Anatomy of the Abdominal Cavity - Introduction

The Abdominal Cavity - Introduction

• The abdomen is the region of the trunk between the thorax and the pelvis.
• The diaphragm separates the abdomen from the thorax.
• The abdominal cavity is lined with peritoneum, a membrane that forms a sac containing the abdominal viscera.
• The pelvis is located inferior to the abdomen and is differentiated by bony structures.
• The peritoneum extends into the pelvis, allowing overlap between the two regions.
• Abdominal and pelvic viscera can intermix. Visceral movement from the pelvis to the abdomen can occur, such as during pregnancy and uterine enlargement.

The Organs of the Abdomen

• The Liver

• The liver is the largest abdominal organ, spanning from the right to the left side of the midline.

• The liver sits just beneath the diaphragm.

• The liver's position changes with diaphragm movement.

• The Stomach

• The stomach is in the left upper abdomen, nestled near the liver.

• The stomach connects to the esophagus, which passes through a diaphragm opening.

• The Greater Omentum

• The greater omentum is a sheet of connective tissue draped from the greater curvature of the stomach.

• It covers many abdominal organs and carries fat, blood vessels, and peritoneum.

• The greater omentum helps limit inflammation from bowel issues.

• The Gastrointestinal Tract

• The gastrointestinal tract is a continuous tube from the esophagus to the anus, located entirely within the abdomen.

• The tract includes the esophagus, stomach, small intestine, and large intestine.

• The small intestine comprises the duodenum, jejunum, and ileum, each suspended from the posterior abdominal wall by the mesentery.

• The large intestine has parts: ascending, transverse, descending, sigmoid colon, rectum, and anal canal..

• The transverse colon, due to its mesentery, can appear droopy or looped on x-rays.

• The Pancreas

• The pancreas lies behind the stomach, in front of the aorta, and behind the duodenum.

• The pancreas has both endocrine (hormone production) and exocrine (digestion aids) functions.

• It secretes hormones (insulin, glucagon) for blood sugar regulation.

• It also secretes pancreatic juice into the duodenum for digestion.

• The Duodenum

• The duodenum is the first part of the small intestine, forming a C-shaped curve around the head of the pancreas.

• The Spleen

• The spleen is located in the left upper abdomen, near the tail of the pancreas.

• The spleen removes old red blood cells and stores blood components (red blood cells, platelets, immune cells).

• The Gallbladder

• The gallbladder is lodged beneath the liver.

• It stores and concentrates liver-produced bile.

• Bile, released via the common bile duct, assists in fat digestion.

The Blood Supply to the Abdomen

• The abdominal aorta supplies blood to the abdomen, pelvis, and lower limbs.

• The Major Branches of the Abdominal Aorta

• Celiac Trunk: supplies blood to pancreas, spleen, stomach, and liver.

• Superior Mesenteric Artery: supplies blood to the small intestine and most of the large intestine.

• Inferior Mesenteric Artery: supplies blood to the descending colon, sigmoid colon, and rectum.

• The Inferior Vena Cava

• The inferior vena cava collects blood from the abdomen, liver, and pelvis, returning it to the heart.

• The Renal Arteries and Veins

• Renal arteries supply blood to the kidneys, located posteriorly to the abdominal aorta.

• Renal veins drain blood from the kidneys, positioned anteriorly to the abdominal aorta.

• The left renal vein is longer than the right because of its anterior positioning.

The Posterior Abdominal Wall

• The posterior abdominal wall consists of muscles supporting trunk movements (lateral flexion, hip flexion).
• Key muscles include psoas major, psoas minor, iliacus, and quadratus lumborum.

The Kidneys

• The kidneys are located in the posterior abdominal wall, behind the peritoneum.
• They regulate the body's water balance, remove waste, and produce blood pressure-regulating hormones.

The Adrenal Glands

• The adrenal glands sit atop the kidneys.
• They control the body's stress response and metabolism through hormones (adrenaline, noradrenaline, cortisol).

The Ureters

• Ureters carry urine from the kidneys to the bladder.

The Urinary Bladder

• The urinary bladder, a urine storage organ, lies in the pelvis.

The Testis

• Testes begin development within the abdomen, then descend to the scrotum during embryonic stages.
• Testicular arteries supply blood and veins drain back to the body; the left testicular vein drains into the left renal vein, the right into the inferior vena cava.

The Iliac Arteries

• The abdominal aorta splits into the left and right common iliac arteries.
• Common iliacs branch into external iliacs (lower limbs) and internal iliacs (pelvis and external genitalia).