In addition to transporting steroids and some fats, albumin is also responsible for maintaining the osmotic pressure of the blood. It is the most abundant protein in the plasma and helps to draw water back into the lumen of the blood vessels.

Fibrinogen is the zymogen of fibrin, an essential clotting protein. Immunoglobulins, also called antibodies, help detect pathogens and tag them for destruction. Hemoglobin is found within erythrocytes and serves to transport oxygen. Vasopressin is not a blood protein; it is a peptide hormone secreted by the posterior pituitary gland. Vasopressin acts on the kidney to increase the hydrostatic pressure of the blood by retaining water, but does not affect the osmotic pressure of the blood in a significant way.

Oxygen-poor blood returns from the body through the superior and inferior venae cavae, which load blood into the right atrium. Blood then flows into the right ventricle, and oxygen-poor blood is pumped through the pulmonary arteries into the lungs, where blood becomes oxygenated. From the lungs, blood returns to the left side of the heart through the pulmonary veins into the left atrium. Remember, regardless of whether blood is oxygen-rich or oxygen-poor, all arteries carry blood away from the heart, and veins deliver blood back to the heart.

The systemic circulation is the part of the cardiovascular system that pumps oxygenated blood from the left ventricle out to the rest of the body to all the tissues that need blood, including the brain, kidney, heart, and lungs. Though the lungs are part of the pulmonary circuit, involved in gas exchange, the cells of the lungs also need blood. There are alveolar cells, macrophages, and connective tissue cells that need blood for metabolism. Also, the myocardium, needs blood (and oxygen) too since it is continuously using lots of ATP to generate contractile force.

During ventricular contraction, both atrioventricular valves (the mitral and tricuspid valve) should be closed in order to prevent backflow of blood into the atria. The papillary muscles and chordae tendinae must both be tense in order to keep this valve closed.

The correct composition of a red blood cell membrane is 18% protein, 79% lipid, and 3% carbohydrate. A myelin membrane around nerve cells is 76% protein and 24% lipid and an inner mitochondiral membrane is 80% protein, 17% lipid, and 4% carbohydrate.

Plasma is not a formed element of blood. Plasma is the extracellular matrix of blood. Platelets are small fragments of cells that assist clotting. Lymphocytes are a type of white blood cells, as are monocytes. Red blood cells are the other formed element found in blood.

Erythrocytes are also known as red blood cells. White blood cells come in a variety of types such as lymphocytes, monocytes, eosinophils, neutrophils, and basophils. Platelets are small fragments of cells that assist clotting. The extracellular matrix of blood is plasma.

Eosinophils are white blood cells that are involved in fighting parasitic infections. Basophils cause inflammation when their histamine-containing granules are released. Neutrophils contain granules that are used to kill infectious organisms. The only type of red blood cell is an erythrocyte. Note that eosinophils, basophils, and neutrophils are named after the types of stains for which they show preferential affinity (eosinophils have a high affinity for the stain eosin, basophils are best seen when stained with a basic dye, and neutrophils are best seen when stained with a neutral dye).

The lymphatic system drains excess tissue fluid as well as fights infections. The renal system is responsible for excretion and reabsorption. The circulatory system is responsible for the transportation of oxygen and nutrients throughout the body.

The left and right coronary arteries branch from the aortic root. This is the portion of the aorta just beyond the aortic valve. Since these arteries supply the heart and the heart must supply the rest of the body, it makes sense for the heart to have top priority.

The ascending aorta just after the aortic root, but before the aortic arch, is the only part of the aorta without branching. The pulmonary artery takes blood to the lungs to be oxygenated. The descending aorta has numerous branches supplying the spinal cord and the rest of the body.