Abdominal Anatomy: Quadrants, Regions, and Peritoneum

Four Abdominal Quadrants: Right Upper Quadrant (RUQ), Left Upper Quadrant (LUQ), Right Lower Quadrant (RLQ), Left Lower Quadrant (LLQ).
Nine Abdominal Regions: Right hypochondriac, Epigastric, Left hypochondriac, Right lumbar, Umbilical, Left lumbar, Right iliac, Hypogastric, Left iliac.

RUQ: Liver, gallbladder.
LUQ: Spleen (lies in the lateral and posterior portion of the LUQ, under the diaphragm and immediately in front of the 9th to 11th ribs).
RLQ: Cecum, ascending colon, appendix (small pouch attached to the lower border of the cecum).
LLQ: Descending and sigmoid portions of the colon.

Small intestine (occupies the central part of the abdomen around the umbilicus, with parts in all four quadrants).
Pancreas (lies behind the abdominal cavity on the posterior abdominal wall in both upper quadrants).
Large intestine (traverses the abdomen, beginning in the RLQ and ending in the LLQ).
Urinary bladder (located behind the pubic symphysis).

Peritoneum: Large, moist, continuous sheet of serous membrane covering most intra-abdominal structures.
- Parietal peritoneum: Lines the walls of the abdominal cavity.
- Visceral peritoneum: Covers the organs within the abdominal cavity.
- Peritoneal cavity: Potential space between the parietal and visceral peritoneum.
Intraperitoneal: Organs located inside the peritoneum.
Retroperitoneal: Organs located behind the peritoneum.

Upper Peritoneal Cavity (Thoracoabdominal component): Diaphragm, liver, spleen, stomach, gallbladder, transverse colon.
Lower Peritoneal Cavity: Small bowel, sigmoid colon, parts of the descending and ascending colon, and in women, the internal reproductive organs.
Retroperitoneal Space: Abdominal aorta, inferior vena cava, pancreas, kidneys, adrenal glands, ureters, most of the duodenum.