Defenses Against Infections

Which of the following is NOT considered a physical barrier against invasive microbes?

What are the three types of barriers that provide the first line of defense against the entry of microbes?

Which of the following is NOT mentioned as a source of molecules that can injure body cells and tissues?

What do the mechanical barriers in the body do?

Which of the following is NOT mentioned as a mechanical barrier that protects the body against invasive microbes?

Barriers Against Invasive Microbes

The skin and mucous membranes are the first line of defense against the entry of microbes, providing a physical barrier.

Types of Barriers

There are three types of barriers that provide the first line of defense against the entry of microbes:
- Physical barriers (e.g., skin, mucous membranes)
- Mechanical barriers (e.g., cilia in the respiratory tract, eyelashes)
- Chemical barriers (e.g., lysozyme in tears, acidity of stomach acid)

Sources of Harmful Molecules

There are several sources of molecules that can injure body cells and tissues, including:
- Exogenous substances (e.g., toxins, chemicals)
- Endogenous substances (e.g., free radicals, lactic acid)

Mechanical Barriers

Mechanical barriers in the body prevent the entry of microbes by physically blocking their path or removing them from the body.
Examples of mechanical barriers include:
- Cilia in the respiratory tract (trap and remove particles and microbes)
- Eyelashes (help keep dust and microbes out of the eyes)
The conjunctiva is NOT a mechanical barrier that protects the body against invasive microbes.

Test your knowledge on the barriers that protect our bodies from infections. Identify the mechanical, chemical, and biologic barriers that prevent microbes from entering and causing harm.