Wednesday, 11 December 2013

The Heart and How Does It Function.

Assalamualaikum wrt and good day to everyone.

In conjunction to our month of cardiovascular system, we from PPIM Moscow are going to talk about the most important organ in this system; which is the heart and how does it function.

We all know that in every thing created, there must be something that drives them to function, like in car there is the engine, and in machine there is some kind of hydraulic pump for them to work. The same applies to us humans, physiologically speaking. The most vital organ that holds our body systems together is the heart, the busiest and the most core of us. Without heart, we will die.

Heart is the busiest organ in our body. It works and beats non-stop for 24 hours per day, supplying us with “life”. How it functions non-stop with amazing complexity of the heart system is beyond our imagination, it marks how great Allah is as He is the best and the only Creator, subhanaAllah.

Few facts and trivias that may blow your mind about the heart.

     Put your hand on your heart. Did you place your hand on the left side of your chest? Many people do, but the heart is actually located almost in the center of the chest, between the lungs. It's tipped slightly so that a part of it sticks out and taps against the left side of the chest, which is what makes it seem as though it is located there.
     Hold out your hand and make a fist. If you're a kid, your heart is about the same size as your fist, and if you're an adult, it's about the same size as two fists.
     Your heart beats about 100,000 times in one day and about 35 million times in a year. During an average lifetime, the human heart will beat more than 2.5 billion times.
     Give a tennis ball a good, hard squeeze. You're using about the same amount of force your heart uses to pump blood out to the body. Even at rest, the muscles of the heart work hard—twice as hard as the leg muscles of a person sprinting.
     Feel your pulse by placing two fingers at pulse points on your neck or wrists. The pulse you feel is blood stopping and starting as it moves through your arteries. As a kid, your resting pulse might range from 90 to 120 beats per minute. As an adult, your pulse rate slows to an average of 72 beats per minute.
     The aorta, the largest artery in the body, is almost the diameter of a garden hose. Capillaries, on the other hand, are so small that it takes ten of them to equal the thickness of a human hair.
     Your body has about 5.6 liters (6 quarts) of blood. This 5.6 liters of blood circulates through the body three times every minute. In one day, the blood travels a total of 19,000 km (12,000 miles)—that's four times the distance across the US from coast to coast.
     The heart pumps about 1 million barrels of blood during an average lifetime—that's enough to fill more than 3 super tankers.

Interesting, right?

So to the not-so interesting part…before we dig much further into this topic, let’s recap our basic information about heart.

Where is the heart located?

Well, heart is located in the chest (obviously) behind the sternum between the lungs and above the diaphragm. It is covered by pericardium and its greater part is to the left of the midline, while only right atrium and both venae cavae are to the right. The long axis of the heart extends obliquely downward from right to left and from back to front.

Topographically, its borders projected on skin are as following:

- apex: may be felt in 5th intercostal space 1 - 1.5 cm from left mamillary line toward the midline
- superior border: superior margin of 3rd costal cartilages
- right border: between 3rd - 5th ribs, 2 - 3 cm to the right of right sternal border
- left border: from cartilage of 3rd rib to heart apex
- inferior border: transversely from cartilage of 5th right rib to apex

Few words about the heart structure:

- It is a hollow muscular organ
- Compose of 2 type of cardiac cell
     Cardiac pacemaker cell
- Mass > 250-350 g
- Size > a size of fist
- Enclosed by pericardium

- Has 4 chambers
     2 atria ( right atrium and left atrium)
     2 ventricles (right and left ventricles)
- 4 valves
     Tricuspid valve (right atrium to right ventricle)
     Pulmonary valve (right ventricle to pulmonary artery > into lung)
     Bicuspid valve (blood from pulmonary vein into left atria to left ventricle)
     Aortic valve ( left ventricle to aorta)
- Has 3 layers
     Outer > epicardium
     Middle > myocardium
     Inner > endocardium

- Conduction of heart
     SA node
     AV node
     AV bundle
     Purkinje Fiber

- Blood vessels that supplies the heart
     Right coronary artery → branches off → marginal artery & posterior interventricular artery
     Left coronary artery → branches off → circumflex artery & anterior interventricular artery
     Veins → great cardiac vein, middle cardiac vein, small cardiac vein & coronary sinus

Easily speaking, heart is more-so like a pump. It pumps out readily oxygenated blood to supply the whole body tissues with oxygen and nutrients, and when it receives deoxygenated blood back, it pumps them out to the lungs to re-oxygenate them back. This means that there are two types of circulations involved with the heart, the pulmonary circulation and the systemic circulation.

In pulmonary circulation, the blood goes from heart to the lungs. This blood is deoxygenated and they are carried to the lung to be re-oxygenase back for the use of our body tissues.

Meanwhile, the systemic circulation refers to part of circulatory system that the blood leaves the heart and supplies the body tissues and re-enters the heart. It leaves through left ventricle to the body’s largest artery; aorta. Then from aorta, the aorta branches into few branches (brachiocephalic, common carotid and subclavian arteries) and continues to thoracic and abdominal part. Few loops give right and left coronary arteries that supplies the heart.
Once the aorta leads to smaller arteries, arterioles and capillaries and finally reach the tissue, the nutrients and oxygen will be passed out and waste with carbon dioxide will diffuse out into the blood. The blood then goes through venous capillaries, veins and reach lower inferior vena cava and upper superior vena cava, which later enter heart at right atrium.

To conclude these two circulation in summary;

As a pump, the heart functions with the help of the most amazing electrical wiring in it. This wiring helps the heart muscles to contract. The contraction of any muscle is associated with electrical changes called “depolarization”, and these changes can be detected by electrodes attached to the surface of the body.

Although the heart has four chambers, from the electrical point of view it can be thought of having only two because two atrias contract together and then two ventricles contract together.

The Amazing Wiring Diagram of Heart

     The electrical discharge for each cardiac cycle normally starts in a special area of the right atrium called the SA node.
     Depolarization then spreads through the atrial muscle fibers.
     There is a delay while the depolarization spreads through another area in the atrium called the AV node.
     Thereafter, the electrical discharge travels rapidly down specialized conduction tissue, the “Bundle of His”, which divides in the septum into right and left bundle branches
     The left bundle branch divides itself into two
     Within the mass of ventricular muscle, conduction spreads slowly through the “Purkinje fibers” at left and right, causing them to contract eventually.
     However there is this thing called Rhythm of Heart
     Electrical activation of heart can sometimes begin in places other than SA node as any part has the ability to be pacemaker
     “Rhythm” refers to the part of the heart which is controlling the activation sequence
     Normal rhythm of hear, which the electrical activation begins in SA node is called, Sinus Rhythm. If its abnormal, it will be called dysrythmia
     Besides pacemaker cells, nerves can change the rate of firing from the pacemaker cells. Sympathetic nervous system increase heart rate and increase force of contraction, while parasymphatetic does the vice versa.

     We can evaluate the electrical waves by using ECG.

     P wave - spreading of electrical activity over atria and indicate the beginning of contraction
     QRS - spreading of electrical activity over ventricles and beginning of contraction
     T wave - connected with ventricles recovery phase

Besides ECG, we can actually listen to our heart by using stethoscope.  Heart sounds are the noises generated by the beating heart and the resultant flow of blood through it. Specifically, the sounds reflect the turbulence created when the heart valves snap shut. The sound is often described as lub-dub lub-dub. In cardiac auscultation, an examiner may use a stethoscope to listen for these unique and distinct sounds that provide important auditory data regarding the condition of the heart.

Some of the common mechanisms by which heart sounds are generated include
(1) opening or closure of the heart valves,
(2) flow of blood through the valve orifice,
(3) flow of blood into the ventricular chambers,
(4) rubbing of cardiac surfaces

These are the first heart sound (S1) and second heart sound (S2), produced by the closing of the AV valves and semilunar valves, respectively. In addition to these normal sounds, a variety of other sounds may be present including heart murmurs, adventitious sounds, and gallop rhythms S3 and S4.

First Sounds
The first heart sound (S1) is produced by vibrations generated by closure of the mitral (M1) and tricuspid valves (T1). It corresponds to the end of diastole and beginning of ventricular systole and precedes the upstroke of carotid pulsation.

Second Sounds
The second heart sound (S2) is produced by the closure of the aortic (A2) and the pulmonary valves (P2) at the end of systole.

Third Sounds
The third heart sound (S3) is a low-pitched, early diastolic sound audible during the rapid entry of blood from the atrium to the ventricle. When arising from the LV, it is best audible at the apex with the patient in left lateral decubitus position with breath held at end expiration. When it is of RV origin, S3 is best audible at the left lower sternal border or the xiphoid with the patient in supine position. These are best heard with the bell of the stethoscope

Fourth Sounds
The fourth heart sound (S4) is a late diastolic sound that corresponds to late ventricular filling through active atrial contraction. It is a low-intensity sound heard best with the bell of the stethoscope. When of LV origin, S4 is best heard at the apex with the patient in the left lateral decubitus position at end expiration. When of RV origin, it is heard best at the left lower sternal border. Maneuvers that increase the preload increase the intensity of S4 by increasing the separation of S4 from S1. Left-sided S4 is also augmented by increased afterload as can happen with hand grip.

Pretty amazing, isn’t it?

With all these information about our heart, we hope that you guys will understand more about the heart. It is actually more to the basic recaps of the things we learned in medical school, but these “not-so-many” information are crucial for us to know as a medical student.

To conclude this post, besides having good knowledge about heart medically, us humans have to remember that in Islam heart is very important too. So many ayahs in quran tell about how important for us to have a healthy and pure heart, and although we do not know exactly is the heart referred in quran is that heart organ in our body, but we know that it is something located in our chest

“So have they not traveled through the earth and have hearts by which to reason and ears by which to hear? For indeed, it is not eyes that are blinded, but blinded are the hearts which are within the breasts - 22:46”

So lets keep our heart healthy and as pure as possible, as in one hadeeth narrated by Bukhari & Muslim;

“Prophet PBUH once said, truly in the body there is a morsel of flesh which, it it be sound, all the body is sound and which, if it be diseased, all of it is diseased. Truly it is the heart.”


1 comment:

  1. It's a very helpful article, in fact when it comes to health; there is nothing more important than managing to eat healthy food and doing exercise regularly.