The Beat of the HEART

                              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:-)

1. You can't exercise the heart directly. So, we exercise the heart indirectly by exercising the other major muscles of the body.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. Dr Christiaan Barnard did the first heart transplant in December 1967. The receipient lived only for 18 days.
8. 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 heart & the blood vessels together called cardiovascular system. The heart is located behind the sternum/breastbone and infront of spinal vertebrae, rests between the lungs and supported from below by the diaphragm. The heart is a two pump in one, has two halves called left & right. The right & left side of the heart is separated by a wall called septum. Each half has two hollow chambers called atrium & ventricle.  It has four valves namely aortic, pulmonary, tricuspid & mitral. The tricuspid valve separates the atrium and the ventricle of the right side of the heart & the mitral valve separates the atrium & the ventricle of the left side of the heart. The valves between the heart chambers ensure that blood flows in proper direction.

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)

http://www.youtube.com/watch?v=xw4nDMgTOrw&feature=related

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

http://www.youtube.com/watch?v=w9ugvV94lUA

Genetics of Heart Disease: Deepak Srivastava, MD at UCSF

http://www.youtube.com/watch?v=WmXuE0g4k64&feature=related

Atherosclerotic Heart Disease

http://www.youtube.com/watch?v=4JVeA-f71Ng&feature=channel
Drug therapy for Heart Disease

http://www.youtube.com/watch?v=hOK5HwANuIc&feature=channel

Pancreas - Diabetes Mellitus (Type I & Type II)

The gland organ Pancreas is a part of the Endocrine & Digestive system.  It lies deep inside the abdomen. It is sandwiched between stomach & spine. It lies partially behind the stomach. The rest of the pancreas is nestled in the duodenum(small intestine). The pancreas comprises endocrine and exocrine cells. The regions of the pancreas that contain endocrine cells are called the islets of Langerhans as it was first discovered by a German Anatomist Paul Langerhans. Endocrine cells are the harmone producing cells and the exocrine cells produce digestive enzymes that are necessary for the food to be digested. The islets constitute roughly 2% of the pancreas and there are different islets cell. But the most important of all are the alpha cells and beta cells of the islets of Langerhans. The alpha cells produce glucagon and the beta cells produce insulin. Alpha cells make up 15-20% and beta cells 65-80% of the total islet cells.

Insulin is a 51 amino acid protein chain. Its regulatory role in blood sugar levels was discovered in 1921. Until 70s, before the Recombinant DNA Technology was discovered, Diabetes Mellitus both T1(Type I) diabetes was considered lethal and T2(Type II) diabetes also leading to severe complications. The only alternative was to restrict the person's diet to low calories or injecting pig or cow insulin. The pig insulin differs by 1 amino acid and cow insulin by 3 amino acids from the human insulin. But some people developed allergies to this 'foreign' insulin.

DNA Recombinant methods were developed in 1972 by Stanley Cohen of Stanford University & Herbert Boyer of University of California, San Francisco. Boyer had written in his high scool year book that he dreamt of becoming a successful businessman one day! Luck knocked on his door through a 26 year old venture capitalist Bob Swanson in 1976 and world's first biotech company 'Genentech' resulted out of that meeting. The hunt for human insulin using recombinant methods was in full swing by Genentech. So, were other researchers joined the race and this crazy race had federal regulations. Genentech was smart as they tried to synthesize the gene chemically and induce E. Coli bacteria to produce insulin. After final experimental confirmations, Genentech would go public in 1980. Immediately the shares rose from $35 to $89 and during that time, it was the rapid escalation in value in the history of Wall Street. Soon, Boyer & Swanson found themselves worth $66 million apiece. Biotech brought big bucks and also dirty politics !!!

The organs involved in diabetes are islet cells of the pancreas that produce insulin, liver, muscle, brain and fat. Insulin is a harmone and also a protein which is made up of amino acids. Insulin regulates the glucose levels in the body. Whatever food we eat is broken down into fat, protein and simple sugars from carbohydrates. Liver is the organ that processes all these nutrients into glucose, a type of simple sugar, which is the main source of energy/fuel for the 400 trillion cells in the human body. Glucose molecules float in the bloodstream waiting to be utilized by the cells. But glucose can enter the cells only in the presence of insulin which stands like a guard at the door. If there is no insulin, then glucose can not enter the cell and glucose deprived cells can lead to serious complications. Since glucose is the source of energy, untreated diabetics, with no or little insulin, feel tired and exhausted all the time. If glucose can't enter the cells, then its level builds up in the bloodstream leading to high blood sugar.  

Remember all the organs perform specific functions and they interact with one another harmoniously to keep the body in optimal health. When one organ is disrupted, it puts pressure on other organs! So, what happens when sugar levels shoot up in the bloodstream? Kidneys work harder to remove the excess sugar by producing urine and thereby excreting it. What is urine? Its mostly water with some elements(am skipping the elements part for the moment)! To produce urine, kidneys have to extract water from tissues. When this occurs, the tissues become dehydrated. So, untreated diabetics feel thirsty and drink lot of water, a condition known as polydipsia. Drinking excessive amount of water is going to lead to frequent urination which is known as polyuria. When cells lack glucose, they begin to burn fat and finally protein. This leads the diabetics to eat excessive eating, to replenish the lost protein, called polyphagia. Do you realize now that body has started going in vicious cycle?

When there is no glucose, the cells look elsewhere for alternative fuel. Liver produces acidic substances called ketones. If too many are produced and not used, then these build up in the blood and lower the pH of blood making it acidic. Blood is alkaline (pH>7 means alkaline; pH<7 means acidic and pH=7 means neutral) and maintains a pH in a narrow range 7.38-7.48. When blood becomes acidic, a condition known as ketoacidosis, it can be life threatening resulting in coma. Some of the symptoms of ketoacidosis are vomiting, rapid breathing, abdominal pain, tiredness & drowsiness.  If diabetes persists, then the walls of the blood vessels may get damaged by cutting the blood supply to the kidneys, eyes and limbs and in some cases leading to amputation of the limbs.

T1, also knowns as Juvenile Diabetes, is autoimmune related. In rare cases, T1 affects elderly people also. Body's own immune system sees insulin producing cells of the Pancreas as foreign/invader and starts attacking them. I had mentioned in one of my other article that there are two types lymphocytes of immune cells(leukocytes) namely T(Thymus) lymphocytes and B(Bone Marrow or shortly BM) lymphocytes. In most of the immune related diseases, it is the rogue cells T that does havoc to the body. Both T & B cells are produced in the bone marrow only but T cells leave the bone marrow and mature in Thymus while B remains in bone marrow. We will see in detail how the two play in many disorders/diseases and also our own well being. In Type 1, the T cells completely disable the insulin producing beta cells of the pancreas and hence patients have to be on insulin injections for life. Or, need to go for pancreas transplant. First of all, the organ is scarce and secondly pancreas transplant is 'far' from being even remotely 'successful' in transplants. In T1, half a dozen genes have been identified so far that play a role for inducing this. Immune system is the only organ other than brain, that has 'memory'. The day we solve the mystery of the 'thinking' of the brain, we will find cures for the immune related diseases. For T1, the best drug is 'insulin' which is available in the form of shot on prescription. In some T2 cases too, the patients may need to take shots.  

Currently Type II(T2) Diabetes affects 15 million people in the United States and 150 million worldwide. If T2 is not treated, can result in serious complications including heart attack, stroke, kidney failure, blindness, and peripheral arterial disease which require amputations. In T2, very little insulin is produced or it is produced but not utilized properly. T2 is known as 'silent killer'. T2 is mainly caused by obesity which is 80% genetically inherited. T2 is a polygenic disorder, meaning many genes are involved. Some 20 genes have been indentified in T2's case.  But it can be controlled with diet, exercise and environment. There are seven class of oral medications for T2, available only on prescription:

1. Amaryl (glimepiride)
2. DiaBeta (glyburide)
3. Diabinese (chlorpropamide)
4. Glucotrol (glipizide)
5. Glucotrol XL (glipizide long-acting)
6. Glynase (glyburide)
7. Micronase (glyburide)
8. Tolazamide
9. Tolbutamide

The first seven drugs have sulfonylureas which stimulate the pancreas to produce insulin which in turn lowers the blood glucose levels. The last two drugs are combination of drugs from the class of seven drugs.

There is a third type known as Gestational Diabetes Mellitus (GDM) which occurs in some women during pregnancy. For most women, who never had diabetes before, the blood sugar levels become normal after the baby is born. Women with GDM deliver healthy babies by following a healthy diet, regular physical activity and maintaining a healthy weight. But these women have a higher risk of developing T2 in later years. In rare cases, women with GDM and without preventive care, can develop complications and deliver babies who are put at risk for hypoglycemia(low blood sugar), jaundice, respiratory disstress syndrome(difficult to breath), and macrosomia(baby's body being larger than normal).

Many people are not even aware of Pancreas in the human body until symtoms occur !