cardiovascular system-blood: platelets (thrombocytes) Flashcards
Thrombocytes (platelets) fragment in the
bone marrow into small fragments, platelets which pass in the blood
thrombocytes (platelets) are destroyed by
phagocytes in the spleen
thrombocytes (platelets) are mainly stored in the
spleen and are released during bleeding
what is thrombocytopenia
low platlet count
due to less platelet production or excessive platelet destruction
what is thrombocytosis
due to accelerated production of platelets in response to infections, inflammation, or cancer
thrombocytopoiesis is the production of
thrombocytes
thrombocytopoiesis
pleuripotent stem cells in the red bone marrow–>
megakaryoblasts–> megakaryocytes (form membranes, enzymes, proteins)–> thrombocytes (by shedding cytoplasm)
pleuripotent stem cells in the red bone marrow stimulated by
Interleukins form megakaryoblasts which will form megakaryocytes
hormonal controls:
- thrombopoietin (TPO)
- Interleukin-6 (IL-6)
- Multi-CSF
hormonal controls:
1.thrombopoietin (TPO)
accelerates platelet production and stimulation productions of megakaryocytes
Hormonal Controls
2.Interlekin-6 (IL-6)
stimulates platelet formation
hormonal controls
3.Multi-CSF
formation and growth of megakaryocyte
megakaryocytes produce
structural proteins, enzymes, and membranes
megakaryocytes shed cytoplasm in
small packets and form spindle shaped platelets
functions of thrombocytes:
initiate and control the clotting process by releasing chemicals important to the clotting process
they clump together at the site of injury by forming a platelet plug
reduce the size of a break in the vessel wall
after a blood clot the platelet filaments contract to shrink the clot
hemostasis and blood coagulation phases
- vascular phase, vascular spasm
- platelet phase
- coagulation phase
- vascular phase, vascular spasm is the constriction of
blood vessels
- platelet phase is the formation of
platelet plug
- coagulation phase is the formation of a
blood clot (coagulation)
hemostasis is a complex cascade in which
many things happen at the same time, interacting together
- vascular phase
lasts 30 minutes
the trauma of the vessel causes the vessel to contract to reduce the flow of blood from the vessel rupture
for smaller vessels, platelets release vasoconstrictor substance, thromboxane A2
vascular phase happens in 3 steps
- the endothelial cells contract and expose the basement membrane to the blood stream
- endothelial cells release chemical factors ADP, tissue factor, local hormones, prostacyclin, and peptide hormones, endothelins
they in together accelerate smooth muscle contraction and cell division
- endothelial plasma membranes become sticky and stick together preventing blood flow
- platelet phase
after injury, it begins within 15 seconds
when platelet come in conduct with a damaged vascular surface, e.g. exposed collagen fibers
to basement membranes
to sticky endothelial surfaces,
they adhere to collagen and is known as platelet adhesion
platelets secrete:
- ADP, stimulates platelet aggregation and
- thromboxane A2 and serotonin- stimulate vascular spasm
- clotting factors
- platelets derived growth factor- promotes vessel repair
- calcium ions which activate more platelets and stick them to the originally activated platelets, thus forming a platelet plug blocking the blood loss
formation of platelet plug
injured tissue—>exposure of subendothelial cells—>vasoconstriction–> platelets aggregate and form a “plug”
injured tissue–>exposure of subendothelial cells–> platelets adhere to exposed cells–> platelets aggregate and form a “plug”
- coagulation phase
begins 30 sec or more after the injury
has 3 steps
3 steps of the coagulation phase
- in response to rupture of a vessel, a complex of activated substances called prothrombin activator is produced
- the prothrombin activator catalyzes the conversion of prothrombin in to thrombin
- the thrombin convert soluble fibrinogen into insoluble fibrin fibers which form a mesh to trap platelets, blood cells and plasma to form the clot
blood coagulation
more than 50 important substances affect blood coagulation
some promote coagulation called procoagulants and others inhibit coagulation called anticoagulants
in the blood anti-coagulants pre-dominate so that blood does not coagulate in the blood stream
but when a vessel is ruptures procoagulants become activated
factors that limit the growth of the platelet plug
- prostacyclin: released by endothelial cells, inhibit platelet aggregation
- inhibitory compounds released by other WBCs
- circulating enzymes break down ADP
- negative (inhibitory) feedback from serotonin
- development of blood clot isolates area
clotting factors (procoagulants)
proteins or ions in plasma
required for normal clotting
3 pathways
the factors released by platelets and endothelial cells and clotting factors interact through either:
extrinsic pathway
intrinsic pathway
common pathway to form the clot
the extrinsic pathway
begins in the blood vessel
outside bloodstream
- damaged cells release tissue factor (TF)
- when Ca2+ is present, forms complex with factor VII–> activated factor VII
- activating factor X
intrinsic pathway
within bloodstream
- activation of factor XII exposed to collagen fibers
- stimulates factor XI, activates IX, stimulates factor VIII, activates VIII platelet phospholipids, and Ca2+ to activate factor X
____ pathway is shorter and faster than ____ pathway and initiates clotting first
Extrinsic pathway is shorter and faster than
intrinsic pathway and initiates clotting first.
the common pathway
it starts with activated factor X from either pathway
activated factor X activates prothrombin factor
prothrombin is a
plasma protein which is formed continually by the liver
Vitamin ___ is necessary for the formation of ___ and clotting factors ___, ___. __, and __
Vitamin K is necessary for the formation of
prothrombin and clotting factors II, VII, IX and X.
activated factor X
- prothrombin activator
- converts prothrombin into thrombin
- thrombin converts soluble fibrinogen into insoluble fibrin—>forms a mesh–>trap blood cells —>clot
