Hema-Lec-Platelet Physiology Flashcards
______ 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
provides an estimation of platelet numbers, size, and distribution.
Wright’s-stained blood film
Platelet number can be obtained by
manual platelet count (hemacytometer) or an electronic cell counter.
is the outer membrane surface. It is rich in glycoproteins, which serve
as membrane receptors.
Glycocalyx
_______ is the receptor for von Willebrand’s factor (vWF) in the presence
of _______.
Glycoprotein Ib; ristocetin
are receptors for vWF and fibrinogen and are exposed
by stimulation of thrombin or adenosine diphosphate (ADP).
Glycoproteins IIb and IIIa
______ is the receptor for thrombin.
Glycoprotein Va
These provide an active means of platelet con- traction to squeeze out the contents of the cytoplasmic granules.
Microtubule and micro filaments
______ form the submembranous band around the circumference of the cell
and structurally support the normal discoid-shaped platelets.
Microtubules
_______ contain actin and are closely
related to the microtubule.
contractile microfilaments (thrombosthenin)
provides direct communication between intracellular
and extracellular compartments.
open canalicular system
forms a circle within the microtubule.
dense tubular system
This system serves as a site for arachidonic acid metabolism.
dense tubular system
This system also functions as a calcium-sequestering pump that maintains platelet
cytoplasmic calcium levels.
dense tubular system
are responsible for energy production.
Mitochondria
provide energy substrate.
Glycogen granules
______ 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
_____ contain nonprotein factors including: (4)
Dense granules
a. Adenosine diphosphate (ADP)
b. Adenosine triphosphate (ATP)
c. 5-Hydroxytryptamine (5-HT; or serotonin)
d. Calcium
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
causetheplatelettochangeshapefromdiscoidtospherical
Tissueplateletactivators
______ and ______ undergo internal contraction and centralization. The complete process is _______.
Dense and α-granules ; calcium dependent
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
_____ 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.
- horseshoe shape
- 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 _____.
- Platelet fields
A. invagination of surface membrane - 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
