Gas exchange

• Counter-current principle in gas exchange across a fish gill

  • water and blood flow in opposite direction to each other
  • maintains concentration gradient of oxygen
  • diffusion gradient maintained across the whole way of the gill lamellae
• Asthma

  • airways become inflamed, usually due to an allergic reaction
  • asthma attack; smooth muscle lining bronchioles contracts and lots of mucus produced
  • airways become constricted
  • air flow in and out of lungs is reduced
  • less O2 enters alveoli and moves into blood, reducing FEV1
• Describe and explain the mechanisms that cause forced expiration

  • external intercostal muscles relax
  • internal intercostal muscles contract
  • Diaphragm muscles relax
  • causes a decrease on thoracic volume
  • air pushed down pressure gradient
• What are the symptoms of asthma

  Tight chest, wheezing, and shortness of breath
• How can asthma be treated?

  relieved by drugs. This causes muscles in bronchioles to relax, opening airways
• Emphysema

  • caused by smoking or air pollution
  • foreign particles become trapped in alveoli
  • causes inflammation which attracts phagocytes that produce an enzyme that breaks down elastin
  • elastin is elastic so loss of it means alveoli cannot recoil and expel air well
  • leads to destruction of alveoli walls
  • decreases surface area so rate of diffusion decreases
  • ventilation rate increased
• what is elastin?

  It’s a protein found in walls of alveoli
• Explain how an asthma attack reduces FEV

  • muscles walls lining bronchioles contract
  • more mucus is secreted from bronchioles
  • diameter of airways is reduced
  • air flow reduced
• The stomata close when there is no light. Why?

  Water is lost through the stomata so closure prevents water loss. This maintains water content of cells.
• Explain the ways in which an insect‘s tracheal system is adapted for efficient gas exchange

  • tracheoles connect directly to cells so oxygen diffuses easily to respiring cells
  • tracheole walls are thin and permeable so short diffusion path for for gaseous exchange to cells. Tracheae connects directly to tissues
  • highly branched tracheoles so large surface area for gas exchange
  • Tracheae provide tubes full of air
• Describe and explain how the structure of the insect gas exchange system provides cells with sufficient oxygen and limits water loss

  • spiracles can open and close to reduce water loss and allow air to enter
  • tracheoles connect directly to cells so oxygen can be supplied easily to respiring cells
  • walls to tracheoles are thin and permeable, increasing diffusion of oxygen to cells
  • hairs around spiracles reduce water loss
  • exoskeleton is impermeable to water, reducing water loss
• Pulmonary Tuberculosis (TB)

  • immune system cells build wall around TB bacteria in lungs; forms small hard lumps called tubercules
  • tissue within tubercules die and gas exchange surface is damaged so tidal volume decreased
  • TB can result in fibrosis
  • reduced tidal volume means less air can be inhaled with each breath so ventilation rate increases to take in more O2
• Fibrosis 


  • is the formation of scar tissues in lungs
  • can be result of infection or exposure to dust or asbestos
  • scar tissue is thicker and less elastic than normal lung tissue so lungs are less able to expand (less recoil)
  • so can’t hold as much air, decreasing tidal volume and FVC
  • decreases rate of gas exchange, diffusion slower across thicker scar tissue
  • faster ventilation rate as tidal volume reduced