Term of the Day

Anaphylaxis: Type of immediate hypersensitivity triggered when allergens cross-link to IgE antibodies attached to mast cells or basophils, resulting in systemic release of inflammatory chemicals.

Concept of the Week

Inflammation: Usually a localized response to tissue damage or injury. It represents the body's attempt to defend itself. The hallmark signs of inflammation include redness, heat, edema, and pain.

1. Injured cells, mast cells, basophils, etc. release histamine and other inflammatory chemicals that increase blood flow to the affected area, leading to erythema of the skin and a feeling of warmth in the affected area.

2. Histamine and other chemicals increase capillary permeability, allowing antibodies and other immune chemicals to leave the capillaries and enter the tissue spaces. This causes localized edema, which, in combination with chemicals released from damaged cells (especially prostaglandins), causes pain.

3. Neutrophils and other leukocytes migrate out of the capillaries and into affected tissue spaces via diapedesis. Neutrophils and macrophages are attracted to the area of damage via positive chemotaxis by chemicals released from damaged cells, activated complement proteins, lymphokines, and other chemical signals.

Term of the Day

Blood-Testes Barrier: This refers to the ability of the sustentacular (Sertoli) cells of the seminiferous tubules to prevent potentially toxic or harmful substances from entering or leaving the tubules. Many proteins, ions, hormones, and drugs are blocked from access to the developing spermatids. This works the other way, too. The barrier prevents the sperm in the tubules from diffusing into the bloodstream. This is a good thing, because sperm are immunogenic. That is, they are not recognized by cells of the immune system, so that if they entered the blood, they would be treated as foreign antigens and antibodies against them would be formed. This could lead to sterility.