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Biology 2108 Lecture
Physiology:
Immune System 


A very powerful set of weapons that hence require very sophisticated, complex regulation.

 
Three lines of defense:

First Line of Defense - External Defenses of the Innate Immunity: Barriers preventing disease-causing organisms (DCO) from entering the body

What is the most obvious barrier and why is this insufficient?

Secretion such as sweat also have low pH and contain the enzyme lysozyme.

What aspects of the digestive and respiratory systems might serve as a first line of defense?
    

The pH of the female reproductive tract is also slightly acidic.  How do sperm survive there?



Second Line of Defense- Internal Defenses of the Innate Immunity: Responses to cells that are not recognized as self
Examples:
Histamine release and temperature response.  Are runny noses and fever, in themselves, a bad thing?

Phagocytes
(leukocytes including neutrophils, monocytes, and eosinophils)
destroy foriegn cells in various ways including engulfing and by secreting lysosomal enzymes.



Leukocytes in general must be able to distinguish cells of the body (self) from cells of disease-causing organisms.  Why?

Immune cells repond to any cells WITHOUT the set of surface proteins (major histocompatibility markers) on the cell membrane unique to all cells of the body in each individual.


i.e. These proteins mark cells of the body  as SELF, analogous to a military uniform used to identify one's own countryman.





There are over 100 different forms (alleles) of MHC in the human population.

Why is it likely that a transplanted tissue is will be rejected unless the donor and recipient are closely related? 








What would be a more effective weapon: one that is designed to combat anything that is recognized as foreign, or one that is designed to combat a specific invading threat?


Third Line of Defense- Acquired Immunity: Specific responses to specific threats

Lymphocytes (another type of leukocyte) -  B cells and T cells 



What to understand about the diagram above:

What if only the antigen of a disease-causing organism were presented to the immune system?


When Europeans colonized the America's, European diseases devastated Native American populations, but few if any major diseases crossed the Altantic in the opposite directions.  Why was the transfer of diseases so one-sided?
   
                                                        http://www.cdc.gov/flu/avian/      


The Big Picture: The body must use immune weapons carefully, balancing power with caution. 
Ability to recognize abnormal cells: