Chapter 14: Blood

• Blood


  Only type of connective tissue with a liquid matrix (plasma)
• Blood


  • Transports vital substances, regulates processes for homeostasis
  • Maintains stability of interstitial fluid
  • Distributes heat
• Blood volume


  Varies with body size, changes in fluid concentration, changes in electrolyte concentration, and amount of adipose tissue
• Blood is about 8% of body weight; adult blood volume is about 4 to 5 liters in a female and 5 to 6 liters in a male
• Blood cells


  Form mostly in red bone marrow, and are called "formed elements"
• Formed elements


  • Red blood cells (RBCs)
  • White blood cells (WBCs)
  • Platelets (cell fragments)
• Plasma


  Clear, straw-colored fluid matrix of blood
• Plasma is about 55% of blood volume
• Red blood cells (RBCs)

  35 to 46% in females, 40 to 54% in males
• Hematocrit (HCT)


  Percentage of RBCs
• White blood cells (WBCs) and platelets

  Make up <1% of blood volume
• Hematopoiesis


  Formation of blood cells (formed elements consist of RBCs, WBCs, and platelets)
• Hematopoietic stem cells


  • Give rise to more stem cells
  • Give rise to more specialized or differentiated cells in response to hematopoietic growth factors
• Hematopoietic stem cells give rise to

  • Lymphoid stem cells
  • Myeloid stem cells
• Lymphoid stem cells


  Give rise to lymphocytes
• Myeloid stem cells


  Give rise to all other types of formed elements: Red blood cells, other types of white blood cells, and platelets
• Red blood cells (RBCs)

  • Biconcave disc shape
  • Consist of one-third hemoglobin, which transports oxygen
  • Lack nuclei and mitochondria
  • Cannot divide
  • Can produce ATP through glycolysis
• Red Blood Cell Count

  Number of RBCs in a cubic millimeter or microliter (μL) of blood
• Red Blood Cell Counts are useful in diagnosis of diseases and evaluation of their progress
• Changes in RBC counts reflect changes in blood's oxygen-carrying capacity
• Erythropoiesis


  RBC formation
• Erythropoietin (EPO)


  Hormone released by kidneys and liver that stimulates RBC production
• Stages in development of a RBC

  1. Hemocytoblast

  2. Erythroblast

  3. Reticulocyte

  4. Erythrocyte
• Average life span of RBC is 120 days
• Vitamin B12 and folic acid


  Required for DNA synthesis; necessary for the growth and division of all cells
• Iron


  Required for hemoglobin synthesis
• Anemia


  Condition in which the O2-carrying capacity of the blood is reduced, due to deficiency of RBCs or hemoglobin
• RBCs lose elasticity and become fragile


  After months of bending and squeezing through narrow capillaries
• Destruction of RBCs


  1. Worn out or damaged RBCs are removed by spleen or liver

  2. Ruptured RBCs are phagocytized by macrophages

  3. Hemoglobin separates into 4 subunits: globin chains with heme groups

  4. Heme groups break down into iron and biliverdin

  5. Iron is transported to red bone marrow by the protein transferrin

  6. Biliverdin is converted into bilirubin

  7. Biliverdin and bilirubin are excreted as bile pigments

  8. Globin chains decompose into amino acids
• White blood cells (Leukocytes, WBCs)


  Protect against disease
• Leukocytes


  Have limited life spans, so they must always be replaced
• Types of WBCs


  • Granulocytes (Neutrophils, Eosinophils, Basophils)
  • Agranulocytes (Lymphocytes, Monocytes)
• Granulocytes


  • Have granular cytoplasm, and short life span
• Agranulocytes


  • Do not have noticeable granules
• Diapedesis


  WBCs can squeeze between the cells of a capillary wall and leave blood vessel, then migrate toward infection site
• Cellular adhesion molecules


  Proteins that direct leukocytes to injury sites
• Phagocytosis


  Engulfing and digestion of pathogens; neutrophils and monocytes are most mobile and active phagocytes
• Inflammatory response


  Reaction that restricts spread of infection; promoted by basophils, by secretion of heparin and histamine; involves swelling and increased capillary permeability
• Positive chemotaxis


  Attraction of WBCs to an infection site, by chemicals released by damaged cells
• Neutrophils


  • Granulocytes with small, light purple granules in acid-base stain
  • Lobed nucleus; 2 to 5 sections
  • First to arrive at infection site
  • Strong phagocytes
  • 54% to 70% of leukocytes; elevated in bacterial infections