Exchange Surfaces and Breathing Flashcards
What are the main factors that warrant whether an organism needs a specialised exchange system?
Size
Surface area to volume ratio
Level of activity
How does the ‘size’ of an organism affect the need for an exchange system?
cytoplasm in small organisms is close to the environment so diffusion will supply enough oxygen and nutrients to keep the cells alive and active
Multicellular organisms may have several layers of cells and so anything diffusing in from the outside has a longer diffusion pathway meaning diffusion will be slow and won’t enable sufficient supply
How does ‘surface area to volume ratio’ affect an organism’s need for an exchange surface?
Some larger animals have small surface area to volume ratios which means it’s difficult to exchange enough substances to supply a large volume of animal with oxygen and nutrients through a small outer surface
How does an organism’s ‘level of activity’ affect its need for an exchange system?
Metabolic activity uses energy from food and requires oxygen to release the energy in aerobic respiration
If an organism is more active, its cells will need good supplies of nutrients and oxygen to supply the energy required for movement
What features do all good exchange features have in common?
A large surface area to provide more space for molecules to pass through
A thin barrier to reduce the diffusion distance and that is permeable to the substances being exchanged
A good blood supply which can bring fresh supplies of molecules, to keep the concentration high or that can remove molecules to keep the concentration low
How is a large surface area often achieved?
By folding the walls and membranes involved
Why is a good blood supply important in a good exchange surface?
It maintains a steep concentration gradient so that fast diffusion can occur
What does the gaseous exchange system in mammals consist of?
The lungs - 2 inflatable sacs lying in the chest cavity - and the associated airways that carry air into and out of them
Lungs are protected by the ribcage and the ribs are held together by the intercostal muscles
How does air get from the environment into the body?
Air passes through the nose, along the trachea, from the back of the mouth to the lungs, down the bronchi and bronchioles, smaller airways leading into the lungs, it then reaches alveoli, folds of the lung epithelium, which is where gas exchange takes place
What happens during inspiration?
Diaphragm contracts and flattens, displacing the digestive organs
External intercostal muscles contract
Rib cage moves upwards and outwards
As volume of thorax increases, the lung pressure drops below atmospheric pressure and air is moved into the lungs
What happens during expiration?
Diaphragm relaxes and is pushed up by displaced organs becoming curved
External intercostal muscles relax
Rib cage moves downwards and inwards
As volume of thorax decreases, the lung pressure rises above the atmospheric pressure and air is moved out of the lungs
Why must the lungs maintain a steep concentration gradient in each direction?
To ensure that diffusion can continue
The blood system transports CO2 from the tissues to the lungs ensuring the concentration in the blood is higher than that in the air of the alveoli - CO2 diffuses into alveoli
The blood transports O2 away from the lungs ensuring the concentration of O2 in the blood is kept lower than that in the alveoli - O2 diffuses into the blood
How are alveoli adapted for gaseous exchange?
Individually are very small but are numerous so have a large surface area to volume ratio
Lined by a thin layer of moisture which evaporates as we breathe out
Internally coated with a surfactant produced by the lungs to reduce the cohesive forces between water molecules preventing collapse
What is the barrier to exchange comprised of?
The wall of the alveolus and the wall of the blood capillary
How are the lungs adapted to reduce the diffusion distance of gases?
Alveolus is one cell thick
Capillary wall is one cell thick
Both walls consist of squamous (flattened) cells
Capillaries are in close contact with alveolus walls
Capillaries are narrow so that red blood cells are squeezed against the capillary wall, making them closer to the air in alveoli
What does ventilation ensure?
The concentration of oxygen in the air of the alveolus remains higher than that in the blood
The concentration of carbon dioxide in the alveoli remains lower than that in the blood
The concentration gradient necessary for diffusion is maintained
What do the elastic fibres in the alveoli walls do?
They stretch during inspiration but recoil during expiration to help push air out
What requirements must the trachea, bronchi and bronchioles meet to be effective?
Be large enough to allow sufficient air to flow without obstruction
Be supported to prevent collapse when the air pressure inside is low during inspiration
Be flexible in order to allow movement
What structure lines the airways?
Ciliated epithelium
What is the function of ciliated epithelium?
It contributes to keeping the lungs healthy
Contains goblet cells which release mucus which traps pathogens
The cilia move the mucus to top of the airway where it’s swallowed
Which is narrower, trachea or bronchi?
Bronchi
What prevents collapse of the airways during inspiration?
Rings of cartilage
C-shaped in the trachea
Why is cartilage C-shaped in the trachea rather than a complete ring?
To allow flexibility and space for food to pass down the oesophagus
What are the walls of the bronchioles comprised of?
Smooth muscle and elastic fibres
What is the function of smooth muscle?
It can contract and so can constrict the airway making the lumen narrower
When might controlling the flow of air to the alveoli be important?
If there are harmful substances in the air
When an allergic reaction is occurring
What is the function of elastic fibres in the trachea?
To elongate the smooth muscle once it has contracted as it cannot reverse this effect on its alone
Why must the smooth muscles relax before the elastic fibres can elongate them?
When the muscle is contracted the elastic fibres are deformed and cannot dilate the airways
How do the elastic fibres dilate the airways after the contraction of smooth muscle?
As the muscles relax, the elastic fibres can recoil to their original size and shape thus dilating the air way
What is a spirometer?
A device that measures the movement of air into and out of the lungs as a person breathes
How do spirometers measure the movement of air in and out of the lungs?
A chamber of medical-grade oxygen with a lid floats on a tank of water
During inspiration, air is drawn from the chamber so that the lid moves down
During expiration, the air returns to the chamber and the lid is raised
Movements are recorded on a datalogger that is attached to the chamber lid to produce a trace
How does a spirometer measure oxygen consumption?
The air exhaled is passed through a chamber of soda lime, which absorbs the carbon dioxide so that the volume of air in the chamber decreases
This decrease can be observed and measured on the spirometer trace and so measuring the gradient of the decrease in volume enables us to calculate the rate of oxygen uptake
What precautions must be taken when using a spirometer?
The subject should be healthy and free from asthma
The soda lime should be fresh and functioning
There should be no air leaks in the apparatus as this would give inaccurate results
The mouthpiece should be sterilised
The water chamber must not be overfilled or water may enter the air tubes
What is one advantage and one disadvantage of modern spirometers?
Advantage -
May be small and simple hand-held devices
Disadvantage -
Many cannot measure the rate of oxygen consumption
What does the total lung volume consist of?
The vital capacity and the residual volume
What is the vital capacity and how can it be measured?
It is the maximum volume of air that can be moved by the lungs in one breath
It is measured by taking a deep breath and expiring all the air possible from the lungs
What factors does vital capacity depend upon?
The size of a person
The age and gender
Their level of regular exercise
What region is vital capacity usually in?
2.5-5.0 dm3
What is the residual volume?
The volume of air that remains in the lungs even after forced expiration - usually in the airways and alveoli
What is the approximate measurement of residual volume?
1.5 dm3
What is the tidal volume and when is it usually measured?
The volume of air moved in and out with each breath which is sufficient to supply all required oxygen
usually measured at rest
What might a typical tidal volume be at rest?
0.5 dm3
How can you calculate oxygen uptake from a spirometer trace?
One trace, draw a line from point A down to the horizontal axis and another line from point B to the horizontal axis
Measure the length of time between these points
Measure the different in volume between points A and B
Divide by the time taken for this decrease
The unit will be dm3 s-1
How can you measure the breathing rate from a spirometer trace?
Count the number of peaks in each minute
What will increase oxygen uptake result from?
Increased breathing rate
Deeper breaths
What do bony fish use their gills for?
In order to absorb oxygen dissolved in the water and release carbon dioxide into the water
What are a bony fish’s gills usually like?
Most have five pairs covered by the operculum
Each gill consists of two rows of primary lamellae attached to a bony arch
These lamellae are very thin and their surface is folded into many secondary lamellae providing a large surface area for where exchange takes place
What arrangement in bony fish creates a countercurrent flow and what is its purpose?
Blood flows along the gill arch and along the lamellae to the operculum
Blood then flows through capillaries in the opposite direction to the flow of water over the lamellae creating a countercurrent flow
This arrangement absorbs the maximum amount of oxygen from the water
How does ventilation work in bony fish?
Buccal-opercular pump keeps water flowing over the gills
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
How are the movements of the buccal cavity coordinated with movements of the operculum?
As water is pushed from the buccal cavity to the gills, the operculum moves outwards
This movement reduces the pressure in the opercular cavity, helping water to flow through the gills
What kind of circulatory system do insects have?
A slow and open circulatory system in which the body fluid acts as both blood and tissue fluid
What mechanism do insects possess that supplies air directly to all respiring tissues?
An air-filled tracheal system
Describe an insects tracheal system and how gaseous exchange occurs
Air enters the system via a spiracle in each body segment
The air is transported into the body through a series of tubes called tracheae
These divide into smaller and smaller tubes called tracheoles which have open ends and the end are filled with tracheal fluid
Gaseous exchange occurs between the air in the tracheole and the tracheal fluid
How can more oxygen be absorbed when the insect is active?
The tracheal fluid can be withdrawn into the body fluid in order the increase the surface area of the tracheole wall exposed to air
How can larger insects ventilate their tracheal system?
By the movements of their body
Describe 2 ways insects can ventilate using body movements
Sections of the tracheal system are expanded and have flexible walls, these act as air sacs which can be repetitively expanded and contracted to ventilate the tracheal system
Movements of the wings alter the volume of the thorax and as the volume decreases, air in the tracheal system is put under pressure and is pushed out of the tracheal system. When the thorax volume increases, pressure inside drops and air is pushed in from the outside
How can locusts alter the volume of their abdomens by specialised breathing movements?
Their breathing movements are 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 leaves the tracheal system
