Heart

The human heart is a marvelous organ.Its function is to move the living stream of blood through all parts of the body,never stopping even for a moment in its endless activity.Although the heart is one single organ,it actually consists of two chambers,receives blood from all parts of the body and propels it to the lungs.There the blood drops its load of carbon dioxide and receives a fresh supply of oxygen,then passes to the left side of the heart(with its two chambers also) and from there it is pumped to all parts of the body.

Each side of the heart operates independently of the other,but they act together in keeping the blood circulation normally.The walls of the heart consist of powerful muscle fibers that have the power to contract or beat rhythmically.This constant rhythmic beating keeps the circulation going.

Your heart does an enormous amount of work.It beats over one hundred thousand times a day,continually pumping the blood through more than 60,000 miles or tiny blood-vessels.these tiny capillaries are only a tenth of an inch long,but if they could be placed end to end,they would nstretch two and half times around thje earth at the equator.To maintain the right pressure,all these vessels must be filled with the right amount of blood;otherwise the tissus of the body would waste away and die.

How the heart beats

The motions of the heart are maintained by a specially designed structure known as the senatorial node or SA node.This little structure is capable of initiating a regular rhythm,and transmitting these electrical impulses to all the muscle fibres of the heart wall.This is how the constant rhythmic contractions are maintained.

This SA node or pace-maker is located near the top of the heart.It really operates like a small radio station,flashing out its signals in regular electric waves.These are the P waves seen on the electro cardiogram or tracing of the heart.These P waves make the atria or auricles(the left and right upper chambers) contract to fill the ventricles(the two lower chambers)

Lower down near the main valves of the heart,another small structure,the atrioventricular or AV node,picks up these radio signals and transmits them through the special conduction fibres or filaments of all the muscle cells of the powerful ventricles or pumping chambers of the heart.These electrical impulses are the QRS waves seen on the electrocardiogram.Almost instantly after the QRS waves the ventricular walls contract,emptying the pumping chambers into the aorta and out to all the arteries.This is the pulse you can feel at your wrist

Then for a split second the heart relaxes and fills with blood.It is now ready for the next contraction or beat.This whole amazing process is an engineering feat without any equal.Because of the simultaneous electric flash,all the heart muscle cells contract as one unit,even though they are each stimulated individually by these electrical impulses coming from above.

The coronary arteries

Naturally,to maintain all this activity,the heart must feed itself. It must also be constantly supplied with oxygen.The heart's own blood supply is maintained by two very important vessels known as the coronary arteries.Centuries ago early students of anatomy discovered these vessel winding their way around the heart and thought they resembled a crown-hence the name coronary.They are among the most important vessels in the body.If one of these should fail,the heart might stop and that would be the end.

As the blood leaves the left side of the heart,it passes through a large artery known as the aorta.This great vessels,nearly an inch in diameter,passes upward from the heart,then curves over to the left,and passes down behind the heart into the abdomen.As mentioned above,the first branches of the aorta are the left and right coronary arteries.These supply the heart itself withy blood.Other large branches supply the head,neck,upper extremities,and all the organs of the chest and abdomen.Down near the pelvis the aorta divides into two major vessels that supply the pelvic organs and the lower extremities.

This great network of vessels is known as the arterial system of the body.Out in the tissues the smaller arteries divide into endless tiny hair-sized vessels called arterioles,and these in turn divide into still smaller vessels called capillaries.It is through these innumerable tiny capillaries that the exchange of oxygen and food substances takes place.

The waste products and carbon dioxide from the tissues are then picked up by the blood stream and brought back through the smaller veins.These,like the tributaries of a river,join together forming larger vessels until eventually the blood reaches the two largest veins,the superior and inferior vena cava and through them returns to the right side of the heart.

Blood coming toward the heart from distant areas of the body is dark red in colour,as you will see whenever you cut yourself.From the right side of the heart this darker blood is pumped to the lungs.There it gives up itd surplus amount to carbon dioxide and takes on a fresh supply of oxygen.This extra oxygen immediately changes the colour of blood to a brighter red.The freshly oxygenated blood then passes through the large pulmonary veins to the left atrium(auricle)of the heart.As soon as the mitral valve opens,the bright red blood flows down into the left ventricle and is immediately pumped by way of the aorta to the entire body.The left ventricle contracts or beats about 70 times each minute,not for an hour,a day,or a year,but for a entire lifetime!

How the heart grows

The heart is such a remarkable organ that perhaps a few words about how it develops and grows are in order.Within the first two weeks after conception a small tube begins to form in the tiny embryo or unborn baby. Believe it or not,this is the forerunner of all the blood-vessels in the body.A few embryonic blood cells also begin to float around within this tiny vessel.This is the beginning of the blood stream.From these early developments the entire circulatory system of the body will eventually form.

As the little tube expands and grows,it begins to twist in a certain way,forming at first just one single chamber.This is the beginning of the heart! With this enlarging area a septum or dividing wall begins to grow, forming not one but four chambers.The two upper chambers are the left and right atria(or auricles);the two lower ,the left and right ventricles.Normally there is no connection between the right and left sides of the heart after birth.But special doors or valves open between the atrium and ventricle on each side of the heart,so that the blood will flow in only one direction.This whole mechanism is surprising simple,considering the enormous amount of work the embryonic heart must do.Any failure in the development of the septum or valves may lead to some form of congenital heart disease


Circulation before birth

During foetal life there is no connection between the baby's blood stream that of his mother.all the blood flowing through the baby's heart is always his own,never his mother's.Her blood circulation is entirely separate.However,the baby's blood stream flows close to the mother's-being divided by a very fine living membrane-so that he can pick up food materials and oxygen necessary for his own growth,and at the same time get rid of the materials he no longer needs.

As the tiny unborn baby grows,so does his heart.The most critical time of growth is during the first three months of pregnancy if at that time his mother should come down with some virus infection,such s German measles,the baby's heart may be deformed by some type of congenital heart disease.

Doctors recongnixe four maor types of heart disease:congenital heart disease,rheumatic heart disease,hypertensive heart disease,and coronary artery disease.Ln addition,there are several minor problems.

Cogenital heart disease

Some babies are unfortunate enough to be born with a damaged heart.This is known as congenital heart disease.The defect apparently arises from infection or injury to the baby's heart during the first three months after conception.congenital heart disease is less common than other forms of heart disease,but when it occurs,it can cause plenty of trouble to all concerned.There are many varieties of the disease,no two cases being exactly alike.

Atrial septal defect

Atrial septal defect is an abnormal opening or shunt between the two upper chambers of the heart,the right and left atria or auricles.Instead of flowing in the normal direction,part of the blood from the left atrium flows across into the right atrium,and is then recirculated through the lungs without having passed out into the tissues to nourish the body.This forces the right side of the heart to work doubly hard for no good reason.This abnormal opening or defect raises the blood pressure on the right side of the heart.The child often suffers from frequent chest colds and may fail to gropw as rapidly as he should.Eventually,because of extra resistance building up in the vessels supplying the lungs,the blood flow may reverse itself,passing from the right to the left side.When this occurs the patient may turn blue,a condition known as cyanosis.

Surgery suitable anesthesia the patient is cooled to a low body temperature.The chest is then opened and the defect repaired.Most patients make a satisfactory recovery following this operation,provided the abnormal opening is not too large and does not involve the mitral valve.once the patient turns blue the risk of operation is the greater,but even at this stage something can usually be done to help.

Ventricular septal defect

Ventricular septal defect means an abnormal opening or shunt between the right and left ventricles or pumping chambers of the heart.Because of the higher pressure on the left,some of the bright red blood coming from the lungs is forced through the defect in the septum or dividing wall,where it floods the right side of the heart.This excess blood is recirculated through the lungs,another waste of energy similar to what occurs in an atrial defect described above.The pressure in the right side of the heart is increased and there is a loud murmur heard over the breastbone or sternum.Not only is there danger from overloading the lungs,but in this type of defect the patient may possibly develop a very serious condition known as sub acute bacterial endocarditis(SBE),or some other serious inflammation involving the heart muscles.

Whenever possible the defect should be closed y a surgical operation on the heart,using the heart-lung machine.In this operation the surgeon usually stops the heart and allows the machine to pump the blood while the defect is being repaired.

Patent ducuts arterious means that a certain vessels called the ductus which normally closes at birth,has remained open,allowing blood to pass fromm the aorta to the pulmonary artery.This produces an effect similar to the atrial and ventricular septal defects described above.The only difference is that the abnormal openning occurs between the great vessels just outside the heart.This produces a continuous"machinery" murmur which is heard mainly in the upper part of the chest on the left.Eventually extra strain upon the circulation may cause the heart to fail.Worse still,the abnormal opening may become the focus of infection for subacute bacterial endocarditis.Eventually the vessels of the lungs may become constricted adn refuse to carry the excess blood.This raises the pressure in the pulmonary artery,so that eventually the shunt may flow i the reverse direction.The patient may complain of shortness o fbreath and pains over the heart.However,a few people do manage to live for many years with this condition,provided the opening is not too large.


Surgery is the best treatment for this condition.The abnormal channel should be closed,preferably some time between the fourth and tenth years of life.Meanwhile,the child should be taking penicillin or some other suitable antibiotic to prevent serious complications.

Coarctation of the aorta means a localized constriction or narowing o the aorta near the point where that vessel crosses behind the pulmonary artery.This is the spot where the ductus arterious or cross-channel between the aorta and pulmonary artery existed before birth.(as we have just noted,in a few children ths vessel fails to close,producing a patent ductus arterisus.)

This narrowing of the aorta means that the lower part of the body has a lower blood pressure than that found in the head and neck.Blood flow is also much slower in the leg than in the arm,unless other vessels open up to supply the lower extremities with blood.The patient may complain of numbness and weakness in the legs,and also severe headaches due to the very high pressure of the blood stream going to the head.There is a loud murmur in the chest,chich may also be heard all over the abdomen.

X-ray films of the ribs show notching along the edges of the ribs because of the increased size and twisting of the intercostal arteried.The condition is serious and should be adequately treated early in life,otherwise three out of four patients with coarctation will die before they reach forty years of age.The best treatment is to remove the narrowed portion of the aorta by surgery,bringing the two ends together and perhaps using a small graft to repair the defect.such operations can be done only by qualified teams of surgeons and cardiologists working together at some large medical centre.

Tetralogy of fallot is a serious malformation in which there is a defect in the ventricular sepctum.This allows the aorta to receive blood from both the right and left ventricles.In addition,there is narrowing or stenosis of the pulmonary valve,and hypertrophy or enlargement of the right ventricle.The large defect in the septum allows the darker and lighter blood to intermingle,so that the patient is bluish may have to squat down to get his breath after attempting to pay like normal children.
Because of the narrowing of the pulmonary artery much of the blood passes from right to left,thus depriving the child of a normal supply of oxygen to meet his needs.There may be retareded.Most of these children die in their early teens unless given the benefit of good surgery.The red blood count tends to rise,the red cell count often going above ten million instead of the usual five million.The greatly thickened blood also slows down circulation.In severe cases the child may have spells of unconsciousness brought on by lack of oxygen in the brain.A rough,harsh murmur is usually hears all over the chest.

The standard treatment for this condition has been the construction of an artificial channel or ductus between the pulmonary artery and the aorta,or between the pulmonary artery and one of the subclavian srteries.This forms an artificial ductus arteriosus condition similar to that described above.But even this defect sill help the child