Gas exchange in humans

• What is ventilation?

  • Inhaling and exhaling in humans
  • controlled by diaphragm and antagonistic interaction of internal and external intercostal muscles
• How does the process of inspiration work?

  • External intercostal muscles contract and internal relax
  • pushing ribs up and out
  • diaphragm contracts and flattens
  • air pressure in lungs drops below atmospheric pressure as lung volume increases
  • air moves in down pressure gradient
• How does the process of expiration work?

  • External intercostal muscles relax and internal contract
  • pulling ribs down and in
  • diaphragm relaxes and domes
  • air pressure in lungs increases above atmospheric pressure as lung volume decreases
  • air forced out down pressure gradient
• State, in the correct order, the structures a molecule of O2 has to go through to get to the site of gas exchange.

  • Mouth / nose -> trachea -> bronchi -> bronchioles -> alveoli
  • crosses alveolar epithelium into capillary endothelium
• Label the diagram of the human gas exchange system.

  Answers:

  A) trachea

  B) bronchus

  C) alveolus

  D) bronchiole

  E) ribs

  F) diaphragm

  G) intercostal muscles

  H) lung

  
• Describe the structure of the alveoli.

  • Tiny air sacs
  • highly abundant in each lung - 300 million
  • surrounded by the capillary network
  • epithelium 1 cell thick
• What is the site of gas exchange in mammals and where in the structure does gas exchange occur?

  The lungs are the site of gas exchange in mammals and the alveoli are where gas exchange occurs.
• What does the ribcage do?

  Protects and supports the lungs
• How do the ribs move?

  By the intercostal muscles
• Where does gas exchange take place?

  Gas exchange takes place between the alveolar epithelium and the blood in the surrounding capillaries
• How does the number of alveoli increase rate of diffusion?

  There are many alveoli in human lungs which creates an extremely large surface area which maximises the rate of diffusion.
• Each alveolus is surrounded by a dense network of capillaries. How does this increase the rate of diffusion?

  It ensures a rich blood supply that helps maintain steep concentration gradients for oxygen and carbon dioxide
• The walls of the alveoli are made up of a single layer of epithelial cells. How does this increase the rate of diffusion?

  It decreases diffusion distance between the air in the alveolus and the blood in the capillaries which increases the rate of diffusion
• How are the lungs adapted for efficient gas exchange?

  Millions of alveoli, each surrounded by a network of capillaries. This creates a large surface area, a short diffusion distance and the circulation of the blood maintains the concentration gradient.
• What do the external intercostal muscles do during inspiration?

  Contract to pull the ribs up and out
• What do the internal intercostal muscles do during inspiration?

  Relax
• What does the diaphragm do during inspiration?

  Contracts to move down and flattens
• What happens to the air pressure in the lungs during inspiration?

  It initially drops and then as air moves in it rises to above atmospheric pressure
• What happens to lung volume during inspiration?

  Increases
• How does air move during inspiration?

  Air moves into the lungs down the pressure gradient as atmospheric pressure is higher than that of the lungs
• What do the external intercostal muscles do during expiration?

  relax
• What do the internal intercostal muscles do during expiration?

  Contract to pull the ribs down and in
• What does the diaphragm do during expiration?

  Relaxes to move up and curves
• What happens to the air pressure in the lungs during expiration?

  Initially greater than atmospheric pressure then drops as air moves out
• What happens to lung volume during expiration?

  Decreases
• How does air move during expiration?

  Air moves out of the lungs down the pressure gradient, as pressure in the lungs is higher than atmospheric pressure