Gas exchange in animals

• The ventilation process


  Thorax:

  1. diaphragm muscle contracts and flattens
  2. (external) intercostal muscles contract moving the rib cage upwards and outwards = increase in volume of thorax.

  Lungs:

  1. Outer pleural membrane attached to the rib cage moves up and out - increasing volume and decreasing pressure in the pleural space
  2. inner pleural membrane on the surface of the lung in pulled upwards and outwards - increasing volume and decreasing pressure in alveoli
  3. air rushes in and the alveoli inflate
• Why do all living animals do gas exchange?

  • O2 is need for aerobic respiration
  • Produces ATP
  • ATP is universal energy currency
• Gas exchange in insects

  • called the tracheal system
  • consists of pairs of spiracles located on the body surface
  • fine hairs keep foreign particles out
  • valves open and close the spiracles to prevent water loss
  • spiracles open into long tubes called tracheae that link to air sacks
  • tracheae have cuticular thickenings around the tube the gives support and prevents them from collapsing during inspiration
• ventilation mechanics in insects

  • Insects can create a one-way airflow through major tracheae
  • Air flows in through the thoracic spiracles
  • Air flows out through the remaining abdominal spiracles
  • The air is moved by contraction and relaxation of the muscles in the abdomen which changes its size and pressure
• Ventilation in fish

  Inhale:

  • The mouth opens
  • The operculum gill cover closes
  • The floor of the mouth cavity lowers - increasing volume and decreasing pressure
  • water is pulled in

  Exhale:

  • The mouth closes
  • the floor of the mouth cavity is raised - decreasing volume and increasing pressure
  • water flows across the gills and is forced out through the operculum gill cover
• Counter Current flow

  • water and blood flow in opposite directions along the gill plate
  • blood is always meeting water with a slightly higher % oxygen saturation
  • This means that there is a diffusion gradient maintained across the whole gill plate
  • blood leaves about 95% saturation with oxygen
  • therefore it is a more efficient system
• parallel flow

  • water and blood flow in the same direction
  • at the start of the gill plate, there is a steep concentration gradient between the water and blood - so oxygen diffuses into the blood
  • however halfway across the the gill plate the % saturation of oxygen in the blood and water reach equilibrium
  • this means the blood leaving the gill is about 50% oxygen saturation so it is less efficient