The hormonal, neural and chemical regulation of responses during physical…

The idea

During exercise the cardiovascular system is adjusted by three linked control routes. Neural control uses the autonomic nervous system: sympathetic stimulation raises heart rate and stroke volume, while parasympathetic (vagal) activity slows it at rest. Hormonal control uses adrenaline and noradrenaline released from the adrenal medulla, which increase heart rate, stroke volume and the strength of ventricular contraction. Chemical control uses chemoreceptors detecting raised carbon dioxide, lowered pH and reduced oxygen, plus baroreceptors sensing blood pressure and proprioceptors sensing movement; these send impulses to the medullary cardiovascular control centre, which alters sympathetic and parasympathetic outflow. The result is increased cardiac output and redirected blood flow to active muscles.

What earns the marks

• Neural regulation: the cardiovascular control centre in the medulla alters sympathetic and parasympathetic (vagal) outflow to the sinoatrial node.
• Sympathetic stimulation increases heart rate, stroke volume and cardiac output; parasympathetic stimulation reduces heart rate at rest.
• Hormonal regulation: adrenaline and noradrenaline from the adrenal medulla increase heart rate, stroke volume and contractile force.
• Chemical regulation: chemoreceptors detect increased carbon dioxide, decreased pH and reduced oxygen, and baroreceptors detect changes in blood pressure.
• Proprioceptors detect movement and inform the control centre, so heart rate rises before and during activity.
• The combined effect is a rise in cardiac output and redistribution of blood to active muscles.

Common mistakes and how to put them right

• Thinking only nerves control the heart.

  Put it right: Hormones such as adrenaline and chemical stimuli detected by chemoreceptors also regulate the response.

• Confusing the roles of the two autonomic branches.

  Put it right: Sympathetic activity speeds the heart while parasympathetic (vagal) activity slows it.

• Believing chemoreceptors detect only oxygen.

  Put it right: They are most sensitive to rises in carbon dioxide and falls in pH, with oxygen also monitored.

• Assuming heart rate rises only after exercise starts.

  Put it right: Proprioceptor and cortical input can raise it before activity begins.

Exam tips

• Name the receptor type and the specific change it detects, rather than writing only that receptors detect exercise.
• Link each control route to a measurable effect such as heart rate, stroke volume or cardiac output.
• Use correct terminology: sinoatrial node, medulla, sympathetic, parasympathetic, adrenal medulla.
• Check that each option in a multiple-choice question matches the control route named in the stem.