Functions of Blood

• Blood transports gases, nutrients, waste products, processed molecules, and hormones.

• Blood protects against disease and is involved in temperature, fluid, pH, and ion regulation.

• Blood clotting prevents fluid and cell loss and is part of tissue repair.

Composition of Blood

• Blood is a connective tissue consisting of plasma and formed elements.

• Total blood volume is approximately 5 liters.

Plasma

• Plasma is 91% water and 9% suspended or dissolved substances.

• Plasma maintains osmotic pressure, is involved in immunity, prevents blood loss, and transports molecules.

Formed Elements

• The formed elements are cells (erythrocytes and leukocytes) and cell fragments (platelets).

Production of Formed Elements

• Formed elements arise (hematopoiesis) in red bone marrow from stem cells.

Erythrocytes

• Erythrocytes are disk-shaped cells containing hemoglobin, which transports oxygen and carbon dioxide. Erythrocytes also contain carbonic anhydrase, which is involved with carbon dioxide transport.

• In response to low blood oxygen levels, the kidneys produce erythropoietin, which stimulates erythrocyte production in red bone marrow.

• Worn-out erythrocytes are phagocytized by macrophages in the spleen or liver. Hemoglobin is broken down, iron and amino acids are reused, and heme becomes bilirubin that is secreted in bile.

Leukocytes

• Leukocytes protect the body against microorganisms and remove dead cells and debris.

• Granulocytes contain cytoplasmic granules: and there are three types of granulocytes: neutrophils are small phagocytic cells, eosinophils reduce inflammation, and basophils promote inflammation.

• Agranulocytes have two types of very small granules: lymphocytes are involved in antibody production and other immune system responses; monocytes become macrophages that ingest microorganisms and cellular debris.

Platelets

• Platelets are cell fragments involved with preventing blood loss.

Preventing Blood Loss

Blood Vessel Constriction

• Blood vessels constrict in response to injury, resulting in decreased blood flow.

Platelet Plugs

• Minor damage to blood vessels is repaired by platelet plugs.

• Platelets use integrins to adhere to collagen, release chemicals (ADP and thromboxanes) that activate other platelets, and connect to one another with fibrinogen to form platelet plugs.

Blood Clotting

• Blood clotting, or coagulation, is formation of a clot (a network of protein fibers called fibrin).

• There are three steps in the clotting process:

  Activation of clotting factors by connective tissue and chemicals, resulting in the formation of prothrombinase.

  Conversion of prothrombin to thrombin by prothrombinase.

  Conversion of fibrinogen to fibrin by thrombin.

Control of Clot Formation

• Anticoagulants in the blood, such as antithrombin and heparin, prevent clot formation.

Clot Retraction and Fibrinolysis

• Clot retraction condenses the clot, pulling the edges of damaged tissue closer together.

• Serum is plasma without clotting factors.

• Fibrinolysis (clot breakdown) is accomplished by plasmin.

Blood Groups

• Blood groups are determined by antigens on the surface of erythrocytes.

• Antibodies can bind to erythrocyte antigens, resulting in agglutination or hemolysis of erythrocytes.

ABO Blood Group

• Type A blood has A antigens, type B blood has B antigens, type AB blood has A and B antigens, and type O blood has neither A or B antigens.

• Type A blood has B antibodies, type B blood has A antibodies, type AB blood has neither A or B antibodies, and type O blood has both A and B antibodies.

• Mismatching the ABO blood group can result in transfusion reactions.

Rh Blood Group

• Rh-positive blood has Rh antigens, whereas Rh-negative blood does not.

• Antibodies against the Rh antigen are produced when an Rh-negative person is exposed to Rh-positive blood.

• The Rh blood group is responsible for hemolytic disease of the newborn.

Diagnostic Blood Tests

Type and Crossmatch

• Blood typing determines the ABO and Rh blood groups of a blood sample.

• A crossmatch tests for agglutination reactions between donor and recipient blood.

Complete Blood Count

• The complete blood count consists of the following: red blood cell count, hemoglobin measurement (grams of hemoglobin per 100 milliliters of blood), hematocrit measurement (percent volume of erythrocytes), and white blood cell count.

White Blood Cell Differential Count

• The white blood cell differential count determines the percentage of each type of leukocyte.

Clotting

• Platelet count and prothrombin time measure the ability of the blood to clot.

Blood Chemistry

• The composition of materials dissolved or suspended in plasma (e.g., glucose, urea nitrogen, bilirubin, and cholesterol) can be used to assess the functioning and status of the body's systems.