In the circulatory system of the human body, there are about 5-6 quarts of blood in the average adult. This blood is considered a tissue because it has many cells. The blood goes to all the parts of the body taking oxygen from the lungs and carbon dioxide to the lungs, while also transporting metabolic wastes and nutrients.
Blood is made up of a fluid called plasma. Plasma is 90% water, but has dissolved substances in it. The substances include blood proteins, like fibrinogen and prothrombin, which are needed for blood clotting. Others include carbohydrates, proteins, carbon dioxide, oxygen, metabolic substances, wastes, and salts like calcium and sodium.
There are 3 main blood vessels: arteries, capillaries, and veins.
Arteries are muscular and elastic since they receive the blood that the heart pumps and carry blood AWAY from the heart. The largest artery is the AORTA. The arterioles (smallest artery branches) connect to the capillaries.
Capillaries have thin walls allowing oxygen, nutrients, wastes, and carbon dioxide to pass. They connect arterioles to venules, the smallest veins.
Veins carry blood BACK to the heart. Veins are thinner and have less muscle than arteries. Valves in the veins keep the blood flowing forward and from backing up. Venules connect with capillaries and join to form bigger veins. The two biggest veins are the superior and inferior vena cava. The superior vena cava brings blood from the upper body and the inferior vena cava brings blood from the lower body.
There are three main blood cells: erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets).
Erythrocytes (red blood cells) are made in the red bone marrow. The count for erythrocytes in the human body is about 25 trillion. The erythrocytes have hemoglobin, which is made of the protein, globin and the iron compund, heme. At first, red blood cells have a nucleus. The nucleus shrinks into the heme an
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