ch. 19 blood

• 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