Which body system is considered the MAIN first line of defense against invasion of the body from foreign objects?

A. The failure of the body to function normally

This is too general and applies to any illness, not specifically infection.

B. A diseased section of the body

This is vague and doesn’t identify causative factors like pathogens.

C. The invasion of the body by a pathogen and the subsequent symptoms in response to the invasion

This accurately defines infection as a host response to pathogen invasion.

D. The invasion of the body by a disease

Diseases don’t invade; pathogens do. This option is not scientifically accurate.

A. Concerned only with destroying RBCs

Only the spleen is partly involved in RBC destruction-this doesn’t apply to all listed organs.

B. Confined to the thoracic cavity

These organs are located in different parts of the body-e.g., spleen in the abdomen, lymph nodes throughout the body.

C. Lymphoid organs

These are all components of the lymphatic/immune system, involved in immune surveillance and lymphocyte production.

D. Concerned only with phagocytosis

While some have phagocytic activity (e.g., macrophages in lymph nodes), their functions go far beyond phagocytosis (e.g., immune cell activation).