One of the most significant is the left renal vein, which drains the kidney, suprarenal gland, and gonad on the same side.
Another is the left common iliac vein, which crosses the midline at approximately vertebral level LV to join with its partner on the right to form the inferior vena cava. These veins drain the lower limbs, the pelvis, the perineum, and parts of the abdominal wall.
Other vessels crossing the midline include the left lumbar veins, which drain the back and posterior abdominal wall on the left side.
All venous drainage from the through the liver
Blood from abdominal parts of the gastrointestinal system and the spleen passes through a second vascular bed, in the liver, before ultimately returning to the heart (Fig. 4.19).
Venous blood from the digestive tract, pancreas, gallbladder, and spleen enters the inferior surface of the liver through the large hepatic portal vein. This vein then ramifies like an artery to distribute blood to small endothelial-lined hepatic sinusoids, which form the vascular exchange network of the liver.
After passing through the sinusoids, the blood collects in a number of short hepatic veins, which drain into the inferior vena cava just before the inferior vena cava penetrates the diaphragm and enters the right atrium of the heart.
Normally, vascular beds drained by the hepatic portal system interconnect, through small veins, with beds drained by systemic vessels, which ultimately connect directly with either the superior or inferior vena cava.
Among the clinically most important regions of overlap between the portal and caval systems are those at each end of the abdominal part of the gastrointestinal system: around the inferior end of the esophagus; around the inferior part of the rectum.
Small veins that accompany the degenerate umbilical vein (round ligament of the liver) establish another important portacaval anastomosis.
The round ligament of the liver connects the umbilicus of the anterior abdominal wall with the left branch of the portal vein as it enters the liver. The small veins that accompany this ligament form a connection between the portal system and para-umbilical regions of the abdominal wall, which drain into systemic veins.
Other regions where portal and caval systems interconnect include: where the liver is in direct contact with the diaphragm (the bare area of the liver); where the wall of the gastrointestinal tract is in direct contact with the posterior abdominal wall (retroperitoneal areas of the large and small intestine); and the posterior surface of the pancreas (much of the pancreas is secondarily retroperitoneal).
Blockage of the hepatic portal vein or of vascular channels in the liver
Blockage of the hepatic portal vein or of vascular channels in the liver can affect the pattern of venous return from abdominal parts of the gastrointestinal system. Vessels that interconnect the portal and caval systems can become greatly enlarged and tortuous, allowing blood in tributaries of the portal system to bypass the liver, enter the caval system, and thereby return to the heart. Portal hypertension can result in esophageal and rectal varices and in caput medusae in which systemic vessels that radiate from para-umbilical veins enlarge and become visible on the abdominal wall.
Abdominal viscera are supplied by a large prevertebral plexus
Innervation of the abdominal viscera is derived from a large prevertebral plexus associated mainly with the anterior and lateral surfaces of the aorta (Fig. 4.20). Branches are distributed to target tissues along vessels that originate from the abdominal aorta.
The prevertebral plexus contains sympathetic, parasympathetic, and visceral sensory components:
Sympathetic components originate from spinal cord levels T5 to L2.
Parasympathetic components are from the vagus nerve [X] and spinal cord levels S2 to S4.
Visceral sensory fibers generally parallel the motor pathways.