Heart and control of the heart rate

Question 1

Atria

Answer 1

• Thin walls - large amounts of elastic tissue
• Stretches when filled with blood
• Pressure increases in chamber = atrioventricular valves forced open

Question 2

Ventricles

Answer 2

• Thicker muscular walls - contract strongly to pump blood long distance
• Fill with blood = pressure increases forcing atrioventricular valves to close and semilunar valves to open

Question 3

Valves

Answer 3

• Prevent backflow of blood - one direction

Question 4

Types of valves

Answer 4

• Atrioventricular valves

- Semi-lunar valves

Question 5

Atrioventricular valves

Answer 5

• Between atria and ventricles

- Close when pressure in ventricle exceeds pressure in atria

Question 6

Semi-lunar valves

Answer 6

• In aorta and pulmonary artery (between ventricles and arteries)
• Close when pressure in arteries exceed pressure in ventricles

Question 7

Left atrioventricular valve

Answer 7

• Bicuspid valve

Question 8

Right atrioventricular valve

Answer 8

• Tricuspid valve

Question 9

Left semi-lunar valve

Answer 9

• Aortic valve

Question 10

Right semi-lunar valve

Answer 10

• Pulmonary valve

Question 11

Cardiac muscle

Answer 11

• Myogenic

- Contraction is initiated from within the muscle (NOT IMPULSE)

Question 12

SAN

Answer 12

• Sinoatrial node - wall of right atrium
• Initial stimulus for contraction of the atria - origin
• Pacemaker - basic rhythm of stimulation

Question 13

The SAN

Answer 13

• Wave of electrical activity spreads out across the atria = contract
• Atrioventricular septum (tissue between A and V) - stops the wave from crossing the ventricles
  = non-conductive
• Wave passes to AVN

Question 14

The AVN

Answer 14

• Between atria
• Stimulus from SAN - short delay - sends wave of electrical activity between ventricles along special muscle fibres
• Purkyne fibres = Bundles of his

Question 15

Bundle of His

Answer 15

• Conducts the wave - atrioventricular septum to the base of the ventricles = branches out into smaller Purkyne tissue
• Wave released = ventricles contract quickly from apex of heart upwards

Question 16

Resting heart rate

Answer 16

• 70 beats per min

Question 17

Why and when does the heart rate alter?

Answer 17

• Meet the changing demands for oxygen

- Exercise/sleep

Question 18

Medulla Oblongata

Answer 18

• Controls changes to the resting heart rate

- 2 centres

Question 19

Centres of the MO

Answer 19

• Centre that increases HR - linked to SAN by sympathetic NS (STRESS)
• Centre that decreases HR - linked to SAN by parasympathetic NS (Peaceful)

Question 20

Chemoreceptors

Answer 20

• Found in the wall of the carotid artery = carotid body

- Detect a change in the blood + regulate breathing and blood pressure

Question 21

Hypoxia

Answer 21

• Lack of O2
  = Increase in ventilation - CO2 levels are high
• Lowers blood pH

Question 22

During exercise

Answer 22

• Increased heart rate
• Increases blood flow
• CO2 is removed more quickly

Question 23

After exercise

Answer 23

• Decreased heart rate
• Decreases blood flow
• Co2 removed at normal rate

Question 24

Pressure receptors

Answer 24

• Found in the wall of carotid artery + aorta
• Always sending impulses + heart is always beating
• Change in more/less impulses sent + HR increases/decreases

Question 25

High BP

Answer 25

• Pressure receptors transmit more nerve impulses to centre in MO
  = Decrease heart rate
• Centre sends impulses via parasympathetic NS to SAN = decrease heart rate

Question 26

Low BP

Answer 26

• Pressure receptors transmit more nerve impulses to centre in MO
  = Increase HR
• Centre sends impulses via sympathetic NS to SAN = increase heart rate

Question 27

A woman takes moderate exercise. Explain what causes her heart rate to increase while she increases. (6 marks)

Answer 27

• Rate of respiration increases in muscle cells
• CO2 concentration increases = pH falls
• Chemoreceptors in aortic/carotid bodies
• Impulses to medulla centre
• Increased frequency of impulses
• Along sympathetic pathway to SAN

Question 28

Describe the route taken when electrical impulses are transmitted from the sinoatrial node to the muscles of the ventricles in a healthy heart. (2 marks)

Answer 28

• Through cardiac muscle
• To atrioventricular node
• Along bundle of His/ Purkyne fibres

Question 29

Explain how information from these ECG traces suggest that the damage caused to the diseased heart is unlikely to have affected the sinoatrial node. (2 marks)

Answer 29

• Sinoatrial node in the right atrium
• Trace from healthy person is identical to the trace for the diseased heart in the region of the atria/ only differences seen in trace for ventricles.

Question 30

A principle of homeostasis is the maintenance of a constant internal environment. An increase in the concentration of co2 would change the internal environment and blood pH. Explain the importance of maintaining a constant blood pH. (3 marks)

Answer 30

• Haemoglobin/amylase in blood is sensitive to change in pH
• Resultant change of charge/ shape
• Less oxygen binds with haemoglobin/ less transport across membrane so fewer substrate can fit active site = fewer enzyme-substrate complexes.

Question 31

The cardiac cycle is controlled by the sinoatrial node (SAN) and the atrioventricular node (AVN). Describe how. (5 marks)

Answer 31

• SAN initiates heartbeat
• SAN sends wave of electrical activity across atria causing atrial contraction
• AVN delays impulses
• Allowing atria to empty before ventricles contract
• AVN sends wave of electrical activity down Bundle of HIS
• Causing ventricles to contract from base up

Question 32

Name the blood vessels that carry blood to the heart muscle. (1 mark)

Answer 32

Coronary artery