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
