4. Ventilation and gas exchange in other organisms

• GASEOUS EXCHANGE SYSTEMS IN INSECTS

  • They have a tough exoskeleton through which little or no gaseous exchange can take place
  • Don’t have blood pigments to carry o2
  • O2 delivered straight to cells
• SPIRACLES

  • Spiracles: small openings through which air enters + leaves, but water is also lost
  • Insects need to --> maximise efficiency of gas exchange but minimise water loss
  • Spiracles can be opened/closed by sphincters [muscle around spiracle] = kept to minimise water loss often
  • Insect inactive + low o2 demands = spiracles closed
  • O2 demands rise/co2 levels build up = spiracles open
• TRACHEA

  • Leading away from spiracles are the = trachea
  • Trachea is 1mm in diameter + run along body of insect
  • Its also lined by spirals of chitin = which keep them open if they're bent/pressed
  • Chitin: material that makes up cuticle + relatively impermeable to gases = so little gas exchange in trachea
• TRACHEOLES

  • Trachea branch to form tracheoles
  • They have a diameter = 0.6-0.8 micrometers
  • Each tracheole = a single greatly elongated cell + no chitin so freely permeable to gases
  • Small size = spread throughout tissues of insect, running between individual cells
  • which is where most of the gas exchange takes place between air + respiring cells

  Water lost from tracheoles lost during exercise to free up SA for gas exchange
• • In most insects air moves along trachea + tracheoles by diffusion alone reaching tissues
  • Vast no. of tiny tracheoles = large SA for gas exchange
  • O2 dissolves in moisture on walls of tracheoles + diffuses into surroundings cells
  • Towards end of tracheoles there's = tracheal fluid --> it limits penetration of air for diffusion
• When o2 builds up:

  • Lactic acid build up in tissues = results in water moving out of tracheoles by osmosis
  • This exposes more SA for gas exchange
• • All of the o2 needed by cells of an insect is supplied by = tracheal system
  • Gas exchange controlled by = opening + closing of spiracles
• Some insects have high energy demands = to supply extra o2 the insects need alternative methods of increasing gas exchange:

  • Abdominal pumping: air actively pumped into system by muscular pumping movements of thorax +/abdomen = this changes the vol of the body = this changes the pressure in the trachea + tracheoles --> air drawn into trachea/tracheoles forced out as pressure changes
  • Collapsible enlarged trachea/air sacs which act as air reservoirs: used to increase amount of air moved through gas exchange system. Usually inflated + deflated by ventilating movements of thorax & abdomen 
• RESPIRATORY SYSTEMS IN BONY FISH

  • Animals that get o2 from water don’t need to prevent water loss like land animals
  • Water is a x1000 denser than air + x100 more viscous + much lower o2 content
  • So easier to move water in 1 direction = move economical energy-wise
• GILLS

  • Active fish have high o2 demands
  • Their SA:V means diffusion not enough to supply o2 to inner cells + scaly outer covering doesn’t allow gas exchange
  • They however maintain a flow of water in 1 direction over the gills
  • Gills = have a large SA, good blood supply, thin layers for gas exchange
  • In bony fish they're contained in a gill cavity + covered by a protective operculum [bony flap] = which is also active in maintaining flow of water over gills
• GILLS 2

  • Gills make up gas exchange surface of fish
  • To allow efficient gas exchange at all times fish need to maintain a continuous flow of water over gills = even when not moving
• WATER FLOW OVER THE GILLS

  • When fish are swimming they can keep a current of water flowing over the gills by opening mouth + operculum
  • When fish stop moving = water flow stops
  • Primitive cartilaginous fish [sharks] = rely on continual movement to ventilate the gills
  • Known as ram ventilation = they ram the water past the gills
  • Bony fish however have a system that allows them to move water over their gills all the time
• • When fish mouth is open:

  1. Buccal cavity [mouth] is lowered = increasing vol of buccal cavity
  2. Pressure decreases in cavity = water moves into buccal cavity
  3. Opercular valve is shut = opercular cavity containing gills expand
  4. This lowers pressure in opercular cavity = floor of buccal cavity moves up
  5. Pressure increases = water moves from buccal cavity over gills

  • When fish mouth closes:

  1. Operculum opens + sides of opercular cavity move inwards
  2. Pressure increases in opercular cavity = water forced over gills + out of operculum
  3. Floor of buccal cavity moves up = maintaining flow of water over gills
• Effective gas exchange in water

  • Gills --> large SA, rich blood supply to maintain steep conc gradient, thin layers, 2 extra adaptations
• ADAPTATION OF GILLS

  1. Tips of adjacent gill filaments overlap:

  • Increases resistance to flow of water over gill surfaces + slows down water movement = more time for gas exchange to take place

  2. Counter-current system
• COUNTER-CURRENT EXCHANGE SYSTEM

  • Water moving over gills + blood in gill filaments flow in diff directions
  • Steep conc gradient needed for fast + efficient diffusion = due to blood + water flowing in opposite directions = counter-current exchange system set up
  • Ensures steep conc gradient maintained = more gas exchange happens
  • Bony fish remove 80% o2 from water
  • Cartilaginous fish with parallel system to remove 50% o2 from water
• COUNTER-CURRENT EXCHANGE SYSTEM 2

  • Blood + water flow in opposite directions so an o2 conc gradient between water + blood maintained along gill
  • O2 continuous to diffuse down conc gradient so a higher level of o2 saturation of blood is achieved