1. Blood Clotting
Robin Gray

2. Blood Clotting AKA CoagulationTQ
Cardiovascular System
Not necessarily a “balancing” effect
It prevents massive blood loss
Hemostatis – the cessation of blood loss from a damaged vessel TQ

3. Organs and Cells Involved
Veins and arteries
Vessel sides
Red blood cells
Platelets
Fibrinogen  fibrin fibers (active form) TQ

4. Causes of Imbalance TQ Upward Downward Cuts Bruises
Any damage to the endothelium of a vessel and connective tissue is exposed to the blood
Downward
When the connective tissue is no longer touching the blood, the process stops
Local fibrinogen stops converting to fibrin because thrombin is no longer produced from clotting factors

5. Maintaining HomeostasisTQ
Vascular constriction occurs first to restrict blood to the site
Platelets, activated by thrombin, form a temporary platelet plug
A fibrin mesh (the clot) forms and entraps the plug
If it’s only platelets  white thrombus
With red blood cells  red thrombus
The clot is dissolved through plasmin TQ TQ TQ

6. Maintaining Homeostasis
Upon vessel injury, platelets adhere to macromolecules in the subendothelial tissues and then aggregate to form the primary hemostatic plug.
The platelets stimulate local activation of plasma coagulation factors, leading to generation of a fibrin clot that reinforces the platelet aggregate.
Later, as wound healing occurs, the platelet aggregate and fibrin clot are broken down.
Mechanisms that restrict formation of platelet aggregates and fibrin clots to sites of injury are necessary to maintain the fluidity of the blood. TQ

7. Maintaining Homeostasis
Fibrin clot formation in response to tissue injury is the most clinically relevant event of hemostasis under normal physiological conditions. This process is the result of the activation of the extrinsic pathway.
The formation of a red thrombus or a clot in response to an abnormal vessel wall in the absence of tissue injury is the result of the intrinsic pathway. The intrinsic pathway has low significance.
Kaolin
Phospholipids (PL)
Calcium
Thromboplastin
(Tissue Factor + PL)
CLOT
Intrinsic Pathway
aPTT prolonged
Extrinsic Pathway
PT prolonged
Common Pathway
aPTT and PT prolonged

8. Negative Feedback Mechanism
In order for coagulation to start connective tissue must be exposed to the blood
Platelets adhere to collagen fibers in the connective tissue and release a substance that makes nearby platelets sticky
Once connective tissue is no longer exposed to the blood the process ends

9. Positive Feedback Mechanism
Blood clotting is more true to a positive feedback mechanism in general
When a blood vessel is injured, platelets start accumulating at the site
Positive feedback occurs as chemicals released by the platelets attract more platelets and the platelet cluster initiates a sequence of chemical reactions that seals the wound with a clot

10. Without Homeostasis… TQ
An inherited defect in any step of the clotting process causes hemophilia, a disease characterized by excessive bleeding from even minor cuts and bruises
Without coagulation, even a minor cut would cause an individual to bleed to death TQ

11. Summary …