Abdominal Anatomy

1. Overview

The abdomen is the anatomical space between the thorax and pelvis. It contains the majority of the digestive organs and associated structures, along with parts of the urinary and vascular systems.

2. Abdominal Wall

a. Layers (Superficial to Deep):

• Skin
• Superficial fascia (Camper’s and Scarpa’s layers)
• Muscles:
  • External oblique
  • Internal oblique
  • Transversus abdominis
• Transversalis fascia
• Extraperitoneal fat
• Parietal peritoneum

3. Abdominal Regions (9-Region System)

Divided using 2 vertical midclavicular lines and 2 horizontal lines (subcostal & transtubercular):

Right Hypochondriac	Epigastric	Left Hypochondriac
Right Lumbar	Umbilical	Left Lumbar
Right Iliac	Hypogastric (Pubic)	Left Iliac

4. Peritoneum & Peritoneal Cavity

• Parietal Peritoneum: Lines internal abdominal wall.
• Visceral Peritoneum: Covers abdominal organs.
• Peritoneal Cavity: Potential space containing lubricating fluid.
• Mesentery: Connects intestines to posterior wall and carries vessels/nerves.

• Omentum: Fatty apron over intestines (greater & lesser).

5. Intraperitoneal vs. Retroperitoneal Organs

Intraperitoneal Organs:

• Stomach
• Liver
• Spleen
• Jejunum, ileum
• Transverse and sigmoid colon

Retroperitoneal Organs:

• Kidneys, Adrenal glands
• Pancreas (except tail)
• Duodenum (except 1st part)
• Ascending and descending colon

6. Digestive Tract (Alimentary Canal)

a. Abdominal Esophagus

Passes through diaphragm at T10 and opens into the stomach at the cardiac orifice.

b. Stomach

• Regions: cardia, fundus, body, pylorus

• Lesser and greater curvature

c. Small Intestine

• Duodenum: C-shaped, surrounds the pancreatic head
• Jejunum: Upper left abdomen, thick wall
• Ileum: Lower right abdomen, thinner wall

d. Large Intestine

• Cecum & appendix
• Colon: ascending, transverse, descending, sigmoid
• Rectum & anal canal
• Features: taeniae coli, haustra, appendices epiploicae

7. Accessory Digestive Organs

a. Liver

• Largest abdominal organ
• Four lobes: right, left, caudate, quadrate
• Porta hepatis: entry of portal triad

b. Gallbladder

Stores and concentrates bile; connected to biliary tree via the cystic duct.

c. Pancreas

• Head, neck, body, and tail
• Retroperitoneal (except tail)
• Produces digestive enzymes and hormones (insulin, glucagon)

d. Spleen

LUQ organ, immune function, filters blood, recycles red cells.

8. Kidneys and Urinary System

• Retroperitoneal, bean-shaped
• Hilum contains renal artery, vein, pelvis
• Ureters descend to the bladder
• Bladder lies in pelvis (hypogastric region)

9. Vascular Anatomy

Arterial Supply (from Abdominal Aorta):

• Celiac Trunk: Liver, stomach, spleen
• Superior Mesenteric Artery (SMA): Midgut (small intestine, right colon)
• Inferior Mesenteric Artery (IMA): Hindgut (left colon, rectum)

Venous Drainage:

• Portal vein: Drains GI tract and spleen into liver
• Inferior vena cava (IVC): Drains lower body and kidneys into right atrium

10. Lymphatic Drainage & Nerve Supply

• Lymph nodes: celiac, SMA, IMA, para-aortic
• Sympathetic: Thoracic & lumbar splanchnic nerves
• Parasympathetic: Vagus (foregut/midgut), pelvic splanchnic (hindgut)