The cardiovascular system is concerned with controlling the supplies of oxygen that enter the body, and transporting them from gaseous exchange areas to the rest of the body. Similarly, it is also concerned with the removal of the carbon dioxide produced by the body tissues. The main organs and features of the heart include the heart, lungs, blood, arteries, veins and capillaries. The cardiovascular system contains two circuits; the pulmonary circuit and the systematic circuit. These can be described as loops through certain parts of the body. The pulmonary circuit loop travels through the lungs to oxygenate blood to be received around the rest of the body. The systematic circuit loop travels through the rest of the body transporting the oxygenated blood to cells and tissues which need them. The heart is the organ which, through a system of contractions, pumps blood to tissues and blood vessels in the body. The diagram on the left illustrates the features of the heart and its main crevices. It is located in the chest cavity and is enclosed inside a sac called the pericardium. The purpose of this sac is to protect the heart, its features and stop the heart from overfilling. The valves of the heart aid in the process mentioned above, whereby blood is oxygenated and released into the body via loops through the body and lungs. These valves are called the pulmonary, aortic, tricuspid and the mitral. The layers of the heart also include the myocardium, endocardium and epicardium. These layers aid in the contraction motions of the heart. The cardiovascular system controls many conditions in the body, and one of these conditions is homeostasis.
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Homeostasis is the ability of the body to control internal conditions, despite the conditions outside of the body. The internal environment is always set at a fixed value to ensure strict operation of the body. These conditions must be kept constant for the cells to work efficiently. Homeostasis has several control systems to ensure these certain conditions remain stable. These control systems are water regulation, glucose level, temperature and PH. Homeostasis mechanisms require several functions to work properly. There must be some kind of input; information is required to maintain the stability of the body through homeostasis. Receptors are also required to detect that information; such as osmo-receptors and skin receptors. The brain acts as the control centre needed for homeostatic control, or thermoregulatory centre. Effectors are also necessary; these bind to protein molecules and therefore change the activity of that molecule. Corrective actions and negative feedback are also highly required for homeostasis. These are mechanisms that oppose or resist changes in the internal or external environment to maintain stability in the body. In relation to temperature regulation, homeostasis keeps the body at a constant 39oC. This is to ensure that the enzymes produced naturally in the body are catalysed in the human cells. Also, heat in the body is produced when body cells respire. However, when motions similar to exercise are not executed, heat produced in the body is mainly the cause of the liver. Mammals also have a fat layer under the skin called the thermal insulator. Chemically, homeostasis in controlling body temperature is the result of messages sent from the thermoregulatory centre; this centre being the main organ in the body, the brain. Blood is the carrier of these messages; as the blood flows through the brain these messages are transmitted. The information in the blood is received from tiny receptors outside of the skin. As the messages reach the thermoregulatory centre, it then adapts the body temperature accordingly; either by the conservation of heat, the production of heat or heat loss. The reason by homeostatic body temperature control is that if the body got too hot, the cells would be killed of immediately; similarly if the body became too cold. The next homeostatic control is that of water regulation. Water is a very important liquid in the body as it makes up most of the blood and dissolves glucose gases and waste urea. It also aids in the process of digestion where enzymes are involved. The thermoregulatory centre is constantly monitoring the concentration of the blood. When we become thirsty or dehydrated the brain seeks to stabilise the condition. It does this by instructing the pituitary glands to release the hormone ADH. Antidiuretic Hormone is concerned with the reabsorption of chemicals in the kidneys. The hormone stimulates the kidneys to reabsorb back into the blood from the urine waste. In this case, the amount of urine decreases and becomes more concentrated. This is the cause for very strong-coloured urine, of a dark yellowish colour. In contrast, when very hydrated or drinking too much water, the blood becomes diluted and in this case less ADH is released into the body. This is the cause for very light coloured urine. Another homeostatic control is blood sugar level, or glucose level control. Glucose is the main energy source for cells in the body and the only one the brain can use. Glucose is produced by the food that you digest, and the level of glucose in your blood rises when you have just eaten a large meal. Scientists recommend the safe limits of glucose concentration in the blood are equal to 0.7 to 1.2 grams per litre. If the concentration rises higher than 1.2 grams, the kidneys cannot reabsorb it. If it becomes lower than 0.6 a person will become unconscious and may enter a coma. To keep these conditions stable, homeostasis causes 2 hormones to be released from the region of the pancreas called the islets of langerhans. These are insulin and glucagon. Insulin is released when a rise in blood glucose is detected and has two polypeptide chains of amino acids and systine amino acids. Glucagon is released when a decrease in blood glucose is detected and is stimulated by adrenaline to produce glycogen into glucose. It is a 29 amino acid polypeptide chain and its structure consists of NHHYPERLINK "http://en.wikipedia.org/wiki/Amine"2-His-Ser-Gln-Gly-Thr-Phe-Thr-Ser-Asp-Tyr-Ser-Lys-Tyr-Leu-Asp-Ser- Arg-Arg-Ala-Gln-Asp-Phe-Val-Gln-Trp-Leu- Met-Asn-Thr-COOH. In relation to diabetes, people who have the condition cannot control the concentration of glucose in their blood. This is caused by the glucose concentration rising too high after meals and falling too low between meals, because insulin is not released by the pancreas and glucose not being stored.
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As previously mentioned, homeostasis is the body's internal remote computer. The system works to maintain a balanced internal environment regardless of the dependant conditions outside of the body. If the body adapts to change then we must consider the effects of exercise on the body's internal functions. We all realise that any routine of prolonged exertion causes the features of the cardiovascular system to change. For example the heart beating faster and the lungs to intake and release more air. However, what is the understanding behind this occurrence. Recently, the Access to Science class undertook a practical experiment, whereby we were instructed to conduct various exercise activities and record several changes in the body such as heart rate. Below is a table
illustrating the class results of the experiment:-
Exercise results for Access to Science practical experiment
Rate At Rest
5 Minute Interval of Rest
10 Minute Interval of Rest
From the results gathered, we can see that immediately after the exercise experiment, the class experienced an increase in pulse rate. Similarly, with blood pressure, it increased immediately after exercise. Scientific evidence states that systolic blood pressure at rest should range from 110-140mmHg, and diastolic blood pressure should range from 60-90mmHg. Simply, this means that in cardiac systole, the heart contracts to allow blood to be pumped out of the heart; whereas, in cardiac diastole, the heart relaxes to let the heart refill with blood after contraction. Observing the results gathered most of the class falls well within the guidelines for appropriate blood pressure measurements. However, after exercise, the results show a major increase on blood pressure. Systolic pressure is usually the aggravating factor in results such as these, for it is usual for the systolic pressure to increase to 200mmHg. This is witnessed in student 1, where their blood pressure rose to 211mmHg after exercise. As the blood pressure at rest of most of the class was within the safe limits recommended by professionals, none of them showed any signs of hypertension. Hypertension is the condition where, at a state of rest, a person's heart works to hard to pump blood around the body. Other conditions caused by an extremely high blood pressure are strokes and coronary heart disease. It must be noted that there is a degree of risk where blood pressure is above the safe limit of 140/90mmHg. This is concerning because at rest two of the students had blood pressure above this. This means that there is a possibility of several cardiovascular diseases in the individuals. Addition, in aerobic exertion, a source of energy is required, so that the body can properly function under the extreme conditions and force on it. This source of energy is ATP, or Adenosine triphoshate. As well as needing ATP for diffusion and active transport, the energy source is mainly responsible for cell activity. We are able to exercise continually because the muscles in our body are constantly using up energy resources. So therefore, a large amount of ATP contained inside the cells in the muscles would ensure that we never get tired during fitness, and maintain a level pulse rate and blood pressure; however, in reality, this is not the case. In fact the cells in the muscles cannot store great amounts of the energy source during continual fitness. This means that the muscles must acquire energy from other sources. Once the energy from these other sources is released, a higher amount of ATP is generated, to aid in long term fitness. These sources include glycogen, glucose and fatty acids. The glucose and fatty acids originate from the blood in our body; whereas, glycogen originates from the cells in the muscles and is eventually broken down into glucose. The energy released from these sources then generates the necessary level of ATP to transport to the muscles to aid in long term fitness routines, needed to maintain the body's natural balance. Relating back to the results of the experiment, we can see that the blood pressure and pulse rates all increased. If the results were on the contrary, then there would be a definite risk to the students. This is because during rapid respiration, there needs to be a constant supply of oxygen to the cells and muscles. This is so that ATP can provide the energy needed to keep the cells in the muscles active and working. An increased blood pressure and heart rate shows that the heart is working to supply these muscles with the correct amount of oxygen needed in respiration, otherwise the cells would die and the consequences would be damaging for the student; Also the increased heart rate and blood pressure tells us that along with oxygen transport, the system is ridding the body of waste products such as carbon dioxide. Next is the introduction of the terms bradycardia and tachycardia. Bradycardia, or slowness of the heart, refers to the heart rate at rest of a person. It can sometimes be problematic for some people; however those such as young people and athletes may have the condition occurring naturally in their body. Bradycardia is simply a heart rate which, at rest, consists of 60 bpm. As mentioned before, the condition is not commonly problematic in young people and athletes. In athletes, as the body is exposed to prolonged fitness and intense exercise regimes, they find that over time, even during tough workouts, their body has adapted to the constant force exerted on it, so develop a lower pulse rate; which means they work out harder and longer than the average person. Problematic bradycardia is said to be brought on by heart diseases or old age. As the heart gets weaker due to circumstances, less oxygen is transported to the heart, and therefore less oxygen is transported out of the heart and into the cells. Extreme cases of bradycardia may lead to serious illness or fatalities. In relation to the class experiment, there were no cases of bradycardia as each student registered a pulse rate of above 60 bpm. In contrast to bradycardia is tachycardia. Tachycardia is simply a heart rate which, at rest, surpasses the recommended rate in a healthy individual. This condition means that the heart beats so fast that it restricts the amount of blood flow in and out of itself. As the heart beat is irregular, the heart stops functioning as a good pump, and as the beats are irregular, so too is the level of blood flow. Similarly to bradycardia, this inefficient nature of the tachycardiac heart means that there is a restriction of
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oxygen to and from the heart, meaning that the cells do not acquire the oxygen and energy they need, so begin to die. To diagnose tachycardia in individuals, we must compare their heart rates against their age. For the class experiment the typical age range we will be using is 15 years - adult. In this category the normal bpm stands at 100 beats per minute. Looking at the results at rest for the class, I can see that no students showed signs of the condition. Although, tachycardia usually refers to the heart rate of individuals at rest, or inactive, we can also compare the symptoms of the condition with our data after exercise. After 5 minutes rest five out of seven students began to show signs similar to that of a tachycardiac. More disturbingly, after 10 minutes of rest, there was still a ratio of five out of seven students showing similar signs to that of a tachycardiac. In some cases the heart rate of several students increased from after 5 minutes rest to after 10 minutes rest. However, the most promising of the group was student seven, who after 5 minutes rest immediately slowed their heart rate. Even after 10 minutes rest, the student showed no change in the number of bpm. This may indicate the level of fitness undertaken by the student in exercise programmes or a healthy lifestyle. Lastly, exercise is a central component to the cardiovascular system, in that they are both dependant on one another. The features cardiovascular system benefits greatly from the exertion of exercise routines. Likewise, the operation of the cardiovascular system contributes greatly to the continuation of fitness regimes, ensuring that the person undergoing the regime does not collapse, due to lack of oxygen transported to the body tissues. The main role of the cardiovascular system during aerobic fitness is to deliver oxygen to respiring muscles, transporting useful hormones, delivers heat to the skin surface and to oxygenate blood.
We have now discovered that the cardiovascular system is mainly concerned with transportation of blood and homeostasis to maintain the body's natural state. However, we must now grasp the understanding of the functions of myoglobin, haemoglobin, leucocytes, erythrocytes and platelets to the structure that is the cardiovascular system. Myoglobin is a protein found in the body tissue of humans and is a very efficient oxygen-binding substance and typically, is the reason for the red-flesh pigment found inside the body tissue. In chemical analysis of the structure of myoglobin, it is comprised of one polypeptide, one haem group and can only join with one oxygen molecule, forming an oxymyoglobin molecule. The function of myoglobin is a product of the function of homeostasis, in that myoglobin stores oxygen and would only release it when certain conditions should arise, for example respiration during exercise. Other substances belonging to the globin family include neuroglobin, cytoglobin and leghemoglobin, which all form a part of the homeostasis
process. However, leghemoglobin is concerned with leguminous plants and oxygen transfer, cytoglobin is concerned with oxygen transfer from blood to the brain and similarly, neuroglobin is concerned with the provision of oxygen to the brain to prevent hypoxia. Nevertheless, these are all haemoproteins of a similar chemical structure and aid in the process of homeostasis. Another haemoprotein is haemoglobin. Haemoglobin is contained inside red blood cells along with oxygen.
The protein has 4 polypeptides that have one haem group attached to each of them. This means that haemoglobin can join with 4 oxygen molecules all together; whereas myoglobin can only join with one. The oxygen is contained within the haemoglobin protein and is released into the body. When the concentration of oxygen in the lungs is high, the haemoglobin in the red blood cells is fully saturated. This means that the red blood cell is carrying a full amount of oxygen to be carried around the body. Additionally, this also means that less oxygen is released into the body. Whereas, when the lungs are less saturated, for example, during exercise or excessive respiration, the haemoglobin is partially full of oxygen. In respiration or exercise, the haemoglobin releases more oxygen to the muscles of the body. The term for concentration of oxygen in the body is called partial pressure, and differs in different circumstances. Additionally, the reaction of haemoglobin and oxygen, and myoglobin and oxygen is a reversible reaction, in relation to biochemistry. When measuring the amount of haemoglobin that reacts with oxygen, biologists use what is called a dissociation curve. The curve represents the saturation percentage of samples of oxygen combined with haemoglobin, against the partial pressure amount of oxygen. Below is an example of a dissociation curve, abstracted from Cambridge Advanced Sciences Biology 1 textbook. The graph illustrates the reaction of partial pressure of oxygen, matched against the saturation of haemoglobin.
Another factor to aid in the understanding of the function of haemoglobin is the bohr effect. The bohr effect relates to the principles of chemical equilibrium and the need to continually balance reactions inside the body. This effect explains how high partial pressures of not oxygen, but carbon dioxide in the body, causes haemoglobin to release oxygen at a faster rate, because of the demand for it in tissues with high concentrations of carbon dioxide. The next features are the leucocytes and enthrocytes. These are the red blood cells and white blood cells. Leucocytes are the white blood cells and although there are many types of the disease fighting cell, they are usually categorised into
two groups. These are lymphocytes and phagocytes. Firstly, the better known phagocytes are those distinguished by their granular cytoplasm, belonging to the group of cells called granulocytes. These blood cells are responsible for the removal of microorganisms that assault the body, by the process of phagocytosis. Also, illustrated in the processes of active bulk transport across cell membranes, phagocytosis is simply the intake of foreign bodies or bacteria by these blood cells. More simply, phagocytes 'eat' or engulf these assaulting organisms to rid the body of harmful bacteria detrimental to the immunity of the body's functioning. Secondly, lymphocytes function differently to phagocytes in the way they rid the body of foreign bodies. Unlike phagocytes, lymphocytes secret antibodies to aid in the defence of the immune system; however, Instead of eating the attacking organisms, they simply attach themselves to them and then destroy them. The two most important types of lymphocyte are B cells and T cells. B cells are responsible for the production of the antibodies which fight of foreign bodies and bacteria. Whereas, T cells are responsible for assaulting and destroying cells which have already become contaminated or malignant. Erythrocytes are the red blood cells and are responsible for carrying oxygen contained in haemoglobin, from the lungs, to the tissues of the body. The haemoglobin is also the reason for the red colour of the cells. The red blood cells have a variety of features. Firstly, they are minute in size, with a diameter of about 7Î¼m. An advantage of this in relation to the structure of the cardiovascular system is that, as the haemoglobin is very close to the cell membrane, gaseous exchange across the membrane can be achieved much quicker. In other words, the oxygen can be transported out of the haemoglobin at a faster rate, and into the surrounding cells and liquids. Secondly, the cell's biconcave disc shape means that there is a greater surface area; meaning that there is a greater surface area to volume ratio. This aids in faster diffusion of the oxygen across the cell membrane. Lastly, red blood cells, unlike other cells, contain no nucleus or mitochondria. This means that there is greater room for the presence of haemoglobin in the cells, and therefore more oxygen can be transported from the lungs to the body tissues, and likewise, carbon dioxide from the tissues, out of the body. The last feature to be discussed is platelets. These small, irregular shaped plates are responsible for controlling blood loss in open wounds. The platelets, calcium mineral, vitamin K and fibrinogen protein combine to stop blood seeping out of wounds in the epidermis and dermis. These substances centre on the opening of the wound and form a clot or what is commonly known as a scab on the dermis and bruise in the epidermis.
(Defintion of Lymphocyte, 1998)