Cardiovascular system: This section talked about the structure of the heart, heart sounds, murmurs, and how the cardiac cycle works. It explained the electrical activity of the heart and how an EKG can help physicians monitor a patient’s heart rhythms.

Blood vessels, including the arteries, are larger and more elastic, which can expand easily when the pressure of the blood rises. The body has over 40 billion capillaries throughout the body, with the total surface area of 1,000 square miles. This makes it easier for exchanges between blood and tissue fluid. Veins expand to take in more blood, with less pressure being in a vein, they need help from other skeletal muscle groups to massage the blood back to the heart (skeletal muscle pump). Veins have valves to prevent back flow of blood. The lymphatic system was also discussed. Functions include: transporting interstitial fluid back to the blood, transporting absorbed fats and the lymphocytes (its cells) which provide immunity against pathogens.

Diseases of the heart and blood vessels, including arteriosclerosis (hardening of the arteries); is where plaque forms in the arteries and ends up reducing the blood flow to the heart. Having high cholesterol contributes to diseases of the heart. We all need to watch our diets regarding the amount of cholesterol we take in. Our bodies make enough that we do not need to eat any. When the blood flow is decreased to the heart ischemia can happen. When there are low oxygen levels in the blood caused by inadequate blood flow, it can give a person a feeling of pain over their heart. If the symptoms are not treated the person may have a myocardial infarction (heart attack). Arrhythmias, which are abnormal heart rhythms, can be bradycardia, which is slower than 60 beats/min. or tachycardia, with beats being greater than 100 beats/min. With the heart rate increasing even faster a flutter or fibrillation occurs.

We also have to understand cardiac output, which is the volume of blood pumped per minute by each ventricle and the total blood volume which is 5.5liters. Our heart rate needs to be regulated at all times. Blood volume is only one part of the total body water. Exchanges of fluids happen between the capillaries and tissues. The kidneys help to regulate the blood volume with formation of urine, filtering of substances, recycling and re-absorption of particles back into the vascular system. Hormones including, Anti-diuretic Hormone (ADH) and Atrial Natriuretic Peptide (ANP); along with salt, help to control the blood volume as well.

Structure of the heart:
A person's heart is the size of their fist. There are 4 chambers: left and right atria, left and right ventricles. The muscular wall between the left and right sides of the heart is called the Septum. Dense connective tissue, fibrous skeleton is between the atria and ventricles on both sides. There are 4 valves: right side includes the Tricuspid and Pulmonary Semilunar, left side includes the Mitral (Bicuspid) and Aortic Semilunar. The heart is made up of layers of muscle tissue. The innermost layer is called the Endocardium and it is made up of endothelial tissue which lines the inside of the heart. The coronary vessels are located in the Pericardial cavity and this is where the blood vessels are located to supply nutrients and oxygen to the heart. The layer of muscle that works the hardest by contracting is the Myocardium. There is a layer of Epicardium which protects the tissues when the heart beats. The heart is protected by the Pericardium which surrounds the entire heart. The Parietal Pericardium, which is fibrous connective tissue, joins the major blood vessels to the sternum and diaphragm so your heart isn't floating in your chest.
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Both of these pictures came from the sight noted between the pictures
Both of these pictures came from the sight noted between the pictures

Blood flow through the heart:
Oxygen enriched blood comes from the lungs by way of the Pulmonary Veins into the Left Atrium through the Mitral Valve into the Left Ventricle through the Aortic Semilunar Valve into the Aorta and out to all organs and systems of the body.
Deoxygenated blood comes back to the heart by way of the Superior and Inferior Vena Cava into the Right Atrium through the Tricuspid Valve into the Right Ventricle through the Pulmonary Semilunar Valve out the Pulmonary Arteries to the lungs to be re-oxygenated.

Pulmonary circulation is the path our blood takes from the heart, through the lungs and back to the heart.
Systemic circulation is the oxygen rich blood being pumped to all the organs in our system and back through the veins to return oxygen poor blood to the heart.
These two systems need to work together to keep our blood oxygen level within normal limits at all times.

I found this movie on how the human heart works and thought it was very helpful. It talks about the flow of blood through the heart and how the valves work. It also talks about diseases of the vessels in the heart and what the electrical system of the heart looks like. It is about 3 minutes long but it goes fast. Please watch.
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What Is Atrial Fibrillation? It is an irregular, rapid rhythm caused by a glitch in the electrical system of the heart. When this is happening, there are several signals that are firing from within the atria, as many as 600 times per minute. These signals make the atria quiver rapidly and contraction is ineffective. The AV node doesn't respond to all the impluses but enough get through to the ventricles to cause a rapid, irregular beat. The irregular heart rate can be anywhere from 150-180 beats per minute, normal range is 60-100 beats per minute. If this is not regulated it can cause heart failure or even a stroke. When the heart is functioning normally the SA node starts the heartbeat, the AV node relays the signals to the chambers so they all pump blood in a perfect rhythm.

What causes Atrial Fibrillation? Any condition that puts a strain on the heart can cause atrial fibrillation. High blood pressure, coronary artery disease and problems with heart valves can all cause problems. Thyroid disorders or a serious infection are also causes of a fibrillation. Some of the first signs might be an uneven pulse or a racing, pounding feeling of the heart. If the fibrillation has been going on for a long time it can be hard on the body causing dizziness, shortness of breath and fatigue. Blood may pool and clots can form because of the heart not being able to contract like it should. If the clot breaks away it can travel to the brain, causing a stroke.

There are several factors that can raise your risk of developing atrial fibrillation. Being a white male, over 60 years of age with history of heart disease and a family history of atrial fibrillation. Other factors, that can be controlled, are being overweight and smoking, which can lead to lung disease. Using illegal drugs, consuming large amounts of alcohol or caffeine can also contribute to having atrial fibrillation.

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The electrocardiogram, otherwise known as EKG, is the surest way to find out if a person has atrial fibrillation. With the body being a good conductor of electricity because of tissue fluids having a high concentration of ions that move creating a current in response to the potential differences produced by the heart. These differences come to the body’s surface where they can be recorded by placing electrodes on the skin. Having an EKG done is painless, it takes more time for the nurse to get the electrodes on the patient then it does for the machine to run the test. There are three waves that are produced during each cardiac cycle, P, QRS and T. P wave is caused by atrial depolarization, QRS wave is caused by ventricular depolarization and the T wave which results from the ventricular repolarization. There are other tests that may need to be done to confirm atrial fibrillation. An echocardiogram or ultra sound of the heart may be ordered to look for any valve damage or heartfailure. A stress test may be preformed to see how well the heart is performing. Treatments may include taking medications, cardioversion, ablation or having a pacemaker placed.

Edema is the accumulation of excess of interstitial fluid. It can appear on the brain, around the heart, intracellular, or generalized usually found in the lower parts of the body and is affected by gravity and position. Edema is usually prevented by proper balance between capillary filtration and osmotic uptake of water and having a lymphatic system that properly drains.
There are several external image 230px-Elephanti.jpgcauses of edema. Having elevated blood pressure causes an increase in capillary pressure which results in excessive filtration. Venous obstruction happens when there is a blood clot in a vein; this causes a congestive increase in capillary pressure. When a person is having an allergic reaction to something or another type of inflammatory reaction there is leakage of plasma proteins into the interstitial fluid. Hypothyroidism is the cause of myxedema. Liver and kidney disease also decrease plasma protein concentrations.

Elephantiasis is an obstruction of the lymphatic vessels caused by a parasite which is transmitted by a certain type of mosquito. This parasite is called the filarial worm which enters the lymphatic system causing an obstruction. The areas mostly affected are the legs and the external genitals. First signs of infection are the inflammation of the lymph nodes, red streaks along the infected area with pain and tenderness along with a fever. Ulcers and tubercles start to form, thickening and discoloring the skin. There are certain drugs that will kill the parasites. Bandaging and elevating the affected area helps to relieve the swelling. With better sanitary control it is easier to eliminate the carrier insects which in the long run, may even eliminate this disease. I put this information in here because I watched a movie on parasites for microbiology, thought it was interesting.

My mother had a heart attack in 1999. This is something I will never forget because my parents were out in the hills for a vacation. My family was in Waverly watching Stan play softball. His cell phone was dead and when we got home there were ten or more calls on our regular phone from my sister. I couldn’t believe it; mom had never said a word about feeling sick or having chest pain. While she was in the hills
Susan, Parents Kenneth and Dorothy
they went on a tour with a lot of steps and she didn’t want to go, later that night the pain got so bad she finally had to say something to my day and he called the ambulance. She ended up having a stent placed, was doing great, had her strength back and we were able to bring her home. Looking back my father could see the signs and I even remember once at a softball game where she wasn’t keeping up with me while walking back to the car. She always kept pace with the rest of us. After she was healed from the surgery, mom needed to have a stress test done. I got to be there to watch, she was doing great, was not short of breath but after 8 min Dr. Dan shut it down and told her that she had failed. There were changes on the EKG, something was not quite right. We took her to Sioux Falls for an angiogram next thing we know Dr. Vaska is talking to us saying how she needs triple bypass and that they will wait until Monday to perform the surgery. My mother kept saying she felt fine, she was not having any chest pains like before. The surgery was a success and she healed fast and has been doing great every since. So reading and learning more about how all these things are related was interesting for me. With working in the clinic, we have our patients that come in with chest pain, indigestion or other symptoms that put up a red flag. They get a chest x-ray and EKG right away plus a cardiac blood work up. We never take a chance when it comes to someone’s heart. The patient may still be in denial but the doctors have the proof in their hands with changes on an EKG or a Troponin level that is elevated. I have preformed several EKGs over the years so this was a good refresher on what to look for when examining the EKG report.

Essential Question: What are the three most important variables that affect blood pressure?
Cardiac Output: Is the amount or volume of blood that each ventricle pumps per min. (ml blood/min). Cardiac output can be affected by the sympathoadrenal system, which includes the autonomic system and the adrenal medulla these work together to monitor the bodies fight or flight response. The two ways the cardiac output is affected is by the positive inotropic effect (increased Ca2+) on the contractility and by the positive chronotropic effect on the cardiac rate. Cardiac output is decreased when the heart beats slower.
Stroke Volume: Is the amount or volume of blood in milliliters (ml) that is pumped out of each ventricle with each heartbeat. There are three things that determine the stroke volume: 1) End diastolic volume (EDV), which is the volume of blood in the ventricles at the end of diastole, this is relaxation. Or you can look at it as the amount of blood in the ventricles before they begin to contract. The experts call this a "preload" because of the workload that the ventricles have prior to the contraction. If EDV is increased then there will be an increase in the stroke volume, this is known as Frank-Starling law of the heart. 2) Total peripheral resistance (TPR) and 3) Contractility, which is the strength of the ventricular contraction. The more blood that is pumped, the harder the ventricles are contracting.
Total Peripheral Resistance: Is the amount of (or lack of) resistance of the blood flow in the vessel walls. The higher the peripheral resistance, the higher the pressure. When the pressure in the atrium is equal to the ventricle pressure the blood flow stops, known as "afterload". The end-systolic volume is the amount of blood left in the ventricles at the end of systole, or after contraction. The greater the total peripheral resistance the lower the stroke volume. Any changes in the diameter of the vessel because of vasoconstriction or vasodilation will affect blood flow.

If there is an increase in any of these, cardiac output, stroke volume or total peripheral resistance, there can be an increase in blood pressure. To help keep things under control one of the other variables will compensate or decrease. The kidneys play a big part in blood pressure by regulating blood volume and stroke volume. The sympathoadrenal system can increase blood pressure with secretion of epinephrine or norepinephrine. It also can stimulate vasoconstriction of arterioles which will increase cardiac output. When the constriction is of the renal blood vessels, there is a decrease in urine output.

For blood pressure to be kept at a normal range there needs to be specialized receptors. Reflexes that help to maintain blood pressure are the baroreceptor reflex and the atrial stretch reflexes.

Baroreceptor Reflex: these are what are called stretch receptors. They consist of: 1) sensors, which are the aortic arch and carotid sinuses. 2) integrating centers, which are the vasomotor and cardiac control centers of the medulla oblongata. 3) effectors, consisting of the parasympathetic and sympathetic axons to the heart and blood vessels. This reflex maintains a normal blood pressure on a beat to beat basis. Baroreceptor reflex is more sensitive to decreases in pressure than to increases and to sudden changes in pressure than to more gradual changes. Example is going from a lying down to a standing position.
Atrial Stretch Receptors: Located in the atria of the heart. These are stimulated by increased venous return. A response to tachycardia since the sympathetic nervous system is stimulated. A decrease in ADH (antidiuretic hormone) will result in more urine output and a lower blood volume. An increase in ANP (atrial natruiretic peptide) will lower the blood volume by increasing the excretion of urinary salt and water.

All information for the cardiology sections were taken from our book Human Physiology, Sturart Ira Fox, 12th Edition. Anatomy and Physiology for Dummies by Donna Rae Siegfried, Wiley Publishing, Inc. Encyclopedia & Dictonary of Medicine, Nursing & Allied Health, 5th Edition, Miller-Keane. WebMD web site.