4. When the heart contracts, blood then goes up the left ventricle and through the aortic valves. Left ventricle is our most muscular chamber of the heart because it is in charge of pushing blood around the body.

5. This aspect of the aortic raps behind the pulmonary artery. This is called the ascending aorta.

6. The curve here is called the aortic arch, goes right down and supplies the lower half of the body.

7. These 3 vessels supply the head and neck.

Blood coming back to the heart:

1. Comes back via two major veins. These are the superior vena cava and inferior vena cava. The superior vena cava brings blood back from the upper body. The inferior vena cava brings blood back from the lower body.

2. This blood pulls into the right atrium

3. Then passes through the Tricuspid valve and into the right ventricle.

4. When the right ventricle pumps, it pumps blood out the pulmonary valve into the main pulmonary artery. Which then subdivides into left and right pulmonary artery.

The Ventricular Septum: is a muscular lining that separates the left and right ventricles.

Atrial Septum: is a thin lining that separates the left and right atrium.

How does blood move through valves?

· Blood moves through valves because of pressure changes within the heart.

· Focusing on the left heart, the systemic circulation side. The pressure of the blood building in the left atrium forces the mitral valves open which allows blood into left ventricle. (One example)

· Same process on the right heart, just that pressures are much lower.

· Blood can only move from areas of high pressure to areas of low pressure.

· Blood only moves down a pressure gradient.

· Valves won’t open until pressure is higher, once pressure is then higher it will shut.

· Contraction causes the pressure to rise inside the chamber.

- Any contraction within the heart forces the chambers to squeeze. When you squeeze that rises the pressure. When we contract, we are pushing down to get the pressure up to force valves open. This pushes blood flow around.

Two phases of cardiac cycle:

· Diastole – heart is relaxing.

- Left and right ventricle start to fill with blood.

- Once their done filling the blood left in the left and right ventricle is called end diastolic volume (EDV).

· Systole – heart is contacting.

- When your heart contracts not all the blood leaves the heart.

- This means there is a small amount of blood left in the left and right ventricle, this is called end systolic volume (ESV)

· Stroke volume – the amount of blood that is ejected from the heart each beat.

- SV = EDV – ESV

Cardiac Structure:

- 3 primary layers of heart:

· Endocardium –

- Most inner lining of the heart.

- direct contact with the blood.

- Layer of endothelium cells

· Myocardium –

- Muscle lining of the heart

- Made up of specialized cells called cardiomyocytes.

- Thickest layer of the heart wall

- It generates contraction and relaxation.

- Heart is a muscle because the myocardium lining.

- Plays a key role in conduction.

· Epicardium –

- Outer layer of heart

- Are mesothelium cells

- Primarily for protection of organs

Myocardial construction

- The myocardium is multi-directional.

- Heart beats in 3 ways at same time.

1. Beats inwards – radial shortening.

2. Beats down on itself – longitudinal shortening.

3. Twisting – circumferential shortening.

Cardiac blood supply

- The heart has a blood supply.

- Hearts blood supply comes from the coronary arteries.

- We have two main coronary arteries: right coronary and left main coronary.

- The left main coronary divides into two different arteries: circumflex and left anterior descending.

Cardiac Contraction:

Cardiac conduction system is a collection of specialised cells that can generate and carry electrical charge.

· Action Potential = change in electrical voltage

· Depolarize – when the voltage becomes more positive.

- Depolarize – cardiomyocyte contraction.

· Repolarize – when the voltage becomes more negative.

- Repolarize – cardiomyocyte relaxation.

How and where the cardiac conduction system starts:

· Depolarization (contraction) at the sinoatrial node (SA), this is in the upper right atrium.

· As we get a depolarization in the SA node, this cause depolarization of all the tissue around it.

· Whilst this is happening, the electrical charge from the depolarization of the SA node is taken to the left atrium through the Bachmann’s Bundle, which is a specialist highway of cells. This cause both atria and the surrounding tissue to contract.

· When our atria contract, this causes the pressure inside the atria to rise and force blood out of atria into ventricles.

· The electrical charge then transmits to the atrioventricular (AV) node.

· As the electrical charge arrives at AV node its job is to wait. AV node job is to deliberately delay.

· Delays for about a hundredth of a second

· AV node deliberately waits for one reason because the AV node doesn’t want the electrical charge to go further down the heart until the atria are finished contracting. This allows as much blood as possible to go into the ventricles.

· Once it has waited roughly a hundredth of a second, it allows the electrical charge to continue through the conduction pathway.

· The bundle of his carries the electrical charge towards the ventricles

· Once it gets to the ventricles it bifurcates (divides into 2)

· Right bundle branch: associated with right ventricle.

· Left bundle branch: associated with left ventricle.

Left bundle branch:

- has a number of branches that come off it.

- It has an anterior branch that wraps around the front of the heart.

- It has a posterior branch that wraps around the back of the heart.

At the end of the left and right branches we have Purkinje Fibres. The Purkinje Fibres get everywhere within the myocardium to ensure that the electrical charge is delivered to all aspects of the myocardium.

Electrocardiogram -

· P-wave:

- tells us that the SA node is depolarising.

- When you can see a P-wave we know that the persons SA node cam depolarizes and therefore the atria’s do contract

- So that’s how we can tell electrical activity in the heart is normal.

· QRS:

- The ventricles contracting.

- Contraction is so much higher compared to P-wave because ventricles are full of muscle.

How does cardio conduction happen?

Cardiomyocytes – have the ability of automatic impulse generate (action potential)

- Ability to generate a pulse with no input from nervous system.

- Any part of the heart can beat on its own.

- Cardio contraction starts at the SA node because it has a regular rhythm of 60-100bpm, making it the fastest generation ability. Therefore, it makes it the pacemaker of the heart.

- If the SA node stopped working, you wouldn’t necessarily die, another part of the heart would take over as the pacemaker, but your heart rate would be very low.

- But because the SA node has the fastest generation ability of any of the tissues within the heart, that makes the SA node the pacemaker of the heart.

Note