Platelets

Platelets are distributed on a Wright-stained blood film, platelets distributed at ____ to ____ cells per 100x field.

Average diameter of platelets is ____um or ___ to ___ fK\

Maturation period: ___ days

Lifespan: ___ days

7 to 21

2.5um or 8 to 10 fL

5 days

9 days

Resting platelets are ___________ or ________-shaped

Activated platelets are ________________ with _____________

Biconvex or disk shaped

Spherical with pseudopods

Stress platelets

Markedly larger than the normal platelets

Exceeds 6μm in diameter, MPV reaches 12 to 14 fL

Carry free ribosomes and fragments of rough ER

Appear in compensation for thrombocytopenia

Reticulated platelets

Cellular ultrastructure unique to the platelet. External surface of the platelet. It absorbs albumin, fibrinogen and other plasma proteins through endocytosis.

It is important in platelet reactions with thrombin, vWD, and fibrinogen

Glycocalyx

Lies beneath the glycocalyx and is composed of a bilayer of asymmetrically

distributed phospholipids embedded with integral proteins, of which arachidonic acid is major component

Plasma Membrane

Messages from the external membrane are translated into chemical signals causing activation and a physical change in platelet

Submembranous area

Composed of actin, a contractile in platelets and anchors the plasma membrane glycoproteins and proteoglycans

Microfilaments

Composed of protein tubulin, which maintains the platelet’s disc shape

Microtubules

50 to 80 granules in each platelet. Stain medium-gray in osmium-dye transmission electron microscopy. Most contents participate in secondary hemostasis

Alpha Granules

2 to 7 granules in each platelet. Stain black/opaque in osmium-dye transmission electron microscopy. Contents are vasoconstrictors and platelet agonists that intensify primary hemostasis Contents:

Dense Bodies

Organelle important for ATP synthesis

Mitochondria