W1 LECT 4: platelets

Question 1

where are platelets formed?

Answer 1

megakaryocytes in the bone marrow

Question 2

how does megakaryocytes differentiate?

Answer 2

hematopoietic stem cell- megakaryocyte progenitor cells - mature megakaryocyte

Question 3

what helps with facilitating fragmentation of
proplatelets into 1 to 2 μm
platelets?

Answer 3

-shear and turbulent blood flow

Question 4

how many platelets does each megakaryote give rise to?

Answer 4

2000- 3000 platelets

Question 5

what is the T1/2 of platelets?

Answer 5

9-10 days

Question 6

what clears the platelets?

Answer 6

liver and spleen

Question 7

what is thrombopiotein?

Answer 7

primary regulator of platelet production

Question 8

what regulates the circulating levels of TPO?

Answer 8

clearance of TPO after it
binds to c-mpl receptors on
circulating platelets

Question 9

what is thrombocytopenia?

Answer 9

Thrombocytopenia is a medical condition characterized by a lower than normal number of platelets in the bloodstream.

Question 10

what is the treatment for thrombocytopenia?

Answer 10

TPO receptor agonist

Question 11

outline the structure of platelets?

Answer 11

Extremely small
(3um by 0.5um)
* High level in
circulation-range
150-400x109
platelets/l
* discoid
* anucleate cells
but have distinct
mitochondria

Question 12

what maintains the discoid shape of platelets?

Answer 12

cytoskeleton
* protects the cell from getting sheared in the blood stream

Question 13

what are the 3 types of platelet storage granules?

Answer 13

• alpha granules
• dense granules
• lysosomes

Question 14

how does platelet promote hemostasis?

Answer 14

-Adhesion to sites of vascular injury
* Granule release
* Aggregation to form a platelet plug, and
* providing a procoagulant surface for activated CF on their phospholipid surfacemembrane

Question 15

what makes platelets active following damage to the vessel wall?

Answer 15

thrombin

Question 16

what is the initial step in platelet activation?

Answer 16

platelet adhesion to subendothelium (collagen, VWF)

Question 17

what mediates adhesion

Answer 17

membrane GP receptors
* expressed by platelets

Question 18

where do vwf bind to on platelet?

Answer 18

glycoprotein Ib/ IX/ V at high shear rates

Question 19

when do platelets release their content?

Answer 19

upon activation

Question 20

what are the examples of alpha granules?

Answer 20

• coagulation factors: fibrinogen, vwf, factor v
• growth factors
• membrane proteins

Question 21

what are the e.g. of dense granules?

Answer 21

ATP, ADP, Ca, serotonin