Gas Exchange in Humans

• Features of gas exchange:

  • Large surface area - Faster diffusion
  • Thin walls - Ensure diffusion distances remain short
  • Good ventilation with air - Maintain diffusion gradient
  • Good blood supply - Maintain high concentration so diffusion occurs faster
• label the lungs

  A) trachea

  B) c-shaped cartilage ring

  C) larynx

  D) external intercostal muscle

  E) bronchioles

  F) bronchus

  G) intercostal muscle

  H) internal intercostal muscle

  I) diaphragm

  J) ribs

  
• Nose

  Lined with moist mucus membrane. Dust and foreign particles trapped by hairs
• Trachea

  Support by C-Shaped cartilage ring which keeps lumen open/keeps trachea open. It is C-shaped to help with swallowing, with ligament helping esophagus to expand
• Ribs are a part of the bone structure that protects internal organs such as the lungs.
• Intercostal muscles are the muscles between the ribs which control their movement causing inhalation and exhalation.
• The diaphragm is a sheet of connective tissue and muscle at the bottom of the thorax that helps change the volume of the thorax to allow inhalation and exhalation.
• The trachea connects the mouth and nose to the lungs.
• Rings of cartilage surround the trachea and bronchi to support the airways and keep them open during breathing.
• If the cartilage were not present, the sides of the airways could collapse inwards when the air pressure inside the tubes drop.
• The larynx, also known as the voice box, produces sound when air passes across it.
• Bronchi are large tubes branching off the trachea with one bronchus.
• Bronchioles are bronchi that split to form smaller tubes called bronchioles in the lungs connected to alveoli.
• Alveoli are tiny air sacs where gas exchange takes place.
• Adaptations of Alveoli:

  • One cell thick - Short diffusion distance
  • Thin film of moisture - Oxygen to dissolve
  • Large surface area
  • Richly supplied with blood capillaries
• O2 diffuses from the alveolus into the bloodstream through the thin walls of the alveoli.
• CO2 diffuses from the bloodstream into the alveoli.
• Goblet cell - Secretes mucus to trap dust and bacteria

  Ciliated cell - Has cilia to sweep the dust trapped by mucus up the trachea
• Gas exchange in Alveoli:

  1. Blood entering lungs (through pulmonary artery) has low concentration of O2 and high CO2
  2. Inhaled air has high content of O2 and low CO2, which creates a concentration gradient
  3. O2 diffuses into capillaries, CO2 diffuse out of capillaries
  4. O2 combines with haemoglobin in red blood cell to form oxyhaemoglobin
• What is the purpose of the diaphragm?

  Separates digestive and respiratory system
• Movement of ribcage and diaphragm during inhalation

  1. Diaphragm contracts --> Flattens
  2. External intercostal muscle contract
  3. Ribs move upward and outward
  4. Volume of thoracic cavity increase
  5. When volume increases, air pressure inside decreases
  6. Atmospheric pressure is now higher than pressure in lungs
  7. Air is forced into the lungs
• Movement of ribcage and diaphragm during exhalation

  1. Diaphragm relaxes --> move upward
  2. External intercostal muscle relaxes
  3. Ribs move downward and inward
  4. Volume of thoracic cavity decreases
  5. When volume decreases, air pressure inside increase
  6. Atmospheric pressure is now lower than pressure in lungs
  7. Air is forced out of the lungs
• Oxygen in inspired air: 21%

  Oxygen in expired air: 16%

  Oxygen is used up by the body so the blood returning to the lungs have low oxygen and high carbon dioxide
• Carbon dioxide in inspired air: 0.04%

  Carbon dioxide in expired air: 4%

  Carbon dioxide is produced by the body as a product of respiration and it is transported to the lungs to be excreted out
• Water vapour in inspired air: Rarely saturated

  Water vapour in expired air: Saturated

  Water evaporated from the moist lining of the alveoli into the expired air as a result of the warmth of the body
• Effect of exercise on breathing:

  ○ Carbon dioxide is acidic in nature

  ○ It has to be removed quickly before it causes any problems

  ○ As blood flows through the brain, increase in carbon dioxide concentration stimulates receptor cells

  ○ These cause pulses to be sent to the respiratory organs causing them to contract more often and with increased strength

  ○ This causes the frequency and depth of breathing to increase until carbon dioxide concentration has been lowered sufficiently.