An organ system inside the human body is made up of a number of individual organs working together to perform a specific function. The Cardio-Respiratory System (CRS) is responsible for the uptake of Oxygen from the air we breathe, the circulation of oxygenated blood and nutrients around the body and the removal of waste from tissues and organs. This essay will explain the normal structure and function of the CRS and to what extent it is damaged by cigarette smoke. The CRS is primarily made up of the lungs, heart, blood and blood vessels and will detail the operation and structure of each component. When all these organs are working in equilibrium, the human organism functions effectively. The smoking of cigarettes and the direct inhalation of toxic gases and poisons disturb these environments and the implications can be extremely damaging and ultimately fatal. These effects will be discussed and furthermore will breakdown the physiological damage which occurs in tissues and organs. It will conclude with a breakdown of findings.
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Breathing is an unconscious action (see appendix 1). For this to take place, signals from the medulla oblongata cause the diaphragm to contract and move downwards allowing space for the lungs to inflate. The intercostals contract expanding the thoracic cavity lifting the lung upwards and outwards. The lungs are connected to the cavity wall by the pleural membrane. This cavity is filled with pleural fluid which acts as a lubricant during respiration. This lifting of the lungs increases the inner volume, lowers the pressure and draws air into the lung. On expiration, the diaphragm and intercostals relax and recoils the lungs, decreasing the internal space, increasing the pressure and therefore forcing air out of the lung. (Clancy, 2010).
The primary respiratory organs in the human body are lungs. Located in the thoracic cavity, they are spongy, elasticised structures enabling inflation and deflation. On inhalation, air travels up the nostril where it is warmed from the blood supply, filtered through tiny hairs and moistened via the mucus secreting, epithelial membrane lining the nostril. Air then reaches the pharynx which is a muscular structure connecting the nose with the trachea and the mouth with the oesophagus. It has a mucus membrane and acts as a passage for both food and air (Rajan, 2010). Air proceeds past the glottis to the larynx which has several folds of elasticised, connective tissue forming the vocal chords. The larynx is connected to the trachea which is c shaped, constructed of cartilage and ligaments to support its structure and is lined with ciliated epithelial tissue which secretes mucus to aid the removal of particles (Powell, 2010). Cilia are microscopic organelles found on the outside of cells. They are fine hairs filtering out particles and dust which may irritate the respiratory tract. The trachea then splits into two smaller airways, the bronchi. They are lined with mucus producing, ciliated epithelium to continue the filtering of particles and contain cartilage to support the process of breathing. As air travels deeper into the lungs, airways become smaller. The left and right bronchus split to form secondary bronchi and tertiary bronchi. The smaller structures are also made up of supportive cartilage but when forming bronchioles, the structure becomes smooth muscle. The bronchioles terminate in the alveolar ducts which then form the alveoli (Clancy, 2009). Alveoli are minute air sacs where gas exchange takes place and are made up of two types of cell. Type one cells are squamous epithelial cells which are long and spread out to form the surface. Type two cells are more compact and secrete surfactant which reduces surface tension enabling them to inflate easily. (Hopkins, 2010).
To reach the blood, oxygen must diffuse through alveolar epithelium and through the walls of capillaries (Appendix 2). Capillaries are found in their millions forming capillary beds and are made up of squamous endothelium which contains pores to allow some substances to travel to different parts of the body. The concentration gradient of oxygen inside the alveolus is higher so diffuses through to equalise. At the point when oxygen is diffusing into blood, the higher concentration of carbon dioxide in the capillaries takes the reverse path and diffuses back into the alveolus to be dispelled on expiration.
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The continuous blood flow around the body is due to the functioning heart (Appendix 3). The heart is formed from three layers of tissue, the pericardium, myocardium and endocardium. The pericardium has two layers, a fibrous sac which is tough connective tissue protecting the heart and preventing it from overinflating and the serous pericardium. The serous pericardium is a weaker structure which has two layers forming a sac around the heart. Between the serous layers is the pericardial cavity which contains fluid preventing friction when the heart contracts. The myocardium is cardiac muscle made up of myogenic cells. The inherent rhythmicity of these cells sustains the coordinated contraction of the myocardium causing the heart to beat. The endocardium is a thin, smooth layer of endothelial tissue which lines the inner surface of the heart, the four chambers and four valves (Bailey, 2010).
The cardiac cycle comprises of three stages. Deoxygenated blood flows into the right atrium from the superior and inferior vena cava whilst oxygenated blood flows into the left atrium from the pulmonary vein. In atrial systole, the tricuspid and bicuspid valves open allowing blood flow from the right and left atria into the right and left ventricles. On ventricular systole, the ventricles contract pumping blood through the pulmonary valve into the pulmonary artery to the lungs on the right side and through the aortic valve into the aorta on the left. The blood pumped into the pulmonary artery passes the lungs where the exchange of gases takes place and blood pumped into the aorta will descend to the rest of the body through further arteries and capillaries. In diastole, the atria and ventricles relax, pulmonary and aortic valves close preventing blood flowing back into the heart and both atria begin to refill for the cycle to repeat. (Franklin, 2010).
The heart is primarily composed of cardiac muscle needing a constant supply of nutrient rich blood supplied by the coronary arteries. They branch off the aorta just after it leaves the heart. The three layers of the artery comprise of an inner smooth endothelium, elasticised tissue to regulate blood flow and connective tissue to support the structure. The epicardial coronary vessels form arterioles and the subsequent formation of capillaries deep inside the myocardium, ensures sufficient delivery of oxygen to myocytes. Blood flow through capillaries then enters venules leading to cardiac veins. This drains carbon dioxide and metabolic waste into the coronary sinus which then leads to the right atrium. There is also an anterior cardiac vein which also drains directly into cardiac chambers (Klabunde, 2007).
Environmental pollutants which human beings are exposed to can affect the respiratory system but the cilia and mucus membranes minimise infection and damage. Inhalation of tobacco smoke however is a potent blend of pollutants and gases which have disturbing effects. Smoking is a key factor in developing chronic bronchitis (Appendix 4). Chronic bronchitis is a long term inflammation of the mucus membranes in the bronchial passages. The inflamed airways produce excess mucus and an exaggerated cough develops to clear the obstruction. Smoking causes the cilia to become paralysed resulting in a build up of bacteria and susceptibility to infection and more severe respiratory problems. The narrowing of the bronchial airways results in a shortage of oxygen reaching the alveoli causing shortness of breath, chest tightening and a lack of oxygen reaching organs of the body (Davis, 2010).
Another chronic lung disease related to smoking is emphysema (Appendix 5). As debris, chemicals from cigarettes and mucous from the epithelium settles in the airways due to the paralysis of cilia, bacteria multiply releasing destructive enzymes further damaging lung tissue. In emphysema patients, the structure of the lung is compromised by the loss of elasticity in the alveoli. This is a response to the chronic inflammation in the bronchiolar airways and the chemicals contained in cigarettes causing the breakdown of squamous epithelium of the alveolar. As smaller air sacs are destroyed, larger, less efficient ones remain. Pressure inside the alveolus builds up causing the sacs to collapse, therefore trapping air inside. As this air builds, carbon dioxide also does which would normally have been exhaled if the alveoli were functioning correctly. The diffusion of oxygen into the blood stream is highly compromised from the damaged air sacs and the uptake of carbon monoxide from cigarettes. Physical effect seen in patients is extreme shortness of breath, wheezing and a chronic cough (Martin, 2007)
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As smoking related affliction to the lungs increases, damage caused to DNA in tissue cells occurs which could lead to abnormalities and lung cancers. Lung cancer is a disease which causes cells to grow and reproduce abnormally and uncontrollably leading to the growth of tumours. There are many different forms of lung cancer but are primarily split into two categories, small oat cell carcinomas and non small cell carcinomas. Small â€˜oatâ€™ cell carcinomas spread more rapidly than other types of cancer and are predominantly caused by smoking. There are variations of non small cell carcinomas known as squamous cell carcinoma and adenocarcinoma. Squamous cell carcinomas develop in the lining of the bronchi, deposit keratin and eventually develop into a necrotic keratinous mass which can lead to infection. Adenocarcinoma is the most common non small cell carcinoma which appears in the peripheral lining of the airways developing from a mucus producing cell. When cancer has affected the lungs in a great capacity, eventually there will not be enough healthy tissue left for the absorption of oxygen. This part of the lung then collapses leading to infection which a patient would be too weak to fight off. This will eventually lead to death (Cancer Research, 2009) (See appendix 6)
The two primary chemicals in cigarettes are carbon monoxide and nicotine. Nicotine is a stimulant which increases heart rate and blood pressure, and causes the body to release fats into the blood stream. Carbon monoxide diffuses into the blood stream through the lungs and attaches itself to haemoglobin with greater affinity than oxygen (see appendix 7). As erythrocytes are bound up with carbon monoxide, they cannot transport oxygen effectively. To overcome this, the heart has to work harder to supply the body with oxygen but in order to do that, it requires more oxygen itself. As the fats in the blood are binding to the inner walls of the arteries in the entire body, the pressure which is put on the heart is devastating (Sweeney, 2010).
Coronary heart disease (CHD) is an illness which changes the structure and function of the arteries supplying the heart with freshly oxygenated blood (see appendix 8). An arterial disease called atherosclerosis is responsible for the abnormal depositing of lipids in the vessel wall which results in the narrowing of the lumen thus restricting blood flow. Early in the disease process, changes in the endothelial lining take place. The production of nitric oxide and prostacyclin required for normal coronary function becomes dysfunctional. Endothelial dysfunction can result in impaired relaxation of arteries, coronary vasospasm and the forming of blood clots. The physiological effect of the narrowing of arteries is a lack of oxygen reaching the myocardium (ischemia). This distinct lack of oxygen can result in anoxia and cardiac arrest will ensue. Acute or chronic ischemia can damage the mechanical and electrical actions within the heart leading to heart failure (Klabunde, 2005).
From the projected evidence, it is clear that smoking does in fact damage the cardio respiratory system to lengths which are beyond doubt, immeasurable. The natural formation of the human body is the most sophisticated set of organ systems in existence and as human beings, to destroy the equilibrium of these environments through voluntary inhalation of toxic gases and substances is disgraceful. Inherited diseases and genetic malformations are of natural cause, and although some respiratory diseases are caused by these, the smoking of tobacco is responsible for limitless more occurrences than what would normally be seen. The information presented has merely scratched the surface on the true extent as to what damage is caused to the human body through the smoking of tobacco products.