Exchange surfaces

• Reasons for specialised exchange surface in multicellular:

  1. Less surface area to absorb nutrients and secrete waste.
  2. Cells in centre of organisms would not receive any materials if relied on diffusion alone due to longer diffusion distance.
  3. High metabolic rates therefore there is a need to exchange a large volume of material.
• Why do single celled organisms not need specialised system?

  • They have a large SA:V which allows for maximum absorption/secretion
  • The small volume means theres a short diffusion distance across the organism.
• surface area to volume calculation.$SA/V$
• Features of efficient exchange system:

  1. Large surface area
  2. Thin layers
  3. Good blood supply to maintain a concentration gradient
  4. Ventilation to help maintain a concentration gradient for faster more efficient diffusion.
• • Tidal Volume is volume of air that is exhaled/inhaled during a normal breath.
  • Vital capacity is the largest volume of air that can be inhaled.
  • Residual volume is the air left in your lungs after forced exhalation.
• Total lung capacity = vital + residual
• Inspiration

  1. External intercostals contact, moving the ribcage out and up.
  2. Diaphragm contacts, moving downwards.
  3. Volume increases, creating a lower pressure.
  4. This draws air into the lungs.
• Expiration

  1. External intercostals relax, moving ribcage down and in.
  2. Diaphragm relaxes, moving up.
  3. Volume of thorax decreases, causing pressure to increase.
  4. This forces air out of your lungs.
• Forced Expiration

  1. Internal intercostals contract to move the ribcage down and in.
  2. This is an active process.
• Mammalian Gas exchange - Tissues

  • Cartilage, strong and flexible, providing structural support.
  • Squamous epithelium, thin and permeable, ideal for diffusion.
  • Smooth muscle, able to regulate air flow by dilating and constricting.
  • Elastic fibres, allow the lungs to stretch and recoil.
• Mammalian Gas exchange - features

  • Nasal Cavity, good supply, moist surface and hairy lining to trap dust.
  • Trachea, C shaped rings of cartilage, lined with ciliated epithelium and goblet cells. Walls contain smooth muscle and elastic fibres.
  • Bronchi, similar to trachea but smaller in diameter/thinner walls. Full rings of cartilage.
  • Bronchioles, usually no cartilage, vary is size and structure dependant on how near to alveoli. Contain large amounts of smooth muscle, elastic fibres and ciliated epithelium.
• Mammalian Gas exchange - Alveoli

  • Main site of gas exchange
  • Made from a single layer of flattened epithelium cells.
  • Lined with collagen and elastic fibres
  • Surfactant to decrease surface tension of alveoli, this prevents them collapsing.
• Spirometry - measures the changes in lung volume.

  1. Test subject breathes in and out through spirometer
  2. The co2 exhaled is absorbed by the soda lime.
  3. As they breathe a trace is drawn on a rotating drum of paper.
  4. This can measure vital capacity/tidal volume/breathing rate/ oxygen uptake (change in volume ).
• Gas exchange - insects - structure

  • Spiracles, pores in the exoskeleton to allow air to enter and leave the body. They have valves to prevent water loss.
  • Tracheae, reinforced with spirals of chitin to provide structural support.
  • Tracheoles, single cells which form a hollow tube and filled with tracheal fluid.
  • Tracheal fluid, moves into muscle cells to draw air into tracheoles.(due to lower water potential in cells after anaerobic respiration produces lactic acid)
• Gas exchange - insects - ventilation

  • contract abdomen to create pumping movement for ventilation.
  • Wings will force air into spiracles during flight.
  • Volume changes in tracheoles creates movement of air.
• Structure of gills

  • Series of gills on each side of the head
  • Each gill arch is attached to 2 stacks of filament
  • Lamellae line the surface of the filament.
  • Lamellae are a series of flattened cells lined with capillaries.
  • Good blood supply, large surface area and short diffusion distance.
• what is the counter current flow system?

  Water flows in opposite direction to blood, this ensures that the oxygen rich blood will meet the oxygen rich water. Maintaining a steep concentration gradient for oxygen across the entire length of the gills.
• Gas exchange - fish- ventilation

  1. Mouth opens and floor of buccal cavity lowers, increases the volume and decreases the pressure.
  2. Pressure outside>pressure inside, so water flows into buccal cavity.
  3. Mouth closes and floor rises, increases pressure as volume decreases.
  4. Water flows from buccal cavity into gill cavity.
  5. High pressure in gill cavity cause operculum to open and for the water to exit the fish.
  6. The cycle repeats.
• Dissections

  1. Lab coat, gloves and goggles should be worn to avoid contamination.
  2. Use scissors for large area of tissue and scalpels to be more precise. (cut with scalpel facing away from you)
  3. limitations include : hard to see fine structures in detail, does not reflect how specimen's tissues would look when it was alive, only dissecting a single specimen leaves chance of anommolies going unnoticed.