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18 Blood Blood Circulation • Circulatory system is divided into • Cardiovascular system • Lymphatic system • Blood • Transport mechanism for • Nutrients • Signaling molecules • Respiratory gases • Waste products Blood Circulation • Powered by the pumping action of the heart • Oxygen and nutrients diffuse across capillary walls to body tissues • Transports hormones from endocrine glands • Conveys cells of immune system • Regulates body temperature Composition of Blood • Blood volume • Males: 5–6 liters • Females: 4–5 liters • Blood has cellular and liquid components • Is a specialized connective tissue • Blood cells—formed elements • Plasma—liquid portion of blood Composition of Blood • Hematocrit • Is the measure of % RBC • Males: 47% ± 5% • Females: 42% ± 5% • Buffy coat • Is portion of blood composed of leukocytes and platelets • Present at junction of plasma and RBCs Blood Plasma • Straw-colored, sticky fluid portion of blood • Approximately 90% water • Contains over 100 kinds of molecules • Ions—Na+ and Cl– • Nutrients • Sugars, amino acids, lipids • • Wastes • Carbon dioxide, urea, ammonia Proteins Blood Plasma • Three main proteins • Albumin • Prevents water from diffusing out of blood vessels • Globulins • Include antibodies and blood proteins that transport lipids, iron, and copper • Fibrinogen • One of the molecules involved in chemical reactions for blood clotting Formed Elements • Blood cells • Erythrocytes, leukocytes, and platelets • Staining of blood cells • Acidic dye—eosin; stains pink • Basic dye—methylene blue; stains blue and purple Erythrocytes • Oxygen-transporting cells—7.5 µm in diameter (diameter of capillary 8–10mm) • Most numerous of the formed elements • Females: 4.3–5.2 million cells/cubic millimeter • Males: 5.2–5.8 million cells/cubic millimeter • Have no organelles or nuclei • Are the ideal measuring tool for estimating sizes of nearby structures Erythrocytes • Are packed with oxygen-carrying hemoglobin • Hemoglobin molecule bears four oxygen molecules • Each O2 molecule bears an iron molecule • Oxidation of iron atoms of hemoglobin molecules • Gives blood its red color Erythrocytes • Pick up O2 at lung capillaries • Release O2 across other tissue capillaries • Structural characteristics contribute to respiratory function • Biconcave shape 30 more surface area • 97% hemoglobin • Lack mitochondria • Do not consume O2 they pick up Leukocytes—White Blood Cells (WBCs) • 4800–11,000/cubic millimeter • • • • Protect the body from infectious microorganisms Function outside the bloodstream in loose connective tissue Diapedesis—circulating leukocytes leave the capillaries Originate in bone marrow Leukocytes—White Blood Cells (WBCs) • Two types of leukocytes • Granulocytes • Agranulocytes • Mnemonic: “Never Let Monkeys Eat Bananas” Granulocytes • Neutrophils • Most numerous WBC—granules pick up acidic and basic stains • Nucleus—has two to six lobes • Attracted by bacterial products and are first line of defense in inflammatory response • Phagocytize and destroy bacteria • Also release enzymes into extracellular matrix of infected tissue Granulocytes • Eosinophils • Represent 1–4% of all WBCs • Granules are large and stain red • Granules contain enzymes active during allergic reactions and parasitic infections • Play a role in ending allergic reactions by phagocytizing allergens • Secrete enzymes that degrade histamines Granulocytes • Basophils—about 0.5% of all leukocytes • Nucleus—usually two lobes • Granules secrete histamines • Function in inflammation mediation • Similar in function to mast cells • Direct later stages of inflammation in allergies and parasitic infections Agranulocytes • Lymphocytes—comprise 20–45% of WBCs • The most important cells of the immune system • Nucleus—stains dark purple • Effective in fighting infectious organisms • Act against a specific foreign molecule (antigen) Agranulocytes • Two main classes of lymphocyte • T cells—attack foreign cells directly • B cells—multiply to become plasma cells • Secrete antibodies Agranulocytes • Monocytes—compose 4–8% of WBCs • The largest leukocytes • Nucleus—kidney shaped • Transform into macrophages • Phagocytic cells Platelets • Cell fragments • Break off from megakaryocytes • Function in clotting of blood Blood Cell Formation • Hematopoiesis—process by which blood cells are formed in red marrow • 100 billion new blood cells formed each day Bone Marrow as the Site of Hematopoiesis • Bone marrow—located within all bones • Red marrow—actively generates new blood cells • Contains immature erythrocytes • In adults, red marrow is located • Between trabeculae of spongy bone of axial skeleton • Girdles • In proximal epiphyses of humerus and femur Bone Marrow as the Site of Hematopoiesis • Yellow marrow—dormant • Contains many fat cells • Located in the long bones of adults Bone Marrow as the Site of Hematopoiesis • Tissue framework of bone marrow • Reticular connective tissue • Fibroblasts covering and secreting the fiber network are reticular cells • Blood sinusoids run throughout the reticular tissue • Mature blood cells enter the blood stream through endothelial cells of sinusoids Bone Marrow as the Site of Hematopoiesis • Reticular tissue of bone marrow • Contains macrophages that extend pseudopods to capture antigens • Some cells of the reticular network are mesenchymal stem cells • Can give rise to • Fat cells, osteoblasts, chondrocytes, fibroblasts, and muscle cells Cell Lines in Blood Cell Formation • All blood cells originate in bone marrow • All originate from one cell type • Hemopoietic blood stem cell (pluripotential hematopoeitic stem cell) • Lymphoid stem cells • Give rise to lymphocytes • Myeloid stem cells • Give rise to all other blood cells Cell Lines in Blood Cell Formation • Genesis of erythrocytes • Committed cells are proerythroblasts • Remain in the reticulocyte stage for 1–2 days in circulation • Make up about 1–2% of all erythrocytes Cell Lines in Blood Cell Formation • Formation of leukocytes • Committed cell type in each granulocyte line are myeloblasts • Monoblasts enlarge and form monocytes • Megakaryoblasts differentiate into megakaryocytes • Break apart into platelets Disorders of the Blood • Disorders of erythrocytes • Polycythemia • Abnormal excess of erythrocytes • Anemia • Erythrocyte levels or hemoglobin concentrations are low Disorders of the Blood • Disorders of erythrocytes (continued) • Sickle cell disease • Inherited condition • Results from a defective hemoglobin molecule • Erythrocytes distort into a sickle shape Disorders of the Blood • Disorders of leukocytes • Leukemia—a form of cancer • Classified as lymphoblastic or myeloblastic • Disorders of platelets • Thrombocytopenia • Abnormally low concentration of platelets The Blood Throughout Life • First blood cells develop with the earliest blood vessels • • • Mesenchyme cells cluster into blood islands Late in month 2: • Liver and spleen take over blood formation Bone marrow becomes major hematopoietic organ at month 7