Blood Circulatory System

The blood circulatory system, also known as the cardiovascular system, delivers oxygen and nutrients to every cell in the human body. Blood vessels( arteries and veins) and heart are the components of the system. The heart pumps blood away through arteries, and veins bring it back to the heart. The cardiovascular system appears like a tree; the trunk the main artery (aorta) divides itself into large arteries, leading to smaller vessels, the smallest forms a network of blood vessels called capillary network. Blood must always flow to uphold life.

Two kinds of the Circulatory System

There are two different types of blood circulatory system operating in the human body. The systemic circulation is responsible for carrying oxygen and other essential nutrients with blood to organs, tissues, and cells. The pulmonary system is a part of the cardiovascular system, which takes away deoxygenated blood and returns oxygenated blood in the system.

How the System Works

Blood circulation starts between the two heartbeats when the heart rests. In expansion, the blood flows from the upper two chambers (atria) to the lower two chambers (ventricles). From ventricles, the blood is supplied in larger arteries, in a stage named the ejection period. 

In the systemic circulation, the heart supplies oxygenated blood from the left vertical to the aorta. From there, the blood travels through the large arteries finish up in the capillary network. In the process, the blood carries necessary oxygen and other nutrients and returns the deoxygenated blood into the right atrium and ventricle of the heart. In the process, the blood carries oxygen, vital nutrients, and collects the resident substance and carbon dioxide. The blood moves to those lungs to replace carbon dioxide for oxygen and return to the left atrium. The oxygenated blood flows from the left atrium to the left ventricle and starts systemic circulation again.

The right ventricle pumps the blood low in oxygen content into the pulmonary artery to begin the pulmonary circulation. The artery, which divides itself into smaller arteries and capillaries, the capillaries in the lungs for a fine network around the pulmonary vesicles, which are air sacs, looks like grapes. Carbon dioxide is released from the bloodstream into the air inside the pulmonary vesicles. When we breathe out, carbon dioxide is released from the body. As we breathe in, new oxygen enters into the bloodstream via alveoli, and oxygen content rises in the blood. The oxygenated blood travels from the lungs through pulmonary veins and into the left ventricle. The next heartbeat initiates a new systemic circulation.


Heart of the Circulation System

The heart is the center of the circulatory system and pumps blood to the rest of the body, to all organs and cells. This hollow muscular body is made up of four chambers; left and right atriums make the upper two chambers and left, and right ventricles form the lower two chambers. One way valves are incorporated between chambers to ensure the right direction of blood flow. Two independent networks of blood vessels, work together to complete the circulation system, they are pulmonary and systemic. A cluster of cells known as sinus node located at the top of the right atrium controls the heartbeat; relaxation and contraction. Electrical signals are emitted from the sinus node, through an electrical conduction system of the heart to direct the muscles to relax or contract.

There are two segments in a heartbeat; the systole and diastole phase. In systole, the ventricles contract and thrust the blood into the aorta or pulmonary artery. The one-way valve situated between the atria and ventricle closes, stopping the blood from flowing backward. In the diastole phase, the valve linking to atria open, allowing the ventricle to be filled with blood. The sinus node controls the pace of these two phases. 

In an average adult human, around five to six liters of blood are pumped through their bodies. A heart beats around 100,000 times per day, pumping 7,570 liters of blood through 96,560 kilometers of blood vessels. In a mere 20 seconds, the blood covers the entire circulatory system. 

The Lymphatic System

The lymphatic system is also a network of vessels that run throughout the body. These vessels do not create a complete circulatory system and is not governed by the heart. This system is an open one, where fluid moves from one direction to limits towards two drainage points into veins, just above the heart. Due to the absence of pressure, lymphatic fluid moves at a slower space than blood. Small lymph capillaries interact with blood capillaries in the interstitial spaces in the tissues. Tissue fluids enter the lymph capillaries and are carried away. The lymph fluids contain a large number of white blood cells. 

The lymphatic system has two kinds of lymphoid tissues; the primary lymphoid tissues constitute of bone marrow and thymus. There are hematopoietic stem cells (HSC) in the bone marrow which gradually matures into a different type of blood cells and lymphocytes. The secondary lymphatic tissues consist of the spleen, lymph nodes, and diffused lymphoid tissues; the spleen is an encapsulated formation which filters blood and screens pathogens and antigens. Lymph nodes are found throughout the body, which are bean-shaped. There are clusters of them in armpits, neck, and in the pelvic region. Swollen lymph nodes indicate your body is fighting an infection. It returns to a standard size when the job is over. 

Structure of the Circulatory System

The heart creates pressure, which pushes the blood into arteries; in pressure, the arteries expand, and blood is forced into the smallest capillaries. There are many smooth muscles around veins, which helps the blood to travel through low-pressure veins back to the heart. A minute is taken to complete the blood circulation system from and to heart. Arteries lead to smaller and smaller forming capillaries that provide oxygenated blood to tissues. Veins carry deoxygenated blood, along with other residual substances back to the heart. The waste products are excreted in the lungs and later filtered by the liver and kidney.

Circulatory System Function

The circulatory system function provide oxygen and necessary nutrients to cells and remove carbon dioxide from the bloodstream, produced by metabolism. Oxygen is bound to molecules called hemoglobin that are situated at the facade of red blood cells. The cardiovascular system is like an internal highway network, linking all parts of the body through blood vessels, arteries and veins, arterioles and venules, and capillaries. Nutrients like glucose generated from digested carbohydrates are delivered to muscles and organs. Hormones secreted by endocrine are transported by blood vessels to targeted organs; waste products are carried to the lungs and urinary system for expelling from the body. The cardiovascular system works with the respiratory system to deliver oxygen to cells and remove carbon dioxide.


Exercise for thirty minutes a day, eat healthy balanced food, and maintain a healthy weight to keep your blood pressure robust and optimal. Avoid fast and processed food as they are rich in saturated fat, which often stiffens the walls of the blood vessels. A finely tuned circulatory system carries nutrients, oxygen, electrolytes and hormones throughout the body.

FAQ (Frequently Asked Questions)

Q. 1. What is the Artery?

A. 1. The artery is one kind of muscular tube followed by smooth tissues which deliver oxygen-enriched blood from the heart to tissues and cells. Each artery consists of three layers; the first one is intima, the second one is the media, and the third one is adventitia. The largest artery is the aorta, situated at the left ventricle of the heart.

Q. 2. What is a Vein?

A. 2. Veins are blood vessels that carry deoxygenated blood from organs to the heart. There are three layers in a vein; tunica externa, tunica media, and tunica intima. There are two types of veins; pulmonary and systemic veins.

Q. 3. What is Blood?

A. 3. Blood is the fluid that delivers oxygen and nutrients to the cells and removes carbon dioxide and other waste products. Blood is made up of blood cells and plasma.

Q. 4. What is RBC?

A. 4. Red blood cells (RBC), also known as erythrocytes, are flattened disk-like objects containing hemoglobin, a protein that carries oxygen.

Q. 5. What is WBC?

A. 5. White blood cells (WBC), also known as leukocytes, are the immunity system cells, which protect the body from infectious disease and foreign invaders. There are different types of WBC, with different life spans.

Q. 6. What are Platelets?

A. 6. Platelets, also known as thrombocytes, are oval-shaped cells which is responsible for blood clotting. When a blood vessel ruptures, platelets gather around the region to seal it. Platelets are generated by the bone marrow and survive for around nine days.

Q. 7. What is Plasma?

A. 7. Plasma is a light yellow fluid, which carries water, salt, and enzymes. The plasma transports the nutrients, hormones, and proteins to various parts of the body. Cells also excrete waste products into plasma.

Q. 8. What is Lymph?

A. 8. Lymph is the fluid that circulates within the lymphatic system. The system arrests the bacteria and brings them to lymph nodes where they are destroyed. It also helps the absorption of fatty acids and distributes fat in the circulatory system.

Q. 9. What are the Blood types?

A. 9. There are four main blood groups; A, B, AB, and O. Each letter refers to the protein or antigen present in the blood cell. The blood group is determined by the genes inherited. Each blood group can be RH positive or RH negative, which makes eight blood groups.

Q. 10. How many muscles in the Human Body?

A. 10. There are over 650 named skeletal muscles in the human body. If one counts other muscle tissues like smooth muscles at the cellular level, there are one has billions of smooth muscle in the body. Muscles perform various activities like facilitating movement, moving food in the digestive tract, and allowing the heart to pump blood.