1. Describe the steps of blood clotting
- A blood clot functions to seal a wound injured, preventing further invasions by bacteria.
- Clotting begins when the wall of a blood vessel is damaged. There are many different clotting factors involved including; platelets, prothrombin, and fibrinogen.
- Platelets are produced in the bone marrow at a rate of 200 billion a day; the bloodstream carries more than a trillion.
- Fibrinogen and prothrombin are proteins manufactured and deposited in blood by the liver.
- Vitamin K is necessary for the production of prothrombin.
- When a blood vessel is damaged, platelets clump at the site of the puncture and partially seal the leak.
- The platelets and the damaged tissues release a clotting factor called thrombokinase, which converts prothrombin to thrombin. This reaction requires calcium ions.
- Thrombin, in turn, acts as an enzyme that severs 2 short amino acid chains from each fibrinogen molecule. These activated fragments then join end to end, forming long threads of fibrin, which is insoluble.
- Fibrin threads wind around the platelet plug in the damaged area of the blood vessel and red blood cells get trapped within the fibrin threads, making the clot appear red.
2. Outline the immune response to an antigen
An antibody response is the culmination of a series of interactions between macrophages, T lymphocytes and B lymphocytes. Antigens are engulfed by antigen presenting cells (APC i.e. macrophages, Langerhans cells, dendritic cells, lymph nodes and monocytes), then they are partially degraded. Fragments of the antigen will appear on the surface of the APC attached to a cell surface glycoprotein known as MHC II (major histocompatibility complex). There are two types of MHC molecules: MHC class I which are expressed on the surfaces of most cells and class II which are expressed exclusively on the surfaces of antigen presenting cells. This antigen-MHC II complex allows helper T cells to bind to the APC which leads to a proliferation of helper T cells. The T cells then bind to the MHC complex on B cells which leads to proliferation and differentiation of the B cells. The B cells change into plasma cells which secrete large quantities of finely tuned antibodies. Some B cells are changed into memory cells which are primed for future challenges.
3. Discuss Active v Passive Immunity
These are two categories of immunity that exist. There are really only these two.
Active immunity is immunity that occurs when YOUR BODY makes the antibodies. That is, if you get strep throat, your body makes antibodies for streptococcus whatever. You will be resistant to this bacteria for years, maybe you'll never get sick from it again. The same goes for illnesses like chicken pox, the flu, and many colds.
Active immunity is also attained by receiving a vaccine. A dead or attenuated virus is injected in your bloodstream and you make antibodies.
Passive immunity is attained 2 ways. First, is that when you're born, you receive antibodies from your mother, actually most frequently from breast milk. Another way is to receive an antibody serum, called an "antidote" in movies...this treatment exists, but is rare and impractical.
Active immunity lasts for years and years. Sometimes an entire lifetime. Other times, you do need booster shots. Passive immunity lasts for a few months at best, as your body is not continuously making these.
Passive immunity can help in an emergency, but such emergencies are rare. Active immunity, if you have the time to allow antibodies to be built up (weeks to months after your first shot), then this is the best method.
