What Is The Circulatory System?

By Author: nidhi dubey
Total Articles: 1
Comment this article

What is the circulatory system?
The circulatory system encompasses a complex network of blood vessels. The heart is a muscular organ and it is made up of small tubules that run throughout our body. There are three types of small tubules that help to transport blood and carry the deoxygenated blood.
The primary function of the circulatory system is to provide oxygen and nutrients throughout the body. The other function includes collecting the waste from the organs and cells. The waste collected is flushed out of the body either by sweat, urine or faecal matter. The circulatory system consists of three major tubules that are listed below.
Arteries
The arteries are small blood vesicles that carry the oxygenated blood from the heart to the other organs. It also helps to circulate other fluids like lymph and water throughout the body. The artery is made of a muscular tubule and it is elastic in nature. The arteries hold a major part of the heart’s structure. The artery has three layers the intima, the media and the adventitia.
The intima is the inner layer that ...
... is lined by a tissue called the endothelium. The media helps arteries handle the high pressure from the heart. The adventitia acts as connective tissue to nearby tissues.
The largest artery in the body is the aorta. The arteries do not change their structure very often but when there is a signal from the brain and the central nervous system they tend to become more elastic in response to external factors like pressure and temperature.
Arteries are made of smooth muscles that allow for constriction and dilation of the blood vessels through the parasympathetic nervous system. Most of the time arteries carry oxygenated blood. However, the pulmonary artery carries the unoxygenated blood from the heart to the lungs for gas exchange.
Capillaries
The capillaries are the smallest blood vessel in the body. Like the arteries, they run throughout the body and help to transport oxygen, nutrients and water throughout the body. The capillaries connect the arteries to the veins. The exchange between the oxygenated and the deoxygenated blood takes place in the capillaries.
The capillaries are about 8 to 10 microns (a micron is 0.001 mm) in diameter, just large enough for red blood cells to pass through them in single flow. The single layer of cells that form their walls are endothelial cells, like those that form the smooth channel surface of the larger vessels.
The capillaries are composed of squamous epithelium, tunica intima and the pericytes. The capsules can transport oxygenated blood from the arteries and also carry the waste products away which will be flushed out by the body.
There is an intra-capillary force that enhances the movement of molecules called Starling force. The pressure exerted by the fluid in the capillary endothelium is called capillary hydrostatic pressure. These pressures are important for the movement of the fluid and nutrients, and the pressure required depends on the length of the capillaries.
Capillaries are divided into three types depending on their function and shape. The continuous fenestrated capillaries, continuous nonfenestrated capillaries and sinusoidal capillaries.
The continuous fenestrated capillaries are found in the small intestine, kidneys and endocrine glands. These capillaries have small openings that help in the exchange of substances.
The continuous nonfenestrated capillaries can be seen in the nervous system, muscles and fat tissues. These capillaries allow only small molecules to pass through.
The sinusoidal capillaries are found in your liver and spleen. They are selectively permeable which allows only certain materials to pass through.
Veins
The blood from the capillaries is received by small veins called venules. The venules are very small and thin-walled. They cannot withstand pressure and are prone to damage easily with excess volume and pressure.
The veins are large blood vessels when compared to the venules. When compared to the arteries the veins are thin-walled and not elastic like arteries. The veins hold a large volume of blood during circulation.
The deoxygenated blood is carried by the veins to the lungs to provide oxygen. The oxygenated blood from the lungs is transported to the heart through the aorta.
What are heart valves?
The heart contains valves that open and close for the blood to flow from the heart to other organs and cells and vice versa. The heart valves open and close, during the opening and closing process, they create a sound known as a heart beat.
Types of heart valves
The heart consist of four chambers and the heart of an adult will be fully matured with extracellular matrix (EC) and valve interstitial cells (VIC) which are surrounded by an endothelial cell layer.
The valves of the extracellular matrix are formed by elastin, collagen and proteoglycan. The heart valve is a complex structure and the blood valves that pass through the chambers let out the blood in one way and the blood enters the heart in the other way.
Aortic valve
The aortic valve is one of the four heart valves that carry oxygen. The function of the aortic valve is to keep the blood flow in the right direction. It is located between the left ventricle and the aorta.
The valve is made up of three cusps (membranes) that mainly consist of collagen. The valve is connected to the heart through a muscular ring. The aortic valve is semilunar with a diameter of 20 mm that has three leaflets.
When the ventricle experiences pressure the aortic valve opens and allows the blood to leave the ventricle and then enter through the aorta. This mechanism happens in a healthy heart during the systolic process.
To reduce the pressure in the left ventricle the aortic valve leaflet closes the left ventricle and the pressure decreases in the ventricle. This process happens during the diastole.
Mitral valve
The mitral and the tricuspid valves are called atrioventricular. It is located between the atrium and the ventricles. The mitral valve is also called a bicuspid valve. The mitral valve is composed of papillary muscles, mitral annulus, anterior leaflet, posterior leaflet and chordae tendinae.
The components of the mitral valve prevent the backflow of the blood from the left ventricle to the left atrium during the systolic process. During the diastolic process, it allows the normal blood flow from the left atrium to the left ventricle.
The surface of the valve is composed of endothelial cells that give mechanical support and also help to communicate with the interstitial cells. The interstitial cells are sensitive to mechanical stimuli and they help to remodel the valve. These cells bring a metabolic and mechanical balance to the valve.
Pulmonary valve
The pulmonary valve is a semilunar valve that is located between the right ventricle and the pulmonary artery. The pulmonary valve has three cusps anterior, left and right. The cusps are separated from one another by a commissure.
The cusps overlap each other in such a way that they close the lumen. The overlapped area is called the lunula. The diameter of the pulmonary valve is about 20 mm.
During the systolic process, the pulmonary valve opens and lets the deoxygenated blood from the right ventricle to the pulmonary circulation. During the diastolic process, it allows for the filling of the right ventricle.
Tricuspid valve
The tricuspid valve is located between the right atrium and right ventricle. The tricuspid valve is responsible for the blood to flow in the correct direction.
The tricuspid valve is composed of a saddle-shaped annulus, asymmetric leaflets, the subvalvular apparatus and the right ventricle. The tricuspid valve is the largest among the four cardiac valves with a diameter of 7-9 cm2.
The tricuspid valves have three papillary muscles and the small muscles connect to septal and posterior leaflets. The anterior papillary muscle is the largest. It arises from the moderator band, and is located at the commissure between anterior and posterior leaflets.
Circulation of blood from the heart to the lungs
There are a few terms that should be familiar before discussing the role of blood circulation.
1. Right atrium: One of the four chambers of the heart. It collects the circulated blood and pumps it to the right ventricle.
2. Tricuspid valve: The valve that ensures that the blood flows in the correct direction.
3. Right ventricle: One among the four chambers. It sends the blood to the pulmonary artery and directs it to the lungs to pick up oxygen.
4. Ventricle: The muscular chamber of the heart that pumps blood out for circulation.
5. Pulmonary valve: One of the four valves that control blood flow into the heart.
6. Pulmonary artery: It is responsible to carry blood from the heart to the lungs.
7.
Pulmonary vein: The vein is responsible to carry oxygenated blood from the lung alveoli to the left atria.
8.Left atrium: One of the four chambers of the heart.
9.Superior vena cava: Superior vena cava carries deoxygenated blood from the upper half of the body to the right atrium of the heart.
10.Inferior vena cava: It is responsible for transporting deoxygenated blood
•The blood first flows through the right atrium.
•Then it flows through the tricuspid valve into the right ventricle.
•The heart beats and the ventricle pushes the blood through the pulmonic valve into the pulmonary artery.
•The pulmonary artery carries blood to the lungs and collects oxygen.
•The blood then leaves the lungs and returns to the heart through the pulmonary vein and enters the left atrium.
•The blood then travels through the mitral valve into the left ventricle.
•The left ventricle pumps blood first through the aortic valve and then into the aorta.
•The circulated blood returns to the heart through two large blood vessels called the superior vena cava and the inferior vena cava. The circulated blood will have a little oxygen content, as it is returning from the body where oxygen was used.
•The vena cava pump blood into the right atrium and again the process of blood circulation begins all over again.
What is the order of blood flow through the heart?
The blood circulatory system delivers blood and nutrients throughout the body. There are two types of circulatory systems that our body has. The pulmonary circulation and the systemic circulation.
The pulmonary circulation provides the blood with fresh oxygen and the systemic circulation provides the cells, tissues and organs with the oxygenated blood and other nutrients.
Systemic circulation
The circulation of blood takes place when between two heartbeats. The blood flows from the atria which are located in the upper chamber and then into the ventricles which are located in the lower chamber.
Both the ventricles will pump blood into the large arteries and this process is called the ejection period.
During the systemic circulation process, the left ventricle pumps the oxygenated blood into the aorta. The oxygenated blood travels from the aorta to both the small and large arteries and then into the capillary network.

The blood drops the vital materials like oxygen, nutrients and other substances. Then the blood picks up the waste materials and carbon dioxide.
The deoxygenated blood or the blood low in oxygen content is collected by the veins and it travels through the right atrium and then into the right ventricle.

Pulmonary circulation
Now, the pulmonary circulation begins. The right ventricle pumps blood that is low in oxygen into the pulmonary artery. The pulmonary artery is branched off into small arteries and capillaries.
These capillaries form a fine network of pulmonary vesicles that forms a sac at the end of airways. The carbon dioxide is emptied into the air sac inside the pulmonary vesicle and is exchanged with fresh oxygen.
The carbon dioxide that is emptied into the air sac is expired out by breathing. The oxygenated blood travels through the pulmonary veins then to the left atrium and then enters the left ventricle. The process repeats and is a cycle of the systemic circulation.
What Are the Coronary Arteries
The coronary arteries are blood vessels that wrap around the heart and are responsible for the blood supply to the heart muscle. The deoxygenated blood is carried away from the heart.
There are two main types of the coronary artery, the right coronary artery and the left main coronary artery.
Right coronary artery
The right coronary artery supplies blood to the right ventricle, the right atrium, the sinoatrial and the atrioventricular nodes. These nodes regulate the heart rhythm.
The right coronary artery is divided into smaller branches. The right posterior descending artery and the acute marginal artery. The right coronary artery together with the left anterior descending artery helps to supply blood to the middle or septum of the heart.
Obtuse marginal is a branch of circumflex artery which is a branch of left coronary artery.
Left main coronary artery
The left main coronary artery will supply blood to the left side of the heart muscle like the left ventricle and left atrium.
The left main coronary is divided into branches
•The left anterior descending artery
•The circumflex artery
The left anterior descending artery branches off the left coronary artery. It supplies blood to the left side of the heart.
The circumflex artery branches off the left coronary artery. It encircles the heart muscle and supplies blood to the outer side and back of the heart.
How does the heart beat?
The heartbeat works on the basis of the electrical system. Both the atria and the ventricles work together to make your heart pump.
The heartbeat starts with the sinoatrial node also known as the heart’s natural pacemaker. The impulse of the heartbeat starts in a small bundle of cells in the right atrium called the sinoatrial node. The sinoatrial node is responsible to maintain a normal rhythm.
The atrioventricular node is a cluster of cells that are located in the centre of the heart between the atria and ventricles. These node acts as a gate that slows down the electrical signal before it enters the ventricles. As a result, the atria contracts before the ventricles do.
Pathways of fibres called the His-Purkinje Network passes the impulses to the muscular walls of the ventricles causing them to contract. The blood is forced out of the heart to the lungs and then to the body. The process will start over again and an impulse is fired by the SA node.
How much blood does your heart pump?
The heart pumps blood throughout your lifetime and it pumps about five litres of blood. The process of pumping blood is called circulation.
The right side of the heart receives blood that is low in oxygen. The heart pumps this blood to your lungs and it picks up a fresh supply of oxygen.
The oxygenated blood returns to the left side of the heart and is pumped back out to the brain and the rest of your body.
Conditions of blood flow disorders
Arrhythmia
Arrhythmia is an irregular heartbeat or rhythm of the heart. Irregular heartbeat occurs when electrical signals do not coordinate properly with the heart rhythm. These faulty signals cause the heartbeat to either beat fast (tachycardia) or slow (bradycardia) or maybe irregular rhythm.
The heart beating fast is common or normal when a person is exercising or running. At the same time, the heartbeat slows down while sleeping. These are automated by body functions and coordinated with the heart. But when the heart suddenly beats fast and slows down slowly, it might indicate some arrhythmia.
The symptoms of arrhythmia include racing heartbeat or a slow heartbeat, fluttering in the chest, shortness of breath, fatigue, sweating, dizziness and chest pain
Congestive heart failure
When the heart fails to pump blood and the heart muscles stop working the condition is diagnosed as congestive heart failure. When the heart fails to pump blood there will be a backflow of blood as a result there will be fluid build-up in your lungs causing shortness of breath.
Heart failure can be caused due to other reasons like narrow arteries and high blood pressure. To control congestive heart failure proper treatment is required and certain lifestyle changes are also required.
The symptoms of congestive failure are fatigue, weakness, shortness of breath, wheezing and persistent cough, lack of appetite, nausea, chest pain, irregular heartbeat, swelling of the abdomen and weight gain.
Coronary artery disease
Among all the heart conditions, coronary artery disease is a common health condition. The coronary arteries, the major blood vessel that supplies blood and other nutrients to the heart will be blocked or cannot pass the blood through the arteries due to partial blockage.
When you have coronary artery disease there will be shortness of breath and chest pain. Once there is a complete block in the arteries heart attack will occur.
Some of the common symptoms of coronary artery disease are chest pain, fatigue and heart attack and shortness of breath.
Heart attack
A heart attack occurs when there is a complete blockage or reduced flow of blood in one of the arteries that supply blood to the heart. The blockage can be caused due to fat deposition and cholesterol.
The deposit of fatty substances is called plaques. The process of plaque deposition is called atherosclerosis. These plaques are dangerous as they can rupture and form a blood clot that can block the blood flow. These blockages can damage the heart muscles.
The symptoms of heart attack can vary from one person to another. Common symptoms include fatigue, heart pain, shortness of breath, nausea and cold sweat.
Heart valve disease
The heart has numerous small tubes called valves that supply blood throughout the body and these valves also run back to the heart bringing in blood. If even one of these valves is blocked or not working properly this might block the blood flow.
Heart valve disease is caused when one of the heart valves does not work properly. The heart has four valves and maintains the flow of the blood in the correct direction. If your valves dysfunction there might be a problem in closing and opening the valves. As a result, there might be a faulty or backflow of blood.
Symptoms of heart valve disease include chest pain, fatigue, abdominal pain, dizziness, fainting, shortness of breath, swelling of your ankles and feet and irregular heartbeat.
Bicuspid aortic valve disease
Bicuspid aortic valve disease affects the aortic valve. This valve is found between your heart and the aorta.
The aortic valve contains flaps that open and closes as your heart beats. It also maintains the blood flows in the correct direction.
The aortic valve contains three cusps and a bicuspid contains two valves. When there is a problem in these valves it might cause a bicuspid aortic valve.
The common symptoms include shortness of breath and chest pain.
Sudden cardiac arrest
When there is a sudden loss of heart function it is diagnosed as sudden cardiac arrest. You tend to become unconscious and you will stop breathing. When there is a problem with your heart’s electrical system there will be a disruption in pumping blood.
Sudden cardiac arrest and heart attack are not the same. A heart attack can sometimes cause a sudden cardiac attack.
If the sudden cardiac attack is not treated properly it can cause death. The symptoms of sudden cardiac arrest include no pulse, sudden collapse and unconsciousness. The sudden cardiac attack happens immediately and you have to act promptly to save the person.
How can I improve my heart health?
Your daily routine determines your health. Do not wait to be diagnosed with some health condition to start your healthy lifestyle.
Achieve and maintain a weight that’s healthy for you
Body weight plays an important role in your health. Eat foods that are rich in nutrients and avoid oily foods. This will help you maintain a healthy weight.
When you maintain a healthy weight you can reduce the risk of getting affected by health illnesses like heart disease, high blood pressure, diabetes and stroke.
Being underweight also can lead to certain health conditions like anaemia and osteoporosis. So don’t skip your meal and eat foods that are rich in nutrients and vitamins.
Eat a healthy diet
Consume foods that are good for the heart and foods that provide healthy fat. Foods like almonds, salmon and prunes are good for the heart. Include steamed foods instead of fried foods to avoid too much oil.
Exercise aerobically for around 150 minutes weekly
The heart is a muscular organ and that organ would require exercise to keep your heart healthy.
Cardio workouts will increase your heart rate and will help you to keep your heart healthy.