Blood = specialized connective tissue Cells = 45% of blood Erythrocytes (red blood cells, RBCs) Leukocytes (white blood cells, WBCs) Platelets (cell fragments) Plasma = 55% of blood - extracellular matrix of blood; 5-6 Liters total blood volume in adult

Functions of Blood Gaseous transport – RBCs carry oxygen and carbon dioxide Transport of metabolites and regulatory molecules (hormones) Homeostatic regulation of body temperature, osmotic balance Transport of cells and antibodies for defense and immunity

Erythrocytes (red blood cells) Most numerous blood cells Transport O2 and CO2 via hemoglobin No nucleus, mitochondria, ER, ribosomes in mature RBCs. All expelled during development. 120-day life span; destroyed by macrophages in spleen and bone marrow. - The only cell in blood stream that remains in blood stream

Erythrocytes Biconcave disk shape provides large surface area relative to volume; good for gas exchange Shape maintained by bendable cytoskeleton Normal adult RBC Sickle cell anemia

Red Blood Cell Physiology Typical RBC count: men: 4.6 – 6.2 million/mm3 women: 4.2 – 5.4 million/mm3 Hematocrit - % of whole blood volume that is RBCs men: 42 – 52% women: 37 – 48% No mitochondria. Energy needs met by anaerobic fermentation

Erythrocyte Membrane Organization Antiporter: Cl- in;HCO3- out

Structure of Hemoglobin (HbA) Typical Hb concentrations: men: 13 - 18 g/dL women: 12 – 16 g/dL

The Life and Death of Eryhrocytes

Correction of Hypoxemia by a Negative Feedback Loop

Sickle Cell Anemia (HbS) Inherited Point mutation in gene for Hb b-chain Deoxygenated HbS  rigid, fragile RBCs  anemia Increases blood viscosity

Relative Sizes of Blood Cells Compared to RBCs (7-8 mm diameter)

Leukocytes (White Blood Cells) Granulocytes Agranulocytes Lymphocyte Neutrophil Eosinophil Basophil Monocyte Numerous secretory vesicles in cytoplasm - Nucleus has 2 or more lobes Do NOT have abundant secretory vesicles Single-lobed nucleus

Neutrophils: 60-70% of circulating leukocytes Nucleus has 3-5 lobes Phagocytosis & destruction of bacteria Motile: exit the blood stream early in response to bacterial infections. Granules contain lysozyme and other antimicrobial enzymes, collagenase plus others. In females, the nucleus has a drumstick (Barr body), contains the condensed, inactivated second X chromosome.

Eosinophils: 2-4% of circulating leukocytes bi-lobed nucleus Eosinophilic granules (red/pink) contain histaminase Allergic & inflammatory reactions and parasitic infections Counteract the effects of basophils in allergic reactions Often found at sites of chronic inflammation, commonly in respiratory or digestives tracts

Basophils: <1% of circulating leukocytes Bilobed nucleus Basophilic granules (blue/black) obscure the nucleus Secrete histamine (vasodilation) and heparin (anti-coagulant) Involved in allergic and inflammatory reactions

Lymphocytes: 20-25% of circulating leukoctyes Agranulocyte Variable in size, 6-18 mm in diameter Single, round, heterochromatic nucleus Function in immunity 2 classes, indistinguishable morphologically B cells: produce antibodies T cells: mature in thymus, cell-mediated immune response

Monocytes: 3-8% of circulating leukocytes Agranulocyte Largest circulating WBC Large indented nucleus Stay in circulation a few days then migrate into the tissues and differentiate into macrophages As macrophages, phagocytize and destroy dead cells

Platelets (Thrombocytes) Anucleated cell fragments 2 mm diameter 10-day life span Main function: blood clotting Produced by megakaryocytes in bone marrow: bud off cytoplasm to form platelets. Bone marrow capillary Platelets

Differential White Blood Cell Count: Neutrophils > Lymphocytes > Monocytes > Eosinophils > Basophils Never Let Monkeys Eat Bananas