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Blood

Blood. 17. Overview of Blood Circulation. Blood leaves the heart via arteries that branch repeatedly until they become capillaries Oxygen (O 2 ) and nutrients diffuse across capillary walls and enter tissues Carbon dioxide (CO 2 ) and wastes move from tissues into the blood.

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Blood

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  1. Blood 17

  2. Overview of Blood Circulation • Blood leaves the heart via arteries that branch repeatedly until they become capillaries • Oxygen (O2) and nutrients diffuse across capillary walls and enter tissues • Carbon dioxide (CO2) and wastes move from tissues into the blood

  3. Overview of Blood Circulation • Oxygen-deficient blood leaves the capillaries and flows in veins to the heart • This blood flows to the lungs where it releases CO2 and picks up O2 • The oxygen-rich blood returns to the heart

  4. Composition of Blood • Blood is the body’s only fluid tissue • It is composed of liquid plasma and formed elements • Formed elements include: • Erythrocytes, or red blood cells (RBCs) • Leukocytes, or white blood cells (WBCs) • Platelets • Hematocrit – the percentage of RBCs out of the total blood volume

  5. Components of Whole Blood Plasma(55% of whole blood) Buffy coat:leukocyctes and platelets(<1% of whole blood) Formed elements Erythrocytes(45% of whole blood) Withdraw blood and place in tube Centrifuge 1 2 Figure 17.1

  6. Physical Characteristics and Volume • Blood is a sticky, opaque fluid with a metallic taste • The pH of blood is 7.35–7.45 • Temperature is 38C, slightly higher than “normal” body temperature • Blood accounts for approximately 8% of body weight • Average volume of blood is 5–6 L for males, and 4–5 L for females

  7. Blood Plasma • Blood plasma contains over 100 solutes, including: • Proteins – albumin, globulins, clotting proteins, and others • Nonprotein nitrogenous substances – lactic acid, urea, creatinine • Organic nutrients – glucose, carbohydrates, amino acids • Electrolytes – sodium, potassium, calcium, chloride, bicarbonate • Respiratory gases – oxygen and carbon dioxide

  8. Formed Elements • Erythrocytes, leukocytes, and platelets make up the formed elements • Only WBCs are complete cells • RBCs have no nuclei or organelles, and platelets are just cell fragments • Most formed elements survive in the bloodstream for only a few days • Most blood cells do not divide but are renewed by cells in bone marrow

  9. Erythrocytes (RBCs) • Biconcave discs, anucleate, essentially no organelles • 97 % hemoglobin (Hb), a protein that functions in gas transport • Contain the plasma membrane protein spectrin and other proteins that: • Give erythrocytes their flexibility • Allow them to change shape as necessary

  10. Erythrocytes (RBCs) Figure 17.3

  11. Erythrocyte Function • Erythrocytes are dedicated to respiratory gas transport • Hemoglobin reversibly binds with oxygen and most oxygen in the blood is bound to hemoglobin • Each heme group bears an atom of iron, which can bind to one oxygenmolecule • Each hemoglobin molecule can transport four molecules of oxygen

  12. Production of Erythrocytes • Hematopoiesis – blood cell formation • Hematopoiesis occurs in the red bone marrow of the: • Axial skeleton and girdles • Epiphyses of the humerus and femur • Hemocytoblasts give rise to all formed elements

  13. Production of Erythrocytes: Erythropoiesis • A hemocytoblast is transformed into a committed cell called the proerythroblast • Proerythroblasts develop into early erythroblasts • The developmental pathway consists of three phases • Phase 1 – ribosome synthesis in early erythroblasts • Phase 2 – hemoglobin accumulation in late erythroblasts and normoblasts • Phase 3 – ejection of the nucleus from normoblasts and formation of reticulocytes • Reticulocytes then become mature erythrocytes

  14. Production of Erythrocytes: Erythropoiesis Figure 17.5

  15. Fate and Destruction of Erythrocytes • The life span of an erythrocyte is 100–120 days • Old erythrocytes become rigid and fragile, and their hemoglobin begins to degenerate • Dying erythrocytes are engulfed by macrophages • Heme and globin are separated and the iron is salvaged for reuse

  16. Fate and Destruction of Erythrocytes • Heme is degraded to a yellow pigment called bilirubin • The liver secretes bilirubin into the intestines as bile • The intestines metabolize it into urobilinogen • This degraded pigment leaves the body in feces, in a pigment called stercobilin • Globin is metabolized into amino acids and is released into the circulation • Hb released into the blood is captured by haptoglobin and phgocytized

  17. Leukocytes (WBCs) • Leukocytes, the only blood components that are complete cells: • Are less numerous than RBCs • Make up 1% of the total blood volume • Can leave capillaries via diapedesis • Move through tissue spaces • Leukocytosis – WBC count over 11,000 per cubic millimeter • Normal response to bacterial or viral invasion

  18. Leukocytes

  19. Eosinophils • Eosinophils account for 1–4% of WBCs • Lead the body’s counterattack against parasitic worms • Lessen the severity of allergies by phagocytizing immune complexes

  20. Basophils • Account for 0.5% of WBCs and: • Have large, purplish-black (basophilic) granules that contain histamine • Histamine – inflammatory chemical that acts as a vasodilator and attracts other WBCs (antihistamines counter this effect)

  21. Lymphocytes • Account for 25% or more of WBCs and: • Are found mostly enmeshed in lymphoid tissue (some circulate in the blood) • There are two types of lymphocytes: T cells and B cells • T cells function in the immune response • B cells give rise to plasma cells, which produce antibodies

  22. Monocytes • Monocytes account for 4–8% of leukocytes • They are the largest leukocytes • They leave the circulation, enter tissue, and differentiate into macrophages • Macrophages: • Are highly mobile and actively phagocytic

  23. Platelets • Platelets are fragments of megakaryocytes • Platelets function in the clotting mechanism by forming a temporary plug that helps seal breaks in blood vessels

  24. Genesis of Platelets • The stem cell for platelets is the hemocytoblast • The sequential developmental pathway is hemocytoblast, megakaryoblast, promegakaryocyte, megakaryocyte, and platelets Figure 17.12

  25. Human Blood Groups • RBC membranes have glycoprotein antigens on their external surfaces • These antigens are: • Unique to the individual • Recognized as foreign if transfused into another individual • Promoters of agglutination and are referred to as agglutinogens • Presence or absence of these antigens is used to classify blood groups

  26. ABO Blood Groups • The ABO blood groups consists of: • Two antigens (A and B) on the surface of the RBCs • Two antibodies in the plasma (anti-A and anti-B) • Agglutinogens and their corresponding antibodies cannot be mixed without serious hemolytic reactions

  27. Rh Blood Groups • Presence of the Rh agglutinogens on RBCs is indicated as Rh+ • Anti-Rh antibodies are not spontaneously formed in Rh– individuals • However, if an Rh– individual receives Rh+ blood, anti-Rh antibodies form • A second exposure to Rh+ blood will result in a typical transfusion reaction

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