3.1 EXCHANGE SURFACES AND BREATHING Flashcards
SA: V ratio.
As the size of an organism increases, the surface area and volume both increase but the volume increases more than the surface area. This means that SA:V ratio decreases with an increase in size. Therefore, larger organisms need to develop specialised exchange surfaces to meet their needs while smaller organisms can depend solely on diffusion. A specialised exchange surface makes it easier for molecules to pass from one side of the surface to another. Examples include microvilli in the small intestine, alveoli in the lungs, root hair cells in plant roots.
What is ventilation?
Ventilation is the process of breathing.
inhalation/inspiration- air moves into lungs
exhalation/expiration- air forced out of lungs
-movement of air in and out of lungs is a result of differences in pressure
What is the mechanism of inhalation?
Inhalation:
-contraction of external intercostal muscles moves ribcage upwards and outwards. diameter of throat increases
-the diaphragm flattens when it contracts. so increases the length of the throat cavity
-overall, the volume of the throat increases which results in pressure in the lungs decreasing below atmospheric pressure
-since atmospheric pressure is greater outside, air rushes in to inflate the lungs
-alveoli elastic tissue is stretched
-stretch receptors on the outside surface of the lungs prevent their overinflation
What is the mechanism of exhalation?
Exhalation:
-diaphragm and external intercostal muscles relax. the internal intercostal muscles contract. so the ribcage moves downwards and inwards. the diameter and length of the throat decreases
-overall, the volume of the thorax decreases which results in an increase in pressure in the lungs compared to atmospheric pressure
-air leaves the lungs which deflate
-elastic fibres between the alveoli recoil and the alveoli recoil and the alveoli return to their natural shape
What is the role of the lungs?
The lungs:
-breathing/ventilation = movement of air into and out of the lungs
-gas exchange = alveoli, o2 into blood, co2 in alveolar sacs
-respiration = break down of glucose in cells to provide energy known as ATP (aerobic uses o2)
What are the features of alveoli and how does this help gas exchange?
Features of alveoli:
large surface area- very small, lots of them = SA in lungs around 50-79m^2
thin layer- thin cell walls (1 cell thick) = short diffusion distance
good blood supply- own blood supply, network 280 million capillaries = pulmonary artery, constant blood flow maintains concentration gradient
good ventilation- breathing moves air into and out of alveoli = maintains steep diffusion gradient
What is the mechanism of breathing?
Breathing:
-mechanical forces cause movement of air
= gases always flow from higher pressure to lower pressure
= for air to enter thorax, pressure of air in it has to be lower than atmospheric pressure
-two kinds of muscle involved
= diaphragm - smooth muscle sheet
= intercostal muscles - skeletal muscle, attached to ribs, external or internal
What are the features of the nasal cavity?
The nasal cavity:
-good blood supply which warms the air
-hairy lining which traps dirt and bacteria
-moist surfaces which increase the humidity of incoming air, reducing evaporation from exchange surfaces
What are the features of the trachea?
Trachea:
-cilia beat to move mucus up the trachea- dust and microorganisms are trapped in mucus and swallowed
-goblet cells secrete mucus onto the lining of the trachea
-incomplete rings of cartilage to prevent trachea from collapsing (allows food to pass down oesophagus)
What are features of the bronchus?
Bronchus:
-trachea divides into left and right bronchus
-are similar to structure of trachea but smaller
What are the features of bronchioles?
Bronchioles:
-each bronchus continues dividing about 23 times
-tubes smaller than 1mm are called bronchioles and have no cartilage
-walls contain smooth muscle which constrict when they contract and dilate when they relax. changes amount of air reaching lungs
-bronchioles are lined with a thin layer of squamous epithelia so some gas exchange is possible
What are features of the alveoli?
Alveoli:
-tiny air sacs - unique to mammalian lungs
-each alveolus has a diameter of 200-300um
-consists of a thin of squamous epithelial cells along with some collagen and elastic fibres
-elastic fibres allow alveoli to stretch as air is drawn in and recoil to squeeze air out (elastic recoil)
What are the challenges for insects:
Challenges for insects:
-relatively small but cannot rely on body surface for gas exchange
-very active at times (high o2 demand)
-tough exoskeleton (chitin impermeable to o2)
-usually lack closed circulatory system (no directed movement of body fluid in main body cavity)
-to overcome
= respiratory system separate from circulatory system
= o2 delivered directly to cells
What are the challenges for insects:
Challenges for insects:
-relatively small but cannot rely on body surface for gas exchange
-very active at times (high o2 demand)
-tough exoskeleton (chitin impermeable to o2)
-usually lack closed circulatory system (no directed movement of body fluid in main body cavity)
-to overcome
= respiratory system separate from circulatory system
= o2 delivered directly to cells
How do insects do gas exchange?
Gas exchange in insects:
1. air enters through holes in exoskeleton (spiracles)
2. connected to tubes called tracheae which are kept open by rings of chitin
3. tracheae branch to form finer branches called tracheoles which extend to run very close to nearly every cell - these have no chitin making them permeable to gases
4. because the tracheal system brings air within a very short distance of virtually every body cell in an insect, it can transport o2 and co2 via diffusion
chitin - rings of chitin to keep trachea open - it is the same material that makes up the cuticle so is relatively impermeable to gases
What is tracheal fluid?
Tracheal fluid:
-limits the SA through which gases can diffuse into cells
-however, if o2 demand increases - e.g during flight - then lactic acid builds up, causes water to move out of tracheoles by osmosis
-exposes more SA for diffusion
What is ventilation in insects?
Ventilation in insects:
-large insects (locusts, wasps, etc) have higher energy demands
-rhythmic body movements that compress and expand their air tubes like bellows
-air sacs which act as reservoirs
How do you measure the volume of air in the lungs?
How to measure volume of air in lungs:
-peak flow meter - measures rate air is expelled from the lungs
-lung capacity bag - gives air volume using scale on bag
-spirometer - measures different aspects of lung volume
= find volume breath in/out
= find breathing rate
= find volume of o2 used (o2 consumption)
What are the precautions with spirometry?
Precautions of spirometer:
-use medical grade o2 to fill chamber
-use soda lime to absorb co2 so that not breathing in rich co2 and so volume o2 taken can be measured
-do not use if any medical conditions related to breathing (e.g asthma)
-stop use if any breathing problems occur
-sterilise mouthpiece in between users
What are the steps of spirometry?
Spirometry:
-static lower half of tank is filled with water
-mobiles upper half of tank is full of oxygen
-breathe out into tank and upper half will rise
-breathe in from tank and upper half will fall
-trace marker is attached to mobile upper half
-when inspiring the trace will dip down
-when expiring the trace will climb up
-from peak of expiration to low of inspiration shows the volume of a single breath
What is ventilation in fish?
Ventilation in fish:
-the gills are contained in a gill cavity and are covered by a protective operculum
-when fish swim they can keep a current of water flowing over their gills by simply opening their mouth and operculum (although if they stop moving the flow of water also stops)
What is the mechanism to take in water for a fish?
Mechanism to take in water:
1. open mouth, lowering floor of buccal cavity
2. increases volume of their mouth and decreases the pressure
3. operculum closes
4. water moves in
What is the mechanism to let out water in a fish?
Mechanism to let out water:
1. close mouth, raises floor of buccal cavity
2. decreases volume of mouth and increases pressure
3. operculum opens
4. water rushes out
What is the gill structure?
Gill structure:
-gill is made up of two piles of filaments attached to a bony gill arch
-bony fish have 4 pairs of bony gill arches arranged in a semi-circle shape
-between the gill arches are 5 slits through which water passes out of the fish
-water allows the gill filaments to separate increasing the surface area for gas exchange (outside of water they stick together)
