of the appendix is subject to a considerable range of movement and may be found in the following positions: • 1.Retrocecal :(most common) • 2.Pelvic • 3.Subcecal • 4.Preilieal • 5.Postileal: least common

  13. BLOOD SUPPLY & LYMPH DRAINAGE & NERVE SUPPLY • Blood Supply • Arteries The appendicular artery is a branch of the posterior cecal artery. • Veins The appendicular vein drains into the posterior cecal vein. • Lymph Drainage • The lymph vessels drain into one or two nodes lying in the mesoappendix and then eventually into the superior mesenteric nodes.

  14. Nerve Supply of Appendix • The appendix is supplied by the sympathetic and parasympathetic (vagus) nerves from the superior mesenteric plexus. • Afferent nerve fibers concerned with the conduction of visceral pain from the appendix accompany the sympathetic nerves and enter the spinal cord at the level of the 10th thoracic segment.

  15. ASCENDINGCOLON • Location and Description • The ascending colon is about 5 in. (13 cm) long and lies in the right lower quadrant. • It extends upward from the cecum to the inferior surface of the right lobe of the liver, where it turns to the left, forming the right colic flexure, and becomes continuous with the transverse colon. • The peritoneum covers the front and the sides of the ascending colon, binding it to the posterior abdominal wall.

  16. TRANSVERSECOLON • Location and Description • The transverse colon is about 15 in. (38 cm) long and extends across the abdomen, occupying the umbilical region. • It begins at the right colic flexure below the right lobe of the liver and hangs downward, suspended by the transverse mesocolon from the pancreas . • It then ascends to the left colic flexure below the spleen. The left colic flexure is higher than the right colic flexure and is suspended from the diaphragm by the phrenicocolic ligament.

  17. DESCENDINGCOLON • Location and Description • The descending colon is about 10 in. (25 cm) long and lies in the left upper and lower quadrants . • It extends downward from the left colic flexure, to the pelvic brim, where it becomes continuous with the sigmoid colon. • The peritoneum covers the front and the sides and binds it to the posterior abdominal wall.

  18. SIGMOIDCOLON • Location and Description • The sigmoid colon is 10 to 15 in. (25 to 38 cm) long and begins as a continuation of the descending colon in front of the pelvic brim. Below, it becomes continuous with the rectum in front of the 3rd sacral vertebra. The sigmoid colon is mobile and hangs down into the pelvic cavity in the form of a loop. The sigmoid colon is attached to the posterior pelvic wall by the fan-shaped sigmoid mesocolon.

  19. RECTUM -1 • Location and Description • The rectum is about 5 in. (13 cm) long and begins in front of the third sacral vertebra as a continuation of the sigmoidcolon. • It passes downward, following the curve of the sacrum and coccyx, and ends in front of the tip of the coccyx by piercing the pelvic diaphragm and becoming continuous with the anal canal. • The lower part of the rectum is dilated to form the rectal ampulla. The rectum deviates to the left, but it quickly returns to the median plane . • On lateral view, the rectum follows the anterior concavity of the sacrum before bending downward and backward at its junction with the anal canal

  20. RECTUM-2 • The puborectalis portion of the levator ani muscles forms a sling . at the junction of the rectum with the anal canal and pulls this part of the bowel forward, producing the anorectal angle. • The peritoneum covers the anterior and lateral surfaces of the first third of the rectum and only the anterior surface of the middle third, leaving the lower third devoid of peritoneum . • The three teniae coli of the sigmoid colon, however, come together so that the longitudinal fibers form a broad band on the anterior and posterior surfaces of the rectum.

  21. RECTUM-3 • The mucous membrane of the rectum, together with the circular muscle layer, forms two or three semicircular permanent folds called the transverse folds of the rectum they vary in position. • Relations • ■■ Posteriorly: The rectum is in contact with the sacrum and coccyx; the piriformis, coccygeus, and levatores ani muscles; the sacral plexus; and the sympathetic trunks.

  22. RECTUM-4 • ■■ Anteriorly: In the male, the upper two thirds of the rectum, which is covered by peritoneum, is related to the sigmoid colon and coils of ileum that occupy the rectovesical pouch. • The lower third of the rectum, which is devoid of peritoneum, is related to the posterior surface of the bladder, to the termination of the vas deferens and the seminal vesicles on each side, and to the prostate .

  23. RECTUM- 5 • Relations • ■ Anteriorly: In the female, the upper two thirds of the rectum, which is covered by peritoneum, is related to the sigmoid colon and coils of ileum that occupy the rectouterine pouch (pouch of Douglas). • The lower third of the rectum, which is devoid of peritoneum, is related to the posterior surface of the vagina .

  24. BLOODSUPPLY OF THE RECTUM • Blood Supply • Arteries • The superior, middle, and inferior rectal arteries supply the rectum. • 1- Superior rectal artery is a direct continuation of the inferior mesenteric artery and is the chief artery supplying the mucous membrane. • 2- Middle rectal artery is a small branch of the internal iliac artery. • 3- Inferior rectal artery is a branch of the internal pudendal artery in the perineum. It anastomoses with the middle rectal artery at the anorectal junction.

  25. Venous drainage of the rectum • The veins of the rectum correspond to the arteries. • 1-Superior rectal vein is a tributary of the portal circulation and drains into the inferior mesenteric vein. • 2-Middle and inferior rectal veins drain into the internal iliac and internal pudendal veins, respectively. The union between the rectal veins forms an important portal–systemic anastomosis).

  26. LYMPHATIC DRAINAGE & NERVE SUPPLY • Lymph Drainage • The lymph vessels of the rectum drain first into the pararectal nodes and then into inferior mesenteric nodes. • Lymph vessels from the lower part of the rectum follow the middle rectal artery to the internal iliac nodes.

  27. Nerve Supply of the rectum • The nerve supply is from the sympathetic and parasympathetic nerves from the inferior hypogastric plexuses. The rectum is sensitive only to stretch

  28. ANALCANAL • Location and Description • The anal canal is about 1.5 in. (4 cm) long and passes downward and backward from the rectal ampulla to the anus • . Except during defecation, its lateral walls are kept in apposition by the levatores ani muscles and the anal sphincters.

  29. Relations of anal canal • ■■ Posteriorly: The anococcygeal body, which is a mass of fibrous tissue lying between the anal canal and the coccyx. • ■■ Laterally: The fat-filled ischiorectal fossae (Fig. 8.5). • ■■ Anteriorly: In the male, the perineal body, the urogenital diaphragm, the membranous part of the urethra, and the bulb of the penis. In the female, the perineal body, the urogenital diaphragm, and the lower part of the vagina.

  30. STRUCTURE • The mucous membrane of the upper half of the anal canal • is derived from hindgut entoderm. It has the following important anatomic features: • ■■ It is lined by columnar epithelium. • ■■ It is thrown into vertical folds called anal columns, which are joined together at their lower ends by small semilunar folds called anal valves (remains of proctodeal membrane). • ■■ The nerve supply is the same as that for the rectal mucosa and is derived from the autonomic hypogastric plexuses. It is sensitive only to stretch. • ■■ The arterial supply is that of the hindgut—namely, the superior rectal artery, a branch of the inferior mesenteric artery. The venous drainage is mainly

  31. STRUCTURE OF THE WALL OF ANAL CANAL • Muscle Coat • As in the upper parts of the intestinal tract, it is divided into an outer longitudinal and an inner circular layer of smooth muscle. • Anal Sphincters The anal canal has an involuntary internal sphincter and a voluntary external sphincter.

  32. STRUCTURE OF THE WALL OF ANAL CANAL • The internal sphincter is formed from a thickening of the smooth muscle of the circular coat at the upper end of the anal canal. The internal sphincter is enclosed by a sheath of striped muscle that forms the voluntary external sphincter

  33. STRUCTURE OF THE WALL OF ANAL CANAL • The external sphincter can be divided into three parts: • ■ A subcutaneous part, which encircles the lower end of the anal canal and has no bony attachments • ■ A superficial part, which is attached to the coccyx behind and • the perineal body in front

  34. Ischioanal Fossae: • The potential spaces surrounding the anal canal, in the anal triangle region, located between the skin of the anal region and the pelvic diaphragm. • The ischioanal fossa (formerly called ischiorectal fossa) is somewhat prismatic in shape, with its base directed to the surface of the perineum, and its apex at the line of meeting of the obturator and anal fasciae • The spaces are triangle-shaped.

  35. BLOOD SUPPLY OF ANAL CANAL • Blood Supply • Arteries • The superior rectal artery supplies the upper half and the inferior rectal artery supplies the lower half. • Veins :-The upper half is drained by the superior rectal vein into the inferior mesenteric vein, and the lower half is drained by the inferior rectal vein into the internal pudendal vein.

  36. LYMPH DRAINAGE & NERVE SUPPLY OF ANAL CANAL • Lymph Drainage • The upper half of the anal canal drains into the pararectal nodes and then the inferior mesenteric nodes. The lower half drains into the medial group of superficial inguinal nodes. • Nerve Supply • The mucous membrane of the upper half is sensitive to stretch and is innervated by sensory fibers that ascend through the hypogastric plexuses. • The lower half is sensitive to pain, temperature, touch, and pressure and is innervated by the inferior rectal nerves. • The involuntary internal sphincter is supplied by sympathetic fibers from hypogastric plexuses.

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