Respiratory System and Gas Exchange

Main Function of Lungs

• Gas Exchange: Involves pulling oxygen into the body and expelling carbon dioxide.

Breathing Mechanics

• Inhalation: Diaphragm contracts, chest muscles open the chest, creating a vacuum to suck in air.
• Exhalation: Muscles relax, allowing lungs to spring back, pushing air out.

Air Pathway

1. Nasal Cavity
   • Air enters through nostrils.
   • Lined with mucus and lysozymes to kill bacteria.
   • Nose hairs trap dust, pollen, and bacteria.
2. Sinuses
   • Four types: frontal, ethmoid, sphenoid, and maxillary.
   • Warm and moisten air, amplify voice.
3. Pharynx
   • Nasopharynx connects nasal cavity to pharynx.
   • Oropharynx connects pharynx to oral cavity.
   • Laryngopharynx connects pharynx to larynx.
4. Larynx and Trachea
   • Epiglottis: Prevents food from entering the larynx.
   • Air moves to trachea, then splits into two bronchi at the carina.
5. Lungs
   • Right lung: Upper, middle, and lower lobes.
   • Left lung: Upper and lower lobes.

Bronchial Structure

• Mainstem Bronchi: Divide into smaller bronchi; trachea and initial bronchi supported by cartilage.
• Smooth Muscle and Autonomic Nervous System
  • Sympathetic (fight or flight) and parasympathetic (rest and digest) systems.
  • Beta 2 adrenergic and muscarinic receptors regulate airway diameter.

Mucociliary Escalator

• Ciliated Columnar Cells: Beat rhythmically to move mucus and trapped particles towards pharynx.
• Goblet Cells: Secrete mucus.

Bronchioles

• Conducting Bronchioles: Narrow, without cartilage, lined with ciliated cells, goblet cells, and club cells.
• Club Cells: Secrete protective glycosaminoglycans and regenerate ciliated cells.

Gas Exchange in Alveoli

• Respiratory Bronchioles and Alveoli:
  • Terminal bronchioles lead to respiratory bronchioles with alveolar outpouchings.
  • Alveolar ducts are lined by pneumocytes.
• Type I and II Pneumocytes:
  • Type I for gas exchange.
  • Type II secrete surfactant and regenerate cells.
• Alveolar Macrophages: Remove particles, move to conducting bronchioles.

Blood-Gas Barrier

• Structure: Alveolar wall, basement membrane, capillary wall.
• Process: Carbon dioxide diffuses out, oxygen diffuses in, oxygenated blood flows to tissues.

Recap

• Pathway: Oxygen travels through pharynx, larynx, trachea, large airways, bronchioles, alveoli, capillary.
• Carbon Dioxide: Travels back the same path to be exhaled.

Conclusion

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