Anatomy and Flow in the Circulatory System

What is the cardiovascular consist of?

heart, arteries/veins, blood

What is cardiovascular system cycle?

The right ventricle ejects the de-oxygenated blood via the pulmonary artery into the lung where the blood receives oxygen and is returned to the left atrium.

The blood then moves to the left ventricle and ejected into the ascending aorta.

The blood then travels to the lower body organs and upper body organs.

At the end of the arterial system at the organ-tissue level, the exchange of oxygen takes place.

The blood then begins its travel back to the right side of the heart carrying the de-oxygenated blood via the venous system and pooled in the upper and lower vena cava.

The blood then goes to the right atrium and from there to the right ventricle, where the blood cycle starts again.

What is the heart made up of?

The heart is a complex pump with 4 chambers, 2 of which are pumping (ventricles) and 2 are for pooling (atriums)

What is the heart wall composed of?

Myocardial tissue which is made up of layers of woven fibres arranged in orientation that rotates with a gradual angle

Why is the heart wall arranged in a certain orientation?

• Withstand tension along its length (long axis direction)

• Withstand the twisting force

• Withstand the pressure in the ventricular cavity

What do heart valves prevent?

Heart valves prevent backflow (leakage) of blood either to the heart or between heart chambers

What happens on the left side of the heart?

The aortic valve: prevents blood returning to the left ventricle from the aorta

Bicuspid valve: prevents blood returning to the left atrium from the left ventricle

What happens on the right side of the heart?

Pulmonary valve: prevents blood returning to the right ventricle from the aorta

Tricuspid valve: prevents blood returning to the right atrium from the right ventricle

What are the atrioventricular valves?

Valves between the atria and ventricles

These valves have leaf-like cusps that attached to the papillary muscles chordae (tendons)

Tricusps on the right side and bicusps on the left side

Heart Conduction System (the heart electric system)

It is the system by which the heart generates its electrical signals to initiate contraction (and hence ejection/pumping blood)

What are the main elements of the heart conduction system

Sinoatrial node, AV node, AV bundle, Purkinje fibers

Sinoatrial node

Mass of autorhythmic cell that sits in the right atrial wall and generates impulses about 100 times per minute; sets pace for the entire heart. The SA node is considered the natural pacemaker of the heart

AV node

Mass of autorhythmic cells located in the inferior portion of the interatrial septum about the tricuspid valve (AV=atrioventricular): here, each impulse is delayed briefly, allowing atria to contract before ventricles

AV bundle

Autorhythmic cells located in the interventricular septum; the only electrical connection between atria and ventricles (AV=atrioventricular); also known as bundle of His. This branches into right and left to deliver the signal to the right and left ventricles.

Purkinje fibers

run through the interventricular septum, penetrate the heart apex, then turn upwards through the ventricular myocardium triggering ventricular contraction and pushes blood through the semilunar valves

What are the 5 main peaks in an ECG

The electrical signal generated by the SA node can be recorded on the skin; commonly known as the ECG

P wave: signals onset of atrial contraction

QRS complex: signals onset of ventricular contraction. Repolarization of atria simultaneously

T wave: repolarization of atria simultaneously

T wave: repolarization of ventricles; precedes ventricular relaxation

PQ interval: atria contract and begin to relax, ventricles begin to contract

QT interval: ventricles contract and begin to relax

ECG

electrocardiogram

What is the coronary circulation

a highly-complex branching system with hundreds/thousands of small scale arteries

What is the main function of the coronary circulation

To provide flow delivering oxygenated blood and nutrients to the myocardium (the heart muscle) and remove carbon dioxide and waste from the myocardium.

What is stenosis

Blockage of any of these arterial segments prevents blood to reach the downstream myocardial muscle. Prolonged periods without enough blood causes the so-called heart attack

Stroke Volume

Volume of blood ejected by the left/right ventricle into the aorta/pulmonary artery per beat

Heart Rate

The number of times the heart contracts and ejects blood into the aorta/pulmonary artery per minute

Cardiac Output

The volume of blood ejected from the left/right ventricle into the aorta/pulmonary artery per minute

How to calculate the cardiac output

CO=HR*SV

How to convert from mmHg to Pa

1mmHg=133.33Pa

What are the normal values of mmHg values for LV and RV

LV: 5mmHg-120mmHg

RV: 5mmHg-40mmHg

What is the arterial system

Highly complex branching system made of flexible vessels

What is the artery composed of

3 layers: intima, media and adventitia

Intima

Innermost layer, a few microns thick, composed of endothelial cells and their basal lamina. The endothelial cells act as a barrier between the blood and the wall

Media

Middle layer, composed of muscle cells, elastin, collagen, and proteoglycans. Determines the elastic properties of the wall

Adventitia

Outer layer, composed of connective tissue containing collagen, nerves, fibroblasts and elastic fibres. In large arteries this also contains the vasa vasorum- a network of vessels providing nutrition to the outer regions of the artery. Provides a protective layer to assist with withstanding the pressure in the arteries. In large arteries this also contains the vasa vasorum, which is a network of vessels providing nutrition to the outer regions of the artery wall.

What happens to arteries when they move from the heart

The arteries taper (reduce in diameter) as they move away from the heart, with a range from 2.5cm in the ascending aorta to 8𝜇m in the capillaries

Mean arterial pressure (MAP)

highly valued clinical parameters as it provides an estimate of the maintained/sustained average load seen by the left ventricle and other bodily organs

Diastolic pressure

known as the afterload and it is indeed what the left ventricles ‘sees/experiences’ at the onset of systole, when the aortic valve opens

MAP equation

MAP=Pd + (1/3) (PP)

PP equation

PP=Ps-Pd

What are normal values of Ps and Pd in healthy adults

120mmHg and 80mmHg

Hypertensive

If Ps and Pd are >=90 and 130 mmHg

Hypotensive

Ps and Pd <90 and 60 mmHg