Lecture 8 - The heart as a pump

Question 1

Design of the mammalian cardiovascular system

Answer 1

Four chambered heart - 2 atria and 2 ventricles
Blood flows in one direction - left side is in charge of pumping oxygenated blood and the right side is in charge of deoxygenated blood and pushing it back up to the lungs to put it in close proximity with a new source of oxygen
Arterial blood flows away from the heart
Venous blood flows towards the heart

Question 2

Heart in terms of pumps…

Answer 2

The heart is two pumps that lie ‘in series’

Right pump (right atrium - right ventricle) - lungs - left pump (left atrium - left ventricle) - all organs

Key feature of these two pumps is that they create two circuits that have equal flow of blood, there is equal flow between the two circuits

Question 3

Right pump and the left pump roles

Answer 3

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

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

Question 4

When do the atria and ventricles contract?

Answer 4

Atria contract first and the ventricles contract second

Question 5

Very general view of the cardiac cycle

Answer 5

Relaxation - atria contract - ventricles contract - relaxation etc etc

Atria contract - walls of the atria are both contracting which allows more blood to get pushed into the ventricles
Ventricles contract - two ventricles contract simultaneously, 2 chambers doing most of the work to get the blood around, atria contribute by contracting before the ventricles and push lots of blood and pressure into the ventricle

Right and left pumps contract simultaneously. Atria contract first and the ventricles contract second

Question 6

Valves and the controlling of blood movement

Answer 6

Blood movement through the heart is gated by valves

Tricuspid and mitral (AV) valves control the valves between the atria and the ventricles
Aortic and pulmonary valves control flow from the ventricles out to the circulatory vessels

Question 7

Valves and the pumps during a heart beat

Answer 7

Relaxation - AV valves on each side care open, allows blood to flow through and start filling up the atria and ventricle but the semilunar valves that lead out to the aorta and the pulmonary artery are closed to prevent the blood from continuing on.

Atria contract - AV valves open, when contracting the pressure and all of the blood in the atria is able to move into the ventricles, pathway for blood to move down into the ventricles, semilunar valves still closed for the same reason

Ventricles contract - atria relaxed, AV valves are closed and this is very important because as the ventricles are contracting they are creating a lot of pressure (putting the blood within them under a lot of pressure) and you don’t want the blood going back into the atria, ejection of blood coccus when the semilunar valves open

Relaxation

Question 8

Cellular mechanism of cardiac contraction

Answer 8

Actin (thin filament) and myosin (thick filament) are the most abundant proteins making up these cells.

The thin filament are the beams that fo through the muscle fibre, acts as a structural element to hold together the muscle fibre, thick filament does the work and it pulls - these working together causes the contraction

Ca2+ levels go up and more Ca2+ is released from the sarcoplasmic reticulum (released when contraction is wanted). Myosin binds to actin to form cross bridges. Myosin pulls on actin to shorten the sarcomere and generate force. Every myocyte is activated during each heart beat.

Question 9

How to increase the force of cardiac contraction?

Answer 9

Every cardiomyocyte is activated during each heartbeat

Extent of cross.-bridges formed not maximised at rest ….increase cytosolic Ca2+ level, increase number of cross bridges formed (therefore more pulling power as more myosin heads are involved), increases the force of contraction (stronger)

Question 10

Cellular mechanism of cardiac relaxation

Answer 10

Decrease in cytosolic Ca2+ levels - Ca2+ is pumped back into the sarcoplasmic reticulum. Cross bridges release when ATP binds to myosin. Reduction in force means that the heart can relax. All cardiac myocytes relax each beat.

For cardiac relaxation we need to decrease the level of Ca2+ as it is the signal to contract

Attach ATP onto myosin head so it is able to disengage and instead be ready for the next contraction - binding of ATP disengages myosin from actin

Question 11

Why does ventricular power differ between the left and right?

Answer 11

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 12

Systole

Answer 12

Contraction, rising pressure

Question 13

Diastole

Answer 13

Relaxation, falling pressure

Question 14

Main phases of the cardiac cycle - names

Answer 14

1-Cardiac cycle begins
2-Atrial systole
3-Atrial diastole
4-Ventricular systole - (first phase (isovolumetric contraction))
5- Ventricular systole - (second phase (ventricular ejection)
6- Ventricular diastole (-early)
7- Isovolumetric relaxation
8 - Ventricular diastole (-late and also known as passive filling)

Question 15

Cardiac cycle overview

Answer 15

1-Cardiac cycle begins - filled with blood and pressure ready for contraction
2-Atrial systole - contraction, packing ventricles with blood and pressure, AV valves open
3-Atrial diastole - atria are relaxing and pressure within the atria is falling and the AV valves close
4-Ventricular systole - (first phase (isovolumetric contraction)) - AV valves are closed, same volume of blood and it won’t change since there are no valves open therefore pressure builds up which it needs in order to get blood around the entire body
5- Ventricular systole - (second phase (ventricular ejection) - what will eventually happen is that the pressure in the ventricles will rise so much that it will overcome the back pressure within the aorta and pulmonary artery and this will cause the semilunar valves to burst open and we have now moved into the ejection phase, big ejection of blood into the aorta and artery, not every bit of blood is dropped out as some remains after each heart beat
6- Ventricular diastole (-early) - relaxing, dilating and filling
7- Isovolumetric relaxation - lost a lot of pressure within the ventricles so now the back pressure of the aorta and pulmonary artery starts to catch up and eventually surpasses the ventricles causes the seminar valves to close and the AV valves are still shut so there is much less blood in the ventricles and at a much lower pressure and now the ventricles relax
8 - Ventricular diastole (-late and also known as passive filling) - Veins fill the atria and the ventricles with blood that has circled all the way around and we get to fill the heart back up with blood and start this whole process over again

Question 16

What does ‘isovolumetric’ mean in the cardiac cycle? How are blood pressure and volume changing during each phase?

Answer 16

No volume change
Artrial systole, Isovolumetric ventricular contraction, ejection = systole = period of heart contraction & high pressure

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

Question 17

Which heart valves are open and which are closed during each phase of the cardiac cycle?

Answer 17

Atrial systole - AV valves open, semilunar are closed
Atrial diastole - AV valves close
Ventricular systole (isovolumetric contraction) - AV valves closed, semilunar valves are closed
Ventricular systole (ventricular ejection) - AV valves closed, semilunar valves open
Ventricular diastole - AV valves open, semilunar closed
Isometric relaxation - AV valves closed, semilunar valves closed
Ventricular diastole - AV valves open, semilunar valves closed

Question 18

Arterial pressure during the cardiac cycle

Answer 18

Arterial pressure increases during systole and decreases during diastole

Systemic - circuit that moves the blood to the rest of our organs, blood pressure that is usually measured, cyclical pressure change, higher pressure than pulmonary

Pulmonary - still has cyclical pressure change, much lower pressure throughout the cardiac cycle compared to systemic

Question 19

Hypertension

Answer 19

Systolic blood pressure is getting very high

Question 20

Hypotension

Answer 20

Both diastolic and systolic pressure are very low

Question 21

Systolic pressure in arterial network

Answer 21

Highest pressure your arteries are under during the cardiac cycle

Question 22

Diastolic pressure in arterial network

Answer 22

Lowest pressure you arteries are under during the cardiac cycle

Question 23

What is pulse pressure?

Answer 23

Pulse pressure is the difference between systolic and diastolic blood pressure. It is measured in millimeters of mercury. It represents the force that the heart generates each time it contracts.

Question 24

What is mean blood pressure?

Answer 24

Average pressure across the cardiac cycle - not halfway between diastolic and systolic because the heart spends more time in diastole than in systole, more time relaxing than it does contracting and since we are averaging the pressure over the cardiac cycle this means that the mean pressure will always (almost) be a little bit lower than the midway point (because more time at low pressure than high pressure)

Question 25

Does the heart spend more time is systole or diastole?

Answer 25

More time in diastole than in systole

Question 26

What are systemic and pulmonary pressure? Which one is typically higher?

Answer 26

Systemic blood pressure refers to the pressure exerted on blood vessels in systemic circulation

Pulmonary blood pressure is normally a lot lower than systemic blood pressure. A type of high blood pressure that affects arteries in the lungs and in the heart.

Question 27

Blood flow in a single vessel is defined as …

Answer 27

Haemodynamics

Question 28

Blood flow formula

Answer 28

Flow = pressure difference/ resistance
Q=ΔP/R

Pressure difference = pressure upstream -pressure downstream

R=ΔP/Q

Question 29

Which circuit has less resistance?

Answer 29

Pulmonary circuit has less resistance than the systemic circuit

Pulmonary circuit is very short and low resistance
Systemic circuit is very long and therefore there is much more resistance and therefore more pressure on the blood to balance out the flow