This document provides an overview of thrombocytes (platelets) including their physiology, formation, structure, properties, functions, and variations. Key points include: - Platelets are minute disc-shaped cell fragments that form clots to stop bleeding. They are produced from megakaryocytes in the bone marrow. - Platelets have a cell membrane, cytoplasm containing proteins, and granules. Their properties include adhesiveness, aggregation, and agglutination which help form clots. - Platelets function in temporary hemostasis, phagocytosis, and blood coagulation by releasing factors that help clots form. Variations include thrombocytopenia and thrombocytosis.

1. THROMBOCYTES
PHYSIOLOGY
PRESENTATION
BY
AKASH MANJHI
MBBS 2021
ROLL NO. -
Peoples College Of Medical
Sciences & R.C. Bhopal

2. Thrombocytes - Thrombosis (clot) + Cytes (cells)
Platelets - minute disc like.
Diameter - 1 to 4 micrometers
Shape
Introduction
Inactivated - Disk shaped
Activated - Develops processes -
Filipodium
Normal Concentration - Between
150,000 and 300,000 per microliter.

3. (Bone Marrow) Magakaryocytes (60 microns)
Pleuripotent Heamopoitic Stem cells
Colony forming unit - Spleen
Colony forming unit - megakaryocytes
Platelets detached vesicles containing pieces
of megakaryocyte cytoplasm
wrapped in plasma membrane
Formation of platelets - Thrombopoiesis
A single
megakaryocyte
typically produces
about 1000 platelets.
Note : Thrombopoietin, produced by liver,
increases the production of platelets

4. Structure of Thrombocytes
Cell membrane
6 nm thick
Extensive invagination of cell membrane forms an open
canalicular system.
Glycoproteins prevent the adherence of platelets to
normal endothelium, but accelerate the adherence of
platelets to collagen and damaged endothelium in
ruptured blood vessels.
Cytoplasm
Proteins von-Willbrand Factor, Contractile proteins, fibrin stabilising factors etc
Platelet granules Alpha granules & Dense granules
Nucleus absent

5. PROPERTIES OF PLATELETS
ADHESIVENESS
Property of sticking to a rough surface.
Collagen from damaged endothelium activates the platelets, after which they gets
adhered to site of injury via interaction with Von-Willbrans factor
AGGREGATION
Grouping of platelets.
Followed by activation of more number of platelets
AGGLUTINATION
Clumping together of platelets.
Aggregated platelets are agglutinated by the actions of some
platelet agglutinins and platelet-activating factor.

6. Vascular injury
Activation of platelets by
collagen exposure
Platelet aggregation
& adhesion
Vasoconstriction
Primary heamostatic plaque is formed
Functions
Temporary hemostasis:
(With help of ADP &
thromboxane A2)

7. Functions
Phagocytosis Phagocytoses small immune molecules & small viruses
Blood coagulation: Platelets contribute to blood coagulation by
releasing platelet factor 4, and synthesizing Clotting
factor VI & XI

8. Platelet count less than 1.5 lakhs/mm
However, significant bleeding occurs when platelet count decreases below
50,000/mm? of blood. There- fore, platelet count below 50,000/mm? of blood is called
critical count.
About 70% of platelets released from bone marrow are present in circulation and 30%
are sequestered in spleen.
Therefore, splenectomy usually causes thrombocy- toss and hypersplenism invariably
causes
Variations
Thrombocytopenia
Thrombocytosis
Occurs in polycythemia Vera, chronic myeloid Lukemia, iron deficiency anemia, splenectomy etc