Mechanism of Breathing
சுவாச இயக்கமுறை
Stop confusing breathing with respiration. Breathing is a physical process of pressure manipulation, not cellular ATP production. If you cannot define the pressure gradient, you have already lost the mark.
The idea
Breathing is driven by pressure gradients between the lungs and the atmosphere. Inspiration occurs when the diaphragm and external intercostal muscles contract, increasing thoracic volume and decreasing intrapulmonary pressure below atmospheric pressure. Expiration follows as these muscles relax, decreasing thoracic volume and raising intrapulmonary pressure above atmospheric pressure. Air moves down its pressure gradient.
Why it matters
Gases move from areas of high pressure to low pressure; creating these gradients allows for the passive flow of air into and out of the lungs.
NEET lens
NEET focuses on the sequence: contraction leads to volume increase, which leads to pressure decrease. Do not confuse 'intrapulmonary' with 'intrapleural' pressure. Memorize that inspiration is an active process while quiet expiration is passive. Expect questions on the specific role of external vs internal intercostal muscles.
Clinical significance
Failure of the diaphragm or intercostal muscles leads to respiratory failure. Conditions like Myasthenia Gravis or phrenic nerve damage paralyze these muscles, preventing the creation of the necessary pressure gradient. Without this mechanical movement, ventilation ceases regardless of gas exchange capacity.
Introduction
Breathing (pulmonary ventilation) is the mechanical process of moving air in and out of lungs by creating pressure differences through muscular contraction — inspiration (inhalation) when intrapulmonary pressure drops below atmospheric, expiration (exhalation) when it rises.
Core concept
Inspiration: Diaphragm contracts (moves down) + external intercostal muscles contract (ribs move up and out) → thoracic volume increases → intrapulmonary pressure drops below atmospheric (~1-3 mmHg below) → air flows IN. Expiration (normal, passive): Diaphragm + external intercostals relax → thoracic volume decreases → intrapulmonary pressure rises above atmospheric → air flows OUT. Forced expiration: internal intercostal muscles + abdominal muscles contract → faster/more complete expiration.
Go deeper
Intrapleural pressure: pleural cavity maintains ~5 mmHg below atmospheric pressure (negative pressure). This keeps lungs expanded against chest wall. If lung is punctured → air enters pleural space → pneumothorax → lung collapses (no longer held by negative pressure). Negative intrapleural pressure is essential for breathing.
From Class 10
When you breathe in, your chest expands and air rushes in. When you breathe out, the chest recoils and air is pushed out. This is driven by pressure changes.