Chapter 5, Problem 1LO

Summary Introduction

To explain: The role of normal defenses in preventing disease.

Concept introduction: Organisms use defense mechanisms to protect from any injurious agent. This can be specific or non-specific.

Explanation of Solution

The defense mechanisms are generally classified into three lines of defense as follows:

• First line of defense
• Second line of defense
• Third line of defense

First line of defense: It is the general, non-specific defense mechanism that includes the mechanical barrier such as skin or mucous membrane. This prevents the entry of bacteria or other harmful particles inside the tissues. Certain body secretions such as saliva or tears act as mechanical barriers. It contains enzymes or chemical substances that inactivate the potential invading particles.

Second line of defense: It is the non-specific defense mechanism that includes the process of phagocytosis and inflammation. Phagocytosis is the process in which macrophages and neutrophils engulf the invading foreign particles, cell debris, or bacteria and destroy them. Inflammation is the sequence of events that limit the effects of injury or any agent in the body. For example, interferons, which protect the healthy tissues from viruses.

Third line of defense: It is the specific defense mechanism that protects the body by stimulating the specific antibodies or lymphocytes against the invading organisms. It creates an immune response against the harmful substances to protect the body.

Pictorial representation:

Fig.1 represents the defense mechanisms of the body.

Fig. 1: Three lines of defense mechanisms in the body.