Human Heart

Heart is a vital muscular organ, about the size of a clenched fist, that acts as a pump, circulating blood throughout the body. It is the central organ of the circulatory system, responsible for delivering oxygen and nutrients to all cells while removing waste products like carbon dioxide.

Other definition:

The heart is a vital muscular organ that acts as the engine of the circulatory system, pumping blood throughout the body to deliver oxygen, nutrients, and hormones and remove wastes like carbon dioxide.

Without the heart, life would not be possible, as every cell in the body depends on the constant supply of blood.

Structure and Anatomy of the Heart

• Shape: Hollow, cone-shaped.

• Location: Lies in the center of the chest (mediastinum) but slightly tilted to the left side, behind the sternum.

• Size: Roughly the size of a person's fist.

• Weight: 250–300 grams in adults.

Heart Chambers

The heart is divided into four chambers:

Chamber	Function
Right Atrium	Receives deoxygenated blood from the body via the superior and inferior vena cava.
Right Ventricle	Pumps deoxygenated blood to the lungs through the pulmonary artery.
Left Atrium	Receives oxygenated blood from the lungs through the pulmonary veins.
Left Ventricle	Pumps oxygenated blood to the entire body via the aorta. (Thickest chamber to generate high pressure.)

The heart is separated into the right and left sides by a septum.

Heart Valves

There are four important valves that prevent the backward flow of blood:

Valve	Location	Function
Tricuspid Valve	Between right atrium and right ventricle	Prevents backflow into right atrium
Pulmonary Valve	Between right ventricle and pulmonary artery	Prevents backflow into right ventricle
Mitral (Bicuspid) Valve	Between left atrium and left ventricle	Prevents backflow into left atrium
Aortic Valve	Between left ventricle and aorta	Prevents backflow into left ventricle

Each valve opens and closes with each heartbeat to maintain the one-way flow of blood.

Blood Circulation Pathway

The human heart follows a double circulation system:

1. Pulmonary Circulation (right side):

   • Right atrium → Right ventricle → Pulmonary artery → Lungs → Oxygenation

2. Systemic Circulation (left side):

   • Left atrium → Left ventricle → Aorta → Body tissues → Oxygen used, carbon dioxide collected

Thus, the right side deals with deoxygenated blood, and the left side handles oxygenated blood.

 How Does the Heart Beat?

• The Sinoatrial (SA) node located in the right atrium initiates the heartbeat.
  ➔ It generates an electrical impulse that causes the atria to contract.

• The impulse travels to the Atrioventricular (AV) node, then down to the Bundle of His and Purkinje fibers to stimulate the ventricles to contract.

• This coordinated contraction and relaxation of the heart chambers is called the cardiac cycle.

Step	Action
Systole	Contraction of heart muscles (pumping blood)
Diastole	Relaxation of heart muscles (filling with blood)

The heart typically beats about 72 times per minute in a healthy adult.

 Key Functions of the Heart

• Pump oxygenated blood to body tissues.

• Pump deoxygenated blood to the lungs.

• Maintain blood pressure and circulation.

• Transport hormones, nutrients, and waste products.

• Regulate body temperature through blood flow.

 Advantages of a Healthy Heart

• Supports strong immune function.

• Boosts physical energy and stamina.

• Reduces risk of stroke, heart attacks, and cardiovascular diseases.

• Improves mental sharpness and mood.

Quick Revision Table for Students

Topic	Key Point
Shape	Hollow, muscular, cone-shaped
Chambers	2 atria + 2 ventricles
Valves	Tricuspid, Pulmonary, Mitral, Aortic
Blood Pathway	Double circulation: Pulmonary + Systemic
Heartbeat Control	SA Node (pacemaker)
Major Function	Pump blood, oxygen, nutrients; remove waste

 Quick Summary

• Function: Pumps blood and maintains circulation.

• Chambers: 4 (Right atrium, Left atrium, Right ventricle, Left ventricle).

• Circulations: Pulmonary and Systemic.

• Heartbeat Control: SA Node (pacemaker).

Interesting Facts About the Heart

• The human heart creates enough pressure to squirt blood up to 30 feet!

• Your heart beats approximately 100,000 times per day.

• Even when removed from the body, a heart can still beat with an external oxygen supply.

• The heart pumps about 2,000 gallons (around 7,500 liters) of blood every day!

• The "lub-dub" sound of a heartbeat is caused by the closing of valves.

FAQ About the Heart

1. Why is the heart considered a muscular organ?

The heart is made mostly of cardiac muscle tissue that contracts rhythmically and involuntarily to pump blood throughout the body, making it a muscular organ.

2. How many times does the heart beat in a lifetime?

On average, the heart beats about 2.5 to 3 billion times in a human lifetime, depending on age, health, and lifestyle.

3. What protects the heart?

The heart is protected by:

• The rib cage (bony protection)

• The sternum (breastbone)

• A double-layered pericardial sac filled with fluid that cushions and reduces friction during heartbeats.

4. Why does the left side of the heart have thicker walls?

The left ventricle has thicker muscular walls because it must generate enough pressure to pump oxygen-rich blood throughout the entire body, unlike the right ventricle, which only pumps blood to the lungs.

5. What is the role of the SA node?

The sinoatrial (SA) node is known as the natural pacemaker of the heart. It generates electrical impulses that initiate each heartbeat and regulate the rhythm of the heart.

6. How much blood does the heart pump daily?

The heart pumps about 7,000 to 7,500 liters (1,800–2,000 gallons) of blood each day through the body.

7. Can the heart beat outside the body?

Yes!
If supplied with oxygen, the heart's muscle cells can continue beating for a short period outside the body because its rhythm is generated by internal electrical activity, not brain signals.

8. What happens during a heart attack?

A heart attack (myocardial infarction) occurs when the blood supply to part of the heart muscle is blocked, usually by a clot, causing damage to the heart tissue due to lack of oxygen.

Quick Bonus: Fun Facts About the Heart

• The beating sound of the heart (“lub-dub”) is caused by the closing of heart valves.

• A child’s heart beats faster (90–120 beats per minute) compared to an adult’s.

• Women's hearts beat slightly faster than men's on average.