Introduction to the Respiratory System

Respiratory System Overview

• Primary Functions:
  • Deliver oxygen ($O_2$) to tissues
  • Remove carbon dioxide ($CO_2$) from tissues
  • Respond to metabolic demand especially during exercise or at high altitudes.

Key Terms

• Pulmonary Respiration:

  • Involves delivering $O2$ to tissues and removing $CO2$.
  • Stimulates chemoreceptors when $CO_2$ builds up, increasing breathing rate.

• Cellular Respiration:

  • Different from pulmonary respiration; refers to the processes that convert biochemical energy from nutrients into $ATP$ (energy currency of the cell).

Ventilation vs. Diffusion

• Ventilation:

  • Definition: Mechanical process of moving air in and out of the lungs.
  • Important Note: Ventilation occurs based on pressure gradients.

• Diffusion:

  • Movement of gases from high concentration to low concentration (e.g., $O2$ and $CO2$ down their gradients).

Respiratory Zones

• Conducting Zone:

  • Extends from the nose to the base of the sternum.
  • Functions: Filters, warms, and humidifies air.

• Respiratory Zone:

  • Extends from the base of the lungs where gas exchange occurs.
  • Contains alveoli, crucial for gas exchange.
  • Interesting Fact: The total surface area of the lungs, if spread out, could cover a tennis court.

Alveolar Functionality and Importance

• Alveoli:
  • Balloon-like structures at the end of the respiratory tree where gas exchange occurs.
  • Very thin walls facilitate efficient gas diffusion.
  • Vulnerable to damage from smoke, pollution, aging, etc.
• COPD and Other Respiratory Issues:
  • Conditions like COPD can damage alveoli, causing air trapping and breathing difficulties.

Pulmonary Ventilation

• Total Minute Ventilation:

  • Volume of air moved in and out of the lungs per minute.
  • Comparable to cardiac output in terms of mechanical effort.

• Dead Space Air:

  • Air remaining in lungs that does not participate in gas exchange (anatomical and mechanical dead space).

Muscular Mechanics of Breathing

• Diaphragm:

  • Primary muscle for inspiration.
  • Contracts to allow air to flow into the lungs by creating a vacuum.

• Expiration:

  • A passive process where relaxation of the diaphragm and intercostal muscles push air out.

Pressure Dynamics

• Intrapulmonary vs. Intrapleural Pressure:
  • Intrapulmonary pressure: pressure within the lung, equals atmospheric pressure at rest (~760 mmHg).
  • Intrapleural pressure: pressure within the pleural cavity, essential for lung inflation.

Gas Exchange and Partial Pressures

• Fick's Law of Diffusion:

  • Rate of gas diffusion is proportional to surface area and pressure gradient, and inversely proportional to membrane thickness.
  • Ideal gas diffusion exhibits a high surface area, low thickness for optimal exchange.

• Partial Pressures:

  • Total pressure is the sum of individual gas pressures (Dalton’s Law).
  • Example: In atmosphere at sea level: 79% nitrogen, 21% oxygen. [ P{O2} = 0.2093 imes 760 ext{ mmHg} = 159.1 ext{ mmHg} ]

Regulation of Breathing

• Chemoreceptors:
  • Detect changes in blood $pH$ due to $CO_2$ levels.
  • Adjust respiratory rate based on changes to maintain homeostasis.

Key Responses During Exercise

• Increased respiratory rate and depth to meet increased $O_2$ demand.
• Frequency becomes more significant due to physical limitations on depth.
• Increased levels of $CO_2$ stimulate chemoreceptors, driving the need for increased respiration.

Summary

• The respiratory system's responsiveness and mechanics are vital for maintaining proper gas exchange and meeting metabolic demands during various physical activities and situations. Understanding these processes helps in comprehending human physiology in both health and disease.