Physiology of the Heart

Physiology of the Heart Anatomy 1. Illustrate and describe the gross anatomy of the heart. Include the layers of the heart wall, chambers, valves, structures and major blood vessels connected to the heart. Indicate direction of flow. Include your own diagram. The heart is a complex biological electrical pump. It is found in mediastinum of the thorax. Surrounding the heart is the pericardium, which contains serous fluid, allowing the heart to move freely within the membrane. (1) The outside surface of the heart is known as the epicardium, the inner surface of the heart muscle; the myocardium and the innermost surface; the endocardium. The heart itself can be separated into 4 chambers which are filled with blood when the heart is relaxed, and pumped out of when the heart contracts. (1) They are separated into the left and right side, which are distinct, and into atria (singular atrium) and ventricles. The atria and ventricles are separated by the coronary sinus or AV groove. Between the right atrium and right ventricle is the Tricuspid Valve which is made up of 3 leaflets. Deoxygenated blood feeds into the right atrium from the Vena Cava (which is separated into the superior and inferior vena cava – superior from the head, neck and arms and the inferior from the lower limbs and the abdomen). (1) The right ventricle feeds into the pulmonary artery which carries deoxygenated blood to the lungs. Blood is then oxygenated and fed back to the heart through the pulmonary vein. This fills the left atrium and subsequently, flows through the Mitral Valve into the left ventricle.. (1) As the heart contracts, this pushe s the blood into the aorta, which feeds through to the major arteries in the body. Within the base of the aorta lies some very small arteries known as the coronary arteries. These feed the heart tissue with oxygenated blood and drain into the right atrium, with the systemic deoxygenated blood. (1) 2. Briefly describe the function of the pericardial cavity As mentioned before, the heart and roots of the great vessels (aorta, vena cava, pulmonary vein and artery) is surrounded with a very strong membrane known as the pericardium. It is a double walled structure, made up of the fibrous pericardium on the outermost surface of the heart, and an inner serous pericardium. (1)The fibrous pericardium is made of very dense connective tissue, and contains many collagen fibres. It prevents overfilling of the heart and anchors it to the surrounding walls of the thoracic cavity.(2) The serous pericardium can be differentiated into two layers, the parietal layer, which is fused and continuous with the fibrous pericardium, and the visceral pericardium which can also be known as the epicardium. Between these layers is a potential space known as the pericardial cavity, filled with about 50mls of serous fluid. (2) This potential space is extremely important as it allows the heart to move freely within the space by keeping the transmural cardiac pressure s very low, as well as facilitating atrial filling during ventricular systole by maintaining a negative pericardial pressure. It also prevents hypertrophy of the heart under strenuous exercise, keeping the heart muscle a relatively constant size. (2) The membranes completely isolate the heart from the thoracic cavity which prevents spread of disease or infection. Its importance is particularly obvious when there are cases of pericardial tamponade – build-up of fluid in the pericardial cavity which causes compression of the heart. (2) Without the pericardial cavity, the heart would not be able to pump as efficiently as it would have to overcome the pressures exerted on it by the surroundings, which would just add to the work of the cardiac muscle.(2) 3. Illustrate and describe the anatomy of the electrical conduction system of the heart. Briefly describe the blood supply to the electrical conduction system. The electrical impulse originates at the Sino Atrial Node in the right atrium. This impulse travels through the cardiac muscle – through the many gap junctions, as well as through the intermodal pathways or Bachman’s bundle. (1) At the level of the atrio-ventricular valves, there is another node called the Atrio-Ventricular Node (AV Node) that has properties that delay the stimulus. Following this, the impulse travels down the left and right bundle branch fibres in the ventricular septum, into the bundles of His which travel up the ventricular walls and branch into Purkinje fibres. The stimulus reaches the apex of the heart first, and then travels up towards the outflow tracts resulting in coordinated depolarisation and contraction. (1) This coordination is a result of both the coordination of the stimulus as well as the layout of the myocytes, as well as the ease at which the electrical signal is able to propagate through cardiac muscle.(3) Sino Atrial Node is usually supplied oxygenated blood by the Right Coronary Artery (RCA) or the Left Coronary Artery (LCA) though this is variable. In most people, the AV Node is supplied by the AV Node Artery branch of the Posterior Descending Artery which is a branch off the RCA, though in some it will be supplied by the same artery, just as a branch of the left Circumflex Artery. (3) All of the fibres downstream from this point are supplied by the Left Anterior Descending artery with exception of the His fibres, which are also supplied by the AV Node Artery. (3) Conduction 1. Illustrate and describe the propagation of a single beat through the electrical conduction system and the relationship to the surface ECG. Include in your answer a discussion on conduction velocity through the various components and list the normal ECG intervals. An ECG works by detecting the electrical change in the heart through sensors that are put on the surface of the skin. Direction is determined through the use of electrical vectors generated by many hundreds of individual cells. (4) The P wave is the first small wave in the ECG. It reflects the spread of depolarisation through the atria from the SA node. The normal range is  ¬0.08-0.1seconds. After the P wave there is a brief isoelectric stage when the current is flowing through the AV node, and the conduction is slowed. This is known as the PR interval and it is usually 0.12-0.2seconds. (4) The QRS complex shows the very strong electrical signal and resulting contraction that forces blood into the aorta and pulmonary artery. It is about 0.06-1seconds, which shows just how fast depolarisation spreads through the ventricles (its shape has been idealised on the schematic below). (1) After the QRS complex there is another isoelectric period which indicates plateau phase of depolarisation. The T wave is the repolarisation of the ventricles – in preparation for the next beat the duration between the P and T waves usually approximately 0.2-0.4seconds, though this is dependent on heart rate.(4) The U wave is a very rarely seen artefact and is thought to reflect the repolarisation of the papillary muscles that control the valves. (1) Figure 3: Electrocardiogram schematic. Based on the diagram from Bruce Shade: Fast and Easy ECGs (4) 2. Briefly describe the ionic movement that occurs during each phase of the myocardial and SA node action potential. Include a labelled illustration of both action potentials in your answer. The myocardial action potential is quite complex with influxes and effluxes of 3 different ions, changing the membrane potential as contraction occurs. There are 5 distinct phases of the myocardial action potential. (1) These are shown in the figure 4 below. Between phase 0 and 2 there is an absolute refractory period where it is impossible to invoke another action potential. This allows even more coordination of the spread of a stimulus.(1) The ECG trace shown below the action potential shows where the stages of contraction occur that can be extrapolated out into the ventricular depolarisation (QRS complex) and the ventricular repolarisation (T wave) Depolarisation Repolarisation ECG Cells in the SA node are pacemaker cells and have a property which is known as automaticity. They do not need activation to fire an action potential.(1) They are very similar to myocytes but have several key differences in their action potentials (see figure 5). Phase 0 is significantly slower in the pacemaker cells of the SA node as it is dependent on the activation of L-type calcium channels instead of Sodium channels, which makes the depolarisation significantly slower at this phase.(1) During Phase 1, repolarisation of the membrane occurs leading to a period of pacemaker potential, where the membrane potential gradually depolarises through constant Na2+ leakage into the cell. When the action potential is triggered automatically, Phase 0 commences. Pacemaker cells do not have phase 1 and 2. (1) Figure 5: SA Node Action Potential 3. Describe the role of escape pacemakers in the conduction system. The SA node is entirely autonomous which means that it does not need external innervation or activation to fire. Other areas of the heart are heteronomous which means they need an external source of action potential to stimulate them to produce one. (1) Some specific cells along the conduction fibres possess both of these properties. This is so that if the SA Node fails for some reason, they can activate themselves and this allows the heart to beat, even without a functional SA Node. (1) Each area will have a slower rate of autonomy as it gets further downstream from the SA Node to prevent competition between the different areas. (5) This is very useful when the SA Node fails, and the AV Node takes over as the AV Node can maintain a BPM of about 40-60 BPM which is still slow but can maintain life for a reasonable amount of time. Further downstream the Bundles of His can maintain about 25-40 BPM and the Purkinje fibers about 15-30BPM which cannot maintain life for any reasonable perio d of time, though it can help during some forms of arrhythmias which prevent the signal reaching the Purkinje fibers/Bundles of His. (6) This is also where Escape beats originate, and this is seen on the ECG as a widened QRS Complex. 4. Discuss the role of decremental conduction in the AV node. Decremental conduction means the more the AV node is stimulated, the slower it conducts the stimulus. This allows a control over how fast the blood is pumped out. The faster the contractions, the less time between them for filling of the heart and therefore less blood is pumped out. (1) The AV Node slows down the stimulus so that there is an element of control of how fast the signal reaches the apex of the heart and prevents the ventricles from contracting so fast that the cardiac output drops too low.(7) It is extremely important that the AV node is able to slow down the conduction velocity, even as it gets activated more and more frequently. It is even able to block out some signals. This is clearly seen in patients with atrial fibrillation. (7) The only way for the signal to travel to the ventricles is through the AV node (due to the insulating fibrous skeleton that prevents atrial cell – ventricular cell depolarisation spread). (7) If the AV node allowed conduction of ever y single depolarisation, an atrial fibrillation would be fatal as the cardiac output would become too low, and the ventricle would go into ventricular fibrillation, which is fatal without intervention. It is the decremental properties of the AV node that prevent this from occurring. (7) 5. Explain the term ‘functional syncytium’ and its significance in the cardiac muscle contraction. A functional syncytium by definition is a group of cells that are both mechanically and electrically bound to one another, so they are able to function as one. This is extremely important in cardiac muscle contraction.(1) One of the main reasons that the heart is able to work so effectively is that the contractions and depolarisations are always coordinated. (8) There is no coordination without communication, which are the electrical signals that are passed between the myocytes. (1) This extremely effective communication is completely useless unless the cardiac myocytes are mechanically bound, so that when they do contract, it is as a whole. The specialization, which is unique to cardiac muscle, that allows it to be a functional syncytium is a structure called intercalated discs. (8) They contain three types of intercellular junctions; many fascia adherens and desmosomes, for mechanical connection, and many gap junctions allowing for direct communication between neighbouring cells. ( 1) Another interesting property that contributes to the functional syncytium is the fact that cardiac muscle has an innate rhythmicity. This means that at the level of the muscle, the myocytes will exhibit the rhythm of the cell with the fastest rhythm. This makes regulating and coordinating the speed of the heart beat very easy and effective. (8) References 1. Boron WF, Boulpaep EL. Medical Physiology [Internet]. Elsevier Health Sciences; 2008 [cited 2014 Apr 9]. Available from: http://books.google.com/books?id=HlMJRw08ihgCpgis=1 2. Watkins MW, LeWinter MM. Physiologic role of the normal pericardium. Annu Rev Med [Internet]. 1993 Jan [cited 2014 Apr 9];44:171–80. Available from: http://www.ncbi.nlm.nih.gov/pubmed/8476238 3. Futami C, Tanuma K, Tanuma Y, Saito T. The arterial blood supply of the conducting system in normal human hearts. Surg Radiol Anat [Internet]. 2003 Apr [cited 2014 Apr 9];25(1):42–9. Available from: http://www.ncbi.nlm.nih.gov/pubmed/12819949 4. Shade BR, Wesley K. Fast and Easy ECGs [Internet]. McGraw-Hill Higher Education; 2007 [cited 2014 Apr 9]. Available from: http://books.google.com/books?id=hibqIAAACAAJpgis=1 5. Adams MG, Pelter MM. Ventricular escape rhythms. Am J Crit Care [Internet]. 2003 Sep [cited 2014 Apr 9];12(5):477–8. Available from: http://www.ncbi.nlm.nih.gov/pubmed/14503433 6. Vassalle M. On the mechanisms underlying cardiac standstill: Factors determining success or failure of escape pacemakers in the heart. J Am Coll Cardiol [Internet]. Journal of the American College of Cardiology; 1985 Jun 1 [cited 2014 Apr 9];5(6):35B–42B. Available from: http://content.onlinejacc.org/article.aspx?articleid=1111307 7. Cardiac Electrophysiology: From Cell to Bedside 5th edition ISBN: 9781416059738| US Elsevier Health Bookshop [Internet]. [cited 2014 Apr 9]. Available from: http://www.us.elsevierhealth.com/cardiology/cardiac-electrophysiology-from-cell-to-bedside-expert-consult/9781416059738/ 8. Cardiac Muscle | histologyolm.stevegallik.org [Internet]. [cited 2014 Apr 9]. Available from: http://histologyolm.stevegallik.org/node/146

Human Nature in Chapter Four of Lord of the Flies Essay -- William Gol

Golding's views about human nature are displayed and developed quite extensively in chapter four. This essay is going to explore what they are and how they are portrayed throughout the duration of this chapter. The chapter reveals that Golding feels that humans enjoy, or are at least fascinated with controlling things. This is first shown when Henry was sitting at the beach and "tried to control the motions of the scavengers", with a stick. "He became absorbed beyond mere happiness as he felt himself exercising control over living things," here, instead of looking after nature and taking responsibility for things as you would do in a society, all he is doing is trying to control them. This is shown again when Jack brings back a pig, "Look! We've killed a pig, we stole up on them, we got in a circle," they enjoyed frightening the pig and controlling its movements by limiting it in a circle. When angered by Piggy and his own hunters, Jack is driven to violence, "He took a step, and able at last to hit someone, stuck his fist into Piggy's stomach. Jack smacked Piggy's head. Piggy's ... Human Nature in Chapter Four of Lord of the Flies Essay -- William Gol Golding's views about human nature are displayed and developed quite extensively in chapter four. This essay is going to explore what they are and how they are portrayed throughout the duration of this chapter. The chapter reveals that Golding feels that humans enjoy, or are at least fascinated with controlling things. This is first shown when Henry was sitting at the beach and "tried to control the motions of the scavengers", with a stick. "He became absorbed beyond mere happiness as he felt himself exercising control over living things," here, instead of looking after nature and taking responsibility for things as you would do in a society, all he is doing is trying to control them. This is shown again when Jack brings back a pig, "Look! We've killed a pig, we stole up on them, we got in a circle," they enjoyed frightening the pig and controlling its movements by limiting it in a circle. When angered by Piggy and his own hunters, Jack is driven to violence, "He took a step, and able at last to hit someone, stuck his fist into Piggy's stomach. Jack smacked Piggy's head. Piggy's ...

Students Deal with Stress

Students Deal With Stress â€Å"Hey, I’m stressed of homework and studying, let’s have a drink†, said by the majority of freshmen students. Alcohol is the easiest coping mechanism to students because we are exposed to alcohol more than anything else. Throughout high school, most students are shown â€Å"the ways† of drinking. Lots of students find out the positive outcomes of drinking; relaxation, relief of stress, temporarily happiness, but they tend to avoid the negative outcomes; laziness, forgetfulness, and physical damage to the body.Everyone has personal stressors that drive them to drinking. Freshmen have very similar and critical stressors though. Home sickness, studies, lack or loss of relationships are things that students deal with every day. With every stressor, there is a way to cope with it, without resorting to alcohol. For example, when students miss home they should try to make their new place just as comfortable and they should never be s hy to call their parents. To deal with lost friends from moving on to university, make new friends!You can still keep in touch with past friends, but making new friends while at university is an essential part of feeling happy and relieving stress while at school. In addition, joining a club or sports team helps to make new friends and is useful as a stress reliever. For example, I joined a volleyball team, and this is a good time to get out of my place to go have some fun, and forget about school for a bit, this usually results in me avoiding drinking. To regards with studying, take breaks, treat yourself and remember trying hard is all you can do, so never be disappointed if you put forth an honest effort.There are several ways to avoid stress. Make new friends, go out for supper to avoid cooking or cafeteria food, call family and friends, have leisure times, join a team, don’t cram study, have effective time management so daily schedules aren’t so jam packed and str essful, these are all great ways to overcome stressors without using alcohol or drugs. This being said, drinking alcohol at high rates is detrimental to health, but drinking responsibly isn’t a bad thing to do. In my opinion, there is always room for a couple of beers on the weekend with friends.There are several ways of coping with stress. Meditation, self-talk, and therapy are all coping strategies used to release psychological stress. Coping mechanisms are better than avoiding them, because these coping techniques actually eliminates stresses on your mind, while things like sports and friends just put stress away temporarily. For example, at the beginning of the year I had my childhood dog pass away, and one of my friends pass away in a car accident. To deal with this major stressor, I chose to get therapy because it was a very hard thing to deal with by myself at university.Of course when this tragedy happened, I thought of drinking the pain away was an option, but I knew this wasn’t the best solution. Therapy worked great, it actually decreased the amount of stress I had every day and it helped me move forward with my life. Stressors are easy to overcome, find something to occupy personal time to avoid stress (sports, friends, leisure time, etc. ) or coping mechanisms to deal with them (therapy, meditation, self-talk, etc. ). Nevertheless, if these stress relievers were taught to students more, there would be less university freshmen resolving to drinking when they are stressed.University students do deal with major and minor stressors day-to-day and they can be dealt with properly rather by overusing drugs and alcohol. Thus, promotion of stress relievers would be beneficial for the student population because it would help their health, budget and success rate. In conclusion, drinking alcohol is a very unhealthy and stupid way of dealing with stress and there are several healthier and smarter ways of dealing and coping with stress. Reference s Fahey, T. D. (2010). Fit and well, core concepts and labs in physical fitness and wellness. (2nd ed. ). Insel, P. (2012). Core concepts in health. (Canadian ed. ).

My Childhood - Original Writing - 989 Words

In various chapters of my childhood, all I can remember is her. In those moments, I am a character shrunk to microscopic proportions, and she is the frightening giant towering over my entire universe. I become invisible. I collapse into myself, engulfed by my mother’s fury and love and contempt: all that threatened to tear me apart only to piece me together again with a soft â€Å"You know how much I love you, don’t you?† And don’t I? Had my mother’s disquieting presence in my childhood overshadowed completely the happy memories of digging flowerbeds, of building the treehouse in the syrupy warmth of some late summer, of the dizzying feeling of being spun around and around in her arms? The answer itself is a paradox. There are two things of which I was certain. The first: that my mother must love me to the best that she is able. The second: that I have never felt safe in her wake. Family picnics go hand in hand with frantic 911 calls, an over-froste d birthday cake precedes a painful divorce, the finger painting taped to the fridge obscures the domestic abuse pamphlet buried in my father’s sock drawer. In the earliest years of my childhood, my mother’s periods of normalcy became punctuated by ever more frequent and pronounced episodes. During these violent outbursts, I found refuge with my brother; together, we would hide under a tent of blankets, pretending that our anxious whispers could drown out the deafening roars of our parents in the living room, wishing to be oceansShow MoreRelatedMy Childhood - Original Writing Essay1683 Words   |  7 Pagesleaves would crunch beneath my steel covered toes and the fresh, cool forest wind would numb my cheeks. In my childhood years, several years after my parents’ divorce, my dad would take my sister and I out to hunting camp on the weekends. It was usually deer hunting season when we would travel there. My sister and I would hunker down and stay quiet in the earl y mornings before the sun would come up and at dusk before it would get dark. These were prime deer hunting times. My little sister Lizzy and IRead MoreMy Childhood - Original Writing Essay1312 Words   |  6 Pagesreminds me of my childhood – perhaps a name, a memory, a smell, a picture - who knows what brings the memories into my head? But recently, a memory came back with the sounds, smells, tastes, and sights that I hadn’t experienced in about 45 years. Those memories comfort me, but now smoke clouds my treasured past. Almost two years ago, my last uncle passed away. That was the end of the older generation for me. I cherish the moments I spent with him the summer before he died. My brother andRead MoreMy Childhood - Original Writing1035 Words   |  5 Pages My mom got remarried the year before I started first grade. We moved from our small two bedroom home in Austin, MN to a four bedroom farmhouse that was built in the 1890’s. I grew up most of my childhood in the farmhouse. When I was in 9th grade my family started to build a house just a few feet away from the farmhouse. It took about 5 years to finish the project, with many setbacks along the way. It wasn’t until March of this year that I actually got to live in the beautiful house that my step-dadRead MoreMy Childhood - Original Writing990 Words   |  4 Pageswas in for a shock. In 2003, my parents announced that they were getting a divorce. At first I didn’t really understand what was going on as I was only 8 years old. I overlooked the fact that there were always tears in mum’s eyes and that most nights I could hear constant yelling. My innocents ignored the reality of what was really going on behind the closed doors. My dad was forced to move out and he struggled to find a permanent house to live in. He stayed with my grandma in the mean while. IRead MoreMy Childhood - Original Writing985 Words   |  4 PagesMy childhood was never exactly normal or easy. My parents had split up when I was three and I was sent to live with my grandparents. My dad moved back to Ohio and I never had much of a relationship with him. My mom stayed in North Carolina, but moved to a different city. She had a nice job, a nice relationship, and she even got to visit her kids. I was always much closer to my mother than my father. A few years later, my mom lost her job and decided to move in with us to help take care of everyoneRead MoreMy Childhood - Original Writing Essay944 Words   |  4 Pagesdid my mom lose her voice?† I asked my grandma with a heavy tone. â€Å"She was 20 years old, almost the same as your current age. I still remember the day that she came to me and said ‘mom, sometimes I feel nothing in my ear. I don t know how to explain my feeling to you but it s painful and scary.’ I got shocked. She was young and she has her dreams to achieve. How can she be stuck at her 20s?† I thought my feelings was the exactly same as my grandma. Slithering beads of rain sluiced down my windowRead MoreMy Childhood - Original Writing1607 Words   |  7 Pagesurbanization, my parents frequently would bring my two younger brothers and I to parks throughout the city. Playing on the jungle gyms, swinging on the swings, and just running around was such a normal part of my childhood. I spent countless hours breathing in fresh air, instilling me with a strong appreciation for the outdoors and a sense of inner peace in the outside world. As I aged, my parents allowed me to venture to the parks nearby by myself. However, I was rarely alone since frequently my youngerRead MoreMy Childhood - Original Writing1005 Words   |  5 PagesMy Protectors â€Å"Family is like branches on a tree we may grow in different directions yet our roots remain as one.† When I think of this quote, I think a lot about my brothers. When I was younger I hated having three brothers. It was probably one of the worst things in my life. It was until I got older that I realized that they were there to protect me. Growing up with three brothers was a constant circus. I don’t think we ever did something that was nice and benefited all of us. Andrew, CoryRead MoreMy Childhood - Original Writing Essay708 Words   |  3 Pagesup that day my life would change. In second grade, during the summer, my parents were fighting. A common occurrence in my household, so there was no reason to be worried. My siblings were at my grandma’s house while I wanted to stay with my mom and dad. Unfortunately, my mom agreed to let me stay. The day seemed normal enough in the morning. I woke up to watch Dora and Diego. I ate my cereal my father made for me. I loved when Emily and Bryce were gone; I had all the attention of my mom and dadRead MoreMy Childhood - Original Writing954 Words   |  4 Pageswere told just like every other child about stranger danger. The only difference in my childhood as opposed to every other child in my neighborhood was my older brother. And he had a very large impact on my life. Salameh, or Sam for short, is a first generation Kuwaiti-American. While all of my schoolmates would head off to vacation with their American-dream family, people would always ask our family if Sam was my boyfriend tagging along on vacation. And when these people (waitresses, sales clerks