PHYSIOLOGY

Physiology

Physiology

Q. Discuss how a person becomes immune to certain diseases after they have been exposed to it. In what way does a vaccine work to prevent an infection?

Ans.

The immune system is a defense system that protects invertebrate and vertebrate animals from microorganisms and substances recognised as foreign and potentially harmful (Goldsby, Kindt, Osborne & Kuby 2003, 7-15). It evolved through a gradual process of increasing diversification that led to the enormous complexity of recognition and elimination mechanisms present in higher vertebrates. These recognition and elimination mechanisms operate and cooperate within the two components of the immune system—that is, the innate immune system and the adaptive immune system, thus leading to immune responses that protect the body from infectious diseases and cancer. Recognition mechanisms allow the detection of foreign organisms and molecules as well as cancer cells through binding by receptors expressed on the cell surface of certain cells of the immune system.

The specific portion of the foreign invader that is detected by the recognition mechanisms is called antigen. Elimination mechanisms are responsible for the destruction of foreign invaders and cancer through the action of specialised cell types. The complement system, a set of plasma proteins, is also involved in destroying foreign invaders. Innate and adaptive immune responses rely on the activity of white blood cells, or leukocytes. Innate immune responses represent the first line of defenses, exist prior to exposure to a pathogen, are nonspecific, occur in a few hours or days, and involve the participation of two major types of leukocytes—neutrophils and macrophages—which are phagocytic cells able to take up and destroy foreign invaders.

Adaptive immune responses develop several days after encounter with the pathogen, are specific, include the development of immunological memory, and require the participation of two types of lymphocytes: B and T lymphocytes.

Vaccination is a process that artificially confers immunity to an individual against a specific type of disease caused by infectious microorganisms (viruses, bacteria, fungi, or parasites). Vaccines work by using the body's ability to remember previous infections. When an individual becomes infected by an infectious organism for the first time, the immune system recognises and then destroys it by mounting an immune response specific for that organism. Upon an individual's second exposure to the same microorganism, the immune system recognises and eliminates it by mounting immune responses that occur more rapidly and are greater in magnitude than those induced on the first encounter. Thus, the infection will not develop to a severe level or to the disease stage. This ability to remember infections, called immune memory, allows people to become immune to a disease after they have caught it once. A vaccine simulates that first infection by exposing an individual to a particular microorganism or portions of that microorganism without causing infection and illness. There are several disease-causing microbes for which vaccines exist. Thus, these diseases can be prevented.

Q. How does the body physiologically respond to stress? What effect does long term stress have on health?

Ans.

Stress has been conceptualised in a number of ways ...