Chapter 6

Functions of Blood

Blood is the primary transport medium of the body. Blood transports gases and nutrients and carries away wastes from all parts of the body. Hormones are also transported in the blood. Blood defends the body against invasion by pathogens in several ways, and blood has regulatory functions for temperature, water/salt balance, and pH.

Disorders of white blood cells

Inherited immune deficiencies such as severe combined immunodeficiency disease (SCID) result from disorders with the production and/or function of white blood cells. Cancer of white blood cells is called leukemia. Mononucleosis is an infectious disease in which a virus infects lymphocytes.

Functions and composition of plasma

Plasma is the liquid portion of blood, made up mostly of water, but also containing salts, small organic molecules, hormones, and plasma proteins. The liver makes most plasma proteins that function to buffer the blood, transport molecules, and maintain osmotic pressure. They also have specific functions: Albumin transports bilirubin; globulin is a component of lipoproteins, which transport cholesterol; gamma globulins are the antibodies of immunity; fibrinogen is involved in blood clotting.

Origin of platelets

Platelets result from the fragmentation of megakaryocytes in the red bone marrow. These are involved in the process of blood clotting.

Characteristics of red blood cells

Red blood cells (erythrocytes) are small, biconcave disks that lack a nucleus when mature. There are 4-6 million red blood cells per mm3 of whole blood.

Life cycle of red blood cells

Red blood cells are produced in the bone marrow. Red blood cells live only about 120 days and are destroyed in the liver and the spleen. Hemoglobin is released when blood cells are broken down. Iron is recovered and recycled to the bone marrow. Pigments from hemoglobin are excreted as bile pigments.

Structure of hemoglobin and how it carries oxygen and carbon dioxide

Red blood cells contain hemoglobin, the respiratory pigment that transports oxygen. Each hemoglobin molecule has four polypeptides that comprise the protein globin and an iron-containing, oxygen-carrying heme portion. Hemoglobin directly transports about 25% of carbon dioxide which binds to the terminal amino groups of the globin molecules.

Blood Capatibility

The antibodies in the plasma must not combine with the antigens on the surface of the red blood cells or agglutination will occur. Type O is sometimes called the universal donor because it has neither type A nor type B antigens on the red blood cells, and type AB blood is sometimes called the universal recipient because this blood type has neither anti-A or anti-B antibodies in the plasma.

Formed elements of blood

The formed elements are red blood cells, white blood cells, and platelets. Red blood cells are two to three times smaller than white blood cells but there are many more of them.

Steps in blood clotting

When tissues are damaged, platelets stick to the damaged area, partially sealing torn blood vessels. Injured tissues release prothrombin activator, which converts prothrombin to thrombin. This step requires calcium ions. Thrombin functions as an enzyme to convert fibrinogen into insoluble fibrin.

Disorders related to blood clotting

An insufficient number of platelets is called thrombocytopenia. Hemophilia is an inherited clotting disorder due to a deficiency in a clotting factor.

Types of white blood cells, structure and funtions

White blood cells (leukocytes) are large and nucleated, and function in immunity. They squeeze through capillaries and invade tissues when needed. Some white blood cells are very good at phagocytosis while others produce antibodies. Colony-stimulating factors (CSFs) are proteins that regulate the production of white blood cells. * Types of White Blood Cells White blood cells are classified into the granular leukocytes and the agranular leukocytes because of the presence of noticeable granules. * Granular Leukocytes Neutrophils engulf bacteria and debris through phagocytosis. Eosinophils are numerous during allergic reactions or parasitic infections. Basophils become mast cells in tissues, releasing histamine. * Agranular Leukocytes Agranular leukocytes include monocytes, which become macrophages that phagocytize pathogens and cellular debris in tissues, and lymphocytes (B lymphocytes and T lymphocytes) responsible for immunity.