Hema-Lec-Platelet Physiology Flashcards by vnlla babe

______ which exist in whole blood in concentrations of 150,000 to 440,000/mm3, are disk-shaped cells necessary for ________. Platelets are formed from the cytoplasm of ________ in the marrow.

Platelets; hemostasis; megakaryocyte

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provides an estimation of platelet numbers, size, and distribution.

Wright’s-stained blood film

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Platelet number can be obtained by

manual platelet count (hemacytometer) or an electronic cell counter.

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is the outer membrane surface. It is rich in glycoproteins, which serve
as membrane receptors.

Glycocalyx

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_______ is the receptor for von Willebrand’s factor (vWF) in the presence
of _______.

Glycoprotein Ib; ristocetin

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are receptors for vWF and fibrinogen and are exposed
by stimulation of thrombin or adenosine diphosphate (ADP).

Glycoproteins IIb and IIIa

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______ is the receptor for thrombin.

Glycoprotein Va

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These provide an active means of platelet con- traction to squeeze out the contents of the cytoplasmic granules.

Microtubule and micro filaments

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______ form the submembranous band around the circumference of the cell
and structurally support the normal discoid-shaped platelets.

Microtubules

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_______ contain actin and are closely
related to the microtubule.

contractile microfilaments (thrombosthenin)

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provides direct communication between intracellular
and extracellular compartments.

open canalicular system

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forms a circle within the microtubule.

dense tubular system

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This system serves as a site for arachidonic acid metabolism.

dense tubular system

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This system also functions as a calcium-sequestering pump that maintains platelet
cytoplasmic calcium levels.

dense tubular system

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are responsible for energy production.

Mitochondria

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provide energy substrate.

Glycogen granules

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______ contain contact-promoting factors, including: (6)

Alpha (α) granules

a. Platelet fibrinogen
b. Platelet-derived growth factor (PDGF)
c. von Willebrand’s factor (factor VIII:R)
d. β -Thromboglobulin (BTG)
e. Platelet factor 4 (heparin-neutralizing)
f. Fibronectin

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_____ contain nonprotein factors including: (4)

Dense granules

a. Adenosine diphosphate (ADP)
b. Adenosine triphosphate (ATP)
c. 5-Hydroxytryptamine (5-HT; or serotonin)
d. Calcium

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Damaged subendothelium releases factors that (3). These factors include: (5)

activate the platelet, transform its
shape, and evolve a “sticky” platelet aggregate to plug the leak

a. Collagen
b. Fibronectin
c. vWF (factor VIII:R)
d. Thrombin
e. ADP

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causetheplatelettochangeshapefromdiscoidtospherical

Tissueplateletactivators

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______ and ______ undergo internal contraction and centralization. The complete process is _______.

Dense and α-granules ; calcium dependent

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The exposure of surface membrane receptors to vWF and fibrinogen results in (3)

cytoplasmic calcium ionization, stimulation of ATP generation, and activation of
the actin monomers in the micro filaments

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_____ result in a centralization of the cytoplasmic granules and a release of
their contents through the canalicular system.

Contractions

Plug formation, or secondary aggregation, is primarily stimulated by (2)

thrombin and
thromboxane A2 (TXA2).

_______ is unmasked by the binding of vWF and collagen to platelet receptors on the membrane.

Phospholipid A2

_____ inhibits adenylate cyclase [thus, it inhibits the formation of cyclic adeno- sine monophosphate (cAMP)] and liberates sequestered calcium into cytoplasm. _______ causes further cytoplasmic contraction, release of granule contents, and platelet aggregation.

TXA2; Calcium

enzymatically cleaves fibrinogen to form fibrin, which is necessary to stabilize the platelet plug.

Thrombin

Growth-limiting factors of the platelet aggregate include: (2)

a. Blood flow, which washes away coagulation-promoting factors b. Release of prostaglandin PGI2 (prostacyclin) by the surrounding vascular tissues

Granularreleaseofsubstancesfromdensegranules,suchasserotonin,prostaglandins (except for TXA2), and lysozymes, causes ______ and ______, which increases blood flow.

local inflammation and vasodilation

Megakaryocytopoiesis development occurs by?

endomitosis

A single megakaryoblast nucleus may contain ______ the normal number of chromosomes

2 to 64 times

______ is densely staining, dispersed early, and more compact at later stages.

Nuclear chromatin

_____ are small at all development stages.

Nucleoli

Stages of megakaryocytic maturation

Megakaryoblasts 6 to 24 μm. Promegakaryocytes 14 to 30 μm Granular megakaryocytes (16 to 56 μm Mature megakaryocytes 20 to 50 μm

descend from a unipotential stem cell (CFU-Meg). They are characterized by overlapping nuclear lobes and basophilic staining cytoplasm; their size ranges from 6 to 24 μm.

Megakaryoblasts

are larger than megakaryoblasts (14 to 30 μm in diameter) and have more cytoplasm.

Promegakaryocytes

Promegakaryocytes are larger than megakaryoblasts (14 to 30 μm in diameter) and have more cytoplasm. (1) The nucleus becomes increasingly lobulated and spreads out into a _______ (2) _______ are visible in the center of the cell.

1. horseshoe shape 2. Red-pink granules

are characterized by increased spreading of nuclear lobes and spreading of pink granules throughout the cytoplasm.

Granular megakaryocytes

have a compact nucleus, and the basophilia of cytoplasm has disappeared.

Mature megakaryocytes

(1) _______ are clusters of pink granules in the cytoplasm. (a) Platelet fields are produced by an ________, sep- arating the cytoplasm into individual platelets. (2) Each mature megakaryocyte produces from _____ platelets that each range in size from _____.

1. Platelet fields A. invagination of surface membrane 2. 2,000 to 7,000; 2 to 3 μm

Maturation time from the blast stage to platelet formation is typically

5 days

Normal marrow contains approximately ______. This equates to approximately _______ when bone marrow smears are microscopically examined.

15 million megakaryocyte; 5 to 10 megakaryocytes per 10× power field

Normal circulation life of a platelet is?

8 to 10 days

Plateletsareremovedby (2)

macrophageintheliverandspleenorbyactiveuseindaily coagulation mechanisms.

Circulating platelets are distributed between the

spleen and blood.

One third of the circulating platelets are always in the

Spleen

The platelet count is higher in patients ______ and lower in patients ________

without a spleen; with splenomegaly (enlarged spleen).

occurs after platelet transfusion.

Rebound thrombocytopenia

occurs after platelet depletion.

Rebound thrombocytosis

______ results in an increased megakaryoblast endomitosis, which increases platelet volume and number. It also affects committed unipotential stem cells, which results in more megakaryoblast.

Feedback stimulus

_______ is an effective in vivo screening test of platelet function by timing the length it takes for platelets to plug broken capillaries after a small cut is made in the forearm.

Bleeding time

Bleeding time: Reference values are approximately

3 to 8 minutes

Increased bleeding times are seen in:

(1) Patients taking drugs with antiplatelet action (e.g., aspirin) (2) Patients with von Willebrand’s disease (vWD) (3) Patients who suffer from congenital platelet abnormalities (4) Patients with platelet counts lower than 100,000/mm3

Platelet aggregation is measured with a ?

Platelet aggregation is measured with a

______ retains aggregating properties but lacks clotting ability.

γ-Thrombin