Regulation Gas Concentrations

Question 1

What causes breathing?

Answer 1

The muscles that cause air to move in and out of the lungs are the diaphragm (stimulated by the phrenic nerve) and the intercostal muscles (stimulated by the intercostal nerve)

Question 2

How are nerve impulses to the diaphragm and intercostal muscles controlled?

Answer 2

• Nerve impulses that travel to the Diaphragm and Intercostal muscles are controlled by a respiratory centre located in the Medulla Oblongata in the brain
• Respiratory centre has two regions: expiration (breathing out) and inspiration (breathing in)
• Messages move between these regions and they control breathing
• O2 and CO2 levels in blood regulate breathing rate

Question 3

How does the concentration of carbon dioxide in the blood plasma affect the concentration of hydrogen ions?

Answer 3

• In the blood carbon dioxide joins with water and forms carbonic acid, this carbonic acid then dissociates into hydrogen ions and bicarbonate ions
• Bicarbonate ions then bind to hydrogen ions to form carbonic acid to then produce water and carbon dioxide to be removed by lungs (breathed out)
• High carbon dioxide levels = high hydrogen ions, thus making plasma acidic detecting change by chemoreceptors

Question 4

What receptors detect a change in gas concentrations in the blood plasma?

Answer 4

Chemoreceptors detect changes in blood plasma:

• Peripheral Chemoreceptors (Aortic and Carotid Bodies)
• Central Chemoreceptors (Medulla Oblongata)

Question 5

How does the concentration of oxygen affect breathing rate?

Answer 5

As Oxygen is consumed by the cells, its concentration in the blood begins to fall. If Oxygen concentration falls below normal there is an increase in breathing rate however oxygen concentration needs to fall significantly to result in an increase in breathing rate, thus playing a minor role in regulating breathing rate

Question 6

How does the concentration of Carbon Dioxide affect breathing rate?

Answer 6

The concentration of carbon dioxide in the blood plasma is a major factor in the regulation of breathing rate. A relatively small increase in the concentration of carbon dioxide is enough to cause a marked increase in the rate of breathing. Any increase in carbon dioxide results in an associated increase in hydrogen ion (H+) concentration which is most sensitive to chemoreceptors. If carbon dioxide is high breathing rate and depth increases to remove the CO2 from the blood.

Question 7

How does the concentration of Hydrogen Ion affect breathing rate?

Answer 7

• As hydrogen ion concretion of the blood increases, the pH decreases causing an increase in the breathing rate
• A decrease in pH directly stimulates chemoreceptors in the aortic and carotid bodies which then transmits to the respiratory centre, resulting in an increase in the breathing rate

Question 8

How can we voluntary control breathing?

Answer 8

• Voluntary Control of breathing comes from the connection in the cerebral cortex to descending tracts in spiral cord (bypasses respiratory centre)
• Is a protective device as it enables us to prevent irritating, toxic gases and water from entering the lungs