- Immunity

The average adult has about five liters of blood inside of their body, moving thru their vessels, delivering nutrients, and removing wastes like CO2. Blood is the fluid of life, transporting oxygen from the lungs to body tissue.  Blood is considered to be a fluid connective tissue composed of cells, platelets, and plasma. Plasma accounts for about 54% of the total volume of normal blood. In addition to water, electrolytes, and nutrients, plasma contains the proteins: albumin, which helps maintain the osmotic balance in capillaries, immunoglobulins (antibodies), and fibrinogen, which is important in the clotting process.

Erythrocytes, or Red Blood Cells, derive their color from the protein hemoglobin, and usually appear round or oval . A drop of blood contains millions of red blood cells.

Hemoglobin is a protein that contains Iron, for transporting oxygen and carbon dioxide. As blood passes through the lungs, oxygen molecules attach to the hemoglobin. As the blood passes through the body's tissue, the hemoglobin releases the oxygen to the cells. The empty hemoglobin molecules then bind with the tissue's carbon dioxide or other waste gases, transporting them away. The average life cycle of a red blood cell is 120 days. As we have seen before, your bone marrow is continually producing new blood cells, replenishing your supply.

Blood platelets, or thrombocytes, are not true cells, but rather cytoplasmic fragments of a large cell in the bone marrow, the Megakaryocyte. Platelets have several types of membrane-bound granules (GR) which contain a number of constituents including fibrinogen and several growth factors (e.g., PDGF). Platelet activation occurs when injury to the vessel wall exposes sub-endothelial components, especially collagen. Platelets adhere to the damaged area and become cohesive to other platelets. This aggregation leads to the formation of a platelet plug, which prevents further blood loss and allows the repair process to begin.

This process is also know as clotting. Clotting must be carefully controlled because a clot in the wrong place, at the wrong time, can lead to stroke, heart attack, or death.

White Blood Cells - White blood cells, also called leukocytes, are outnumbered by red blood cells by about six hundred to one. Lymphocytes originate in the bone marrow and become specialized as they are released into the blood stream. There are several different (~5) types of leukocytes which then become the many different specialized cells that are the Immune System.

Five types of Leukocytes

1. Lymphocytes 2. Eosinophils 3. Basophils 4. Monocytes 5. Neutrophils

The white cells are an army of defenders which battle infections and disease. Leukocytes are specialists, some circulate in the blood while the rest are surveying the tissues for invaders.

Bacteria, viruses, fungi and parasites are constantly sneaking in through cuts in the skin or into the linings in the respiratory and digestive tracts. Some white cells, called Neutrophils, Macrophages or Monocytes, rush in and literally gobble up these invaders (Macrophage means "big eater"); other white blood cells swarm all over the bacteria and coat and absorb them. Still other types of leukocytes grow-up to become:
Eosinophils, Mast Cells, Basophils, Natural Killer Cells, and the B- and T- Cells These cells play several different complex roles in our Immune system.