3.3.2 - gas exchange Flashcards
what are the key structures within the human gas exchange system?
alveoli, bronchi, bronchioles, trachea, lungs
what is the role of cartilage in the human gas exchange system?
it holds the trachea and bronchi open so they don’t collapse during exhalation
what does antagonistic mean?
muscles work in opposite ways - when one contracts, the other relaxes
what is an example of an antagonistic muscle pair in the human gas exchange system?
the external and internal intercostal muscles (muscles between ribs)
what happens when the external intercostal muscles contract?
inspiration/inhalation
what happens when the internal intercostal muscles contract?
expiration/exhalation
what happens during inspiration?
external intercostal muscles contract and internal intercostal muscles relax
diaphragm contracts (pulls downwards from dome position so flattens)
air pressure in lungs decreases (below atmospheric pressure) because lung volume increases
air moves into lungs down pressure gradient (higher pressure in atmosphere than lungs)
what happens during exhalation?
external intercostal muscles relax and internal intercostal muscles contract
diaphragm relaxes (returns to domed position)
air pressure in lungs increases (above atmospheric pressure) because lung volume decreases
air moves out of the lungs down pressure gradient (higher pressure in lungs than atmosphere)
what happens in the thoracic cavity during inspiration and exhalation?
inspiration - thoracic cavity expands so pressure decreases as large volume
exhalation - thoracic cavity reduces so pressure increases as less volume
what are alveoli?
tiny air sacs at the end of the bronchioles
how is the alveolar epithelium adapted for gas exchange?
- there are 300 million alveoli in each lung creating a large surface area for gas exchange
- the alveoli epithelium cells are thin (one cell thick as made of squamous/flattened cells) to minimise diffusion distance
- each alveolus is surrounded by a network of capillaries in close contact with the alveolus walls to remove exchanged gases, maintaining a concentration gradient
- capillaries are narrow so red blood cells are squeezed against the walls - this reduces the rate they flow in the blood so there is more time for gas exchange
how are the lungs protected from drying out to aid gas exchange?
the alveoli are tucked deep in the body, away from exposure to air
a thin layer of moisture lines the alveoli (some is lost via evaporation when we exhale)
the lungs secrete a surfactant which reduces the cohesive forces between the molecules lining them so the alveoli don’t collapse
what is tidal volume?
the volume of air breathed in and out of the lungs per breath
what is vital capacity?
the volume of air that can be forcibly expired after a maximal intake of air
what is residual volume?
the volume of air remaining in the lungs at the end of a maximal expiration
what is total lung capacity?
vital capacity + residual volume
what is pulmonary ventilation?
the total volume of air that is moved into the lungs during one minute
how do you calculate pulmonary ventilation rate (PVR)?
tidal volume x breathing rate (no. of breaths per minute)
tidal volume in dm3
breathing rate in min-1
PVR in dm3 min-1
what device is used to measure lung capacity?
a spirometer
what is Fick’s law?
rate of diffusion is proportional to:
surface area x difference in concentration/ thickness of surface
what are the key structures in the tracheal system of an insect?
spiracles - small pores on surface of exoskeleton allowing gases to diffuse in and out
trachea - tube of approx 1mm which branches directly from spiracles
tracheoles - narrow tubes of less than 1um which branch from trachea in large numbers
what is unique about insects?
they don’t contain blood as they have no red blood cells (contain hemolymph instead)
how are gases drawn into an insect through the spiracles?
- during high activity, insects cary out anaerobic respiration and produce lactate
- lactate is soluble in water, so it decreases the water potential of respiring cells
- this creates a concentration gradient - water in the tracheal fluid found at the ends of the tracheoles moves into the cells via osmosis
- this movement of water decreases the pressure in the tracheoles, creating suction pressure which draws gases through the spiracles and down the tracheae and tracheoles
how are insects adapted to reduce water loss?
they have a waxy cuticles made of chitin
a muscular sphincter surrounding the spiracles can contract to close them so water doesn’t escape
