Lecture 19: Gas transport and respiratory control Flashcards
What are the 2 ways in which oxygen is carried in the blood?
- Dissolved in the blood
- Bound to haemoglobin in RBC’s
How much oxygen can dissolve in a litre of blood?
3mL
Is oxygen being dissolved in the blood an efficient way to deliver oxygen around the body?
No
What is the most efficient way to transport oxygen?
Bind oxygen to haemoglobin
What does oxygen form an easily reversible combination with?
Haemoglobin
What does oxygen binding with haemoglobin give?
Oxyhemoglobin
What does oxygen binding to haemoglobin depend on?
The partial pressure of Oxygen
What does oxygen bind to in haemoglobin?
To the iron in the heme of the haemoglobin
How many oxygens can haemoglobin bind?
4 one to each heme
What is haemoglobin saturation?
Percentage of heme units containing bound oxygen at any given moment
What is the average oxygen saturation of blood entering the systemic circuit?
95%
What is the average saturation of oxygen in blood leaving peripheral tissues?
75%
What is the average saturation of oxygen in active muscle tissue?
20-25%
What is the shape of the oxygen-haemoglobin curve?
Sigmoidal
Where the oxygen-haemoglobin slope is steep what happens when there is a very small change in the partial pressure of oxygen?
A large change in the amount of oxygen bound to the haemoglobin
The oxygen haemoglobin saturation curve does what with conditions?
Varies to improve oxygen uptake / delivery
What causes the Oxygen haemoglobin curve to be moved to the right?
(3)
- Reduced pH (Bohr’s effect)
- Increased partial pressure of carbon dioxide
- Increased temperature
(usually the effects of exercise)
What causes the Oxygen haemoglobin curve to be moved to the left?
(3)
- Increased pH (Bohr’s effect)
- Decreased partial pressure of carbon dioxide
- Reduced temperature
What does exercise cause pH and temperature to do?
Causes pH to drop and temperature to rise
What 3 forms can carbon dioxide be transported in?
- Dissolved in plasma
- As bicarbonate
- Combined with proteins as carbamino compounds
How many times more soluble is carbon dioxide in plasma then oxygen?
20 times
What % of carbon dioxide is transported in plasma?
7%
What % of carbon dioxide is transported as bicarbonate?
70%
What % of carbon dioxide is transported combined with proteins as carbamino compounds?
23%
What happens when carbon dioxide reacts with water?
Carbonic acid forms
What enzyme mediates the formation of carbonic acid?
Carbonic anhydrase
As a result of carbonic acid being a very unstable molecule what does it dissociate into?
(2)
- Hydrogen ions
- Bicarbonate ions
How do hydrogen ions get to the alveoli?
They bind to haemoglobin and get transported there
What are the central controllers of the brain?
3
- Pons
- Medulla
- Other parts of the brain
What signals are sent from the brain to control breathing?
Efferent signals
What are the effectors that control breathing?
Muscles of respiration
What are the 4 sensors that control breathing?
- Chemoreceptors
- Baroreceptors
- Lung stretch receptors
- Protective reflexes
What composes the higher centres in respiratory control?
3
- Cerebral cortex
- Limbic system
- Hypothalamus
What do the higher centres do?
Control and alter the activity of the pneumotaxic centres
Where are the Apneustic and Pneumotaxic centres found?
In the pons
What do the Apneustic and Pneumotaxic centres do?
Adjust the output of the respiratory rhythmicity centres
Of the Pneumotaxic and Apneustic centre which is superior?
Pneumotaxic centre
How does the Apneustic centre adjust the output of the respiratory rhythmicity centres?
Causes the centres to speed up
How does the Pneumotaxic centre adjust the output of the respiratory rhythmicity centres?
Sends inhibitory signals causing the centres to slow down
What is the most superior centre of the respiratory rhythmicity centres?
Dorsal respiratory group (DRG)
What is the most inferior centre of the respiratory rhythmicity centres?
Pre-Botzinger complex
Where are the respiratory rhythmicity centres found?
Medulla oblongata
What is the role of the respiratory rhythmicity centre?
2
- Generate cycles of contraction and relaxation in the diaphragm, establishing the pace of respiration
- Modify activity in response to chemical and pressure signals
What does the inspiratory centre of the dorsal respiratory group (DRG) control?
(2)
- Signals to the diaphragm
- Signals to the external intercostal muscles
What does the ventral respiratory group (VRG) contain?
2
- Inspiratory centres
- Expiratory centres
What does the inspiratory centres in the ventral respiratory group control?
Sending signals to the accessory inspiratory muscles
What does the expiratory centres in the ventral respiratory group control?
Sending signals to the accessory expiratory muscles
What does the Pre-Botzinger complex do?
Acts as the pace maker of respiration
What is an increase in arterial partial pressure of carbon dioxide called?
Hypercapnia
What is a decrease in arterial partial pressure of carbon dioxide called?
Hypocapnia
What are chemoreceptors?
Carbon dioxide receptors
What is the most important receptor in determining carbon dioxide respiratory activity?
Chemoreceptors
What are the 2 types of chemoreceptor?
- Peripheral chemoreceptors
- Central chemoreceptors
Where are peripheral chemoreceptors found?
- Carotid bodies
- Aortic arch
Where are central chemoreceptors found?
Ventral side of the medulla
What do central chemoreceptors respond to?
Hydrogen ions due to changes in carbon dioxide
Baroreceptors are blood pressure receptors as well as what?
Respiratory receptors
What happens when arterial blood pressure goes down and reduces flow?
It is sensed by the baroreceptors causing the respiratory minute volume to go up increasing the uptake of air
What happens when arterial blood pressure goes up and increases flow?
It is sensed by the baroreceptors causing the respiratory minute volume to go down decreasing the uptake of air
What happens as the lungs inflate or deflate?
They send afferent input from stretch receptors
Following the brain receiving signals from stretch receptors in the lungs what happens?
The brain sends efferent output preventing them from stretching to far either way
What happens when receptors detect irritation and alert the brain?
The brain sends efferent signals that trigger a sneeze or a cough
