H em ostatic m echanism s involved in p rev en tin g b lo o d loss • Figure 10.7
Three processes that prevent blood loss—a. vascular
spasm, b. platelet plug formation, and c. blood clotting—
occur on the order of seconds to minutes after damage to
a blood vessel. Each varies in its effectiveness, depending
on the extent of the damage.
Immediate
Damage to blood vessel
Seconds to minutes
a.
Vascular spasm
• Smooth muscles in the
vessel wall contract,
thereby reducing blood
flow and loss.
• Vascular spasm lasts
minutes to hours.
Blood
Artery
spasm
b. Platelet plug formation can temporarily stop
blood loss completely if the hole in the vessel is
small enough.
Red blood cell
Platelet \ P
.Collagen fibers
;and damaged
endothelium
Platelets stick to collagen fibers at
damage site.
'Liberated ADP
serotonin, and
thromboxane A2
Platelets secrete chemicals (ADP,
serotonin, thromboxane A2) to
activate nearby platelets.
Activated platelets stick together
to form a plug that blocks blood
flow in the vessel.
c.
Clotting - Blood clot forms and seals the wound.
PROTHROMBINASE
0
The enzyme
prothrombinase
2+
is formed.
Ca2+
PROTHROMBIN
THROMBIN
t
FIBRINOGEN
Prothrombinase
along with Ca2+
converts a plasma
protein,
prothrombin
into
thrombin
.
Thrombin
converts plasma
protein
fibrinogen
into
fibrin. Fibrin forms
threads, traps blood cells,
and forms blood clot.
Loose FIBRIN threads------► Strengthened fibrin threads
Red blood cell
Fibrin threads
(SOM i600x
When several small blood vessels in the skin get cut
with a sharp knife, what is the first event that leads to
hemostasis and eventual repair of the damage?
a. Platelet plug forms.
b. Common pathway occurs.
c. Vascular spasm occurs.
d. Fibrin clot is created.
PROCESS DIAGRAM
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