Lesson 15- Barriers to Infection and Disease

First Line of Defense includes the skin and mucous membranes throughout the body that serve as physical or chemical barriers to infection and disease.

The skin contains numerous barriers to infection including: the close packing of epithelial cells making up the skin tissue, the acidic pH, salt production in sweat and the normal flora of the skin.

The eye contains mechanical barriers such as eyelashes and the eye lid as well as chemical barriers found in tears.

Ears contain hair and wax that serve as barriers to infection.

The Respiratory Tract contains mucous and cilia which serve as barriers as does the reflex of coughing and sneezing.

The Digestive Tract contains many chemicals that aid in the digestion of foreign substances and also contains a large population of normal flora.

The Circulatory System's ability to bleed and form blood clots serves as a barrier as well.

The Nervous System's blood-brain barrier is essential to protect the brain from infection.

The Urogenital System has sphincter muscles which serve as a physical barrier and urine of an acidic pH which acts as a chemical barrier to foreign invaders.

The liquid component of blood is known as plasma. It makes up 60% of the blood volume. The gamma globulin fraction of blood contains immunoglobulins or antibodies that are important in specific immunity.

Erythrocytes are the cells responsible for the oxygen-carrying capacity of blood.

Leukocytes are those cells important in non-specific and specific immunity.

Platlets are involved in blood clotting.

Neutrophils are circulating phagocytes. Eosinophils phagocytize parasites. Basophils initiate the inflammatory response as well as many allergic responses. Monocytes are phagocytes that can differentiate to become macrophages which are important in specific immunity. Lymphocytes also play a crucial role in the specific immune response

Organs of the lymphatic system contain lymphocytes absolutely critical to specific immunity, primarily the appendix and tonsils. Enlargement of these organs or of the lymph nodes are indicative that specific lymphocytes are responding to the presence of some foreign pathogen or tumor cells.

That specific lymphocytes are responding to the presence of some foreign pathogen or tumor cells

It is a type of non-specific immunity that occurs in response to tissue damage as a result of injury or infection.

Calor (heat), rubor (redness), tumor (swelling) and dolor (pain).

Histamine production by basophils which stimulates vasodilation(increased blood flow). This leads to the common characteristics of inflammation including heat, redness and swelling.

Blood clotting is stimulated which walls off the injured area to prevent spread.

Bradykinins are produced which stimulate the sensation of pain.

Leukocyte migration is stimulated as phagocytes and lymphocytes migrate to the injured area. See the web link on chemotaxis to see what calls a phagocyte to the area.

Fever production is induced. That elevated temperature is a bonus that may actually slow down the growth of pathogens.

Swelling that occurs due to histamine production and vasodilation can cause serious damage to the brain or lead to severe breathing constriction. Blood clotting may make it difficult to deliver phagocytes (or medication) to an injured or infected area and require surgical intervention. Chronic inflammation which results from diseases like rheumatoid arthritis can cause devestating tissue damage.

Interferons are a series of chemicals which aid in immunity by interfering with the growth of foreign agents such as virus particles and tumor cells. Some interferons prevent the spread of virus particles. Others seem to stimulate the immune response to certain types of tumors. Genetically engineered interferon is used as a chemotherapeutic to treat diseases such as Hepatitis or certain cancers such as malignant melanoma.

Complement is a series of 20 proteins produced by the liver which, as the name implies, complement immune function. The 3 activities of complement are: opsonization (enhancing phagocytosis), enhancing inflammation and the production of membrane attack complexes which lead to pathogen destruction.

True

False. Eosinophils phagocytize parasites.