Protection of the Body

 

Immune System

The immune system is a remarkably complex and highly coordinated defense network designed to protect the human body against foreign pathogens, including bacteria, viruses, fungi, and parasites, as well as mutated host cells like cancer cells. The immune system operates through two main, interconnected lines of defense: innate immunity and acquired (adaptive) immunity. Innate immunity serves as the body’s first line of protection, consisting of non-specific barriers like the skin, chemical secretions, phagocytic cells (such as neutrophils and macrophages), and the complement system that react within minutes or hours to destroy invading microorganisms.

When innate mechanisms are bypassed or overwhelmed, the body activates its acquired immunity a highly specific defense system capable of recognizing, targeting, and remembering distinct foreign antigens. Acquired immunity is broadly divided into two complementary responses:

Humoral Immunity (B-Cell Mediated):

Specialized B lymphocytes recognize specific antigens and differentiate into plasma cells, which secrete large quantities of targeted proteins called antibodies (immunoglobulins). These circulating antibodies neutralize toxins, block viral attachment, and mark foreign cells for destruction by phagocytes.

Cell-Mediated Immunity (T-Cell Mediated):

T lymphocytes are activated by antigen-presenting cells to execute targeted cellular responses. Helper T cells (CD4^+) secrete lymphokines that orchestrate the entire immune response, while Cytotoxic T cells (CD8^+) directly identify and destroy virus-infected or cancerous cells.

• The immune system includes white blood cells and lymphoid tissues.
• It protects against bacteria, viruses, parasites, and fungi.
• It distinguishes self cells from foreign invading cells.
• Invaders are destroyed by phagocytosis, lymphocytes, or antibodies.
• The integumentary system includes skin, hair, nails, and glands.
• Skin protects deeper tissues from the external environment.
• The Integumentary system regulates temperature and excretes wastes.
• Skin comprises about 12 to 15 percent body weight.

Role of Reproduction:

• Reproduction replaces dying individuals with new beings.
• It helps maintain long-term continuity of human life.

Control Systems of the Body:

• The body contains thousands of complex control systems.
• Genetic control systems manage intracellular and extracellular functions.
• Organ-level control systems regulate specific organ functions.
• Body-wide control systems coordinate interrelations between organs.
• The respiratory system and nervous system regulate carbon dioxide.
• Liver and pancreas regulate extracellular glucose concentration.
• Kidneys regulate extracellular ion and hydrogen concentrations.

Regulation of Carbon Dioxide and oxygen: 

• Hemoglobin maintains precise extracellular oxygen concentrations.
• Hemoglobin binds oxygen while passing through the lungs.
• It releases oxygen only when tissue levels fall low.
• This process is called the oxygen-buffering function of hemoglobin.
• High carbon dioxide stimulates the brain's respiratory center.
• Rapid breathing increases expiration of excess carbon dioxide.
• Removal of carbon dioxide restores fluid concentrations to normal.

Regulation of Arterial Blood Pressure:

• The baroreceptor system rapidly regulates arterial blood pressure.
• Baroreceptors lie in carotid arteries and aortic arch.
• Arterial wall stretch stimulates these sensory baroreceptors.
• High pressure sends inhibitory signals to the brain medulla.
• Inhibited vasomotor center reduces sympathetic nervous output.
• Reduced signals decrease heart pumping and dilate vessels.
• Low pressure relaxes baroreceptors, increasing vasomotor activity.
• Increased vasomotor activity causes vasoconstriction and raises pressure.