Many people don't even know that the heart is a muscle. There are more than 600 muscles in the human body. There are three types of muscles in the human body namely smooth, striated/skeletal & cardiac. Heart is a cardiac muscle. Before we go into the details of its functioning, have an appreciation for the heart. Remember, we never keep track if it beats or not when we are awake or asleep:-) It beats on its own as an involuntary muscle movement.
Heart Exterior
Cross section of a healthy heart
Heart Facts:-)
Cross section of a healthy heart
Heart Facts:-)
- You can't exercise the heart directly. So, we exercise the heart indirectly by exercising the other major muscles of the body.
- The primordial heart begins beating at four weeks after conception and doesn't stop beating until death. Because the heart has its own electrical impulse, it can continue to beat, even after separated from the body, as long as, it has an adequate supply of oxygen O2.
- The heart beats 3 billion times if a person lives upto 80 years. A woman's heart beats(78 beats per minute) slightly faster than a man's heart (70 beats per minute). The fetal heart beats approximately twice an adult, at 150 beats per minute.
- It weighs 11 ounces(1 pound or 450 grams) roughly(men have slightly larger organs than women do), pumps 2,000 gallons of blood through 60,000 miles of blood vessels(arteries, veins, capillaries) each day.
- Blood accounts for 8% of human body weight. Hence the volume of blood pumped by the heart can vary from 5 to 30 liters per minute.
- Cardiac catheterization, a common procedure now, was invented by a German Surgeon Werner Frossmann in 1929. The surgeon experimented this device with his own heart ! The procedure involves passing a thin flexible tube/catheter into the right or left side of the heart from the groin or arm. Procedure (a) collects blood samples from the heart (b) measure pressure and blood flow in the heart chambers and in the large arteries around the heart (c) measures oxygen in different parts of heart (4) performs a biopsy on the heart muscle (5) gives 'real-time' pictures of X-ray images of the arteries of the heart.
- Dr Christiaan Barnard did the first heart transplant in December 1967. The receipient lived only for 18 days.
- French Physician Rene Laennec (1781-1826) invented the stethoscope when he felt it was inappropiate to place his ear on his large-buxomed female patients chests !!!
The 'lub-dub' sound of the heartbeat heard through Stethoscope is actually the snap of the 'opening & closing' of the valves as the heart contracts. The atria has relatively thin walls, while the ventricles have thick muscular walls that enable them to pump & circulate the blood round the clock. The ventricles are the pumping stations that pump blood out of the atria into blood vessels with different destinations. Some heart valve disease is congenital and don't pose threat but some may require surgery to replace the defective valve. For unknown reasons, the only valve that very rarely gets infected(due to virus or bacteria), is the pulmonary valve. All other three valves get infected. Surgeons use either a pig valve or mechanical valve to replace defective valves.
The heart's main function is to pump oxygen rich blood into every cell in the body. Right atrium of the right side of the heart receives deoxygenated blood from tissues and supplies to the right ventricle through tricuspid valve and pumps it through pulmonary valve to the lungs on each side(remember we have two lungs!), and left atrium receives oxygenated blood from the lungs and then passed to the left ventricles via mitral valve, and the left ventricles pumps the blood through the aortic valve into the aorta to the rest of the body. Blood is pumped through arteries with high pressure and is retrieved through veins with low pressure. The arteries & the veins are not connected directly because the veins can not handle the high pressure of the arteries. The largest artery in the body is Aorta and the largest vein is Vena Cava. The arteries become smaller into arterioles and then become much smaller capillaries that act as buffering system.
Electrical Conduction of the Heart
The electrical impulses for the heartbeat come from within the heart. These signals regulate the rate & rhythm of the heart. The signals are a group of cells called 'Sinoatrial(SA) node' or 'Pacemaker' located at the top of the right atrium. The signals from pacemaker stimulate the right atrium to contract and travels to the left atrium and also to the 'Atrioventricular(AV) node' which in turn signals to the right ventricle to contract. There are muscle fibers called 'bundle of His' that conducts electrical signals from the AV node to the inner walls of the ventricles, called Purkinje fibers. Wilhelm His was a Swiss Cardialogist who discovered these special fibers that regulate ventricular conduction. Bundle of His run along the septum and into the inner walls of the ventricles.
When these conducting fibers between the atria and the ventricles are damaged, 'heart block' develops. As a result, the ventricles contract at only 30 beats per minute. An artificial pacemaker can restore the normal rhythm. Without artificial pacemaker, such a low heart rate makes all activities and consciousness impossible. If the SA node is faulty, then AV node can take on the role of setting the heart rate but at a maximum of 50 beats per minute. An affected person may feel lethargic due to reduced blood flow. Some of the factors that can affect the operation of the natural pacemaker are stress, anxiety, alcohol, coffee, nicotine that can overexcite part of the heart muscle and as a result the chambers may contract before the electrical signal arrives from the pacemaker. When the signal arrives, the heart chamber have been filling with blood for longer than normal and when they contract again due to the signal, the person feels a 'knock' in the chest.
The normal heartbeat is 70-80 beats per minute. In a condition called Bradycardia, the resting heart rate is less than 60 beats per minute. Some drugs and other factors can trigger bradycardia. But it is common among endurance athletes such as marathoners, cyclists, swimmers. In this case, due to aerobic training, the heart muscle enlarges and therefore can pump more blood during each cardiac cycle. When people are not actively exercising, and they experience this, they require medical attention.
Heart's electrical activity can also become irregular which is known as arrhythmia. Not all arrhythmias are of concern. Small children often have heart murmurs even though their heart is healthy. This abnormal sound is heard when the walls of the child's heart vibrates as the blood moves through. In other cases, it can also mean defective heart valve. There is another condition called Tachycardia in which the heart beats 100 or more per minute. Even more serious condition is Fibrillation which is a rapid, chaotic heart rhythm. When one or both atria are affected and can not supply blood to the ventricles, it can lead to ventricular fibrillation. It is a Medical Emergency that is associated with massive stroke or strong electrical shock.
There are two loops/circulations within the cardiovascular system and are linked by the two sides of the heart. The 'pulmonary' loop picks up oxygen poor blood from the right ventricle to the lungs and then picks up oxygen rich blood back to the left atrium. The 'circulatory/systemic' loop pumps blood out of the left ventricle of the heart to the rest of the body and bring deoxygenated blood back to the right atrium of the heart. These two loops may appear as separate but they work together as a whole to circulate blood through the entire body.
The cardiac cycle is the time taken by the ventricles of the heart to contract & relax and this process takes slightly under a second. When the ventricles contract, they exert a higher pressure on the walls of the arteries to push the blood throughout the body. Remember that it is the blood that carries iron, oxygen and other nutrients to all the cells in the body and also picks up the waste carbon-dioxide from the cells to the lungs through which it is exhaled. By the time blood reaches the veins and back to the heart, the blood pressure falls steeply. The contraction is called 'systole' and relaxation is called 'diastole'. In Blood Pressure reading 120/80 the first number is the systolic and the second one is diastolic pressure. Blood pressure is measured with an instrument sphygmometer.
| BLOOD PRESSURE VALUES | ||
| BLOOD PRESSURE | SYSTOLIC (mmHg) | DIASTOLIC (mmHg) |
| Normal | 100-119 | 60-79 |
| Low(hypotension) | Less than 100 | Less than 60 |
| Prehypertension | 120-139 | 80-139 |
| Hypertension | 140 and above | 90 and above |
Brain alone receives 13% of the heart's output of blood, 3% goes to the heart itself, kidneys receive 25%, around 32% goes to the digestive tract and skeletal muscles depending on the demand. Rest goes to bones, liver and other parts of the body.
In the United States alone, 900 people die everyday due to SCD(sudden cardiac death), an unrecognized epidemic. This is due to ventricular arrhythmia. 30,000 aortic valve replacement surgeries are carried out every year in US. Atherosclerosis is another major factor that contribute to heart disease. In atherosclerosis, plaques(saturated fat) form in the walls of the blood vessels that can finally block the blood flow resulting in death. Coronary artery disease is a No.1 killer in the US. In this case, the arteries of the heart itself, that supply blood to the heart to keep it oxygenated, become damaged. Hypertension is a major cause for Stroke. Recent Genetics studies show that aortic valve disease is linked to Chromosome 9q34(All chromosomes have a shorter arm 'p' and a longer arm 'q' ; 9q34 means at location 34 on the long arm of chromosome 9). At DNA level, GATA4 is a protein that is necessary for normal heart formation. When there is a mutation in the gene that codes for this protein, there is a congenital heart defect(holes or atrial/ventricular septal defect).
Bottomline, try to incorporate a healthy diet, that has protein, good carbohydrates, good fat, rich in vitamins & minerals, regular exercises, no/less to moderate alcohol, no smoking and minimal stress for a healthy living.
If any of you are more interested in knowing about the details of the heart, you can watch the following videos.
Healthy human heart beat
http://www.youtube.com/watch?v=v7jbwb1NnJc&feature=related
Atrial Fibrillation
http://www.youtube.com/watch?v=VKxQgjj2yVU&feature=related
Heart Rhythm Abnormalities (Must watch)
http://www.youtube.com/watch?v=E5OQL6KY_2g&feature=related
http://www.youtube.com/watch?v=FBvAOiSJlUo&feature=channel
Cardiac Arrhythmia(sound of heartbeat from normal to abnormal)
Cardiac Arrhythmia(sound of heartbeat from normal to abnormal)
Cardiology: A lecture by Professor of University of California, Berkeley
http://www.youtube.com/watch?v=4FScPwj_Wdc&feature=related
Cardiovascular Physiology: Lectures by Professor at Yale University
http://www.youtube.com/watch?v=It_cV56Dxtk&feature=related
Rhythms of the Heart: Surgeon at University of California, San Francisco
http://www.youtube.com/watch?v=QPY8aJ3JtWQ&feature=related
Heart Valve Disease: Surgeon at UCSF
Genetics of Heart Disease: Deepak Srivastava, MD at UCSF
Atherosclerotic Heart Disease
http://www.youtube.com/watch?v=4JVeA-f71Ng&feature=channelDrug therapy for Heart Disease
http://www.youtube.com/watch?v=hOK5HwANuIc&feature=channel
