Human Circulatory System

A human circulatory system is a system that helps in the transportation of oxygen, blood, nutrients, etc throughout the body. It is also known as the cardiovascular system. This system is essential for the health of muscles, tissues, and organs.

• In order to receive oxygen into the blood, the cardiovascular system pumps blood from the heart to the lungs.
• The other parts of the body receive oxygenated blood from the heart via arteries. 
• Oxygen-depleted blood is returned to the heart by veins to restart circulation. 

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What is Human Circulatory System? 

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A human circulatory system refers to the organ system wherein nutrients, metabolic components, hormones, etc. travel to various parts of the body. Not only that, but it also helps to remove toxic wastes from the cells and organs of the body. This system is present both in humans and animals. 

• It is composed of circulatory organs like the heart, arteries, veins, capillaries, and blood.
• The heart pumps blood to the body via blood vessels (arteries and veins).
• Here, the heart acts as a central pump, and the blood helps in the transportation of components. 

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Human Circulatory System Diagram 

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The following shows the diagram of the human circulatory system: 

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Functions of Circulatory System

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Moving blood across the body is the primary role of the circulatory system. Organs, muscles, and tissues need to be kept in good condition and well-functioning to support survival. This is ensured by the circulatory system.

• Cells are supplied with oxygen, nutrition, and hormones through the circulatory system.
• It serves as a channel for communication between cells.
• This system also helps to eliminate waste from the body.
•  These wastes consist of carbon dioxide produced by breathing, organ chemical waste products, and waste from food and drinks.

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Features of the Circulatory System

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The following are the main features of the circulatory system.

• The heart, blood, and blood vessels are the main components of the cardiovascular system.
• Human beings have a double circulatory system, which means they have two loops for the circulation of blood to take place.
• One loop is for oxygenated blood while the deoxygenated blood travels via the second loop.
• These loops are called pulmonary circuit and systematic circuit.
• The human heart is four-chambered consisting of two arteries and two ventricles.
• The main function of the cardiovascular system is to transport nutrients, hormones, and oxygen in the body.
• Blood vessels in the circulatory system stretches to about 60,000 miles.

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Organs of Circulatory System

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As we have discussed earlier, the human circulatory system is composed of the following four organs.

• Heart
• Blood 
• Blood vessels
• Lymphatic system

Heart

The human heart is known to be the centralized component of the circulatory system and is constructed of specialized heart muscle. The heart contains four chambers where the lower chambers of the heart are called ventricles and the upper two chambers are called atria (singular atrium).

• The two primary veins supply the two atria with blood. 
• Both the body as well as the lungs receive blood from two ventricles. 
• Blood is pumped throughout the body by the heart. 
• The muscular heart is covered by a sheath of tissue known as pericardium. 
• The wall that divides the heart chambers is the septum.
• The repetitive contraction and relaxation of the heart muscles causes the heart to beat.

Atrium 

The right side of the heart is called the atrium. It receives carbon dioxide-rich, deoxygenated blood.

• Its main function is to transport the blood to the lungs.
• Carbon dioxide is exchanged for oxygen after it has been forced downward into the ventricle.

Ventricle

After returning to the heart, the oxygenated blood enters the ventricle.

• The main function of the left ventricle is that it pumps oxygenated blood to all body parts.

Double Circulation

A double circulation is a type of blood circulation system found in humans. The term "double circulation" refers to a circulatory system in which the heart receives blood twice during each body cycle. 

• In a double circulatory system, there are two kinds of circuits: pulmonary and systematic.
• The blood that flows from the heart to the lungs and back to the heart is known as pulmonary circulation.
• When the blood travels from the heart to the rest of the body and back to the heart is called systemic circulation. 
• These two types of circulation collectively, make double circulation.
• In this circulation, both oxygenated and deoxygenated blood do not mix together.

Blood

A specialized body fluid connective tissue that travels throughout our bodies is called blood. The red color of blood is caused by the presence of the pigment hemoglobin in the red blood cells. The main components of blood are: plasma, red blood cells, white blood cells, and platelets. 

• Apart from this, blood is composed of proteins and minerals like sodium, potassium, magnesium, etc.
• Plasma is a liquid component composed of 90% of water. 

Red blood cells 

These are also called erythrocytes. They play an essential role in transporting oxygen to all body parts from the lungs.

• They are round in shape and lack a nucleus. 
• Red blood cells have a shorter lifespan.

White blood cells 

These are also called leukocytes. White blood cells defend the body against disease and fight infections

• Some white blood cells can consume pathogenic microorganisms, such as bacteria.
• To combat infection, other white blood cells produce substances called antibodies. 
• They contain a nucleus, unlike red blood cells.

Platelets

Platelets are also called thrombocytes and are defined a tiny cell fragments produced in the bone marrow.

• In case of a cut or wound, platelets aid in blood coagulation or clotting.
• Thrombocytes do not possess a nucleus

Blood Vessels

The channels through which the blood travels throughout our body are called blood vessels. Blood vessels consist of arteries, veins, and capillaries. 

Arteries

They are responsible for transporting blood from the heart to every region of the body.

• Except for the lungs, all organs receive oxygen-rich blood through the arteries.
• The deoxygenated blood is transported to the lungs through another artery known as the pulmonary artery.

Capillaries

The capillaries are very tiny blood channels and are known to be the smallest vessels in the cardiovascular system.

•  They have very thin walls that join arteries and veins. 
• Oxygen, food, carbon dioxide, etc. are exchanged between the blood and the cells through capillaries.

Veins

They are the blood vessels with thin walls that transport low-pressure blood to the heart.

• The pulmonary vein carries oxygenated blood from the lungs to the heart. 
• The vena cava, another main vein, carries the body's deoxygenated blood to the heart.

Lymphatic system

The lymphatic system is a system that produces a group of organs, vessels, and tissues. Lymph capillaries, lymph vessels, lymph nodes, and lymph are all parts of this system.

• Lymph is a pale yellow fluid that helps in filtering out harmful substances from our body.
• Lymph nodes help to detect the pathogens or antigens present in the body.
• The lymphatic system transports protein molecules into the bloodstream.
• Digested fat is also transported by lymph for the nutritive process.

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Circulatory System Diseases

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Diseases of the circulatory system impede blood flow throughout the body and have an impact on heart and blood vessels. While some illnesses have symptoms, others may be asymptomatic. Chest pain, edema, heart palpitations, and shortness of breath are typical symptoms of circulatory system diseases. The following diseases can have an impact on the circulatory system:

Atherosclerosis

The stiffening of the arteries is called atherosclerosis.

• A high-fat diet commonly contributes to it by leaving fatty deposits on the blood vessel walls.
• High blood pressure caused by atherosclerosis can harm the heart and kidneys and possibly cause strokes.

Heart attack

The medical name for a heart attack is myocardial infarction (MI).

• A heart attack can happen when the heart's blood supply is interrupted, frequently by a blood clot.
• Reduced or lack of blood flow can damage the heart muscle. 

Cardiac ischemia

In cardiac ischemia, the heart muscle does not receive enough oxygen to function correctly.

High cholesterol

An unhealthy diet and a sedentary lifestyle are the causes of high cholesterol.

• Additionally, some people may be genetically predisposed to high cholesterol.
• It can cause other heart-related disorders.

High blood pressure

When the blood flows at high pressure through the walls of arteries is referred to as high blood pressure or hypertension.

• Various factors affect blood pressure like obesity, age, gender, etc.

Stroke

When a blood clot blocks or bursts one of the blood arteries that supply blood to the brain, a stroke may occur.

• This causes the blood flow to stop and the brain cannot receive oxygen.

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Things to Remember

• A system where nutrients and hormones are transported to the body is called the circulatory system.
• The removal of wastes from the body is the secondary function of the cardiovascular system.
• Blood circulation throughout the body is the main function of the circulatory system. 
• Arteries, capillaries, and veins are the different types of blood vessels.
• Digested food and absorbed fat in the tissues are transported and circulated by lymph.