Circulatory system

The circulatory system is also known as the cardiovascular system or vascular system is a type of system in the organisms which allows the blood to circulate in the body and transport nutrients to body tissues to maintain their normal state.

Circulatory system also transports oxygen, carbon dioxide, hormones, and blood cells to and from the cells.

Thus the circulatory system helps the body in fighting diseases, stabilize the temperature and maintains the body PH.

This system also includes the lymphatic system which has the function to circulate lymph in the body and this transport takes longer time than the blood.


The functions of the circulatory system are done through the transport of a fluid which is known as blood.

So let’s begin first understand that what is blood?

Blood is a fluid that is transported through the circulatory system in the whole body. Blood consists of plasma, red blood cells, white blood cells, and platelets.

The function of blood is that it has the capability to carry oxygen, carbon dioxide, nutrients, and waste to and from the cells and tissues.

After the brief introduction of blood, let’s return to the main topic.

The circulatory system consists of blood, heart, and blood vessels.

The circulatory system of the blood is divided into two parts which are,
1. Systemic circulation
2. Pulmonary circulation

The circulatory system of humans and most of the vertebrates are the same which means they have a closed cardiovascular system while some invertebrate possesses open cardiovascular system.


A person who specializes in the heart is known as a cardiologist while a person who specializes in operating the heart is known as a cardiothoracic surgeon.

But here the question arises that who is a vascular surgeon?

The answer is simply that the vascular surgeon deals with the other parts of the cardiovascular system.

To avoid confusion lets understand it,

Cardiologist. Specializes in the heart
Cardiothoracic surgeon. Specializes in operating the heart
Vascular surgeon. Focus on other parts of the human cardiovascular system.

What is the structure of the circulatory system?

The cardiovascular system of the human consist of heart, blood vessels, and blood.

The circulatory system completes the circulation of the blood via systemic circulation and pulmonary circulation.

In pulmonary circulation, the blood is oxygenated while in the systemic circulation it is transported to all parts of the body.

The systemic circulation also occurs in two ways which are,

1. Microcirculation
2. Macrocirculation

An average person contains 4.7 to 5.7 liters of blood which takes approximately seven percent of their body weight.

Blood consists of plasma, RBC, WBC, and platelets.

Also, many systems work in cooperation with the circulatory system and among them, the digestive system, respiratory system, and excretory system are very important.

The human circulatory system is a closed system which means that blood never leaves the blood vessels.

What are the vessels involved in the circulatory system?

The blood vessels involved in the cardiovascular system are
And capillaries.


These are vessels that carry oxygenated blood. Blood from the left ventricle of the heart to the aorta through the aortic semilunar valve.

Aorta is a thicked walled artery.

Aorta goes a little upward and then arches and gives many branches to the upper part of the body. and then descend down and pass through the aortic opening present in the diaphragm at the level 10 thoracic vertebrae and enters the abdomen and gives branches to the lower part of the body.

Aorta then divides into smaller arteries and these arteries then divided into arterioles.


As the small arteries divide into arterioles then further the arterioles divide into capillaries which brings blood to the venous system.


Capillaries join venues which then merge into venules and these venules then combine and make a vein.

These veins then drain into two large veins which are,

1. Superior vena cava
2. Inferior vena cava

These large veins the drain into the right atrium of the heart.

Coronary vessels

The heart also needs oxygen which is provided by coronary vessels via coronary circulation.

Portal veins

The general rule of the circulatory system is that arteries branch out into capillaries but the portal vein does not follow the rule.

Portal veins are an exception.

The example of a significant portal vein in the body is the hepatic portal vein which combines from the capillaries around the GIT.


The heart acts as a pump. It pumps the oxygenated blood into the body and deoxygenated blood to the human lungs via systemic and pulmonary circulation respectively.

There are four chambers in the heart which are,

Right atrium
Left atrium
Right ventricle
Left ventricle.

The right atrium is the upper part and it receives deoxygenated blood.

The blood from the right atrium is passed into the right ventricle from where it goes to the lungs for oxygenation.

The oxygenated blood then comes into the left atrium.

Blood then goes into the left ventricle from where it is pumped into the body via systemic circulation.

The heart receives blood from the coronary vessels via coronary circulation.

Coronary circulation consists of,

Coronary arteries
Coronary veins
Coronary sinus.


Lungs also play a very important role in the cardiovascular system because it receives the deoxygenated blood from the right atrium via the artery which is known as the pulmonary artery. It then oxygenates the blood and transports it to the heart back via the pulmonary vein.

The Lungs also need blood so it receives their blood from the bronchial circulation.


The brain receives the blood via anterior and posterior circulation so it has a dual supply system.

The anterior and posterior circulation arises from the internal carotid arteries and vertebral arteries respectively.


The kidney receives its blood via renal circulation.

20% of cardiac output comes into the renal circulation.

What are the types of circulatory systems?

There are three main types of the circulatory system which are
Open circulatory system
Closed circulatory system
No circulatory system.

What are the functions of the circulatory system?

The functions of the vascular system are,

1. Transport of oxygen
2. Transport of carbon dioxide
3. Oxygenation
4. Nutrient transport
5. Hormones transport

What are cardiovascular diseases?

Diseases that affect the vascular system are known as cardiovascular diseases.

Some of the cardiovascular diseases are,

Acute coronary syndrome
Deep venous thrombus
Pulmonary embolism
Transient ischaemic attacks

What are the surgical procedures performed on the circulatory system?

The surgical procedures which are performed on the system are,

Coronary artery bypass surgery
Vascular surgery
Vein stripping
Cosmetic procedures