Circulatory System in Humans (Complete Explanation)

Friends of the portal of science, we have previously explained many things about the motion system in the human body . Starting from the bones to the muscles. In fact, do not forget we also learn about abnormalities in bones and muscles.

To further broaden our horizons on Biology, this time we will learn about the circulatory system in humans. What do you know about the circulatory system in humans?

This article will explore thoroughly the human circulatory system. So, consider carefully the explanation below.

In the human circulatory system will be discussed about the components of blood , heart , blood vessels , lymph circulation and blood type .

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Components and Functions of Blood

As is well known that blood is red. Why is that? This is due to the red color of red blood cells or erythrocytes which contain red pigments carrying iron or Fe, known as Hemoglobin.

This hemoglobin easily binds to oxygen. Then, carry it throughout the body. The red color in the blood can change according to the content of oxygen. Human blood is not only made up of red blood cells.

Human blood also contains pieces of blood or platelets and white blood cells or leukocytes. Where the types can be divided into five types, namely lymphocytes , monocytes , basophils , neutrophils , and eosinophils .

To prove the constituent components of blood can be done by confusing the blood which is placed in a test tube in the centrifuge so that two separate liquids are obtained.

The top which berning approximately 55% is plasma. This blood plasma is composed of water, protein, minerals, and organic matter. Solid deposits at the bottom of the red tube are about 45% containing a mixture of red blood cells, white blood cells and platelets.

By using the dizziness technique, a comparison is also obtained between the constituents of solid and liquid blood. This is known as the Hematocrit. The value of hematrokit describes the total volume of erythrocytes.

The value of this hematocit in humans can vary. The value of normal hematrokit as much as 40-50%, while in adult men the value is 35-45%, 30-35% for adult women. Next will be explained about erythrocytes or red blood cells, leukocytes or white blood cells, platelets or pieces of blood, and blood plasma.

Erythrocytes or red blood cells

Erotrocytes are a major part of the blood. Erythrocytes are formed by bone marrow. The formation of erythrocytes is called erythropolesis.

Its formation is regulated by the glycoprotein hormone called eitroprotein. Every 1mm 3 of blood in men contains 5 million cells and women’s blood as much as 4 million cells.

The form of erythrocytes is a biconcraph disc, does not have a core, with a diameter of 8 microns, an average volume of 83 microcubics, cannot move freely, and is unable to penetrate capillary walls. Furthermore, the age of erythrocytes is approximately 120 days.

The first cell to be known as a series of red blood cells is called a proeritroblas. With appropriate stimulation, these stem cells can form proetrocytes in large quantities.

Once this proeritroblas is formed, the preoriroblast will divide several times until finally formed into eight to sixteen adult erythrocytes. These new cells from the first generation are called erythroblast basophils.

This is due in being painted with alkaline substances. These cells contain a small amount of hemoglobin, but in the next generation called erythoblast polycromatophyll will begin to form enough hemoglobin.

After another division, more hemoglobin will be formed and these cells are called orthochromatic erythoblasts. Where the color becomes red because it is influenced by hemoglobin which reaches a concentration of approximately 34%.

Thus, nukleas will solidify to the size of a small and pushed from the cell. Erythrocytes in it contain hemoglobin which consists of hemin double protein and globulin. This hemin protein can bind iron atoms so that it has the ability to bind oxygen.

Hemoglobin has a function that can be described as follows. First, hemoglobin can carry oxygen and carbon dioxide. Second, hemoglobin maintains the balance of acid-base or buffer as the buffer in the blood.

Thus the explanation about red blood cells. Next will be explained about white blood cells or leukocytes.

Leukocytes or white blood cells

Leukocytes have a function as a body defense tool. These leukocytes are formed in the reticuloendothelium of the bone marrow. Where every 1 mm 3 of blood contains 6000-9000 cells. Leukocytes have various forms.

Leukocytes have these, the size of 6-12 millimicron leukocytes. Its age is 12 days. Leukocytes can move freely amoebid and can penetrate capillary walls or diapendensis. The types of leukocytes can be explained as follows.

Monocyte. Monocytes have 5.3% with a large nucleus. It is phagocytic, with sizes 9-12.

Platelets or pieces of blood

Platelets play a role in the process of blood clotting during an injury. This platelet count is around 300,000 per mm 3 of blood. Platelets are formed in the bone marrow and can live for 8 days.

The form of platelets is round or oval and has no nucleus. Platelets break easily if they come out of a vein or come into contact with an object that has a rough surface.

If a wound occurs, blood will come out of the veins. This causes the platelets to rupture. A broken platelet will produce the enzyme thrombokinase or thromboplastin.

This thrombokinase functions to convert prothrombin in blood plasma to thrombin with the help of Ca 2+ ions and vitamin K.

Thrombin will convert fibrinogen in plasma into fibrin threads. Fibrin threads are fine threads that can stop bleeding and close the wound.

The following is a table of the differences between erythrocytes , leukocytes , and platelets .


Differentiator Erythrocytes
Size 7.5 m
amount Approximately 5,000,000 / mm3
Shape Biconkraf discs
Structure Has hemoglobin and has no nucleus
Production place Red bone marrow pipe and flat bone
Function Carry oxygen from the lungs throughout the body and carbon dioxide from all body tissues to the lungs


Differentiator Leukocytes
Size 5-9 m
amount Approximately 7,000 / mm3
Shape Irregular
Structure It doesn’t have hemoglobin, but it has a nucleus
Production place Bone marrow and lymph glands
Function Lymphocytes produce antibodies to kill germs and phagocytes eat germs


Differentiator Platelets
Size 2-4 m
amount Approximately 300,000 / mm3
Shape Irregular
Structure Do not have hemoglobin and have no nucleus
Production place Spinal cord
Function Blood clots

After understanding about the differences between erythrocytes, leukocytes, and platelets. Next will be explained about blood plasma.

Blood plasma

Blood plasma is a liquid from blood that has a composition of 55%. This blood plasma is composed of: First, as much as 8% protein consisting of albumin, prothrombin, fibrinogen, globulin, and hormones.

Second, water as much as 90%. Third, as much as 0.1% organic material consisting of glucose, amino acids, fats, urea, uric acid, enzymes, and antigens. Fourth, mineral salts as much as 0.9% consist of NaCl, NaHCO 3 , calcium salts, phosphorus, magnesium, and iron.

The function of blood protein is an important substance for the body because each has a special function, namely albumin, prothrombin, fibrinogen, glubulin, and hormones. Each can be explained as follows.

Hormones are a protein booster and control the body’s metabolism. Fibrinogen as much as 0.3% is a blood clotting protein made in the liver and after being changed by thrombin will become fibrin threads so that the bleeding stops, because blood cells are trapped by the thread.

Blood plasmas that lose fibrinogen are called serums. Globulin as much as 2.7% is formed by lymphocytes or liver, is a protein that functions as an ingredient to make immune substances or antibodies in the form of gamaglobulin or lymphocytes.

As much as 0.01% prothrombin is made in the liver with the help of vitamin K. This prothrombin is an enzyme protein that has not been activated, after being activated it will be a trmobin that functions for blood clotting enzymes.

As much as 4% albumin is made in the liver, serves to maintain the osmotic pressure of the blood so that the blood cells are not damaged caused by the osmosis event.

Furthermore, antibodies work in two different ways. The aim is to defend the body against disease.

The way antibodies work is to directly attack the cause of the disease and activate the complement system which will then damage the cause of the disease. In addition, antibodies can weaken the disease in one of the ways that can be explained as follows.

First, lysis, some antibodies that have very strong antigenic properties are sometimes able to directly attack the cell membrane of the disease agent, causing the cell to become damaged.

Second, neutralization is an antibody that has antigenic properties that will cover the toxic sites of the causative agent of the disease.

Third, precipitation, the formation of large molecules between antigens that are soluble with antibodies so that it turns insoluble and will settle.

Fourth, agglutination, the formation of clumps consisting of large structures in the form of antigens on its surface, bacteria, or red blood cells.

Thus the presentation of the components and functions of blood. The next discussion will be explained about the structure and function of the heart and blood vessels . Pay attention to the explanation below.

Structure and Function of the Heart, and Blood Vessels


The location of the human heart is in the chest cavity slightly to the left. The size of a human heart is more or less the same as each person’s fist. The human heart has a function as a blood pumping device.

The human heart is composed of three layers, namely the endocardium , myocardium , and pericardium . The explanation of each layer is as follows.

Endocardium is a membrane that limits the heart’s chambers. This endocardial layer contains many blood vessels and nerves.

Myocardium is a heart muscle whose structure is striated but its working nature is autonomous. Pericardium , is a heart wrapping membrane that has a function for mechanical protection.

The heart chamber consists of four parts, namely the atrium dexter, sinister atrium, ventricle dexter, and ventricular sinister. Each space can be explained as follows.

Atrium dexter has the function to receive blood from the whole body. Atrium sinister has the function of receiving blood from the lungs.

Ventricular dexter has the function to pump blood to the lungs. Ventister sinister has the function to pump blood throughout the body.

Furthermore, systolic and diastolic pressures in healthy people range from 120 mmHg and 80 mmHg. Under normal circumstances the heart beats 60-90 times. If the pressure is above normal then someone can be said to be hypertensive, but if below normal is called hypotension.

Blood vessel

Humans have blood vessels that consist of two types, namely arteries and veins. The order of arteries from the largest to the smallest is the aorta, arteries, arterioles, and veins.

Veins are divided into cava veins and venous veins. In addition to veins and arteries there are capillary vessels that have the function to connect between arteries and veins. The difference between arteries and veins can be explained as follows.

Arteries have thick, elastic walls. The direction of flow from the arteries is to leave the heart. The pressure is strong, if it is cut off, the blood will radiate.

Arteries contain a lot of oxygen, except the pulmonary arteries. Its location is more inward. Has one valve at the base.

Veins have thin walls and are less elastic. The direction of venous flow is towards the heart. The pressure is weak, and if it is cut it will drip.

Veins contain a lot of carbon dioxide, except for the pulmonary vein. Its location near the surface of the body. Veins have many valves along the veins.

Thus the explanation of the structure and function of the heart, and blood vessels. Next will be explained about the process of blood circulation.

Blood Circulation Process

Human blood circulation as a whole can be divided into two, namely small blood circulation and large blood circulation.

The small circulatory system is the circulation of blood from the heart to the lungs – back again to the heart. In summary, the small circulatory system can be explained as follows.

Blood from the right ventricle or right ventricle exits through the pulmonary artery into the lungs, exchanging carbon dioxide with oxygen. Then, from the lungs, blood returns through the pulmonary veins to the left ventricle or ventricular sinister.

The large circulatory system is the circulation of blood from the heart or left ventricle to circulate throughout the body and back again to the heart or right atrium.

In summary, the large circulatory system can be explained as follows. Blood from the left ventricle enters the aorta and arteries next to capillaries throughout the body. From capillaries throughout the body to venules proceed to veins and vena cava.

Until finally, enter the heart again on the right porch or atrium atrium. Circulation of human blood in one circulation throughout the body through the heart twice. First, when the lungs – the small blood circulation.

Second, when the whole body is in the circulation of large blood. Therefore, human blood circulation is called double blood circulation.

Besides being known as a small and large circulatory system also known as the portal system. The port system in humans is only known as the hepatic port system.

The hepatic portal system is a circulatory system where blood from the intestine before returning to the heart enters the liver first through the portal vein and then exits from the liver through the hepatic vein (Cavendish in Susilowarno, 2007).

After understanding about the circulatory system, the following is explained about lymph circulation as follows.

Also see:  Definition, Function and Types of Enzymes

Lymph Nodes

Lymph or lymphatic circulation is a circulatory system that is parallel with the circulatory system. In the circulation of lymph which is lymph fluid.

This lymph fluid contains white blood cells that come out of the circulatory system through blood capillaries and fat that is absorbed by the kill vessels in the human intestine.

This lymph circulation system has a function to kill the disease that enters the body. It also serves to circulate or transport fat throughout the body.

This lymphatic circulation system is composed of lymph nodes, lymph vessels, and lymphatic fluid. The structure of these lymph vessels is similar to a small vein with many valves. As a result, it looks like a merjan series.

These lymph vessels are located between muscles with smooth branches with open ends. This is intended as a place for the entry of body tissue fluid as a substance forming lymph fluid.

Along the lymph vessels there are large lymph glands. This gland serves to filter out germs. Some large lymph glands include the lymph nodes of the armpits, neck, groin folds, folding elbows, knees, tonsils or tonsils, intestinal mucous membranes, and follicles under the tongue.

Furthermore, these lymph vessels are divided into two namely right chest lymph vessels and left chest lymph vessels. Each vessel has a function.

The right chest lymph vessels have a function to collect lymph fluid from the head, neck, chest, and right hand. The lymph vessels empty into veins below the right collarbone.

Meanwhile, the left thoracic lymph vessels have a function to accommodate the lymph coming from the head, neck, chest, and left hand and lower body parts. These lymph vessels lead to veins on the bottom of the left collarbone.

This lymphatic circulation starts from body tissue in the form of tissue fluid that enters the smooth lymph vessels and turns into lymph fluid.

Furthermore, several other lymph vessels join the right chest lymph vessels which lead to veins below the right collarbone. Then, the left lymph vessel which empties into the vein below the left collarbone.

The driving force of lymph flow in lymph vessels is from contraction of skeletal muscle.

After being given an explanation about lymph circulation. Next will be explained about blood clotting and blood transfusion in the next section.

Blood Classification and Blood Transfusion

Commonly known blood groups are ABO blood groups. This blood group was discovered by Karl Landsteiner from Austria.

According to Landsteiner’s blood grouping, blood is grouped into four types, namely A, B, AB, and O. The basis of naming this blood type is the presence and type of agglutinogen contained in the blood.

In human blood there are agglutinogens or antigens present in erythrocytes and agglutinins or antibodies present in blood plasma.

The discovery of blood grouping stems from the occurrence of agglutination or blood clots when a person’s erythrocytes are mixed with blood serum from another person. However, in others, the mixture does not cause blood clots.

Antigen or agglutinogen carried by erythrocytes in certain people can react with antibodies or agglutinins carried by blood serum.

Therefore, there are two types of antigens, namely antigen or agglutinogen A and antigen or agglutinogen B. Meanwhile, agglutinin is divided into α agglutinin and β agglutinin.

There are people who have only A or B antigens, but others who have A and B antigens or do not have A and B antigens. The following is a classification of blood classification, based on agglutinin and agglutinogen.

First, people who do not have antigens, but have anti α and β, then the person is classified O.

Second, people who have antigens A and B, but do not have anti α and β, so they have blood type AB.

Third, people who have B antigens, but have anti α, then that person has blood type B.

Fourth, people who have antigen A do not have anti α, but anti β in plasma serum, so that person has blood type A.

The blood type and the main elements of antigens and antibodies can be explained below

Blood Glucose Antigen in erythrocytes Antibodies in plasma
A Antigen A Β antibody
B Antigen B Α antibodies
O. Antigen does not exist Α and β antibodies
AB Antigens A and B

Furthermore, agglutinogen A has the enzyme glycosyl transferase which contains acetyl glucosamine in its glycoprotein skeleton. Meanwhile, agglutinogen B, containing the enzyme galactose in the glycoprotein skeleton.

Agglutinogen AB has both of these enzymes. The enzymes in the agglutinogen that will encourage the formation of blood clotting reactions if they meet the type of agglutinin from plasma that is not appropriate.

The application of blood type is in blood transfusion. To be exact, giving blood to a person called a donor to someone in need is called a recipient.

In that event the donor will give erythrocytes which contain antigens, will give erythrocytes in which there are antigens.

If this antigen is incompatible with antibodies in recipient plasma, agglutination will occur. Therefore, what needs to be considered in blood transfusion is the compatibility between agglutinogen or donor antigen with antibodies or agglutinin from recipients.

Furthermore, in order to avoid blood clots in the process of blood collection for the purpose of blood transfusion. This can be prevented in the following way

First, prevent contact with rough fields. This method can be achieved by using sharp needles, tubes and bags of blood that are smooth and smooth.

Second, it is stored in a cold place or with a temperature below zero degrees Celsius so that the thrombokinase enzyme is inactive and thrombin is not formed.

Third, provide blood anticoagulation substances such as heparin and dukamarol. Fourth, give sodium citrate or sodium oxalate which aims to bind Ca ++ so that it prevents the formation of thrombin as an active enzyme in the process of blood clotting.

Thus the explanation of blood classification and blood transfusion. The next discussion will be explained about the immune system.

Immune system

The human body has the ability to survive and to fight all kinds of organisms and toxins. This can damage cells, tissues, and organs. This ability is called the immune system or the immune system.

The human immune system is composed of main components in the form of white blood cells or leukocytes. White blood cells in carrying out the immune mechanism is done in two ways, namely by phagocytosis or eating antigens and the formation of antibodies.

Phagocytosis is carried out by monocytes and macrophages. Meanwhile, the formation of antibodies is carried out by lymphocytes. The working system of antibodies against antigens can be done in several ways.

The method is agglutinin by agglomerating antigen, presiptin by prioritizing antigen, opsonin by activating monocytes to eat antigens by phagocytosis, lysis by destroying antigens, and antitoxin by offering poisons.

The cells that make up the immune system are formed by stem cells in the spinal cord. One of the cells formed in the bone marrow is lymphocytes. Lymphocytes in the body consist of one of two types of lymphocytes, namely T lymphocytes or B lymphocytes.

These T lymphocytes are formed in the bone marrow and head to the thymus gland. This is intended to differentiate so that it becomes mature and ready to work.

T lymphocytes have a function to prevent bacterial, viral, fungal infections, and are resistant to cancer and allergies.

B lymphocytes are formed and mature in the bone marrow, then go to the bursa of fabricius in the lymph glands of the digestive tract to differentiate to form plasma cells.

These plasma cells will then produce immunoglobin. This immunoglobin has a function to fight influenza bacteria, streptococcus, meningococcus, measles virus, and polio.

Furthermore, the human immune system is divided into two namely the innate immune system and the artificial immune system. Each of which is divided into passive and active immune systems. Each can be explained as follows.

Natural active immunity. Natural active immunity can be formed because cells produce antibodies. These antibodies are produced as a response to the presence of antigens from germs that enter the body.

Natural passive immunity. Natural passive immunity is an immune system in the form of antibodies given by a mother to a child conceived during pregnancy through the placenta or breast milk or breast milk. This immunity only functions in a relatively short time after the baby is born.

Active Immunity. Artificial active immunity is an immune system that is deliberately created by adding a small amount of vaccine antigen to the body.

A vaccine is a germ or a disease that has been weakened so that the pathogenicity is not harmful to the body. The entry of the vaccine into the body will activate antibody-producing cells to secrete antibodies if there are germs of the same disease that enter the body.

This technique is called immunization. Examples of artificial active immunity are smallpox immunization, DPTP, BCG, and others.

Artificial passive immunity. Artificial passive immunity is immunity in the form of antibodies that have become imposed into the body. This immune system does not stimulate antibody-producing cells to produce antibodies.

The inserted antibodies can be obtained by injecting certain antigens into the appropriate animals. Then, the antibodies in the animal’s body will be formed and taken to be injected into humans.

Intake of antibodies from animal blood is done by extracting blood that already contains antibodies. After understanding about the human immune system, the following will be explained about diseases of the circulatory system as follows.

Diseases of the Circulatory System

Disease in the human circulatory system can be explained as follows

1. Anemia

Anemia is caused by a lack of red blood cells due to lack of hemoglobin, iron or lack of erythrocytes. Erythrocyte deficiency can occur because of the consumption of red blood cells, such as malaria and hookworms. Prevention can be done by living in a clean environment and eating – nutritious food.

2. Thalassemia

Thalassemia is an inherited anemia. Thalassemia is often present in infants and children.

In patients with thalassemia, the binding capacity of red blood cells to oxygen is low because of the failure of hemoglobin formation. People with severe thalassemia or thalassemia major require blood transfusion every month.

3. Hemophilia

Hemophilia is a disease that makes it difficult for blood to clot if a wound occurs. This disorder is caused by heredity or genetic factors. The disorder can not be treated, but can be prevented. Patients must avoid the occurrence of bleeding so that blood does not flow continuously.

4. Leukemia

Leukemia or blood cancer is a disease that increases white blood cells that are not controlled.

Symptoms of leukemia are weakness and headaches, frequent infections, fever, cold and flu symptoms, weight loss, sweating, especially at night, and bone or joint pain.

Thus is an explanation of the human circulatory system to the abnormalities in the circulatory system. Hopefully this article helps friends of the science portal in understanding the circulatory system. Good luck.


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