Chapter 6.1, Problem 1QC

Summary Introduction

To explain: The way by which physical and mechanical barriers contribute to defense mechanism.

Concept introduction: The body has a defense system that consists of many biological structures and processes inside an organism to protect that functions against the diseases are known as immune system. The body’s defense system has many line of defense mechanism which functions together for preventing the foreign body from entering and eliminating the invaded antigen from the body.

Explanation of Solution

The body has several barriers for inhibiting the penetration, growth and infection of external agents.

The external parts of the body are covered by physical barriers for providing protection against damage and infection. Physical barriers are composed of tightly packed epithelial cells in the skin and in the linings of respiratory, gastrointestinal, and genitourinary tract.

• Epithelial cells present in the physical barrier secrete numerous substances such as perspiration (saliva, mucus, tears that contains lysozyme to kill bacteria), mucus, and ear wax.
• Sebaceous gland is present in the skin kills bacteria and fungi by secreting lactic acid and fatty acids.
• Epithelial cells secrete antimicrobial peptides for inhibiting the growth of microorganism.

Mechanical barriers are one of the natural barriers along with the physical and biochemical barriers. Invading antigens that escape the physical barrier are trapped through the mechanical barrier. Those include as follows:

•  Discarded through dead skin.
•  Expelled by means of coughing and sneezing.
•  Vomiting.
• Flushing out from urinary tract.
•  Low pH of skin and stomach inhibits microbes.