Blood Composition and Function

Blood Composition and Function • General Composition of Blood • Plasma • Formed Elements • Erythrocytes • Leukocytes • Hematopoesis • Hemostasis (Clotting) • Transfusion and Blood Typing • Developmental Aspects of Blood

Blood Composition • The only fluid tissue in the human body • Classified as a connective tissue • Living cells = formed elements • Non-living matrix = plasma • Color range • Oxygen-rich blood is scarlet red • Oxygen-poor blood is dull red • pH must remain between 7.35–7.45 • Blood temperature is slightly higher than body temperature Hematocrit: Percent of blood volume that is RBCs • 47% ± 5% for males • 42% ± 5% for females Figure 10.1

Blood Cell Types

Erythrocytes (Red Blood Cells) • Main function is to carry oxygen • Biconcave disks • Essentially bags of hemoglobin; few organelles • Anucleate (no nucleus) • Outnumber white blood cells 1000:1 • Contain the plasma membrane protein spectrin and other proteins • Major factor contributing to blood viscosity

Hemoglobin • Molecular structure • Protein globin: two alpha and two beta chains • Heme pigment bonded to each globin chain • Iron atom in each heme can bind reversibly to one O2 molecule • Each Hb molecule can transport four O2

Sickle Cell Hemoglobin Causes Clotting • Normal hemoglobin = HbA • Sickle cell hemoglobin = HbS (mutation in single amino acid - missense)

Pleiotropic Effects Seen if HbS present HbAHbA = normal HbAHbS = sickle cell trait HbSHbS = sickle cell disease/anemia

Fetal Hemoglobin Binds O2 More Avidly • Fetal circulation must extract oxygen from maternal circulation • Fetal hemoglobin (HbF) binds O2 more avidly than normal hemoglobin (HbA) does • Replaced by “adult” hemoglobin just after birth

Leukocytes (White Blood Cells) Differential WBC count (All total 4800– 10,800/l) Formed elements Platelets Granulocytes Neutrophils (50–70%) Leukocytes Eosinophils (2–4%) Basophils (0.5–1%) Erythrocytes Agranulocytes Lymphocytes (25 – 45%) Monocytes (3 – 8%) Figure 17.9

Leukocyte Levels in the Blood • Normal levels are between 4,000 - 11,000 cells per millimeter • Abnormal leukocyte levels • Leukocytosis • Above 11,000 leukocytes/ml • Generally indicates an infection (bacterial, fungal, parasitic) • Also caused by some cancers, (including lymphocyte leukemia), hemhorrage, pneumonia • Leukopenia • Abnormally low leukocyte level (< 3,500/ml) • Commonly caused by certain drugs, radiation • Neutropenia (low neutrophil count) common in cancer patients receiving chemotherapy • HIV-AIDS, TB, malaria, influenza also cause leukopenia • Requires careful sanitation and “gowning up” for medical staff

Types of Leukocytes • Granulocytes • Granules in their cytoplasm can be stained • Include neutrophils, eosinophils, and basophils • Agranulocytes • Lack visible cytoplasmic granules • Include lymphocytes and monocytes Figure 10.4

Characteristics of Formed Elements of the Blood N E B

Characteristics of Formed Elements of the Blood L M

Hematopoiesis • Subdivided into erythropoesis and leukopoesis • Erythropoesis ccurs in red bone marrow • Erythropoesis Steps • Ribosome synthesis • Hemoglobin accumulation • Ejection of the nucleus and formation of reticulocytes • Reticulocytes then become mature erythrocytes Stem cell Committed cell Developmental pathway Phase 1 Ribosome synthesis Phase 2 Hemoglobin accumulation Phase 3 Ejection of nucleus Figure 17.5 Reticulo- cyte Erythro- cyte Proerythro- blast Early erythroblast Late erythroblast Normoblast Hemocytoblast

Fate of Erythrocytes • Unable to divide, grow, or synthesize proteins • Wear out in 100 to 120 days • When worn out, are eliminated by phagocytes in the spleen or liver • Iron is salvaged for reuse • Heme is degraded to yellow the pigment bilirubin • Liver secretes bilirubin (in bile)) into the intestines • Lost cells are replaced by division of hemocytoblasts

Control of Erythrocyte Production • Rate is controlled by a hormone (erythropoietin) • Kidneys produce most erythropoietin as a response to reduced oxygen levels in the blood (hypoxia) • Hypoxia can develop from hemorrhage, low O2 in air, insufficient hemoglobin • Homeostasis is maintained by negative feedback from blood oxygen levels

Platelets Important in Clotting • Small fragments of megakaryocytes • Formation is regulated by thrombopoietin • Blue-staining outer region, purple granules • Form a temporary platelet plug that helps seal breaks in blood vessels Stem cell Developmental pathway Hemocyto- blast Megakaryocyte Platelets

Hemastasis: Blood Clotting 1 Step Vascular spasm • Smooth muscle contracts, causing vasoconstriction. 2 Step Platelet plug formation •Injury to lining of vessel exposes collagen fibers; platelets adhere. Collagen fibers •Platelets release chemicals that make nearby platelets sticky; platelet plug forms. Platelets 3 Step Coagulation •Fibrin forms a mesh that traps red blood cells and platelets, forming the clot. Fibrin Figure 17.13

Hemastasis

Undesirable Clotting • Thrombus • A clot in an unbroken blood vessel • Can be deadly in areas like the heart • Embolus • A thrombus that breaks away and floats freely in the bloodstream • Can later clog vessels in critical areas such as the brain, causing a stroke (CVA)

Bleeding Disorders • Thrombocytopenia • Platelet deficiency • Even normal movements can cause bleeding from small blood vessels that require platelets for clotting • Hemophilia • Hereditary bleeding disorder • Normal clotting factors are missing or deficiency in Vit. K. mild hemophilia

Blood Groups and Transfusions • Large losses of blood have serious consequences • Loss of 15 to 30 percent causes weakness • Loss of over 30 percent causes shock, which can be fatal • Transfusions are the only way to replace blood quickly • Transfused blood must be of the same blood group

Human Blood Groups • Blood contains genetically determined proteins • A foreign protein (antigen) on a donated RBC may be attacked by the immune system • Blood is “typed” by using antibodies that will cause blood with certain proteins to clump (agglutination)

Human Blood Groups • There are over 30 common red blood cell antigens • The most vigorous transfusion reactions are caused by ABO and Rh blood group antigens ABO Blood Groups and Alleles Components of Blood of this Type anti-A anti-B anti-B anti-A

Rh Blood Groups and Hemolytic Deaseas of Newborns • Named because of the presence or absence of one of eight Rh antigens (agglutinogen D) • Most Americans are Rh+ • The danger is only when the mother is Rh– and the father is Rh+,and the child inherits the Rh+ factor Dd dd This baby, if from the second or subsequent pregnancy, could have complications in an Rh- mother • Problems can occur in second and subsequent pregnancies when the baby’s Rh+ blood enters Rh– maternal circulation: erythroblastosis fetalis (hemolytic disease of the newborn) • RhoGAM injections contain anti-Rh antibodies that quickly clear the maternal circulation of Rh protein Dd dd

Blood Composition and Function