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
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).
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 resting adult’s heart rate is approximately 70 beats per minute (Alexander et al. 2000).
There are several functions of the cardiovascular system. One function is for the blood to deliver oxygen and nutrients from the outside environment to all cells in the body. (Klabunde 2005). The other part of this function is for waste products to be removed from the body such as carbon dioxide (Batzel et al. 2007), and for oxygen to be put back into the blood for the next cardiac cycle. These functions and systems in the body need to be controlled to ensure stability within the body by homeostasis.
Homeostasis is the relative steadiness of the inner environment of the body even though external conditions may vary (Mader 2006) and Schulkin (2003) describes homeostasis as the control and maintenance of variables within the body such as blood pressure or temperature. Homeostasis is important within the body as it allows receptors in the heart, brain and blood vessels to detect the heart beat and control it using messages from the autonomic nervous system (Elling et al. 2005). Homeostasis, with regards to heart beat, works by the nerve receptors of the body detecting what is going on in the external environment and helps the body react. The stimulation of the external environment could be fear, stress, exercise or rest. The nerve receptors of the body send messages to the CNS, which in turn send messages to the heart via a sympathetic or parasympathetic nerve, so that the heart can react to the stimulation and speed up the heart beat or slow it down respectively (Nowak and Handford 2004).
An example of how this works is if I was to start running at a steady pace, the muscles in my legs would require more oxygenated blood at a faster rate then when I am resting, so a greater portion of the oxygenated blood is directed to the active muscle (McArdle et al. 2007). The receptors in the tissue would detect this need, relay messages to the CNS, which would in turn send impulses to the heart via the sympathetic nerve to make it beat at a faster rate. This in turn would mean that oxygen rich blood would be constantly delivered to the muscles at a faster rate (Brown et al. 2006) and my respiratory rate would increase to get more oxygen into the blood. The brain also stimulates the adrenal glands so they release adrenaline as this increases oxygen intake and muscle performance according to Viru (1985).
When the human body is at rest, a mechanism called negative feedback, helps keep variables in the body, such as heart rate, close to its normal range (Bassett 2005). It does this by resisting or adjusting the variable when an abnormal change in value is detected.
Health promotion is an approach of promoting positive health to the population and identifying the risk factors of poor health and promoting strategies for good health (Bunton and Macdonald 1992). There are three types of prevention involved with health promotion. These are primary, secondary and tertiary prevention (Dever 1984). Primary prevention is the stage of health promotion where action is taken to prevent, rather than treat a disease (Department of Health 2008); Secondary prevention is where the disease is detected in its early stage and the appropriate intervention is used such as treatment or education, and tertiary prevention is where the main aim is to minimise the impact of the disease.
There are many groups and organisations who promote health preventions, but the main type that will be talked about is primary prevention. One health promotion group, whose main initiative is for a healthy heart, is the British Heart Foundation. The British Heart Foundation (2008) states that “Our vision is of a world in which people do not die prematurely of heart disease”. They have many heart health initiatives in place, with some being at least 30 minutes of exercise, five days a week, eating healthily such as five portions of fruit and vegetables a day and reducing high fat intake. The rationale behind reducing a high fat intake is to reduce the amount of cholesterol in the body. Daniels (2002) suggests that a high fat intake can cause high cholesterol which in turn can lead to atherosclerosis, and Null (2006) suggests that a high fat diet can lead to hardening of the arteries. A low cholesterol diet can reduce the chances of a person developing coronary heart disease (British Heart Foundation 2008). Cholesterol is a waxy fat that travels around the body via the bloodstream (Freeman and Junge 2005); but it is not always bad for the body.
Cholesterol plays a vital part in many cellular functions (Pottle 2007). The positive and negative effects of cholesterol all depends on what type of fat is mainly eaten in a person’s diet. If a person was to have a high saturated fat intake, then this could lead to an increase in the amount of low density lipoproteins (LDL) in there blood stream (Institute of Medicine 2005); lipoproteins being made up of cholesterol and protein. These ‘bad’ LDL’s carry cholesterol around in the blood stream and deposit it in cells. This is what can cause the build up of an atheroma, an abnormal growth of cholesterol, within the arteries which can lead to atherosclerosis (Faergeman 2003). It is fats such as monounsaturated fat that is good for the body. This is found in foods such as nuts, seeds and olive oil. Monounsaturated fats’s help lower LDL in the bloodstream and keep High density lipoproteins (HDL) at a stable level within the body (British Heart Foundation 2007). It is these HDL’s that carry any surplus cholesterol out of the bloodstream back to the liver for excretion, which means that the fat is not deposited in the arteries (McArdle et al. 2007) and so the risk of coronary heart disease is lowered.
The British Heart Foundation (2008) also suggest that swimming is a good form of exercise for the heart, but state that any form of exercise is good. They suggest that the aim is to do 30 minutes of exercise, five times per week. Part of the rationale behind this is that regular exercise has been shown to increase the amount of HDL’s in the body (Porth 2006). This means that the ‘good’ cholesterol will be increased in the body, leading to LDL levels being low. It has also been shown that people who exercise regularly could develop extra coronary arteries, which would mean that they have a richer blood supply around the heart (Corbin and Lindey 2006). The Department of Health (2004) has a report based around the five a week exercise scheme called ‘At least five a week: evidence on the impact of physical activity and its relationship to health’. In this, there are details on how to implement this initiative, but there are also warnings about how to go about it, especially if the person has an existing health problem such as a history of heart attacks. For this, they provide information on how to slowly build up an exercise plan in a safe way.
The Department of Health (2008) also carried out a recent study that found for each portion of fruit or vegetables a day, it lowered the risk of coronary heart disease by 4% and the risk of stroke by 6%. This backs up the British Heart Foundations (2008) claims as they also suggest that regular exercise can lead to a healthier heart.
The Department of Health (2008) also suggest that fruit and vegetables contain a good variance of vitamins and minerals and its not only these on their own that are good for the heart, but the way in which they interact together.
I think that the British Heart foundation presents their information well, in an easy to understand format, but they need to reach out to the wider population. I have looked in chemists and General Practitioners surgeries for British heart foundation material, but was disappointed not to see their booklets. I think they need to reach out to places like this, including clinics, so that every one can benefit from their information, not just people mainly with computers. However, everything that the British heart foundation do state has sound research behind it, and many other sources and authors i have looked at say the same, such as the Food standards agency (2008) who also state that a low fat diet can reduce the chances of narrowing of the coronary arteries so they suggest a low fat diet to keep the heart healthy. From my own point of view, I would say that these health promotion groups do make me think a little about my diet and lifestyle, but don’t have the desired impact and I do not feel empowered by them. I have not been influenced by their initiatives greatly and I think this is partly down to their sources of information not being accessible in many places. If they do want to make an impact on the general public, they need to promote themselves more!
To conclude, the cardiovascular system has many functions and plays an important role in the delivery of oxygen and nutrients around the body using the blood. The healthy functioning of this system is important to ensure the risk of coronary heart disease is reduced. There are many initiatives in place that promote this healthy functioning, such as the five fruit and vegetables a day initiative, and they are all backed up with sound research, but they all do not promote themselves well enough and so their impact will not be as much as it could be!
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