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Medsci 142 > respiratory 22 > Flashcards

respiratory 22 Flashcards

1
Q

why is pulmonary circuit low pressure?

A

the pulmonary arteries are not as muscularized as their systemic counterparts. Thinner, less muscular vessels are more easily distended.
+avoid bleeding/oedema in the lungs

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2
Q

what are the 2 circulations in the lung?

A

Pulmonary circulation: blood from the right ventricle goes to the alveoli to be oxygenated and returns to the left ventricle via pulmonary veins
Systemic circulation: An artery branches off from the aorta and takes blood to the tracheobronchial tree. This deoxygenated blood drains back via 2 routes: 1 goes back to the right atrium, but the other half drains into the oxygenated blood from the pulmonary vein( anatomical shunt).

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3
Q

Anatomical shunt

A

the return of deoxygenated blood from the lungs(from systemic circulation) through pulmonary veins

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4
Q

Sheet flow

A

Densely packed capillaries fuse
Blood moves like a sheet instead of a tube. Increases contact area

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5
Q

What is the response of the pulmonary system to increased pulmonary arterial pressure?

A

Recruit more vessel(distension of vessels)-> increased crosss-sectional area-> decreased resistance
More vessels open AS WELL AS distending the lumen of the vessels that were already open, which also helps decrease the resistance.

DECREASED RESISTANCE
This helps to avoid the build-up of pressure and potentially oedema in the lungs

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6
Q

What does hypoxia cause in pulmonary circulation?

A

Vasoconstriction (the opposite in systemic circulation)
If one pathway is blocked the airflow is diverted to the pathway of least resistance.
Oxygen lvl in the blocked alveoli is low. Blood going through these alveoli will not get good oxygenation-> contamination. Regional vasoconstriction to the hypoxic alveoli, which defers blood to the better-oxygenated alveoli.

The direction is directed by the Law of Mass action. At lower pH hemoglobin has a greater affinity for CO2.

(in systemic -vasodilation)

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7
Q

why is the blood flow to the lung uneven?

A

Majority of blood flow- bottom of the lung. Much less at the top. Due to gravity.
Lying down helps bring blood higher.

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8
Q

what can help increase perfusion to the top of the lung?

A

Exercise can increase perfusion at the top of the lung as it increases Pa(pulmonary arterial pressure) which gets>PA( Pulmonary Alveolar P)

Lying down also helps

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9
Q

what is the ideal ventilation-perfusion ratio?

A

1

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10
Q

What causes pulmonary hypertension?

A

• right heart failure
• hypoxia = vasoconstriction
can lead to increased pulmonary arterial BP-> pulmonary oedema

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11
Q

what can cause pulmonary oedema?

A

-pulmonary hypertension
-left heart failure (build-up of blood, as blood takes longer to get back to the heart)-> oedema-> pulmonary hypertension
-systemic hypoxia
-breathlessness – ‘dyspnoea’

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12
Q

what is the respiratory surface?

A

the distance between the air in the alveoli and blood

want it as narrow as possible

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13
Q

what is the downside of a narrow respiratory surface?

A

exposure to contaminants, bacteria and viruses

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14
Q

what factors regulate the movement of gas across the respiratory surface?

A
  1. Area. 300 million alveoli in the human lung
    0.3 mm in diameter. Surface area = 50 to
    100 m2 and volume 4 litres approximately
  2. Thickness of tissue. 0.5 um
  3. Partial pressure differential across the tissue
  4. Solubility of gas in the blood
  5. Molecular weight of the gas

*Solubility more important than MWt of gas

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15
Q

how is the diffusion of volume of a gas calculated?

A
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16
Q

what is the thickness of the tissue between blood and air?

A

~0.5 um

17
Q

what is the partial pressure of O2 in the air of alveoli and the blood?

A

100mmHg in the air
40 mmHg in the arterial blood

Driving force is much greater than for CO2

18
Q

what is the partial pressure of CO2 in the air in the alveoli and the blood?

A

40 mmHg- in the air
46 mmHg - in the arterial blood.

Driving force out of the blood

19
Q

What is more soluble in blood: CO2 or O2?

A

CO2 is 25 times more soluble

20
Q

How is the movement of gases across the alveolar membrane balanced?

A

CO2 is 25 times more soluble in blood than O2.
But, release time of CO2 from haemaglobin is slower
than O2, so on balance movement of both gases
across alveolar membrane are balanced.

21
Q

How much time does a RBC spend in the alveolar-capillary?

A

3/4 s = 750 msec( at rest)

22
Q

how long does it take to completely saturate hemoglobin with O2?

A

0.25 sec
This is good as if the speed of flow is increased there is still time to
Offload/pick up O2

23
Q

what gases are perfusion limited?

A

N2O and O2 and CO2 are perfusion limited.
further gas exchange is only possible by increasing blood flow, or perfusion, in the pulmonary capillary.

24
Q

what gases are diffusion limited?

A

CO.
further gas exchange is possible by increasing diffusion time.

25
Q

CO poisoning

A

takes a long time to offload CO from hemoglobin. Strong affinity.
CO prevents O2 from loading-> severe hypoxia

26
Q

what is mean pulmonary pressure?

A

14mmHg

27
Q

what is mean systemic pressure?

A

93 mmHg

28
Q

how is mean pressure calculated?

A
29
Q

why is the pressure in the pulmonary system always larger than the pressure in the left atrium?

A

Important to keep the flow of blood back to the heart

30
Q

is there a significant difference in the thickness of walls in pulmonary arteries compared to pulmonary veins?

A

NO. Pulmonary arteries and vein are both quite thin walled as both have relatively low pressures. In contrast, in systemic circulation, there is a big difference in pressure in arteries compared to veins, leading to a significant difference in wall thickness

31
Q

when standing upright the apex of the lung has higher/lower ventilation than the base?

A

lower

32
Q

is alveoli volume larger or smaller in the apex than the base of the lung?

A

Larger. Pleural pressure is more negative at the top of the lung due to gravity, meaning that alveoli here at the apex are a larger size at FRC.

Pleural pressure is less -ve at the bottom of the lung due to gravity, meaning that alveoli are less inflated at rest compared to those at the top of the lung.

33
Q

how does destruction of alveolar elastic tissue( e.g. in emphysema ) affect surface area for gas exchange?

A

decrease

Medsci 142 (32 decks)

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