Cardiovascular system and health promotion

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Alice Pryce-Williams: NUR 261                                                                                    

This assignment is going to be based on the structure and function of the cardiovascular system and how homeostatic mechanisms work with the system to regulate it.  The many functions of the heart will be recognised, but the main focus will be on the regulation of heart beat.  Various Health Promotion initiatives will then be looked at in context to how they help people maintain a healthy heart and how successful these initiatives are in doing this.  At some point, a definition of homeostasis and a definition of health promotion will also be given.  Throughout the assignment, my own personal thoughts and accounts will be given to demonstrate the workings of the cardiovascular system and how effective health promotion is in reality.  

The cardiovascular system consists of two components.  Firstly there is the heart and secondly the blood vessels.  The heart is a muscular organ which is about the size of a fist and is cone shaped, according to Mader (2006). It is situated in-between the lungs directly behind the sternum.  There are three layers of tissue that make up the heart according to Waugh and Grant (2006); the myocardium, which makes up the largest proportion of the heart and consists largely of cardiac muscle; the endocardium which consists of connective tissue and the pericardium, which consists of two sacs and secretes a small amount of lubricating liquid to ensure that the heart can work without extensive damage (Hills 1988).

The heart works along with the blood vessels to form the system for the flow of blood around the body.  These blood vessels form two pathways; one pathway of blood vessels through the lungs is called the pulmonary circuit and the other pathway to the rest of the body is called the systemic circuit (Cohen and Taylor 2005).  Within both of these circuits there are veins and arteries.  The veins are blood vessels that take blood towards the heart and the arteries take blood away from the heart (McCall and Tankersley 2007).

Within the heart, there are four chambers; two ventricles and two atria’s, one of each on the right side and on the left side of the heart (Katz 2006). The ventricles are thick walled as they pump the oxygenated blood from the heart around the body, whereas the atriums are thin walled as they receive the venous blood according to Seifter et al. (2005).  Contained inside the heart are also four valves which control the flow of blood and prevent the backflow of blood.  These valves are called the tricuspid, pulmonary semilunar, mitral and aortic semilunar valves (Ehrlich and Schroeder

2004).

The hearts cardiac cycle is controlled by two pacemakers which are the sinoatrial node (SA node), which is a collection of specialized cardiac fibres located in the right atrium and the atrioventricular node (AV node) which is situated between the two ventricles (Margulies 2004).  There is also the bundle of His within the heart that stems off to left and right branches, which conducts impulses from the AV node down through the ventricles (Hargrove-Huttel 2004).  Marieb (2006) states that cardiac muscle, unlike skeletal muscle, does not require nerve impulses to stimulate it, but it can contract independently.  However, the heart still does receive impulses form the central nervous system (CNS) anyway.  It is the intrinsic system that is responsible for the heart not requiring impulses as this is the system that automatically stimulates the cardiac muscle according to Waugh and Grant (2006).  The reason for this is that the heart has unique nodal tissue which is made up from muscular and nervous tissue as suggested by Mader (2006).  This tissue is located at the SA and AV nodes.  The intrinsic system works hand-in-hand with the autonomic nervous system.  The autonomic nervous system controls the heart beat by altering the speed of impulses generated by the SA node (Alexander et al. 2000).    The autonomic nervous system has two sub divisions to do this, which are the parasympathetic division which is responsible for decreasing SA and AV activity when the body is at rest, and the sympathetic division which is responsible for increasing SA and AV activity when the body is active (Brown et al. 2006).  

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The cardiac cycle, or heart beat, starts at the top of the heart at the SA node.  This sends the impulses, or beat, down the cardiac muscle fibres of the atria to the AV node (Won Chung and Chung 2007).  When the impulses reach here, there is a slight delay so that the atria can finish contracting before the ventricles start contracting (Porth 2005).  The impulses are then sent from the AV node down through the ventricles via the AV bundles.  Each one of these cycles take approximately 0.8 seconds in the normal resting adult and so the average ...

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