Overview
This lecture covers the structure, function, and regulatory mechanisms of the respiratory system, focusing on anatomy, physiology, and the control of breathing for exam preparation.
Anatomy of the Respiratory System
- Air enters through the nasal cavity, where it is warmed, humidified, and filtered by mucus, hairs, and cilia.
- The pharynx directs food to the esophagus and air to the larynx (voice box).
- The epiglottis prevents food from entering the trachea (windpipe).
- The trachea is supported by cartilage rings and splits into the primary bronchi, one for each lung.
- The right lung has 3 lobes; the left lung has 2 lobes and a cardiac notch for the heart.
- Bronchi branch into secondary and tertiary bronchi, then into bronchioles, leading to alveolar ducts and alveolar sacs.
- Alveoli are tiny sacs where gas exchange occurs between air and blood.
Zones and Gas Exchange
- The conducting zone includes the trachea, bronchi, and terminal bronchioles; it only moves air and does not exchange gases (anatomical dead space).
- The respiratory zone (respiratory bronchioles, alveolar ducts, and alveoli) is where actual gas exchange takes place.
- Extensive surface area and blood supply in the alveoli make them efficient for oxygen and carbon dioxide exchange.
System Interactions and Regulation
- Red blood cells in capillaries pick up oxygen and release carbon dioxide for removal.
- The skeletal (ribs) and muscular (diaphragm, intercostal, abdominal) systems support breathing by expanding and contracting the thoracic cavity.
- Breathing is largely involuntary, controlled by the nervous system based on blood pH levels.
- Increased carbon dioxide raises blood acidity, signaling the brain to increase breathing rate and depth to restore pH (around 7.4).
Mechanics of Breathing
- Inspiration (inhaling) is active: diaphragm contracts and flattens, external intercostals lift the rib cage, increasing thoracic volume and drawing air in.
- Expiration (exhaling) is usually passive: diaphragm and intercostals relax, decreasing thoracic volume and pushing air out.
- Forced expiration during exercise or coughing becomes active.
Ventilation, Perfusion, and Breathing Disorders
- Ventilation moves air in/out of alveoli; perfusion is blood flow to alveolar capillaries.
- Ideal gas exchange requires balanced ventilation and perfusion.
- Hypoventilation: too little breathing leads to high CO2 (hypercapnia) and low oxygen (hypoxia).
- Hyperventilation: excessive breathing lowers CO2 (hypocapnia), raising oxygen (hyperoxia) and causing respiratory alkalosis.
Key Terms & Definitions
- Cilia — Microscopic hairlike structures in the nasal cavity that filter air.
- Epiglottis — Flap that prevents food from entering the trachea.
- Alveoli — Tiny air sacs where gas exchange occurs.
- Conducting Zone — Airways that transport air but do not exchange gases.
- Respiratory Zone — Airways and structures where gas exchange takes place.
- pH — Scale measuring acidity or alkalinity of blood.
- Hypoventilation — Inadequate ventilation leading to CO2 buildup.
- Hyperventilation — Excessive ventilation leading to CO2 loss.
Action Items / Next Steps
- Review major respiratory system structures and their functions for the AIT's exam.
- Understand the difference between the conducting and respiratory zones.
- Practice identifying disorders caused by ventilation-perfusion imbalances.