Understanding the Human Immune System: Functions and Processes

Understanding the Human Immune System

Innate and Acquired Immunity

The immune system is a complex network of organs and structures responsible for defending the body from toxic microbial aggression. It operates through two primary mechanisms:

• Innate (Natural) Immunity:
  • Passive: Represented by maternal antibodies.
  • Active: Involves antigen-antibody reactions.
• Acquired Immunity:
  • Active: Developed through vaccines.
  • Passive: Achieved via the administration of antibodies, such as those found in antibiotics.

Key Components of the Immune System

The immune response involves several processes, including:

• Chemotaxis: The attraction of immune cells to the site of infection.
• Diapedesis: The movement of immune cells out of blood vessels.
• Phagocytosis: The process of engulfing and degrading foreign particles.

Skin

The skin acts as a primary barrier, preventing the entry of germs into the body. Skin regeneration eliminates germs attached to the outer layers—epidermis, hypodermis, and endodermis. The generating layer lies between the epidermis and endodermis, facilitating the production of new skin.

Lymph Nodes

Lymph nodes, located in areas like the armpits, groin, and neck, are crucial for cell production and immune response. They swell during infections, indicating active immune activity.

Mucous Membranes

Mucous membranes in the respiratory and gastrointestinal tracts trap microbes. Mucus is composed of water, mucin, and antiseptic substances. Types of mucus include nasal, oral, and vaginal/seminal.

Thymus

The thymus is a gland that produces T lymphocytes, a type of white blood cell crucial for immune function.

Liver

The liver stores carbohydrates, proteins, and fats. It produces bile and plays roles in red blood cell production and destruction, anticoagulation, iron production, and detoxification.

Spleen

The spleen produces B lymphocytes and granulocytes, both essential for hematopoietic functions.

Bacterial Flora

Bacterial flora comprises beneficial microbes that inhabit the body and help process nutrients.

Peyer's Patches

Peyer's patches are specialized immune tissues found in the body, particularly in the stomach and mouth, contributing to our defenses.

Defensive System Mechanisms

Barriers

Physical barriers include skin, hair, and mucous membranes with cilia. These structures filter out dust and microbes, preventing their entry into the body.

Secretions

Secretions play a vital role in defense:

• Tears: Lubricate and help remove irritants.
• Saliva: Contains lysozyme, an antibacterial enzyme, and mucin for cleaning the mouth and teeth.
• Urine: Helps flush microbes out of the urethra.
• Defecation and Vomiting: Expel harmful substances and microbes from the body.
• Sweat and Sebaceous Glands: Eliminate microbes on the skin's surface.
• Gastric Epithelium: Hydrochloric acid and gastric juice kill ingested bacteria.

Cells

Specialized immune cells include:

• NK Cells (Natural Killer Cells or Lymphokines): Eliminate microbes and tumor cells.
• T Lymphocytes: Destroy infected cells and microbes.
• B Lymphocytes: Produce antibodies.

Processes

Key immune processes are:

• Inflammation: A localized response that helps destroy microbes. It is facilitated by substances like cytokines and histamine.
• Fever: An increase in body temperature, regulated by the hypothalamus, which helps kill microbes.
• Phagocytosis: The degradation of microbes by macrophages (derived from monocytes).
• Complement System: A series of processes leading to microbial death, phagocytosis, and inflammation.