Exchange surfaces and breathing Flashcards
What are the 3 main factors that affect the need for an exchange system?
- size
- surface area to volume ratio
- level of activity
How does size affect the need for an exchange system?
- small organisms (single celled) can receive a sufficient supply of oxygen from environment by diffusion
- for multicellular organisms diffusion is too slow to enable sufficient supply to innermost cells
How does SA:V affect the need for an exchange system?
- small organisms have a large SA:V, SA is large enough for sufficient oxygen to diffuse into all cells.
- large organisms have small SA:V
How does level of activity affect the need for an exchange system?
- some organisms are more active than others
- cells of active organism need good supplies of nutrients and oxygen to supply energy for movement
- organisms (mammals) that keep themselves warm need more energy.
What are the features of a good exchange surface?
- large surface area to provide more space for molecules to pass through. Walls are often folded (root hair cells).
- permeable and thin barrier to reduce diffusion distance (alveoli)
- good blood supply to maintain steep conc gradient for fast diffusion ( and removal of metabolic waste products that can be toxic)
What are alveoli?
tiny folds of the lung epithelium to increase the SA
What are bronchi and bronchioles?
smaller airways leading into the lungs
What’s the diaphragm?
layer of muscle beneath the lungs
What are intercostal muscles?
muscle between the ribs
What’s the trachea?
main airway leading from the back of the mouth to the lungs
What’s ventilation?
the refreshing of the air in the lungs so there’s a higher oxygen concentration than in blood, and lower carbon dioxide conc for fast diffusion
Why are alveoli so numerous?
large SA to provide more space for molecules to pass through
Why does surfactant coat internal surface of alveoli?
to reduce the cohesive forces between water molecules as they make alveoli collapse
What the barrier to exchange comprised of?
- wall of alveolus
- wall of capillary
- cells readily allow diffusion of oxygen and carbon dioxide as they’re small and non polar
How is the barrier to exchange thin to reduce diffusion distance?
- alveolus and capillary walls are one cell thick
- both consist of squamous epithelium (flattened or very thin cells)
- capillary in close contact with alveolus wall
- capillaries have narrow lumen so RBCs are close to air in alveoli.
Why is it important for blood to carry carbon dioxide from tissues to lungs?
ensures conc gradient of CO2 in blood is higher than that in air in alveoli so carbon dioxide diffuses into alveoli
Why is it important for blood to carry oxygen away from lungs?
ensures that the conc of oxygen in blood is kept lower than that in alveoli so oxygen diffuses into the blood
Explain inspiration
- diaphragm contracts to move down and becomes flatter (this displaces the digestive organs downwards)
- external intercostal muscles contract to raise ribs
- volume of chest cavity increases
- pressure in chest cavity drops below atmospheric pressure
- air moves into the lungs
Explain expiration
- diaphragm relaxes and moves upwards (is pushed up by displaced organs underneath)
- external intercostal muscles relax and ribs fall
- during exercise, coughing, sneezing, internal intercostal muscle contract to push air out more forcefully
- volume of chest cavity decreases
- pressure in lungs rises above atmospheric pressure
- air is moved out of lungs
What kind of fibres do alveoli contain and why?
- elastic fibres help them stretch during inspiration but then recoil to help push air out doing expiration
What must airways have to be effective?
- be large enough to allow sufficient air to flow in without obstruction
- be supported to prevent collapse when the air pressure inside is low during inspiration
- be flexible in order to allow movement
What do airways contain?
- lined by ciliated epithelium, keeps lungs healthy
- goblet cells in epithelium release mucus to trap pathogens
- cilia move mucus to top of throat where it’s swallowed
- glandular tissue in the loose tissue also produces mucus
- supported by C-shaped rings of cartilage to prevent collapse during inspiration
- C-shaped rings allow flexibility for food to pass down oesophagus
Difference between trachea and bronchi?
- similar wall structure but bronchi are narrower
Features of bronchioles
- much narrower than bronchi
- smaller ones don’t have cartilage
- wall made of smooth muscle and elastic fibres
- smallest ones end in clusters of alveoli
Explain contraction of smooth muscle in airways
- constricts airways
- lumen becomes narrower
- restricts airflow to and from alveoli
- important if there’s a harmful substance in the air
- not voluntary (may be allergic reaction)
- can’t be reversed on its own
- smooth muscle elongated again by elastic fibres
- elastic fibres deformed (during contraction) then recoil (during muscle relaxation), dilating the airway
What’s a spirometer?
- device that can measure the movement of air into and out of the lungs
What’s vital capacity?
maximum volume of air that can be moved by the lungs in one breath
What’s tidal volume?
the volume of air inhaled or exhaled in one breath, usually measured at rest
What’s oxygen uptake?
volume of oxygen absorbed by the lungs in one minute
What’s residual volume?
volume of air that remains in the lungs even after forced expiration
What factors can affect vital capacity?
- size of person (height)
- age and gender
- level of regular exercise
How to calculate oxygen uptake from a spirometer trace?
- assume volume of carbon dioxide released and absorbed by soda lime equals the volume of oxygen absorbed by blood
- measure gradient of the decrease in volume
How to calculate breathing rate from spirometer trace?
- count number of peaks in each minute
What factors can increase oxygen uptake?
- exercise
- increased breathing rate
- deeper breaths
equation for pulmonary ventilation rate
PVR = tidal volume x breathing rate
What’s the buccal cavity?
the mouth
What’s counter current flow?
blood flows through capillaries in gill filament in opposite direction to flow of water over lamellae for maximum absorption of oxygen from water.
what are gill filaments/primary lamellae?
slender branches of tissue that make up the gill
what is secondary lamellae/gill plate?
folds of the gill filament to increase SA
what’s the operculum?
bony flap that covers and protects gills
what’s a spiracle?
pore that allows air in or out of trachea
define tracheal fluid
fluid found at the end of tracheoles in the tracheal system
define tracheal system?
system of air-filled tubes in insects
How many pairs of gills in bony fish?
5
Structure of gills and advantages of this
- two rows of gill filaments (primary lamellae) attached to a bony arch.
- filaments are very thin and their surface is folded into many secondary lamellae (or gill plates)
- provides large SA
- blood capillaries carry deoxygenated blood close to surface of secondary lamellae where exchange occurs
How does ventilation in fish occur?
- floor of buccal cavity moves downward drawing water inside
- mouth closes, floor raised pushing water through the gills
- operculum moves outwards which reduces pressure in the opercular cavity (space under the operculum) helping water flow through gills
Describe the circulatory system in insects
- open circulatory system where body fluid acts as both blood and tissue fluid
- circulation is slow and affected by body movements
How does gaseous exchange occur in insects?
- occurs between air in tracheole and the tracheal fluid
- some exchange occurs across thin walls of the tracheoles
-tracheal fluid withdrawn into body fluid to increase SA of tracheole wall exposed to air for more diffusion of oxygen in very active insects
How is the tracheal system ventilated?
- rhythmic abdominal movements change volume of their bodies and move air in and out of spiracles
- when larger insects are flying, wing movements pump their thoraxes too.
