3.1 Heart anatomy, congenital defects, valves, cardiac cycle

HEART ANATOMY

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Where is the human heart located?

Just beneath the breastbone (sternum) in the thoracic cavity.

What is the approximate size of the heart?

About twice the size of a clenched fist.

What is the approximate mass of the heart?

Females: 250–300 g; Males: 300–350 g.

What tissue makes up most of the heart?

Cardiac muscle, making up approximately 70% of cardiac cell volume.

What is the primary function of the heart?

To pump blood throughout the body.

Name the four chambers of the heart.

Right atrium; Right ventricle; Left atrium; Left ventricle.

Function of the right atrium?

Receives deoxygenated blood returning from the body.

Function of the right ventricle?

Pumps deoxygenated blood to the lungs.

Function of the left atrium?

Receives oxygenated blood from the lungs.

Function of the left ventricle?

Pumps oxygenated blood to the systemic circulation.

Why is the left ventricle more muscular than the right ventricle?

Because it must generate much greater pressure to pump blood around the entire body.

Approximately how much blood does the heart pump over a lifetime?

Around 189,800,000 litres.

CONGENITAL HEART DEFECTS

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What is a congenital heart defect?

A structural abnormality of the heart present at birth.

VENTRICULAR SEPTAL DEFECT

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What is a ventricular septal defect?

Failure of the superior interventricular septum to form, creating an opening between the ventricles.

What happens physiologically in a ventricular septal defect?

Blood mixes between the ventricles.

Why is blood usually shunted left to right in a ventricular septal defect?

Because the left ventricle contracts more strongly due to its thicker muscle wall.

Prevalence of ventricular septal defect?

Approximately 1 in 500 live births.

COARCTATION OF THE AORTA

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What is coarctation of the aorta?

Narrowing of part of the aorta.

Effect of coarctation of the aorta?

Increased resistance to blood flow.

Why does coarctation increase left ventricular workload?

The left ventricle must generate greater force to pump blood through the narrowed vessel.

Prevalence of coarctation of the aorta?

Approximately 1 in 1500 live births.

TETRALOGY OF FALLOT

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What is Tetralogy of Fallot?

A congenital heart condition involving four structural abnormalities causing poorly oxygenated blood to reach systemic circulation.

What are the four abnormalities in Tetralogy of Fallot?

Pulmonary valve narrowing; Right ventricular hypertrophy; Overriding aorta; Ventricular septal defect.

Why does pulmonary valve narrowing occur in Tetralogy of Fallot?

It obstructs blood flow to the lungs, increasing right ventricular workload.

Why does right ventricular hypertrophy develop in Tetralogy of Fallot?

Due to chronic increased workload from pulmonary obstruction.

Why is an overriding aorta problematic?

It receives mixed blood from both ventricles, reducing oxygen delivery.

Prevalence of Tetralogy of Fallot?

Approximately 1 in 2000 live births.

HEART VALVES

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Main function of heart valves?

Prevent backflow of blood.

Name the four heart valves.

Tricuspid; Pulmonary; Mitral (bicuspid); Aortic.

ATRIOVENTRICULAR VALVES

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Which are the atrioventricular valves?

Tricuspid and Mitral.

Where are atrioventricular valves located?

Between atria and ventricles.

Function of atrioventricular valves?

Prevent backflow into atria during ventricular contraction.

What prevents atrioventricular valves from turning inside out?

Strong fibrous attachments called chordae tendineae.

SEMILUNAR VALVES

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Which are the semilunar valves?

Pulmonary valve and Aortic valve.

Where are semilunar valves located?

At exits of ventricles into major arteries.

Function of semilunar valves?

Prevent blood flowing back into ventricles after contraction.

VALVULAR DISEASE

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BICUSPID AORTIC VALVE

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What is bicuspid aortic valve?

Congenital abnormality where the aortic valve has 2 leaflets instead of 3.

How common is bicuspid aortic valve?

1–2% of the general population.

Why is bicuspid aortic valve clinically important?

It predisposes to earlier calcification and aortic stenosis.

Typical age of stenosis in bicuspid vs normal valves?

Bicuspid: 40s–50s; Normal tricuspid: 60s–70s.

CLEFT MITRAL VALVE

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What is cleft mitral valve?

Congenital defect in mitral valve structure causing stenosis.

AORTIC STENOSIS

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What is aortic stenosis?

Narrowing or stiffening of the aortic valve restricting blood flow.

Causes of aortic stenosis?

Calcification; Rheumatic heart disease.

What is rheumatic heart disease?

Inflammatory disorder often caused by bacterial infection damaging valves.

EFFECTS OF VALVE DISEASE

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Why does calcification impair valve function?

It makes valves stiff and unable to open or close properly.

What happens when valves leak?

Blood flows backwards (regurgitation).

Why is regurgitation dangerous?

It increases cardiac workload and pressure.

Long-term consequence of severe valvular disease?

Heart failure.

TREATMENT

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Treatment for severe valvular disease?

Valve replacement surgery.

Types of replacement valves?

Mechanical valves; Bioprosthetic valves.

CARDIAC CYCLE

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Define cardiac cycle.

One complete sequence of filling and pumping by the heart.

Two major phases of cardiac cycle?

Diastole and Systole.

Define diastole.

Relaxation/filling phase.

Define systole.

Contraction/ejection phase.

Duration of one cardiac cycle at 75 bpm?

About 0.8 seconds.

PHASE 1

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What happens in the relaxation phase?

Atria and ventricles relax; blood returns from veins and fills chambers.

Duration of relaxation phase?

Approximately 0.4 seconds.

PHASE 2

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What happens during atrial systole?

Atria contract, pushing blood into ventricles.

Duration of atrial systole?

Approximately 0.1 seconds.

PHASE 3

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What happens during ventricular systole?

Ventricles contract, ejecting blood into arteries.

Duration of ventricular systole?

Approximately 0.3 seconds.

How long are the atria relaxed for?

About 7/8 of the cardiac cycle.