Anatomy & Physiology: BLOOD

    

      INTRODUCTION

•          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.

          FUNCTION OF BLOOD

•          Transportation

–         O2, CO2, metabolic wastes, nutrients, heat & hormones

•          Regulation

–        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

      COMPONENT OF BLOOD

•          Hematocrit

–         plasma

–         cells

•          Blood plasma consists of water and solutes.

   BLOOD PLASMA

•          0ver 90% water

•          7% plasma proteins

•          created in liver

•          confined to bloodstream

–        albumin

•          maintain blood osmotic pressure

–        globulins (immunoglobulins)

•          antibodies bind to foreign
substances called antigens

•          form antigen-antibody complexes

–        fibrinogen

•          for clotting

•          2% other substances

–        electrolytes, nutrients, hormones, gases, waste products

      RED BLOOD CELLS OR ERYTHROCYTES

•          Contain oxygen-carrying protein hemoglobin that gives blood its red color

•          Biconcave

–        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

         WHITE BLOOD CELLS

•          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

       NEUTROPHILS(GRANULOCYTE)

•          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

  EOSINOPHILS(GRANULOCYTE)

•          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

        BASOPHILS (GRANULOCYTE)

•          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

     LYMPHOCYTE(AGRANULOCYTE)

•          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

  MONOCYTE(AGRANULOCYTE)

•          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

  PLATELET(THROMBOCYTE)

•          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

 HEMOSTASIS

•          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

HEMOSTASIS

•          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.

  HEMOSTASIS

•          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)

  VASCULAR SPASM

•          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

 PLATELET PLUG FORMATION

•          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 CLOTTING

•          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

   HEMOSTATIC CONTROL MECHANISMS

•          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.