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DrX Whiz Niraj
Respiratory System: Anatomy & Physiology
Master the Human Respiratory System. Complete notes on Lungs Anatomy, Mechanism of Breathing, Lung Volumes (Spirometry), Gas Transport, and CPR Resuscitation.
The Respiratory System consists of the nose, pharynx (throat), larynx (voice box), trachea (windpipe), bronchi, and lungs. Its primary function is the exchange of gases (Oxygen and Carbon Dioxide) between the atmosphere, blood, and cells.
The Lungs
- Pleura: Each lung is enclosed by a double-layered serous membrane called the pleural membrane (Parietal pleura outside, Visceral pleura inside).
- Right Lung: Larger, wider, and has 3 Lobes (Superior, Middle, Inferior) separated by horizontal and oblique fissures.
- Left Lung: Smaller (to accommodate the heart) and has 2 Lobes. It features a concave depression called the Cardiac Notch.
Alveoli (The Air Sacs)
The terminal bronchioles branch into microscopic air sacs called Alveoli. They are the actual sites of gas exchange.
- Type I Alveolar Cells: Form the lining for gas exchange.
- Type II Alveolar Cells: Secrete Surfactant (a fluid that lowers surface tension and prevents alveoli from collapsing).
Breathing (Pulmonary Ventilation) is based on Boyle's Law: The pressure of a gas is inversely proportional to its volume.
| Phase | Process / Muscles Involved | Result |
|---|---|---|
| Inspiration (Active Process) |
Diaphragm contracts (moves down). External intercostals contract. Thoracic cavity volume INCREASES. | Lung pressure DECREASES below atmospheric pressure. Air rushes IN. |
| Expiration (Passive Process) |
Diaphragm relaxes (moves up/dome-shaped). Thoracic cavity volume DECREASES. | Lung pressure INCREASES above atmospheric pressure. Air rushes OUT. |
Regulation of Respiration (Nervous Control)
- Medullary Rhythmicity Area: Located in the Medulla Oblongata. It controls the basic rhythm of breathing (Inspiratory & Expiratory areas).
- Pneumotaxic Area: Located in the Pons. It turns off inspiration before lungs get too full.
- Apneustic Area: Located in the Pons. It prolongs inspiration for deep breathing.
Chemical Control: Chemoreceptors detect levels of CO₂, H⁺, and O₂ in the blood. A rise in PCO₂ (Hypercapnia) strongly stimulates breathing.
The measurement of lung volumes is called Spirometry. It is vital for diagnosing respiratory disorders like Asthma and COPD.
1. Volumes
- Tidal Volume (TV): Volume of air breathed in and out during normal quiet breathing (~500 mL).
- Inspiratory Reserve Volume (IRV): Extra air inhaled forcibly after a normal inspiration (~3100 mL).
- Expiratory Reserve Volume (ERV): Extra air exhaled forcibly after a normal expiration (~1200 mL).
- Residual Volume (RV): Air that always remains in lungs to prevent collapse (~1200 mL).
2. Capacities (Sums of Volumes)
- Vital Capacity (VC): The max amount of air exhaled after max inspiration. VC = TV + IRV + ERV (~4800 mL).
- Total Lung Capacity (TLC): Total volume of lungs. TLC = VC + RV (~6000 mL).
| Gas | Transport Mechanisms |
|---|---|
| Oxygen (O₂) |
1. 1.5% is dissolved in blood plasma. 2. 98.5% is bound to the iron of hemoglobin inside RBCs (Forms Oxyhemoglobin). |
| Carbon Dioxide (CO₂) |
1. 7% is dissolved in blood plasma. 2. 23% binds to the globin part of hemoglobin (Forms Carbaminohemoglobin). 3. 70% is transported as Bicarbonate ions (HCO₃⁻) in the blood plasma. |
When a person stops breathing (apnea) or their heart stops beating, immediate Cardiopulmonary Resuscitation (CPR) is required to maintain oxygen flow to the brain.
CPR Steps (CAB approach):
- C - Compressions: Push hard and fast on the center of the chest. (Rate: 100-120 per minute. Depth: At least 2 inches for adults).
- A - Airway: Open the airway by tilting the head back and lifting the chin.
- B - Breathing: Provide 2 rescue breaths (mouth-to-mouth) after every 30 compressions. (Ratio = 30:2).
Pharmacy Alert: Asthma & COPD
Asthma is characterized by chronic airway inflammation and bronchospasm (narrowing of bronchioles). Pharmacists commonly dispense Bronchodilators (like Salbutamol/Albuterol). These drugs act on Beta-2 receptors in the lungs to relax the smooth muscles and open the airways, restoring normal TV (Tidal Volume).