Hormonal Regulation and Immune System Barriers

Negative and Positive Feedback in Hormonal Regulation

Negative feedback: This is the most widespread type and occurs when increased hormone levels, above a certain value, inhibit hormone secretion. Positive feedback: In this case, an increase in the values of a hormone causes an increase in its secretion. This type of regulation occurs in special situations, such as ovulation.

Immune System Barriers

The immune system can recognize and usually eliminate altered elements of itself.

In humans and higher vertebrates, three types of defensive barriers are distinguished: primary, secondary, and tertiary. Their function is to prevent the entry and development of pathogens.

Primary Barriers

• The skin: The first defensive barrier that prevents the entry of pathogens into the body. Keeping it clean is essential.
• Sweat: It has a slightly acidic pH, preventing the survival of many microorganisms.
• Fatty acids: Produced by sebaceous glands, they inhibit the growth of certain bacteria.
• Tears and saliva: They produce lysozyme, chemicals capable of destroying the bacterial cell wall.
• Digestive juices: Rich in hydrochloric acid, causing the destruction of microorganisms in food.
• Gut flora bacteria: They colonize the intestine and prevent the development of other harmful bacteria.

Secondary Barriers

When primary barriers have been overcome, pathogens adhere to tissue via different mechanisms, penetrate it, colonize it, and develop. That's when leukocytes come into action, mainly PMNs (polymorphonuclear neutrophils) or granulocytes, as well as monocytes and macrophages, known as general phagocytes. The lysosomes that possess polymorphic nuclei destroy pathogens.

Phagocytosis

Phagocytes wrap or cover the pathogen and destroy it by the action of enzymes. Phagocytosis is a fundamental mechanism by which all animals defend themselves against infection. But, in vertebrates, the process is somewhat more complex. The cells of the wound area adjacent secrete histamine and other chemicals, which increase blood flow and capillary permeability in the surrounding area. Circulating leukocytes, attracted by these chemicals, pass through cell walls and gather at the site of the wound. This property is known as diapedesis. Macrophages will be released after antigenic determinants are recognized by T cells.