Overview of Neurovascular Structures

2 Overview of Neurovascular Structures

2.1 Branches of the Abdominal Aorta: Overview and Paired Branches

A Overview of the abdominal aorta and pelvic arteries (abdominal organs removed)

Anterior view (female pelvis). The esophagus has been pulled slightly inferiorly, and the peritoneum has been completely removed. The abdominal aorta is the distal continuation of the thoracic aorta. It descends slightly to the left of the midline to approximately the level of the L 4 vertebra, as shown in B (or possibly to the L 5 vertebra in older individuals). There it divides into the paired common iliac arteries (aortic bifurcation). The common iliac arteries divide further into the internal and external iliac arteries. The abdominal aorta (see C) and its major branches give origin to various “subbranches” that supply the abdomen and pelvis (see D).

B Projection of the abdominal aorta and its major branches onto the vertebral column and pelvis

Anterior view of the five major arterial trunks. The major branches of the abdominal aorta can be identified in imaging studies based on their relationship to the vertebrae.

C Sequence of branches from the abdominal aorta

D Functional groups of arteries that supply the abdomen and pelvis

The branches of the abdominal aorta and pelvic arteries can be divided into five broad functional groups (→ = give rise to). For details about the areas supplied by the unpaired branches see p. 213.

Paired branches (and one unpaired branch) that supply the diaphragm, kidneys, suprarenal glands, posterior abdominal wall, spinal cord, and gonads (see C)

• Right and left inferior phrenic arteries

→ Right and left superior suprarenal arteries

• Right and left middle suprarenal arteries

• Right and left renal arteries

→ Right and left inferior suprarenal arteries

• Right and left testicular (ovarian) arteries

• Right and left lumbar arteries (first through fourth)

• Median sacral artery (with lowest lumbar arteries)

One unpaired trunk that supplies the liver, gallbladder, pancreas, spleen, stomach, and duodenum (see C, pp. 213 and 265)

• Celiac trunk with

– Left gastric artery

– Splenic artery

– Common hepatic artery

One unpaired trunk that supplies the small intestine and large intestine as far as the left colic flexure (see C, pp. 213 and 269)

• Superior mesenteric artery

One unpaired trunk that supplies the large intestine from the left colic flexure (see C, p. 213)

• Inferior mesenteric artery

One indirect (see below) paired trunk that supplies the pelvis (see A, p. 213)

• Internal iliac artery (from the common iliac artery, not directly from the aorta, hence an “indirect paired trunk”)

2.2 Branches of the Abdominal Aorta: Unpaired and Indirect Paired Branches

A Classification of arteries supplying the abdomen and pelvis

Red: Branches of the celiac trunk. These supply the proximal bowel segments from the abdominal esophagus to the pancreas and duodenum.

Green: Branches of the superior mesenteric artery. These supply the middle bowel segments from the pancreas and duodenum to the left colic flexure.

Blue: Branches of the inferior mesenteric artery. These supply the distal bowel segments from the left colic flexure to the rectum.

B Right common iliac artery with subbranches

The aortic bifurcation is the point where the abdominal aorta bifurcates into the two common iliac arteries, which give off multiple subbranches that supply the viscera and pelvic walls (see D).

C Abdominal arterial anastomoses

1 Between the celiac trunk and superior mesenteric artery via the pancreaticoduodenal arteries

2 Between the superior and inferior mesenteric arteries (middle and left colic arteries; Riolan and Drummond anastomoses, see A)

3 Between the inferior mesenteric artery and internal iliac artery (superior rectal artery and middle or inferior rectal artery)

These anastomoses are important in that they can function as collaterals, delivering blood to intestinal areas that have been deprived of their normal blood supply.

D Classification of the arteries supplying the abdomen and pelvis

For the area supplied by the paired branches see p. 211 (→ = is continuous with).

Note the anastomoses particularly between the unpaired trunks (see Fig. A and C).

One unpaired trunk that supplies the liver, gallbladder, pancreas, spleen, stomach, and duodenum (see A)
• Celiac trunk with – Splenic artery	→ Left gastro-omental artery → Posterior gastric artery (and short gastric arteries) → Pancreatic branches → Caudal pancreatic artery → Great pancreatic artery → Dorsal pancreatic artery → Inferior pancreatic artery → Transverse pancreatic artery
– Left gastric artery	→ Esophageal branches
– Common hepatic artery	→ Gastroduodenal artery → Supraduodenal artery (inconstant branch of the gastroduodenal artery) → Retroduodenal artery → Right gastro-omental artery → Anterior or posterior superior pancreaticoduodenal artery → Duodenal branches → Right gastric artery → Proper hepatic artery → Cystic artery
One unpaired trunk that supplies the small intestine and large intestine as far as the left colic flexure (see A)
• Superior mesenteric	→ Inferior pancreaticoduodenal artery artery → Jejunal and Ileal arteries → Ileocolic artery → Right colic artery → Middle colic artery
One unpaired trunk that supplies the large intestine from the left colic flexure (see A)
• Inferior mesenteric artery	→ Left colic artery → Sigmoid arteries → Superior rectal artery
One indirect (see below) paired trunk that supplies the pelvis (see B)
• Internal iliac artery (from the common iliac artery, not directly from the aorta, hence an “indirect paired trunk”) with branches that supply
	→ Umbilical artery → Superior vesical artery → Artery of ductus deferens → Inferior vesical artery → Uterine artery → Middle rectal artery → Internal pudendal artery
The pelvic walls (parietal branches)
	→ Iliolumbar artery → Lateral sacral artery → Obturator artery → Superior and inferior gluteal arteries

2.3 Inferior Vena Caval System

A Tributaries of the inferior vena cava in the posterior abdomen and pelvis

Anterior view of an opened female abdomen. All organs but the left kidney and suprarenal gland have been removed, and the esophagus has been pulled slightly inferiorly.

The inferior vena cava receives numerous tributaries that return venous blood from the abdomen and pelvis (and, of course, from the lower limbs), analogous to the distribution of the paired abdominal aortic branches in this region. The inferior vena cava is formed by the union of the two common iliac veins at the approximate level of the L 5 vertebra (see C), behind and slightly inferior to the aortic bifurcation.

Note the special location of the left renal vein and its risk of compression by the superior mesenteric artery (see p. 269): The left renal vein passes in front of the abdominal aorta but behind the superior mesenteric artery. Veins in the male pelvis are described on p. 347. The veins in the pelvis have numerous variants. For example, the tributaries of the internal iliac vein are frequently multiple (unlike those shown above) but unite to form a single trunk before entering the iliac vein (see also p. 349).

B Tributaries of the inferior vena cava

The difference in the venous drainage of the right and left kidneys is displayed more clearly here than in A. The continuity of the right ascending lumbar vein with the azygos vein is also shown.

Direct tributaries return venous blood directly to the inferior vena cava without passing through an intervening capillary bed. Direct tributaries drain the following organs:

• The diaphragm, abdominal wall, kidneys, suprarenal glands, testes/ovaries, and liver

• For the pelvis (via the common iliac vein) from the pelvic wall and floor, uterus, uterine tubes, bladder, ureters, accessory sex glands, lower rectum, and lower limb.

Indirect tributaries return blood that has passed through the capillary bed of the liver via the hepatic portal system (see p. 217). The following organs have indirect tributaries:

• The spleen

• The organs of the digestive tract: pancreas, duodenum, jejunum, ileum, cecum, colon, and upper rectum

Note: Venous blood from the inferior vena cava may drain through the ascending lumbar veins into the azygos or hemiazygos vein and thence to the superior vena cava. Thus a connection between the two venae cavae exists on the posterior wall of the abdomen and thorax: a cavocaval or intercaval anastomosis. The location and significance of cavocaval anastomoses are discussed on p. 218. Frequently an anastomosis exists between the suprarenal vein and inferior phrenic vein (not shown here, see A) on the left side of the body.

C Projection of the inferior vena cava onto the vertebral column

The inferior vena cava ascends on the right side of the abdominal aorta and pierces the diaphragm at the caval opening located at the T 8 level. The common iliac veins unite at the L 5 level to form the inferior vena cava (see also A).

D Direct tributaries of the inferior vena cava

• Right and left inferior phrenic veins

• Hepatic veins

• Right suprarenal vein

• Right and left renal veins at the L 1/L 2 level (the left testicular/ovarian vein and left suprarenal vein terminate in the left renal vein)

• Lumbar veins

• Right testicular/ovarian vein

• Common iliac veins (L 5 level)

• Median sacral vein (often terminates in the left common iliac vein)

2.4 Portal Venous System (Hepatic Portal Vein)

A The portal venous system in the abdomen

The arterial blood supply and venous drainage of the abdominal and pelvic organs differ in their functional organization: While they derive their arterial blood supply entirely from the abdominal aorta or one of its major branches, venous drainage is accomplished by one of two different venous systems:

1. Organ veins that drain directly or indirectly (via the iliac veins) into the inferior vena cava, which then returns the blood to the right heart (see also p. 214);

2. Organ veins that first drain directly or indirectly (via the mesenteric veins or splenic vein) into the portal vein—and thus to the liver—before the blood enters the inferior vena cava and returns to the right heart.

The first pathway serves the urinary organs, suprarenal glands, genital organs, and the walls of the abdomen and pelvis. The second pathway serves the organs of the digestive system (hollow organs of the gastrointestinal tract, pancreas, gallbladder) and the spleen (see D). Only the lower portions of the rectum are exempt from this pathway and drain directly through the iliac veins to the inferior vena cava. This (re)routing of venous blood through the hepatic portal system ensures that the organs of the digestive tract deliver their nutrient-rich blood to the liver for metabolic processing before it is returned to the heart. It also provides a route by which elements of degenerated red blood cells can be conveyed from the spleen to the liver. Thus, the portal vein functions to deliver blood to the liver to support metabolism. This contrasts with the proper hepatic artery, which supplies the liver with oxygen and other nutrients. Anastomoses may develop between the portal venous system and vena caval system (portacaval anastomosis) and function as collateral pathways in certain diseases (see p. 218).

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