Controlling Heart Rate (chapter 6 of hormonal communication)

Question 1

How many times does the human heart beat at rest (approximately)?

Answer 1

70 bpm

Question 2

What area of the brain is responsible for controlling heart rate and making any necessary changes?

Answer 2

• Medulla oblongata - has two centres which are linked to the SAN in the heart via motor neurones
• One centre increases heart rate - impulses, transmitted by the accelorator nerve, are sent through the sympathetic nervous system
• The other centre decrease heart rate - impulses, transmitted by the vagus nerve, are sent through the parasympathetic nervous system
• which centre is stimulated depends on the information received by receptors in the blood vessels

Question 3

Baroreceptors (pressure receptors)

Answer 3

• Detect changes in blood pressure - e.g. if blood pressure is low, the heart rate needs to increase to prevent fainting
• Present in the aorta, vena cava, and carotid arteries

Question 4

Chemoreceptors (chemical receptors)

Answer 4

• Detect changes in the levels of particular chemicals in the blood, i.e. carbon dioxide - sensitive to changes in the pH level of the blood (increased carbon dioxide levels in the blood means decreased pH levels in the blood due to the formation of carbonic acid (reaction of carbon dioxide and water in the blood))
• Located in the aorta, carotid artery, and the medulla

Question 5

If blood pressure is too high

Answer 5

1. Impulses are sent to the medulla oblongata centre which decreases heart rate
2. The medulla oblongata will send impulses along the parasympathetic neurones to the SAN
3. Heart rate decreases
4. Blood pressure decreases

Question 6

If blood pressure is too low

Answer 6

1. Impulses are sent to the medulla oblongata centre which increases heart rate
2. The medulla oblongata sends impulses along sympathetic neurones to the SAN
3. Heart rate increases
4. Blood pressure increases

Question 7

If a decrease in pH is detected

Answer 7

1. A response is triggered to increase heart rate
2. Blood will flow more quickly to the lungs
3. Carbon dioxide is exhaled
4. pH levels in the blood increase

Question 8

If an increase in pH is detected

Answer 8

1. Frequency of the nerve impulses being sent to the medulla oblongata reduced
2. Frequency of impulses being sent to SAN via sympathetic nervous system reduced
3. Heart rate reduced
4. pH levels in blood reduced

Question 9

Which hormones are able to affect the pacemaker region of the heart?

Answer 9

Adrenaline, noradrenaline - these speed up heart rate which increases the frequency of impulses produced by the SAN