The heart, energy and exercise

Question 1

What is meant by cardiac output

Answer 1

• heart rate x stroke volume in one minute (the amount of blood pumped out in one minute)

Question 2

Explain why sprinters usually have a low percentage of slow twitch fibres

Answer 2

• sprinting requires rapid release of energy
• fast twitch fibres respire anaerobically, producing ATP by glycolysis
• slow fibres generate ATP by respiring aerobically and have more mitochondria and myoglobin

Question 3

Discuss the benefits and potential dangers of exercise of humans

Answer 3

• too much exercise suppressors immune system, reduces number of T killer cells, suppressors inflammation and production of antibodies
• immune system most effective with moderate exercise
• joint, cartilage, muscle, bursae damage, e.g. the fluid sacs which cushion the joints may swell with extra fluid, swollen sacs press on other tissues causing inflammation and pain
• effects of exercise on cardiovascular system, prevents diabetes and obesity, improves HDL to LDL ration, decreases blood pressure due to increased arteriole vasodilation

Question 4

Describe the role of SAN in controlling heartbeats

Answer 4

• initiates heartbeat
• starts wave of excitation/depolarisation
• determines heart rate

Question 5

Describe how the cardiovascular centre, in the medulla oblongata, affects the SAN

Answer 5

• increased impulses to SAN
• via sympathetic nervous system
• stimulates more frequent depolarisation in SAN
• increases heart rate and cardiac output

Question 6

Describe the effect of the ectopic beat on heart activity and suggest an explanation for this effect

Answer 6

• ectopic beat occurs when a region of the ventricle has a similar effect on the heart as the SAN
• changes in depolarisation of heart
• peak is reversed
• peak is earlier than expected
• no change in pressure pulmonary artery
• because little blood in ventricles
• longer gap before next wave
• missed contractions
• early depolarisation leaves ventricle insensitive
• wave of depolarisation is prevented

Question 7

Explain what is meant by myogenic

Answer 7

• stimulation generated from within muscle, no external stimulations
• brings about depolarisation

Question 8

Describe how the sequence of muscular contraction in the heart is coordinated and how the movement of blood through the heart is controlled

Answer 8

• SAN initiates depolarisation
• depolarisation passes through wall of atria
• causes atrial systole
• AVN conducts depolarisation to ventricles
• depolarisation passes to bundle of his and purkyne fibres
• ventricle systoles follows from apex upwards
• atrioventricular valves closes and prevent flow of blood to atria
• semilunar valves opened by pressure
• blood forced into arteries
• changed pressure in diastole closes semilunar valves

Question 9

Explain what is meant by repolarisation of a cardiac muscle cell

Answer 9

• redistribution of ions across the cell membrane

- causes change in potential difference