Regulation of Respiration & Respiratory Disorders - Biology Class 11 -

Regulation of Respiration

Human beings possess a well-developed ability to regulate and modify the respiratory rhythm according to the metabolic demands of body tissues. This regulation is carried out by the neural system, which adjusts the rate and depth of breathing to maintain proper gas exchange.

Neural regulation of breathing

The primary control of respiration is located in the brainstem.

• Respiratory rhythm centre
  This specialised centre is present in the medulla oblongata. It is mainly responsible for generating and maintaining the basic rhythm of respiration, including inspiration and expiration.

• Pneumotaxic centre
  This centre is located in the pons region of the brain. It moderates the activity of the respiratory rhythm centre. Neural signals from the pneumotaxic centre can reduce the duration of inspiration, thereby regulating the respiratory rate.

A chemosensitive area, situated close to the respiratory rhythm centre, plays a crucial role in chemical regulation. This area is highly sensitive to changes in carbon dioxide (CO₂) and hydrogen ion (H⁺) concentration.

Chemical regulation of respiration

• An increase in CO₂ or H⁺ concentration stimulates the chemosensitive area.

• Activation of this area sends signals to the respiratory rhythm centre, resulting in adjustments in breathing that help eliminate excess CO₂ and restore normal pH.

In addition to this central mechanism:

• Receptors present in the carotid artery and aortic arch can detect changes in CO₂ and H⁺ concentration in the blood.

• These receptors send appropriate signals to the respiratory rhythm centre for corrective action.

The role of oxygen (O₂) in the regulation of respiratory rhythm is comparatively insignificant under normal conditions.

Functions of Respiration

• Energy production
  Respiration supplies oxygen required for cellular respiration and removes carbon dioxide produced during metabolism.

• Regulation of acid-base balance
  By controlling the removal of CO₂, respiration helps maintain blood pH.

• Temperature regulation
  Exchange of heat during breathing contributes to regulation of body temperature.

• Assistance in circulation
  Respiratory movements aid venous and lymphatic return by creating pressure changes within the thoracic cavity.

Altitude and Hypoxia

At high altitudes, atmospheric pressure decreases, resulting in reduced availability of oxygen. Rapid ascent to such regions can lead to hypoxia, commonly referred to as mountain sickness.

Symptoms of altitude sickness include:

• Loss of appetite, nausea and vomiting

• Breathlessness and difficulty in breathing; severe cases may lead to pulmonary oedema

• Headache, disturbed sleep, disorientation, fatigue, weakness and depression

Respiratory Disorders

The respiratory system is susceptible to infections, allergic reactions, obstructive and occupational diseases and pressure-related problems. Key disorders are described below with their causes, symptoms and common preventive or management approaches.

1. Bronchial asthma

Definition: A condition characterised by reversible bronchoconstriction due to spasms of smooth muscle in bronchioles, often associated with airway hyper-responsiveness and inflammation.

Features and causes:

• Symptoms include episodic wheezing, coughing and difficulty in breathing, often worse during expiration.
• Frequently caused by hypersensitivity (allergic) reactions to specific airborne allergens, infections or irritants.
• Excess mucous secretion can further obstruct airways.

Prevention and management:

• Avoid known allergens and triggers; allergen avoidance is the primary preventive measure.
• Hyposensitisation (allergen-specific immunotherapy) may be considered when the patient reacts to a limited number of identifiable allergens.
• Treatment includes inhaled bronchodilators (short- and long-acting), inhaled corticosteroids to reduce inflammation and, where needed, oral drugs and emergency measures for severe exacerbations.

2. Emphysema

Definition: Permanent enlargement of air spaces distal to the terminal bronchioles, with destruction of alveolar walls and loss of elastic recoil.

Features and causes:

• Air remains trapped in alveoli during expiration, producing over-inflated lungs and reduced gas exchange surface.
• Major causes include long-term cigarette smoking and chronic bronchitis; it is a chronic obstructive lung disease.

Prevention and management:

• Smoking cessation and avoidance of airborne pollutants reduce risk and progression.
• Emphysema is largely irreversible; treatment is symptomatic to slow progression and improve quality of life (bronchodilators, oxygen therapy, pulmonary rehabilitation).

3. Occupational lung diseases

Definition: Lung diseases caused by chronic exposure to harmful dusts, gases or fumes in the workplace. Examples include silicosis (silica dust) and asbestosis (asbestos fibres).

Features: These conditions often cause fibrosis (excessive fibrous connective tissue) of the lung, reduced lung compliance, impaired gas exchange and progressive respiratory disability.

Prevention and management:

• Minimise exposure to harmful dusts and fumes at the workplace through engineering controls and good ventilation.
• Inform and train workers about hazards and safe practices.
• Use personal protective equipment (masks, protective clothing) where exposure cannot be eliminated.
• Regular medical check-ups and health surveillance for early detection.
• Job rotation or periodic leave to reduce cumulative exposure.
• Many occupational lung diseases are irreversible once established; treatment is largely symptomatic and aims to prevent secondary infections (bronchodilators, antibiotics when needed).