Page 174 - 84 human physiolofy part-1

Chapter 9

immediate hypersensitivity include bee stings, pollen and certain foods. Allergies that cause chronic
allergic rhinitis and asthma are highly due to dust mites (dermatophgoides). It is not their bodies that
cause the reaction, but rather it's feces. Allergic attacks usually stop when the histamine has been
depleted. This can be stopped faster with an antihistamine drug or nasal spray.

What happens in a delayed hypersensitivity? It could take hours or days for symptoms to occur in a
delayed hypersensitivity. Delayed hypersensitivity is cell mediated with a T lymphocyte response.
Secretion of lymphokines, instead of histamine, happens in a delayed hypersensitivity. So, the
treatment would be a corticosteroid instead of an antihistamine. Examples of a delayed hypersensitivity
would be, poison sumac, poison oak and poison ivy. Skin tests for certain diseases are also considered
examples like TB test and the Mantoux test.

Infectious Organisms and Immunization

Beneficial Organisms

Intestinal bacteria

• Bacteria are prokaryotic (before nucleus) cells that we see usually as bacilli (rods) or cocci
(spheres). While they are the major cause of many diseases both fatal and mild, bacteria are also
our friends and can be of great service to us. Many bacteria in our bodies help prevent
pathogens from becoming established. "Good bacteria" helps protect us from "bad bacteria".
The large intestine is packed with normal microflora that digest substances otherwise
indigestible. This process provides our bodies with additional vitamins, fatty acids and
nutrients. Another example is the microflora that is in the vagina that helps maintain an acidic
pH, which discourages the growth of infectious organisms. These are examples of our immune
system's first line of defense.

Harmful Organisms

Viruses

• Viruses are non-living particles consisting of protein and nucleic acid that infect cells in
biological organisms. They can reproduce only by invading and taking over other cells as they
lack the cellular machinery for self reproduction. A virus is about ten times smaller than a
bacteria. Some viruses you will recognize are: influenza, herpes, measles, and the common cold.
Some viruses are particularly dangerous because they can undergo a period of latency, during
which they are hidden in the cell and do not reproduce. Influenza and HIV are examples of
viruses that frequently mutate, thus making it nearly impossible to achieve a long-lasting
immunity.

Bacteria

• Bacteria can be deadly. They are the major cause of preventable infections and death. Some
well known illnesses are caused by bacteria: staph infections, strep infections, tuberculosis,
food poisoning, tetanus, leprosy, and pneumonia. Because bacterial cells are different from

174 | Human Physiology