Regulation of Breathing

Question 1

Control of Ventilation

Answer 1

• rhythmic contractions of the diaphragm and intercostal muscles control the ventilation of the lungs
• breathing is controlled by the ventilation centre in the medulla oblongata:
  1. inspiratory region controls inspiration (breathing in)
  2. expiratory region controls expiration (breathing out)
• messages are passed from respiratory centre via motor neuron in spinal nerves to the:
  1. intercostal muscles by the intercostal nerves
  2. diaphragm by the phrenic nerve

Question 2

Breathing rate is effected by

Answer 2

1. Blood concentration of:

- oxygen

- carbon dioxide

- hydrogen ions

2. Stretch receptors in the lungs
   - there transmits messages to the respiratory centre via the vagus nerve

Question 3

Transport of CO2 in the blood

Answer 3

• once carbon dioxide enters the blood in can be carried in 3 ways:
  1. Dissolve in plasma
  2. Attach to haemoglobin to form carbaminohaemoglobin
  3. React with water in the plasma to form hydrogen and bicarbonate ions:
• an increase in CO2 means an increase in hydrogen ions which makes blood plasma more acid (low pH)

- changes to CO2 in blood plasma are a major factor in regulating breathing rate. More than O2.

Question 4

Receptors for detecting changes

Answer 4

- chemoreceptors detect the change in the concentration of hydrogen ions, carbon dioxide and oxygen in the blood

• Chemoreceptors are located in two locations:
  1. Peripheral chemoreceptors in the aortic and carotid bodies detect H+ ions and O2
  2. Central chemoreceptors in the medulla oblongata detect CO2

Question 5

Chemoreceptors

Answer 5

• chemoreceptors detect a change in concentration levels and send a message to the respiratory centre in the medulla oblongata via sensory neurons
• respiratory centre will initiate a change in the rate of contraction of the intercostal muscles (via the intercostal nerves) and the diaphragm (via the phrenic nerve). Both intercostal muscles and diaphragm are skeletal muscles.
• the diaphragm and intercostal muscles contract at a fast rate
• breathing rate increases as a result
• all three contrations (CO2, O2, H+) work simultaneously to control breathing rate

Question 6

Receptors and Response - Oxygen

Answer 6

• Chemoreceptors located in aorta and carotid artery called aortic and carotid body

- detect decrease in oxygen

• has only a slight effect on increasing breathing rate

Question 7

Receptors and Response - Carbon Dioxide

Answer 7

- Chemoreceptors in medulla oblongata (most sensitive in carbon dioxide)

• detect increase in carbon dioxide

- noticable increase in breathing rate (70 - 80% responsible)

- Slow response (a few minutes)

Question 8

Receptors and Response - Hydrogen Ions

Answer 8

• Chemoreceptors located in aorta and carotid artery called aortic and carotid body

- Detect inrease in H+ ions (low pH)

- Increase breathing rate (20% responsible)

• Fast/Immediate Response

Question 9

Stretch Receptors

Answer 9

• these receptors are found in the bronchioles to monitor lung inflation. They prevent the lungs from over-inflating.
• As the lungs inflate, impulses are sent by the vagus nerve to the inspiratory region of the respiratory centre
• This inhibits inspiration of air into lungs
• Expiration then begins

Question 10

Control of Breathing

Answer 10

• breathing rate and depth can be under voluntary control as we regulate our breathing for speaking, singing etc.
• We can control breathing as there are connections between the cerebral cortex and the descending tract of the spinal cord
• voluntary control bypasses the respiratory centre
• protective device

Question 11

Hyperventilation

Answer 11

• is when rapid, deep breathing occurs
• often triggered by stress but can be voluntarily triggered
• it is dangerous as lungs inhale more oxygen and exhale more carbon dioxide than necessary
• results in the urge to stop breathing as the chemoreceptors are not stimulated
• in situations such as swimming it can result in becoming unconscious due to a lack of oxygen before the urge to take a breath occurs. This is due to the chemoreceptors not being stimulated due to the artifically low carbon dioxide levels in the blood, can result in an individual drowning

Question 12

Exercise and Breathing Rate

Answer 12

• depth and rate of breathing increases to supply cells with increased need for oxygen and carbon dioxide removal
• increase determined by levels of carbon dioxide, oxygen and hydrogen ions in plasma