3.1 Exchange Surfaces Flashcards
Generally, how do unicellular organisms get substances from their environment and get rid of waste?
- Through cell membrane (or outer surfaces)
- Have a large SA:VOL ratio + lower demands for nutrients, oxygen etc as less volume
Generally, how to multicellular organisms get substances from their environment and get rid of waste?
- Have specialised systems for exchange to occur
- Larger so cannot get substances from their outer surfaces; greater distance to diffuse across + this would be too large + slow for an exchange to occur across
- Larger organisms habve more demand for oxygen and nutrients as they are more active
- So large organisms need specialised exchange surfaces as well as transport systems
- Larger have a smaller SA:VOL ratio
What kind of animals have the largest surface area to volume ratio?
The smaller the organism, the greater the SA:VOL ratio
Define exchange surface
A specialised area that is adapted to make it easier for molecules to cross from one side of the surface to the other
What is the equation to work out SA:VOL ratio?
surface area (cm2) / volume (cm3)
How does SA:VOL ratio affect the rate of diffusion?
The smaller the SA:VOL ratio the slower the rate of diffusion
Define gaseous exchange.
The movement of gases by diffusion between an organism and its environment across a barrier eg. alveoli
How are the lungs adapted for efficient gaseous exchange?
- Large surface area (alveoli)
- Thin barrier to minimise diffusion distance (1 cell thick alveoli)
- Permeable to exchange molecules
- Good capillary network to maintain concentration gradient
How thick is the barrier between the alveoli and the c apillaries in the lungs?
2 cells thick (one from alveoli and one from the capillary)
How is a concentration gradient maintained between the alveoli and the capillaries?
- Constant supply of blood means oxygen removes as soon as it diffuses into the blood to keep the concentration in the blood low compared to the alveoli to keep a steep concentration gradient
- Reverse for CO2, high in blood and low in alveoli as it is breathed out
What is a surfactant and what is its function in the alveoli?
- Water film lining the alveoli
- Breath out: evaporates and leaves the lungs
- Cohesion between water molecules would cause alveoli to collapse
- Compound (surfactant) produced in alveoli lines them
- Reduces surface tension + cohesion + stops alveoli collapsing
How does inspiration occur?
- Diaphragm contracts, flattens and moves downwards
- External intercostal muscles contract + move the ribs up + out
- Increases the volume inside the thorax + lungs
- Reduces pressure inside thorax/lungs below atmospheric pressure
- Air moves into the lungs down a pressure gradient
How does expiration occur?
- Diaphragm relaxes + moves outwards
- External intercostal muscles relax + move ribs in + down
- The internal intercostal muscles can contract to help push air out more forcefully
- Decreases volume inside thorax + lungs
- Induces the pressure inside thorax/lungs above atmospheric pressure
- Air moves out of the lungs down a pressure gradient
What features of the alveoli make it ideal for gas exchange?
- Plasma membrane permeable to oxygen and carbon dioxide
- Large surface area through the infoldings
- Wall of the alveoli is one cell thick
- Good blood supply
What are the features of the mammalian gas exchange system that improve efficiency of gaseous exchange?
- Many alveoli
- The epithelium of the alveoli is very thin
- There are capillaries running over the surface of the alveoli
- The lungs are surrounded by the diaphragm and intercostal muscles
How does the many alveoli in the mammalian gas exchange system improve the efficiency of gas exchange?
Increases the surface area across which oxygen and carbon dioxide can diffuse
How does the thinness of the epithelium of the alveoli in the mammalian gas exchange system improve the efficiency of gaseous exchange?
Decreases the diffusion distance so increases the rate of diffusion
How does the capillaries running over the surface of the alveoli in the mammalian gas exchange system improve the efficiency of gaseous exchange?
Gives a good blood supply to maintain the concentration gradient by taking away oxygen and delviering carbon dioxide
How does the lungs being surrounded by the diaphragm and intercostal muscles in the mammalian gas exchange system improve the efficiency of gaseous exchange?
Allows ventilation as the diaphragm by contracting and relaxing to adjust the volume in the thorax to adjust the pressure: low pressure and contracting during inspiration and vice versa so that air goes down a pressure gradient
Define tissue.
A group of similar cells working together to perform a particular function
What are the tissues in the alveoli?
- Squamous epithelium
- Elastic fibres
What is the squamous epithelium?
It is the walls of the alveoli that are one cell thick to provide a short diffusion distance for gaseous exchange
What is the role of the cartilage in the respiratory system?
- Keeps airways open and prevent collapse during inspiration when there’s a low pressure in the thorax
- Allows some flexibility to move neck without constricting airways
What is the role of the smooth muscle in the respiratory system?
- Contracts to constrict airways
- Reduces flow of air
Why might the smooth muscles reduce the flow of air?
To reduce harmful substances going into the lungs, relates to asthma
What is the role of the elastic fibres in the respiratory system?
- They do not contract or relax
- Stretch when the smooth muscle contracts
- Recoil when the smooth muscle relaxes to help dilate the airway again
What is the role of the goblet cells in the respiratory system?
Secrete mucus to trap bacteria and other partciles to be removed from the lungs to reduce infection
What is the role of the ciliated epithelium in the respiratory system?
Waft to and fro to remove mucus from airways up to throat
What is the role of the blood vessels in the respiratory system?
Supply lung tissues like the smooth muscle with oxygen for aerobic respiration
What lung tissues are there in the trachea?
Cartilage (C-shaped), ciliated epithelium, goblet cells, smooth muscle and elastic fibres
What lung tissues are there in the bronchi?
Cartilage (not C-shaped), ciliated epithelium, goblet cells, smooth muscle and elastic fibres
What lung tissues are there in the bronchioles?
Ciliated epithelium, smooth muscle, elastic fibres and goblet cells (only in the larger ones)
What lung tissues are there in the alveoli?
Elastic fibres
How does a spirometer work?
- During inspiration: take in oxygen from chamber so it goes down
- During expiration: air pushes into the chamber so it goes up
- Movements are recorded on the trace (graph) by a data logger
Why do we have a residual volume?
- Lungs can’t be completely compressed
- Trachea and bronchi held open by cartilage
- Bronchioles and alveoli held open by elastic fibres
- Residual volume stops respiratory system from collapsing as they can’t have a vacuum there
How do you work out the tidal volume from a spirometer trace?
- Patient breathes normally
- Measure height of wave (tidal volume) of at least 3 waves and calculate a mean
When using a spirometer, why does the patient have to wear a nose plug?
To make sure they only take air from the chamber and not from the environment so you can accurately measure the volume inspired/expired
How do you work out the breaths per minute from a spirometer trace?
- Count the number of breaths taken 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
During spriometry, why will the total volume of gas in the spirometer decrease?
- Soda lime absorbs the carbon dioxide breathed out
- Tells you how much carbon dioxide is breathed out showing how much oxygen is taken in for aerobic respiration
- The volume of carbon dioxide removed=volume of oxygen used by person. Measures the rate of oxygen intake
Using a spirometer trace, how do you measure the rate of oxygen intake?
- Calculate the difference in volume between 2 peaks/troughs on the trace (in dm3)
- This gives you the volume of oxygen used
- Measure the time taken to use this volume of oxygen
- Divide the volume by the time to give the rate
- If time is in seconds, to give rate in dm3min-1 you need to divide by the number of seconds then multiply by 60
What are the three main factors that affect the need for an exchange system?
- Size
- Surface area to volume ratio
- Level of activity
How does gaseous exchange occur in small organisms?
- Happens over the surface of the body
- Don’t need a specialised exchange system
What exchanges happen in organisms and why?
- Supply of oxygen and nutrients
- Remove waste products so they don’t build up and become toxic
How do larger organisms more than 2 layers of cells) exchange substances?
Through specialise exchange systems
Why do larger organisms need specialised exchange surfaces but smaller organisms do not?
- Small: cytoplasm close to the environment. Diffusion gives them enough oxygen to keep cells alive/active
- Multicellular: several layers of cells Any oxygen/nutrients diffusing from outside have a longer diffusion pathway. Too slow to give innermost cells sufficient supply
What is the surface area to volume ratio like in smaller organisms?
- Small surface area
- Small volume
- Large surface area to volume ratio (surface relatively large compared with volume)
What is the surface area to volume ratio like in larger organisms?
- Large surface area
- Large volume
- Small surface area to volume ratio (surface relatively small compared with volume)
What size organisms have the largest surface area to volume ratio?
Smaller organisms
How do some organisms increase their surface area?
Adoptiong different shapes e.g. flatworm (thin, flat body)
Why do larger organisms have a smaller surface area to volume ratio?
As they get thicker, the volume increases as does the surface area, just not by as much
How does level of activity affect the demand for oxygen and nutrients?
- Increases the metabolic activity of the cells
- Metabolic activity uses energy from food + requires oxygen to release energy from aerobic respiration
- Cells of active organisms need good supply of nutirents/oxygen to supply energy from movement
- Need for energy is increased to keep themselves warm ie in mammals
What are the features of a good exchange surface?
- Large surface area
- Thin, permeable barrier
- Good blood supply
How does a large surface area help to make a good exchange surface?
- More space for molecules to pass through them
- Often through folding walls + membranes involved e.g. root hair cell
How does a thin, permeable barrier help to make a good exchange surface?
- Reduces diffusion distance
- Shown in alveoli in lungs
How does a good blood supply help to make a good exchange surface?
- Brings fresh supply of molecules to one side to keep concentration high
- Or removes molecules from demand side to keep concentration low
- Maintains a steep concentration gradient so diffusion can occur rapidly
- e.g. gills in fish
What is the gaseous exchange system in mammals?
Lungs and associated airways that carry air into and out of lungs
What are the lungs?
A pair of inflatable sacs lying in the chest cavity
How does air get from the nose to the lungs?
Along the trachea (windpipe), then bronchi, then bronchioles, then the alveoli (these are the surfaces where exchange of gases takes place)
What are the alveoli?
Tiny air filled sacs in the lungs
What are the lungs protected by?
The ribcage
What are the ribs held together by?
The intercostal muscles
How do gases get exchanged between the alveoli and the blood capillaries?
- By diffusion through thin walls of alveoli
- Oxygen passes from air in alveoli to blood capillaries
- Carbon dioxide passes from blood to air in alveoli
- Lungs maintain steep concentration gradient so diffusion continues
How does the large surface area help with gas exchange in the lungs?
- Individual alveoli are very small but there are lots so have a large surface area
- Total surface area in lungs is about 70m2
- Alveoli lined with thin layer of moisture, evaporating + is lost as we breathe out
- Lungs produce surfactant to coat the internal surface of alveoli to reduce cohesive forces between water molevules as these tend to make the alveoli collapse
How does the barrier being permeable to oxygen and carbon dioxide help with gas exchange in the lungs?
- Barrier is just wall of alveolus and wall of capillary (2 cells thick)
- Cells and their plasma (cell surface) membranes readily allow diffusion of oxygen and carbon dioxide as molecules are small and non-polar
How does the thin barrier to decrease diffusion distance help with gas exchange in the lungs?
- Alveolus wall one cell thick
- Capillary wall one cell thick
- Both walls consist of squamous cells (flattened or very thin)
- Capillaries are in close contact with alveolus walls
- Capillaries are so narrow that RBCs are squeezed against capillary wall, closer to air in alveoli to reduce their rate of flow
- Toyal barried to diffusion is 2 flattened cells, less than 1μm
What does squamous mean?
Flattened or very thin
How does a good supply of blood help with gas exchange in the lungs?
- Maintains a steep concentration gradient so gases continue diffusing
- Blood system tranpsorts carbon dioxide from tissues to lungs so conc is higher than air of alveoli so it can diffuse into the alveoli
- Blood system transports oxygen away from lungs so conc is lower than air of alveoli so oxygen diffuses into blood
What features of the lungs make it good for gas exchange?
- Large surface area so more space for molecules to pass through
- Barrier permeable to oxygen and carbon dioxide
- Thin barrier to decrease diffusion distance
- Good blood supply to maintain concentration gradient
How are the lungs ventilated?
By breathing movements, replacing used air in lungs to bring in more oxygen and remove carbon dioxide
How does ventilation affect the concentration of oxygen and carbon dioxide in the blood and alveoli?
- Ensures concentration of oxygen in air of alveolus is higher than that in the blood
- Ensures concentration of carbon dioxide in alveoli is lower than in the blood
How does inspiration occur?
- Diaphragm contracts to move down + become flatter (displacing digestive organs downwards)
- External intercostal muscles contract to raise ribs
- Volume of chest cavity is increased
- Pressure in chest cavity drops below the atmospheric pressure
- Air is moved into the lungs down a pressure gradient
How does expiration occur?
- Diaphragm relaxes + pushed up by displaced organs underneath
- External intercostal muscles relax + ribs fall. Internal intercostal muscles can contract to help push air out more forcefully (usually only during exercise, coughing or sneezing)
- Volume of the chest cavity decreases
- Pressure in lungs increases above pressure in surrounding atmosphere
- Air is moved out of the lungs down a pressure gradient
What do the elastic fibres in the walls of the alveolus do?
Stretch during inspiration and recoil to dilate airways to push air out during expiration
What features must there be of the trachea, bronchi and bronchioles in order for them to be effective?
- Large enough to allow sufficient air to flow without obstruction
- Supported to prevent collapse when air pressure inside is low during inspiration
- Flexible to allow movement
What are the aiways lined with?
Ciliated epithelium
Which, the trachea or the bronchus, are narrower?
The bronchi are narrower
What is the benefit of the cartilage being C-shaped in the trachea?
Allows flexibility and space for the food to pass down the oesophagus
What airways does cartilage support?
Trachea and the bronchi
What is the wall of the bronchioles mostly comprised of?
Smooth muscle and elastic fibres
What do the smallest bronchioles end in?
Clusters of alveoli
What does the smooth muscle do?
- Contracts
- Contricts the airways
- Constriction of lumen restricts flow of air to and from the alveoli
- Helps when there’s harmful substances in the air
- Contraction of smooth mucle is involuntary and may be because of an allergic reaction
- Cannot reverse the effect of contracting on its own
What do the elastic fibres do?
- Smooth muscle elongated by elastic fibres
- When smooth muscle relaxes, deforms elastic fibres
- As muscle relaxes, elastic fibres recoil to original shape+ size to dilate airway
What does a spirometer measure?
- Lung volume
- Measures movement in and out of lungs as person breathes
How does a spirometer work?
- Consists of a chamber of air/medical grade oxygen floating on a tank of water
- Inspiration: air drawn from chamber so lid moves down
- Expiration: air returns to chamber, raising the lid
- Movements may be recorded on a data logger
- Carbon dioxide rich air exhaled is passed through a chamber of soda lime, absorbing the carbon dioxide so oxygen consumption can be measured
Why does the air exhaled in spirometry go passed and therefore get absorbed by the soda lime?
So that the change of volume measured in the chamber is from the oxygen only, and not from the carbon dioxide exhaled
Why can’t spirometry be done for too long at a time?
Oxygen concentration in the chamber will become too low that it does not go into the body
What precautions must be taken when using a spirometer?
- Subject should be healthy and free from asthma
- Soda lime should be fresh and functioning
- Should be no air leaks in the apparatus as this would give invalid/inaccurate results
- Mouthpiece should be sterilised
- Water chamber must not be overfilled (or water may enter the air tubes)
What 2 things does lung capacity consist of?
Vital capacity (which can be measured) and residual volume (which can’t be measured)
What is the vital capacity?
The maximum volume of air that can be moved by the lungs in one breath
How is the vital capacity measured using a spirometer?
Taking a deep breath and expiring all the air possible from the lungs
What factors affect the vital capacity of a person?
- Size of person
- Age and gender
- Level of regular exercise
What is the vital capacity of a person generally in the region of?
2.5-5.0dm3
What might cause the vital capacity of a person to increase?
Being a trained athlete
What is the residual volume?
Volume of air that remains in the lungs even after forced expiration. Air remains in the airways and alveoli
What is the general residual volume?
1.5dm3
What is the tidal volume?
The volume of air moved in and out with each breath, normally measured at rest
What is the typical tidal volume of a person?
0.5dm3 - usually sufficient to supply all the oxygen required by the body at rest
What does breathing do?
Supplies oxygen for aerobic respiration and removes carbon dioxide produced in respiration
How is the oxygen uptake measured using a spirometer?
- As person breathes through spirometer, oxygen is absorbed by blood and replaced by carbon dioxide
- Carbon dioxide is absorbed by the soda lime in spirometer so volume of air in chamber decreases
- Decrease can be observed and measured in spirometer trace
- Can assume volume of carbon dioxide released/absorbed by soda lime equals volume of oxygen absorbed by blood
- Measuring gradient of decrease in volume enables us to calculate rate of oxygen uptake
How do you measure oxygen uptake from a spirometer trace?
- Draw line down to horizontal from two points (both peaks/troughs). Measure the length of time between these points.
- Measure difference in volume between 2 points
- Divide by time take for this decrease (unit in dm3s-1 - multiply by 60 for dm3min-1)
How can breathing rate be measured from a spirometer?
Count the number of peaks in each minute
What is the usual breathing rate of a person?
12-14 breaths per minute
Why might someone have a higher oxygen uptake?
Increased demand, e.g. during exercise when muscles are respiring (aerobically) more
What will result in an increased oxygen uptake?
- Increased beathing rate
- Deeper breaths
How do bony fish get oxygen?
From the water they live in, using gills to absorb oxygen dissolved in the water + release carbon dioxide into the water
Is the concentration of oxygen higher in the air or in water?
The air
How many pairs of gills to mnost bony fish have?
5
What is the bony plate that covers the gills in bony fish called?
Operculum
What does each gill consist of?
2 rows of gill filaments (primary lamellae)
What is the structure of the gill filaments?
- Very thin
- Surface folded into many secondary lamellae (gill plates)
- Provides a large surface blood
- Lamellae covered in capillaries
What do the capillaries around the gill lamellae do?
Carry deoxygenated blood close to the surface of secondary lamellae where exchange takes place
How and why do bony fish use a countercurrent flow?
- Blood flows along gill arch + out along filaments to secondary lamellae
- Blood flows through capillaries in opposite direction to flow of water over lamellae
- Arrangement causes a countercurrent flow to absorb the maximum amount of water
What is the journey of the water from entering the fish to leaving it?
- Mouth opens (operculum is closed)
- The buccal cavity floor is lowered
- This increased volume + decreases pressure in buccal cavity compared to outside
- Water moves into mouth down a pressure gradient
- Opercular cavity expands (lowering pressure)
- Buccal cavity floor is raised (increasing pressure)
- Pressure in buccal cavity is higher than opercular cavity
- Water moves from buccal cavity over gills to opercular cavity
- Mouth is now closed + operculum opens
- Sides of opercular cavity move inwards, increasing pressure
- Water rushes out of fish through operculum
What is the name of the system that bony fish use to keep water flowing over the gills?
Buccal-opercular pump
Why do insects have an open circulatory system?
Circulation is slow and can be affected by body movements
What is the journey of the air through an insect?
- Enters through a pore in each segment: spiracle
- Air transported into body through a series of tubes called tracheae
- Tracheae divide into smaller tubes calle tracheoles
- Ends of tracheoles are open + filled with tracheal fluid
- Gas exchange occurs between tracheole and tracheal fluid
- Some exchange also occurs across thing walls of tracheoles
What kind of circulatory system do insects have?
An open circulatory system
What is the system of getting air around in an insect called?
Tracheal system (air filled, supplies air directly to all respiring tissues)
What happens when an insect is active and has a higher demand for oxygen?
- Tracheal fluid can be withdrawn into body fluid
- Increases surface area of the tracheole wall exposed to air
- Means more oxygen can be absorbed when insect is active
How do many insects ventilate their circulatory system using flexible walls?
- Many have sections of tracheal system expanded with flexible walls
- These act as air sacs which can be squeezed by action of flight muscles
- Repetitive expansion + contraction of these sacs ventilate the tracheal system
How do some insects use their wings to ventilate their circulatory system?
- Some use movements of wings to alter volume of thorax
- As thorax volume decreases, air in tracheal system put under pressure + pushed out of tracheal system
- When thorax increases in volume, pressure inside drops + air is pushed into tracheal system from outside
How do locusts ventilate their tracheal system?
- Can alter volume of abdomen by specialised breathing movements
- Coordinated with opening + closing valves in spiracles
- As abdomen expands, spiracles at front end of body open + air enters tracheal system
- As abdomen reduces in volume, spiracles at rear of body open + air can leave the tracheal system
