Contol Of Heart Rate

Question 0

Explain the hormonal response

Answer 0

• adrenaline is secreted in response to stress, shock etc
• presence of adrenaline in the blood increases heart rate
• prepares body for activity
• action of adrenaline (cyclic AMP)

Question 1

Explain how heart rate is controlled

Answer 1

• SAN –> sends a wave of excitation across the the atria which causes them to contract
• non conductive collagen fibres block transmission of wave of excitation into ventricles
• Impulse is delayed at the AVN (allows ventricles to empty)
• AVN –> sends impulse down purkyne fibres to apex of the heart
–> impulse spreads out over ventricles from the apex up, ventricles contact from the apex up

Question 2

What happens to heart rate when the body is experiencing high blood pressure?

Answer 2

• baroreceptors in the aorta and vena cava detect high blood pressure
• impulses are sent to cardiovascular centre of the medulla
• this causes an impulse to be sent along the vagus nerve
• this causes acetylcholine to be secreted which bind to receptors on the SAN
• this causes heart rate to slow down to reduce the blood pressure back to normal

Question 3

What happens to heart rate when the body is experiencing low blood pressure?

Answer 3

• baroreceptors in the aorta and vena cava detect low blood pressure
• impulses are sent to cardiovascular centre of the medulla
• this causes an impulse to be sent along the accelerator nerve
• this causes noradrenaline to be secreted which binds to receptors on the SAN
• this causes heart rate to speed up to increase the blood pressure back to normal

Question 4

What happens to heart rate when the body is experiencing high blood O2, low co2 or high pH levels?

Answer 4

• chemoreceptors in the aorta and carotid artery detect chemical changes in the blood
• impulses are sent to cardiovascular centre of the medulla
• this causes an impulse to be sent along the vagus nerve
• this causes acetylcholine to be secreted which binds to receptors on the SAN
• this causes heart rate to decrease to return O2, co2 and pH levels back to normal

Question 4

What happens to heart rate when the body is experiencing low blood O2, high co2 or low pH levels?

Answer 4

• chemoreceptors in the aorta and carotid artery detect chemical changes in the blood
• impulses are sent to cardiovascular centre of the medulla
• this causes an impulse to be sent along the accelerator nerve
• this causes noradrenaline to be secreted which binds to receptors on the SAN
• this causes heart rate to increase to return O2, co2 and pH levels back to normal