Lymphatic System and Body Defenses

Introduction to Body Defenses

The lymphatic system and associated body defenses provide resistance to fight infection, illness, and disease. The immune system is divided into two main types of defenses: innate (nonspecific) immunity and adaptive (specific) immunity.

• Innate immunity: Provides general protection against any type of invading agent.

• Adaptive immunity: Targets specific pathogens and is based on the activities of lymphocytes.

Structures and Categories of Body Defenses

Innate (Nonspecific) Immunity

Innate immunity works the same way against any type of invading agent and is also called nonspecific resistance. It is present at birth and does not require previous exposure to pathogens.

• Surface barriers: Physical and chemical barriers that prevent pathogen entry.

• Internal defenses: Mechanisms that destroy pathogens that breach surface barriers.

Adaptive (Specific) Immunity

Adaptive immunity develops after exposure to environmental hazards and provides resistance against specific pathogens. It is based on the coordinated action of T cells and B cells.

• Humoral immunity: Mediated by B cells and antibodies, targets pathogens in body fluids.

• Cellular immunity: Mediated by T cells, targets abnormal cells and pathogens inside cells.

Overview of Innate and Adaptive Defenses

Innate Defenses

• Surface barriers:

  • Skin

  • Mucous membranes

• Internal defenses:

  • Phagocytes

  • Natural killer (NK) cells

  • Inflammation

  • Antimicrobial proteins

  • Fever

Adaptive Defenses

• Humoral immunity:

  • B cells

• Cellular immunity:

  • T cells

Categories of Innate (Nonspecific) Defenses

Physical Barriers

Physical barriers are the first line of defense and include the skin and mucous membranes.

• Skin: Multiple layers of keratinized cells form a tough barrier.

• Mucous membranes: Line internal passageways and trap pathogens.

• Secretions: Sweat glands, mucus, and urine flush away materials.

• Chemical barriers: Enzymes, antibodies, and stomach acid kill or inhibit microorganisms.

Phagocytes

Phagocytes are cells that engulf and destroy pathogens.

• Neutrophils: Most abundant phagocytes, found in bloodstream and tissues.

• Macrophages: Derived from monocytes, distributed throughout the body.

• Eosinophils: Attack parasites and participate in allergic responses.

Immune Surveillance

Natural killer (NK) cells monitor tissues and destroy abnormal cells, such as cancer cells and virus-infected cells.

Interferons

Interferons are chemical messengers released by activated lymphocytes, macrophages, and fibroblasts. They stimulate production of antiviral proteins in normal cells, blocking viral replication.

Complement System

The complement system consists of circulating proteins that assist antibodies in the destruction of pathogens. Activation leads to cell lysis and enhances inflammation.

Inflammation

Inflammation is a localized tissue-level response that limits the spread of injury or infection.

• Signs: Redness, heat, swelling, pain.

• Functions: Prevents spread of damaging agents, disposes of cell debris and pathogens, sets stage for repair.

Fever

Fever is an elevation of body temperature above 37.2°C (99°F), which can inhibit pathogen growth and enhance immune reactions.

Summary Table: Innate vs. Adaptive Immunity

Key Terms and Definitions

• Antigen: Any substance that can trigger an immune response.

• Antibody: Protein produced by B cells that binds to specific antigens.

• Lymphocyte: White blood cell involved in adaptive immunity (includes B cells and T cells).

• Phagocytosis: Process by which phagocytes engulf and digest pathogens.

• Inflammation: Tissue response to injury or infection, characterized by redness, heat, swelling, and pain.

• Fever: Elevated body temperature that enhances immune function.

Example: Immune Response Timeline

After infection, innate immunity acts within hours, while adaptive immunity develops over several days. B cells produce antibodies, and T cells target infected cells.

Additional info:

• Adaptive immunity provides long-lasting protection due to memory cells.

• Innate immunity is always present and acts as the first line of defense.