Human Respiratory System

Respiratory System

• Oxygen enters the body through the mouth or nose and passes through the trachea, which splits into two bronchi, one for each lung.
• The left lung has a cardiac notch, a depression that allows space for the heart, whereas the right lung does not have this notch.

Alveoli and Gas Exchange

• Alveoli are the smallest functional units of the lung, responsible for gas exchange.
• There are millions of alveoli in the lungs.
• Oxygen molecules diffuse from the alveolus into the blood through several layers: liquid lining the alveolus, epithelial cells, basement membrane, connective tissue, endothelial cells, and plasma.

Layers of the Alveolus

• Liquid lining the alveolus: a thin layer of fluid that coats the inside of the alveolus.
• Epithelial cells: flat, pancake-shaped cells that make up the walls of the alveolus.
• Basement membrane: a layer that offers structural support to the lungs.
• Connective tissue: a layer that provides additional structural support and contains proteins.
• Endothelial cells: flat, pancake-shaped cells that make up the walls of the capillary.
• Plasma: a liquid layer that carries oxygen molecules into the red blood cell.

Oxygen Binding to Hemoglobin

• Oxygen molecules bind to hemoglobin in the red blood cell.
• Hemoglobin has four binding sites for oxygen molecules.
• Once oxygen binds to hemoglobin, the red blood cell carries oxygen to the rest of the body.

Visualizing the Journey of Oxygen

• Imagine a rectangular cube with different layers, starting from the alveolus (gas phase) and ending at the red blood cell (liquid phase).
• The oxygen molecule must pass through several layers of liquid to reach the red blood cell.
• This process can be divided into two categories: gas and liquid.

Equations and Oxygen Diffusion

• The alveolar gas equation calculates the partial pressure of oxygen in the alveolus.
• Fick's law of diffusion calculates the amount of oxygen diffusing over time.
• Factors affecting oxygen diffusion include:
  • Gradient of partial pressures (P1 - P2)
  • Surface area (e.g., number of functional alveoli)
  • Thickness of the layers (e.g., increased fluid in connective tissue)
  • Diffusion coefficient (stable in oxygen within water at body temperature)

Troubleshooting Abnormal Oxygen Diffusion

• If the amount of oxygen diffusing over time is abnormal, consider the following factors:
  • Partial pressure of oxygen in the alveolus (P1)
  • Surface area (e.g., number of functional alveoli)
  • Thickness of the layers (e.g., increased fluid in connective tissue)
  • Other factors affecting oxygen diffusion (e.g., Fi O2, altitude, respiratory quotient)

Learn about the structures and functions of the human respiratory system, including the pathway of oxygen into the body and the role of alveoli in gas exchange.