Lesson 5: Small Intestine – Large Intestine – Peritoneum

I. Introduction

This article will provide detailed information about the small intestine, large intestine, and peritoneum, including their structure, function, relationship between the organs, blood supply, and some important notes.

II. Small Intestine

• Structure: The small intestine is the longest part of the digestive tract, about 6-7 meters long, divided into 3 parts:

• Duodenum: The first part, about 25 cm long, C-shaped, encircling the head of the pancreas.

• Jejunum: The second part, the longest, accounting for about 2/5 of the length of the small intestine, located in the upper left of the abdominal cavity.

• Ileum: The third part, about 3/5 of the length of the small intestine, located in the lower right of the abdominal cavity.

• Function: The small intestine plays a major role in digesting and absorbing nutrients from food.

• Digestion: Enzymes secreted from the pancreas and small intestine help break down food into small monomers.

• Absorption: Nutrient monomers are absorbed through the intestinal wall into the blood and lymph.

• Blood Supply: The small intestine is supplied by the superior mesenteric artery, originating from the abdominal aorta.

• Notes:

• The major duodenal papilla and minor duodenal papilla are located in the descending part of the duodenum, where the pancreatic and biliary ducts drain into the small intestine.

• The ileocecal valve is located in the mucosal layer of the small intestine, preventing food from the large intestine from flowing back into the small intestine.

III. Large Intestine

• Structure: The large intestine is shorter than the small intestine, about 1.5 meters long, divided into parts:

• Cecum: The first part, pouch-shaped, connected to the ileum.

• Appendix: A small, cylindrical part, growing out of the cecum.

• Ascending colon: The next part, running upwards, located on the right side of the abdominal cavity.

• Transverse colon: The part running horizontally, located in the upper part of the abdominal cavity, connecting the ascending colon and descending colon.

• Descending colon: The part running down, located on the left side of the abdominal cavity.

• Sigmoid colon: The last part, S-shaped, located in the lower part of the abdominal cavity, connecting to the rectum.

• Rectum: The last part of the large intestine, located in the pelvis, connecting to the anus.

• Function: The large intestine functions to absorb water, electrolytes, create feces and excrete feces.

• Blood Supply:

• The large intestine is supplied by the superior mesenteric artery and inferior mesenteric artery, originating from the abdominal aorta.

• The ileocolic artery, a branch of the superior mesenteric artery, supplies the ileum, cecum and appendix.

• The right colic artery, a branch of the superior mesenteric artery, supplies the ascending colon.

• The middle colic artery, a branch of the superior mesenteric artery, supplies the right half of the transverse colon.

• The left colic artery, a branch of the inferior mesenteric artery, supplies the left half of the transverse colon.

• The inferior mesenteric artery supplies the descending colon, sigmoid colon and upper segment of the rectum.

• The middle and inferior rectal arteries originate from the internal iliac artery, supplying the rectum.

IV. Peritoneum

• Structure: The peritoneum is a thin, smooth serous membrane that lines the organs in the abdominal cavity. The peritoneum is divided into two leaves:

• Visceral peritoneum: Covers the organs in the abdominal cavity.

• Parietal peritoneum: Covers the abdominal wall.

• Function: The peritoneum plays a role in protecting, lubricating and fixing the organs in the abdominal cavity.

• Relationship to the organs:

• Gastric peritoneal cavity: The visceral peritoneum covers the stomach.

• Lesser omentum: The two peritoneal leaves rejoin, going from the liver to the lesser curvature of the stomach.

• Greater omentum: The two peritoneal leaves rejoin, going from the greater curvature of the stomach, going down in front of the small intestine.

• Mesentery of the small intestine: The two peritoneal leaves cover the small intestine, attached to the root of the mesentery.

• Root of the mesentery: Where the mesenteries of the small intestine attach, going from the left of the first lumbar vertebra, slanting to the right to the right sacroiliac joint.

• Transverse mesocolon: The two peritoneal leaves cover the transverse colon, rejoin, go behind the stomach, attach to the pancreas and duodenum.

• Falciform ligament: The two peritoneal leaves lie between the left and right lobes of the liver, rejoin and attach to the anterior abdominal wall.

• Mesosalpinx: The two peritoneal leaves go from the ovary to the fallopian tube.

• Suspensory ligament of the ovary: Peritoneum covers the ovarian vessels.

• Median umbilical fold: Peritoneum covers the median umbilical ligament (bladder suspension).

• Medial umbilical fold: Peritoneum covers the medial umbilical ligament (obliterated umbilical artery).

• Lateral umbilical fold: Peritoneum covers the inferior epigastric vessels.

• Spermatic cord: Peritoneum covers the vas deferens, spermatic vessels and nerves.

• Notes:

• Round ligament of the liver is part of the obliterated umbilical vein, not peritoneum.

• Bare area of the liver is the area without peritoneal covering, located on the upper surface of the liver.

• Coronary ligament: Two peritoneal leaves, running from the anterior surface of the liver to the diaphragm, the anterior and posterior leaves attach to the diaphragm.

• Right triangular ligament: The two leaves of the coronary ligament, the anterior and posterior leaves meet at the right lobe of the liver, attach to the diaphragm.

• Left triangular ligament: The two leaves of the coronary ligament, the anterior and posterior leaves meet at the left lobe of the liver, attach to the diaphragm.

V. Inguinal Region

• Supravesical fossa: Lies between the median umbilical fold and medial umbilical fold.

• Inguinal fossa: Lies between the medial umbilical fold and lateral umbilical fold.

• Lateral inguinal fossa: Lies outside the lateral umbilical fold.

VI. Conclusion

The small intestine, large intestine and peritoneum are important organs in the digestive and reproductive systems. Understanding their structure, function and relationship between them gives us an overview of the body and how these organs work.

VII. Notes:

• This article is for reference only, not a substitute for medical advice.

• If you have any health problems, please contact a doctor for advice and timely treatment.