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Blood (Formed elements: (Platelets (Platelets quickly and degenerate in…

- - - - Whenever white blood cells are mobilized for action the body speeds up their production and their numbers may double.
  - - - If not in clotting, circulate freely
- - - - damaged blood vessels respond to injury to vascular smooth muscle, chemicals released by endothelial cells and platelets, & reflexes initiated by local pain receptors.
        
        valuable because artery can reduce blood loss for 20-30 min
    - - Platelets play key role by sticking together.
        
        forming a plug that seals the break in the vessel wall, also help events that form a blood clot.
        
        Serotonin: messengers that enhance vascular spasm and platelet aggregation.
        
        ADP: potent aggregating agent that causes more platelets to stick to area and release contents.
      - Step 3: Coagulation
        
        Referred as blood clotting reinforces the platelet plug with fibrin threads that act as "Molecular glue" for aggregated platelets.
        
        Blood transformed from liquid to gel in a multi-step process that involves series of substances called " clotting factors"
        
        Most clotting factors are plasma protien synthesized by liver. clotting together form a blood clot.
        
        Activation turns clotting factors into enzymes by clipping off a piece of protein causing it to change shape.
        
        Once clotting cell is activated , it activates into the next sequence & so on in cascade.
- - - - made up of the red heme pigment bound to the protien globin.
        
        Globin consists of 4 polypeptide chains :
        
        Two alpha (a)
        
        Two beta (b)
        
        a hemoglobin molecule can transport 4 molecules of oxygen because each iron atom can combine reversibly with one molecule of oxygen.
  - - - Thalassemias - erythrocytes are thin, according to which hemoglobin chain is affected , range in severity from mild to severe.
      - Hemorrhagic anemia- caused by blood loss.
      - Sickle-cell Anemia- caused by abnormal hemoglobin results from change in just one of the 146 amino acids.