mechanisms of breathing Flashcards
what regulates breathing
the diaphragm and intercostal muscles
where are lungs sealed
in the pleural membranes
what are pleural membranes joined to
the thorax wall
what does change in thorax volume change
lung volume
how does air flow in and out of the lungs
due to alternately reversing pressure gradients
because air tends to move from area of high pressure to low
what is Boyles law
at any constant temp, the pressure exerted by a gas varies inversely with the volume of gas
Boyles law formula
P1V1=P2V2
does increase in volume decrease pressure
yes and vice versa
what happens when intra-alveolar pressure is low
atmospheric pressure is high and air flows into the lungs
what happens when air flows into the lungs
the intra-alveolar pressure increases and the atmospheric pressure decreases
air flows out of the lungs
what is the first stage of inspiration
- the diaphragm contracts and flattens and the external intercostal muscles contract
what is the second stage of inspiration
the volume of the thorax and lungs increase
what is the third stage of inspiration
the pressure inside the lungs decreases to below atmospheric pressure (-3mmHg) and air flows into the lungs
why do the lungs expand more as air comes in
because there is a negative pressure between the lungs and the thorax
(achieved by the pleural membranes)
what does contraction of external intercostal muscles cause
elevation of ribs
what does lowering of diaphragm on contraction do
increases vertical dimension of thoracic cavity
what happens during passive expiration
- diaphragm relaxes
- lungs recoil
- volume of thorax decreases
- lung volume decreases
- inside the lung the pressure rises to +3mmHg
- air moves out along pressure gradient
how do pleural membranes stop the lung collapsing
because they join the lungs to the outer wall
what happens with forced inspiration and expiration
external intercostal muscles and diaphragm contract
principle stays the same but much larger changes in pressure
what do pleural membranes do
- surround the lung tissue as a double membrane fluid filled bag
- creates a vacuum round the lungs
- when the thorax expands the intrapleural pressure decreases
is normal breathing voluntary or involuntary
involuntary - doesnt rely on conscious input
what regulates normal breathing
neurones in the medulla oblongata and pons
what neurons in the medulla oblongata controls inspiration and expiration
I neurons = inspiration
E neurons = expiration
what do I and E neurons from the medulla oblongata do
fire rhythmically and send impulses down the nerve to the diaphragm
what happens when one set of I neurons fire
it inhibits the second neurons and vice versa
called RECIPROCAL INHIBITION
what does the medulla oblongata contain
- the dorsal respiratory group (inspiratory centre)
- the ventral respiratory group (inspiratory and expiratory centre)
where are signals from the medulla oblongata sent to
the intercostal muscles and the diaphragm
what does centres in the PONS of the brain control
further rate of breathing
what des the apneustic centre do
sends impulses to I neurons to keep inspiration going
what does the pneumotaxic centre do
sends impulses to the dorsal respiratory group that switches off I neurons limiting the time of inspiration
what are mechanoreceptors sensitive to
changes in mechanics/movement
what are proprioceptors
stretch receptors in the smooth muscle of the bronchioles
what does stretch in the lung tissues activate
mechanoreceptors and proprioceptors to send a nerve impulse to the medulla oblongata to inhibit I neurones
called the Hering Breurer Reflex
where are peripheral chemoceptors found
outwith brain
in aortic and carotid bodies
where are central chemoceptors found
within brain
near respiratory centres of medulla oblongata and on the surface of the brain ventricle
what does peripheral chemoceptors consist of
specialised cells called glomus cells
what are peripheral chemoceptors sensitive to
changes in arterial blood gas
have high metabolic rate and good blood perfusion which makes them sensitive
what do peripheral chemoceptors respond to
oxygen - when there is less oxygen there is more firing
can also respond to changes in CO2
what happens when decreased O2 is detected by sensor proteins in glomus
it leads to increase in calcium which mediates release of neurotransmitters
eg. dopamine, ACh
what do central chemoreceptors do
respond direct to the H+ concentration of the CSF
do central chemoceptors respond to changes in plasma pH
no as H+ cannot diffuse into the CSF
what happens when CO2 diffuses into CSF
it forms H+ and decreases pH
step 1 of activation of central chemoreceptors
blood PCO2 rises
step 2 of activation of central chemoreceptors
CO2 diffuses into the CSF
step 3 of activation of central chemoreceptors
CO2 is converted into carbonic acid by the enzyme carbonic anhydrase
step 4 of activation of central chemoreceptor
carbonic acid dissociates to give bicarbonate ions
what does an increase in H+ ions do (activation of central chemoceptors)
send impulses to the respiratory centres
