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hematology > lecture 10 > Flashcards

lecture 10 Flashcards

1
Q

what are platelets? are they true cells?

A
  • not true cells
  • cytoplasmic fragments of giant cells called megakaryocytes
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2
Q

platelets and megakaryocytes do not contain a nucleus

(T/F)

A

false,
platelets have no nucleus while megakaryocytes have a huge nucleus

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3
Q

why are the megakaryocytic cells unsual?

A
  • their nuclei can undergo several mitotic divisions without cytoplasmic divisions
  • generating giant multinucleated or polyploid cells
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4
Q

what are the characteristics of the multiple nuclei & the chromosomes in a megakaryocytic cell?

A
  • they usually remain attached to each other
  • often are superimposed
  • give a multilobulated appearance
  • multiple nb of chromosomes (polyploid)
  • multiple of the original 2 sets of chromosomes (2n)
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5
Q

the divison that the megakaryocitic cells undergo is also referred to as:

A

endomitosis or endoreduplication

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6
Q

what are the different stages in megakaryopoeisis?

(shu asamiyon lal shramit)

A
  1. megakaryoblast
  2. promegakaryocyte
  3. megakaryocyte (mature)
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7
Q

what is the megakaryoblast?
what are the characteristics of its nucleus, cytoplasm…

d=?

A
  • earliest recognizable cell
  • large (d=15-50 micro m)
  • irregularly shaped
  • single nucleus or severel round/oval nuclei
  • blue, non-granular cytoplasm
  • may have bluish pseudopods or protrusions from the cytoplasmic membrane
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8
Q

what is the promegakaryocyte?
what are the characteristics of its nucleus, cytoplasm…

d=?

A
  • nucleus has divided 1 or more times
  • cell has increased in size (d=20-80 micro)
  • cytoplasmic protrusions
  • cytoplasm has bluish granules
  • cytoplasm rich in RNA –> basophilic
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9
Q

with maturation. cytoplasmic basophilia increases

(T/F)

A

false, basophilia fades and cytoplasm becomes filled with reddish-purple granules

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10
Q

what is the mature megakaryocyte?
what are the characteristics of its nucleus, cytoplasm…

A
  • huge cell (d= ~150 micro)
  • segmented nucleus
  • dense nuclear chromatin
  • cytoplasm appears pinkish
  • highly granular
  • abundant
  • irregular peripheral border (shape)
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11
Q

the megakaryoblast has few bluish granules

(T/F)

A

false, its non-granulated

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12
Q

how are platelets formed/ produced?

A
  • platelets are produced directly from the megakaryocyte cytoplasm
  • megakaryocyte puts out pseudopods into the BM sinosoids
  • detach and fragment into individual platelets
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13
Q

what happens to the cytoplasm and nucleus of the megakaryocyte after the production of platelets?

A
  • entire cytoplasm is broken away
  • leaving the nucleus naken in the BM
  • nucleus without cytoplasm will not survive
  • nucleus will undergo degeneration
  • nucleus will be taken by the macrophages
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14
Q

how many platelets are produced by megakaryocytes?

A

between 2000-4000 platelets

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15
Q

in what case do we have higher production of platelets?

(shu lezim ykun fiyo l megakaryocyte aktar)

A
  • the more nuclear lobes
  • the larger the cytoplasmic mass
  • the more platelets are produced
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16
Q

what stimulates platelet production?

A

thrombopoeitin

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17
Q

what happens to the megakaryocytes when thrombopoiesis is activated?

A
  • nb & size of megakaryocytes increase
  • maturation time decrease
  • younger & larger platelets are seen in PB
  • they are metabolically more active and effective in hemostasis
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18
Q

how long is the platelet’s life span?

in circulation

A

9-11 days

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19
Q

after circulating, where do platelets go to?

A

spleen

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20
Q

are all platelets trapped in the spleen?

A

no, only 30%
the remaining 70% circulate

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21
Q

platelets in the spleen are interchangeable with those found in the blood

(T/F)

A

true

22
Q

platelet structure:

(shape-color-diameter-consist of..) BALA L MEMBRANE W CYTOPLASM

A
  • discoid structure
  • d=1-3 micro m
  • appears light blue to purple in color
  • very granular
  • consists of 2 parts: chromomere & hyalomere
23
Q

what is the chromomere?

A
  • part of a plaetelet
  • granular
  • located centrally
24
Q

what is the hyalomere?

A
  • part of a platelet
  • agranular
  • surrounds the chromomere
  • light blue
25
Q

platelet membrane comes from:

A

the plasma membrane of megakaryocyte

26
Q

platelet membrane characteristics + constituents:

briefly

A
  • has a trilaminar unit structure (3 layers)
  • surface coat –> glycocalyx
  • membrane & glycocalyx are smooth
  • contain pore-like indentations
  • nb of glycoproteins
  • contractile protein (thrombosthenin)
  • phospholipid constituents & other fatty acid pools
27
Q

why does the platelet membrane contain pore-like indentations?

A

opens communication channels between the platelet cytoplasm and its surroundings

28
Q

glycoproteins found on the platelet membrane are important for:

A
  • adhesion
  • aggregation
  • coagulation (provides a surface to which coagulation factors may adhere)
29
Q

contractile protein found on the platelet membrane is also called:

A

thrombosthenin

30
Q

thrombosthenin is important for:

A
  • maintain platelet shape
  • responsible for changes in platelet shapes
31
Q

phospholipid constituents & other fattu acid pools found on the platelet membrane are required for:

A

fattu acid metabolism

32
Q

platelet cytoplasm constituents:

briefly

A
  • few mitochondria
  • glycogen deposits
  • 3 types of granules
33
Q

what are the 3 types of granules present inside the platelets cytoplasm?

only their names

A
  1. alpha granules
  2. electron dense granules
  3. lysosomes
34
Q

what are the alpha granules rich in?

A

various substances of biological importance
* clotting factors (fibrinogen, factor V)
* PF4
* PDGF (platelet derived growth factor)

35
Q

what are the electron dense granules rich in?

A
  • Ca2+
  • Mg2+
  • serotonin (contracts blood vessels)
  • ADP
  • ATP
36
Q

what are the lysosomes rich in?

A

digestive enzymes

37
Q

platelets are not capable of phagocytosis

(T/F)

A

false, they are capable

they contain lysosomes rich in digestive enzymes (microphagocytosis)

38
Q

what is hemostasis?

A

process by which bleeding from an injured blood vessel is controlled and stopped

39
Q

what factors are involved in hemostasis?

A
  • blood vessels
  • platelets
  • coagulation factors
40
Q

hemostasis occurs in 2 phases, what are they:

A
  1. primary hemostasis: involves the vascular and platelet response to vessel injury
  2. secondary hemostasis: includes the response of coagulation process leading to the formation of a stable fibrin - platelet plug

=> vessel healing

41
Q

what are the basic events in primary & secondary hemostasis after vessel injury?

briefly name the steps

A
  1. vasoconstriction
  2. platelet adhesion
  3. platelet aggregation
  4. fibrin-platelet plug formation
42
Q

what happens during the 1st event of hemostasis?
what causes it?

A
  1. vasoconstriction
    * first response
    * damaged blood vessel constricts
    * decreasing the blood flow through the injured area
    * serotonin causes vasoconstriction
43
Q

what happens during the 2nd event of hemostasis?

briefly

A
  1. platelet adhesion
    * when there is an injury, platelets adhere to exposed collagen
    * activation & change in platelet shape (round to spiny)
    * series of biochemical reactions take place
44
Q

in the circulation platelets appear as a relatively active cell

(T/F)

A

false, inactive

show little tendency to interact with other platelets/ endothelial cells

45
Q

platelet surface contains receptors for a nb of substances, important among these is the substance called:

A

collagen

46
Q

when do platelets change shape from round to spiny?

A

following pseudopodia formation

47
Q

what is the exposed collagen?

A

fibrous tissue underneath the endothelium

48
Q

what are the series of biochemical reactions that take place during platelet adherence?

A
  • when platelet is activated, membrane phospholipases are activated
  • in turn liberate arachidonic acid (fatty acid) from platelet phospholipid stores
  • enzyme cyclooxygenase acts on arachidonic acid to liberate thromboxane A2
  • thromboxane A2 produced –> stimulates granules to release their content, important = ADP
49
Q

what happens during the 3rd event of hemostasis?

A
  1. platelet aggregation
    * ADP has a receptor for it on the platelet membrane
    * once ADP is released, it comes to the receptor
    * causes platelet aggregation
    * platelets will not only stick to the collagen surface but will also stick to each other
    * form the initial plug that inhibits bleeding

serotonin will contract blood vessels

50
Q

what happens during the 4th event of hemostasis?

A
  • fibrin-platelet plug formation

coagulation factors interact on the platelet surface to produce fibrin (clot)

51
Q

what are the 2 pathways that lead to the formation of a fibrin clot?

A
  1. intrinsic pathway
  2. extrinsic pathway

the 2 converge in a common pathway that leads to clot formation

52
Q

what happens during the clotting cascades?

A
  • platelets stuck by aggregation
  • we get a strong block which will obstruct the vessels leading to stoppage of bleeding
    *

hematology (10 decks)

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