Question

If you cut your arm badly and lost a lot of blood, what local process(es) would take place at the site of the injury to stop the bleeding. Explain the three phases of this process.

In the same situation as the question above, how would your body replace the red blood cells that you lost? Provide 3 relevant pieces of information to obtain

Answer 1

3 phases of the process:

• Vasoconstriction
• Platelet plug formation
• Coagulation

Phase of vasoconstriction

• After , injury to the blood vessels, smooth muscle of blood vessels undergo spasm which causes vasoconstriction. Which decreases blood flow and prevents leakage from the vessels.  

Phase of platelet plug formation:

• Platelet wich flows in the plasma gets adhered to collagen in the ruptured blood vessel.
• Ater this they secrete thromboxane and adp wich cause more platelets recruitment to the site.
• all these platelets adhere each other at the injured vessel wall forming temporary platelet plug , which prevents further loss of blood .
• Platelets aggtegation is increased by paf ( platelet activating factor ).

Phase of coagulation :

• Coagulation of blood cause permanent platelet plug formation it involves 3 process
• Prothrombin activator formation
• Conversion of prothrombin to thrombin .
• conversion of fibrinogen to fibrin.

1). Prothrombin activator formation:

• It is by intrinsic or extrinsic pathway .
• In intrinsic pathway , during injury to blood vessel the collagen in blood vessel is exposed it activates prothrombin activator
• In extrinsic pathway surrounding tissue injury produce tissue thromboplastin wich activates prothrombin activator .

2). Prothrombin activator activates prothrombin to thrombin formation in presence of calcium ions

3). Thrombin then converts inactive fibrinogen to fibrin molecules wich form strong mesh like network , which prevents blood lekage .

How body replace blood loss , mainly rbc .

Following injury blood loss is maintained by stimulating adh secretion, which reabsorb water in the kidney and decrease urine production , to maintain the blood volume , the rbc in this blood will be low and dilute blood with low hematocrit is formed as compensation.  

Rbc is replaced by sensors in peritubular capillaries in kidney , which sense low hemoglobin concentrations and oxygen carrying capacity .

This then stimulates erythropoietin secretion from kidneys . An hormone for rbc production .

This erythropoietin travels through blood to bone marrow, where erythropoietic stem cells are present, this erythropoietin stimulates these stem cells causing rbc formation .

In our body excess iron is stored in muscles and liver in the form of ferritin , following blood loss these stores are stimulated and iron is used up for rbc formation , all thses process takes 4 to 8 weeks to produce the lost rbc .