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Phys Exam 3: Ch 3


What 3 mechanisms prevent blood loss when a blood vessel is cut? 1) Vascular spasm (neural pain reflex, myogenic contraction); 2) Platelet plug; 3) Fibrin clot
Where are platelets formed? About how many are there per mL of blood? In BM from megakaryocytes; 150K-300K
What is a platelet? Fragment of cell w/o nucleus; cytoplasm has actin, myosin, mitochondria, and ATP
What do platelets produce? Prostaglandins & fibrin-stabilizing factor
What do platelets store? Ca & serotonin
What is the half-life of a platelet 8-12 days
What specific surface glycoprotein do platelets have Collagen
How are dead platelets removed? Recycled by macrophages, mostly in the spleen
What happens when platelets contact exposed collage (in the presence of vWF) Begin to form the platelet plug: (1) Swell & extend pseudopods; (2) Become adhesive - esp to collagen; (3) Secrete ADP, serotonin, and thromboxane A2
How are adjacent platelts activated? By the secreted ADP, serotinin, and thromboxane A2
Are serotonin & thromboxane A2 vasodilators or vasoconstrictors? Potent vasoconstrictors
How quickly is blood clot formation initiated? W/in seconds after injury
What substances does formation of a blood clot require? platelets, plasma proteins,and the vessel wall
Discuss fibrin clot contraction Contracts w/in a few minutes. Contraction is due to (1) actin & myosin in platelets bound in the clot, (2) Ca from the platelets, (3) covalent cross-links from fibrin-stabilizing factor
Created by: hclark86