human gas exchange Flashcards
(25 cards)
what is ventilation?
air constantly being moved in and out of the lungs to maintain diffusion of gases across the alveolar epithelium
what is inspiration?
when the air pressure of the atmosphere is greater than that of the thorax, air enters the lungs
what is expiration?
when air pressure of the thorax is greater than that of the atmosphere, air is forced out of the lungs
what does each of the intercostal muscles contracting do?
internal- contraction leads to expiration
external- contraction lead to inspiration.
what is released during which causes inspiration to occur?
-respiratory centre of the medulla of the brain generates electrical nerve impulses
-these nerve impulses travel to the external intercostal muscles and the diaphragm
what do muscles do as a result of the nerve impulses from then medulla in inspiration?
-external intercostal muscles contract which pulls the ribcage up and out
-diaphragm contracts which causes it to flatten
what does the movements of the muscles in inspiration lead to?
increased volume of thorax so pressure decreases
pressure of thorax lower than atmosphere so air flows down the pressure gradient into the lungs.
what kind of process is expiration at rest and why?
passive because muscle contraction is not required
what kind of process is expiration during exercise and why?
active as it involves contraction of muscles
what happens to do with nerve impulses during expiration at rest?
nerve impulses stop being released from the inspiratory section of the respiratory centre of the medulla
since nerve impulses stop being released during expiration at rest, what effect does this have on muscles?
external intercostal muscles relax
ribcage falls down, as a result of gravity
diaphragm also relaxes and pressure from the abdomen pushed the diaphragm back up into its dome shape
what do the muscle movements during expiration at rest result in?
decrease volume of thorax
pressure of thorax increases above that of the atmospheric pressure
air flows out of lungs down the pressure gradient
what important feature MUST we mention about the lungs during expiration at rest and during exercise?
there is elastic recoil of the lungs!
what is released during expiration during exercise which makes it different to expiration during rest?
electrical nerve impulses are released from the the expiratory section of the respiratory centre of the medulla
what do electrical nerve impulses released during expiration during exercise do to muscles?
internal intercostal muscles contract
ribcage pulled down and in
they also stimulate muscle in the abdomen wall to contract (increasing pressure in the abdomen) so that there is a force pushing the diaphragm upwards
what do muscle movements during expiration during exercise lead to?
decrease volume of thorax
pressure of thorax increases above that of atmospheric pressure
air flows out of the lungs down pressure gradient
describe flow of air in the human respiratory system?
nose and mouth
trachea
bronchi
bronchioles
alveoli
what 3 things are needed for high rate of diffusion?
large surface area
steep concentration gradient maintained
short diffusion pathway
what is the gas exchange surface of humans?
alveoli wall
how do alveoli provide large surface area? how is this maintained?
many alveoli
there is surfactant in the alveoli- this reduces surface tension of water and prevents alveoli from collapsing
how is a steep concentration gradient maintained?
the ventilation mechanism
capillary network around every alveoli provides a good blood flow
what provides us with a ventilation mechanism?
antagonistic muscles that move rib cage and change size of thorax
how do alveoli provide a short diffusion pathway?
the alveoli walls and capillary walls are both one cell thick with flattened epithelial/endothelial cells
alveoli wall and capillary wall in close contact also
how does capillary width affect diffusion?
capillaries are very narrow and only one red blood cell can pass through at any one time
this slows blood flow down so more time for diffusion
