Breathing and Exchange of Gases

Introduction

• Importance: Human Physiology chapters in NEET have consistent question trends.
• Goals: Discuss differences between breathing and respiration, types of respiration, and respiratory organs.

Breathing vs. Respiration

• Breathing: Mechanical process; inhalation and exhalation.
• Respiration: Oxidation of food with oxygen from breathing to produce energy.

Types of Respiration

Direct Respiration

• Occurs in simple organisms like amoeba and sponges.
• Oxygen diffuses directly through body surface.

Indirect Respiration

• Involves complex organisms.
• Examples include humans where exchange occurs in lungs with breathing organs.

Aerobic and Anaerobic Respiration

Aerobic Respiration

• Use: Requires oxygen; produces more energy.
• Byproducts: CO2, H2O, and energy.

Anaerobic Respiration

• Use: No oxygen; produces less energy.
• Examples: Skeletal muscles, RBCs, yeast fermentation.

Respiratory Organs in Animals

• Variation based on Habitat and Complexity
• Simple Organisms: Diffusion through body (Poriferans, Cnidarians).
• Earthworm: Cutaneous respiration.
• Insects: Tracheal tubes.
• Aquatic Arthropods and Mollusks: Gills.
• Vertebrates: Gills in fish, lungs in mammals, amphibians, and reptiles.

Human Respiratory System

Structure

• Respiratory Passages: Nostrils → Nasal Cavity → Pharynx → Larynx → Trachea → Bronchi.
• Respiratory Organ: Lungs.

Functions

• Nasal Cavity: Conditions air with mucus and hair; divided into vestibular, respiratory, and olfactory regions.
• Trachea and Bronchi: Supported by cartilaginous rings; prevent collapse.

Lung Structure

• Lobes: Right lung (3 lobes), left lung (2 lobes with cardiac notch).
• Pleura: Double membrane with pleural fluid for shock absorption.

Alveoli

• Structure: Simple squamous epithelium; site for gas exchange.
• Cells: Type I (epithelium), Type II (surfactant production), macrophages.

Breathing Mechanics

Inspiration

• Muscles Involved: Diaphragm and external intercostals contract, increasing thoracic volume.

Expiration

• Types: Normal (passive) and forceful (active with intercostal and abdominal muscles).

Lung Volumes and Capacities

• Tidal Volume (TV): Air in/out during normal breath.
• Inspiratory Reserve Volume (IRV): Extra air inhaled forcefully.
• Expiratory Reserve Volume (ERV): Extra air exhaled forcefully.
• Residual Volume (RV): Air remaining post-forceful expiration.
• Capacities: Combinations of the above volumes.

Gas Exchange

Sites

• Alveoli-Blood Exchange: Primary site for oxygen and CO2 exchange.
• Blood-Tissues Exchange: Secondary site for gas exchange.

Factors Affecting Exchange

• Pressure Gradient: Higher gradient, higher exchange.
• Solubility: Higher solubility, higher exchange.
• Thickness of Membranes: Thinner membranes, higher exchange.

Oxygen Transport

• Hemoglobin: 97% as oxyhemoglobin.
• Dissolved in Plasma: 3%.

CO2 Transport

• Dissolved in Plasma: 7%.
• Carbaminohemoglobin: 20-25%.
• Bicarbonate Ions: 70%.

Oxygen Dissociation Curve

• Shape: Sigmoid; shows hemoglobin saturation with varying oxygen partial pressures.
• Shifts: Right (increased CO2, H+, temp, DPG); Left (increased O2, decreased CO2, H+, temp).

Regulation of Respiration

Centers

• Respiratory Rhythm Center: Controls normal breathing.
• Pneumotaxic Center: Alters breathing rate.

Chemosensitive Areas

• Central and Peripheral Receptors: Detect changes in CO2 and H+ but not O2.

Respiratory Disorders

• Asthma: Inflammation leading to wheezing.
• Emphysema: Alveolar damage, often linked with smoking.
• Occupational Disorders: Caused by prolonged exposure to industrial dusts (e.g., silicosis).

Other Conditions

• Altitude Sickness: Low oxygen pressure at high altitudes.
• Decompression Sickness: Nitrogen bubble formation during rapid ascent from deep water.
• Carbon Monoxide Poisoning: CO binds to hemoglobin, preventing oxygen transport.

Conclusion

• Importance of Understanding: These concepts are critical for NEET aspirants for their exams as well as practical understanding of human physiology.