19.6-19.7 platelets & hemostasis

Question 1

platelets (dimensions, concentrations, life span, location)

Answer 1

cell fragments; 4 micrometer diameter, 1 micrometer thick; 350,000 platelets per microlieter; removed by phagocytes after 9-12 days; most are locate in vascular organs (1/3 in spleen)

Question 2

thrombocytes

Answer 2

nucleated platelet cells in nonmammalian vertabrates

Question 3

thrombocytopenia

Answer 3

low platelet count <80,000/microliter

signs: bleeding alond digestive tract, within skin, inside CNS

Question 4

thrombocytosis

Answer 4

platelet count > 1,000,000/microlieter

-accelerated formation in response to infection, or cancer

Question 5

platelet functions

Answer 5

• release chemicals important to clotting
• form temp. patch in walls of damaged vessels
• reduce size of break in vessel wall

Question 6

thrombocytopoiesis

Answer 6

process of platelet formation, occurs in red bone marrow

Question 7

megakaryocytes

Answer 7

enormous cells w/ large nuclei.. shed cytoplasm in small membrane-enclosed packets (platelets)
-mature megakaryocyte produces ~4000 platelets before nucleus is engulfed by phagocytes

Question 8

rate of megakeryocyte activity influenced by:

Answer 8

• thrombopoietin (TPO) aka thrombocyte-stimulating factor
• interleukin-6 (IL-6)
• multi-CSF

Question 9

interleukin-6 (IL-6)

Answer 9

stimulates platelet formation

Question 10

thrombopoietin (TPO)

Answer 10

accelerates platelet formation, stimulates megakaryocyte production
-produced in kidneys

Question 11

multi-CSF

Answer 11

promotes formation & growth of megakaryocytes

Question 12

hemostasis

Answer 12

the stopping of bleeding. Three phases:

• vascular phase
• platelet phase
• coagulation phase

Question 13

vascular spasm:

Answer 13

local contraction of vessel triggered by cutting the vessel (decreases diameter of vessel site at injury)
-lasts ~30mins

Question 14

vascular phase

Answer 14

lasts ~30mins

• endothelial cells contractto expose basement membrane to bloodstream
• endothelial cells release chemical factors, hormones, & endothelins
• endothelial plasma membranes become sticky

Question 15

endothelins

Answer 15

peptide hormones that stimulate smooth muscle contraction & promote vascular spasms, stimulate divisions of endothelial cells , smooth muscle cells, and fibroblasts to accelerate repair

Question 16

platelet phase

Answer 16

• platelets attach to sticky endothelium, basement membrane, & to collagen fibers
• platelets release compounds
• positive feedback loop begins within few seconds of injury

Question 17

platelet adhesion

Answer 17

attachment of platelets to exposed surfaces

Question 18

platelet aggregation

Answer 18

platelets sticking to each other (begins within 15 seconds of injury)

Question 19

platelet plug

Answer 19

can close the break in the vessel if not too severe, or if vessel is relatively small

Question 20

compounds released by platelets

Answer 20

1) adenosine diphosphate (ADP) - platelet aggregation, 2) thromboxane A2 & serotonin - stimulate vascular spasms, 3) clotting factors, 4) platelet-derived growth factor (PDGF) - promotes vessel repair, 5) Ca2+ - platelet aggregation & clotting

Question 21

factors limiting growth of platelet plug

Answer 21

1) prostacyclin - inhibits platelet aggregation (released by endothelial cells), 2) inhibitory compounds released by WBCs, 3) circulating plasma enzymes that break down ADP, 4) compounds that inhibit plug formation at high concentrations, 5) development of clot

Question 22

coagulation phase

Answer 22

starts 30+ seconds after injury

-blood clotting

Question 23

clotting factors

Answer 23

aka procoagulants

-includes fibrinogen (liver), Ca2+ (bone, platelets), prothrombin (liver, vitamin K)….

Question 24

proenzymes

Answer 24

direct essential reactions in clotting response.. activation of one proenzyme often initiates a cascade

Question 25

extrinsic pathway

Answer 25

-release of factor III (aka tissue factor TF) by damaged endo cells. TF combines w/ Ca2+ & factor IV to form enzyme complex that activates factor X (first step in common pathway)

Question 26

intrinsic pathway

Answer 26

activation of proenzymes (factor XII) exposed to collagen fibers. Proceeds with assistance of PF-3 (platelet factor). Activated factors VIII and IX combine to form enzyme complex that activates factor X

Question 27

common pathway

Answer 27

begins when factor X is activated, forming prothrombinase. Converts prothrombin to thrombin, which converts fibrinogen to fibrin

Question 28

prothrombinase

Answer 28

converts prothrombin to thrombin

Question 29

coagulation time

Answer 29

8-18 min

Question 30

bleeding time

Answer 30

1-4 min

Question 31

thrombin stimulates clotting by…

Answer 31

stimulating formation of TF and release of PF-3

Question 32

heparin

Answer 32

(released by basophils) accelerates activation of antithrombin-III

Question 33

aspirin

Answer 33

inhibits production of thromboxane A & prostaglandins

Question 34

thrombomodulin

Answer 34

converts thrombin to enzyme that activates protein C

Question 35

protein C

Answer 35

inactivates several clotting factors & stimulates plasmin formation (enzyme that eventually breaks down fibrin strands)

Question 36

_____ & _____ affect almost every aspect of the clotting process

Answer 36

Ca2+ and vitamin K

Question 37

clot retraction

Answer 37

aka syneresis, “a drawing together”

-pulls torn edges of vessel closer together, reduces size of damaged area

Question 38

fibrinolysis

Answer 38

dissolving of the clot
-activation of plasminogen by thrombin & tissue plasminogen activator (t-PA) produces plasmin, which begins digesting fibrin strands