3.1.1 Transport surfaces

• Why we need specialized gas exchange surfaces

  • Large, multicellular organisms require specialized exchange surfaces for 3 main reasons:
  • High metabolic activity
  • Low surface area to volume ratio
  • Large diffusion distance
• Organisms without specialized exchange surfaces

  • Amoeba
  • Tapeworm
  • Jellyfish (HINT: THEY ARE SLUGGISH)
• Properties of exchange surfaces

  • High surface area
  • Thin surface
  • Good blood supply
  • Good ventilation (for gas exchange)
• Structures involved in mammalian gas exchange

  • Nasal cavity
  • Trachea
  • Bronchi
  • Bronchioles
  • Diaphragm
  • Alveoli
• Exhalation

  1. Diaphragm RELAXES, returning to dome shape

  2. Ext. intercostal muscles RELAX, moving ribs DOWN and IN

  3. Volume of thoracic cavity DECREASES

  4. Pressure INCREASES w.r.t atmospheric pressure

  5. Air rushes out
• Inhalation

  1. Diaphragm CONTRACTS and flattens

  2. Ext. intercostal muscles CONTRACT, pushing ribs UP and OUT

  3. Volume of thoracic cavity INCREASES

  4. Pressure DECREASES w.r.t atmospheric pressure

  5. Air rushes in
• Ventilation


  The movement of air in and out of the lungs due to pressure changes created in the thoracic cavity
• Terms to know for spirometer readings

  • Tidal volume
  • Vital capacity
  • Inspiratory reserve volume
  • Expiratory reserve volume
  • Residual volume
  • Total lung capacity
• Ventilation rate


  The volume of air inhaled in a minute = tidal volume x breathing rate (cm3/min or dm3/min)
• Breathing rate


  The number of breaths taken per minute
• Challenges for insects

  • Exoskeleton -Impermeable to gases due to chitin and waxy cuticle
  • No blood pigments - Gases cannot be carried in the blood
  • Relatively high metabolism - High energy needs, high 02 demands and CO2 production
• Structures involved in insect gas exchange

  • Spiracles
  • Tracheae
  • Tracheoles
  • Muscle cells
• What happens to the tracheolar fluid when active

  1. Increased activity means increased energy demands. Lack of O2 leads to anaerobic respiration in the muscle cells

  2. Lactic acid builds up in the muscle cells, reducing the water potential of the cells compared to the tracheoles

  3. Tracheal fluid enters the muscle cells by osmosis, carrying the dissolved oxygen with it

  4. Tracheoles become air filled, increasing the surface area for gas exchange
• Adaptations to aid ventilation in insects

  • Pumping movements of the thorax and abdomen
  • Selective opening and closing of the spiracles
  • Air sacs (Enlarged trachea)
• Challenges faced by fish for gas exchange

  • Water is dense and viscous, lots of energy is needed to move this water
  • Water has a low O2 Content and diffusion is slower, larger volume of water needs to be moved unidirectionally over their gills compared to air in lungs
  • High energy demands, low SA:V and impermeable scaly surface, lots of energy required to pass large volumes of water
• Structures involved in fish gas exchange

  • Gills
  • Opercular cavity
  • Gill filaments
  • Lamellae
  • Capillaries
• Countercurrent exchange


  • Parallel flow: Only 50% O2 diffuses into blood from water as equilibrium is reached. (in cartilaginous fish)
  • Countercurrent: Concentration gradient maintained throughout as conc. of O2 in water is ALWAYS higher than in blood, allowing continuous diffusion from water to blood. 80% of O2 diffuses. (bony fish)
• How fish achieve ventilation

  EXHALATION:

  1. Mouth closes and floor of buccal cavity raises
  2. Volume of buccal cavity decreases so pressure increases
  3. Operculum is open and moves inwards
  4. Water is forced out through the operculum, over the lamellae
• FISH

  INHALATION:

  1. Mouth opens and floor of buccal cavity lowers
  2. Volume of buccal cavity increases so pressure decreases
  3. Operculum is closed but expands, further increasing volume and decreasing pressure
  4. Water rushes in
• C-shaped rings of CARTILAGE


  • trachea and bronchi
  • strong, flexible
  • provides support
  • prevents collapse
• Smooth Muscle


  • trachea, bronchi, bronchioles
  • constricts and relaxes to regulate air entering - smoky environments, exercise
• Goblet cells


  • trachea, bronchi
  • mucus - traps microorganisms and dust
• Ciliated epithelia


  • trachea and bronchi
  • with goblet cells
  • wafts mucus away from lungs
• Elastic fibres

  • trachea, bronchi, bronchioles, alveoli
  • stretch to aid inhalation
  • recoil to aid exhalation
• Epithelium

  • goblet cells, ciliated - trachea, bronchi and larger bronchioles
  • flattened - smaller bronchioles
  • squamous - alveoli
• ALVEOLI FEATURES

  1. large surface area
  2. permeable
  3. one-cell thick alveoli and capillary walls
  4. steep concentration gradient
  5. moist walls + surfactant
• HUMAN INHALATION

  An active process as muscles contract and works against gravity
• HUMAN EXHALATION

  A passive process as muscles relax, along gravity, elastic recoil in alveoli aid process
• TIDAL VOLUME


  Volume of air in a normal breath at rest
• VITAL CAPACITY


  Maximum volume of air that can be inhaled and exhaled
• INSPIRATORY RESERVE VOLUME


  maximum volume of air that can be inhaled above the tidal volume of air
• EXPIRATORY RESERVE VOLUME


  maximum volume of air that can be exhaled above the tidal volume of air
• RESIDUAL VOLUME

  volume of air that can never be expelled from the lungs
• TOTAL LUNG CAPACITY

  vital capacity + residual volume
• SPIROGRAM

  A) TOTAL LUNG CAPACITY

  B) TIDAL VOLUME

  C) VITAL CAPACITY

  D) RESIDUAL VOLUME

  
• SPIRACLES - insects

  • openings in the body surface
  • controlled by sphincter muscles
• TRACHEAE - insects

  • carry air into and along the body
  • spirals of chitin
• TRACHEOLES - insect

  • single elongated cells
  • contact with every cell
  • filled with TRACHEOLAR fluid
  • no chitin, so permeable
• MUSCLE CELLS - insects

  • gases dissolve in tracheolar fluid and diffuse into muscle cells
• Pumping movements of the thorax and abdomen - insects


  • change volume of the body cavity, creating pressure differences
  • happens via wing movements