L15: Respiration (Gas Exchange)

Question 1

What is the composition of air in the atmosphere and in the alveoli?

Question 2

What factors influence gas exchange at the lungs and at other tissues?

Question 3

A patient at a local hospital is having difficulty breathing and the PO2 in his alveoli is 92 mmHg. What would be the PO2 to be in the blood leaving his lungs (i.e. in the pulmonary veins)?

a) 92 mmHg
b) 100 mmHg
c) 50 mmHg
d) 160 mmHg

Answer 3

a)

Question 4

Why does co2 enter the blood and o2 enter tissue?

Answer 4

This is due to the partial pressures and the gases moving down their pressure gradient.

The blood that leaves the lungs to go to tissue has a high 02 pressure and low co2 pressure.

This blood then reaches the tissue where the pressure of 02 is lower and pressure of co2 is higher.

Since gas moves down its pressure gradient from low to high, o2 moves into tissue and co2 moves out into the blood.

Question 5

Key factors that influence gas exchange

Question 6

What is partial pressure gradients

Question 7

Composition of air in atmosphere

Question 8

What changes when you take into consideration humidity in the lungs pressure (pH2O)

Question 9

What is the composition of hemoglobin and where is it found?

Answer 9

A molecule that binds oxygen
Oxygen binds to the 4 iron groups present in a single hemoglobin molecule
Found in RBC, RBS’s have thousands of hem. molecules present

Question 10

Hemoglobin in arterial blood vs. venous blood?

Answer 10

98.5% saturated with oxygen, almost all oxygen binding sites are taken up versus 75% saturation in venous blood

Question 11

What is positive cooperativity?

Answer 11

Means when 1 o2 molecule binds to Hb, it increases the affinity of another o2 molecule to bind Hb

Question 12

Why is the Hb/O2 curve a sigmodal shape?

Answer 12

Due to positive cooperativity property of O2 binding to Hb

Question 13

What is the Hb- 02 dissociation curve, what does it include, how to make curve?

Answer 13

What it is: Shows the o2 saturation in Hb at different partial pressures of o2 (pO2)

Includes:
- Shows o2 sat. in Hb in arterial blood
- Shows o2 sat. in Hb in venous blood
- The diff b/w these two values is the % of o2 unloaded by Hb in the tissues

To make the curve:
-Blood is removed from the body
- And subjected to different partial pressures of oxygen
- % [ ] of Hb is plotted

Question 14

When would Hb curve shift to right? And what is the effect?

Answer 14

1. increase in temp
2. increase in pCO2
3. more 2,3 BPG
4. decrease in pH

Effect is more unloading of 02 at the tissues by Hb

Question 15

When would Hb curve shift to left? And what is the effect?

Answer 15

1. decrease in temp
2. decrease in pCO2
   3.less 2,3 BPG
3. increase in pH

Effect is less unloading of o2 at the tissues by Hb

Question 16

Bohr effect

Answer 16

Effect of pH

Question 17

2,3 BPG and its 2 functions?

Question 18

Which of the following will increase the unloading of oxygen at the tissues?

increased H+
lower PCO2
decreased 2,3 DPG
increased pH

Answer 18

increased H+,

increase in protons means decrease in pH

Question 19

How is co2 transported in blood?

Answer 19

1. dissolved in plasma (5-6%)
2. bound to Hb to form carbaminohemoglobin (5-8%)
3. converted to bicarb. in erythrocytes then transported into plasma (86-90%)

Question 20

How is o2 transported in blood?

Question 21

Why is a shift to make more bicarbonate and protons favoured in the tissues? Which direction does the equation shift?

Answer 21

At the tissue:
1. Protons can bind to Hb for buffering (maintaining pH)
2. Bicarb can be exchanged for Cl-ions into cell (chloride shift) (helps maintain pH)

These processes help maintain pH so the equation moves to the right.

Question 22

Why is a shift to make more co2 favoured at the lungs? Which direction does the equation shift?

Answer 22

At the lungs:
1. protons release from Hb
2. bicarb moves into cell in exchange for chloride (reverse chloride shift)

this increase in protons and bicarb will propel the reaction in the left direction which produces more co2 to leave the cell into the alveoli.

Question 23

How does Co2 convert to bicarbonate and where does this occur?

Answer 23

H2O + CO2 <=(CA)=> H2CO3 <=> H+ and HCO3-

Occurs in the RBC because CA, carbonic anhydrase, is present there

Question 24

Heldane effect

Answer 24

As PO2 increases the total amount of CO2 in the blood decreases

Question 25

Which process is favoured at the lungs?

a CO2 and H2O combining to form H2CO3
b HCO3- transport into red blood cells
c Formation of carbaminohemoglobin
d Binding of protons to hemoglobin

Answer 25

HCO3- transport into red blood cells