Hemostasis Hemostasis is stoppage of bleeding Three hemostatic mechanisms vascular spasm platelet plug formation blood clotting coagulation Hemostatic mechanisms are effective in stopping bleeding in small vessels These mechanisms cannot stop easily control bleeding from medium to large size arteries Stopping bleeding is less of an issue with venous bleeding bc of slow blood loss due to low BP and low F in veins 18 1 Platelets Small fragments of megakaryocyte Form off of bone marrow cannot undergo mitosis Have lysosomes digestion mitochondria microtubules and microfilaments granules chemical release Have no nucleus not cells Form pseudopods and amoeboid movement Second most abundant component of blood but smallest of formed elements in blood Functions secrete vasoconstrictors such as serotonin chemically attract neutrophils and monocytes to sites of inflammation phagocytize bacteria phytocytose then digest in lysosome adhere to each other to form temporary platelet plugs secrete pro coagulants clotting factors 18 2 Hemostasis Vascular Spasm Most immediate response to blood loss injury stimulates pain receptors Short term vessel constriction of broken vessel ONLY at site of broken vessel very localized damaged endothelial cells release endothelians at point of damage injury to smooth muscle cause long term constriction constricts with damage tenses provides time for other two hemostatic pathways to begin 18 3 Hemostasis Platelet Plug Formation Endothelium normally smooth coated with prostacyclin which inhibits platelet aggregation For platelets do not adhere to undamaged endothelium Prostacyclin is produced by undamaged endothelial cells which also produce NO a vasodilator and inhibitor of platelets Platelet plug formation When vessel is broken underlying collagen fibers in the walls are exposed causing platelets to adhere to eachother and the fibers forming a platelet plug Upon contact with collagen as platelets aggregate platelets degranulate releasing a variety of chemical agents from secretory vesicles serotonin is one substance platelet activation induce changes in platelets shape change which leads to even more aggregation positive feedback cycle 18 4 Hemostasis Platelet Plug Formation Platelet plug formation continued positive feedback cycle starts until break in vessel is sealed With more platelets aggregating then more degranulating then more activated and more aggregating and so on upon contact with collagen platelet grow pseudopods that stick to damaged vessel and other platelets pseudopods contract and draw walls of vessel together forming a platelet plug In general as platelets aggregate acin and myosin in platelets contracts both forming and compacting the platelet plug As platelets adhere to collagen they also make and release theomboxane A2 which promotes more platelet aggregation and degranulation TA2 causes smooth muscle to contract which reduces blood flow and pressure in area of plug 19 5 Hemostasis Coagulation Clotting is most effective defense against bleeding The clot supports and reinforces the plug Coagulation is one of the most complex body processes involving over 30 chemical reactions more discovered every day Procoagulants clotting factors are proteins present in plasma made by liver and platelets When endothelium is disrupted contact between the blood and underlying collagen or tissue initiates a series of chemical reactions activate one factor and it will activate the next to form a reaction cascade Most of the factors fxn as enzymes when activated This cascade is an amplification process for each reaction yields more activated factor than previous reaction End result is the conversion of prothrombin to activated thrombin 18 6 Hemostasis Coagulation Thrombin converts plasma protein fibrinogen into fibrin threads to form framework of clot sticky insoluble protein allowing easy adherence to vessel walls Thrombin activates an enzyme which stabilizes the fibrin Thrombin activates several factors in cascade which lead to network more thrombin Platelets are activated by cascade and thrombin Some of the reaction cascade occurs on the surface of platelets The clot is mass of fibrin blood cells and platelets forms This mass is not the same as agglutination of blood cells for blood cells stick together due to the antigen antibody binding e g anti A antibodies in type B blood bind to A antigens on a blood cell during a mismatch transfusion 19 7 Hemostasis Coagulation Extrinsic pathway Intrinsic pathway factors released by damaged tissues begin cascade factors found within blood begin cascade Several plasma protein factors oppose excessive clot formation to ease eventual clot deformation fibrinolytic system a complex fibrinolytic system is activated activates plasmin which dissolves fibrin and the clot 19 8 Hemostasis 18 9 Lymphatic System Functions read slide 11 on own also see supporting notes Lymph capillary read slides 12 14 on own also see supporting notes supporting notes Lymph flow read slides 15 17 on own also see Lymphatic tissues organs The lymphatic system is composed of a network of vessels that reach into nearly every tissue and also a collection of tissues and organs exists which produce immune cells Lymph system consists of lymph lymphatic vessels lymphatic tissue and lymphatic organs 19 10 Functions of Lymphatic System fluid continually filters from the blood capillaries into the blood capillaries on average reabsorb about 85 interference with lymphatic drainage leads to severe Fluid recovery tissue spaces edema Immunity the tissues excess fluid removes foreign cells and chemicals from passes through lymph nodes where immune cells can activate a immune response Lipid absorption lacteals in small intestine absorb dietary lipids that are not absorbed by the blood capillaries 21 11 Lymph and Lymphatic Capillaries Lymph clear colorless fluid similar to plasma but much less protein starts as tissue fluid Lymphatic vessels are arranged in a similar pattern as blood vessels Lymphatic capillaries terminal lymphatic associated with blood capillaries closed at one end endothelial cells loosely overlapped bacteria and cells enter with fluid into lymphatic capillary creates valve like flaps that open when interstitial fluid pressure is high and close when it is low 21 12 Lymphatic Capillary 21 13 Lymphatic and Immune Systems 21 14 Route of Lymph Flow Collecting vessels the lymphatic capillaries converge and become larger collecting vessels which run