SA:Vol Ratio and Gas Exchange (HUMAN)

• What 3 features do our lungs have to increase the rate of diffusion (Ficks Law)?

  • Large surface area to volume ratio.
  • A thin surface so short diffusion distance.
  • A diffusion gradient.
• What is a squamous cell?

  • A flattened cell
• What do our lungs have to increase the SA:V ratio?

  • Many alveoli
  • Many capillaries
  • A folded alveoli epithelium wall
• What does our lung have to decrease diffusion distance?

  • Squamous alveolar epithelium cells (1 cell thick)
  • Blood capillaries are close to the alveolus epithelium
  • Capillary epithelium/endothelium are one cell thick
• What does our lung have to maintain a diffusion gradient? (2 things)

  • Good circulation so that blood with a high O2 concentration is carried away, replacing it with blood with a low O2 concentration
  • Lung ventilation brings in air with a higher O2 concentration, removing air with a lower O2 concentration
• What happens when we breathe in?

  • External intercostal muscles contract while the internal relax
  • Ribcage lifts up and out
  • Diaphragm contracts and flattens
  • Volume of thorax increases so pressure decreases in the thoracic cavity
  • Air moves down a pressure gradient into the lungs
• What happens when we breathe out?

  • Internal intercostal muscles contract while the external relax.
  • Ribcage drops down and in.
  • Diaphragm relaxes and lifts up.
  • Volume of thorax decreases so pressure increases in thoracic cavity.
  • Air moves down a pressure gradient out of the lungs.
• What is tidal volume?

  • The volume of air taken in during each breath while resting
• What's the equation for ventilation (breathing rate)?

  • 60 seconds / Time taken for one breath = Breaths (min^-1)
• What is the equation for pulmonary ventilation?

  • Pulmonary ventilation (dm^3 min^-1) = Tidal volume (dm^3) x Ventilation rate (min^-1)
• What is inspiratory reserve volume?

  • The extra volume which can be breathed in during maximum inspiration
• What is expiratory reserve volume?

  • The extra volume which can be breathed out during maximum expiration
• What is vital capacity

  • The maximum volume which can be breathed in/out in one breath
• For exchange of materials to be effective should the SA:Vol ratio be large or small?

  • Large
• Does SA:Vol ratio get bigger or smaller as an object gets bigger?

  • It gets smaller
• Why do smaller organisms not require a specialised gas exchange system?

  • Their surface area to volume ratio is large enough that they can meet their gas exchange needs by diffusion across their surface.
• Why do larger organisms require a specialised gas exchange system?

  • They have a smaller surface area to volume ratio
  • So need a specialised gas exchange system to ensure rapid diffusion of gases.
• What is another factor that the SA:Vol ratio of an organism effects?

  • Heat loss
• Why do smaller organisms have a larger respiration rate?

  • They have a greater metabolic rate than larger organisms due to their small surface area to volume ratio so lose heat faster.
• What is ficks law?

  • Diffusion rate = (surface area x difference in concentration gradient) ÷ length of diffusion pathway
• What five factors make a good exchange surface?

  • Large surface area
  • Large concentration gradient (associated with an efficient transport system)
  • Thin exchange surface (short diffusion pathway)
  • Permeable
  • Moist (gases diffuse rapidly in solution)
• What is the trachea?

  • The trachea is a tube like structure that carries air from the mouth to the lungs.
• What are the bronchi?

  • The bronchi are after the trachea as it splits off into two bronchi as it enters the lungs, allowing air to go to the left or right lung.
• What are the bronchioles?

  • The bronchioles are the smaller branches after the bronchi which supply the alveoli with air.
• What are the alveoli?

  • The alveoli are the small sacks at the end of the bronchioles that act as the interface between the air and the lungs and the blood.
• How are the alveoli adapt to provide a large surface area?

  • Their walls are folded
• What helps the alveoli maintain a good concentration gradient?

  • They have a very rich blood supply which circulates blood and combined with ventilation, helps to provide a large concentration gradient between the gases in the blood and the alveoli.
• Which vessel brings deoxygenated blood to the lungs from the heart.

  • The pulmonary artery
• Which vessel brings oxygenated blood from the lungs to the heart.

  • The pulmonary vein.
• How can the pulmonary ventilation rate be changed?

  • By altering either the ventilation rate or the tidal volume or both
• What is pulmonary ventilation?

  • The amount of air exchanged in one breathing cycle
• Describe the condition fibrosis.

  • It causes damage to and scars the lung epithelium.
  • This results in the deposition of fibrous tissue in the lung epithelium
• What 2 effects can the scarring of the lung epithelium by fibrosis cause?

  • A reduced rate of diffusion (longer diffusion pathway and less permeable).
  • Reduced elasticity of the lungs, therefore breathing out if not as efficient.
• What can cause asthma to trigger and give examples?

  • Asthma can be triggered by an allergic reaction.
  • This may be due to; pollen, air pollution, dust, infection, or stress.
• What happens during an asthma attack?

  • The effected area is infiltrated by a type of white blood cell called macrophage.
  • These white blood cells release inflammatory chemicals such as histamine.
  • The inflammation causes reduced air flow through the bronchioles.
• Describe the condition of emphysema and what causes it and hat happens - link to SA

  • Emphysema is caused by exposure to irritants such as excessive dust and smoking.
  • The elastic tissue becomes damaged and the elastic tissue cannot recoil as normal and remains permanently stretched.
  • The alveolar wall starts to breakdown, reducing surface area for diffusion and the alveoli may start to fill with fluid also reducing surface area.
• Why do surfaces for gas exchange also have to consider water loss along with gas exchange?

  • The most effective surface for gas exchange is the same for evaporation, which is a large, thin and permeable area.
  • This leaves room for the potential of fatal dehydration
• Fill in the following diagram

  A - Cartilage ring

  B - Trachea

  C - Ribs

  D - Heart

  E - Bronchiole

  F - Diaphragm

  G - Alveoli

  H - Lung

  I - External Intercostal Muscle

  J - Internal Intercostal Muscle

  K - Bronchus

  
• Fill in the blank:

  A - Alveolar Air sack

  B - Epithelium

  C - Endothelium

  D - Capillary blood vessel