• 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
– 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
COMPONENT 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
substances called antigens
• form antigen-antibody complexes
• 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
– 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
• 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
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 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.