Exercise and control of heart rate 7.9

Question 1

What two things happen when you exercise?

Answer 1

• Increased breathing rate and depth to get more oxygen and get rid of CO2
• Increased heart rate to deliver oxygen to muscles faster and to remove extra CO2

Question 2

What part of the brain controls breathing rate + what areas does it contain?

Answer 2

The medulla oblongata contains two ventilation centres: inspiratory centre and expiratory centre

Question 3

Describe how the rate of breathing is controlled:

Answer 3

• Sends nerve impulses to intercostal muscles and diaphragm = contraction which increases the volume of the lungs which lowers pressure
• Nerve impulses sent to expiratory centre which inhibit action
• Air enters the lungs due to pressure differences between outside and inside
• Lungs inflate causing stretch receptors to become stimulated = nerve impulse back to MO which inhibit action of inspiratory centre
• Expiratory centre no longer inhibited do nerve impulses sent to diaphragm and lungs to relax = lungs deflate = stretch receptors no longer active and process repeated

Question 4

How does exercise trigger an increase in breathing rate? Describe the steps:

Answer 4

It decreases blood pH

• Level of CO2 in blood increases = decrease of pH
• Chemoreceptors detect a decrease in blood pH and send nerve impulses to MO which sends more frequent nerve impulses to intercostal muscles and diaphragm = increase rate and depth of breathing
• Gaseous exchange speeds up and pH and breathing rate returned to normal

Question 5

What are chemoreceptors?

Answer 5

Monitor oxygen, CO2 and pH levels in the blood found in the aortic bodies, carotid bodies and MO

Question 6

Define ventilation rate:

Answer 6

The volume of air breathed in or out in a period of time

Question 7

What part of the brain controls heart rate?

Answer 7

Controlled by the cardiovascular control centre in the medulla oblongata

Question 8

What does the cardiovascular centre control the rate of?

Answer 8

The rate at which the sino-atrial node fires

Question 9

What does the SAN do?

Answer 9

Generates electrical impulses that cause the atria to contract which sets the rhythm of the heartbeat

Question 10

What are baroreceptors?

Answer 10

Receptors that detect pressure found in the aortic and carotid bodies

Question 11

What are the two types of neurones that the cardiovascular centre can send impulses along to the SAN?

Answer 11

Sympathetic and parasympathetic

Question 12

Describe the sympathetic nervous system:

Answer 12

Helps increase heart rate during exercise – fight or flight

Question 13

Describe the parasympathetic nervous system:

Answer 13

Helps decrease heart rate after exercise – rest and digest

Question 14

How does the heart respond to high blood pressure?

Answer 14

• Baroreceptors detect high blood pressure
• Impulses sent to cardiovascular centre = send impulse along parasympathetic neurones that secrete acetylcholine which bind to receptors on the SAN
• SAN fires impulses less frequently = heart rate slows = reduces blood pressure

Question 15

How does the heart respond to low blood pressure?

Answer 15

• Baroreceptors detect low blood pressure
• Impulses sent to cardiovascular centre = send impulse along sympathetic neurones that secrete noradrenaline which bind to receptors on the SAN
• SAN fires impulses more frequently = heart rate increases = increases blood pressure

Question 16

How does the heart respond to high blood O2/low CO2/high pH levels?

Answer 16

• Chemoreceptors detect chemical changes
• Impulses sent to cardiovascular centre = send impulse along parasympathetic neurones that secrete acetylcholine which bind to receptors on the SAN
• SAN fires impulses less frequently = decrease heart rate = levels returned to normal

Question 17

How does the heart respond to low blood O2/high CO2/low pH levels?

Answer 17

• Chemoreceptors detect chemical changes
• Impulses sent to cardiovascular centre = send impulse along sympathetic neurones that secrete noradrenaline which bind to receptors on SAN
• SAN fires impulses more frequently = increase heart rate = levels returned to normal

Question 18

Define cardiac output:

Answer 18

Total volume of blood pumped by a ventricle every minute

Question 19

Equation for cardiac output:

Answer 19

Cardiac output (cm3 min-1) = heart rate (bmp) x stroke volume (cm3)

Question 20

Define stroke volume:

Answer 20

The volume of blood pumped by one ventricle each time it contracts

Question 21

What happens to cardiac output during exercise?

Answer 21

It increases as heart rate and stroke volume increase