ch. 19 blood

Cards (130)

  • The Blood
    • A unique, fluid connective tissue
  • the blood constitutes about 8% of body weight
  • In a healthy adult, volume is 5-6 L for a male and 4-5 L for a female
  • the blood is about 4-5 times as viscous as water
  • the blood has a pH of 7.35-7.45
  • blood color varies from scarlet (O2-rich) to dark red (O2-poor)
  • blood functions to transport, regulate, and protect
  • Transport
    • O2 and nutrients to cells
    • CO2 and metabolic wastes away from cells
    • hormones and enzymes
  • Regulate
    • body temperature
    • pH of body tissues
    • water content of tissues
  • Protect
    • against blood loss (by clotting mechanisms)
    • against infection (by defense mechanisms of white blood cells)
  • Blood is composed of two portions:
    1. Plasma (55%)
    2. Formed elements (45%)
  • Plasma (55%)
    • watery fluid that contains dissolved substances
  • Formed elements (45%)
    • red blood cells (erythrocytes)
    • white blood cells (leukocytes)
    • platelets (thrombocytes) are cell fragments
  • Blood Plasma
    • Fluid portion of blood; straw-coloured
    • Composed of 90% water and 10%solutes
  • Solutes include:
    • electrolytes: Na+, K+, Ca2+, Mg2+, Cl-, HCO3-
    • nutrients: amino acids, glucose, fatty acids, glycerol
    • enzymes and hormones gases: CO2, O2
    • metabolic wastes- urea, ammonia, bilirubin
    • plasma proteins produced mainly by liver
  • Plasma Proteins account for 8% of the 10% of dissolved solutes in plasma
  • plasma proteins have 3 main categories
    1. Albumin
    2. Globulins
    3. Fibrinogen
  • 1)Albumin (smallest size)
    • 54% of plasma protein
    • helps with the maintenance of osmotic pressure (helps keep water in blood plasma)
    • acts as a blood buffer (maintains pH)
    • carrier molecule of fatty acids and steroid hormones
  • Globulins
    • 38% of plasma protein
    • i)alpha and beta globulins – transport iron, metals, lipids, fat-soluble vitamins
    • ii)immunoglobulins (antibodies) – released by plasma cells during immune response
  • Fibrinogen
    • 7% of plasma protein
    • soluble precursor of fibrin
    • acts in blood clotting
  • Red Blood Cells
    • Function in the transport of respiratory gases - O2 and CO2
    Biconcave disc - lacks nucleus and other organelles when mature
    • Contain about 250 million molecules of hemoglobin (Hb) per cell
  • Hb molecule consists of:
    • a globin molecule composed of four polypeptide chains (2 alpha & 2 beta)
    • an iron-containing ‘heme’ pigment bound to each of the four chains
  • Each heme binds one O2 molecule reversibly
    • globin binds CO2
  • Lifespan of RBCs is about 120 days
  • red blood cells are formed constantly by erythropoiesisin red bone marrow (rate of 2 million per sec)
  • cells take about one week to mature
  • the main stimulus for increased erythropoiesis is a decrease in the O2-carrying capacity of the blood
  • Number of RBCs and platelets stays fairly constant because regulated by negative feedback systems
  • Number of WBCs varies because it depends on invading pathogens and other foreign antigens
  • blood cell formation is called hematopoiesis
  • All blood cells arise from a Pluripotent stem cell in red bone marrow (hemocytoblast)
  • the hemocytoblast goes on to form 2 stem cell lines:
    1. myeloid stem cells- form RBC’s, Platelets, Eosinophils, Basophils, Neutrophils & Monocytes
    2. lymphoid stem cells- form Lymphocytes
  • Erythropoiesis requires a dietary intake of iron, vitamin B12, and folic acid
  • iron is needed for heme synthesis
    • stored in the liver and spleen as portein-iron complexes
    • transported in the blood by transferrin (plasma protein) to red bone marrow and is taken up by developing RBCs
  • Vitamin B12
    • found in dietary liver, eggs, and meat
    • requires production of an intrinsic factor by the stomach mucosal cells to allow B12 to be absorbed in the small intestine
  • B12 is stored in the liver and transported to red bone marrow when needed
  • Vitamin B12 AND Folic Acid are needed for cell division and DNA synthesis that occurs in RBC formation = erythropoiesis
  • RBCs are anucleate so they can't grow and divide
  • old or damaged RBC’s are destroyed by macrophages in the spleen, liver, and bone marrow
  • hemoglobin is salvaged and degraded to heme and globin