HEMOSTASIS
 Hemostasis: (Stoppage of blood flow after damage)

A break in a blood vessel stimulates hemostasis, a fast, localized response to
reduce blood loss through clotting.
1. Vascular spasms are the immediate vasoconstriction response to blood vessel
injury slows the flow of blood and thus helps to limit blood loss.
2. Platelet Plug Formation: When a blood vessel is damaged, the blood is
exposed to collagen fibers in the basement membrane of the vessel and the
platelets become sticky and spiky, adhering to each other and the damaged vessel
wall. Once attached, other platelets are attracted to the site of injury, activating a
positive feedback loop for clot formation.
3. Coagulation, or blood clotting, is a multi-step process (clotting cascade) in
which blood is transformed from a liquid to a gel. Factors that promote clotting are
called clotting factors (These factors are proteins that exist in the blood in an
inactive state), those that inhibit clot formation are called anticoagulants.
Physiology (GRPS-101) Practical notes
Freshmen 2011 - 2012

Clotting of Blood
Blood clotting is the transformation of liquid blood into a semisolid gel. Clots are
made from fibers (polymers) of a protein called fibrin (see the diagram below).
Fibrin monomers come from an inactive precursor called fibrinogen. This
process requires thrombin, the enzyme that converts fibrinogen to fibrin. This
process also requires calcium, which acts as a kind of glue to hold the fibrin
monomers to each other to form the polymeric fiber. The fibrin fibers form a
loose meshwork that is stabilized by clotting factor XIII. The stabilized
meshwork of fibrin fibers traps erythrocytes, thus forming a clot that stops the
flow of blood.
Clotting is initiated by two pathways i.e intrinsic pathway and extrinsic pathway.
 Intrinsic Pathway: which is triggered by elements that lie within the blood
inself (intrinsic to the blood).
 Extrinsic Pathway is triggered by
tissue damage outside of the blood
vessel.


Clot Removal
The clot itself stimulates the secretion of
tissue plasminogen activator (TPA) from
the surrounding vascular epithelium. TPA
is an enzyme that catalyzes the conversion
of plasminogen to plasmin.
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Physiology (GRPS-101) Practical notes
Freshmen 2011 - 2012
Introduction
Hemostasis is the stopping of bleeding or blood flow through a blood vessel or
organ.
- The termination of bleeding by mechanical or chemical means or by the
complex coagulation process of the body, which consists of vasoconstriction,
platelet aggregation, and thrombin and fibrin synthesis.
Steps
Physiological - Red blood cells(RBCs)
status
- White blood cells (WBCs)
- Platelets
- Clotting factors (tiny proteins)
- All float in a liquid called
plasma
Platelets
adhesion
- When vessel wall torn open
blood begin to escape
Vessel contract as reaction to
damage to reduce flow of blood
( for few minutes )
- Platelets stick to the damaged
surfaces
- Platelets change shape
(become activated) , release
chemicals (cytokines) to draw
more platelets and keep vessels
contracted
Platelets
aggregation
Secondary hemostasis
hemostasis
Primary hemostasis
Bleeding
Form plug (loose platelets plug)
Exposed collagen and tissue
factors (protein– phospholipids
mixture ) imitate a series of
reaction (coagulation cascade )
Coagulation
The cascade is a series of
enzymatic reactions that ends in
the formation of a fibrin protein
fiber mesh that stabilizes the
platelet plug ( clot )
Eventually, as the damaged vessel repairs itself, the clot retracts and is slowly
dissolved by the enzyme plasmin.
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Physiology (GRPS-101) Practical notes
Freshmen 2011 - 2012
 Bleeding time
It is time interval between skin puncture (coming out of blood from vessel) and
cessation of flow of blood (the time taken from blood vessels construction and
platelets plug formation to occur)
To determine bleeding time
Equipments:
1. Disposable gloves
2. Sterile disposable lancet.
3. Filter paper
4. Stop watch
5. Cotton Swab
6. Alcohol Swab.
Procedure:
1. Keep ready filter paper. (With patient data
[name, Age, Sex, date of test, Name of test,
Method]) in corner of it. Neatly bordered.
3. Disinfect the ball of finger (or ear lobe) to be
pricked. Allow to dry.
4. Take a lancet, have deep skin puncture about 3-5
mm depth and immediately start the stop watch.
5. touch the blood with filter paper , repeat every
30 seconds.
6. Till there is no stain on filter paper stop the stop
watches.
7. Count and number the spots of blood on filter
paper.
8. Calculate and record bleeding time.
Result:
Bleeding time is ------ min ----- sec.
Normal bleeding time:
1 to 3 min
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Physiology (GRPS-101) Practical notes
Freshmen 2011 - 2012
 Clotting time
It is the time interval in between onset of bleeding and appearance of jelly like
semisolid mass i.e. blood clot.
To determine clotting time
Equipments:
1. Disposable gloves
2. Sterile disposable lancet.
3. Capillary tube or glass slide
4. Stop watch
5. Cotton Swab
6. Alcohol Swab.
Procedure:
 using glass slide:
1. Wear gloves
2. Disinfect the ball of finger to be pricked. Allow to dry.
3. Take a lancet, have deep skin puncture
about 3-5 mm depth and immediately
start the stop watch.
4. Put three full drops on the glass slide
5. After 30 seconds, using stopwatch, try
to pull fibrin thread from a blood drop on
the slide using new lancet or syringe
needle
6- Use new drop every 3 minutes
7. Repeat trying at regular time intervals 30 seconds), till fibrin thread appears
between the needle and slide.
8. Record time interval between pricking finger and first appearance of fibrin
thread. That is clotting time of blood.
Result:
Clotting time is ----- min ----- sec.
Normal clotting time:
4 to 9 mins
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