胎盘大小和静脉体积 血流量 血流量

Fetal circulation is a unique system that facilitates the exchange of gases, nutrients, and waste products between the developing fetus and the mother. This intricate process takes place through a special organ called the placenta.
Two umbilical arteries transport blood from the fetus to the placenta. At the placenta, the blood absorbs oxygen and nutrients while simultaneously eliminating waste products. This oxygen-enriched and nutrient-rich blood then returns to the fetus through one...

The development of the vascular system in a fetus is a complex and intricate process that begins as early as 15 to 16 days post-conception. This process starts outside the embryo, specifically in the mesoderm of the yolk sac, chorion, and connecting stalk. Approximately two days later, the formation of blood vessels occurs within the embryo itself.
The initial formation of this system is facilitated by the small amount of yolk present in the ovum and yolk sac. Blood vessels originate from...

The human body is a complex system of interconnected parts, and the circulatory system plays a crucial role in maintaining overall health. One key component of this system is the inferior vena cava, a large vein responsible for returning blood from the abdominopelvic viscera and abdominal walls to the heart.
The inferior vena cava is fed by numerous smaller veins. The lumbar veins, for instance, drain the posterior abdominal wall, emptying both directly into the inferior vena cava and into the...

Blood is pumped by the heart into the aorta, the largest artery in the body, and then into increasingly smaller arteries, arterioles, and capillaries. The velocity of blood flow decreases with increased cross-sectional blood vessel area. As blood returns to the heart through venules and veins, its velocity increases. The movement of blood is encouraged by smooth muscle in the vessel walls, the movement of skeletal muscle surrounding the vessels, and one-way valves that prevent backflow.

Veins, while chiefly responsible for circulating blood back to the heart, also function as storage vessels for blood. They house approximately 64 percent of the body's total blood volume, a feat made possible by their high capacitance—the inherent ability to expand and accommodate large volumes of blood, even under low pressure. The large diameter and thin walls of veins augment their distensibility, significantly more so than arteries, due to their classification as capacitance...

Systemic veins are crucial blood vessels that return deoxygenated blood from various body tissues back to the heart. There are three systemic veins that return deoxygenated blood to the heart, they are as follows.
The coronary sinus, the heart's principal vein, resides in the coronary sulcus on the heart's posterior aspect. This broad venous channel receives nearly all venous blood from the myocardium, the heart muscle. It is fed by three primary veins: the great cardiac vein, the...