Page 511 - Clinical Hematology_ Theory _ Procedures ( PDFDrive )

CHAPTER 25 ■ Principles of Hemostasis and Thrombosis: Vasculature and Platelets 495

ch nnels o the open c n licul r syste n ense tubul r

syste ppe r to constitute the c lciu -regul ting ech -

nis o the cell.

Micro lam ents and Microtubules

Directly bene th the cell e br ne is series o sub e -

br ne f l ents n icrotubules th t or the cellul r

cytoskeleton. In ition to provi ing the structure or

int ining the circul ting iscoi sh pe o the cell, the

cytoskeleton lso int ins the position o the org nelles. A

secon ry syste o icrof l ents is unction l in inter-

n l org niz tion n secretion o bloo co gul tion pro -

ucts, such s f brinogen. T e icrof l ents inter ct with the

ense tubul r syste in sequestering c lciu , which initi lly

c uses centr liz tion o intern l org nelles. T ese subcellu-

l r n cytopl s ic f l ents ke up the contr ctile syste

FIGURE 25.6 Pl telet with its inventory o gr nul r content. (ADP, (sol gel zone) o the pl telet.

enosine iphosph te; A P, enosine triphosph te; FV, ctor V;
GPIb, pl telet sur ce glycoprotein Ib; PDGF, pl telet- erive Granules

growth ctor; PF4, pl telet ctor 4; GF-β, tr ns or ing growth

ctor-β; vW , von Willebr n ctor.) (Reprinte ro Koop n T ree i erent types o stor ge gr nules rel te to he ost -
WJ, Morel n LW. Arthritis and Allied Conditions: A extbook o sis re present in the ture pl telet. T ese gr nules re alpha

Rheumatology, 15th e , Phil elphi , PA: Lippincott Willi s & granules, dense granules or delta granules, n lysosomes.

Wilkins, 2005, with per ission.) Te lph gr nules re the ost bun nt. Alph gr n-
ules cont in hep rin-neutr lizing pl telet ctor 4 (PF 4),

bet -thro boglobulin, pl telet- erive growth ctor, pl te-
The Glycocalyx
let f brinogen, f bronectin, vWF, n thro bospon in.

Ultr structure ex in tion o the pl telet (Fig. 25.6) reve ls Dense bo ies, n e bec use o their ppe r nce when

th t the cellul r e br ne is surroun e extern lly by viewe by electron icroscopy, cont in serotonin, enosine

u y co t or glycocalyx. T is glycoc lyx is unique ong the iphosph te (ADP), enosine triphosph te (A P), n c l-

cellul r co ponents o the bloo . It is co pose o pl s ciu . Lysoso es, the thir type o gr nule, store hy rol se

proteins n c rbohy r te olecules th t re rel te to the enzy es. Extrusion o the contents o these stor ge gr nules

co gul tion, co ple ent, n f brinolytic syste s. T e GP requires intern l, cellul r contr ction. Secretions ro the

receptors o the glycoc lyx e i te the e br ne cont ct gr nules re rele se into the open c n licul r syste .

re ctions o pl telet herence, ch nge o cellul r sh pe,

intern l contr ction, n ggreg tion. Other Cytoplasm ic Constituents

In ition to cont ining subst nti l qu ntities o the con-
Cytoplasm ic Mem brane
tr ctile proteins, inclu ing cto yosin (thro bosthenin),
A j cent to the glycoc lyx is the cytopl s ic e br ne yosin, n f l in, the cytopl s o the pl telet cont ins

whose che ic l co position n physic l structure. glycogen n enzy es o the glycolytic n hexose p thw ys.

Exten ing through the pl s e br ne n into the Energy or et bolic ctivities n cellul r contr ction is

interior o the pl telet is n open c n licul r or sur ce- erive ro erobic et bolis in the itochon ri n

connecting syste . It is this syste th t or s the inv gi- n erobic glycolysis–utilizing glycogen stores. T e pl telet is

n te , sponge-like portion o the cell th t provi es n very high-energy cell with et bolic r te 10 ti es th t o

exp n e re ctive sur ce to which pl s clotting ctors n erythrocyte. B se on energy v il bility n en ogenous

re selectively sorbe . Cont ct ctiv tion o the e br ne constituents, the pl telet is e ectively equippe to ulf ll the

phospholipi s lso gener tes proco gul nt ctivity n r - role o protecting the bo y g inst v scul r tr u .

chi onic ci to the bloo -clotting process. T e cytopl s ic

e br ne n open c n licul r e br ne syste rticul te Platelet Kinetics, Life Span, and Normal

with the ense tubul r syste th t is not sur ce connecte . Reference Values

Although the c n liculi penetr te the cytopl s in r n-

o nner, they re gener lly in close proxi ity to gr n- An ver ge eg k ryocyte pro uces bout 1,000 to 2,000

ules n other org nelles. T ere ore, pro ucts rele se by pl telets. M rrow tr nsit ti e, or the tur tion perio o

the gr nules or cytopl s c n be tr nsporte to the exte- the eg k ryocyte, is pproxi tely 5 ys.

rior environ ent through the c n liculi. In ition to the It is believe th t pl telets initi lly enter the spleen, where

ove ent o extr cellul r teri ls g inst the concentr - they re in or 2 ys. Following this perio , pl telets re

tion gr ient through the c n liculi, ph gocytosis is lso in either the circul ting bloo or the ctive splenic pool. At

likely to occur through these ch nnels. A ition lly, the ll ti es, pproxi tely two thir s o the tot l nu ber o