Blood

The average human body contains about four to six liters of blood. All vertebrates contain blood which is in our bodies for many vital functions. There are four constituents that blood is composed of: plasma, red blood cells, white blood cells, and platelets.

If you were to take a centrifuge ( a tool that spins mixtures to separate its components) with blood as the sample, two layers would form as the ending result. The top layer which would appear to be a clear and yellow fluid which is called plasma. Plasma consists of many solutes dissolved in water which are inorganic salts, plasma proteins which sometimes act as escorts for lipids(commonly known as fats) which are insoluble in water but only travel when bound to a protein, nutrients, waste products, and gases.

Each cubic millimeter of blood contains about five million red cells(erythrocytes). For oxygen to be transported, it must diffuse through the plasma membranes of red blood cells. This transfusion occurs due to molecules of hemoglobin, a protein containing iron, located in the red blood cells. As oxygen passes through gills or lungs, oxygen passes through membranes and binds to the hemoglobin. Erythrocytes are produced in the red marrow of bones particularly in the ribs, vertebrae, breastbone, and pelvis. If tissues are not receiving the correct amount of oxygen, a hormone called erthropoitin stimulate s the production of red blood cells in red blood cells in bone marrow.

White blood cells (leukocytes) fight infections in our body. There are a great concentration of white blood cells in lymph nodes and other parts of the lymphatic system which include the spleen, thymus, tonsils, adenoids, and lymph nodes. One type of leukocytes fight infections by eating bacteria, and the other produce antibodies to react against foreign substances.