Gas Transport and Respiratory Control

Question 1

Describe the two ways that oxygen is carried in the blood

Answer 1

• Dissolved O2
• Bound to haemoglobin in RBCs

Oxygen dissolved poorly especially in blood because it is warm (gas doesn’t’t like to dissolve in war fluids)

Question 2

Describe the sigmoidal shape of the haemoglobin binding curve and how this reflects its function

Answer 2

Binds cooperatively which means that it has low O2 affinity initially but once one binds, the next one can bind easier, and then easier for the next and so on. This is why the shape of the binding curve is sigmoidal.
- Oxygen is distributed to the tissues that need it the most.
- Keeps O2 levels high in case of emergencies
- Sigmoidal curve means that it holds the O2 tightly in high PP of O2 places until it gets to tissues that need it the most (low PP of O2 areas) and at that point it rapidly offloads the O2.
- This means that the haemoglobin preserves the O2 until it reaches the tissues that really need it.

Question 3

What are the two roles of haemoglobin?

Answer 3

• Move oxygen fro air in the alveolus to the blood in the capillary
• Move oxygen from blood in the capillary into the surrounding tissue
  The sigmoidal shape of the curve shows that it is designed so that it can do these two roles well

Question 4

How can the haemoglobin binding curve be shifted?

Answer 4

Binding curves are not static, they can change. These two things shift the binding curve to the right and result in O2 being offloaded more easily:
- Lower pH environment (more acidic) reduces the O2 affinity
- Higher temperature also reduces oxygen affinity

When exercising the pH drops and temperatures rises in skeletal muscle so this system makes sense as it means when haemoglobin comes to these areas it will drop off the O2 here where it is needed the most.

Question 5

What are the three modes that carbon dioxide can be transported by?

Answer 5

1. Dissolved in plasma (not much)
2. Bound to haemoglobin (not much)
3. Converted to bicarbonate (most of CO2 transported this way!!)

Question 6

Describe the formation of bicarbonate

Answer 6

• Carbon dioxide and water combine to form carbonic acid
• Carbonic acid disassociates into bicarbonate and a hydrogen ion as soon as it is in aqueous solution.
• This lowers the pH and results in the blood getting more acidic.

Question 7

Describe control of breathing

Answer 7

• We need to maintain normal levels of O2 and CO2 for metabolic and biochemical stability (eg. pH)
• But O2 usage and CO2 production are quite variable
• Despite this, O2 and CO2 are normally kept within close limits due to tight control of ventilation

Question 8

Describe the afferent and efferent pathways that control breathing

Answer 8

Sensors:
- Chemoreceptors
- Baroreceptors
- Lung stretch receptors
- Protective reflexes

Afferent signal

Central controller:
Pons, medulla, other part of brain (brainstem)

Efferent signal

Effectors

Question 9

How do chemoreceptors monitor ventilation?

Answer 9

• Receptors that monitor O2 and CO2 levels in our blood
• If O2 is down or CO2 Is up, chemoreceptors send afferent input to the brain, resulting in increased breathing frequency and tidal volume
• Our most critical system that regulates breathing, as it can override your voluntary control
• CO2 receptors play the PRIMARY role… O2 receptors are secondary
  
  • CO2 doesn’t really get out of range because chemoreceptors will not allow it to. O2 levels can be much more dynamic in the system.

Question 10

How do baroreceptors monitor ventilation?

Answer 10

Baroreceptors are blood pressure sensors mainly founding the carotid artery and aorta, but they also affect respiratory function

In general, there is an opposite affect between Arterial BP and Respiratory minute volume:
Arterial BP down, which reduces flow:
- Sensed by the baroreceptors
- Respiratory minute volume goes up
- Increased uptake of air

Arterial BP up, which increases flow:
- sensed by the baroreceptors
- Respiratory minute volume goes down
- Decreased uptake of air

Brain uses these mechanisms to try and compensate for the change in BP while working to try and restore it to normal.

Question 11

How do Inflation/Deflation monitor respiration?

Answer 11

• As the lugs inflate or deflate, they send afferent input from stretch receptors (as there are nerves in the lungs that lead up into the brainstem)
• The brain then sends efferent output preventing them from stretching too far either way

Question 12

How do protective reflexes monitor respiration?

Answer 12

• Receptors also detect irritation
• Brain sends efferent signal that triggers sneeze or cough