Mechanics of breathing

Question 1

what is breathing regulated by?

Answer 1

the diaphragm and intercostal muscles

Question 2

what are the lungs sealed in?

Answer 2

pleural membranes

Question 3

what does a change of thorax volume cause ,

Answer 3

changes in lung volume

Question 4

how does air tend to move relative to pressure?

Answer 4

from a region of higher pressure to lower pressure

Question 5

what is boyles law?

Answer 5

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

Question 6

what is the equation for boyles law?

Answer 6

P1V1 = P2V2

Question 7

what happens when intra-alveolar pressure is less than atmospheric pressure?

Answer 7

air flows into the lungs

Question 8

what is the stages of inspiration?

Answer 8

1) diaphragm contact and flattens and the external intercostal muscles contract
2) the volume of the thorax and lungs increases
3) the pressure inside the lungs decreases to below atmospheric pressure and air flows into the lungs

Question 9

why does the lungs expand more as air enters the lungs?

Answer 9

there is a negative pressure between the lungs and the thorax, achieved by pleural membranes

Question 10

what does contraction of external intercostal muscles cause?

Answer 10

elevation of the ribs

Question 11

what happens during expiration?

Answer 11

• diaphragm relaxes
• lungs recoil
• volume of the thorax decreases
• inside the lung pressure rises to +3
• air moved out along a pressure gradient

Question 12

what does pleural membranes stop?

Answer 12

the lungs from collapsing

Question 13

what are pleural membranes ?

Answer 13

-surround the lung tissues as double membrane fluid filled bag
-Creates a vacuum round the lungs
-When the thorax expands the intrapleural pressure decreases

Question 14

what happens to pleural membranes during inspiration?

Answer 14

• diaphragm contracts
  -thorax expands
• intrapleural pressure becomes sub-atmospheric
• transpulmonary pressure increases (pressure between pleural membranes and alveolar space)
• lungs expand
• alveolar pressure sub-atmospheric
• air flows in

Question 15

what is the normal control of breathing regulated by?

Answer 15

by a group of nerve cells (neurones) in the lower centre of the brain called the medulla oblongata and pons

Question 16

what neurones controls inspiration and expiration in the medulla oblongata?

Answer 16

I neurones - control inspiration
E neurones - control expiration

Question 17

what is it called when one set of neurons fire inhibits the second set of neurons ?

Answer 17

reciprocal inhibition

Question 18

what does the medulla oblongata contain?

Answer 18

the dorsal respiratory group or inspiratory centre

the ventral respiration group of inspiratory and expiratory centre

Question 19

what is the apneustic centre?

Answer 19

sends impulses to I neurones to keep inspiration going

Question 20

what is the apneustic centre?

Answer 20

sends impulses to I neurones to keep inspiration going

Question 21

what is the pneumotaxic centre?

Answer 21

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

Question 22

what are mechanoreceptors?

Answer 22

sensitive to changes in mechanics/movement

Question 23

what are proprioceptors?

Answer 23

stretch receptors in the smooth muscle of the bronchioles

Question 24

what does stretch receptors in the lung activate?

Answer 24

activates mechanoreceptors and proprioceptors to send nerve impulses to the medulla oblongata to inhibit I neurones
- hering breurer reflex

Question 25

what are features of peripheral chemoreceptors?

Answer 25

• found in aortic and carotid bodies
• consist of specialised cells called glomus cells
• have a high metabolic rate and good blood perfusion so are sensitive to changes in arterial blood gas
• respond to oxygen
• less oxygen more firing
• may also respond to changes in CO2

Question 26

what does decreases oxygen detected on sensor proteins on glomus cell cause ?

Answer 26

leads to an increase in Ca2+ which mediates release of neurotransmitters

Question 27

where are central chemoreceptors found?

Answer 27

near respiratory centre of medulla oblongata on the surface of the brain ventricle

Question 28

what do central chemoreceptors respond to?

Answer 28

H+ ion concentration of the cerebrospinal fluid (CSF)

Question 29

why does central chemoreceptors not respond to changes in plasma pH

Answer 29

H+ cannot diffuse into the CSF

• CO2 can diffuse into CSF, forming H+ and decreasing pH

Question 30

what causes the activation of central chemoreceptors,

Answer 30

• blood PCO2 increases
• CO2 diffuses into CSF
• CO2 is converted into carbonic acid by the enzyme carbonic anhydrase
• carbonic acid dissociates to give bicarbonate ions
• increase in H+ ions sends impulses to the respiratory centres