Introduction to Blood

Describe the components of blood

  • Blood contains red blood cells, white blood cells, platelets, proteins, and plasma made up of serum and clotting factors

Gain a general understanding of hematopoiesis and definition of a stem cell

  • Need for hematopoesis because about 1 trillion cells turns over/hr in adults. In stress situations, the marrow will respond to cytokines and produce more cells to meet body demand
  • Process: stem cell -> colony forming unit (CFU - high proliferative rate, multilineage potential, limited self-renewal) -> committed CFU (high proliferative rate, lineage specific)
  • Red Blood Cells
    • RBCs are initially made in the yolk sac of the zygote, then in the liver and spleen 5-6 weeks after gestation. Finally, the manufacturing migrates to the bone marrow starting at 3 months gestation
    • Stimulation to make more cells come from the peritubular cells in the kidney through erythropoetin. This is done mainly for maintanence purposes (RBC life = 120 days), replacing ~1% of total RBCs/day. However, it can be used during stress to increase the production of RBCs
  • White Blood Cells
  • Platelets
    • Are pieces of the larger megakaryocyte, which is formed in the bone marrow
  • Stem cells
    • Only a small pool in the bone marrow (<0.1%)
    • Normally quiescent, with only 5% in cell cycle at one time
    • This pool is maintained through asymmetric division (i.e. one daughter cell replenishes line, the other differentiates)
    • Hematopoetic stem cells are located in the bone marrow. There are 2-3 characteristics that define a stem cell:
      1. Pluripotency
      2. Ability for self-renewal
      3. Expresses surface markers CD34 and CD 117

Gain general understanding of pathogenesis of hematologic cancers

  • Cancers of the blood usually arises from a mutation in the DNA of a stem cell
  • This mutation most likely occurs from an initial monoclonal growth
  • Can also be caused by epigenetic changes

Describe role and function of red blood cells and hemoglobin

  • Primary gas exchange work horse in the blood
  • Picks up oxygen from the lungs and delivery to tissue
  • Picks up carbon dioxide from periphery and delivery to the lungs
  • Scavenges nitric oxide (NO), and releases (some hypothesizes induces release) into blood vessels causing vasodilation and perfusion
  • Structurally a biconcave disk, flexible enough to squeeze through 4um capillaries while being 10um
  • 90% by mass is hemoglobin

Describe role and function of white blood cells

  • White blood cells are divided into granulocytes, lymphocytes, and monocytes
  • Granulocytes include neutrophils (most abundant, phagocytic), eosinophils (parasites, and allergic reactions), and basophils (histamin release, allergy, similar to mast cells. It is the least abundant)
    • These cells can contain some of the three granules (1o, 2o, and 3o). both 1o and 2o granules are peroxidases responsible for digestion of phagocytosed materials (e.g. debris, allergens, etc)
  • Lymphocytes include B, T, and NK cells. They contribute to humoral and cell immunity
  • Monocytes play a large role in infection, giving rise to macrophages and dendritic cells. When stimulated by inflammatory signals, monocytes also travel to the site and rapidly differentiate into these 2 cell types

Describe components of plasma and general function

  • Plasma makes up 55% of the blood. It contains serum (protein and water - 95%), and clotting factors
  • Albumin is present in large numbers in the plasma
  • Also contains immunoglobulins, electrolytes, and glucose, fats, minerals

List of changes occurring with age and pregnancy

  • Volume expansion leading to hemodilution even though RBCs increases by 20-50% in mass
  • Hb concentration falls by 10-15 g/L (from 145-150 -> ~120)
  • WBC increase during pregnancy, then normalizes postpartum
  • No changes in platelets
  • Coagulation factors increase, but insignificantly (through lab tests)
  • This decrease in blood pressure contributes to improving perfusion to the fetus
  • With age, the blood count should stay the same

Define the terms: hematocrit, MCV, and RDW

  • Hematocrit: proportion of the height of red blood cells in a centrifuged compared to the entire height. As we move to modern technology, centrifuges are no longer being used, so the definition has changed to red cell count (RBC) x mean corpuscular volume (MCV)
  • MCV : Mean corpuscular volume. The average size of red blood cells
  • RDW : Red blood cell distribution width. The standard deviation of the widths of red blood cells measured.

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