U3 Homeostasis: Regulation of gas concentrations Flashcards
Cellular respiration
- Oxygen + glucose → carbon dioxide + water + energy
- Occurs in cells to provide energy for sits functions
- Uses oxygen and produces carbon dioxide so cells need:
- continuous supply of oxygen
- consintous removal of carbon dioxide
What does the respiratory system do?
- Takes oxygen into body
- Secretes carbon dioxide from body
- Lungs are the organs where the exchange of carbon dioxide for oxygen occurs
- Changes in breathing change:
- amount of oxygen taken in
- amount of carbon dioxide excrted
What does the circulatory system do?
- Carry oxygen from the lungs to be used by cells
- Cary carbon dioxide produced by cells to the lungs for exccretion from the body
How is breathing controlled?
Skeletal muscles that move air in and out of the lungs and require stimulate from nerve impulses to initiate contraction
These nerve impulses are controlled by the respiratory centre in the medulla oblongata of the brain
Diaphragm:
- stimulated by impulses from phrenic nerve
Intercostal muscles:
- stimulated by impulses from intercostal muscles
Chemicals that affect breathing
- The concentrations of oxygen and carbon dioxide carried in the blood affect the breathing rate and depth
- The concentration of carbon dioxide in the blood plasma affects the concentration of hydrogen ions
- When CO2 dissolves in water, it forms carbonic acids which breaks down to form hydrogen ions
Chemoreceptors and breathing
When chemoreceptors are stimulated, they send a nerve impulse to the area of the respiratory centre that regulates breathing
Central chemocreptros
- Located in medulla oblongata
- Sensitive to changes in changes in concentration of CO2 in blood and hydrogen ions in cerebrospinal fluid
Peripheral chemicerecptors
- Groups of cells (called aortic and carotid bodies) in the walls of the aorta and carotid arteries
- sensitive to change sin concentration of O2, CO2 and hydrogen ions in blood plasma
Oxygen concentration
- O2 concentration in the blood falls as it is consumed by cells
- if the concentration of O2 falls below normal and other factors remain constant, the breathing rate increases
- when the blood oxygen concentration is within the normal range, there’s only a slight effect on breathing
- so under normal circumstances, O2 doesn’t have much effect in the regulation of breathing
What happens if blood oxygen concentration falls to very low levels?
- Peripheral chemoreceptors are stimulated →
- Nerve impulses are transmitted to the respiratory centre →
- Nerve impulses stimulate transmission of messages to diaphragm and intercostal muscles →
- Breathing rate and depth↑
Carbon dioxide concentration
- a relatively small increase in the concentration of CO2 is enough to cause a noticeable increase in breathing rate and depth
- chemoreceptors in the medulla oblongata are the most sensitive to changes in concentration of CO2 in the plasma
What happens when the concentration of carbon dioxide in the blood increases
- Concentration of CO2 in blood↑ →
- Concentration of hydrogen ions in blood ↑→
- Central & peripheral chemoreceptors stimulated →
-The chemoreceptors transmit nerve impulses to the respiratory centre →
- Breathing rate and depth↑
What happens when the concentration of hydrogen ions in the blood increases?
- Hydrogen ion concentration in blood↑ →
- pH↓ →
- Chemoreceptors in aortic and carotid bodies stimulated →
- Impulses transmitted to the respiratory centre →
-Breathing rate and depth ↑
Voluntary control of breathing
- Humans are able to voluntarily control their rate and depth of breathing
- This voluntary control comes via connections from the cerebral cortex to descending tracts in the spinal cord
- Voluntary control therefore bypasses the respiratory centre in the medulla oblongata
- This is a protective device as it enables it to prevent irritating gases and water from entering the lungs
Holding our breath
- It’s possible for humans to stop breathing for a limited period
- The buildup of carbon dioxide in the plasma stimulates the inspiratory centre to send impulses to the inspiratory muscles, eventually forcing a breath to be taken whether it is wanted or not
Hyperventilation
- Hyperventilation: extremely rapid, deep breathing which can provide more oxygen than required and remove more carbon dioxide than necessary
- Can occur voluntarily or be stimulated by physical stress (severe pain or emotional stress)
- Ysually corrects itself as the reduction in carbon dioxide concentration means the chemoreceptors are not stimulated, reducing the rate and depth of breathing until carbon dioxide levels return to normal
Why is hyperventilating before swimming under water dangerous?
- It allows a person to stay under water longer due to a loss of carbon dioxide
- The breath holding ability may be increased to the extent that the individual loses consciousness from lack of oxygen to the brain before feeling the urge to breath
