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Q6:
Explain the process of inspiration under normal conditions.
Solution :
Initial Theoretical Framework: The Mechanics of Breathing
The process of inspiration is governed by Boyle’s Law, which states that for a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional ($P \propto 1/V$). Inspiration occurs when the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure, creating a negative pressure gradient that forces air into the lungs.
Step 1: Initiation by the Diaphragm
Inspiration begins with the contraction of the diaphragm muscle. Under normal conditions, the diaphragm is dome-shaped. Upon stimulation by the phrenic nerve, the muscle fibers contract, causing the diaphragm to flatten and move caudally (downward) toward the abdominal cavity. [Reference: Contraction of the phrenic nerve impulse]. This action increases the vertical dimension of the thoracic cavity.
Step 2: External Intercostal Muscle Action
Simultaneously, the external intercostal muscles (EIM) contract. This pulls the ribs and the sternum upward and outward. This action increases the diameter of the thoracic cavity in the antero-posterior and dorso-ventral axes. [Per the anatomical mechanics of the rib cage].
Step 3: Volume Expansion and Pressure Reduction
The overall increase in the thoracic volume leads to a corresponding increase in the pulmonary volume. Due to the anatomical coupling of the lungs to the thoracic wall via the pleura (intrapleural pressure), an increase in thoracic volume results in an expansion of the lungs. As $V$ increases, $P$ decreases inside the lungs below atmospheric pressure. [By Boyle's Law: $P_1V_1 = P_2V_2$].
Step 4: Airflow into the Alveoli
Because the intra-pulmonary pressure is now lower than the atmospheric pressure (approximately $-1$ to $-2$ mmHg relative to the atmosphere), air from the external environment is forced into the lungs through the respiratory tract until the pressures equalize. [Per the Law of Mass Flow].
Comparison of Pressure States
| Parameter | At Rest | During Inspiration |
|---|---|---|
| Thoracic Volume | Baseline | Increased |
| Intra-pulmonary Pressure | Equal to Atmospheric | Less than Atmospheric (Negative) |
| Airflow | None | Into the Lungs |
Final Solution: Inspiration is an active process initiated by the contraction of the diaphragm and external intercostal muscles, which increases the thoracic volume. This creates a negative intra-pulmonary pressure relative to the atmosphere, drawing air into the lungs to equalize the pressure gradient.
More Questions from Class 11 Biology Breathing and Exchange of Gases EXERCISES
- Q1: Define vital capacity. What is its significance?
- Q2: State the volume of air remaining in the lungs after a normal breathing.
- Q3: Diffusion of gases occurs in the alveolar region only and not in the other parts of respiratory system. Why?
- Q4: What are the major transport mechanisms for $CO_2$? Explain.
- Q5: What will be the $pO_2$ and $pCO_2$ in the atmospheric air compared to those in the alveolar air ?
- Q7: How is respiration regulated?
- Q8: What is the effect of $pCO_2$ on oxygen transport?
- Q9: What happens to the respiratory process in a man going up a hill?
- Q10: What is the site of gaseous exchange in an insect?
- Q11: Define oxygen dissociation curve. Can you suggest any reason for its sigmoidal pattern?
- Q12: Have you heard about hypoxia? Try to gather information about it, and discuss with your friends.
- Q13(a): Distinguish between (a) IRV and ERV
- Q13(b): Distinguish between (b) Inspiratory capacity and Expiratory capacity.
- Q13(c): Distinguish between (c) Vital capacity and Total lung capacity.
- Q14: What is Tidal volume? Find out the Tidal volume (approximate value) for a healthy human in an hour.
CBSE Solutions for Class 11 Biology Breathing and Exchange of Gases
Chapters in CBSE - Class 11 Biology
- The Living World
- Biological Classification
- Plant Kingdom
- Animal Kingdom
- Morphology of Flowering Plants
- Anatomy of Flowering Plants
- Structural Organisation in Animals
- Cell – The Unit of Life
- Biomolecules
- Cell Cycle and Division
- Transport in Plants
- Mineral Nutrition
- Photosynthesis
- Respiration in Plants
- Plant Growth and Development
- Digestion and Absorption
- Body Fluids and Circulation
- Excretory Products and Elimination
- Locomotion and Movement
- Neural Control and Coordination
- Chemical Coordination and Integration
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