Gaseous Exchange Lecture Notes

Key Concepts

• Breathing: Mechanical process of air exchange in lungs.
• Gaseous Exchange: Exchange of oxygen and carbon dioxide across a surface.
• Cellular Respiration: Release of energy from organic compounds like glucose in the presence of oxygen.

Importance of Gaseous Exchange

• Absorbs oxygen for cellular respiration.
• Removes carbon dioxide to prevent toxicity, as high levels can lower pH in body fluids.

Requirements for Efficient Gaseous Exchange

1. Large Surface Area: Human lungs cover a surface area as large as a tennis court.
2. Thin Surface: For quick diffusion.
3. Moist Surface: Gases must dissolve to diffuse through membranes.
4. Protection: Ribs protect delicate gaseous exchange surfaces.
5. Transport System: Blood serves as the transport medium for gases.

Adaptations in Different Organisms

Earthworms

• Gaseous exchange occurs through moist skin (no lungs).

Fish

• Use gills, which have a large surface area due to their structure and are moist due to water.

Plants

• Gaseous exchange occurs through stomata, which open/close based on environmental conditions.

Human Gaseous Exchange Structure

Air Passages

• Nasal Cavities: Filter inhaled air with hairs and mucus membranes containing ciliated cells.
• Pharynx (Throat): Connects nasal cavities to the trachea and esophagus.
• Trachea (Windpipe): Lined with c-shaped cartilage rings, allowing esophagus expansion.

Lungs and Bronchi

• Bronchi: Trachea divides into left and right bronchi, leading to lungs.
• Bronchioles: Smaller branches leading to alveoli, with o-shaped cartilage rings.
• Alveoli: Tiny air sacs where gaseous exchange occurs, surrounded by capillaries.

Respiratory Muscles

• Diaphragm: Dome-shaped muscle that aids in inhalation and exhalation.
• Intercostal Muscles: Muscles between ribs that assist with breathing movement.

Mechanism of Breathing

Inhalation

• Active process: Diaphragm contracts, thoracic cavity enlarges, air is drawn into lungs.

Exhalation

• Passive process: Diaphragm relaxes, thoracic cavity decreases in size, air is expelled from lungs.

Composition of Air

• Inhaled Air: 21% Oxygen, 0.04% Carbon Dioxide
• Exhaled Air: 15% Oxygen, 4% Carbon Dioxide

Gaseous Exchange Process

In Alveoli

• Oxygen from inhaled air diffuses into blood; carbon dioxide diffuses from blood into alveoli to be exhaled.

In Tissues

• Oxygen-rich blood from lungs diffuses into tissue cells; carbon dioxide produced by cells diffuses into blood.

Transport of Gases in Blood

• Oxygen: Carried as oxyhemoglobin.
• Carbon Dioxide: Mostly converted to bicarbonate; also forms carbaminohemoglobin with hemoglobin.

Effects of Exercise

• Increased demand for oxygen and carbon dioxide removal.
• Increases breathing rate and depth, heart rate accelerates to meet oxygen needs.

Lung Capacity

• Total Lung Capacity: ~5 liters.
• Tidal Volume: Air breathed in/out during normal breathing.
• Inspiratory/Expiratory Reserve Volume: Additional air inhaled/exhaled after normal breathing.
• Vital Capacity: Tidal volume + reserve volumes.
• Residual Volume: Air remaining in lungs after full exhalation.

Homeostatic Control of Breathing

• Chemoreceptors in arteries detect carbon dioxide levels and send impulses to medulla oblongata, increasing breathing and heart rate to maintain homeostasis.