Human body
Blood vessels carry blood throughout the body, which moves because of the beating of the heart. Venules and veins collect blood low in oxygen from tissues throughout the body. These collect in progressively larger veins until they reach the body's two largest veins, the superior and inferior vena cava, which drain blood into the right side of the heart. From here, the blood is pumped into the lungs where it receives oxygen and drains back into the left side of the heart. From here, it is pumped into the body's largest artery, the aorta, and then progressively smaller arteries and arterioles until it reaches tissue. Here blood passes from small arteries into capillaries, then small veins and the process begins again. Blood carries oxygen, waste products, and hormones from one place in the body to another. Blood is filtered at the kidneys and liver.
Liver cytology
Cytology is the name given to the branch of biology that deals with the formation, structure and functionality of the cells. Liver cytology specializes in the study of liver cells. The main liver cells are called hepatocytes; however, there are other cells that can be observed in a liver sample such as Kupffer cells (macrophages). The liver is the biggest gland of the body. It has a wide variety of functions that range from the destruction of old blood cells to the control of the whole metabolism of macromolecules. In the fetus, the liver works as a principal center for hematopoiesis, function that is later replaced by the bone marrow. This hematopoietic function is not normally seen after birth; however, in certain pathological conditions this function may still be seen. It is important to note that the liver is an essential organ and it is the only one in the body that has the ability to regenerate itself after surgery or damage.