Blood Composition and Function

• Blood functions to distribute, regulate, and protect.
• Blood is viscous, red, has a volume of about 5L, and a pH between 7.35-7.45

Composition

• Blood consists of plasma and formed elements.
• Plasma contains mostly water, albumins, globulins, clotting proteins, and other solutes like electrolytes, nutrients, wastes, hormones, and gases.
• Formed elements include erythrocytes, leukocytes, and platelets.

Erythrocytes

• Erythrocytes, or red blood cells, have a concentration of about 5 million per microliter, are biconcave, anucleate, and contain hemoglobin.
• Hematocrit refers to the percentage of red blood cells in whole blood.
• Hemoglobin contains heme, an iron-containing component that carries oxygen, and globin, a protein which carries carbon dioxide.
• Heme carries 4 oxygen molecules
• Heme has a higher affinity for carbon monoxide than oxygen, leading to suffocation in carbon monoxide poisoning.
• Erythropoiesis, the production of red blood cells, occurs in red bone marrow and arises from hemocytoblasts.
• Erythropoiesis is regulated by erythropoietin, a hormone made by the kidneys and released in response to low oxygen levels.
• Anemia is defined as low oxygen carrying capacity and can result from iron deficiency, pernicious anemia, or sickle cell disease.
• Polycythemia is a condition marked by excess red blood cells.

Leukocytes

• Leukocytes, or white blood cells, include granulocytes and agranulocytes.
• Granulocytes include neutrophils, eosinophils, and basophils.
• Neutrophils are bacteria slayers and the most abundant leukocyte.
• Eosinophils target parasites and are associated with allergies and have bright pink granules.
• Basophils release histamine, are involved in inflammation, have dark blue granules and are the least abundant.
• Agranulocytes include lymphocytes and monocytes.
• Lymphocytes, including B and T cells, are involved in immunity.
• Monocytes are the largest leukocytes, have a horseshoe-shaped nucleus, and become macrophages in tissues.
• Leukopoiesis, the production of white blood cells, occurs in red bone marrow, all arise from hemocytoblasts.
• Lymphoid progenitor cells give rise to lymphocytes.
• Myeloid progenitor cells give rise to all other blood cells.
• Disorders of leukocytes include leukemia, leukopenia, and leukocytosis.
• Leukemia involves nonfunctional white blood cells.
• Leukopenia is characterized by low white blood cell count.
• Leukocytosis is characterized by high white blood cell count, representing a normal response to infection.

Platelets

• Platelets, or thrombocytes, are derived from megakaryocytes (thrombopoiesis).

Hemostasis

• Hemostasis, or blood clotting, involves three main steps: vascular spasm, platelet plug formation, and coagulation.

Clotting Disorders

• Clotting disorders include hemophilia, thrombocytopenia, thrombus formation, and embolus formation.
• Hemophilia is a genetic disorder that impairs the body's ability to control blood clotting.
• Thrombocytopenia is a condition characterized by a deficiency of platelets in the blood.
• Thrombus refers to a clot in an unbroken vessel.
• Embolus refers to a free-floating clot.

Blood Typing

• ABO blood typing is based on the presence or absence of A and B antigens.
• Type A blood has A antigens and B antibodies.
• Type B blood has B antigens and A antibodies.
• Type AB blood has both A and B antigens and no antibodies.
• Type O blood has no antigens and both A and B antibodies.
• Rh factor is another important blood group system, where individuals are either Rh positive or Rh negative.
• Rh negative individuals only make antibodies after exposure to Rh positive blood.

Erythroblastosis Fetalis

• Erythroblastosis fetalis can occur when an Rh-negative mother carries an Rh-positive baby.
• After the first pregnancy, the mother may develop antibodies against the Rh factor.
• In subsequent pregnancies with Rh-positive babies, the mother's antibodies can attack the baby's blood.