Hemodynamics and Vascular Systems of the Liver
The liver has unique hemodynamics, as it receives blood from two independent sources. The hepatic artery (a. hepatica propria) supplies oxygenated blood, while the portal vein (v. portae hepatis) delivers venous blood from the stomach, intestines, and spleen, which is rich in nutrients and toxins. The portal vein is formed posterior to the head of the pancreas by the confluence of the splenic, superior, and inferior mesenteric veins. It runs toward the porta hepatis as part of the hepatoduodenal ligament.
Inside the organ, the vessels divide into two independent systems:
- Portal (Glisson's) system: includes branches of the portal vein, hepatic artery, and bile ducts. They enter through the porta hepatis (porta hepatis) and run parallel to each other. Modern Couinaud surgical classification, which divides the liver into 2 lobes, 5 sectors, and 8 segments, is based precisely on their branching.
- Caval system: represented by the hepatic veins, which drain blood into the inferior vena cava. Their direction does not coincide with the course of the portal system vessels.
Renal Vascular Anatomy and Surgical Access
The blood supply to the kidney has a strict hierarchy, knowledge of which is critical for percutaneous access (e.g., during nephrostomy). The main renal artery divides the blood flow into a larger anterior and a smaller posterior branch. These then pass into segmental, interlobar, and finally arcuate arteries, which course along the periphery of the renal calyces.
Key anatomical factors:
- Posterior arterial branch is the only major trunk passing posterior to the collecting system (usually behind the upper part of the renal pelvis).
- Safe puncture zone is located strictly at the center of the calyx. The posterior calyx is most frequently used because it lies closer to the skin surface and provides convenient intrarenal navigation.
- Danger zones: puncture into the infundibulum (neck) of the calyx or the renal pelvis can lead to massive hemorrhage due to injury to major arterial branches.
Variant anatomy must also be considered: up to 25% of kidneys have accessory arteries, and 3–17% have variant veins.
Evolution of the Circulatory System in Chordates
During phylogeny, the circulatory system underwent significant changes, the stages of which are recapitulated in human embryogenesis. In all vertebrate embryos, 6–7 pairs of arterial pharyngeal arches branch off from the ventral aorta. Their ultimate fate depends on the animal class:
- Fish: a single circulatory loop, a two-chambered heart through which only venous blood passes.
- Amphibians and reptiles: with the advent of pulmonary respiration, two incomplete loops are formed. The heart becomes three-chambered. In amphibians, blood streams in the ventricle are separated by the spiral valve of the conus arteriosus and trabeculae; in reptiles, by an incomplete interventricular septum.
- Birds and mammals: complete separation of circulatory loops and a four-chambered heart.
During mammalian ontogenesis, pharyngeal arches I, II, and V regress. The carotid arteries form from the 3rd pair, and the pulmonary arteries from the 6th. The main difference in warm-blooded animals: in birds, only the right aortic arch persists from the 4th pair, whereas in mammals and humans, the left arch persists.
To remember the arrangement of structures within the hepatoduodenal ligament (from right to left), use the mnemonic: Duct is more right, Vein is posterior, Artery is more left.
Class and exam questions
Why is the segmental structure of the liver based specifically on the portal system?
Branches of the portal vein, hepatic artery, and biliary tracts run parallel to each other inside the liver. This allows the identification of distinct areas (segments) with isolated blood supply and bile drainage.
Where is the safe zone for a renal puncture located?
Strictly at the center of the renal calyx. Puncture in the area of the neck (infundibulum) or pelvis threatens rupture of major arterial branches.
Which veins form the hepatic portal vein?
It is formed behind the head of the pancreas by the convergence of the splenic, superior mesenteric, and inferior mesenteric veins.
Which aortic arch persists in humans during embryogenesis?
In mammals and humans, only the left aortic arch persists from the embryonic primordia (4th pair of pharyngeal arches), unlike birds, which retain the right one.
What else to study on this topic
- Division of the liver according to the Couinaud classification (8 segments and 5 sectors)
- Anatomy of the renal pelvicalyceal system and organ syntopy
- Transformation of the 6 pairs of arterial pharyngeal arches in human ontogenesis
- Structural features of the heart and hemodynamics in amphibians and reptiles
- Variant anatomy of renal vessels (accessory arteries and veins)
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