Chapter 7

• Why is diffusion alonge enough for single-celled organisms?

  • metabolic activity of a single-celled organism is usually low - demands for O₂ & CO₂ low
  • large SA:V ratio
• Why are specialised exchange surfaces needed?

  • higher metabolic activity - more energy - higher O₂ & CO₂ demands
  • diffusion distance is too far
  • smaller SA:V ratio - gases can't be exchanged fast enough or in large enough demands
• Features of an efficient exchange surface

  • large surface area
  • thin layers
  • good blood supply
  • ventilation to maintain diffusion gradient - e.g. gills
• How does a large surface area allow for an efficient exchange surface?

  provides area needed & overcomes limitations of a small SA:V ratio
• How do thin layers allow for an efficient exchange surface?

  short diffusion distance - fast & efficient
• How does a good blood supply allow for an efficient exchange surface?

  steeper concentration gradient - faster diffusion - substances constantly delivered to & removed
• Features of the nasal cavity

  • large surface area with a good blood supply - warms air to body temp
  • hairy lining - secretes mucus to trap dust & bacteria protecting delicate lung tissue from irritation & infection
  • moist surfaces - increase humidity of incoming air, reducing evaporation from exchange surface
• Describe the trachea & its function

  • wide tube supported by incomplete rings of strong, flexible cartilage - stop trachea collapsing & allow food down the oesophagus
  • lined w ciliated epithelium cells w goblet cells between & below which secrete mucus onto lining - traps dust & microorganisms which cilia move to throat to be swallowed, preventing lung infection
  • carries air to bronchi
• Describe the bronchi & their function

  • like trachea, lined by ciliated epithelium cells & supported by rings of cartilage
  • are narrower
  • one for each lung (left bronchus & right bronchus)
  • carry air into bronchioles
• Describe the bronchioles & their function

  • in lungs bronchi divide to form many small bronchioles
  • no cartilage - have smooth muscle - contracts to constrict bronchioles & relaxes to dilate - changes amount of air reaching the lungs
• Describe the alveoli & their function

  • tiny air sacs lined w epithelium cells and w some collagen & elastic fibres - main gas exchange surfaces
  • elastic tissues allow alveoli to stretch as air is drawn in & when they return to resting size they help squeeze air out - known as elastic recoil
• Adaptations of alveoli for effective gaseous exchange

  • large surface area
  • thin layers - walls 1 epithelial cell thick - short diffusion distance
  • good blood supply - constant flow of blood through network of millions of capillaries - maintains steep concentration gradient
  • good ventilation - breathing moves air in & out of alveoli - maintaining steep diffusion gradients for O2 & CO2 between blood & air in lungs
• Inspiration 


  • diaphragm contracts & flattens & lowers
  • external intercostal muscles contract - ribs move up & out
  • volume of thorax increases - pressure lower than atmospheric air - air is drawn into lungs
• Normal expiration

  • diaphragm relaxes - moves up into domed shape
  • external intercostal muscles relax - ribs move down & in
  • volume of thorax decreases - pressure inside is greater than atmospheric air - air moves out of lungs
• Forced exhalation 


  • internal intercostal muscles contract - ribs move down hard & fast
  • abdominals contract - force diaphragm up - increases pressure in lungs rapidly
• How does a spirometer work?

  • measures lung volume
  • person breathes into an airtight chamber which leaves a trace on a graph which shows the volume of breaths
• Tidal volume 


  volume of air that moves in & out of lungs w each resting breath
• Vital capacity


  volume of air that can be breathed in when strongest possible exhalation is followed by deepest intake of breath
• Inspiratory reserve volume 


  max volume of air you can breathe in over and above a normal inhalation
• Expiratory reserve volume 


  extra amount of air you can force out of lungs over & above normal exhalation
• Residual volume 


  volume of air left in lungs when you have exhaled as hard as possible
• Total lung capacity 


  = vital capacity + residual volume
• Label spirometer

  A) total lung capacity

  B) tidal volume

  C) inspiratory reserve volume

  D) expiratory reserve volume

  E) inspiratory capacity

  F) residual volume

  G) vital capacity

  H) tidal volume increasing during exercise

  
• Breathing rate


  number of breaths taken per minute
• Ventilation rate


  = tidal volume x breathing rate
• What happens when O2 demands increase?

  • tidal volume can increase
  • breathing rate increases
  • inc ventilation of lungs & so O2 uptake during gas exchange can be increased to meet demands
• 3 main features of an insects gas transport system

  • spiracles
  • tracheae
  • tracheoles
• Where are spiracles found?

  along thorax & abdomen as small openings
• How do the spiracles work?

  • open & close by sphincters
  • opened - when O2 demand raised or CO2 levels build up
  • closed - when O2 demands are very low & insect is inactive
  • closed as much as possible to minimise water loss
• Tracheae 


  • largest tubes in insect respiratory system
  • carry air into body
  • run into & along body
  • tubes lined by spirals of chitin - keep them open if they're bent or pressed
• Tracheoles 


  • smaller branches dividing off tracheae
  • small size - spread throughout tissues of insect, running between individual cells
  • where most of gaseous exchange takes place between air & respiring cells
• How is oxygen taken up in insects?

  • air moves along tracheae & tracheoles
  • O2 diffuses from tracheoles into surrounding cells
  • end of tracheoles there's tracheal fluid which limits penetration of air for diffusion
• How does carbon dioxide leave in insects?

  • CO2 diffuses from tissues into the tracheae down a concentration gradient
• Label gaseous exchange system in an insect

  A) muscle

  B) tracheoles

  C) tracheae

  D) spiracles

  E) water in the tracheoles

  
• Methods of gaseous exchange in large insects

  • more active - higher O2 demands
  • muscular pumping system of the thorax and/or abdomen - changes volume of the body - as pressure changes in tracheae & tracheoles air is drawn in & out
  • collapsible enlarged tracheae or air sacs - inflated/ declared by movements of thorax nd abdomen to increase amount of air move through exchange system
• Why do fish their own specialised respiratory system?

  • water is denser than air, more viscous & has much lower oxygen content
  • it would use too much energy to move dense, viscous water in & out of lung-like respiratory organs
  • moving water in one direction is simpler and wastes less energy
• Water flow over gills when bony fish are swimming


  keep current of water flowing over their gills by opening their mouth & operculum
• Countercurrent flow in the gills

  • water moving over gills & blood in the gill filaments flow in different directions
  • ensures steep concentration gradient maintained
  • oxygen continues to diffuse down conc gradient so higher level of oxygen saturation of blood is achieved

  
• Water flow over the gills

  • water enters through mouth
  • continuous flow of water across gills is achieved by floor of buccal cavity (mouth) being lowered (which takes water into mouth) & then raised (which forces water over gills)
  • water leaves a fish when the operculum (flap covering gills) opens

  
• How is oxygen taken up in a fish?

  • water & blood in lamellae flow in opposite directions (countercurrent flow) ensuring oxygen concentration gradient maintained along gill
  • oxygen diffuses into gill lamellae which are thin plates packed w blood capillaries. Lamellae are attached to gill filaments