Anatomy

The heart works as a system and a pump together at the same time. It begins from the lungs, when you take a breath in. After your lungs have oxygen in them, your Pulmonary Artery brings blood with no oxygen from the heart to the lungs. Then from the lungs, it goes back through the Pulmonary Vein and into the Left Atrium. From the left Atrium, the heart pumps the blood through the Mitral Valve into the Left Ventricle, where once all of the blood is out of the Left Atrium, the valve shuts and the second part of each beat occurs where the ventricles contract, specifically the Left Ventricle, through the Aortic Valve into the Aorta where the blood is sent through every artery into the rest of the body. The blood is then used and sent back through tiny veins until they combine into the Vena Cava. Once the blood is received back from the Vena Cava, the unoxidized blood goes through the Tricuspid Valve and into the Right Atrium. It then goes through the Pulmonary Valve during the second part of the pump into the Right Ventricle where it is then picked up by the Pulmonary Artery, starting the cycle over again.

As I mentioned before, the heart has two parts of a beat. The first part is when the blood comes back through the pulmonary and aortic valves into the atriums and once it is full, the beat pumps the blood from atrium to ventricle. The second part of the beat is when the ventricles contract and push the blood into the Aorta or Pulmonary Artery. The beats are offset slightly to ensure blood flows out of the atrium completely before flowing into a big artery. The beats are caused by the cardiac conduction system, which is a set of nerves that control the heart’s beats. The first part is the SA node, which is near the Atria and signals them to contract when full to move the blood into the lower ventricle. The AV node is the second part, which is lower down by the ventricles and delays the signal slightly until the Atria are empty of blood. Once it is empty, the signal is sent to the atrioventricular bundle, which then leads into the Purkinje Fibers, which finally tell the muscles around the ventricles to contract.

The last part is the heart muscles. They are so different from every other muscle in your body in the way that they need to be operating for 24 hours a day, 7 days a week, for the rest of your life. This means that the arteries that supply oxygen to your heart muscles, the Coronary Arteries, are massively important to ensure a long life. This is why Coronary Artery Disease is so deadly. The heart muscles are mainly just the divides between chambers, which have the function of contracting on beat as received from the Conduction System as well.

The Atria or Atriums of the heart are the top two of the four chambers. Their main purpose is to be a temporary storage area for blood in the heart between beats. It is the airlock of the heart, making sure each valve closes before the next one opens to pump blood into the ventricle. Problems that can occur around this area are if it is too big, small, or the muscles are too ineffective at pumping blood that it doesn’t fully complete each pump. The Left Atrium takes oxidized blood from the pulmonary veins and brings it through the Mitral Valve into the Left Ventricle. The Right Atrium does the same but with un-oxidized blood through the Tricuspid Valve into the Right Ventricle. The reason for separation is to maintain the specific type of blood between arteries and veins based on oxygen level. The Atria are the important first part of the heart beat.

The Ventricles are the bottom two chambers of the heart and they are the second part of each beat. They receive blood from the Atria through the Mitral and Tricuspid valves. The Ventricles and their function can be affected by more things than the Atria, like Heart Valve Diseases, Coronary Artery Disease, and Cardiomyopathies, commonly affected by Mitral Regurgitation and Arrhythmias. The Right is slightly larger than the Left as it pumps oxygen rich blood to the rest of the body and it is the key second part of each heartbeat that keeps your body running.

The Cardiac Conduction System is a complicated bundle of nerves that can be split into four parts. Essentially, though, it times each heart beat to what you are doing at the current moment and gauges how much blood your body needs. The SA node, which is the started nerve for the entire reaction of a heartbeat, receives signals from the Sympathetic and Parasympathetic nervous systems. It then is able to time how many beats per minute your heart needs to keep your body fueled. The SA node, AV node, and Purkinje Fibers all serve a purpose throughout a heart beat and are each important. Some complications that can occur are when they are mistimed, an Arrhythmia can occur, making the heart beat sporadically. This causes problems throughout your whole body and can even damage the heart as it isn’t used to handling the irregular heartbeat. This is why it is of utmost importance to keep it healthy to live a long life.

The heart is a powerful, automatic pump made of specialized tissue called cardiac muscle, or the myocardium It is made of two main types of cells: contractile cells that do the actual pumping and autorhythmic cells that act like a built-in electrical timer to coordinate every beat. The muscle is organized into specific bands; the top rooms, called atria, have thin bands of muscle, while the bottom rooms, the ventricles, are made of thick muscles called the deep sinospiral, superficial sinospiral, and superficial bulbospiral muscles. These fibers are wrapped in a special "figure eight" pattern so that when they contract, the heart twists and wrings itself like a washcloth, which helps it squeeze out blood much more effectively. On a microscopic level, the heart is filled with sarcomeres, which are small units where proteins called actin and myosin pull together to create force. The muscle cells are joined by intercalated discs, which use gap junctions to share electrical signals and desmosomes to glue the cells together so they don't pull apart during a heavy squeeze. Because the heart never gets a day off, its cells are packed with mitochondria (the "powerhouses" of the cell), which take up about 30% to 35% of the heart's volume to provide a constant supply of energy. As a whole, the atria act as reservoirs that give an "atrial kick" to finish filling the ventricles with blood. The ventricles do the main work, and the left ventricle has a muscle wall three times thicker than the right because it must generate much higher pressure to pump blood to your entire body instead of just to the nearby lungs. Finally, finger-like papillary muscles pull on cords to keep your heart's valves from flipping the wrong way when the ventricles squeeze.

The heart has a variety of blood vessels, but they can be summed up into two types: the arteries and the veins. The arteries are typically the vessels that carry oxidized blood to important parts of the body to transfer fuel and the veins bring that used up blood to be refueled by the heart and lungs. The only exception is the Pulmonary Artery, which carries blood with no oxygen to the lungs to get refueled and the Pulmonary Vein, which carries oxidized blood back to the heart to be redistributed. Think of it more that arteries transfer blood away from the heart and veins bring the blood back towards the heart.

The important arteries are the Aorta, Pulmonary Artery, and the Coronary Arteries. The Aorta is the fuel line for your whole body, the blood is pumped out of the left ventricle into the Aorta during the second part of the beat and the Aorta distributes the blood to smaller and smaller arteries as the blood spreads out across the body. Some of these arteries are the Coronary Arteries. These are important because they give the fuel directly to the heart muscles, meaning that the whole system shuts down if the heart doesn’t get enough blood flow to keep pumping. This is why Coronary Artery Disease is the deadliest disease, not because of it being big and affecting every part of the body, but because it breaks one little wire that powers the jet engine that flies your body. Steps to avoiding Coronary Artery Disease can be found in the Prevention section if that sounds absolutely terrifying to you. The last Artery is the Pulmonary Artery, which is a huge fuel line that brings all the blood back to the lungs to be re-used and re-fueled with oxygen. Veins are a little less, but still very important to the body. The heart has 2 main veins, the Vena Cava and the Pulmonary Vein. The Pulmonary Vein brings all the freshly oxidized blood back to the heart, ready to be shipped off, so it is part of the crucial fuel line of life. The second Vein is the Vena Cava, which is split into two parts: the superior and inferior Vena Cava. The smaller veins take used blood back from each little artery and congregate it until it is flowing into one big vein, either the superior and inferior vena cava if it is flowing from the top or bottom half of the body respectively, divided at the line of the heart of course.