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respiratory physiology > gas exchange (R3) > Flashcards

gas exchange (R3) Flashcards

1
Q

structure of trachea

A

cartilaginous rings

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2
Q

anatomical dead space

A
  • the portions of the respiratory tract that are ventilated but not perfused by pulmonary circulation
    (the airways of the mouth, nose, pharynx, larynx, trachea, bronchi, and bronchioles)
    -therefore some air remains in the airways/anatomical dead space, where it is not available for gas exchange
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3
Q

pulmonary ventilation (L)

A

= tidal volume (L/breath) x respiratory rate (breath/min)

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4
Q

pulmonary ventilation in resting conditions

A

0.5L x 12 breath/min = 6 L per min under resting conditions

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5
Q

airway dead space volume

A

150ml

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6
Q

tidal volume

A

Liters per breath

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7
Q

respiratory rate

A

breaths per minute

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8
Q

why is alveolar ventilation less than pulmonary ventilation

A

due to the presence of anatomical dead space

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9
Q

alveolar ventilation

A

= (tidal volume (L/breath) - dead space volume) x respiratory rate (breath/min)

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10
Q

alveolar ventilation in resting conditions

A

(0.5-0.15) x 12 = 4.2 L/min

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11
Q

what happens to the anatomical dead space volume during inspiration and expiration

A
  • after inspiration, before expiration there is 150ml present in anatomical dead space
  • during expiration,500ml is expired to atmosphere (150ml of fresh air from dead space that is left from the preceeding inspiration, and 350ml of old alveolar air) and 500ml is expired from alveoli (350ml to atmosphere and 150ml remains in anatomical dead space)
  • during inspiration 500ml of fresh air enters from the atmosphere (350ml enters alveoli and 150ml remains in anatomical dead space) and 500ml enter alveoli (350ml of fresh air from alveoli and 150ml of old air from dead space from preceeding expiration)
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12
Q

pulmonary ventilation

A

volume of air breathed in and out per minute

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13
Q

alveolar ventilation

A
  • volume of air exchanged between the atmosphere and alveoli per minute
  • this is more important than pulmonary ventilation as it represents new air available for gas exchange with blood
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14
Q

how and when is pulmonary ventilation increased

A
  • both the depth (tidal volume) and rate of breathing (RR) increase
  • during exercise etc
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15
Q

why is it more advantageous to increase the depth of breathing rather than rate when increasing pulmonary ventilation

A
  • because of the dead space
  • therefore short shallow breaths are more likely to increase alveolar ventilation as well as pulmonary ventilation (whereas shallow rapid breathing could increase pulmonary ventilation but not affect alveolar ventilation)
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16
Q

the transfer of gases between the body and atmosphere depends on which two things

A
  • ventilation = the rate at which gas is passing through the lungs
  • perfusion = the rate at which blood is passing through the lungs
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17
Q

ventilation

A

the rate at which gas is passing through the lungs

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18
Q

perfusion

A

the rate at which blood is passing through the lungs

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19
Q

ventilation perfusion

A
  • both blood flow and ventilation vary from bottom to top of the lung (both decrease from bottom to top, blood flow significantly)
  • the result is that the average arterial and average alveolar partial pressures of oxygen are not exactly the same
  • normally this effect is not significant but it can be in disease
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20
Q

alveolar dead space

A

-ventilated alveoli which are not adequetly perfused with blood are considered as alveolar dead space

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21
Q

affect of health on alveolar dead space

A
  • in healthy people, the alveolar dead space is very small and of little importance
  • this alveolar dead space could increase significantly with disease
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22
Q

physiological dead space

A

=anatomical dead space + alveolar dead space

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23
Q

why is the match between the air in the alveoli and within the blood in the pulmonary capillaries not always perfect

A

due to the alveolar dead space

24
Q

how ventilation perfusion matched in the lungs

A
  • local controls work on the smooth muscles of airways and arterioles to match airflow and blood flow
  • accumulation of carbon dioxide in alveoli as a result of increased perfusion, decreases airway resistance to increase airflow
  • an increase in alveolar oxygen concentration as a result of increased air flow/ventilation causes pulmonary vasodilation which increases blood flow to match the larger airflow
25
Q

what control mechanisms happen in the lungs when perfusion (blood flow) is greater than ventilation (air flow)

A
  • as there is decreased oxygen in the area, the local pulmonary arteriolar smooth muscles are contracted, and blood vessels are constricted causing vascular resistance which decreases blood flow
  • as there is an increased volume of carbon dioxide in the area, the local airway smooth muscle is relaxed, local airways are dilated and airway resistance is decreased, increasing airflow
26
Q

what control mechanisms happen in the lungs when ventilation (air flow) is greater than perfusion (blood flow)

A
  • as there is an increase in oxygen in the area, local pulmonary arteriolar smooth muscle is relaxed, local blood vessels are dilated and vascular resistance is decreased, causing an increase in blood flow
  • as there is a decrease in carbon dioxide in the area, local airway smooth muscle is contracted, local airways are constricted, airway resistance is increased and airflow is decreased
27
Q

vascular resistance

A

refers to the resistance that must be overcome to push blood through the circulatory system and create flow

28
Q

effects of decreased/increased oxygen on pulmonary arterioles

A
  • decreased oxygen causes vasoconstriction

- increased oxygen causes vasodilation

29
Q

effects of decreased/increased oxygen on systematic arterioles

A
  • decreased oxygen causes vasodilation

- increased oxygen causes vasoconstriction

30
Q

4 factors that influence the rate of gas exchange across the alveolar membrane

A

1-partial pressure gradient of oxygen and carbon dioxide
2-diffusion coefficient for oxygen and carbon dioxide
3-surface area of alveolar membrane
4-thickness of alveolar membrane

31
Q

what is the partial pressure of gas

A
  • the pressure that ONE gas in a mixture of gases would exert if it were the only gas present in the whole volume occupied by the mixture at a given temperature (eg. if the total pressure exerted by gas mixture is 100kPa, and half of the mixture is gas 1, the partial pressure for gas 1 is 50kPa)
  • it determines the pressure gradient of a gas (gases move across membranes etc by pressure gradients)
32
Q

dalton’s law of partial pressures

A
  • the total pressure exerted by a gaseous mixture=the sum of each individual component in the gas mixture
  • Ptotal= P1+P2+P3…. +Pn
33
Q

compositions and partial pressures of gases in atmospheric air

A
  • total atmospheric pressure =760mmHg
  • 79% nitrogen therefore partial pressure of nitrogen = 600mmHg (79% of 760)
  • 21% oxygen in air therefore partial pressure of oxygen= 160mmHg (21% of 760)
34
Q

is it possible to work out an average value for the partial pressure of oxygen in alveolar air (PAO2) when oxygen is continuously diffusing from the alveoli into the blood?

A

-PAO2=PiO2-[PaCO2/0.8]
-the air in the respiratory tract is saturated with water and the water contributes about 47mmHg to the total pressure in the lungs, therefore the pressure of inspired air=atmospheric air -water vapour pressure(760-47=713mmHg at sea level)
-PiO2 would then equal 713x0.21 (as oxygen makes up 21% of inspired air)
-at a normal arterial PCO2 of 40mmHg,
PaO2= 150-[40/0.8]=150-50=100mmHg at sea level

35
Q

PAO2

A

PAO2=PiO2-[PaCO2/0.8]

  • PAO2= partial pressure of oxygen in alveolar air
  • PiO2=partial pressure of oxygen in inspired air
  • PaCO2= partial pressure of CO2 in arterial blood
  • 0.8 is the respiratory exchange ratio (RER) aka the ratio of carbon dioxide produced/oxygen consumed, for someone eating a mixed diet
36
Q

RER

A

-respiratory exchange ratio (the ratio of carbon dioxide produced/oxygen consumed), for someone eating a balanced diet

37
Q

partial pressure gradient

A

movement of gases from a higher to lower partial pressure

38
Q

units of partial pressure

A

-kPa (kilopascals) in the UK
-mmHg in American texts
(to convert to kPa divide mmHg by 7.5)

39
Q

direction of net diffusion gradients for oxygen and carbon dioxide between lungs and tissues

A

from lungs - tissues goes from:

  • high PO2-lowPO2
  • low PCO2-highPCO2
40
Q

what causes the difference in partial pressure gradient for CO2 and O2

A
  • partial pressure gradient for CO2 is much smaller than the partial pressure gradient for O2
  • CO2 is more soluble in membranes than O2
  • Diffusion coefficient for CO2, is 20 times that of O2
41
Q

diffusion coefficient definition

A

the solubility of gas in membranes

42
Q

degree of gradient between alveolar and arterial PO2

A
  • a small gradient between alveolar PO2 (PAO2) and arterial O2 (PaO2) is normal as ventilation perfusion match is not normally perfect
  • A big gradient between PAO2 and PaO2 would indicate problems with gas exchange in the lungs or a right or left shunt in the heart
43
Q

Ficks Law of diffusion

A

The amount of gas that moves across a sheet of tissue in unit time is proportional to the area of the sheet but inversely proportional to its thickness

44
Q

factors which increase gas diffusion

A
  • lungs provide very large surface area with thin membranes to facilitate effective gas exchange
  • airways divide repeatedly to increase surface area for gas exchange
  • the small airways form outer pockets (alveoli), which helps to increase surface area
  • lungs have a very extensive pulmonary capillary network
45
Q

cardiac output and pulmonary circulation

A

the pulmonary circulation receives the ENTIRE cardiac output

46
Q

respiratory tree

A

trachea->bronchi->bronchioles->terminal bronchioles->respiratory bronchioles->alveolar ducts->alveolar sacs

47
Q

conducting zone of respiratory tree

A

trachea->bronchi->bronchioles->terminal bronchioles

48
Q

transitional and respiratory zones of respiratory tree

A

respiratory bronchioles->alveolar ducts->alveolar sacs

49
Q

alveoli

A
  • thin walled inflatable sacs
  • function in gas exchange
  • walls consist of a single layer of type I alveolar cells
50
Q

pulmonary capillaries

A

encircle each alveolus

51
Q

respiratory membranes

A
  • alveoli

- pulmonary capillaries

52
Q

4 factors that influence the rate of gas transfer across the alveolar membrane

A
  • partial pressure gradients of O2 and CO2
  • surface area of the alveolar membrane
  • thickness of the barrier separating the air and blood across the alveolar membrane
  • diffusion coefficient (solubility of the gas in the membrane)
53
Q

influence of partial pressure gradients of O2 and CO2 on the rate of gas transfer across the alveolar membrane

A

rate of transfer increases as partial pressure gradient increases

54
Q

influence of surface area of the alveolar membrane on rate of gas transfer across the alveolar membrane

A
  • rate of transfer increases as surface area increases
  • surface area increases during exercise as more pulmonary capillaries open up when the cardiac output increases and the alveoli expand as breathing becomes deeper
  • surface area decreases with pathological conditions such as emphysema and lung collapse
55
Q

influence of thickness of the barrier separating the air and blood across the alveolar membrane on rate of gas transfer across the alveolar membrane

A
  • rate of transfer decreases as thickness increases
  • thickness normally remains constant
  • thickness increases with pathological conditions such as pulmonary edema, pulmonary fibrosis and pneumonia
56
Q

influence of diffusion coefficient (solubility of the gas in the membrane) on rate of gas transfer across the alveolar membrane

A

rate of transfer increases as diffusion coefficient increases
-diffusion coefficient for CO2 is 20x that of O2, offsetting the smaller partial pressure gradient for CO2 therefore, approximately equal amounts of CO2 and O2 are transferred across the membrane

57
Q

list of non respiratory functions of the respiratory system

A
  • route for water loss and heat elimination
  • enhances venous return (CVS physiology)
  • helps maintain normal acid-base balance (respiratory and renal physiology)
  • enables speech,singing and other vocalizations
  • defends against inhaled foreign matter
  • removes, modifies, activates, or inactivates various materials passing through the pulmonary circulation
  • nose serves as the organ of smell

respiratory physiology (7 decks)

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