Exchange surfaces and breathing Flashcards
Living organisms need certain substances to survive including:
- OXYGEN for aerobic respiration
- GLUCOSE as an energy source
- PROTEIN for growth and repair
- FATS for membranes and an energy store
- MINERALS to maintain water potential , enzyme function and other metabolic processes.
These are obtained from the environment or made in the cytoplasm.
Living organisms must be able to remove metabolic waste products:
- carbon dioxide
- oxygen from photosynthesis in plants
- ammonia or urea containing excess nitrogen
Single celled organisms VS larger organisms
Single celled organisms ~ have a large SA: volume ratio meaning they can readily exchange gases, nutrients and waste across their outer surfaces.
Larger organisms ~ they have a small SA: volume ratio meaning their outer surface is not large enough to enable gases and nutrients to enter its body fast enough to keep it alive.
This also means waste products can not leave fast enough before damaging cells.
3 factors affecting the need for an exchange surface:
- size
- SA : volume
- activity ~ more active organisms need a good supply of oxygen and nutrients for movement.
Features of an efficient gas exchange surface and examples
- large surface area ~ provides a large area over which the exchange of materials can occur.
- thin barrier ~ creates a short diffusion path
- good blood supply ~Steep diffusion gradient so diffusion occurs more rapidly.
Examples:
- the lungs
-small intestine
-liver
- root hairs of plants
- hyphae of fungi
Mammalian gas exchange system:
mammals are:
- active
- small SA:V
- constant body temperature ~ increased rate of aerobic respiration (these created a high demand of oxygen)
- nasal cavity
- trachea
- bronchi
- bronchioles
- alveoli
- Nasal cavity
- hairs trap pathogens and dust particles
- warms and moistens the air before entering the lungs
- trachea
- C shaped cartilage ~ firm but flexible, prevents the trachea from collapsing during inhalation and allow food to pass down the oesophagus
- goblet cells ~secrete mucus to trap pathogens
- ciliated epithelia ~ tiny hair like projections, that move mucus to the throat
- elastic fibres ~ deform and recoil due to the muscle contacting and relaxing
3.bronchi
- bronchioles
bronchi ~
carry air to the lungs
(have same features as trachea)
Narrower than the trachea
bronchioles ~ has smooth muscle which when relaxed , allows bronchioles to widen allowing more air to enter. Can also prevent harmful substances from the air entering.
They are much narrower than the bronchi.
- Alveoli
Air spaces divided by thin walls.
The site of gas exchange:
- large SA for diffusion of gases
- one cell thick ~short diffusion path
- good blood supply ~ steep concentration gradient for oxygen.
- elastic fibres ~ provide strength and flexibility and stretch and recoil to allow the alveolar volume to increase and decrease during ventilation.
Ventilation (breathing)
Increases the rate of diffusion:
- brings fresh air from outside the body into the alveoli.
- this increase the concentration of oxygen in the alveolar air spaces whilst decreasing the concentration of carbon dioxide.
- this increases the concentration gradient of these gases causing an increased rate of diffusion.
Components of the breathing system
- ribs
- intercostal muscles ~ external (normal breathing) and internal (strong breathing)
- diaphragm
Their role :
- change volume of thorax
-change pressure of the air in the lungs
- draw air in or expel air from lungs.
Inhalation
Active process (requires energy) :
- EXTERNAL INTERCOSTAL contract.
- RIBS pulled upwards and outwards
- DIAPHRAGM contracts causing it to flatten
- THORAX and LUNGS volume increase
- AIR PRESSURE is less than atmospheric pressure.
- air is DRAWN IN
- air moves into the ALVEOLI and ELASTIC FIBRES between the alveoli stretch to increase the surface area for exchange.
Exhalation
Passive process (less energy) :
- EXTERNAL INTERCOSTAL muscles relax
- DIAPHRAGM relaxes (dome shaped)
- THORAX and LUNG volume decreases
- AIR PRESSURE in lungs is GREATER than atmospheric pressure
- air is PUSHED OUT of lungs
- ELASTIC FIBRES (provide strength and flexibility) of alveoli RECOIL helping air to be pushed out.
gas exchange in lungs
- The movement of gases by diffusion between an organism and its environment across a barrier. example ~ alveolus wall.
- Takes place in the alveoli
- OXYGEN diffuses from the air int the alveoli into the blood where it combines with haemoglobin.
- CARBON DIOXIDE diffuses in the opposite direction from the blood to the air in the alveoli
Efficient gas exchange surface of the lungs
LARGE SURFACE AREA:
more space for molecules to pass through
MOIST MEMBRANE:
Allows gases to dissolve and diffuse through membrane.
SURFACTANT:
Produced by the lungs which coats the alveoli to prevent them from collapsing from the cohesive forces of the water molecules.
THIN BARRIER:
- To reduce the diffusion distance
- Many adaptions to achieve this :
- the alveolus walls are one cell thick
- the capillary wall is one cell thick
- both walls contain squamous cells (flattened)
- the capillaries are in close contact with the alveolus walls.
GOOD BLOOD SUPPLY:
Maintain a steep concentration gradient so that the gases continue to diffuse.
PERMEABLE TO OXYGEN AND CARBON DIOXIDE:
The cells and their plasma membranes readily allow the diffusion of oxygen and carbon dioxide as the molecules are small and non-polar.
Measuring lung volumes
- To measure the different volumes of air moved in and out during breathing, we use a SPIROMETER.
-consists of a chamber filled with OXYGEN that floats on a tank of water
- Person breathes from mouthpiece connected to the chamber of oxygen.
- breathing IN takes oxygen from the chamber , which then sinks down.
- breathing OUT pushes air into the chamber , which then floats up.
- the movements are recorded on a trace called a KYMOGRAPH.
Tidal volume
The volume of air moved in and out with each breath when at REST.
About 0.5 dm^3
Provides enough oxygen to the body and remove carbon dioxide to maintain safe levels.
if a persons tidal volume is lower , they are smaller (lower than normal volume)
Vital capacity
The LARGEST volume of air that can be moved in and out of the lungs in any one breath.
About 5 dm^3
Varies between , men and women , size , age and fitness levels.
Inspiratory reserve volume
&
expiratory reserve volume
How much more air can be breathed IN , over and above tidal volume.
How much more air can be breathed OUT , over and above tidal volume.
Residual volume
The volume of air that always remains in the lungs, even after the biggest expiration.
About 1.5 dm^3
Air always remains int the lungs as alveoli are held open by elastic fibres and air ways are held open by cartilage with the space filled with air.
Total lung capacity
Vital capacity + residual volume
Dead space
Air in the bronchioles , bronchi and trachea , where no gas exchange takes place.
Kymograph calculations
Tidal volume = value of one space x the height of one peak
Breathes per minute = 60/ time interval x number of peaks in that time interval
Ventilation rate = Tidal volume x breathes per minute
Oxygen uptake = 20% (oxygen in air) x ventilation rate.
