Coag Part 1/3

Add bulk and structural integrity to final fibrin clot

Help stimulate wound healting
Mono and lymphs can have tissue factor on surface that can trigger coagulation

Procoagulant only — initiate and control hemostasis

Do not prevent clotting or breakdown;
only adhere, aggregate, and secrete their granule contents to help form clot

Vasoconstriction and platelet plug formation

Megakaryocytes (MK) through Endomitosis

Largest cells in BM (30-50 um)
multilobulated nucleus
hypergrnaular cytoplasm
polyploid (multiple copies of xsomes)

CFU-FEMM under the influence of IL-3, TPO and Meg-CSF

BFU-meg (clones hundreds daughters)
CFU-meg (clones dozens daughters)
LD-CFU-meg (undergoes first stage of endomitosis)

Without cell division

MKs become polyploid
most have ploidy of 16N (range 4N-64N)
MK progenitors enter terminal diff stages as proliferation continues

MKs (largest normally occurring cells in marrow 30-100 um)

More DNA = larger cell or more cytoplasm synthesized = more platelets

MK 8N or 16N can produce 2000-4000 platelets

TPO
MEG-CSF
IL-3

Kidney
also by liver and smooth muscle cells

Attached to circulating platelets via membrane receptor

Increase circulating TPO
stimulates plt production

50-80/plt

Contain proteins
(fibrinogen, factor V, vWF, B-thromboglobulin, HMWK, PAI-1, plasminogen)

2-7/plt

ADP, ATP, serotonin, Ca2+, Mg2+

Complex, metabolically active cells that interact with their environment
initial and control hemostasis

Adhesion (to site of injury)
aggregation (with ea other)
secretion (of granule content)

Plts bind collagen directly through GPVI and GPIa/IIa or indirectly through vWF (which binds GPIb/IX/V on plts)
ADP, TXA2, inside out outside in signaling

(Key step)
plts bind to each other through GPIIb/IIa, shape change, membrane PL flip-flopping

Plts release granular contents (alpha and dense)
mostly coat proteins
launching platform for secondary hemostasis

Platelet or vascular abnormalities

qualitative or quantitative
congenital or acquired
manifest as mucocutaneous bleeding

Bruising
petechiae
purpura
ecchymosis
epistaxis
gingival bleeding

Reactive thrombocytosis (2ndary to other conditions)
myeloproliferative disorders

Post surgery, post splenectomy, IDA, inflammation or disease, strenuous exervise

Not associated with thrombosis or hemorrhage

Disappears when underlying condition is under control

Essential thrombocytosis, polycythemia Vera, CML, or primary myelofibrosis

Thrombosis or bleeding

Marked and persistent elevations in plt counts

By plt count of <150x109/L

Thrombosis or bleeding <100x109/L

1. Imparted/decreased plt production
2. Increased/accelerated platelet destruction
3. Abnormal plt distribution or dilution

Lack of adequate BM MK
ineffective thrombopoiesis

Caused by immunologic responses
caused by mechanical dmg, consumption, or sequestration

Splenic sequestration due to splenomegaly - abnormal sequestration

Acute and chronic immune thrombocytopenia purpura
drug induced immunologic
heparin induced
neonatal alloimmune/autoimmune
post transfusion purpura
secondary autoimmune

Gestation
human immunodeficiency virus
HDFN
microangiopathies (TTP, HUS, aHUS)
DIC
Bacterial infection
drug induced

Splenic sequestion
Kasabach-Merritt syndrome
hypothermia
loss of plt: massive blood transfusions, extracorporeal circulation

Rare disorder of plt adheion

Autosomal recessive inheritance
(Discovered in early childhood)

Ecchymosis, epistaxis,and gingival bleeding

Mutation in GPIba of the GP Ib/IX/V receptor complex (vWFR)

Defective plt adhesion

Thrombocytopenia
giant plt
aggregometry: normal response to ADP, collagen, thrombin, epinephrine, AA but lack of aggregation in response to ristocetin)

Autosomal dominant disorder

Thrombocytopenia
characteristic abnormally enlarged or misshapen plts

Thrombocytopenia with giant plts
basophillic inclusions (Dohle bodies) within granulocytes and occasioanl monocytes)

Normal

Giant plt syndrome

Shift right ???

Bleeding time (old)
PFA-100 analyzers (auto plt function test)
Plt aggregometry studies (measures how well plt aggregate together)

Automated system for analyzing plt aggregation

Citrate whole blood aspirated at high shear rates through disposable test cartridge

Contains 2 membranes: one coated collagen/epinephrine (CEPI) and the other one coated in collagen/ADP (CADP) and an aperture

Agonists induce plt adhesion, activation, and aggregation

Time req for a plt to plug to occlude aperture

For inherited, acquired, or drug-induced plt dysfunction

Desmopressin (DDAVP) therapy in pre-surgical pts
platelet dysfunction due to Aspirin
initial screening for impaired primary hemostasis

Antidiuretic drug that releases VWF from the cells as a side effect in order to assist with any mucocutaneous bleeding

measures how well plts aggregate together to form clots

must NOT activate plt
use larger bore needle

spin low to produce plt rich plasma (PRP)

Spin low to produe PRP
Allow plt to regain function (sit for 30 min)
test within 4 hrs to avoid in vitro plt activation & loss of normal activity

chilling
samples need to be held at 15-25C until testing

PRP in ccuvette with plasticized magnetic stir bar
keeps plt in suspension at 800-1200 rpm (gentle)
warm for 37C for 5 mins

photometer directs light through cuvette to photodetector

high
baseline = 0% light transmission

platelets shape change, start aggregating, and form large aggregates (all increasing %T to eventually 100%T)

1. resting plt (stable)
2. shape change
3. primary aggregation
4. secretion
5. secondary aggregation

plts contain defective or low GPIIb/Iia (fibrinogen receptor)

DECREASE ADP, collagen, epinephrine, arachidonic acid, thrombin
NORMAL Risocetin

NORMAL ADP, collagen, epinephrine, arachidonic acid
DECREASE thrombin
DECREASE Ristocetin

prolonged bleeding time or abnormal PFA-100
decreased plt aggregation to some agonists