exchange surfaces

• diffusion is the net movement of particles from a region where there is a higher concentration to a region where there is a lower concentration
• features of the perfect exchange surface

  • large surface area - larger sa greater diffusion
  • thin - shorter distance to diffuse across
  • concentration gradient -
  • protection from drying out
• alveolus structure

  • surfactant which reduces the surface tension increasing the stability and preventing collapsing
  • thin capillary membrane
  • small surface area individually but large overall
  • blood constantly flows past
• cartilage

  • found in trachea, bronchi
  • function - support, holding open and preventation of collapse
• smooth muscle

  • found in walls of trachea, bronchi and bronchioles
  • function - involuntary muscle that contracts to narrow the lumen
• elastic fibres

  • found in walls of the airways areas and alveoli
  • function - recoil of elastic tissue, widen airways after contraction and force air out of alveoli
• goblet cells

  • found throughout the ciliated epithelium
  • function - secretes a sticky mucus to trap particles and prevent drying out of tissues
• ciliated epithelium

  • found in the trachea, bronchus and bronchioles
  • function - cilia move in a synchronised pattern to waft mucus up the airway to the back of the throat
• respiratory system - the organs and tissue that carry out gas exchange and ventilation
• ventilation - the movement of gases in and out of the lungs
• breathing - the physical changes in the rib cage and diaphragm to cause ventilation
• process of inspiration

  1. external intercostal muscles contract, rib cage moves up and out
  2. volume inside the thoracic cavity increased
  3. pressure in the thoracic cavity decreased and air flows in down the pressure gradient
• process of expiration

  1. external intercostal muscles and muscles in the diaphragm relax
  2. elastic fibres recoil
  3. volume decreases and pressure increases forcing air out
• tidal volume - the volume of air that moves in and out of the lungs within each breath when at rest
• vital capacity - the largest possible volume that can be moved in and out during one breath
• forced breathing process

  1. more air can be forced in and out by contraction of the internal intercostal muscles, moving the rib cage down and in
  2. contraction of the abdominal muscles raises diaphragm
• inspiratory reserve volume - the amount of air that can be inspired after the normal tidal volume
• expiratory reserve volume - the amount of air that can be expired after a normal tidal volume
• vital capacity = tidal volume + inspiratory reserve volume + expiratory reserve
• residual volume - the volume of air that is always remaining in the lungs after biggest possible exhalation
• dead space - air in bronchus, bronchioles and trachea not involved in gas exchange
• countercurrent flow - where two fluids flow in opposite directions
• filaments - slender branches of tissue that make up the gill. these are often known as primary lamellae
• adaptations of gills

  • large sa provided by filaments and lamellae = increased area for diffusion
  • rich blood supply
  • thin layers
  • water moving over gills in the opposite direction to blood
• buccal-opercular pump

  1. the mouth is opened and buccal cavity lowered
  2. volume inside buccal cavity increases
  3. pressures inside decreases
  4. water moves in down pressure gradient
  5. mouth closes and buccal cavity raised, increasing pressure and forces water over the gills
  6. valve in opercular cavity open
• spiracle - a hole in the abdomen of insects that allows air to enter
• tracheal fluid - the fluid found at the ends of the tracheoles in the tracheal system
• tracheal system - a system of air-filled tubes in insects
• gas exchange in insects

  1. small openings in the throat = spiracles
  2. air enters and leaves by spiracles
  3. water is lost to increase the efficiency but to minimise water loss spiracle sphincters can open or close the spiracles
• arrangement of tissues inside insects

  • from the spiracles are the tracheae which are lined with chitin
  • tracheae branch into tracheoles where gas is exchanged
  • tracheal fluid limits the penetration of air, during activity lactic acid builds up in the tissues and water moves out by osmosis
• to supply extra oxygen insects have adapted to

  • mechanical ventilation of the tracheal system - muscular pumping movements of the thorax or abdomen change the volume of the body and lower the pressure changes
  • collapsible air sacs - act as air reservoirs increasing the volume of air moving through the exchange system, usually defaulted and inflated by the movement of the abdomen