Circulatory system the areas above the heart) and the inferior vena cava (roughly speaking from areas below the heart). These two great vessels empty into the right atrium of the heart. The heart itself is supplied with oxygen and nutrients through a small "loop" of the systemic circulation and derives very little from the blood contained within the four chambers. The general rule is that arteries from the heart branch out into capillaries, which collect into veins leading back to the heart. Portal veins are a slight exception to this. In humans the only significant example is the hepatic portal vein which
Endometrial arteries arteries are coiled and is why they are also called spiral arteries. The spiral arteries are coiled towards the upper part of the endometrium and straight towards the base of the endometrium. In the endometrium there are straight and serial arteries. Straight arteries specifically branch to the base of the endometrium therefore supplying blood to the base of the endometrium. Spiral arteries supply blood to the rest of the endometrium. They grow rapidly, covering much of the space of the endometrium and end up coiled. When hormones levels are low, the endometrial arteries react by becoming narrow. Endometrial arteries supply