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What is the function and macrostructure of the lymphatic system?
 
  What will be an ideal response?

Question 2

Describe the series of events that occurs during a normal clotting mechanism. How is this interrupted in persons with hemophilia A?
 
  What will be an ideal response?

Answer to q. 1

The lymphatic system collects extracellular fluid and returns it to the venous system via a series of lymph capillaries and larger lymph vessels. Lymph vessels have valves to prevent backward flow. Lymph nodes occur at intervals along the lymph vessels, and are populated with white blood cells, which monitor the fluid (the lymph), for foreign cells or debris. The lymphatic system also consists of lymph organs, two of which are the thymus and the spleen. The thymus is involved in the immune system, and the spleen has several functions: to filter blood, produce some white blood cells, and store platelets and other blood cells.

Answer to q. 2

After there is a break in a blood vessel, the vessel itself constricts by the action of smooth muscle cells in the walls of the vessel. Platelets release seratonin that results in the muscular contraction. Platelets also stick to the inside of the vessel, beginning the clot formation. Then the injured cells release activators, which cause prothrombin to be converted into thrombin, which is an enzyme that changes fibrinogen (normally circulating in the blood) to fibrin. Fibrin is a tough insoluble fibrous protein. These create the blood clot. Persons with hemophilia A lack a gene that produces one of the proteins in this series of steps, and therefore lack normal clotting mechanisms.

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