Circulation, Cardiac Cycle andHeart Sounds

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The circulatory system

The circulatory system consists of two major sub-circuits, the systemic circulation and the pulmonary circulation. 2

The circulatory system

The Heart:Four chambered double pump.

Blood vessels:Carry Blood from the heart to the vital organs and back.

Arteries carry blood away from the heart and branch to form the arterioles. They all carry oxygenated blood except the pulmonary arteries.

Veins return blood to the heart and start as venules. They all carry deoxygenated blood except the pulmonary veins.

Blood capillaries are found as a network Between arteries and veins. 3

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Human and animal hearts

Which one is a human heart?

Exterior structure of the heart

• Inflow ports consisted of the superior and inferior vena cava and pulmonary veins.

• Outflow ports mainly the aorta, and pulmonary arteries.5

Structure of the heart (interior view)

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• Atria (right atrium and left atrium)

• Ventricles (right ventricle and left ventricle)

Right and left heart sides are normally completely separate.

Right atrium and left ventricles open in the corresponding ventricles by a valve.

Atrioventricular valves The atria are connected to the ventricles by atrioventricular valves.

Tricuspid valve on the right side. Bicuspid valve (mitral valve) on the lefty side

The valves are passively operated by the difference in blood pressure between the heart champers.

The papillary muscles are connected to the valves by tendons called Chordae tendinae which help to keep them in place.

There are other valves, called semilunar valves at the entrance of the aorta and the pulmonary artery. They are one way valves!.

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Blood vessels

Arteries have muscular walls and smaller lumen.

Veins have thinner walls and bigger lumen.

Blood capillaries are single layer of endothelial cells.

Arteries are high pressure vessels while veins have lower pressure and blood flow is helped by valves to go back to the heart.

Generalized look at the blood vessels

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Histology of the blood vesselsBoth arteries and veins are composed of three coats (layers), tunica externa (tunica adventitia), tunica media and tunica interna (intima).

Tunica interna consists of three parts. Elastic tissue fibers, the basement membrane and the inner endothelium.

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Tunicainterna

Elastin

Tunicamedia

Tunicaexterna

Serosa

Valve

Artery Vein

Capillary

The blood capillary is single cell thick which is endothelium.

Cardiac cycle

Cardiac cycle is a repeated pattern of contraction and relaxation. The phase of contraction is systole and relaxation is diastole.

Even before contraction of atria, the ventricles are filled with blood by up to 80%, the remaining 20% enter the ventricles after contraction of atria.

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Average heart rate (beat per minutes) is ~ 75 B/min cardiac cycle lasts about 0.8 sec.

0.5 secdiastole

0.3 secsystole

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When the ventricles fill up with blood this is called end diastolic volume (EDV).

The one third left is the end-systolic volume (ESV).

Stroke volume (SV): volume of blood ejected during one cardiac cycle.

States of heart during cardiac cycle

The ventricle contract during systole to eject two third of the amount it contains (stroke volume (SV)).

Heart and Circulation-Right Atrium = RA-Left Atrium = LA-Right Ventricle = RV-Left Ventricle = LV

1- Venous blood containing CO2 returns from body tissues to RA

2- From RA RVTricuspid valve

3- From RV LungsPulmonary artery

4- From Lungs LAPulmonary vein

6- From LV BodyAorta

5- From LA LVBicuspid valve

Pressure changes during cardiac Cycle

-Ventricles are filled with blood (e.g. 120 ml) and ventricular muscle contracts without -change in length this is called isovolumic contraction:

The pressure produced by the left ventricle during systole is about 120 mmHg and during diastole is about 80 mmHg. The blood pressureis represented by systole/diastole = 120/80.

Intraventricular pressure > Aortic

pressure Ejection

Isovolumetric contraction

No change in volume

Increase in intraventricular pressure

Ejection Volume and pressure decrease

Isovolumic relaxation

Heart Sounds- The valves between atria and ventricles are called atrio-ventricular (AV) valves -and the valves between right ventricles and pulmonary artery + left ventricle and -aorta are called semilunar valves.

- Closing of the AV valves and semilunar valves produces sounds that can be heard by stethoscope. These sounds are called heart sounds. They sound like “lub-dub”.

- First sound (“lub”) is produced by closure of AV valves. Second heat sound (“dub”) isproduced by closure of semilunar valves

dublub

The cardiac cycle

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