Anatomy of the Gastrointestinal Tract - 2 PDF

Anatomy of the Gastrointestinal Tract - 2 By: Dr. Razan Alotaibi Dr. Islam Salama  Learning Objectives After participating successfully in this session and related activities, students should be able to: Describe the structure, blood supply, innervati...

Anatomy of the Gastrointestinal Tract - 2 By: Dr. Razan Alotaibi Dr. Islam Salama  Learning Objectives After participating successfully in this session and related activities, students should be able to: Describe the structure, blood supply, innervation and relations of the appendix, caecum, colon, rectum and anal canal and their clinical relevance. Anatomy of the Gastrointestinal Tract  LARGE INTESTINE Extends from ileum to anus Length- 1.5 m Parts: Cecum & appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum & anal canal Function: absorption of water & electrolytes & storage of undigested materials until it is expelled from the body as feces ▪ The large intestine extends from distal end of ileum to the anus, a distance of approximately 1.5 m in adults. ▪ Beginning in the right groin as caecum, with its associated appendix, the large intestine continues upward as the ascending colon through the right flank and into the right hypochondrium. ▪ Just below the liver, it bends to the left, forming the right colic flexure(hepatic flexure) and crosses the abdomen as transverse colon to the left hypochondrium. ▪ At this position, just below the spleen, the large intestine bends downwards, forming the left colic flexure (splenic flexure) and continues as the descending colon through the left flank and into the left groin. Anatomy of the Gastrointestinal Tract It enters the upper part of the pelvic cavity as the sigmoid colon, continues on the posterior wall of the pelvic cavity as the rectum, and terminates as the anal canal. The general characteristics of most of the large intestine are: Its large internal diameter compared to that of the small intestine. Peritoneal-covered accumulations of fat (the omental appendices) are associated with the colon. The segregation of longitudinal muscle in its walls into three bands (the taeniae coli, which are primarily observed in the caecum and colon and less visible in the rectum. The sacculations of the colon (the haustra of the colon) Anatomy of the Gastrointestinal Tract  Cecum Definition: ▪ It is a blind-ended pouch of the large intestine located within the right iliac fossa and completely covered with peritoneum ▪ The caecum is the first part of the large intestine. It is inferior to the ileocecal opening and in the right iliac fossa. ▪ It is generally considered to be an intra-peritoneal structure because of its mobility even though it normally is not suspended in the peritoneal cavity by a mesentery. ▪ The caecum is continuous with the ascending colon at the entrance of the ileum and is usually in contact with the anterior abdominal wall. ▪ It may cross the pelvic brim to lie in the true pelvis. The appendix is attached to the posteromedial wall of the caecum just inferior to the end of ileum. Anatomy of the Gastrointestinal Tract  RH Epigastric LH RU LU Umbilical RL LL RL LL Location of Hypo- RI LI cecum & appendix gastric Anatomy of the Gastrointestinal Tract  Relations of the cecum Psoas major Iliacus Relations of the cecum: ▪ Anteriorly: anterior abdominal wall, coils of small intestine ▪ Posteriorly: iliacus & psoas major muscles Anatomy of the Gastrointestinal Tract  Blood supply of cecum: Anterior & posterior cecal arteries Ileocolic artery Superior mesenteric artery The arterial supply of cecum and appendix includes: The anterior cecal artery from the ileocolic artery (from the superior mesenteric artery) The posterior cecal artery from the ileocolic artery (from the superior mesenteric artery) Anatomy of the Gastrointestinal Tract - 2 Nerve supply and lymphatic drainage of Cecum Nerve supply: Autonomic nerves (symp & parasymp) from the superior mesenteric plexus Lymphatic drainage: into superior mesenteric lymph nodes Anatomy of the Gastrointestinal Tract  Interior of the cecum Ileocecal valve The ileocecal fold comes together to form ridges. Musculature from the ileum continues into each flap forming a sphincter. Possible functions of the ileocecal fold includes preventing reflux from the cecum to the ileum and regulating the passage of contents from the ileum to the cecum. Anatomy of the Gastrointestinal Tract  Appendix ▪ Definition: it is a narrow, hollow, blind-ended muscular tube with a large amount of lymphoid tissue in its wall attached to the posteromedial surface of the cecum (approximately 1 inch below the ileocecal junction). ▪ It is suspended from the terminal ileum by the mesoappendix which contains the appendicular vessels. ▪ Its point of attachment to the cecum is consistent with highly visible free taeniae leading directly to the base of the appendix but the location of the rest of the appendix varies considerable. ▪ It varies in length from 2-22 cm (commonly 6 - 9 cm ) ▪ Its lumen is wide in the young child Anatomy of the Gastrointestinal Tract  Surface marking of the base of the appendix McBurney’s point Anatomy of the Gastrointestinal Tract  Variations in the location of the appendix The different locations of appendix can be: ▪ Posterior to the cecum or the lower ascending colon or both, in a retrocecal or retrocolic position. ▪ Suspended over the pelvic brim in a pelvic or descending position ▪ Below the cecum in a subcecal location or ▪ Anterior to the terminal ileum, possibly contacting the body wall in a pre- ileal position or posterior to the terminal ileum in a postileal position. In 75% it is located behind the cecum (retrocecal or retrocolic) In 20% it lies below the cecum (subcecal) or hangs down into the pelvis In 5% it passes in front of or behind the terminal ileum or in front of the cecum. Anatomy of the Gastrointestinal Tract  Blood supply of Appendix Appendicular artery (end artery) Posterior cecal artery Ileocolic artery Superior mesenteric artery Anatomy of the Gastrointestinal Tract  Lymphatic drainage and nerve supply of appendix Lymphatic drainage: ▪ Into superior mesenteric lymph nodes Nerve supply: ▪ Autonomic plexus Anatomy of the Gastrointestinal Tract Clinical Notes ▪ Appendicitis ▪ Appendectomy Anatomy of the Gastrointestinal Tract Anatomy of the ascending, transverse, descending and sigmoid colon ▪ The colon begins in the right groin as caecum, with its associated appendix, the large intestine continues upward as the ascending colon through the right flank and into the right hypochondrium. ▪ Just below the liver, it bends to the left, forming the right colic flexure(hepatic flexure) and crosses the abdomen as transverse colon to the left hypochondrium. ▪ At this position, just below the spleen, the large intestine bends downwards, forming the left colic flexure (splenic flexure) and continues as the descending colon through the left flank and into the left groin. ▪ Immediately lateral to the ascending and descending colon are right and left paracolic gutters. Because major vessels and lymphatics are present on the medial and posteromedial side of the ascending and descending colon, a relatively blood free mobilization of ascending and descending colon is possible by cutting the peritoneum along these paracolic gutters. ▪ The final segment of the colon (sigmoid colon) begins above the pelvic inlet and extends to the level of third sacral vertebra where it is continuous as rectum. This S- shaped structure is mobile except at its beginning and end. Between these 2 points its suspended by the sigmoid mesocolon. Blood supply of the colon - The Rectum & Anal Canal Anatomy of the Gastrointestinal Tract  The Rectum ▪ Length 13 cm ▪ Extends from sigmoid colon to anal canal ▪ Begins at the level of S3, where: ✓ the sigmoid mesocolon is lost ✓ the taenia coli are lost ✓ the appendices epiploica are lost ▪ Rectal ampulla: lower dilated part Anatomy of the Gastrointestinal Tract Transverse folds of the rectum: These are 3 permanent folds formed by the mucous membrane and the circular muscle layer. Anatomy of the Gastrointestinal Tract  Anal Canal ▪ Length: 4 cm ▪ Opens to the exterior at anus guarded by a voluntary external anal sphincter & an involuntary internal anal sphincter Anorectal angle: formed by the forward pull of the puborectalis part of the levator ani external anal sphincter muscle Internal anal sphincter Anatomy of the Gastrointestinal Tract Blood supply of rectum & anal canal Anatomy of the Gastrointestinal Tract  Important Porto-Systemic Anastomosis Blood supply of rectum & anal canal Venous drainage: Veins correspond to the arteries 1.The superior rectal vein→ inferior mesenteric vein→ portal circulation 2.The middle rectal vein→ internal iliac vein→ systemic circulation 3.The inferior rectal vein→ internal pudendal vein→ systemic circulation Anatomy of the Gastrointestinal Tract  Ulcerative colitis Ulcerative colitis is an idiopathic, chronic inflammatory disorder of the colonic mucosa, which starts in the rectum and generally extends proximally in a continuous manner through part of, or the entire, colon; however, some patients with proctitis (inflammation of the lining of the rectum) or left-sided colitis might have a caecal patch of inflammation. Bloody diarrhea is the characteristic symptom of the disease. The clinical course is unpredictable, marked by alternating periods of exacerbation and remission. Although the basis of ulcerative colitis treatment is medical, about 20–30% of patients eventually need surgery. The patient can also opt for elective surgery to get relief from this disease. The aim of emergency and urgent surgery is to restore patient health by removal of the burden of the inflamed colon. Hence, the main procedure in these situations is a subtotal colectomy with a temporary ileostomy with no removal of the rectal stump. Proctocolectomy with IPAA (ileal pouch anal anastomosis) is the standard of care for elective surgery.  Proctocolectomy operation In the Proctocolectomy operation entire colon is removed. Reference: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(12)60150-0/fulltext#secd1593638e1501 Portal venous system Anatomy of the Gastrointestinal Tract Anatomy of the Gastrointestinal Tract  Study Guide ▪ Pages: 307-322 4th edition Thank you ! Anatomy of the Gastrointestinal Tract