16-4: Thrombocytes and Hemostasis

Question 1

thrombocytes

Answer 1

tiny round or oval discs without nuclei

Question 2

Platelets are produced in the __ as ___.

Answer 2

red bone marrow; large megakaryocytes break off fragments that enter the blood and become platelets

Question 3

Thrombocytopenia

Answer 3

“clotting cell deficiency” - deficiency of platelets leading to spontaneous bleeding from small vessels and petechiae on the skin

Question 4

Platelets have a ___ lifespan of about ___.

Answer 4

short; 10 days (less if involved in clotting)

Question 5

function of platelets

Answer 5

initiate a chain of reactions causing blood to clot

Question 6

What are the relative frequencies of the various blood cells, starting with the most?

Answer 6

Erythrocytes
Thrombocutes
Leukocytes: (Never Let Monkeys Eat Bananas)
neutrophils
lymphocytes
monocytes
eosinophils
basophils

Question 7

hemostasis

Answer 7

the stoppage of bleeding - when a blood vessel is damaged or ruptured, a series of events takes place to stop blood loss. There are three major phases which occur in rapid sequence

Question 8

What are the three major phases of hemostasis?

Answer 8

1. vascular spasm
2. platelet plug formation
3. coagulation

Question 9

vascular spasm

Answer 9

the smooth muscle in the wall of a damaged vessel contracts immediately to slow blood loss; this lasts 20-30 minutes

Question 10

platelet plug formation

Answer 10

when platelets come in contact with a torn (rough) blood vessel, they stick to the exposed collagen fibers in the torn surface and clump together, temporary plugging the whole and further reducing blood loss (occurs w/in a minute)

Example of positive feedback - they release chemicals to attract more platelets

Question 11

coagulation

Answer 11

the formation of a blood clot. The platelets in the plug release a variety of factors which stimulate a chain of reactions, where the activation of 1 factor catalyzes the activation of the next factor in the sequence.

Question 12

What are the three main steps in coagulation?

Answer 12

1. Formation of prothrombin activator
2. prothrombin (plasma protein formed by liver, always present but inactive) —> thrombin (active enzyme)
3. fibrinogen (soluble plasma protein) —> fibrin (insoluble threads)

Question 13

Fibrin

Answer 13

insoluble threads - molecules clump together forming a network to trap RBCs and platelets, and pull the damaged edges of the vessel closer together

Question 14

What is the last stage of blood clotting?

Answer 14

once the clot plugs the ruptured area, permanent repair can take place and new endothelial cells restore the torn lining. Once repaired, the unneeded clot is removed by fibrinolysis

Question 15

hemophilia

Answer 15

a heredictary bleeding disorder; due to a mutation on the X chromosome, the person lacks one of the platelet clotting factors needed to form prothrombin activator. As a result, their blood fails to clot properly and small cuts cause serious bleeding that can be life-threating

Question 16

Hemophilia A lacks factor __, B lacks __, and C lacks ___.

Answer 16

A VIII; B IX; C XI

Question 17

What is the treatment for hemophilia?

Answer 17

transfusions of fresh plasma or injections of the missing clotting factor (only lasts a few days - needs continuous administration)