Abdominal Regions, Peritoneum, Spleen, and Liver Anatomy

Posted on Mar 11, 2025 in Biology

Regions of the Abdomen

Two horizontal lines:

  1. The top line links the lowest point of the ribs.
  2. The bottom line joins the points of the elevated iliac crests.

Two vertical lines extend from a point midway between the anterior superior iliac spine and the symphysis pubis.

These lines define nine regions:

  • Right and left hypochondriac
  • Epigastric
  • Right and left lumbar (flank)
  • Umbilical
  • Right and left iliac fossa (inguinal)
  • Hypogastric

Peritoneum

The peritoneum is a smooth serous membrane consisting of two separate layers:

  • The parietal peritoneum lines the abdominal cavity.
  • The visceral peritoneum covers the abdominal organs. Some organs are completely surrounded by peritoneum, while others are only covered on the front.

Mesentery

The mesentery is a fold of peritoneum through which the bowel is fixed to the posterior wall of the abdomen.

Omentum

The omentum is a fold of peritoneum attached to the stomach.

  • Greater Omentum (apron of omentum): Dangles from the bottom edge of the stomach.
  • Lesser Omentum (gastrohepatic ligament): The lesser sac is accessed by the foramen of Winslow, located between: the 1st part of the duodenum, the caudate lobe of the liver, the anterior boundary of the lesser omentum, and the posterior-parietal peritoneum with the inferior vena cava.

Pelvic Peritoneum

  • Pouch of Douglas: A fold of peritoneum between the rectum and uterus.
  • Broad Ligament: A fold of peritoneum on both sides of the uterus, suspending the fallopian tube.

Peritoneum Functions

  1. Allows frictionless sliding of the abdominal organs.
  2. Partially or completely overlies the abdominal organs.
  3. Forms ligaments and mesenteries, which help maintain organs in position.
  4. Fat deposit.
  5. Defense.
  6. Can absorb a lot of liquids.

Spleen

The spleen is an intraperitoneal, red-purple lymphoid organ, located in the left hypochondrium behind the last rib (approximately 11x7x3 cm).

Relations

  • Anterior: Diaphragm
  • Posterior: Anterior part of the left kidney
  • Inferior Pole: Left colic flexure
  • Medial: Stomach and splenic hilum with splenic vessels, reaching the pancreatic tail.

Spleen Substance

  • Red Pulp: A large network of sinusoids filled with blood.
  • White Pulp: Lymphoid tissue formations scattered in lymphoid follicles (LB) and periarteriolar sheaths (LT).

Spleen Features

  1. Not essential for life.
  2. Destroys red blood cells.
  3. Involved in the production of antibodies.
  4. Supplies some of the blood lymphocytes: neoformed and “parked”.
  5. In some animals, acts as a storage organ for red blood cells.
  6. Can destroy platelets.
  7. In the fetal period, involved in erythropoiesis.

Vascularization

  • Splenic Artery: Major branch of the celiac trunk.
  • Splenic Vein: Drains to the portal vein.
  • Both are on the superior edge of the pancreas.

If the capsule ruptures due to abdominal trauma, internal bleeding can be fatal.

Liver

The liver is the largest organ in the body (approximately 1.5 kg).

Location

Located under the diaphragm in the right hypochondrium, epigastrium, and left hypochondrium.

Relations

  • Anterior-Superior Surface: Diaphragm
  • Inferior Surface: Right kidney and colic flexure, gallbladder, fundus of the stomach, and esophagus
  • Posterior Surface: Vertebral column, inferior vena cava, and aorta

Parts

Right lobe, left lobe, caudate lobe, quadrate lobe.

Hilus

Contains the inferior vena cava, portal vein, hepatic artery, and hepatic duct.

Liver Structure

Formed by lobules, hexagonal prism-shaped. At the junction of the lobules, there are portal triads containing a hepatic artery branch, a portal vein branch, and a bile canaliculus.

Main Functions of the Liver

  1. Secretes bile.
  2. Protein metabolism.
  3. Carbohydrate metabolism.
  4. Fat metabolism (oxygen desaturation).
  5. Storage of Vitamins B12 and Fe++.
  6. Inactivation and detoxification of hormones and substances.

Bile Duct

Small canaliculi unite into larger ducts. The right and left hepatic ducts meet at the porta hepatis to form the common hepatic duct. The cystic duct (from the gallbladder) joins the common hepatic duct to form the bile duct. The bile duct ends with the duct of Wirsung in the ampulla of Vater and the sphincter of Oddi.