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Respiratory > Gas Exchange > Flashcards

Gas Exchange Flashcards

1
Q

What is Daltons’s law?

A

partial pressure of a gas mixture is equal to the sum of the partial pressures of the gas in the mixture

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2
Q

What is Fick’s law?

A

diffusion rate is proportional to the concentration gradient* the exchange surface area * the diffusion capacity of the gas / the thickness of the exchange surface

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3
Q

What is Henry’s law?

A

At a constant temp, amount of a gas that dissolves in a particular type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid

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4
Q

What is Boyle’s Law?

A

At a constant temperature, the volume of a gas is inversely proportional to the pressure of that gas

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5
Q

What is Charles’ law?

A

At a constant temperature, the volume of gas is directly proportional to temperature of that gas

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6
Q

What are the % of nitrogen, oxygen, argon and carbon dioxide in air?

A

N - 78.09%
O - 20.95%
A - 0.93%
C - 0.04%

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7
Q

How does the composition of air differ between room air and high altitude air?

A

No difference, just the relative volumes are smaller in high altitudes in atmosphere

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8
Q

As air is breathed in and it reaches the alveoli, what 3 things change?

A

The air is warmed, humidified and slowed (protects the lungs)

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9
Q

Compare the partial pressures of O2, CO2 and H20 in dry air, conducting airways and respiratory airways.

A

dry air -
O2 = 21.3kPa
CO2+H20 = 0

Conducting airways -
O2 = 20
CO2 = 0
H20 = 6.3

Respiratory airways -
O2 = 13.5
CO2 = 5.3
H20 = 6.3

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10
Q

Explain how the the partial pressures of O2, CO2 and H20 differ in dry air, conducting airways and respiratory airways.

A

Oxygen highest in air, no C02 and H20. In conducting airways main change is water saturation. In respiratory airways, the O2 decreases, and C02 increases

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11
Q

Why can’t dissolved oxygen meet metabolic demands?

A

Only 16ml of oxygen will dissolve per min.

Oxygen consumption is 250ml/min.

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12
Q

Hb is allosteric, what does this mean?

A

It changes shape depending on what binds or doesn’t bind to it

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13
Q

When oxygen binds to Hb which changes occur?

A

Conformational change so the structure relaxes and greater affinity for oxygen. The middle area changes too - becomes a binding site for 2,3 - DPG

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14
Q

If more ATP is being made, what is happening to 2,3 - DPG production?

A

Increasing as it is a product of glycolysis

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15
Q

What does 2,3 - DPG do?

A

It binds to Hb and squeezes oxygen out so more is used by tissues. It decreases the affinity for oxygen so more unloading occurs.

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16
Q

What is cooperativity of Hb?

A

The changing of its shape and affinity depending on the amount of bound oxygen

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17
Q

What is methaemoglobin?

A

Fe2+ gets oxidised to Fe3+ and this cannot bind oxygen. Causes functional anaemia. Nitrites can cause MetHb formation

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18
Q

Why is it beneficial that the oxygen dissociation curve is sigmoidal and not linear?

A

If it was linear, then there would be a large variation in oxygen loading in the lungs (might not get max) and very little unloading in tissue (not max efficiency. As it is sigmoidal, you get 100% saturation in lungs across a range of pO2 and in tissues, the saturation can go decrease a lot so lots of unloading

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19
Q

What does p50 tell us?

A

The partial pressure of oxygen where 50% of haemoglobin is saturated. Find it by drawing a line at 50% saturation.

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20
Q

What factor shifts the ODC to the right?

A

Increase in energy consumption - exercise

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21
Q

Which changes occur during exercise?

A
  • increase in temp
  • acidoisis
  • hypercapnia (high co2)
  • increase in 2,3 - DPG
22
Q

Which things cause the ODC to shift to the left?

A
  • decrease in temp
  • alkalosis
  • hypocapnia
  • decrease in 2,3 - DPG
23
Q

What does carbon monoxide poisoning do to the ODC?

A

Curve shifts downwards and left

24
Q

Why does carbon monoxide shift the ODC the way it does?

A
  • Hb has greater affinity for CO
  • It binds to Hb and reduces amount of O2
  • Those O2 molecules binding to Hb are bound more tightly and less likely to unload
  • The overall effect is that the is an increase in affinity but decreased capacity to bind O2
25
Q

In an anaemic person what happens to the ODC?

A

It moves down, as the Hb conc is lower but saturation of the Hb is the same

26
Q

What does polycythaemia do to the ODC?

A

Curve shifts up. Polycythaemia is when the haematocrit is higher due to more RBCs. This leads to more oxygen carrying capacity so blood flows slower, reducing oxygen delivery

27
Q

Why is pulse oximetry not useful alone?

A

It tells us the saturation of Hb but not the amount of Hb so both should be used together

28
Q

Where do foetuses get oxygen?

A

From the placenta - they take oxygen as they have higher affinity

29
Q

What does the oxygen dissociation curve for myoglobin look like?

A

It is hyperbolic. It isn’t Hb but it is a monomeric protein in muscle that keeps oxygen for later.

30
Q

What is the type of blood arriving at the alveoli?

A

It is mixed venous blood not deoxygenated as it contains 75% oxygen - around 5.3 kPa

31
Q

How does oxygen move from the alveoli to the red cell?

A

Higher pressure in the alvelous so oxygen dissolves into the blood and due to the concentration being higher than the pressure in the cell, it diffuses in. Hb is 100% concentrated

32
Q

When the blood arrives at the tissue what is its saturation and why?

A

It is around 97% because the blood is diluted by bronchial circulation which supplies the lungs with blood to survive. This blood trains into the pulmonary circulation before returning to the left atrium

33
Q

What happens to oxygen concentration and saturation in the tissues?

A

from 20 to 15 mL/dL

97 - 75%

34
Q

What is oxygen flux?

A

The overall amount of oxygen being deposited in tissues - around 5mL/dL

35
Q

What is a normal CO?

A

5 L/min

36
Q

What happens to carbon dioxide once it dissolves in the blood?

A

Carbon dioxide is more soluble than oxygen so once in blood can form carbonic acid after meeting water - this can dissociate into proton and bicarbonate (very slow)

37
Q

What happens to carbon dioxide inside of RBC and how does it compare to what happens in the plasma?

A

CO2 can move into RBC where enzymes are (carbonic anhydrase) so then bicarbonate is made at a faster rate than in plasma

38
Q

How is the homeostasis of water maintained inside the RBC?

A

Inside the RBC, the carbonic acid dissociates into bicarbonate and proton so the bicarbonate diffuses into plasma via AE1 protein and Cl- enters (maintains equilibrium anion in for anion out). Cl- moving in draws in water. This prevents cell drying as water was being used to make bicarbonate

39
Q

Where does carbon dioxide bind in Hb?

A

Carbon dioxide can bind to the amine end of a globin chain in Hb making carbaminohaemoglobin

40
Q

What happens if the H+ concentration in the RBC increases, and how is it dealt with?

A

If H+ conc is high in the red cell, pH will decrease. This is solved by Hb - the residues on globin chains accept H+ acting as a buffer.

41
Q

What is the flux of CO2 in venous and arterial blood?
What is the difference in CO2 conc between venous and arterial blood?
How much CO2 is made per minute?

A

CO2 flux changes from 52 to 48 (venous TO arterial)
There is a 4mL/dL increase in CO2 conc in venous blood
200mL of CO2 made a min

42
Q

Is oxygen consumption equal to carbon dioxide production?

A

No, as water is lost in metabolism

43
Q

What is pulmonary transit time?

A

Amount of time that blood is in contact with respiratory surface - around 0.75 s

44
Q

How long does exchange take to occur?

A

Exchange occurs in 0.25 s

45
Q

What can cause exercise induced hypoxia?

A

Cardiac output is higher and pulmonary blood flow increases so the time taken for oxygen to diffuse is longer

46
Q

Does CO2 or O2 diffuse faster and why?

A

CO2 diffuses faster than O2 as it is more soluble

47
Q

Why is blood flow to the whole lung not uniform? What does the bottom of the lung get more of?

A

Blood flow to lung is not the same because of gravity. Bottom of lung gets more perfusion and ventilation - less resistance

48
Q

How do the V/Q ratios differ in the base and apex?

A

In the base, the V/Q ratio tends towards 0 but towards infinity in apex (V/Q is ventilation perfusion)

49
Q

Where the lines for V and Q cross, what is the significance?

A

Ventilation is equal to perfusion

50
Q

How do the 3 zones of the lung differ in the alveolar, arterial and venous pressure?

A

Zone 1 (apex) - alveolar pressure>arterial>venous

Zone 2 (middle) - arterial>alveolar>venous

Zone 3 (base) - arterial>venous>alveolar

(arterial always greater than venous or blood flows back)

51
Q

What is the Haldane effect (CO2 dissociation curve)?

A

Hb binding to oxygen allows more unloading of CO2 in lungs. When Hb is 100% saturated with O2 no CO2 bind and opposite at 75% saturation. Deoxyhaemoglobin binds CO2 and protons more readily

Respiratory (23 decks)

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