4.18 Blood

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susaneers
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48658
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4.18 Blood
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2010-11-11 00:53:27
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Composition blood blood cell formation disorders
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Composition of blood, blood cell formation, disorders of the blood, blood throughout life
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  1. General Functions of Blood
    Circulation initiated by pumping action of the heart

    • Blood:
    • Carries respiratory gases and nutrients
    • Transports hormones from the endocrine glands to their target organs
    • Conveys cells of the body's defense system to sites where they can fight infection
    • Also helps regulate body temperature

    • Accounts for 8% of body mass
    • 5-6 liters in men
    • 4-5 liters in women
  2. Composition of Blood
    • Blood:
    • Contains both cellular and liquid components
    • Is a specialized type of connective tissue in which blood cells, called formed elements, are suspended in a fluid called plasma.

    • Centrifugation:
    • Heavier formed elements are packed down
    • Less dense plasma remains at the top

    • *Red mass at bottom: erythrocytes (red blood cells)
    • % of blood volume that consists of erythrocytes = hematocrit (~45%)
    • *thin, gray layer in the middle: buffy coat (contains leukocytes (white blood cells) and platelets or thrombocytes (cell fragments that help stop bleeding)) ~1%
    • *Plasma = ~55%
  3. Composition of Blood:
    Blood Plasma
    • Straw colored, sticky fluid
    • ~90% water
    • Contains over 100 different kinds of molecules:
    • ions (like Na+ and Cl-)
    • nutrients (simple sugars, amino acids, lipids)
    • wastes (urea, ammonia, carbon dioxide)
    • oxygen, hormones, and vitamins

    • Plasma also contains 3 types of proteins:
    • 1. albumin: helps keep water from diffusing out of the bloodstream
    • 2. globulins: include both antibodies and the blood proteins that transport lipids, iron, and copper
    • 3. fibrinogen: one of several molecules involved in blood clotting

    **Hemochromatosis: absorption of too much iron from the diet; iron gradually accumulates in tissues, oxidizes, and poisons organs; treatment is through weekly blood removal
  4. Composition of Blood:
    Formed Elements
    • Formed Elements, or blood cells
    • erythrocytes, leukocytes, and platelets

    • neither erythrocytes nor platelets are true cells:
    • - lack nuclei and organelles; re just cell fragments
    • - cannot divide, survive only a few hours to months

    • Staining of blood cells: (Wright's stain)
    • - eosin: pink, acidic dye
    • - methylene blue: blue and purple, basic dye
  5. Composition of Blood: Formed Elements
    Erythrocytes
    
    • Erythrocytes, or Red Blood Cells
    • - small, oxygen transporting cells, ~7.5um diameter
    • - most numerous formed element
    • - have no nuclei or organelles
    • - packed with oxygen carrying hemoglobin (each hemoglobin has 4 polypeptides, each containing an iron atom that binds oxygen)

    Pick up O2 at lung capillaries and release it at tissue capillaries

    • Special structural characteristics:
    • 1. biconcave shape: provides 30% more surface area than spherical
    • 2. over 97% hemoglobin (discounting water): contain lots of oxygen
    • 3. lack mitochondria; generate energy anaerobically- efficient O2 transporters
    • also picks up 20% of CO2 transported by the blood; live up to 100-120 days; originate from red bone marrow

    **Thalassemia: inherited anemias characterized by insufficient production of one polypeptide chain of hemoglobin; usually low RBC counts; symptoms include fatigue, spleen enlargement, bone marrow and bone enlargement; treatments include blood transfusions every month for life
  6. Composition of Blood: Formed Elements
    Leukocytes (overview)
    White Blood Cells (WBCs)

    • Far less numerous than RBCs, but crucial to defense against disease
    • Spherical, the only formed elements that are complete cells (with organelles and nucleus)
    • - Function outside the bloodstream in loose connective tissues, where infection occurs

    Diapedesis: process by which leukocytes leave capillaries by actively squeezing between endothelial cells that form capillary walls in response to chemicals released at infection sites

    WBC count is used as an indication for infection or inflammation (leukocytosis = 11000/mm3)

    • There are five types of leukocytes, divided into two groups based on presence or absence of membrane-bound cytoplasmic granules
    • Granulocytes: (neutrophils, eosinophils, and basophils) contain many obvious granules; much larger and much shorter lived than erythrocytes; have nonspherical nuclei and purple staining lobes; functionally all phagocytic
    • Agranulocytes: (lymphocytes and monocytes) lack obvious granules

    • From most abundant to less abundant cell type:
    • Never Let Monkeys Eat Bananas
  7. Composition of Blood: Formed Elements
    Leukocytes: Neutrophils
    Granulocytes; Bacteria-destroying; most abundant WBC (~60%)

    • - Nucleus consists of 2-6 lobes interconnected by chromatin threads
    • - Two types of granules, more abundant stains light pink, others stain reddish purple (both acidic and basic dyes)
  8. Composition of Blood: Formed Elements
    Leukocytes: Eosinophils
    Granulocytes; Relatively rare (~1-4% of leukocytes)
  9. - Nucleus usually two-lobed interconnected by broad band
    • - Granules stain red with acidic dye (eosin)
    • - Function during parasitic infections and ending allergic reactions
  10. Composition of Blood: Formed Elements
    Leukocytes: Basophils
    Granulocytes; Rarest WBC (~0.5% of leukocytes)

    • - Nucleus usually has 2 lobes, may be bent into U or S shape
    • - Granules are large and stain dark purple (basic dye)
    • - Granules contain histamine and other molecules secreted to mediate inflammation during allergic responses and parasitic infections (later stages)
  11. Composition of Blood: Formed Elements
    Leukocytes: Lymphocytes
    Agranulocyte; most important cells of the immune system

    • - 20-45% of all leukocytes in the blood
    • - Nucleus large, contains chromatin that stains dark purple
    • - Play crucial role in immunity
    • - each lymphocyte recognizes and acts against a specific antigen

    • Two main classes of lymphocytes:
    • 1. T-Cells: attack foreign cells directly
    • 2. B-Cells: differentiate and produce antibodies (proteins that bind to the antigen and mark it for destruction by macrophages)
  12. Composition of Blood: Formed Elements
    Leukocytes: Monocytes
    Agranulocyte; largest leukocyte

    • - ~4-8% of WBCs
    • - Nucleus usually kidney shaped, chromatins not as condensed
    • - Transform into macrophages that move through connective tissue and ingest foreign cells, molecules, and tiny particles of debris
  13. Composition of Blood: Formed Elements
    Platelets
    Also called thrombocytes, "clotting cells"

    • - disc-shaped, plasma membrane-enclosed fragments of cytoplasm that form by breaking off larger cells called megakaryocytes.
    • - Plug small tears in the walls of blood vessels to limit bleeding.
    • - Release thromboplastin, PF3, that helps initiate clotting.

    **Thrombus: a clot that develops in an intact blood vessel; can lead to heart attack or stroke, depending on where the clot blocks blood flow
  14. Disorders of the Blood
    • Disorders of Erythrocytes:
    • Polycythemia: excess of erythrocytes in the blood; causes an increase in viscosity of blood, which slows or blocks flow in smaller vessels; treated by dilution of blood in saline
    • Anemia: erythrocyte levels or hemoglobin concentrations are low, diminishing the blood's capacity for carrying oxygen; anemics are constantly tired, pale, short of breath, and chilly
    • Sickle Cell Disease: defect in hemoglobin that causes it to crystallize when O2 levels are low or erythrocytes become dehydrated; causes cells to become distorted, rigid, fragile, and easily destroyed

    • Disorders of Leukocytes:
    • Leukemia: form of cancer resulting from uncontrolled proliferation of a leukocyte-forming cell line in bone marrow

    • Disorders of Platelets:
    • Thrombocytopenia: "lack of platelets"; an abnormally low concentration of platelets in the blood; diminished blood clot formation and by internal bleeding from small vessels.

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