Lec 02: Platelets Structure

1. peripheral zone

2. submembrane area

3. sol-gel zone

4. organelle zone

platelets structure

peripheral zone

includes platelet membrane

platelet membrane

contains membrane-bound glycoproteins, glycocalyx, and cytoskeleton with actin and myosin fibrils and microtubules

maintains shape

actin & myosin function in platelets

glycocalyx

is a fluffy coat that surrounds the cellular membrane externally

platelet, ABO, HLA

glycocalyx possesses these, which act as receptors for thrombin, vWF, epinephrine, ADP, and platelet activating factor (PAF)

Ia

glycoprotein: adhesion to collagen

Ib

glycoprotein: binds vWF

IIb-IIIa

glycoprotein: binds fibrinogen and vWF

IV

glycoprotein: binds thrombospondin

V

glycoprotein: binds thrombin

IX

associated with Ib complex

submembrane area

contains membranes derived from megakaryocyte smooth ER organized into a dense tubular system which is responsible for thromboxane A2 synthesis

dense tubular system

connected to the surface of platelet membrane to aid in thromboxane A2 release

thromboxane A2 (TXA2)

type of thromboxane produced by activated platelets during hemostasis and has prothrombic properties

thromboxane A2

• stimulates activation of new platelets

• increases platelet aggregation

Sol-Gel zone

composed of microfilaments: actin & myosin that interacts to form actomyosin

actomyosin

actin + myosin

actomyosin

contractile protein that is important for clot retraction aka thrombostenin

Sol-Gel zone

composed of microtubules, tubulin, protein that maintains platelet shape

Organelle zone

metabolic center to influence platelet function in response to exogenous stimuli such as hypercoagulation, viruses, and foreign bodies

mitochondria, alpha granules, dense granules, lysozomes

Sol-Gel zone is composed of