Immune System Basics

Key Functions & Terms

The immune system is responsible for defending the body against harmful invaders and maintaining internal health. Understanding its basic components and terminology is essential for studying human physiology.

• Primary Function: The immune system protects the body from pathogens and foreign substances.

• Pathogens: Microorganisms such as bacteria, viruses, fungi, or parasites that can cause disease.

• Antigens: Substances (often proteins) on the surface of pathogens or foreign particles that trigger an immune response.

• Antibodies: Y-shaped proteins produced by B cells that specifically bind to antigens to neutralize or mark them for destruction.

Defense Types

The immune system employs two main types of defense mechanisms: innate (nonspecific) and adaptive (specific) defenses.

• Innate (Nonspecific) Defenses: These are the body's first line of defense and respond to all pathogens in the same way. Examples include skin, mucous membranes, phagocytic cells, and inflammation.

• Adaptive (Specific) Defenses: These responses are tailored to specific pathogens and involve lymphocytes (B cells and T cells). They provide long-lasting immunity.

• Memory B Cells: After an initial infection, some B cells become memory cells, which respond more rapidly and effectively upon subsequent exposures to the same antigen.

Example: If you recover from chickenpox, memory B cells help prevent you from getting it again.

Lymphatic System

Structure and Function

The lymphatic system is a network of vessels and organs that helps maintain fluid balance, absorb fats, and defend against pathogens.

• Lymph Fluid: Mostly made of interstitial fluid that leaks from blood capillaries into tissues.

• Lymph Nodes: Small, bean-shaped structures that filter lymph and house lymphocytes.

• Tonsils and Adenoids: Lymphatic tissues in the throat that trap pathogens from food and air.

• Thymus: Organ where T cells mature.

• Spleen: Filters blood, removes old red blood cells, and helps mount immune responses.

• White Pulp (Spleen): Contains lymphocytes and is involved in immune functions.

• Red Pulp (Spleen): Removes old or damaged red blood cells and stores platelets.

• Enlarged Spleen: May indicate infection, inflammation, or blood disorders.

Additional info: The lymphatic system also transports dietary lipids from the intestines to the bloodstream.

Diagram Practice

• Be able to draw and label: tonsils, adenoids, thymus, spleen, lymph nodes, lymph vessels.

• Label where T cells mature (thymus) and where B cells produce antibodies (lymph nodes and spleen).

Digestive System

Main Functions and Organs

The digestive system breaks down food into nutrients, absorbs them, and eliminates waste. It consists of the alimentary canal and accessory organs.

• Main Function: To digest food, absorb nutrients, and expel waste.

• Esophagus: Muscular tube that transports food from the mouth to the stomach via peristalsis.

• Stomach: Secretes acid and enzymes to begin protein digestion; churns food into chyme.

• Small Intestine: Major site of digestion and nutrient absorption; divided into duodenum, jejunum, and ileum.

• Large Intestine: Absorbs water and electrolytes; forms and stores feces.

• Accessory Organs:

  • Liver: Produces bile, processes nutrients, detoxifies substances.

  • Gallbladder: Stores and concentrates bile.

  • Pancreas: Produces digestive enzymes and bicarbonate; also has endocrine functions.

Bile

• Production: Bile is produced in the liver.

• Storage: Bile is stored in the gallbladder.

• Function in Digestion: Bile emulsifies fats in the small intestine, aiding in their digestion and absorption.

Additional info: Bile contains bile salts, bilirubin, cholesterol, and electrolytes.

Diagram Practice

• Be able to draw and label: mouth, esophagus, stomach, small intestine, large intestine, liver, gallbladder, pancreas.

• Identify white pulp/red pulp in the spleen and lymph nodes.

• Indicate where enzymes act (amylase in mouth, pepsin in stomach, lipase in small intestine) and where bile helps (small intestine).

Key Digestive Enzymes and Their Sites of Action

Additional info: Bile does not contain enzymes but aids lipase by emulsifying fats.