Bihar Board - Class 11 biology - Chapter 17: Breathing and Exchange of Gases Handwritten Notes

Breathing and the exchange of gases are essential processes in humans and other organisms to supply oxygen to cells and remove carbon dioxide. This chapter define the mechanism of breathing and the structure of human respiratory system, and how gases are exchanged between the lungs and blood in human respiratory system.

Key Points

1. Respiratory System Overview

   • Nasal Cavity: Filters, warms, and moistens the air.
   • Pharynx and Larynx: Passageways for air, where the vocal cords are located.
   • Trachea and Bronchi: Airways that lead to the lungs.
   • Lungs: Contain bronchioles and alveoli, where gas exchange occurs.

2. Mechanism of Breathing

   • Inhalation: The diaphragm contracts, expanding the thoracic cavity, decreasing pressure and allowing air to enter the lungs.
   • Exhalation: The diaphragm relaxes, increasing pressure and pushing air out of the lungs.
   • External Respiration: The exchange of gases between the air in the alveoli and the blood in the capillaries. Oxygen diffuses into the blood, and carbon dioxide diffuses into the alveoli.

3. Gas Exchange

   • Oxygen Transport: Oxygen binds to hemoglobin in red blood cells and is transported to tissues.
   • Carbon Dioxide Transport: Most CO₂ is transported as bicarbonate ions in plasma, with a small amount dissolved in plasma and bound to hemoglobin.

4. Factors Affecting Gas Exchange

   • Partial Pressure: The difference in oxygen and carbon dioxide partial pressures between the alveoli and blood drives gas diffusion.
   • Surface Area: The large surface area of the alveoli facilitates efficient gas exchange.
   • Thickness of Respiratory Membrane: Thinner membranes allow faster diffusion of gases.
   • Ventilation Rate: The rate of airflow into and out of the lungs affects the efficiency of gas exchange.

5. Respiratory Volume and Capacities

   • Tidal Volume (TV): The amount of air inhaled or exhaled in a normal breath.
   • Vital Capacity (VC): The maximum amount of air that can be exhaled after a deep inhalation.
   • Total Lung Capacity (TLC): The maximum volume of air the lungs can hold.

6. Control of Breathing

   • Medullary Respiratory Centers: Located in the brainstem, they regulate the rate and depth of breathing based on CO₂ levels in the blood.
   • Chemoreceptors: Detect changes in blood pH and CO₂ concentration, influencing the rate of breathing.

7. Respiratory Disorders

   • Asthma: Inflammation and narrowing of airways, making breathing difficult.
   • Pneumonia: Infection causing fluid accumulation in the alveoli, impairing gas exchange.
   • Chronic Obstructive Pulmonary Disease (COPD): A group of diseases, including emphysema and chronic bronchitis, that lead to difficulty in breathing and reduced oxygen intake.
   • Tuberculosis: A bacterial infection that primarily affects the lungs, leading to coughing and difficulty breathing.

Conclusion

Breathing and gas exchange are vital processes that ensure cells receive oxygen for energy production and remove metabolic waste products like carbon dioxide. The efficiency of these processes depends on the structure and functioning of the respiratory system, as well as the regulation of breathing. Understanding these processes helps in managing respiratory health and addressing related disorders.

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