Introduction to Blood
Table of Contents
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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
- Granulocytes and B Lymphocytes are made in the bone marrow, whereas T lymphocytes are made in the Thymus gland anterior to the heart
- 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:
- Pluripotency
- Ability for self-renewal
- 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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page revision: 32, last edited: 24 Oct 2011 05:12