The casting of new red blood cells is stimulated by the hormone erythropoietin (EPO), released from the kidneys. Recall that all blood cells are made in the bone marrow. This hormone may increase as much as 1000 fold in times of oxidative stress.

Thyroxine is T4, the most biologically active form of thyroid hormone. Vasopressin, or anti-diuretic hormone, is part of the body's fluid-balance system. Luteinizng hormone is a hormone of the reproductive tract: in females it triggers ovulation, while in males it stimulates Leydig cells to produce testosterone.

Erythropoietin is produced by the peritubular interstitial cells of the kidney. These cells are very sensitive to tissue oxygen pressure. When oxygen demand increases, erythropoietin is released, stimulating the casting (hematopoiesis) of new red blood cells in bone marrow. 

Supraoptic and paraventricular cells of the hypothalamus are the site of vasopressin (antidiuretic hormone) production. Lactotroph cells in the pituitary gland are responsible for the production of prolactin. Zona fasciculata cells of the adrenal glands produce cortisol.

Neutrophils are the most common type of white blood cell, making up 55-70% of the total white blood cell population in the average blood sample. 

Eosinophils are the leukocytes that are largely responsible for response to parasitic infections and allergies. They make up 1-3% of the average white blood cell count. They form the second smallest population of white blood cells, after basophils, which normally make up less than 1% of white blood cells in whole blood. 

Monocytes, the largest of all the leukocytes, make up just 2-10% of the average white blood cell count. These white blood cells will mature into macrophages to phagocytose foreign matter.

Macrophages consume bacteria, cancer cells, and cellular debris via phagocytosis. Once these elements are within the cell, the macrophage is able to use lysosomes to break them down and prepare them for release into the blood as waste, which will eventually be excreted. 

Platelets are small cell fragments that play an important role in hemostasis, or clot formation. Once activated, platelets release clotting factors that recruit more platelets till a clot is formed and bleeding stops.  

Diapedesis, also known as leukocyte extravasation, is the process by which white blood cells move into and out of blood vessels. This process includes four stages: chemoattraction, rolling adhesion, tight adhesion, and endothelial transmigration. This process is integral in the delivery of white blood cells to sites of infection and in their return into the blood stream to mobilize and facilitate the excretion of waste.

Neutrophils, eosinophils, and basophils are all granulocytes, meaning they contain visible granules within their cytoplasms. These granules contains acids and antimicrobial enzymes, and are released at the site of infection. Monocytes and lymphocytes are agranulocytes, meaning they do not contain granules in their cytoplasm but rather destroy foreign proteins by other means, such as phagocytosis and cytotoxicity.

Platelets are derived from megakaryocytes, cells produced in bone marrow, kidney, liver, and spleen, with large, lobed nuclei. Platelets are formed within the cell and then released into plasma. Erythrocytes (mature red blood cells), plasma cells (a type of B cell) and progranulocytes (precursors to neutrophils, basophils, and eosinophils) take no part in the creation of platelets, which are fragments of cells, not whole cells.