Sunday, March 18, 2012

Anatomy & Physiology: BLOOD


          Blood inside blood vessels
          To obtain nutrients and remove wastes, cells must be serviced by blood and interstitial fluid.
          Blood, a connective tissue, is composed of plasma and formed elements.
          The branch of science concerned with the study of blood, blood-forming tissues, and the disorders associated with them is called hematology.
         O2, CO2, metabolic wastes, nutrients, heat & hormones
        helps regulate pH through buffers
        helps regulate body temperature
        helps regulate water content of cells by interactions with dissolved ions and proteins
          Protection from disease & loss of blood
          Blood plasma consists of water and solutes.

          0ver 90% water
          7% plasma proteins
          created in liver
          confined to bloodstream
          maintain blood osmotic pressure
        globulins (immunoglobulins)
          antibodies bind to foreign
substances called antigens
          form antigen-antibody complexes
          for clotting
          2% other substances
        electrolytes, nutrients, hormones, gases, waste products

          Contain oxygen-carrying protein hemoglobin that gives blood its red color
        increased surface area/volume ratio
        flexible shape for narrow passages
        no nucleus or other organelles
          Worn out cells removed by fixed macrophages in  spleen & liver
          All WBCs (leukocytes) have a nucleus and no hemoglobin
          Granular or agranular classification based on presence of  cytoplasmic granules made visible by staining
        granulocytes are neutrophils, eosinophils or basophils
        agranulocytes are monocyes or lymphocytes
          Nuclei = 2 to 5 lobes connected by thin strands
          Neutrophils and wandering or fixed macrophages (which develop from monocytes) do so through phagocytosis.
          Fastest response of all WBC to bacteria
          Nucleus with 2 or 3 lobes connected by a thin strand
          Large, uniform-sized granules stain orange-red with acidic dyes
          Leave capillaries to enter tissue fluid
          Release histaminase
        slows down inflammation caused by basophils
          Attack  parasitic worms
          Phagocytize antibody-antigen complexes
          Large, dark purple, variable-sized granules stain with basic dyes
          Irregular, s-shaped, bilobed nuclei
          Involved in inflammatory and allergy reactions
          Leave capillaries & enter connective tissue as mast cells
          Release heparin, histamine & serotonin
          Dark, oval to round nucleus
          Cytoplasm sky blue in color
        amount varies from  rim of blue to normal amount
          B cells
        destroy bacteria and their toxins
        turn into plasma cells that produces antibodies
          T cells
        attack viruses, fungi, transplanted organs, cancer cells & some bacteria
          Natural killer cells
        attack many different microbes & some tumor cells
        destroy foreign invaders by direct attack
          Nucleus is kidney or horse-shoe shaped
          Largest WBC in circulating blood
        does not remain in blood long before migrating to the tissues
        differentiate into macrophages
          macrophages, are active in phagocytosis.
          Destroy microbes and clean up dead tissue following an infection
          Take longer to get to site of infection, but arrive in larger numbers
          Platelets help stop blood loss from damaged vessels by forming a platelet plug.
          Their granules also contain chemicals that promote blood clotting.
          Disc-shaped, 2 - 4 micron cell fragment with no nucleus
          A clot is a gel consisting of a network of insoluble protein fibers (fibrin) in which formed elements of blood are trapped
          The chemicals involved in clotting are known as coagulation (clotting) factors; most are in blood plasma, some are released by platelets, and one is released from damaged tissue cells
          Blood clotting involves a cascade of reactions that may be divided into three stages:
         formation of prothrombinase (prothrombin activator), conversion of prothrombin into thrombin
         conversion of soluble fibrinogen into insoluble fibrin
          The clotting cascade can be initiated by either the extrinsic pathway or the intrinsic pathway.
          Normal coagulation requires vitamin K and also involves clot retraction (tightening of the clot) and fibrinolysis (dissolution of the clot).
          The fibrinolytic system dissolves small, inappropriate clots and clots at a site of damage once the damage is repaired.
          Plasmin (fibrinolysin) can dissolve a clot by digesting fibrin threads and inactivating substances such as fibrinogen, prothrombin, and factors V, VIII, and XII.

          Stoppage of bleeding in a quick & localized fashion when blood vessels are damaged
          Prevents hemorrhage (loss of a large amount of blood)
          Methods utilized
        vascular spasm
        platelet plug formation
        blood clotting (coagulation = formation of fibrin threads)
          Damage to blood vessel produces stimulates pain receptors
          Reflex contraction of smooth muscle of small blood vessels
          Can reduce blood loss for several hours until other mechanisms can take over
          Only for small blood vessel or arteriole
          Steps in the process
        (1) platelet adhesion  (2) platelet release reaction (3) platelet aggregation
          Platelets stick to exposed collagen underlying damaged endothelial cells in vessel wall
          Extend projections to make contact with each other
          Release thromboxane A2 & ADP are vasoconstrictors decreasing blood flow through the injured vessel
          Activated platelets stick together and activate new platelets to form a mass called a platelet plug

          Blood drawn from the body thickens into a gel
        gel separates into liquid (serum) and a clot of insoluble fibers (fibrin) in which the cells are trapped
          If clotting occurs in an unbroken vessel is called a thrombosis
          Substances required for clotting are Ca+2, enzymes synthesized by liver cells and substances released by platelets or damaged tissues
          Clotting is a cascade of reactions in which each clotting factor activates the next in a fixed sequence resulting in the formation of fibrin threads
        prothrombinase & Ca+2 convert prothrombin into thrombin
        thrombin converts fibrinogen into fibrin threads
          Clot Retraction & Blood Vessel Repair
          Clot plugs ruptured area of blood vessel
          Platelets pull on fibrin threads causing clot retraction
          Edges of damaged vessel are pulled together
          Fibroblasts & endothelial cells repair the blood vessel

          Fibrinolytic system dissolves small, inappropriate clots & clots at a site of a completed repair
        fibrinolysis is dissolution of a clot             
          Inactive plasminogen is incorporated into the clot
        plasminogen becomes plasmin (fibrinolysin) which digests fibrin threads
          Clot formation remains localized
        fibrin absorbs thrombin
        blood disperses clotting factor
          Anticoagulants present in blood & produced by mast cells
        Hemostatic Control Mechanisms
          Clots are generally localized due to fibrin absorbing thrombin into the clot, clotting factors diffusing through blood, and the production of prostacyclin, a powerful inhibitor of platelet adhesion and release.
          Substances that inhibit coagulation, called anticoagulants, are also present in blood. An example is heparin.
          Despite the anticoagulating and fibrinolytic mechanisms, blood clots sometimes form within the cardiovascular system.
          Clotting in an unbroken blood vessel is called thrombosis.
          A thrombus (clot), bubble of air, fat from broken bones, or piece of debris transported by the bloodstream that moves from its site of origin is called an embolus.