Lymphatic System

The Innate Immune System

The innate immune system provides the body's first line of defense against pathogens through non-specific mechanisms. It includes physical and chemical barriers, as well as cellular responses.

• Key Components: Complement system, skin, phagocytes (such as neutrophils and macrophages), inflammation, mucous membranes, and chemotaxis.

• Physical Barriers: The skin and mucous membranes act as physical barriers to prevent pathogen entry.

• Chemical Barriers: Secretions like mucus, stomach acid, and enzymes destroy or inhibit pathogens.

• Cellular Defenses: Phagocytes engulf and destroy invaders; natural killer cells target infected or abnormal cells.

• Difference from Adaptive Immunity: Innate immunity is non-specific and immediate, while adaptive immunity is specific and develops over time.

• Example: The skin prevents bacterial entry, while phagocytes in the blood can engulf bacteria that breach the skin.

The Adaptive Immune System

The adaptive immune system provides a specific response to pathogens and develops memory for faster responses upon re-exposure.

• Humoral Immunity: Involves B cells producing antibodies that target extracellular pathogens.

• Cellular Immunity: Involves T cells (helper and cytotoxic) that target infected or abnormal cells.

• Antigen Recognition: T cells recognize antigens presented by major histocompatibility complex (MHC) molecules on antigen-presenting cells.

• Key Cells and Molecules:

  • T cell receptors (TCRs)

  • Helper T cells (CD4+)

  • Cytotoxic T cells (CD8+)

  • B cells

  • Antigen-presenting cells (APCs)

  • Cytokines

• Primary vs. Secondary Immune Response: The primary response is slower and occurs upon first exposure; the secondary response is faster and stronger due to memory cells.

• Example: Vaccination induces a primary response, so the body can mount a rapid secondary response upon real infection.

Clinical Application: Allergic Reactions and Anaphylaxis

Allergic reactions are hypersensitivity responses of the immune system to harmless antigens, such as bee venom.

• Symptoms: Swelling, redness, hives, difficulty breathing, increased heart rate (HR), increased blood pressure (BP), blue lips and fingernails (cyanosis).

• Mechanism: Sensitization occurs when the immune system produces IgE antibodies against an allergen. Upon re-exposure, mast cells release histamine and other mediators, causing systemic effects.

• Clinical Condition: Anaphylaxis is a severe, life-threatening allergic reaction.

• Treatment: Immediate administration of epinephrine is recommended to counteract symptoms.

• Example: A child stung by a bee develops widespread swelling and difficulty breathing, indicating anaphylaxis.

Respiratory System

Anatomy of the Respiratory System

The respiratory system consists of structures that conduct air and facilitate gas exchange.

• Conducting Division: Nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles.

• Respiratory Division: Respiratory bronchioles, alveolar ducts, alveoli (sites of gas exchange).

• Function: Conducts air to the lungs, filters, warms, and humidifies air, and enables gas exchange.

• Example: The trachea conducts air to the bronchi, which branch into smaller bronchioles ending in alveoli.

Mechanics of Normal Ventilation

Ventilation is the process of moving air in and out of the lungs, driven by pressure changes.

• Boyle's Law: (Pressure and volume are inversely related at constant temperature.)

• Inspiration: Diaphragm and external intercostal muscles contract, increasing thoracic volume and decreasing pressure, drawing air in.

• Expiration: Muscles relax, thoracic volume decreases, pressure increases, and air is expelled.

• Accessory Muscles: Used during forced breathing (e.g., exercise, respiratory distress).

• Example: During quiet breathing, the diaphragm is the primary muscle involved.

Oxygen-Hemoglobin Dissociation Curve

The oxygen-hemoglobin dissociation curve describes the relationship between the partial pressure of oxygen (pO2) and hemoglobin saturation.

• X-axis: pO2 (mmHg); Y-axis: % saturation of hemoglobin.

• Curve Shifts:

  • Right Shift: Decreased affinity (e.g., increased CO2, temperature, H+); oxygen is more easily released to tissues.

  • Left Shift: Increased affinity (e.g., decreased CO2, temperature, H+); oxygen is held more tightly.

• Clinical Relevance: Carbon monoxide exposure shifts the curve left, reducing oxygen delivery to tissues.

• Example: During exercise, increased CO2 and temperature shift the curve right, enhancing oxygen delivery.

Bicarbonate Buffer System

The bicarbonate buffer system maintains blood pH by balancing carbon dioxide and bicarbonate ions.

• Equation:

• Function: Buffers excess acids or bases in the blood.

• Disorders: Hypoventilation leads to acidosis; hyperventilation leads to alkalosis.

• Example: During intense exercise, increased CO2 production can lower blood pH.

Respiratory Control Centers

Breathing is regulated by centers in the brainstem that respond to chemical and neural signals.

• Medullary Respiratory Center: Controls basic rhythm of breathing.

• Pontine Centers: Modulate the rate and pattern of breathing.

• Factors Affecting Rate and Depth: CO2 levels, pH, O2 levels, emotional state.

• Example: High CO2 levels stimulate increased respiratory rate.

Digestive System

Major Functions of the Digestive System

The digestive system breaks down food, absorbs nutrients, and eliminates waste.

• Six Major Functions:

  1. Ingestion

  2. Propulsion

  3. Mechanical digestion

  4. Chemical digestion

  5. Absorption

  6. Defecation

• Example: Chewing is mechanical digestion; enzymes in saliva begin chemical digestion.

Digestion and Absorption

Digestion involves both mechanical and chemical processes to break down food into absorbable units.

• Mechanical Digestion: Chewing, churning in the stomach, segmentation in the intestines.

• Chemical Digestion: Enzymatic breakdown of carbohydrates, proteins, and fats.

• Absorption: Nutrients are absorbed primarily in the small intestine and transported to the body via the bloodstream.

• Example: Amylase in saliva breaks down starch into maltose.

Structure and Function of the Intestines

The small and large intestines have specialized structures for digestion and absorption.

• Small Intestine: Villi and microvilli increase surface area for absorption; main site for nutrient absorption.

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

• Comparison: The small intestine is longer and has more surface area; the large intestine is wider and involved in water absorption.

• Example: Most vitamins and minerals are absorbed in the small intestine.

Regulation of Digestive Activity

Digestive processes are regulated by neural and endocrine systems.

• Hormones:

  • Gastrin: Stimulates gastric acid secretion.

  • Secretin: Stimulates bicarbonate secretion from the pancreas.

  • Cholecystokinin (CCK): Stimulates bile release and pancreatic enzyme secretion.

• Neural Control: Enteric nervous system coordinates local reflexes; autonomic nervous system modulates activity.

• Example: The sight or smell of food can trigger gastric secretions via neural pathways.

Accessory Organs and Their Functions

Accessory organs such as the liver, pancreas, and gallbladder play essential roles in digestion.

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

• Gallbladder: Stores and concentrates bile.

• Pancreas: Produces digestive enzymes and bicarbonate.

• Example: Bile emulsifies fats, aiding in their digestion and absorption.