Module 3: Exchange Surfaces & Breathing Flashcards
Why do organisms need exchange surfaces?
All organisms need to be able to take up simple substances from the environment e.g. Oxygen.
They also need to get rid of waste products e.g. CO2.
How do very large and very small organisms differ in the way they exchange substances?
Very small organisms (singe-celled organisms) are able to exchange nutrients, gases and other waste across their surface membrane.
Very large organisms (multicellular) require exchange surfaces.
Why do very small organisms not require exchange surfaces and large organisms do?
Small organisms have a very small surface-area:volume ratio and very low demands for nutrients and oxygen.
Large organisms have a very small surface area: volume ratio. This means that their outer surface is not large enough to enable oxygen to exchange fast enough into the body to keep all the cells alive.
Large organisms are also very active which means that they have very high demands for nutrients and oxygen etc.
What is an exchange surface?
A specialised area that makes it easier for a substance to travel from one side of the surface to another.
Examples of exchange surfaces
alveoli, vili of small intestine, root hair cells
What are features of a good exchange surface?
1) Large surface area- more space for molecules to pass through
2) Thin walls- shorter diffusion pathway
3) Fresh supply of molecules on one side- keeps conc high
4) Removal of molecules on other side- keep conc low
5) Permeable to exchange molecules
SA:VOL
SA:VOL= surface area (cm2) / volume (cm3)
Larger organisms have a smaller surface-area to volume ratio
What is gaseous exchange?
The movement of gas by diffusion between an organism and its environment across a barrier. e.g. alveoli
The function of the lungs
The function of the lungs is for ventilation for gaseous exchange.
Air is breathed into the lungs. Oxygen passes from the air in the alveoli into the capillaries and is used for aerobic respiration.
Veins carry deoxygenated blood to the lungs which contain CO2 which is breathed out.
Ventilation
Breathing
Inspiration (breathing in)
1) Diaphragm contracts, flattens and moves downwards.
2) Intercostal muscles contract- ribs move up and out.
3) This increases the volume in the thorax and lungs.
4) This reduces the pressure in the thorax and lungs below atmospheric pressure.
5) Air moves down a pressure gradient into the lungs
Expiration (breathing out)
1) Diaphragm contracts and moves upwards.
2) Intercostal muscles contract- ribs move down and in
3) This decreases the volume in the thorax and lungs
4) This increases the pressure in the thorax and lungs above atmospheric pressure
5) Air moves down a pressure gradient out of the lungs
Why are the lungs good for gaseous exchange?
- Millions of alveoli provide a large S.A. for more space for O2 and CO2 to diffuse across (NOT SA:VOL).
- Thin barrier- 2 cells thick, walls of alveoli and capillaries are made of squamous epithelial cells. Alveoli and capillary only one cell thick.
- Plasma membranes of the capillaries and alveoli are fully Permeable to O2 and CO2.
Maintaining the conc gradient in the lungs
SUMMARY:
good blood supply - many capillaries ‐ to carry dissolved gases to and from the alveoli
ventilation caused by intercostal muscles and diaphragm ‐ to refresh the air in the alveoli to keep conc of O2 in the alveoli high.
Surfactant
Alveoli are lined with a thin water layer. As we breathe out the water evaporates and leaves the lungs
The cohesion between water molecules would cause the alveoli to collapse.
A compound called surfactant produced in the alveoli lines the alveoli. This reduces the cohesion to prevent alveoli collapsing.
Tissues in the trachea and bronchi
1) C shaped rings of cartilage (not in the bronchioles)- Prevent the lungs from collapsing and allow flexibility and space for food to pass down the oesophagus.
2) Smooth muscle- Involuntary muscle that contracts without the need for conscious thought.
3) Goblet cells and ciliated epithelium- The airways are lined by ciliated epithelium. Goblet cells in the epithelium release mucus, which traps pathogens. The cilia then move the mucus to the top of the airway, where it is swallowed.
4) Elastic fibres- Stretch during inhalation then recoil to help push air out during expiration.
5) Blood vessels
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Tissues in the alveoli
Elastic fibres
• DO NOT CONTRACT/RELAX
• stretch during inhalation to increase the lung volume and prevent the alveoli from bursting
• recoil during exhalation to expel more air from the alveoli
Squamous epithelium
• alveoli walls one cell thick to provide a short diffusion distance for gaseous exchange
How does a spirometer work?
When person breathes in, they take oxygen from the chamber, causing it to go down. When they breathe out it pushes air into the chamber, causing it to go up. These movements are recorded on the trace (graph) by a data logger.
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Describe the precautions that must be taken to ensure valid results using a spirometer.
Make sure everything is airtight so no oxygen is lost through leaks.
Nose clip ‐ to ensure all air breathed comes from chamber
otherwise invalid results.
Describe 2+ precautions that must be taken to ensure the safety of the patient when using a spirometer.
- Check health of patient ‐ e.g. no bronchitis.
- Disinfect mouthpiece.
- Water level must not be too high and enter tubes.
- Use medical grade oxygen ensure there is enough oxygen.
- Soda lime/calcium hydroxide to absorb CO2 from chamber
Spirometer Trace
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Tidal volume- Is the volume of air moved in and out with each breath. A typical tidal volume would be 0.5 dm3.
Vital capacity- Is the max volume of air that can be moved by the lungs in one breath. This is measured by taking a deep breath and expiring all possible air from the lungs. This depends on:
- The size of a person (height)
- Age and gender
- Their level of regular exercise
Residual volume- The volume of air that remains in the lungs after forced expiration. This air remains in the airways and alveoli. This is approximately 1.5 dm3.
This air cannot be expelled because:
‐ Lungs can’t be completely compressed.
‐ Trachea and bronchi held open by cartilage.
‐ Bronchioles and alveoli held open by elastic fibres.
Using a spirometer to measure mean tidal volumes
1) Patient breaths normally.
2) Measure the height (tidal volume) of at least 3 of the waves from trace.
3) Mean = Add volumes together and divide by number of breaths. 1 breath = peak to peak.
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Using a spirometer to calculate breathing rate (breaths per minute)
- count the number of breaths take in a set period of time.
- divide the number of breaths by this time (in seconds).
- multiply by 60 to find the number of breaths per minute.
5 breaths in 30s (35s ‐ 5s)
5/30 x 60 = 10 breaths min‐1
In a trace over a period of time, the total volume of gas in the spirometer will decrease. Why?
When you exhale into the spirometer, the carbon dioxide is absorbed by the soda lime. This decreases the volume of gas in the spirometer and causes the trace line to fall gradually. This volume of carbon dioxide removed is equal to the volume of oxygen used by the person.
We can use this to measure the rate of oxygen uptake.
Measuring rate of oxygen uptake from a spirometer.
- calculate the difference in volume between two peaks/troughs on the trace (in dm3)
- this will give the you volume of oxygen used.
- measure the time take to use this volume of oxygen.
- divide the volume by the time to give the rate.
Bony Fish
Bony fish must exchange gases with the water in which they live. They use gills in order to absorb oxygen dissolved in the water and release carbon dioxide into the water. The oxygen concentration will be typically much lower than is found in air. Most bony fish have five pairs of gills which are covered by a bony plate called the operculum.
Each gill consists of two rows of gill filaments (primary lamellae) attached to a bony arch. The filaments are very thin, and their surface is folded into many secondary lamellae (or gill plates).
This provides a very large surface area. Blood capillaries carry deoxygenated blood close to the surface of the secondary lamellae where gas exchange takes place.
Describe the mechanism of ventilation and gas exchange in a bony fish- Countercurrent flow and ventilation
Countercurrent flow:
Blood flows along the gill arch and out along the filaments to the secondary lamellae. The blood then flows through capillaries in the opposite direction to the flow of water over the lamellae. This arrangement creates a countercurrent flow that absorbs the maximum amount of oxygen from the water.
Ventilation in bony fish:
Bony fish can keep water flowing over the gills by using a buccal- opercular pump. The buccal cavity (mouth) can change volume. The floor of the mouth moves downwards, drawing water into the buccal cavity. The mouth closes and the floor is raised again pushing water through the gills. Movements of the operculum are coordinated with the movements of the buccal cavity. As water is pushed from the buccal cavity, the operculum moves outwards. This movement reduces the pressure in the opercular cavity (the space under the operculum), helping water to flow through the gills.
Bucal Cavity
The mouth
Countercurrent flow
Where two fluids flow in opposite directions.
Filaments
Slender branches of tissue that make up the gill. They are often called primary lamellae.
Gill plates
Folds of the filament to increase surface area. They are also called gill plates.
Operculum
A bony flap that covers and protects the gills.
Dissection of fish gill
- Find the operculum (bony covering on each side of the fish∔s head).
- Lift the operculum and observe the gills. Note their colour.
- Cut away one operculum to view the gills. Note the gill
slits or spaces between the gills. - Carefully cut out one gill. Note the bony support (gill
arch) and the soft gill filaments that make up each gill. Draw the gill.
Insects
Insects do not transport oxygen in blood. Insects have an open circulatory system in which the body fluid acts as both blood and tissue fluid. Circulation is slow and can be affected by body movements.
Insects possess an air‐filled tracheal system, which supplies air directly to all the respiring tissues. Air enters the system via a pore in each segment, called a spiracle. The air is transported into the body through a series of tubes called tracheae (singular ‘trachea’). These divide into smaller and smaller tubes, called tracheoles. The ends of the tracheoles are open and filled with fluid called tracheal fluid. Gaseous exchange occurs between the air in the tracheole and the tracheal fluid. Some exchange can also occur across the thin walls of the tracheoles.
Ventilation in insects
Larger insects can also ventilate their tracheal system by movements of the body. This can be achieved in a number of ways:
- Flexible tracheal walls act as air sacs which can be squeezed repetitively by the action of the flight muscles to ventilate the tracheal system.
- In some insects, movements of the wings alter the volume of the thorax. As the thorax volume decreases, air in the tracheal system is put under pressure and is pushed out of the tracheal system. When the thorax increases in volume, the pressure inside drops and air is pushed into the tracheal system from outside.
- Locusts can alter the volume of their abdomen by specialised breathing movements, coordinated with opening and closing valves in the spiracles. As the abdomen expands, spiracles at the front end of the body open and air enters the tracheal system. As the abdomen reduces in volume, the spiracles at the rear end of the body open and air can leave the tracheal system.
