Lecture 9: Platelet

Question 1

What are platelets involved in?

Answer 1

primary hemostasis
halting bleeding following vascular injury

Question 2

What are platelets made from?

Answer 2

cellular fragments of cytoplasm from megakaryocytes in the bone marrow

Question 3

What are the 3 zones of platelets?

Answer 3

the peripheral zone
the sol-gel zone
the organelle zone

Question 4

Peripheral Zone

Answer 4

the stimulus receptor/transmitter region

Question 5

Peripheral Zone components

Answer 5

Glycocalyx
Plasma membrane
open canalicular system
specialized microfilaments

Question 6

glycocalyx

Answer 6

important component of the platelet membrane

Question 7

What are glycoproteins responsible for?

Answer 7

blood group specificity (ABO)
tissue compatibility (human leukocyte antigen [HLA])
platelet-unique immunologic antigenicity
serve as receptors and facilitate transmission of stimuli

Question 8

What is the purpose of the phospholipids in the Peripheral zone?

Answer 8

serves as a surface for the interaction of the plasma proteins involved in blood coagulation

Question 9

What is also in platelet surface?

Answer 9

Coagulation factors V and VIII
participate in the formation of fibrin

Question 10

What is the purpose development of stickiness in the peripheral zone?

Answer 10

essential for the platelet functions of adhesion and aggregation

Question 11

Sol-Gel Zone

Answer 11

the cytoskeletal/contractile region
contains microtubules and microfilaments

Question 12

Thrombosthenin

Answer 12

microfibrillar “contractile” protein
form the platelet’s cytoskeleton, which contracts as the platelet’s shape changes
together with microfilaments: actin and myosin

Question 13

What is the cytoskeleton responsible for?

Answer 13

maintaining its normal discoid shape

Question 14

Organelle Zone

Answer 14

the metabolic/organellar region
responsible for the metabolic activities of the platelet

Question 15

platelet granules

Answer 15

most numerous organelles
heterogeneous in size and differentiated by their electron density and chemical contents

Question 16

Types of platelet granules

Answer 16

Alpha and dense granules

Question 17

Alpha granules

Answer 17

more numerous
contain a number of different proteins
physiologic role not clearly defined; but PF 4 does neutralize the anticoagulant heparin

Question 18

Dense bodies

Answer 18

fewer in number
densely opaque granules in (TEM) preparations

Question 19

storage pool

Answer 19

intragranular concentration of ADP and ATP found in the dense bodies

Question 20

release reaction

Answer 20

contents of both the alpha granules and dense bodies are released
energy dependent
additional platelets are drawn to the site of the vascular injury- platelet aggregates

Question 21

dense tubular system (DTS)

Answer 21

another important structure present in the cytoplasm in organelle zone
Similar to sarcotubules in skeletal muscle
site of prostaglandin synthesis and sequestration of calcium

Question 22

What does the release of calcium from the DTS do?

Answer 22

triggers contraction of thrombosthenin and subsequent internal activation of platelets

Question 23

The role of platelets in hemostasis includes what?

Answer 23

(1) maintenance of vascular integrity
(2) initial arrest of bleeding by platelet plug formation
(3) stabilization of the hemostatic plug by contributing to the process of fibrin formation

Question 24

Maintenance of Vascular Integrity

Answer 24

Platelets are involved in the nurturing of endothelial cells lining the vascular system
Platelet adheres to cell, cytoplasm b/n cell and platelet decreases, platelet becomes part of cell
This process has an effect of “nurturing” or “feeding”

Question 25

How much platelets are used in maintaining vascular integrity?

Answer 25

10% in circulation

Question 26

Platelet Plug Formation: processes

Answer 26

platelet adhesion platelet aggregation platelet release reaction

Question 27

Platelet Plug formation: Adhesion

Answer 27

a reversible process whereby platelets stick to foreign surfaces involves the interaction of platelet surface glycoproteins with the connective tissue elements of the subendothelium Exposure to subendothelial connective tissue, such as collagen fibers begins process

Question 28

Adhesion of platelets to subendothelial fibers depends on a plasma protein called what?

Answer 28

on Willebrand factor (vWF)

Question 29

What does adhesion do for platelets?

Answer 29

Platelets adhere to the area of injury at the endothelial lining or to each other when injured acting to arrest the initial episode of bleeding

Question 30

Platelet Plug Formation: Aggregation

Answer 30

injured platelet changes shape from discoid to spheric, with pseudopod formation caused by ADP, which is released from adherent platelets or endothelial cells

Question 31

Adenosine diphosphate

Answer 31

potent initiator of aggregation By binding specific membrane receptors resulting in the transformation of ambient discoid platelets to reactive spiny spheres

Question 32

Aside from Adenosine diphosphate (ADP) what else is needed for aggregation?

Answer 32

Both calcium and the plasma protein fibrinogen

Question 33

Platelet Plug Formation: Platelet Release reaction

Answer 33

from dense granules involves the secretion of ADP, serotonin (a vasoactive amine), and calcium

Question 34

What does the release of ADP do?

Answer 34

further aggregation of more platelets

Question 35

Stabilization of Hemostatic Plug

Answer 35

The last stage involved in arresting bleeding after vessel damage achieved through the formation and deposition of fibrin, the end product of coagulation

Question 36

platelets require energy in the form of ATP for what?

Answer 36

cellular movement active transport of molecules across the membrane biosynthetic purposes maintenance of a hemostatic steady state

Question 37

Why is The study of ATP and ADP in platelets complicated?

Answer 37

adenine nucleotides are present in two pools

Question 38

adenine nucleotides metabolically active pool

Answer 38

participates in metabolism found in the cytoplasm, mitochondria, and membranes

Question 39

adenine nucleotides inactive storage pool

Answer 39

found in the dense granules and plays a role in the release reaction