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Controlling Heart Rate

Applied Science: BTEC Level 3 National Extended Diploma, topic 4.5.9

Controlling Heart Rate

There are two main receptors involved in controlling heart rate: chemoreceptors and baroreceptors. When stimulated these receptors send a signal to a region in the brain called the medulla oblongata.

Chemoreceptors

Chemoreceptors

  • Sensitive to changes in CO2 concentration.
  • If CO2 concentration is high, heart rate increases.
  • Found in the aortic body, in the wall of the aorta.
  • Found in the carotid body, in the wall of the carotid artery in the neck.
Baroreceptors

Baroreceptors

  • Sensitive to changes in blood pressure.
  • If blood pressure increases, heart rate decreases.
  • Found in the walls of various arteries but particularly in the carotid sinus (in the wall of the carotid artery).
Medulla oblongata

Medulla oblongata

  • When stimulated, chemoreceptors and baroreceptors send a signal to a region in the brain called the medulla oblongata.
  • The region in the medulla which modifies heart rate is the cardiovascular centre.
  • The cardiovascular centre has two regions:
  • Cardio-inhibitory centre.
  • Cardio-acceleratory centre.
  • Nervous impulses are sent from these centres along the autonomic nervous system to the sinoatrial node (SAN).

The heart responds to pressure and chemical stimuli by increasing or decreasing the heart rate. The different responses are:

High blood pressure

High blood pressure

  • Detected by baroreceptors.
  • Impulses are sent from the medulla along parasympathetic neurones to the sinoatrial node (SAN.)
  • Acetylcholine is released (a neurotransmitter).
  • Heart rate slows down and blood pressure decreases.
Low blood pressure

Low blood pressure

  • Detected by baroreceptors.
  • Impulses are sent from the medulla along sympathetic neurones to the SAN.
  • Noradrenaline is released (a neurotransmitter).
  • Heart rate rises and blood pressure increases.
High O2/low CO2

High O2/low CO2

  • Detected by chemoreceptors.
  • Impulses are sent from the medulla along parasympathetic neurones to the SAN.
  • Acetylcholine is released (a neurotransmitter).
  • Heart rate slows down and O2 levels decrease/CO2 levels increase.
Low O2/high CO2

Low O2/high CO2

  • Detected by chemoreceptors.
  • Impulses are sent from the medulla along sympathetic neurones to the SAN.
  • Noradrenaline is released (a neurotransmitter).
  • Heart rate rises and O2 levels increase/CO2 levels decrease.

Test yourself on Controlling Heart Rate

  • Which of these are NOT the main receptors involved in controlling heart rate?

  • Which of the following statements are true for controlling heart rate?

  • In which artery walls are baroreceptors mainly found?

  • Stages in the response to high O2/lowCO2

  • What neurotransmitter is released in response to low O2 or high CO2?

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