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Cardiovascular System and Blood Help (page 2)

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By — McGraw-Hill Professional
Updated on Aug 18, 2011

Platelets

Platelets, or thrombocytes, are small cellular fragments that originate in the bone marrow from a giant cell, a megakaryocyte. Megakaryocytes form platelets by pinching off bits of cytoplasm and extruding them into the blood. Platelets contain several clotting factors, calcium ions, ADP, serotonin, and various enzymes; they play an important role in hemostasis (the arrest of bleeding).

The major events in hemostasis are:

  1. constriction of the blood vessels;
  2. plugging the wound by aggregated platelets; and
  3. clotting of the blood into a mass of fibrin that augments the plug in sealing the wound and providing a framework for repair.

In the event of a vessel defect or injury, platelets aggregate to form a plug. Adenosin diphosphate (ADP) and thromboxane A2 released from the platelets further enhance platelet aggregation. The platelet plug aids in reducing blood loss at the site by:

  1. physically sealing the vessel defect,
  2. releasing chemicals that cause vasoconstriction, and
  3. releasing other chemicals that stimulate blood clotting. There are multiple clotting factors produced in the liver involved in clotting.

Leukocytes

There are five types of leukocytes (white blood cells).

Blood Plasma

Blood plasma is composed of the following:

  • Water
  • Proteins (albumins, globulins, and fibrinogens)
  • Electrolytes (Na+, K+, Ca2+, Mg2+, Cl, HCO3 –, HPO42–, SO42–)
  • Nutrients (glucose, amino acids, lipids, cholesterol, vitamins, trace elements)
  • Hormones
  • Dissolved gasses (CO2, O2, N)
  • Waste products (urea, uric acid, creatinine, bilirubin)

Albumins, the smallest and most abundant proteins in the blood, maintain the osmotic pressure of the blood, buffer the blood, and contribute to the viscosity of blood. The globulin proteins in the blood function in transport, enzymatic action, clotting, and immunity. The electrolytes are necessary for membrane transport, blood osmolarity, and neurological function.

Practice problems for these concepts can be found at:

Cardiovascular System: Blood Practice Problems

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