Respiratory System and Gas Exchange

Overview of Lung Function

Main job: Gas exchange (Oxygen intake and Carbon dioxide removal).
Inhale: Diaphragm and chest muscles contract to pull air in, creating a vacuum.
Exhale: Muscles relax, lungs return to normal size to expel air.

Nasal Cavity
- Air enters through nostrils.
- Lined with mucus-releasing cells containing lysozymes.
- Nose hairs trap dust, pollen, and bacteria.
- Connects with paranasal sinuses (frontal, ethmoid, sphenoid, maxillary).
- Sinuses warm and moisten air.
Pharynx (Throat)
- Divided into nasopharynx, oropharynx, laryngopharynx.
- Soft palate and uvula prevent food from entering nasopharynx.
Larynx (Voice Box)
- Epiglottis prevents food from entering the airway.
- Cough reflex removes non-air particles.
Trachea and Bronchi
- Air travels down the trachea, splits into mainstem bronchi at the carina.
- Right lung: 3 lobes; Left lung: 2 lobes.
- Right bronchus is wider, more vertical.
- Supported by cartilage rings.

Smooth Muscle
- Sympathetic nerves: "Fight or flight" - increase airway diameter.
- Parasympathetic nerves: "Rest and digest" - decrease airway diameter.
Mucociliary Escalator
- Ciliated columnar cells and goblet cells line airways.
- Mucus traps particles; cilia move them towards the pharynx.

Conducting Bronchioles
- Narrower than bronchi, no cartilage support.
- Lined with ciliated cells, goblet cells, and club cells.
- Club cells secrete protective glycosaminoglycans.
Terminal Bronchioles lead to Respiratory Bronchioles.

Alveolar Structure
- Alveolar ducts contain millions of alveoli.
- Alveoli lined by epithelial cells (type I and type II pneumocytes).
- Type II pneumocytes secrete surfactant to reduce surface tension.
Gas Exchange
- Occurs at alveolar-capillary interface (blood-gas barrier).
- Oxygen diffuses into blood; carbon dioxide diffuses into alveoli.