Anatomy: Neurovascular Supply and Spleen

Anatomy: Neurovascular Supply and Spleen

Abdominal Aortic Branches

The abdominal aorta (enters abdomen at T12 through aortic hiatus) gives unpaired ventral branches to the GI tract: coeliac trunk (T12/L1), superior mesenteric artery (SMA, L1), inferior mesenteric artery (IMA, L3), and bifurcates into common iliac arteries at L4. The IVC lies to the right of the aorta. Renal arteries arise at L2.

Coeliac trunk (trifurcates into left gastric, splenic, and common hepatic arteries): Left gastric → runs along lesser curvature. Splenic artery → tortuous along upper pancreatic border → spleen + short gastric arteries (fundus) + left gastroepiploic (greater curvature). Common hepatic → right gastric + gastroduodenal artery (GDA, → right gastroepiploic + superior pancreaticoduodenal) + proper hepatic → left and right hepatic arteries.

SMA branches: jejunal and ileal arteries, ileocolic artery (→ appendicular artery), right colic, middle colic (→ right 2/3 transverse colon). These form vascular arcades with vasa recta.

IMA branches: left colic, sigmoid arteries, superior rectal artery. The marginal artery of Drummond runs along the inner border of the colon anastomosing SMA and IMA territories.

Porto-Systemic Anastomoses

Portal and systemic veins communicate at: (1) oesophagus (left gastric + azygos); (2) umbilicus (para-umbilical + epigastric veins); (3) anorectal (superior + inferior/middle rectal); (4) retroperitoneum (veins of Retzius — posterior colon veins + lumbar veins). These become clinically significant in portal hypertension.

Lymphatic Drainage

Lymph from the colon drains via epicolic → paracolic → intermediate (along named arteries) → preaortic (coeliac, SMA, IMA) lymph nodes. Lymph from small intestine drains via lacteals (chylomicrons) → mesenteric nodes → cisterna chyli → thoracic duct.

Transpyloric Plane (L1)

A horizontal plane at the midpoint between xiphisternum and umbilicus (L1 vertebral level). It passes through: fundus of gall bladder, body of stomach, pylorus, neck of pancreas, origin of SMA, 1st part of duodenum, hilum of kidneys, conus medullaris, and duodenojejunal flexure.

Spleen

The spleen (150 g) lies in the left hypochondrium (9th–11th ribs). It is entirely intraperitoneal (gastrosplenic ligament medially, splenorenal ligament posteriorly). Blood supply: splenic artery (from coeliac trunk); splenic vein → joins SMV → forms portal vein. Functions: immune surveillance (white pulp), red blood cell destruction and storage (red pulp), platelet storage. Splenomegaly: portal hypertension (most common), infection, haematological malignancy. Rupture in trauma → haemoperitoneum; delayed rupture can occur due to subcapsular haematoma.