Large intestine, structure, divisions (draw scheme), syntopy, vascular supply, innervation, positions of vermiform appendix

Large Intestine - Structure, Divisions, Syntopy, Vascular Supply, Innervation, and Positions of Vermiform Appendix

Introduction-

The large intestine is the terminal part of the gastrointestinal tract. It functions in water absorption, electrolyte balance, and fecal storage. It exhibits distinct macroscopic and microscopic features compared to the small intestine.

Structure

Macroscopic Characteristics:

1. Length and Diameter:
   • Approximately 1.5 meters in length.
   • Wider diameter compared to the small intestine.
2. Distinct Features:
   • Taeniae coli: Three longitudinal muscle bands.
   • Haustra: Pouches formed by the taeniae coli.
   • Epiploic appendages: Fat-filled peritoneal projections.
3. Wall Layers:
   • Mucosa (simple columnar epithelium with goblet cells).
   • Submucosa (vascular and lymphatic networks).
   • Muscularis externa (inner circular and outer longitudinal layers).
   • Serosa/adventitia.

Divisions

The large intestine is divided into six regions:

1. Cecum:
   • Blind pouch located in the right iliac fossa.
   • Continuous with the ileum at the ileocecal valve.
2. Ascending Colon:
   • Retroperitoneal.
   • Extends from the cecum to the hepatic flexure.
3. Transverse Colon:
   • Intraperitoneal.
   • Spans between the hepatic and splenic flexures.
4. Descending Colon:
   • Retroperitoneal.
   • Extends from the splenic flexure to the sigmoid colon.
5. Sigmoid Colon:
   • Intraperitoneal.
   • S-shaped, located in the pelvic cavity.
6. Rectum and Anal Canal:
   • Terminal portions, leading to the anus.

division

Syntopy

1. Cecum and Appendix:
   • Anterior: Abdominal wall.
   • Posterior: Iliacus and psoas major muscles.
2. Ascending Colon:
   • Anterior: Small intestine loops, anterior abdominal wall.
   • Posterior: Right kidney, quadratus lumborum.
3. Transverse Colon:
   • Superior: Liver, stomach.
   • Inferior: Small intestine loops.
4. Descending Colon:
   • Anterior: Small intestine.
   • Posterior: Left kidney, iliacus muscle.
5. Sigmoid Colon:
   • Anterior: Bladder in males, uterus in females.
   • Posterior: Sacrum.
6. Rectum:
   • Anterior: Prostate, seminal vesicles in males; vagina in females.
   • Posterior: Sacrum and coccyx.

Vascular Supply

1. Arterial Supply:
   • Superior Mesenteric Artery (SMA): Supplies the cecum, appendix, ascending colon, and proximal two-thirds of the transverse colon.
   • Inferior Mesenteric Artery (IMA): Supplies the distal one-third of the transverse colon, descending colon, sigmoid colon, and rectum.
2. Venous Drainage:
   • Corresponds to the arterial supply via the superior and inferior mesenteric veins, which drain into the portal venous system.

blood supply

Innervation

1. Sympathetic:
   • Lumbar splanchnic nerves (L1-L3) for the midgut.
   • Sacral splanchnic nerves for the hindgut.
2. Parasympathetic:
   • Vagus nerve (cranial nerve X) for the midgut.
   • Pelvic splanchnic nerves (S2-S4) for the hindgut.
3. Enteric Nervous System:
   • Myenteric (Auerbach's) and submucosal (Meissner's) plexuses.

Positions of the Vermiform Appendix

1. Retrocecal (most common): Posterior to the cecum.
2. Pelvic: Hanging into the pelvis.
3. Subcecal: Below the cecum.
4. Paracecal: Lateral to the cecum.
5. Preileal: Anterior to the terminal ileum.
6. Postileal: Posterior to the terminal ileum.

vermiform appendix

Sources

1. Gray’s Anatomy for Students, 4th Edition.
2. Sobotta Atlas of Human Anatomy, 16th Edition.