Mechanism of Breathing

• During inhalation:
  • The diaphragm and external intercostal muscles contract.
  • This increases the volume of the thoracic cavity.
  • The lungs expand.
• Increased lung volume during inhalation lowers lung pressure below atmospheric pressure.
  • Air rushes into the lungs down a pressure gradient.
• During exhalation:
  • The diaphragm and external intercostal muscles relax.
  • The volume of the thoracic cavity decreases.
  • The lungs decrease in volume.
  • Air pressure inside the lungs increases above atmospheric pressure, pushing air out.
• Tidal volume refers to the volume of air inhaled or exhaled during each breath at rest.
• Vital capacity is the maximum volume of air exhaled after maximum inhalation.
• Even after forceful exhalation, some air remains in the lungs, preventing collapse, known as residual volume.
• Total lung capacity equals vital capacity plus residual volume.
  • It's the volume of air filling the lungs after maximum inhalation.
• Exhaled air composition differs from inhaled air.
  • Gas exchange in the alveoli results in lower oxygen and higher carbon dioxide levels in exhaled air.
• During exercise or physical activity, higher energy amounts are needed for muscle contraction.
  • This energy is supplied through increased cellular respiration.
• An increased rate of cellular respiration requires higher oxygen amounts.
  • These are supplied by an increased breathing rate.

Common Respiratory Diseases

• The common cold is a viral infection affecting upper respiratory tract organs.
• Pneumonia can be caused by bacterial or viral infections.
  • It mainly affects the alveoli, causing inflammation and fluid accumulation.
• Asthma is characterized by inflammation and narrowing of airways, mainly the bronchi and bronchioles.
  • This causes increased muscle contraction, congestion, and reversible airway constriction.
• Chronic Obstructive Pulmonary Disease (COPD) includes emphysema and chronic bronchitis.
• Emphysema involves irreversible enlargement of the alveoli and weakening of alveolar walls.
  • The alveoli break, merge, reduce air spaces, and decrease gas exchange surface area.
• Chronic bronchitis is a persistent bronchitis type linked to smoking and air pollution.
  • Irritants increase mucus secretion and destroy cilia, which propel mucus away from the lungs.
• COPD and lung cancer are often caused by long-term cigarette smoking.
• Smoking is linked to lung cancer due to carcinogenic material accumulation following cilia destruction.
  • Cilia normally remove harmful substances.