2-PLATELETS Flashcards
1
Q
Who first recognized platelets as a distinct cell structure in 1882?
A
Bizzozero
2
Q
When did the relationship of platelets to hemostasis and thrombosis become important?
A
1970
3
Q
How many platelets are present in 1 cubic millimeter of blood?
A
One-fourth of 1 billion platelets
4
Q
How many total platelets are present in the blood of an average woman?
A
Approximately 1 trillion
5
Q
How many trips does each platelet make through the bloodstream during its lifespan?
A
14,000 trips
6
Q
What is the lifespan of a platelet?
A
7 to 10 days
7
Q
What are platelets also called?
A
Thrombocytes
8
Q
What is the size range of platelets?
A
0.5 to 3.0 μm
9
Q
Where are platelets synthesized?
A
Bone marrow
10
Q
What hormone stimulates platelet production?
A
Thrombopoietin
11
Q
How does the size of younger platelets compare to older ones?
A
Younger platelets are larger than older ones
12
Q
What is the average diameter of a platelet?
A
2 to 4 μm
13
Q
How do platelets appear in blood collected using EDTA?
A
They ‘round up’
14
Q
How do platelets appear on a Wright-stained blood smear?
A
Circular to irregular, lavender, and granular
15
Q
What stain makes platelets appear dense blue to purple?
A
Romanowsky stain
16
Q
Why is it difficult to examine the internal structure of platelets using light microscopy?
A
Because of their small size
17
Q
What type of stem cell gives rise to platelets?
A
Pluripotent stem cell
18
Q
What cells produce colony-stimulating factors (CSF) that influence platelet development?
A
Macrophages, fibroblasts, T-lymphocytes, and stimulated endothelial cells
19
Q
What is the parent cell of platelets?
A
Megakaryocyte
20
Q
Where are megakaryocytes found?
A
Bone marrow
21
Q
What is the size range of megakaryocytes?
A
80 to 150 μm
22
Q
What process do megakaryocytes undergo instead of complete cell division?
A
Endomitosis (endoreduplication)
23
Q
How many platelets does one megakaryocyte produce?
A
About 2,000 platelets
24
Q
What organ primarily produces thrombopoietin?
A
Kidney
25
What two other organs contribute to thrombopoietin production?
Spleen and liver
26
Where are platelets primarily stored in the body?
No reserve in the bone marrow; 80% in circulation, 20% in the spleen (red pulp)
27
How do platelets behave in circulation?
Flow smoothly through veins, arteries, and capillaries
28
How do platelets differ in movement compared to leukocytes?
Platelets cluster near erythrocytes, while leukocytes roll along the vascular endothelium
29
Do platelets have a nucleus?
No
30
What two types of granules do platelets contain?
Alpha granules and dense granules
31
What active components do platelet granules release?
Serotonin, ADP, and ATP
32
What system destroys platelets?
Reticuloendothelial (RE) system
33
What is the normal lifespan of platelets?
9 to 12 days (4 to 9 days in circulation)
34
What is the normal platelet count in peripheral blood?
150 to 400 × 10⁹/L
35
How does platelet count change with age?
It decreases after age 65
36
What is the platelet count range for men and women over 65?
Men: 122 to 350 × 10⁹/L; Women: 140 to 379 × 10⁹/L
37
What fraction of the body’s total platelets is in circulation?
Two-thirds
38
Where is the remaining one-third of platelets located?
Sequestered in the spleen
39
When are sequestered platelets released into circulation?
During acute inflammation, injury, major surgery, or plateletpheresis
40
What does the peripheral zone of platelets consist of?
Outer membrane and related structures
41
What functions are associated with the peripheral zone?
Platelet adhesion and aggregation
42
What is the surface coat of platelets called?
Glycocalyx
43
What is the glycocalyx composed of?
Plasma proteins and carbohydrate molecules
44
What systems are related to the glycocalyx?
Coagulation, complement, and fibrinolytic systems
45
What glycoproteins (GP) are involved in platelet adhesion and aggregation?
Ia, Ib, Ic, IIa, IIb, III, IV, & V
46
What functions do glycoprotein receptors mediate?
Platelet adherence, shape change, internal contraction, and aggregation
47
Which coagulation factors adhere to the glycocalyx?
I, V, VIII, X, XI, XII, & XIII
48
What lies beneath the glycocalyx?
Plasma membrane
49
What are the functions of the plasma membrane?
Physical and chemical barrier; Site of receptors for clotting factors
50
Where is the submembrane area located?
Under the plasma membrane (below the peripheral zone)
51
What is the function of the submembrane area?
Prevents contact between organelles and the platelet cell wall
52
What role does the submembrane area play in platelet shape?
Regulates normal platelet discoid shape
53
How does the submembrane area connect different parts of the platelet?
Links the membrane to the inner cell body
54
What is another name for the sol-gel zone?
Matrix or muscle & skeletal portion of the platelet
55
What is the function of the sol-gel zone?
Maintains internal organelle arrangement and platelet shape
56
What is the role of the jelly-like part in the cytoplasm?
Prevents organelles from colliding with each other
57
How does the sol-gel zone influence platelet function?
Facilitates communication between organelles and external surroundings
58
What structures are present in the sol-gel zone?
Microtubules and microfilaments
59
What is the function of microtubules in platelets?
Provide cytoskeletal support and maintain discoid shape
60
What happens to platelets when they are activated?
Change from discoid to spherical shape and form pseudopods
61
What protein is responsible for platelet contraction and pseudopod formation?
Thrombosthenin (actomyosin)
62
What is another name for thrombosthenin?
Actomyosin
63
What is the importance of thrombosthenin in clot retraction?
Contracts the clot, squeezing out serum and making the clot smaller
64
What two types of proteins does thrombosthenin contain?
Myosin and actin
65
What structures are found in the organelle zone of platelets?
Granules, dense bodies, lysosomes, peroxisomes, and mitochondria
66
What is the function of the organelle zone?
Metabolic center influencing platelet function in response to hypercoagulation, viruses, and foreign bodies
67
What portion of the platelet cytoplasm does the organelle zone constitute?
Major portion
68
How do alpha granules compare in size to dense granules?
Larger than dense granules
69
What is the function of platelet factor 4 (PF4)?
Binds heparin and neutralizes its anticoagulant effect
70
What is the function of platelet-derived growth factor (PDGF)?
Stimulates smooth muscle cell growth and proliferation
71
Why is PDGF important in clotting and healing?
Helps regenerate new cells after clot formation until the wound is healed
72
What happens once the wound is healed?
Fibrinolysis occurs via plasminogen activator to dissolve the clot
73
Name three growth factors found in alpha granules.
PDGF, TGF-beta, and endothelial growth factor
74
What coagulation-related factors are present in alpha granules?
Fibrinogen, Factor V, von Willebrand Factor (vWF), and Factor VIII
75
What adhesion molecules are found in alpha granules?
Fibronectin and thrombospondin
76
What protein in alpha granules suppresses megakaryocytopoiesis?
Platelet Factor 4 (PF4)
77
What alpha granule component controls fibrinolysis?
Plasminogen activator inhibitor-1 (PAI-1)
78
What substances are secreted by dense granules?
ADP, ATP, calcium, magnesium, epinephrine, phosphate, and serotonin (5-HT)
79
What is the function of ADP in platelet aggregation?
Promotes primary platelet aggregation by binding P2Y1 and P2Y12 receptors
80
What is the function of serotonin in dense granules?
Acts as a vasoconstrictor, binding to endothelial cells and platelet membranes
81
What is the function of calcium (Ca²⁺) and magnesium (Mg²⁺) in platelets?
Support platelet activation and coagulation
82
What is the known function of ATP in dense granules?
Unknown, but ATP release is detectable upon platelet activation
83
What do lysosomes in platelets contain?
Acid hydrolases
84
What is the role of lysosomes in clot formation?
Digest cellular debris and foreign materials at the site of the thrombus
85
How do lysosomes contribute to clot breakdown?
They participate in clot lysis
86
What is the primary function of mitochondria in platelets?
ATP synthesis for platelet metabolism
87
What alpha granule protein supports mitosis of vascular fibroblasts and smooth muscle cells?
PDGF, Endothelial Growth Factor, TGF-β
88
Which alpha granule proteins function as adhesion molecules?
Fibronectin, Thrombospondin
89
What alpha granule protein neutralizes heparin and suppresses megakaryocytopoiesis?
Platelet Factor 4 (PF4)
90
Which alpha granule protein is found only in platelet alpha granules?
β-Thromboglobulin (β-TG)
91
What alpha granule protein promotes fibrinolysis?
Plasminogen
92
Which alpha granule proteins control fibrinolysis?
Plasminogen Activator Inhibitor-1 (PAI-1), Alpha-2 Antiplasmin
93
Which alpha granule protein controls coagulation?
Protein C Inhibitor
94
What dense granule supports neighboring platelet aggregation by binding P2Y1 and P2Y12 receptors?
ADP
95
What dense granule has an unknown function but is released upon platelet activation?
ATP
96
Which dense granule acts as a vasoconstrictor by binding to endothelial cells and platelet membranes?
Serotonin (5-HT)
97
Which dense granules support platelet activation and coagulation?
Calcium (Ca²⁺), Magnesium (Mg²⁺)
98
Which dense granules store and release phosphate?
Phosphate
99
What are the two main structural components of platelets?
Surface-Connecting Canalicular System (SCCS) and Dense Tubular System (DTS)
100
Which platelet structure serves as a delivery route for substances ingested or extruded?
Surface-Connecting Canalicular System (SCCS)
101
Which platelet structure is sponge-like and twists throughout the platelet?
Surface-Connecting Canalicular System (SCCS)
102
What is the function of the SCCS in relation to hemostatic proteins?
Stores additional quantities of the same hemostatic proteins found on the glycocalyx.
103
How does the SCCS enhance platelet interaction with its environment?
By increasing access to the platelet interior and promoting egress of platelet release products.
104
What is the primary route for endocytosis and secretion of alpha granule contents upon platelet activation?
Surface-Connecting Canalicular System (SCCS)
105
Which platelet structure contains specific peroxidase activity important for prostaglandin synthesis?
Dense Tubular System (DTS)
106
Where does prostaglandin and thromboxane synthesis occur in platelets?
Dense Tubular System (DTS)
107
Which enzymes in the DTS support platelet activation?
Phospholipase A2, Cyclooxygenase, Thromboxane Synthetase, and Phospholipase C
108
Which molecule produced in the DTS is essential for clotting?
Thromboxane A2
109
What is the DTS a condensed remnant of?
The rough endoplasmic reticulum
110
Which metabolic pathway takes place in the DTS?
Arachidonic acid metabolism
111
How is the DTS positioned in relation to the SCCS?
Parallel and closely aligned
112
What is the process of stopping blood flow called?
Hemostasis
113
Which molecule in platelets acts as a vasoconstrictor to slow down bleeding?
Serotonin
114
What is the first response in hemostasis?
Vasoconstriction
115
What is the difference between primary and secondary hemostasis?
Primary: Platelet plug formation; Secondary: Stabilization of platelet plug
116
What is the process of solidifying blood fluid called?
Blood coagulation
117
Which platelet granules contain chemicals that promote blood coagulation?
Alpha and dense granules
118
Which platelet membrane component activates the intrinsic coagulation system?
Phospholipids
119
Which contractile proteins are responsible for clot retraction?
Thrombosthenin and Actomyosin
120
What happens to the serum when clot retraction occurs?
It is released, causing the clot to shrink.
121
What is an observable effect of clot retraction in a test tube with clotted blood?
The clot gets smaller, and the serum increases.
122
Which substances promote the growth and multiplication of vascular endothelial cells, vascular smooth cells, and fibroblasts?
Platelets secrete growth factors.
123
Which three components are important for maintaining vascular integrity?
Platelets, Vitamin C, and Adrenocorticosteroids
124
What condition results from vascular fragility due to deficiencies in platelets, Vitamin C, or adrenocorticosteroids?
Purpura
125
Why are capillaries more fragile than veins and arteries?
Capillaries only have an endothelial cell lining, lacking a cell wall.
