mechanisms of breathing

Question 1

what regulates breathing

Answer 1

the diaphragm and intercostal muscles

Question 2

where are lungs sealed

Answer 2

in the pleural membranes

Question 3

what are pleural membranes joined to

Answer 3

the thorax wall

Question 4

what does change in thorax volume change

Answer 4

lung volume

Question 5

how does air flow in and out of the lungs

Answer 5

due to alternately reversing pressure gradients

because air tends to move from area of high pressure to low

Question 6

what is Boyles law

Answer 6

at any constant temp, the pressure exerted by a gas varies inversely with the volume of gas

Question 7

Boyles law formula

Answer 7

P1V1=P2V2

Question 8

does increase in volume decrease pressure

Answer 8

yes and vice versa

Question 9

what happens when intra-alveolar pressure is low

Answer 9

atmospheric pressure is high and air flows into the lungs

Question 10

what happens when air flows into the lungs

Answer 10

the intra-alveolar pressure increases and the atmospheric pressure decreases

air flows out of the lungs

Question 11

what is the first stage of inspiration

Answer 11

1. the diaphragm contracts and flattens and the external intercostal muscles contract

Question 12

what is the second stage of inspiration

Answer 12

the volume of the thorax and lungs increase

Question 13

what is the third stage of inspiration

Answer 13

the pressure inside the lungs decreases to below atmospheric pressure (-3mmHg) and air flows into the lungs

Question 14

why do the lungs expand more as air comes in

Answer 14

because there is a negative pressure between the lungs and the thorax
(achieved by the pleural membranes)

Question 15

what does contraction of external intercostal muscles cause

Answer 15

elevation of ribs

Question 16

what does lowering of diaphragm on contraction do

Answer 16

increases vertical dimension of thoracic cavity

Question 17

what happens during passive expiration

Answer 17

• 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

Question 18

how do pleural membranes stop the lung collapsing

Answer 18

because they join the lungs to the outer wall

Question 19

what happens with forced inspiration and expiration

Answer 19

external intercostal muscles and diaphragm contract

principle stays the same but much larger changes in pressure

Question 20

what do pleural membranes do

Answer 20

• 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

Question 21

is normal breathing voluntary or involuntary

Answer 21

involuntary - doesnt rely on conscious input

Question 22

what regulates normal breathing

Answer 22

neurones in the medulla oblongata and pons

Question 23

what neurons in the medulla oblongata controls inspiration and expiration

Answer 23

I neurons = inspiration
E neurons = expiration

Question 24

what do I and E neurons from the medulla oblongata do

Answer 24

fire rhythmically and send impulses down the nerve to the diaphragm

Question 25

what happens when one set of I neurons fire

Answer 25

it inhibits the second neurons and vice versa called RECIPROCAL INHIBITION

Question 26

what does the medulla oblongata contain

Answer 26

- the dorsal respiratory group (inspiratory centre) - the ventral respiratory group (inspiratory and expiratory centre)

Question 27

where are signals from the medulla oblongata sent to

Answer 27

the intercostal muscles and the diaphragm

Question 28

what does centres in the PONS of the brain control

Answer 28

further rate of breathing

Question 29

what des the apneustic centre do

Answer 29

sends impulses to I neurons to keep inspiration going

Question 30

what does the pneumotaxic centre do

Answer 30

sends impulses to the dorsal respiratory group that switches off I neurons limiting the time of inspiration

Question 31

what are mechanoreceptors sensitive to

Answer 31

changes in mechanics/movement

Question 32

what are proprioceptors

Answer 32

stretch receptors in the smooth muscle of the bronchioles

Question 33

what does stretch in the lung tissues activate

Answer 33

mechanoreceptors and proprioceptors to send a nerve impulse to the medulla oblongata to inhibit I neurones called the Hering Breurer Reflex

Question 34

where are peripheral chemoceptors found

Answer 34

outwith brain in aortic and carotid bodies

Question 35

where are central chemoceptors found

Answer 35

within brain near respiratory centres of medulla oblongata and on the surface of the brain ventricle

Question 36

what does peripheral chemoceptors consist of

Answer 36

specialised cells called glomus cells

Question 37

what are peripheral chemoceptors sensitive to

Answer 37

changes in arterial blood gas have high metabolic rate and good blood perfusion which makes them sensitive

Question 38

what do peripheral chemoceptors respond to

Answer 38

oxygen - when there is less oxygen there is more firing can also respond to changes in CO2

Question 39

what happens when decreased O2 is detected by sensor proteins in glomus

Answer 39

it leads to increase in calcium which mediates release of neurotransmitters eg. dopamine, ACh

Question 40

what do central chemoreceptors do

Answer 40

respond direct to the H+ concentration of the CSF

Question 41

do central chemoceptors respond to changes in plasma pH

Answer 41

no as H+ cannot diffuse into the CSF

Question 42

what happens when CO2 diffuses into CSF

Answer 42

it forms H+ and decreases pH

Question 43

step 1 of activation of central chemoreceptors

Answer 43

blood PCO2 rises

Question 44

step 2 of activation of central chemoreceptors

Answer 44

CO2 diffuses into the CSF

Question 45

step 3 of activation of central chemoreceptors

Answer 45

CO2 is converted into carbonic acid by the enzyme carbonic anhydrase

Question 46

step 4 of activation of central chemoreceptor

Answer 46

carbonic acid dissociates to give bicarbonate ions

Question 47

what does an increase in H+ ions do (activation of central chemoceptors)

Answer 47

send impulses to the respiratory centres