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Chapter IV

Blood Circulation Edited by Liu Sufang

Electrical activity Cardiovascular System

Heart— Contracti Dynamic on open and closure Valves organ arteries Vessels vein s

—Blood pathway

Recall anatomy The normal human heart is a strong, muscular pump a little larger than a fist.Each day an average heart “beats” (expands and contracts) 100,000 times and pumps about 2,000 gallons of blood. In a 70-year lifetime, an average human heart beats more than 2.5 billion times.

Heart pump

Pulmonary circulation (smaller circulation) circulation

Systemic circulation (greater circulation)

Chapter Overview The heart as a pump Electrophysiology of the heart Physiology of vessels Regulation of cardiovascular activity

circulation

Section I The heart as a pump 1.The cardiac cycle 2.Cardiac muscle contractility 3.Cardiac output

1. The cardiac cycle

1) Definition of cardiac cycle 2) Pumping function of heart 3) Heart sounds

1) Definition of cardiac cycle The cardiac events that occur from the beginning of one heartbeat to the beginning of the next are called the cardiac cycle.

Heart rate is the number of heart beats per minute. The average rate of the heartbeat in normal adults is 75 beats/minute.

0.1s

0.7s

Atria systole

Atria diastole 0.3s

ventricle diastole

ventricle systole

0.5s

ventricle diastole

In a cardiac cycle, atria systole accounts for 0.1s , and its diastole is 0.7s. When the atria begins diastole, ventricle begins to systole, which accounts for 0.3s. And the ventricle diastole is 0.5s. In general, a cardiac cycle is about 0.8s. Within a cycle, there are 0.4 s for both atrium and ventricle relaxation.

summary Cardiac cycle includes systole and diastole. Atria contracts ahead of the ventricle. Diastole is longer than systole.

2) Pumping function of heart  How blood flowed uni-directionally out from ventricles and returned to atrium ?  What happened with the valves open and closure?  How blood return to the heart after one trip in vessels system?

Heart Valves The heart has four chambers. The upper two are the right and left atria. The lower two are the right and left ventricles. Blood is pumped through the chambers, aided by four heart valves. The valves open and close to let the blood flow in only one direction.

What are the four heart valves?

•The tricuspid valve is between

the right atrium and right ventricle.

•The pulmonary valve is between the right ventricle and the pulmonary artery.

•The mitral valve is between the left atrium and left ventricle.

•The aortic valve is between the left ventricle and the aorta.

**Each valve has a set of flaps (also called leaflets or cusps). When working properly, the heart valves open and close fully.

Events of heart cardiac cycle The cardiac cycle consists of a period of relaxation called diastole, during which the heart fills with blood, followed by a period of contraction called systole. Isovolume contraction

systole

Rapid ejection Reduced ejection

diastol e

Isovolume relaxation Rapid filling Reduced filling

Pumping of heart

Prior to atrial systole, blood has been flowing passively from the atrium into the ventricle through the open A － V valve. During atrial systole the atrium contracts and tops off the volume in the ventricle with only a small amount of blood. Atrial contraction is complete before the ventricle begins to contract.

Atrial contraction

Characters of Atrial systole  Atrial contract  Final phase of ventricular filling  Pressuer: Aorta>Atrium>Ventricles  Atrialventricular valves open  Semilunar closed

Example: Left ventricle contraction and relaxation a. Isovolume contraction

systole

b. Rapid ejection c. Reduced ejection

diastole

a. Isovolume relaxation b. Rapid filling c. Reduced filling

 systole

a.Isovolumetric contraction (The beginning of systole) The atrioventricular (AV) valves close at the beginning of this phase. Mechanically, ventricular systole is defined as the interval between the closing of the AV valves and the opening of the aortic valves.

Pressures & Volume The AV valves close when the artery pressure

Ventricular pressure volume

pressure in the ventricles (red) exceeds the pressure in the atria (yellow). As the ventricles contract isovolumetrically -- their volume does not change (white) -- the pressure inside increases, approaching the pressure in the aorta arteries (green).

characters of Isovolumetric

ventricular contraction

 Ventricles contract  A-V closed  Semilunar closed  ventricular pressure rises rapidly without a change in ventricular volume  Pressure: Aorta>Ventricles

b. Rapid ejection

The semilunar (aortic) valves open at the beginning of this phase.

Pressures & Volume: While the ventricles continue artery pressure

contracting, the pressure in the ventricles (red) exceeds the pressure in the aorta

Ventricular pressure

(green); the semilunar valves open, blood exits the ventricles, and the volume in

volume

the ventricles decreases rapidly (white). As more blood enters the arteries, pressure there builds until the flow of blood reaches a peak.

Characters of Rapid ventricular Ejection  Ventricles contract  Pressure in ventricles reach peak  Ventricular eject blood into arteries  Aorta pressure reaches peak  Pressure: Ventricle >Aorta

Aortic Valves Open A-V closed

c.Reduced ejection The end of systole At the end of this phase the aortic valves close.

Pressures & Volume:

artery pressure

Ventricular pressure volume

After the peak in ventricular and arterial pressures (red and green), blood flow out of the ventricles decreases and ventricular volume decreases more slowly (white). When the pressure in the ventricles falls below the pressure in the arteries, blood in the arteries begins to flow back toward the ventricles and causes the semilunar valves to close. This marks the end of ventricular systole

Characters of Reduced ventricular ejection  Ventricles eject blood into arteries (slower rate)  Aorta pressure starts to fall as blood runs off into arteries  Pressure: V>A  Aortic Valves Open  AV Valves Remain Closed

 diastole

a. Isovolumetric relaxation The beginning of diastole At the beginning of this phase the AV valves are closed.

Pressures & Volume:

artery pressure Ventricular pressure

volume

The pressure in the ventricles (red) continues to drop. When Its pressure is lower than aorta, the artory valve close. Ventricular volume (white) is at a minimum and is ready to be filled again with blood.

Characters of Isovolumetric relaxation  Ventricles relaxed  Ventricular pressure decreased  Ventricular volume is constant  Pressure : Aorta>Ventricle  All valves closed

b.Rapid ventricular filling

Once the AV valves open, blood that has accumulated in the atria flows rapidly into the ventricles.

Pressures & Volume

artery pressure

Ventricular pressure

Ventricular volume (white) increases rapidly as blood

volume

flows from the atria into the ventricles.

Characters of Rapid ventricular filling  Ventricles relaxed  Ventricles fill passively with blood from atria  Ventricular volume increases  Ventricular pressure is lower  Pressure: Aorta>Ventricles
c.Reduced ventricular filling

At the end of this phase the AV valves close.

Pressures & Volume: Ventricular volume artery pressur e Ventricular pressure

volume

(white) increases more slowly now. The ventricles continue to fill with blood until they are nearly full.

Characters of reduced ventricular filling  Ventricles relaxed  Final phase of ventricular filling  A rel="nofollow">V
Answers  Drive blood to flow • Atria and ventricular contraction  Uni-directional blood flow • Valves closure and open companied with cardiac contraction and relaxation  Isovolumetric systole or diastole • Ventricular pressure raising or falling dramatically

Related diseases

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