Anatomy of the Abdominal Region

Musculoskeletal Borders of the Abdominal Region

• Rib Cage: Ribs 1-10 with associated cartilages attach to the sternum. Ribs 11-12 (floating ribs) lack this attachment.
• Clavicles: Upper landmarks useful for orientation.
• Vertebral Column: Lumbar Region (L1-L5) and sacrum (leading to the pelvic region).
• Oscoxy (hip bones): Made up of ilium, ischium, and pubis.
• Iliac Crest: Upper portion relevant for determining abdominal borders.

Dividing the Abdomen

Four Quadrant Scheme

• Midline: From sternum to pubic symphysis.
• Transverse Line: Through the umbilicus (belly button).
• Four Quadrants: Right Upper (RUQ), Left Upper (LUQ), Right Lower (RLQ), Left Lower (LLQ).
• Clinical Use: Adequate for teaching basic anatomy.

Nine Region Scheme

• Midclavicular Lines: From middle of clavicles to inguinal ligament.
• Intertubercular Line: From tubercle of iliac crest across and through vertebral body.
• Subcostal/Transpyloric Line: Just below the tenth rib cartilage/through pylorus of stomach.
• Nine Regions: Epigastric, Umbilical, Hypogastric, Right and Left Hypochondriac, Right and Left Lumbar, Right and Left Inguinal.
• Clinical Use: More precise for diagnosing pain and referred pain patterns.

Muscles of the Abdominal Wall

Anterior Wall

• Rectus Abdominis: Strap muscles; segmented; helps flex lumbar vertebral column. Enveloped in the rectus sheath. Midline: Linea Alba.
• Pyramidalis: Small muscle, absent in 20% of people, puts tension on Linea Alba.

Lateral Wall

• External Oblique: Wraps from thoracic cavity inwards; helps twist body (unilaterally) or flex vertebral column (bilaterally).
• Internal Oblique: Fibers perpendicular to external oblique; similar function.
• Transversus Abdominis: Compresses abdomen (bilaterally) or helps twist body (unilaterally); fibers run transversely.

Posterior Wall

• Quadratus Lumborum: Stabilizes; lateral flexion; forms true back wall.
• Psoas Major and Minor: Hip flexors; sometimes considered part of back wall.

Internal Anatomy of the Abdomen

Diaphragm

• Function: Separates thoracic cavity from abdominal cavity; essential for breathing.
• Relation: Rests on liver.

Peritoneum

• Parietal Peritoneum: Lines internal wall of the abdominal cavity.
• Visceral Peritoneum: Encompasses organs (e.g., small intestine).
• Peritoneal Reflections: Greater omentum (folded peritoneum; connects to stomach), lesser omentum.
• Intraperitoneal vs. Retroperitoneal: Complete coverage vs. anterior only (e.g., kidneys, pancreas).
• Function: Blood vessels, lymphatic vessels, nerves.

Organs and Structures

Right Upper Quadrant (RUQ)

• Liver: Sometimes extends to LUQ due to enlargement (e.g., cancer).
• Gallbladder: Removed in this case.
• Duodenum: Partially in RUQ, extends towards LUQ.
• Right Kidney and Adrenal Gland.

Left Upper Quadrant (LUQ)

• Stomach: Includes part of pylorus.
• Pancreas: Digestive and endocrine functions.
• Spleen: Lymphatic and red blood cell destruction.
• Left Kidney and Adrenal Gland.

Lower Quadrants (RLQ & LLQ)

• Small Intestine: Predominantly in both lower quadrants.
• Large Intestine: Cecum, ascending colon (RLQ), transverse colon (both quadrants), descending colon (LLQ), and sigmoid colon.
• Retroperitoneal Structures: Duodenum (partially), kidneys, pancreas, adrenal glands.

Nine Region Analysis: Clinical Insights

• Epigastric Region: Stomach, part of duodenum; epigastric pain (e.g., gastritis).
• Umbilical Region: Greater omentum, small intestines; mesentery anchors intestines.
• Hypogastric Region: Bladder (upper portion), rectum.
• Hypochondriac Regions: Spleen, part of liver, stomach.
• Lumbar Regions: Ascending/descending colon.
• Inguinal Regions: Cecum, appendix; appendix pain indicates appendicitis.

Conclusion

• Abdominal Anatomy Complexity: Internal organs and structures vary greatly, and understanding their division helps with diagnosis and learning.
• Pain Localization: Quadrant and region schemes assist in determining sources of abdominal pain.