Every human on Earth, has a heart. Before I knew how complicated and complex the heart is, I thought it was just another organ. The heart is an extremely important and complex organ in the body. The heart is responsible for the whole body and all the organs in it. There is quite alot more to the heart then just pumping blood. The heart is a very strong muscle that pumps multiple times a minute for our entire life! Without the proper function of the heart, we would die. There are chambers, valves, muscles, and much more that help the heart complete it's tasks. The lymphatic system is also considered a part in the circulatory system, which includes, the heart, vessels, lymph nodes, and more. With everything working together homeostasis is maintained in the body.

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Concept #1: Structure of the heart

The heart is about the size of your first and composed of cardiac muscle. Inside the heart are four chambers. The right and left ventricles pump blood to the rest of the body, while the left and right atria receive the blood. Each chamber and atria are separated by the septum, which helps to prevent the flow of blood into the wrong area. There are two main circulations throughout the whole body. The pulmonary circuit flows through the lungs and back to the heart. The systemic circuit is the circulation of blood throughout the rest of the body. There are many arteries, which carry the blood away from the heart, and veins which return the blood to the heart. When the heart pumps blood, it's actually opening and closing different valves in the heart to move the blood. The atrioventricular valve (AV) is located between the right atrium and ventricle and contains three flaps, so it's also called the tricuspid valve. The AV valve between the left ventricle and left atrium has only two flaps, so that one is called the bicuspid valve. The main vessels that are attatched to the heart are the right and left pulmonary vessels, the aorta, and the superior and inferior vena cava. The valves and vessels are one way circuits. The semilunar valves help the one way circuit by being located at the beginning of the aorta and pulmonary artery. When the heart pumps the blood, it contracts and relaxes. The closing of the valves creates a sound heard through a stethoscope. "Lub" is the first sound and the second sound is "dub". When the heart contracts it's in systole, and diastole is when it's relaxed. The contraction and relaxation of the heart needs to be in a constant rythmn. The vessels help to transport gases and other nutrients to the whole body. If any of the circulatory system is off balance, the body will not be in homeostasis.

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Concept #2: Electrical activity of the heart

The rythmic pumping of the heart is controlled by electrical activity. No one usually thinks that the heart contains electricity. The SA node, or the sinoatrial node, acts like the pacemaker of the heart. The heart contains myocardial cells which conducts the action potential of the heart. Action potential helps to send the message to the other cells in the heart to do the pumping action. During diastole, the SA nodes shows its a slow spontaneous depolarization which is called the pacemaker potential. There is a membrane that surrounds each and every atom in the myocardial cells. Ions, which contain a charge, move across the membrane that surrounds the atom causing a change in the charge of the atom. The specific permeability of the cell, causes a concentration gradient to be formed. An electrical gradient is also formed because the ions contain a charge. The imbalance in electrical charge across the cell membrane is called the membrane potential. The rapid change in the membrane potential causes the action potential. The movement of sodium and potassium ions in the myocardial cells produce the action potential. The atria and ventricles are separated from the myocardial cells, so the heart has specialized cells the help transport the message. The atrioventricular node, or the AV node, is the first place the impulse goes from the atria. Once through the AV node, is continues through the bundle of His, which is at the top of the interventricular septum. The bundle of His separates into left and right bundle branches, that are continuous with the Purkinje fibers. The Purkinje fibers are found within the walls of the ventricles. The myocardium within the ventricles spreads the action potential through the inner and outer sides. When this message, or action potential is sent correctly, it causes both ventricles to pump in a rythmic form. This whole process happens at a rate of 0.8 - 1.0 meter per second. The action potential and all the electrical activity of the heart needs to happen in the right direction and way. All of these processes happen so fast, but are so important.

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Concept #3: Blood vessels

Throughout the entire body, are blood vessels which act as a transportation method. Each vessel is made of muscle which allows them to contract and expand. Blood flows through the vessels to deliver nutrients to the body. When blood leaves the heart it flows through an artery, then through an arteriole, and finally capillaries. Capillaries are at a microscopic level and are the sight of exchange. When the exchange is complete, the blood flows from the capillaries into a venule, and then into a vein which returns the blood to the heart. The three layers to the vessels are, the tunica externa, or the outside, the tunica media is the middle layer, and the inner most layer is the tunica interna. The tunica interna also consists of three parts. The simple squamos epithelium is the innermost layer, while a basement membrane overlies some connective tisse fibers. Elastin forms the last part of the tunica interna, forming an internal elastic lamina. The arteries and veins has some similarities but they also contain many differences. Arteries are larger then veins, and contain more elastic fibers. When the blood pressure increases the arteries expand and when the blood pressure decreases the arteries recoil. There are about 40 million capillaries in the body. The capillaries are composed of only one cell layer, a simple squamos epithelium or endothelium. There are different kinds of capillaries. Continuous capillaries are when adjacent endothelial cells are closely joined together. Fenestrated capillaries have wide intercellular pore. Discontinuous capillaries have a great distance between the endothelial cells. Veins contain the most blood during circulation, and are unable to expand. The blood flow back to the heart is aided by skeletal muscle. Venous valves ensure a one way circuit back to the heart. There are miles and miles or vessels throughout the body. This transportation system of the body is essential for all the organs to receive and release molecules.

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Heart disease is a top leading cause of death in America. Women are more likely to get heart disease then men. If someday I become a nurse, understanding about a leading cause of death is vital. I would be dealing with quite a lot of patients that suffer from a diseases of the heart. If a patient asks me why or how this happens, I need to know the anatomy and physiology of the cardiovascular system. In my family, there is a history of high blood pressure, and heart disease. I want to know how the disease is caused and ways to prevent it so I can do everything in my power to not get those diseases. There are alot of people in the world that suffer from high and low blood pressures, and being able to coach them in ways to relieve some of their symptoms is something I need to know as a nurse. If I see a patient that has high blood pressure, education them why their blood pressure is high is key. Telling that patient that eating healthy, exercising, and reducing stress could help to lower their blood pressure would great as a nurse. Heart attacks are also another emergency that is common in the world. Knowing symptoms and ways to prevent one could save someone's life someday. The heart is responsible for everything in the body, and being educated on the heart is essential.

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Essential question:

Blood pressure is affected by three main variables. The end diastolic volume (EDV), total peripheral resistance (TPR), and contractility. The EDV is the amount of blood in the ventricles after diastole. EDV affects blood pressure because the more amount of blood in the heart after it pumps, the more the heart has to pump next time. The second variable that affects blood pressure is TPR. TPR is the amount of resistance to the flow of blood in the arteries. The greater the resistance on the flow of blood through the arteries causes higher blood pressure. Contractility is the strength of the muscular contraction of the heart. If the strength of the muscular contraction is too weak or too strong, it affects blood pressure. The more the ventricles can contract, more blood is pumped out. The two reflexes that help maintain blood pressure within limits are the metabolic control mechanisms, and the myogenic control mechanisms. Myogenic control mechanisms makes the cerebral vessels to dilate or constrict according to how high or low the blood pressure is. The vessels dilate if blood pressure is low to let more blood flow to the brain on the other hand vessels constrict to prevent a vessel from rupturing if the blood pressure gets too high. Metabolic control mechanisms kick in as vasodilation from chemical environments happen in an organ. This happens for four reasons; the first is a decrease oxygen concentrations, second is an increase in carbon dioxide, third is a decreas in tissue pH, and lastly a release of adenosine or K+, signaling to blood vessels that the tissue needs a larger supply of oxygen. Blood pressure is controlled by so many aspects throughout the body, but the blood pressure needs to stay within it's limits in order to maintain homeostasis.

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