DIMS Lectures Respiratory Physiology PDF

Kindly scroll down for  the complete pdf lecture of respiratory physiology by Dr. Tahir Malik scroll down .

Summary:

1. Anatomy and Structure of the Respiratory System 

The respiratory system comprises two major sections:

A. Upper Respiratory Tract

Nose & Nasal Cavity: Filters, warms, and humidifies air.

Pharynx: Connects the nasal cavity to the larynx and esophagus.

Larynx (Voice Box): Prevents food from entering the airways and produces sound.

B. Lower Respiratory Tract

Trachea (Windpipe): A rigid tube that transports air to the lungs.

Bronchi and Bronchioles: Branches of the trachea that regulate airflow.

Alveoli: Tiny air sacs where gas exchange occurs.

Each of these structures plays a vital role in maintaining a patent airway and efficient gas exchange.

2. Mechanics of Breathing

Breathing consists of two main phases: inspiration (inhalation) and expiration (exhalation).

A. Inspiration

An active process where the diaphragm and external intercostal muscles contract.

Expands lung volume, creating a negative pressure that pulls air in.

B. Expiration

A passive process at rest, where lung elasticity and muscle relaxation push air out.

Forced expiration, involving abdominal muscles, occurs during strenuous activity.

Key Concept: Boyle’s Law (Pressure ∝ 1/Volume) explains how air moves into the lungs during low pressure and out during high pressure.

3. Pulmonary Ventilation and Lung Volumes

Pulmonary ventilation refers to the amount of air inhaled and exhaled per minute.

Lung Volumes & Capacities:

1. Tidal Volume (TV) – Air exchanged in a normal breath (~500 mL).

2. Inspiratory Reserve Volume (IRV) – Extra air inhaled after a normal breath (~3100 mL).

3. Expiratory Reserve Volume (ERV) – Extra air exhaled forcefully (~1200 mL).

4. Residual Volume (RV) – Air remaining after full exhalation (~1200 mL).

Vital Capacity (VC) = TV + IRV + ERV

(Indicates lung efficiency and varies with age, gender, and fitness.)

4. Gas Exchange and Transport

Gas exchange occurs through diffusion at the alveoli-capillary interface.

A. Oxygen Transport

98% of oxygen binds to hemoglobin in red blood cells.

2% dissolves directly in plasma.

B. Carbon Dioxide Transport

70% converted into bicarbonate ions (HCO₃⁻).

20% binds to hemoglobin as carbaminohemoglobin.

10% dissolves in plasma.

Key Law: Fick’s Law states that diffusion rate is dependent on surface area, membrane thickness, and pressure gradient.

5. Regulation of Respiration

The respiratory system is regulated by nervous control and chemical feedback.

A. Nervous Control

Medulla Oblongata: Controls involuntary breathing.

Pons: Modifies breathing rhythm.

B. Chemical Control

Chemoreceptors in the brain detect CO₂ levels.

Peripheral chemoreceptors (carotid and aortic bodies) respond to low O₂.

An increase in CO₂ (hypercapnia) stimulates breathing, while low CO₂ (hypocapnia) reduces respiratory rate.

6. Clinical Relevance of Respiratory Physiology

A. Respiratory Diseases

1. Chronic Obstructive Pulmonary Disease (COPD) – Includes emphysema and chronic bronchitis.

2. Asthma – Characterized by airway constriction and wheezing.

3. Pneumonia – Infection causing lung inflammation.

4. Pulmonary Fibrosis – Thickened alveolar walls reducing gas exchange.

B. Effects of High Altitude

At higher altitudes, oxygen pressure drops, leading to hypoxia.

The body compensates by increasing respiratory rate and producing more red blood cells.

C. Role of Spirometry

Diagnostic tool to assess lung function.

Measures FVC (Forced Vital Capacity) and FEV1 (Forced Expiratory Volume in 1 second).

Used for diagnosing asthma, COPD, and restrictive lung diseases.

7. Importance of Respiratory Health & Tips

To maintain a healthy respiratory system, follow these guidelines:

Avoid smoking (prevents lung damage and diseases like COPD).

Exercise regularly (improves lung capacity and efficiency).

Stay hydrated (keeps airway mucus thin and easier to clear).

Practice deep breathing exercises (enhances lung expansion).

Avoid air pollution and allergens (reduces risk of respiratory illnesses).

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