Heart and Cardiovascular System

The Cardiovascular System

The cardiovascular (or circulatory) system is responsible for delivering nutrients and oxygen to virtually all of the body's cells.  It also removes carbon dioxide and other wastes. 

This complex system is comprised of the heart, blood and blood vessels.  The heart functions as a pump, beating regularly to send oxygen-filled blood into elastic tubes known as arteries.  These tubes carry the blood around the body.  Arteries divide into tiny capillaries which are thin enough so that nutrients, oxygen and other substances can pass through them to the surrounding tissues and cells. 

Waste products are released from the cells and tissues into the blood for disposal.  The capillaries in the body join and enlarge and form veins, which flow blood back to the heart.  This network is some 150,000km (90,000) miles long.

Take a closer look at some of the parts of this network:

  • Arteries - The arteries carry blood away from the heart and to the tissues and organs.  Aside from the pulmonary arteries, all arteries carry oxygenated blood.  As the heart pumps blood, the thick walls and elastic, muscular layers of the arteries are able to withstand this pressure.
  • Veins - Veins are more flexible than arteries and have much thinner walls.  The blood travelling through veins is under a relatively low pressure and flows smoothly and slowly.  The larger veins, in particular those in the legs, contain valves which prevent the backflow of blood.  The muscles around the veins help with the prevention of backflow by contracting during movement.
  • Capillaries - The most numerous and smallest of the blood vessels are called capillaries.  They convey blood between veins and arteries.  The average capillary is only about 0.01mm, or 1/2500 of an inch, in diameter, which is only slightly wider than a red blood cell.  Some capillaries enter tissues to form capillary beds, where nutrients and oxygen are released and where waste matter moves into the bloodstream.

The Heart

The heart supplies oxygen and blood to the various parts of the body.  The heart is actually a muscle which produces electrical impulses through a process which is called cardiac conduction.  These impulses make the heart contract and then relax, producing a heartbeat.  This beating creates the cardiac cycle, pumping blood to cells and tissues.

About the size of a clenched fist, the heart is in between the lung just left of the center of the chest.  Four chambers are found in the heart, with the lower two (ventricles) having thicker muscle walls than the upper two chambers (the atria).  The septum, which is mostly muscle, divides the two sides.  The ventricles pump blood into circulation and the atria receive blood from the various parts of the body.

The myocardium is the muscular wall of the heart.  The myocardium is always active and needs a large supply of oxygen and energy from blood.  In order to provide this, the heart muscle has its own blood vessels called the left and right coronary arteries.  These blood vessels branch out from the aorta, which is the main artery, just after it leaves the heart and sends smaller blood vessels into the heart muscle.  Waste is removed from heart tissue by the coronary veins, and particularly by the coronary sinus, which is a large vein at the back of the heart.

Four rigid, cuff-life rings are found in the upper heart and are called the cardiac skeleton.  They provide points of attachment for the heart valves and for the heart muscle.  The rigidity of these rings prevent the heart valves from becoming deformed.

The four valves in the heart control blood flow.  Each has the same basic characteristics even though they do differ in some details.  Two atrioventricular valves lie between the ventricles and the atria.  The mitral valve is located on the left side and has two cusps.  On the right is the tricuspid valve with three cusps.  Two semilunar valves are located at the exits from the ventricles.

The tricuspid valve controls blood flow from the right atrium to the right ventricle.  The pulmonary valve controls blood flowing from the right ventricle into the pulmonary artery.  The mitral valve moves blood from the left atrium to the left ventricle, and the aortic valve controls blood flow from the left ventricle into the aorta.

The heart typically beats from 60 to 100 times per minute but can go faster when required.  The heart beats around 100,000 times per day and about 30 million times per year.  In a 70-year lifetime, the heart beats about 2.5 billion times.

The circulatory system is intertwined with the other systems in the body.  It works with the respiratory system to supply oxygen and nutrients.  The circulatory system also helps to carry waste products and carbon dioxide out of the body.

Produced by the endocrine system, hormones are also transported through the blood in the circulatory system.  Hormones are the body's chemical messengers, transferring information and instructions from one set of cells to another.  For instance, one of the hormones which is produced by the heart helps to control the release of salt by the kidneys.

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Heart and Cardiovascular System Disorders


High blood pressure, also known as hypertension, is a condition where the blood in an individual’s body puts too much pressure on that person’s arterial walls, veins, and capillaries. High blood pressure is serious, as it can cause heart attack, heart failure, stroke, damage to blood vessels, aneurysm, kidney failure, brain damage, and loss of vision. The heart pumps around 2,000 gallons of blood each day through a person’s veins, arteries, and capillaries, and variations in pressure are natural. Blood pressure is higher during activities such as exercising, and lowers when the body is not as active. While high blood pressure during bodily activities is not dangerous, high blood pressure over extended periods of time can cause much bodily harm.


Low blood pressure may be caused by uncontrolled bleeding, severe infections, pregnancy, heart arrhythmias, heart disease, endocrine disorders, dehydration, taking too much hypertension medication (which is designed to lower blood pressure), or life-threatening allergic reactions. Additionally, certain medications may cause low blood pressure, such as tricyclic antidepressants, beta-blockers, narcotics, and medications which treat Parkinson’s disease.

Varicose Veins

Varicose veins begin to develop when the valves in the leg veins start to fail from excessive pressure or simply from age. The blood pools and the vein wall is stretched as injuries are caused to the lining. Varicose veins occur most often in the legs, and are usually found along the inner thighs and on the calves. However, varicose veins can also occur elsewhere: when they occur around the anus they are called hemmorhoids, and when they develop in the scrotum they are known as varicoceles.

Raynaud’s Disease

Raynaud’s disease is a condition in which the extremities exhibit a higher sensitivity to cold. Raynaud’s disease is classically characterized by a white, blue, and red color sequence when the digits lose blood supply then warms up again.


The heart is an amazing muscle, beating about 100,000 times per day, and more than 2.5 billion times over a lifespan of 80 years. The normal rate is 60 to 100 beats per minute, and this fist-sized organ gets its power from electrical impulses that control the rhythm of the heartbeats.

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