Gaseous exchange

• Gas exchange

  1. Occurs at the alveoli in the lungs

  2. Takes place by diffusion
• Alveoli

  • Surrounded by capillaries
  • Oxygen and carbon dioxide diffuse between the air in the alveoli and the blood in the capillaries
• Diffusion


  The movement of gas from an area of high concentration to an area of low concentration
• High concentration of oxygen in the alveoli

  Oxygen diffuses from the alveoli into the blood
• High concentration of carbon dioxide in the blood

  Carbon dioxide diffuses from the blood into the alveoli
• Haemoglobin

  An iron-rich protein in the blood that is capable of combining with oxygen and carbon dioxide
• Haemoglobin


  1. Carries oxygen to be exchanged at the working muscles

  2. Carries carbon dioxide to be exchanged at the lungs
• Oxygenated blood is then transported back to the heart through pulmonary veins.
• Deoxygenated blood is pumped by the right ventricle to the lungs via the pulmonary artery.
• Pothowdy of air


  Pathway of air
• Pathway of air


  1. Mouth

  2. Nose

  3. Bronchi

  4. Bronchioles

  5. Alveoli
• Inspiration (breathing in)


  1. Diaphragm moves down

  2. Contracts and flattens

  3. Volume of air in lungs increases

  4. Volume of chest cavity increases

  5. Pressure in lungs decreases

  6. Air is drawn into the lungs
• Expiration (breathing out)


  1. Diaphragm relaxes and moves up

  2. Intercostal muscles relax and move down and in

  3. Volume of air in lungs decreases

  4. Volume of chest cavity decreases

  5. Pressure in lungs increases

  6. Air is forced out of the lungs
• Anatomy and Physiology of the mechanics of breathing
• During exercise, breathing rate increases to meet the increased demand for oxygen in the working muscles
• Mechanics of breathing during exercise

  1. Sternocleidomastoid contracts

  2. Diaphragm contracts further

  3. Abdominal muscles contract

  4. Increases the size of the chest cavity

  5. Assists the process of exhalation
• Expiration (exhalation) is assisted by the use of abdominal muscles
• large surface area to increase diffusion speed, thin walls to speed up diffusion rate, capillaries have large surface area for gaseous exchange, large blood supply to transport carbon dioxide and oxygen, movement of gas from high to low concentration this means there is a pressure gradient that allows diffusion to occur.