Mammalian Gaseous Exchange System

• What is the problem with the diffusion pathway of larger organisms?

  too great to supply each cell with enough oxygen for aerobic respiration and to remove carbon dioxide
• Why are the lungs needed for terrestrial organism?

  + to balance the need for gas exchange with water loss

  + terrestrial organisms have to balance need for gas exchange and need for water

  + conditions for efficient gas exchange (i.e. moist lining) leads to increased evaporation
• How is the nasal cavity adapted to its function?

  + moist surface - increases the humidity of air entering the lungs and reduces evaporation from exchange surface

  + large surface area with good blood supply: warms air to body temperature

  + hairy lining which secrete mucus - trapds dust and bacteria to protect lung tissue
• Which two components are the lungs made up of?

  lung tissue and airways
• How is the lung tissue of the alveoli adapted to its function?

  + squamous epithelial cells which are flat and very thin

  + allows efficient gas exchange (short diffusion distance)

  + elastic tissue of elastin and collagen which can recoil to expel air
• How are the capillaries adapted?

  + very thin walls (made of squamous epithelial cells - endothelial cells) - short diffusion distance

  + large surface area (500 million alveoli)

  + alveolus wall contain elastin fibres that can stretch and recoil (letting push air out during expiration)

  + moist: gases dissolve and diffuse in solution

  + good blood supply to maintain conc gradient

  + flat and smooth to reduce friction and maintain blood flow
• What is lung surfactant and what is its function?

  + lung surfactant is solution including phospholipid that coats surface of lungs

  + without lung surfactant, watery lining of alveoli would create surface tension -> cause them to collapse
• Why are the airways large?

  allows sufficient air to flow without obstruction
• Why are the airways supported ( held open)?

  prevents collapse with air pressure is low
• Why are airways flexible?

  allows for movement
• How are the trachea, bronchi and larger bronchioles supported?

  + with rings of C-shaped cartilage

  + C-shaped cartilage can change shape when smooth muscle contracts and relaxes
• What happens during inspiration?

  + requires energy as muscles are contracting

  + diaphragm contracts and moves down and becomes flatter

  + displaces the digestive organs downwards

  + external intercostal muscles contract to move the ribs up and out

  + volume of chest cavity (thorax) increased

  + pressure in chest cavity drops below atmospheric pressure

  + air moved into lungs due to pressure gradient
• What happens during expiration?

  + diaphragm relxes and pushed up by displacement of organs underneath

  + now dome-shaped

  + external intercostal muscles relax and the ribs fall

  + elastic fibres in alveoli recoil

  + volume of chest cavity (thorax) is decreased

  + pressure in lungs increase and rises above pressure in surrounding atmosphere

  + air moved out of lungs
• What is forced expiration?

  + an active process (normal expiration is passive)

  + when breathing out forcibly e.g. sneezing, you empty your lungs out of most of air

  + exhaling forcibly uses energy (active)

  + internal intercostal muscles contract - pull ribs down hard and fast

  + abdominal muscles contract - force diaphragm up to rapidly increase pressure in lungs
• What does the pleural cavity do?

  + outer part of pleural membrane attaches to chest wall

  + inner membrane covers lungs and fluid is filled to reduce friction