Everyone knows that the heart is a vital organ. We cannot live without our heart. However, when you get right down to it, the heart is just a pump. A complex and important one, yes, but still just a pump. As with all other pumps it can become clogged, break down and need repair. This is why it is critical that we know how the heart works. With a little knowledge about your heart and what is good or bad for it, you can significantly reduce your risk for heart disease.
The heart is a hollow, cone-shaped muscle located between the lungs and behind the sternum (breastbone). Two-thirds of the heart is located to the left of the midline of the body and 1/3 is to the right
The apex (pointed end) points down and to the left. It is 5 inches (12 cm) long, 3.5 inches (8-9 cm) wide and 2.5 inches (6 cm) from front to back, and is roughly the size of your fist. The average weight of a female human heart is 9 ounces and a male's heart is 10.5 ounces. The heart comprises less than 0.5 percent of the total body weight.
The heart has three layers. The smooth, inside lining of the heart is called the endocardium. The middle layer of heart muscle is called the myocardium. It is surrounded by a fluid filled sac call the pericardium.
The heart is divided into four chambers
Each chamber has a sort of one-way valve at its exit that prevents blood from flowing backwards. When each chamber contracts, the valve at its exit opens. When it is finished contracting, the valve closes so that blood does not flow backwards
When the heart muscle contracts or beats (called systole), it pumps blood out of the heart. The heart contracts in two stages. In the first stage, the right and left atria contract at the same time, pumping blood to the right and left ventricles. Then the ventricles contract together to propel blood out of the heart. Then the heart muscle relaxes (called diastole) before the next heartbeat. This allows blood to fill up the heart again. The right and left sides of the heart have separate functions. The right side of the heart collects oxygen-poor blood from the body and pumps it to the lungs where it picks up oxygen and releases carbon dioxide. The left side of the heart then collects oxygen-rich blood from the lungs and pumps it to the body so that the cells throughout your body have the oxygen they need to function properly.
Why does it happen this way? Because blood returning from the body is relatively poor in oxygen. It needs to be full of oxygen before being returned to the body. So the right side of the heart pumps blood to the lungs first to pick up oxygen before going to the left side of the heart where it is returned to the body full of oxygen.
Blood now returns to the heart from the lungs by way of the pulmonary veins and goes into the left atrium (LA) . When the LA contracts, blood travels through the mitral valve and into the left ventricle (LV) . The LV is a very important chamber that pumps blood through the aortic valve and into the aorta . The aorta is the main artery of the body. It receives all the blood that the heart has pumped out and distributes it to the rest of the body. The LV has a thicker muscle than any other heart chamber because it must pump blood to the rest of the body against much higher pressure in the general circulation (blood pressure).
Here is a recap of what we just discussed. Blood from the body flows:
The blood picks up oxygen in the lungs, and then flows from the lungs:
Have you ever wondered what makes your heart beat? How does it do it automatically, every second of every minute of every hour of every day? The answer lies in a special group of cells that have the ability to generate electrical activity on their own. These cells separate charged particles. Then they spontaneously leak certain charged particles into the cells. This produces electrical impuses in the pacemaker cells which spread over the heart, causing it to contract. These cells do this more than once per second to produce a normal heart beat of 72 beats per minute.
The natural pacemaker of the heart is called the sinoatrial node (SA node). It is located in the right atrium. The heart also contains specialized fibers that conduct the electrical impulse from the pacemaker (SA node) to the rest of the heart
The electrical impulse leaves the SA node and travels to the right and left atria, causing them to contract together. This takes .04 seconds. There is now a natural delay to allow the atria to contract and the ventricles to fill up with blood. The electrical impulse has now traveled to the atrioventricular node (AV node) . The electrical impulse now goes to the Bundle of His , then it divides into the right and left bundle branches where it rapidly spreads using Purkinje fibers to the muscles of the right and left ventricle, causing them to contract at the same time.
Any of the electrical tissue in the heart has the ability to be a pacemaker. However, the SA node generates an electric impulse faster than the other tissue so it is normally in control. If the SA node should fail, the other parts of the electrical system can take over, although usually at a slower rate. Although the pacemaker cells create the electrical impulse that causes the heart to beat, other nerves can change the rate at which the pacemaker cells fire and the how strongly the heart contracts. These nerves are part of the autonomic nervous system. The autonomic nervous system has two parts - The sympathetic nervous system and the parasympathetic nervous system. The sympathetic nerves increase the heart rate and increase the force of contraction. The parasympathetic nerves do the opposite. All this activity produces electrical waves we can measure. The measurement is typically represented as a graph called an electrocardiogram (EKG).
On an EKG each part of the tracing has a lettered name:
Electrical system abnormalities can range from minor premature beats (skipped beats) that do not require treatment, to slow or irregular beats that require an artificial pacemaker.
Coronary arteries are the ones that we try to keep clear by eating a healthy diet. If coronary arteries are blocked a heart attack results. The heart, just like any other organ, requires blood to supply it with oxygen and other nutrients so that it can do its work. The heart does not extract oxygen and other nutrients from the blood flowing inside it -- it gets its blood from coronary arteries that eventually carry blood within the heart muscle. Approximately 4 percent to 5 percent of the blood output of the heart goes to the coronary arteries (7 ½ ounces/minute or 225 ml/min). There are two main coronary arteries - The left main coronary artery and the right coronary artery which arise from the aorta. The left main coronary artery divides into the left anterior descending branch and the left circumflex arteries. Each artery supplies blood to different parts of the heart muscle and the electrical system.
The heart also has veins that collect oxygen-poor blood from the heart muscle. Most of the major veins of the heart (great cardiac vein, small cardiac vein, middle cardiac vein, posterior vein of the left ventricle, and oblique vein of the left atrium) drain into the coronary sinus which opens into the right atrium. Coronary artery disease is caused by a blockage in one of the coronary arteries. When a coronary artery is partially blocked, that artery cannot supply enough blood to the heart muscle to meet its needs during exertion. When someone with coronary artery disease exerts himself or herself, it causes chest pain. This is due to lack of blood and oxygen to that part of the heart muscle and is called angina. If the obstruction worsens (more frequent angina episodes, with less exertion) a condition called unstable angina can occur. A heart attack happens when a coronary artery is completely blocked and no blood or oxygen is getting to the heart muscle served by that artery. This also causes chest pain and causes death to the heart muscle served by that artery.
An average heart pumps 2.4 ounces (70 milliliters) per heartbeat. And, as we already mentioned, an average heartbeat is 72 beats per minute. Therefore an average heart pumps 1.3 gallons (5 Liters) per minute. In other words it pumps 1,900 gallons (7,200 Liters) per day, almost 700,000 gallons (2,628,000 Liters) per year, or 48 million gallons (184,086,000 liters) by the time someone is 70 years old. That's not bad for a 10-ounce pump.