Circulatory System In Human – How Heart is working

Circulatory System In Human – How Heart Is Working – Do you know how does the human heart works? What is the shape of the heart? More similar questions are asked in the exam like 9th, 10th, 11th, 12th, graduation, and One Day Exam Like SSC, Railway, Bank, UPSC, Delhi Police, UP Police, MPSC, RAS, Rajasthan Police, BPSC, RO/ARO, and many more.

The circulatory system in humans is an important topic in which we read about the human heart, circulation of blood, blood vessels (artery, vein, and capillaries), different types of blood (red blood cells, white blood cells, and platelets), etc.

In this post, I have given information about all these topics as well as provided a PDF which is in both English and Hindi language with some MCQs Important Questions for Exams. Download link is given below

William Harvey discovered the blood circulation system. The 3 main parts of blood/heart circulation

1. Heart 2. Blood vessels 3. Blood

The heart is a red-colored triangular cone-shaped hollow and fleshy organ located in the ventral cavity towards the ventral palate. The heart is surrounded by a thin membrane, which is known as cardiac. The heart wall is made up of three different levels of endocardium, myocardium, and epicardium.

The study of the heart is called Cardiology. ECG (Electro Cardio Gram) is used to measure it and the Electro Cardio Graph machine is used for viewing it.

The weight of the heart is found to be 250 grams in women and 300 grams in men.

The human heart has 4 chambers, the heart is divided into 4 parts, with two chambers in the right part, called the left atrium and left ventricle, and similarly, two chambers are found in the right part of the heart, Which is called the right atrium and right ventricle.

Number of Chambers in Heart

Fishes have 2 chamber heart.

In reptiles like snakes and lizards, there are 3 chamber heart 2 atria, and 1 ventricle but 4 chamber hearts are found in Crocodiles, Aligator, etc.

Birds also have 4 chamber hearts. Mammals and birds have a dual and closed circulatory system and insects have an open circulatory system.

Heartbeat Phase

There are two stages in the heart called the systole and diastole.

When the heart shrinks, it throws the blood outward, which is called systole and after throwing the blood back to its old state, it is called Diastole.

The time cycle of the heart is 0.8 seconds. The acceleration of the heartbeat is called tachycardia and slowing is called bradycardia. The heart pumps 70ml of blood in one beat.

Heartbeat Lowest in blue whale 25 / min largest mammal

800m / min In Shrew (छछूंदर) smallest mammal

Newborn Baby – 160 / min

1 Month old Baby – 100 / min

Adult – 72 / min

With which machine blood pressure is measured? – Sphygmomanometer

The normal blood pressure of a person is 120/80 mm Hg, in which 120 systole and 80 diastole are called.

Blood Pressure Measurement

Hypertension more (> 140/90)

Hypotension less (<110/70)

The closing and opening of the valves give a sound of lub & dub in the heart.


The pacemaker is also known as SAN (Sino Atrial Node), where electrical activation of the healthy atria begins.

AVN (Atrio Ventricular Node) – Responsible for channeling electrical conduction to the ventricles and serving as a backup pacemaker when the SAN fails.

The heart is surrounded by a membrane called the pericardium.

It controls the heart rate.

It is also called the heart of the heart. Its place is in the right side of the heart.

Blood Vessels (heart circulation of blood)

Three Type of blood vessels are:

1. Artery 2. Vein 3. Capillaries

Arteries – The blood vessels that carry oxygenated blood from the heart to the whole body are called artery.

Note – There is carbon dioxide-rich blood in the Palmonary artery.

Vein – The blood vessel that carries carbon dioxide-rich blood from the lungs to the heart is called vein.

Note- Palmonary vein contains oxygenated blood.

Capillaries – These are the smallest (thinner than the hair) blood vessels, which connect the artery and vein.

1. Arteries: main transporters of oxygenated blood

2. Arterioles: diameter is adjusted to regulate blood flow

3. Capillaries: diffusion occurs across thin walls

1. Blood flows from capillaries into venules, then on to veins

2. Veins are large-diameter vessels with some smooth muscle in wall

3. Valves in some veins prevent blood from flowing backward

Some Heart Diseases

– Cordial Arrest – Interruption of the flow of information

– Heart attack

– Heart failure

– PericardiaI Disease

– Cardiomyopathy Disease

First Heart Transplant

The first in the African country of the world was done by Dr. C. Bernard on 3 December 1967.

In AIIMS by Dr. Venu Gopal on 3 August 1994 in India.

Blood Volume and Composition

Blood is alive! Blood contains 90% water.

1. Plasma portion

• 50-60 percent of volume

• Water, plasma proteins, dissolved ions and molecules

2. Cellular portion

• 40-50 percent of volume

• Red cells, white cells, and platelets


1. Red blood cells transport oxygen from lungs to aerobically respiring cells and carry carbon dioxide wastes from them.

2. Red blood cells have no nucleus (no DNA).

They are created in bone marrow with enough proteins to last about 120 days.

3. Phagocytes engulf old cells


(White Blood Cells)

1. Cleaners and defender – engulf damaged and dead cells and anything tagged as foreign.

2. Some signal the immune system to mount a defense.

3. Elevated levels of white blood cells indicate to physicians that there is an infection.

Platelets (Megakaryocytes)

1. There are thousands of platelets circulating in blood.

2. They live for about 8 days.

3. They respond to injury by releasing chemicals that initiate blood clotting.



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