Respiration IV

Question 1

The amount of dissolved gas carried by the blood is directly proportional to […], according to […] Law.

Answer 1

the partial pressure of the gas, according to Henry’s Law.

Question 2

How much O2 is dissolved in 100 ml of plasma? What is its partial pressure?

Answer 2

0.3 ml of O2 at a partial pressure of 100 Hg.

Question 3

How does the amount of oxygen dissolved in plasma compare to the oxygen requirements of cells?

Answer 3

There is around 0.3 ml of O2 dissolved in 100 ml of plasma, but the O2 consumption of the body is about 300 ml per minute. Thus, only the O2 transported in plasma is not sufficient to meet our needs.

Question 4

Hemoglobin allows the blood to take up […] times as much oxygen as plasma

Answer 4

65

Question 5

Hemoglobin constitutes […] of the total weight of red blood cells.

Answer 5

1/3

Question 6

Describe the structure of hemoglobin.

Answer 6

Each molecule has 4 subunits. Each subunit has a heme joined to a globin. Heme contains an Fe2+ ion that can bind 1 molecule of O2.

Question 7

Write the formula for the rapid and reversible combination of hemoglobin with oxygen.

Answer 7

Hb + O2 <-> HbO2

Question 8

The total amount of O2 in arterial blood is about […] vol. %

Answer 8

20

Question 9

What is included and not included in the calculation of PO2 of the blood?

Answer 9

The O2 that is bound to hemoglobin does not contribute to the partial pressure of O2 in the blood. Only molecules physically dissolved in the blood plasma are responsible for PO2.

Question 10

What is the O2 dissociation curve?

Answer 10

It depicts the amount of O2 carried by hemoglobin for a given partial pressure of oxygen in the plasma.

Question 11

Draw and describe the shape of the O2 dissociation curve.

Answer 11

The curve is flat at high values of PO2 (80-100 mm Hg) and is steep at low values of PO2 (below 60 mm Hg).

Question 12

Explain the reason behind the shape of the O2 dissociation curve

Answer 12

Hemoglobin provides an automatic mechanism that matches the oxygen supply to the oxygen needs. If it’s needed, it lets it go. If it’s not needed, it transports it to where it is needed.

At low values of PO2, as seen in the peripheral tissues, a small drop in PO2 unloads a lot of O2 from Hb to the tissue.

Question 13

What is myoglobin and where is it found?

Answer 13

Myoglobin is another oxygen carrier like hemoglobin. It is fund in muscle cells.

Question 14

The affinity of hemoglobin for O2 is determined by its […]

Answer 14

quaternary structure

Question 15

What is cooperative binding in hemoglobin?

Answer 15

The combination of the first heme with Hb in a hemoglobin molecule increases the affinity of the second heme for O2.

Question 16

How does myoglobin differ structurally from hemoglobin?

Answer 16

It binds only one O2 molecule, while hemoglobin binds 4.

Question 17

What is the function of myoglobin?

Answer 17

Myoglobin is a safety net - it releases its oxygen at very low PO2. If there’s no other source of PO2, myoglobin will release its O2. This only occurs at very low PO2.

Question 18

Describe and draw the shape of the O2 dissociation curve for myoglobin.

Answer 18

It is hyperbolic in shape, as myoglobin will only release oxygen at very low PO2 level.

Question 19

How does the O2 dissociation curve change with differing Hb concentrations in the blood? Explain the implications of this.

Answer 19

The total amount of O2 in the blood depends mostly on Hb concentration. Under conditions of decreased Hb concentration (anemia), even when O2 saturation is 97.5%, less O2 can be carried in the blood by Hb.

Question 20

What is the Bohr effect?

Answer 20

The Bohr effect is the shift of the HbO2 dissociation curve to the right when blood CO2 or temperature increases or blood pH decreases. Also happens with increasing DPG.

Question 21

Explain the logic behind the Bohr effect.

Answer 21

The shift of the curve to the right with increased temperature, increased PCO2, or decreased pH implies that under these conditions, the tissues will need more oxygen. Therefore, more oxygen will be released at a given PO2, making oxygen available

Question 22

When might a shift to the left occur (Bohr effect)?

Answer 22

If there is a decrease in temperature, a decrease in PCO2, or an increase in pH.

Question 23

What is the effect of carbon monoxide poisoning on the O2-hemoglobin curve? Explain why.

Answer 23

It will shift the O2-hemoglobin curve to the left. CO has a high affinity for O2 binding sites in hemoglobin, reducing the amount of O2 bound to hemoglobin. There is little stimulation to increase ventilation because PaO2 remains normal.

Question 24

On average, a person uses about […] ml/min of O2 and produces about […] ml/min of CO2 at rest.

Answer 24

300, 250

Question 25

CO2 is carried in what three forms in the blood? State the percent breakdown.

Answer 25

1. Physically dissolved in blood (10%)
2. Combined with Hb to form HbCO2 (11%)
3. As bicarbonate (79%)

Question 26

How does CO2 combine with hemoglobin? What is it called when this occurs?

Answer 26

Contrary to O2 that combines with the heme portion of hemoglobin, CO2 combines with the globin portion. There is therefore no competition for binding on hemoglobin.

Question 27

Write the reactions for CO2 as bicarbonate in plasma?

Answer 27

CO2 + H2O -> H2CO3 (carbonic anhydrase)
H2CO2 -> HCO3- + H+

Question 28

Describe the reactions that occur with CO2 as it enters red blood cells in the tissue capillaries.

Answer 28

CO2 enters RBC, some combines with Hb, and some combines with water to create carbonic acid, which will ionize into bicarbonate. This bicarbonate will be carried in the plasma. There will also be Cl- that comes into the cell to maintain cell neutrality.

Question 29

Describe the reactions that occur with CO2 as it exits red blood cells in the pulmonary capillaries.

Answer 29

In the lungs, CO2 is low, so CO2 from plasma will diffuse into the alveoli. The Hb that had the CO2 will let it go so that it can diffuse back into the plasma. The bicarbonate will move back into the cell and chlorine will move out. You will be able to expire the CO2.

Question 30

If CO2 production increases, how does it affect bicarbonate production?

Answer 30

If CO2 production increases, the production of HbCO2, HCO3-, and H+ increases.

Question 31

How does the lowering of blood PCO2 affect the production of bicarbonate? When does this happen?

Answer 31

Lowering of blood PCO2 results in HCO3- getting transformed into H2CO3 and further into CO2 and H2O, and HbCO2 generating Hb and CO2. This situation occurs when venous blood flows through the lung capillaries.

H+ + HCO3- -> H2CO2 -> (CA) H2O + CO2,
HbCO2 -> Hb + CO2

Question 32

What is the Haldane effect? Exlain it.

Answer 32

In the tissue capillaries, Hb free of O2 (once O2 has diffused to the tissues) may combine with H+ in the reaction:
H+ + HbO2 <–> HHb + O2
This acts as a buffer.

Question 33

What is the purpose of the Haldane effect? Explain its mechanism.

Answer 33

Hb being reduced to HHb after picking up a proton will help with blood loading of CO2 by pushing equations 1 and 2 to the right. This allows mixed venous blood to carry more CO2 than arterial blood can.

Question 34

How does the concentration of HbO2 affect CO2 content in the blood?

Answer 34

If the blood is deoxygenated (75% saturation of Hb in oxygen), the CO2 content is higher than if the blood contains a lot of oxygen. This is an upwards shift of the curve if the blood is deoxygenated.

Question 35

Explain how the curves of CO2 and O2 vol % content in the blood change as alveolar PO2 or PCO2 rise. How does this affect hypo and hyperventilation?

Answer 35

O2 content is sigmoidal, as it will plateau eventually (past around 60 mm Hg).

CO2 content increases relatively linearly. So, if we hypoventilate and alveolar PCO2 rises, then blood CO2 will rise everywhere. Doubling alveolar ventilation will halve alveolar PCO2.