3RD HEMA - Part 5 Flashcards
Anchors the plasma membrane.
Actins
Formed by: Actins
MICROFILAMENTS
○ Also present throughout the
platelet cytoplasm
○ Globular and amorphous (in
resting platelets)
MICROFILAMENTS (Actins)
○ As cytoplasmic calcium concentration increases → actin becomes filamentous and contractile
MICROFILAMENTS (Actins)
What protein makes the microtubules?
Tubulin
Location of the Microfilaments
Between the microtubules and the membrane
Cytoplasm: Also contains intermediate filaments
(Desmin and Vimentin)
Which connects with the actin and the tubules → maintaining the platelet shape.
Desmin and Vimentin
Flow through the SCCS
ALPHA GRANULES & LYSOSOMES
Travel to the plasma membrane
DENSE GRANULES
50-80 granules per platelet
○ Most abundant of the 3 different kinds
ALPHA GRANULES
● Most of the a-granule contents are proteins that participate in
secondary hemostasis (coagulation)
ALPHA GRANULES
As the platelets becomes
activated
Alpha granule membrane fuse
with SCCS
○ Surface connected canalicular system (SCCS)
● Stain medium-gray (Osmium dye transmission electron microscopy preparations)
ALPHA GRANULES
In the nearby environment, the contents of the a-granule:
● Participate in platelet adhesion
● Participate in platelet aggregation
● Support plasma coagulation
Alpha Granules
Contain coagulation factors
● Fibrinogen
● vWF
● HMWK
α-granules (but not in the
cytoplasm)
● HMWK
● PAI-1 (plasminogen activator
inhibitor-1)
● Plasminogen
● Protein C inhibitor
α-granules (but not in the
cytoplasm)
Inhibits heparin:
● β-thromboglobulin
● PF-4 (platelet factor-4)
α-granules (but not in the cytoplasm)
Supports mitosis of vascular fibroblast and smooth muscle cells
● EGF (endothelial growth factor)
● PDGF (platelet-derived growth
factor)
● TGF-β (transforming growth
factor-β)
α-granules and platelet
cytoplasm
● Fibrinogen
● Fibronectin
● Albumin
● Immunoglobulins
● VWF
● Thrombospondin
● Factor V (F5)
α-granule membrane
● P-selectin
α-granule membrane and
plasma membrane
● GP IIb/IIIa (2b/3a)
● GP IV (4)
● GP Ib/IX/V (1b/9/5)
Which of the following platelet granules contain coagulation factors?
A. Alpha granules
B. Dense granules
C. Lysosomes
D. None of the Above
A. Alpha granules
● They migrate to the plasma membrane and release their contents directly into the plasma
upon platelet activation
DENSE GRANULES/ DELTA GRANULES
A.k.a DELTA GRANULES
DENSE GRANULES/ DELTA GRANULES
● 2-7 dense granules per platelet
● Stain black (opaque) when treated with osmium in transmission electron microscopy
DENSE GRANULES/ DELTA GRANULES
● Vasoconstrictors
● Platelet agonists that intensify
primary hemostasis
DENSE GRANULES/ DELTA GRANULES
A substance that initiates a response when combined with a receptor
AGONIST
“MP-CHASE” mnemonics
● Magnesium
● Phosphate
● Calcium
● Histamine
● Adenosine diphosphate (ADP) and
Adenosine triphosphate (ATP)
● Serotonin/ 5-hydroxytryptamine (5-HT)
● Epinephrine/ Adrenaline
All of the following are found in the dense granules EXCEPT:
a. Epinephrine
b. Fibrinogen
c. Serotonin
d. Magnesium
b. Fibrinogen
Fibrinogen is found in the alpha granules NOT dense granules. Dense granules contain the MP-CHASE.
All of the following are found in the alpha granules EXCEPT:
a. Platelet Factor 4
b. PDGF
c. Fibrinogen
d. Adrenaline/ Epinephrine
d. Adrenaline/ Epinephrine
Supports neighboring platelet
aggregation by binding to P2Y1
and P2Y12.
ADP
Function is unknown, but ATP
release is detectable upon platelet activation.
ATP
Action: Alpha Granules or Dense/Delta Granules
● The alpha-granule membrane fuses with the SCCS.
● Participate in platelet adhesion and aggregation and support plasma coagulation.
Alpha Granules
Vasoconstrictors that bind/ endothelial cells and platelet
membranes
Serotonin (5-Hydroxytryptamine)
Divalent cations support platelet
activation and coagulation.
Calcium and Magnesium (Ca2+ and Mg2+)
Granules: Alpha Granules or Dense/Delta Granules
● 50–80 granules in each platelet
Alpha Granules
Granules: Alpha Granules or Dense/Delta Granules
● 2–7 dense granules per platelet
Dense/Delta Granules
Stain: Alpha Granules or Dense/Delta Granules
Black (opaque) when treated with
osmium in transmission electron
microscopy
Dense/Delta Granules
Stain: Alpha Granules or Dense/Delta Granules
Medium-gray (Osmium-dye
transmission electron microscopy
preparations)
Alpha Granules
Proteins and components present: Alpha Granules or Dense/Delta Granules
● β-thromboglobulin
● PF-4 (platelet factor-4)
● HMWK
● PAI-1
(plasminogen activator inhibitor-1).
● Plasminogen
● Protein C inhibitor
● EGF (endothelial growth factor)
● PDGF (platelet-derived growth factor)
● TGF-β (transforming growth factor-β)
● Fibrinogen
● Fibronectin
● Albumin
● Immunoglobulins
● VWF
● Thrombospondin
● Factor V (F5)
● P-selectin
● GP IIb/IIIa (2b/3a)
● GP IV (4)
● GP Ib/IX/V (1b/9/5)
Alpha Granules
Hemostasis: Alpha Granules or Dense/Delta Granules
Secondary hemostasis
Alpha Granules
Action: Alpha Granules or Dense/Delta Granules
Migrate to the plasma membrane and release their contents directly into the plasma upon platelet activation.
Dense/Delta Granules
Hemostasis: Alpha Granules or Dense/Delta Granules
Primary hemostasis
Dense/Delta Granules
● Few in number
● Stain positive for arylsulfatase, B-glucuronidase, acid phosphatase, and catalase
LYSOSOMES
Proteins and components present: Alpha Granules or Dense/Delta Granules
2–7 dense granules per platelet
Dense/Delta Granules
● ____________’ contents flow through the SCCS.
● __________ probably digest vessel wall matrix components during in vivo aggregation and may also digest autophagic debris
LYSOSOMES
● Glycocalyx is less developed in the _____ and lacks some of the glycoprotein receptors present on the platelet surface
SURFACE-CONNECTED CANALICULAR SYSTEM
(SCCS)
● The plasma membrane invades the platelet interior, producing _____.
SURFACE-CONNECTED CANALICULAR SYSTEM
(SCCS)
SCCS is the route for:
- Endocytosis
- Secretion of a-granule contents
- Secretion of lysosome contents
● These enzymes include:
- Support the eicosanoid synthesis pathway that produces thromboxane A2
(3)
■ Phospholipase A2
■ Cyclooxygenase
■ Thromboxane synthetase
“Control center” for platelet activation
DENSE TUBULAR SYSTEM (DTS)
● Parallel and closely aligned to the SCCS
● A condensed remnant of the rough endoplasmic reticulum
DENSE TUBULAR SYSTEM (DTS)
● Sequesters calcium and bears a series of enzymes that support platelet activation.
DENSE TUBULAR SYSTEM (DTS)
- Supports the production of inositol triphosphate (IP3) and diacylglycerol (DAG)
(1)
■ Phospholipase C
Brand name from Bayer Company
ASPIRIN
Also known as: acetylsalicylic acid
ASPIRIN
● Most frequently used antiplatelet therapy or drug
● Cyclooxygenase inhibitor
ASPIRIN
Parts of platelets that can be found using the light microscope:
● Chromomere and Hyalomere
● For smaller structures, use an electron microscope.
● To see the ultrastructure of the platelet
○ Molecular sequencing
○ Flow cytometry
For smaller structures,
use an electron microscope.
