Lecture Notes: The Respiratory System

Introduction

• The primary function of the respiratory system is to intake oxygen and expel carbon dioxide.
• Oxygen availability decreases with altitude, exemplified by challenges faced in climbing Mount Everest.
  • First successful climb was in 1953 by Edmund Hillary and Tenzing Norgay, using supplemental oxygen.
  • Climbers need to acclimatize by ascending and descending gradually.

Respiratory Adaptations in Animals

• Worms: Use skin as their respiratory surface, requiring moisture and a large surface area.
• Insects: Use spiracles (holes on the body) connected to a network of tubes to facilitate gas exchange.

Respiratory Solutions in Fish vs Humans

• Fish (Gills):

  • Gills are exposed to water and efficiently extract oxygen through countercurrent exchange.
  • Can reclaim about 80% of oxygen from water.

• Humans (Lungs):

  • Lungs are internal to maintain moisture and utilize ambient air's higher oxygen concentration.
  • Air pathways include trachea, bronchus, bronchioles, terminating in alveoli.
  • Countercurrent exchange is not used; instead, a complex branching system maximizes surface area.

Alveoli and Gas Exchange

• Structure:

  • Alveoli are tiny sacs at the end of bronchioles, lined with simple squamous cells.
  • Contain surfactants to prevent collapse by reducing surface tension.

• Function:

  • Oxygen transfers to capillaries surrounding alveoli; carbon dioxide is expelled.

Mechanics of Breathing

• Diaphragm:
  • Primary muscle for breathing; its contraction and relaxation change thoracic pressure, drawing air in and out.

Oxygen and Carbon Dioxide Transport

• Hemoglobin:

  • A protein in red blood cells that binds oxygen using iron (heme group), giving blood its red color.

• Carbon Dioxide Conversion:

  • Mostly converted to bicarbonate in blood plasma, with the process reversible in alveoli to release CO2 for exhalation.

Conclusion

• The respiratory system is crucial for gas exchange and works in tandem with the circulatory system (to be discussed further).

This lecture provided an overview of the respiratory system, illustrating both biological adaptations and the physiological mechanisms that facilitate breathing and gas exchange.