control of breathing Flashcards
What is the composition of atmospheric, dry air?
N2 = 79.04% O2 = 20.93% CO2 = coc3% others = <1%
What is the total atmospheric pressure?
760mmHg at sea level
or 101.08 kPa –> divide by 7.5
Define Partial Pressure
pressure which an individual gas in a mixture contributes to the total pressure
What happens to barometric pressure as altitude increases?
less atmospheric pressure, therefore partial pressure of oxygen is also lower (will be 21% of new total pressure)
What is meant by gas tension
partial pressure of gases in a liquid (e.g. blood)
The amount of gas dissolved in a liquid/ blood depend on what 2 factors?
1) solubility of gas in blood around alveolus - CONSTANT
2) pressure of gas (gas tension) in alveolar air - VARIABLE
*there will be a pressure gradient between alveoli and blood
What will happen to O2 if PO2 in alveoli > PO2 in pulmonary capillaries?
Diffuse into blood until PO2 alveolar = PO2 blood
What are the two reasons for why the alveolar PO2 (100mmHg) differs from atmospheric PO2 (160mmHg - remember 21% of 760mmHg)?
1) it becomes saturated with water vapour
2) because of dead space not all air is fresh with every breath
Taking into account saturation from water vapour, how would you calculate initial PO2 in alveolar air?
- Pwater at body temperature = 47mmHg
- need to factor in that the air breathed in is diluted by this
- so, PO2 = (760-47)x(21/100)
= 150mmHg
Explain the dilution factor of dead space
- PO2 is already lowered by dilution of water
- only 350/500 mL is new air
- so, alveolar PO2 = 100mmHg (of 160mmHg in atmospheric air)
- remains pretty constant
why does PO2 remains fairly constant during resp. cycle?
1) only small change in alveolar air/ breath
2) O2 being removed by passive diffusion into blood
PCO2 of alveolar differs from atmospheric PCO2, but remains quite constant in the tissues because:
1) CO2 is removed from blood to alveoli by passive diffusion
2) CO2 leave alveoli expiration
composition of dry (atmospheric) and saturated (alveolar) air
DRY Pgas: ALVEOLAR Pgas: N2 = 593 567 O2 = 160 150 -> 100 CO2 = 0.23 0.21 -> 40 H2O = 0 47 others = v.low v.low
What is the partial pressure gradient of O2 and CO2 across pulmonary capillaries?
O2:
- from alveoli to blood
- 60mmHg (100->40)
CO2:
- from blood to alveoli
- 6mmHg (46->40)
changes in PO2 from atmosphere to tissue cell
160 > 100 > 40 (mmHg)
why do we need to control breathing?
acid/base balance
PCO2, PO2 and [H+] need to be controlled within narrow limits
how do we achieve alveolar Pgas change -> Pgas change in pulmonary capillaries -> Pgas change in systemic arterial blood?
varying pulmonary ventilation
VE = TV x RF
(typically 500mL x 12bpm =6000mL/min… can range from 6L at rest to 100L/min during exercise)
how is the rate and depth of breathing altered by the CNS
changing the discharge of the motor neurons supplying the respiratory muscles
what happens if VE is increased?
CO2 is flushed out so alveolar PCO2 decreases
alveolar PO2 increases and approaches atmospheric PO2
what happens if VE is decreased?
CO2 is retained in the lungs so alveolar PCO2 is increased
PO2 in the alveoli decreases
what are the key elements of the respiratory control system?
Sensors: chemoreceptors, mechanoreceptors, cerebral cortex, hypothalamus
central controller: pons (1 resp. group with 2 areas: pneumotaxic centre and apneutic area), medulla (2 resp. groups: ventral and dorsal)
Effectors: respiratory muscles (cause ventilation)
where is our basic respiratory rhythm generated?
medulla
What neurons/ area of the brain stem generates rhythm for inspiratory breathing movements?
pre-Botzinger complex (ventral resp. group)
how does the pre-Botzinger complex drive inspiration?
fires to Dorsal respiratory group (most fundamental role in the control of resp by initiating inhalation) that then fires in bursts, leading to contraction of respiratory muscles. when firing stops, you get passive expiration