The Functions of Blood.

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Cardiovascular System Overview and Blood functions

Overview:

  • Procides a system for rapid transport within the body.
    -Nutrients.
    -Hormones.
    -Waste products.
    -Respiratory gases.
    -Cells.
    -Heat.

Blood functions:

  • Transport of cells and compounds.
  • Regulate pH and electrolytes of interstitial fluids.
  • Limit blood loss through damaged vessels.
  • Defend against pathogens and toxins.
  • Absorb, distribute heat as part of temperature regulation.
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Blood collection and analysis and Plasma Basics.

  • Whole blood can be fractionated (divided) into:
    -Plasma (liquid component).
    -Formed elements (cellular components).
      -Red blood cells (RBC's).
      -White blood cells (WBC's).
      -Platelets.

Plasma Basics:

  • Makes up about 55% of whole blood.
  • Water makes up about 92% of plasma.
  • Has more protein and oxygen than interstitial fluid.
  • Plasma proteins fall into three classes:
    -Albumins.
    -Golbulins.
    -Fibrinogen.

Approximately half the volume of whole blood consists of cells and cell products (the formed elements). Plasma resembles interstitial fluid but contains a unique mix of proteins not found in any other extracellular fluid.

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Key words.

  • Hematocrit- Percentage of whole blood volume taken up by formed elements (mostly RBCs). In clinical short hand, its called the crit.
  • Hemopoiesis- The cellular pathways by which the formed elements are produced. (also spelt haemopoiesis)
  • Stem cells (hemocytoblasts)- Cells that divide and mature to produce all three classes of formed elements.
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Red Blood Cells/ Erythrocytes.

  • Make up about 45% of whole blood volume.
  • Make up 99.9% of the formed elements.
  • Biconcave shape.
  • No nucleus, organelles or mitochondria.
  • 1 RBC contains 280 million hemoglobin molecules.
  • Transports oxygen and carbon dioxide in the blood stream.
  • Have large surface to volume ratio.
    -Speeds up gas loading/unloading.
  • Lack most organelles.
    -Makes more room for hemoglobin.
  • Degenerate after about 120 days (in the spleen, recycled by phagocytes).
  • Formed in red bone marrow.
  • Their function is to transport respiratory gases.
  • Hemoglobin makes up 95% of RBC protein.
  • Globular protein composed of four subunits (each subunit):
    -A globin protein chain.
    -A molecule of heme.
    -An atom of iron.
    -A binding site for one oxygen molecule.
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Red Blood Cells/ Erythrocytes cont and Key Note.

  • Erythropoiesis- Process for the formation of red blood cells.
    -Occurs mainly in the bone marrow.
    -Stimulated by erythropoietin (EPO- Produced by kidney).
      -EPO increases when oxygen levels are low.
    -Development stages include:
      -Erythroblasts.
      -Reticulocytes (after nucleus is expelled).

Red blood cells are the most numerous cells in the body. They circulate for about four months before being recycled- 2.5 to 3 million are produced each second. The hemoglobin inside transports oxygen from the lungs to peripheral tissues and carbon dioxide from the tissue to the lungs.

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Blood types and Platelets.

Blood types:

  • Determined by presence or absense of specific antigens (agglutinogens) on the outside surface of red blood cells.
  • Antigens are called A, B, and Rh.
  • Antibodies (aggulutinins) in plasma react with foreign antigens on RBCs.
    -RBCs clump and break open.
  • Anti-Rh antibody made after exposure to Rh-positive blood cells.

Platelets:

  • Produced in bone marrow.
  • Released from megakaryocytes as cytoplasmic fragments into the blood.
  • Essential to the clotting process.
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Haemostasis.

  • Processes that stop the loss of blood from a damaged vessel. Largely dependent on platelets and soluble proteins (clotting factors).
  • Three phases in haemostasis:
    -Vasucluar phase- local contraction of injured vessel.
    -Platelet phase- platelets (platelet plug formation) stick to damaged vessel wall.
    -Coagulation phase- clotting factors in plasma form blood clot.
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White Blood Cells/ Leukocytes.

  • Defend the body against:
    -Pathogens/ Toxins.
    -Abnormal/ damaged cells.
  • Perform diapedesis- Push between cells to cross blood vessel walls and enter the tissues.
  • Exhibit chemotaxis- Move toward specific chemicals released by bacteria or injured cells.
  • Consists of two groups:
    -Granulocytes (cytoplasmic granules). Three typxes of this:
      -Neutrophils- 50-70% of circulating WBCs. Phagocytic.
      -Eosinophils- Less common. Phagoctic. Attracted to foreign proteins.
      -Basophils- Release histamine. Promote inflammation.
    -Agranulocytes (no granules). Two types of this:
      -Lymphocytes- Found mostly in lymphatic system. Provide specific defenses (attack foreign bodies, produce antibodies, destroy abnormal (cancer) cells).
      -Monocytes- Migrate into tissues. Become macrophages. Live as phagocytic amoeba.

WBCs outnumber RBCs by a 1000 to 1. WBCs defend the body and assist in the repair of damaged tissue. Most numerous are neutrophils which engulf bacteria, and lymphocytes, which are responsible for the specific immune defences.

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