the process that stops bleeding while keeping blood fluid in the vessels
hemostasis
form a barrier → stop blood loss
maintain blood flow → prevent unnecessary clotting
what are the key cellular elements of hemostasis and the plasma components
● Key cellular elements of hemostasis
1. Cells of the vascular intima
[inner lining of blood vessels; help start clotting]
2. Extravascular tissue factor (TF)
[protein outside blood vessels that triggers clotting when a vessel is injured]
3. Platelets
[stick to damaged sites and form a temporary plug]
● Plasma components:
1. Coagulation factors
[proteins in plasma that trigger a cascade to form fibrin clot]
2. Fibrinolytic proteins and their inhibitors
[break down clots after healing and regulate clotting]
[cells start the plug → plasma makes the clot → fibrinolysis cleans up]
hemostatic mechanism
(trans)
1️⃣ Primary Hemostasis – Platelet Plug Formation
- First step after a blood vessel injury
- Platelets stick to the damaged vessel wall
= temporary “platelet plug” to slow down bleeding
💡 Think: “First responders – platelets arrive to stop the leak”
2️⃣ Secondary Hemostasis – Stable Fibrin Clot
- Strengthens the platelet plug
- Coagulation factors trigger a cascade → form fibrin threads
- Fibrin locks the platelets together → stable clot
💡 Think: “Construction crew – build a strong barrier”
3️⃣ Fibrinolysis – Clot Removal
- After healing, excess clot is removed
- Body dissolves clot via fibrinolytic system
- Without fibrinolysis:
Clot may persist
Can block blood vessels → cause heart attack, stroke, or thrombosis
💡 Think: “Cleanup crew – remove the clot after repair”
what are the components and end products in primary and secondary hemostasis
PRIMARY
Components
● Vascular system
● Platelets
End Product
● Platelet plug
SECONDARY
● Components
- coagulation factors
- intrinsic pathway
- extrinsic pathway
- coagulation pathway
● End product
- stable fibrin clot
First response to injured blood vessel
vasoconstriction
- narrowing of the lumen of the blood vessel which decreases the flow of blood in the injured vessel
- initiated by:
○ Serotonin
○ Thromboxane A2
steps in primary hemostasis
1️⃣ Vasoconstriction
- BV narrow to reduce blood flow
- Helps limit blood loss immediately
💡 Think: “Vessel squeezes to slow the leak”
2️⃣ Formation of Primary Hemostatic Plug
- Platelets arrive at injury site
- Stick together and start forming a temporary plug
💡 Think: “First barrier to stop bleeding”
3️⃣ Platelet Adhesion
- Platelets stick to exposed collagen in the damaged vessel wall
- Von Willebrand Factor (vWF) helps platelets attach
💡 Think: “Platelets anchor themselves to the wall”
4️⃣ Platelet Activation
- Platelets change shape → spiky projections
- Release chemical signals to attract more platelets
- Activate GP IIb-IIIa receptors for aggregation
💡 Think: “Platelets wake up and call for backup”
5️⃣ Secretion (Platelet Granule Release)
- Platelets release granule contents:
- ADP → recruits more platelets
- Serotonin → vasoconstriction
- Calcium → helps clotting
- Alpha & dense granules contribute
💡 Think: “Platelets throw out supplies to reinforce the plug”
6️⃣ Platelet Aggregation
- Platelets stick to each other using fibrinogen + GP IIb-IIIa
- Form a stable primary platelet plug
💡 Think: “Platelets hold hands to form a plug”
disorders of platelet adhesion and platelet aggregation
ADHESION
1. Bernard Soulier Syndrome
- GP1b / IX / V receptor is absent
- von Willebrand Disease
- vWF is absent or defective
AGGREGATION
1. Afibrinogenemia
- Fibrinogen is absent
2. Glanzmann Thrombasthenia
- GPIIb-IIa receptor is absent
what triggers platelet adhesion
trauma to the BV wall exposes
subendothelial collagen and tissue factor
- ability of platelets to bind to non-platelet surfaces like subendothelial collagen
- occurs in the presence of von Willebrand Factor, vWF links platelet to collagen through GP-Ib/IX/V
(glycoprotein)
vWF digits subendothelial cells to
GP-Ib/IX/V
thromboxane pathway
transes
it is when morphologic and functional changes in platelets
platelet activation
this inhibits the enzyme cyclooxygenase
aspirin
[which prevents formation of thromboxane A2 which normally helps plt stick tgt
aspirin → blocks COX → platelets don’t stick as easily]
Release of platelet granules during adhesion and aggregation
secretion
Platelet attachment to each other
platelet aggregation
- requires
Fibrinogen
■ GPIIb-IIIa: receptor for fibrinogen
■ links two glycoproteins to form
platelet clot
Calcium
■ helps the aggregation process
laboratory tests for primary hemostasis
● Platelet cont
[measure no. of plt]
● Bleeding time
[checks how quickly bleeding stops]
● Platelet adhesion and platelet aggregation test
[see how well plt sticks tgt and to vessel wall]
● Capillary fragility test
[test BV strength, how easily small vessels break]
● Clot retraction time
[measures how well plt contract to tighten the clot]
briefly explain the different platelet count methods
MANUAL PLATELET METHOD
1. Indirect method
(Blood smear)
○ Platelet count estimate, look at stained smear under microscope
○ example: Fonio’s methods
- Direct method
(counts in counting chamber)
○ Rees-Ecker method
○ Unopette System
○ Brecher-Cronkite method
AUTOMATED PLATELET METHOD
1. Indirect manual count
- Platelet count estimate (Qualitative test)
- Stain: Giemsa/Wright stain
[Manual = look & count
Automated = machine counts]
principle of automated platelet method
Voltage pulse counting or electro optical counting
[plt pass → signal changes → machine counts]
steps in manual platelet method in indirect manual count
(qualitative)
Purpose: Estimate platelet count under the microscope
Stain: Giemsa or Wright stain
Steps:
1. Prepare a blood smear
2. Choose a portion of the smear
3. Count platelets in 10 fields using the battlement pattern
- move across the smear like a zig-zag
4. Calculate average:
Average platelets per field
= Total platelets counted in 10 fields/10 x 20,000
**use battlement pattern to ensure coverage of the smear
- manual count is less accurate than automated but useful if machine is not available
range of platelets estimate
(trans)
formula used if the patient is anemic or has erythrocytosis
(trans)
○ 200 is the average number of RBCs per oil immersion field
Fonio’s Method
Diluting Fluid: 14% Magnesium Sulfate
Stain: Wright Stain
Dilution: 1:5
Computation: (trans)
steps when doing fonio’s method
- Place a large drop of diluting fluid on the site of puncture. Then press blood from the puncture site.
- Mix one-part blood and five parts magnesium sulfate
- Make a smear using the mixture.
- Allow the smear to dry, then apply staining fluid.
- Examine under OIO and count the platelets until 1,000 RBCs are counted.
briefly explain the direct manual count
1. Rees - Ecker Method
2. Unopette system
3. Brecher and Cronkite Method (Reference method)
(trans - table)
Rees-Ecker method and Unopette system/ Brecher-Cronkite method computation
(trans)
*shortcut for rees-ecker method
𝑃𝑙𝑎𝑡𝑒𝑙𝑒𝑡 𝑐𝑜𝑢𝑛𝑡 = 𝑐𝑒𝑙𝑙𝑠 𝑐𝑜𝑢𝑛𝑡𝑒𝑑 × 2000
For Unopette System / Brecher Cronkite method
- if fewer than 50 platelets are counted on each side, a 1:20 dilution should be made
- if more than 500 platelets are counted on each side, 1:200 dilution should be made
Rees-Ecker Method
preparation:
charging:
manual counting:
post analytical phase:
(trans)
