Lecture 6: The heart as a pump

Question 1

The heart is two pumps ‘in series’. Describe the right and left pump

Answer 1

the RIGHT pump, pumps blood to the pulmonary system = lungs

the LEFT pump, pumps blood to the systemic system = all organs

Question 2

The left and right pumps contract simultaneoulsy. When do the atria and ventricles contract?

Answer 2

• Atria contract 1st

- Ventricles contract 2nd

Question 3

Why does ventricular power differ between the right and left ventricles?

Answer 3

Left ventricle = greater power as it can pressurise itself - left ventricle pumps blood to all the body organs
right ventricle = less power - pumps blood to the pulmonary circuit - lungs - which are closer

Question 4

How is there equal blood flow t through the left and right ventricles?

Answer 4

Resistance of the systemic circuit is much greater than the pulmonary circuit and thus requires much greater pressure
—–> left ventricle has higher power and pressurisation so there is equal blood flow

Question 5

What are the phases of the cardiac cycle?

Answer 5

1. Artrial systole
2. Isovolumetric ventricular contraction
3. Ejection
4. Isovolumetric ventricular relaxation
5. Passive Ventricular filling

Question 6

What happens during the first 3 stages of the cardiac cycle?

Answer 6

1. Artrial systole
2. Isovolumetric ventricular contraction
3. Ejection
   = systole = period of heart contraction & high pressure

Question 7

What happens during stages 4 & 5 of the cardiac cycle?

Answer 7

4. Isovolumetric relaxation
5. Passive Ventricular filling
   = diastole = period of heart relaxation, ventricles passively fill & lowest pressure

Question 8

What is the blood pressure wave?

Answer 8

A wave of pressure that accelerates away from the volume of blood ejected into the aorta and it can be felt in the peripheral tissue as a ‘pulse’
- pulse wave is a pressure wave which travels along the arteries ahead of the blood

Question 9

Is the pressure high or low in the:

• systemic circuit
• pulmonary circuit

Answer 9

systemic = high pressure
pulmonary = low pressure

Question 10

What happen during cardiac contraction?

Answer 10

• increase in cytosolic Ca 2+ levels, Ca is released from SR
• Ca binds to tropin —> causing a shift in tropomyosin —> exposes actin
• Myosin binds to sites on actin —> forms a cross bridge —–> powestroke —> sarcomeres shorten —> contraction
• —> each myocyte activated each heart beat

Question 11

What happens during cardiac relaxation?

Answer 11

• ATP binds to myosin & decrease in cytosolic CA 2+ levels
• —-> cross bridges release - actin & myosin separate
• –> reduction in force - all myocytes relax each beat