Lecture 19: Gas Exchange and Respiratory Control

Question 1

Oxygen is carried in the blood in what two forms?

Answer 1

• dissolved O2 in the plasma

- bound to haemoglobin in red blood cells

Question 2

Why is only a small amount of O2 dissolved in plasma?

Answer 2

Because O2 does not dissolve well, especially in the warmth

Question 3

Briefly describe the cooperatively of haemoglobin

Answer 3

The most difficult oxygen to bind is the first one; the more O2 binds, the more tightly all the others bind

Question 4

What is the benefit of having a sigmoidal curve to describe the affinity of haemoglobin for O2?

Answer 4

It means that less O2 can be released to tissues that do not need it and more can be released to tissues do need it

Question 5

How does pH affect O2 affinity?

Answer 5

lower pH means a reduced O2 affinity which means more O2 can be dropped off at the tissue

Question 6

How does the temperature affect O2 affinity?

Answer 6

higher temperature means reduced O2 affinity which means more can be dropped off at the tissue

Question 7

Why is the oxygen binding curve a sigmoidal shape?

Answer 7

Because at low O2 pressure, few haem are occupied so the binding is slow
As O2 begin to bind, the affinity increases so the others bind a lot faster and stronger
The curve slows and plateaus because as more O2 bind, there are less binding sites so the remaining O2 take a while to find the empty sites

Question 8

During exercise, why is it helpful that skeletal muscles produce lactic acid and heat during exercise?

Answer 8

Because the decrease in pH and increase in heat reduce O2 affinity which means that less O2 binds and more O2 is released into the tissue

Question 9

What are the three forms that CO2 is transported in?

Answer 9

1. dissolved in plasma
2. bound to haemoglobin
3. converted to bicarbonate

Question 10

Of the CO2 that is bound to haemoglobin, some of it is bound as carbaminohaemoglobin and the rest is converted to _________ _________ by _______ ________

Answer 10

carbonic acid

carbonic anhydrase

Question 11

The carbonic acid dissociates into

Answer 11

H+ and bicarbonate ion

Question 12

The production of H+ by the dissociation of carbonic acid means

Answer 12

the pH is lowered

Question 13

Describe the system to control breathing

Answer 13

sensors send afferent information regarding gas levels to the central controller in the pons, medulla and other parts of the brain, then efferent signal is sent from the brain to the effectors to administer the change

Question 14

What are respiratory sensors?

Answer 14

1. chemoreceptors
2. baroreceptors
3. lung stretch receptors
4. protective reflexes

Question 15

What do chemoreceptors control?

Answer 15

CO2 levels

Question 16

Describe the process the decrease CO2 levels after an increase?

Answer 16

• the chemoreceptors sense the increase
• they activate the effectors (respiratory muscles)
• this increases respiratory rate with increased elimination of CO2 at alveoli
• this decreases the arterial CO2 pressure

Question 17

Describe how the baroreceptors affect respiratory function by using arterial BP going down as an example

Answer 17

• Arterial BP decreases which reduces the flow
• this is sensed by the baroreceptors
• they increase the respiratory minute volume
• this increases the uptake of air

Question 18

Describe the role of the lung stretch receptors

Answer 18

• as the lungs inflate or deflate, they send afferent input from stretch receptors
• the brain then send efferent output preventing them stretching too far either way

Question 19

What are the protective reflexes?

Answer 19

they detect irritation and the brain responds by sending efferent signal that triggers a sneeze or a cough