Physiological Effects of Smoking on Homeostasis

effects of smoking on homeostatic balance

When a cigarette is lit, heat causes the chemicals in the tobacco to be released. These chemicals are then ingested as a person inhales the smoke released from the cigarette. These released chemicals and substances travel through the trachea, bronchi and bronchioles until they reach the alveoli. They are then quickly absorbed into the blood stream across the thin alveolar walls into the surrounding capillary network. As a major part of the body’s first line of defence, the internal surface of the trachea, bronchi, and bronchioles is lined with small hairs called cilia. The cilia beat rhythmically to remove the lining of mucus, produced by goblet cells, which acts as a barrier to trap and prevent foreign and harmful particles from entering the blood (Huxley & Walter, 2005).Unfortunately, the tobacco smoke causes the cilia to stop beating (Roberts & Ingram, 2001), resulting in a build-up of mucus within the lungs. Without the natural movement of this mucus to the mouth and nasal passages, the trapped toxins are unable to be removed, thus resulting in a higher susceptibility to respiratory infections (Pietrangelo, 2014). Prolonged exposure to such infections results in cell damage which in turn may result in lung cancer or emphysema.

Nicotine, a chemical compound found in tobacco (Dr Ananya Mandal, 2014), is well known for its highly addictive nature. This mood-altering drug is a stimulant that gives the smoker a high (Pietrangelo, 2014), so when the smoke from the cigarette is inhaled, the nicotine is absorbed into the bloodstream through the alveolar walls, where it is delivered to the brain almost instantaneously. Once there, the nicotine activates the brain’s ‘pleasure centre’ (sciencemuseum.org, Unknown), and being a stimulant, this results in the smoker feeling energised and happy. However, the stimulating effects of the nicotine subside soon after it reaches the brain, leaving the smoker tired, and as a result craving more. When under stress, the brain releases a hormone called corticosterone. This stress hormone acts as a suppressant which in turn lowers the effects of nicotine. This means a larger quantity of nicotine is required to achieve the desired effect (Pietrangelo, 2014).

Among the list of harmful substances travelling through the lungs is carbon-monoxide. This poisonous gas is diffused into the capillary network much like nicotine. Once there, it binds with passing red blood cells containing a complex protein by the name of haemoglobin. Despite its affinity for oxygen, its affinity for carbon-monoxide is stronger, resulting in these molecules taking the place of oxygen. By preventing the uptake of this much needed oxygen, the body is deprived of an essential element, thus causing an accumulation of carbon-dioxide which in turn alters pH levels in tissue fluids (Huxley & Walter, 2005). With increased exposure to these chemicals the alveolar walls lose their elasticity, impacting the effective exchange of gasses. This loss of elasticity results in an increased difficulty to transfer oxygen and carbon-dioxide (Association, 2008). This means that every time a person smokes, their tissues are deprived of oxygen and the lungs begin to lose their ability to function.

Contributing also to the deprivation of oxygen is once again nicotine. The nicotine causes blood vessels to vasoconstrict, which decreases and, in some cases, blocks the flow of blood to the heart. However, this does not only impact oxygen delivery, but due to the cessation of blood flow, the heart is unable to function normally, resulting in heart failure and/or a heart attack. In extreme cases, this will often lead to death. Nicotine also causes changes within the blood itself such as the clustering of platelets and decreased

clotting time. This leads to clots within the blood which may also result in a heart attack (Metrohealth, Unknown). However, if one of these clots happens to reach the brain, a stroke is likely to occur as a result of this blockage. A stroke will result in major, and usually permanent, health issues such as paralysis in part of the body or even death (Staff, 2015).

One of the body’s core homeostatic mechanisms is the ability of the heart to alter the rate of blood flow throughout the body, so as to ensure conditions within the body remain constant. A lack of oxygen in the body causes the stimulation of receptors in the medulla, and carotid and aortic bodies which act to regulate the imbalance of carbon-dioxide. The heart rate, controlled by a centre in the brain, is increased so as to ensure a rapid delivery of oxygen to deficient areas and carbon-dioxide to the lungs. The thoracic muscles are also stimulated to increase the rate of ventilation which removes the excess carbon-dioxide from the body. Included within these reactions is the vasodilation of blood vessels to remove the unwanted carbon-dioxide. However, despite the increase in the removal CO2, there is still limited oxygen which cannot sufficiently service all areas. This means the homeostatic mechanism of negative feedback is unable to reverse these actions as the balance is not achieved. Not only does this place immense strain on the heart and lungs, but brain cells, requiring a constant level of oxygen are unable to function, thus resulting in further homeostatic imbalance (Huxley & Walter, 2005). Moreover, these brain cells, if not fed oxygen, will die resulting in a possible stroke, or brain damage (Staff, 2015).

Further affected by this imbalance is the ability of the body to maintain a constant internal temperature, allowing for the normal function of cells and systems. This mechanism, known as endothermy, relies on an effective double circulation in which oxygenated and de-oxygenated blood is completely separated. With the heart continuously pumping oxygen poor blood, tissues are deprived of oxygen, affecting constant cell metabolism, and the uptake of oxygen from respiratory surfaces becomes less effective. As the heart continues to pump at an increased rate, the release of energy in the form of heat is also increased. This results in an increased body temperature in which enzymes requiring an optimum temperature are denatured. In turn, this reduces the body’s ability to effectively metabolise. Without the proper functioning of this vital mechanism, the homeostatic balance becomes further imbalanced (Huxley & Walter, 2005).

Overall it can be seen that smoking poses an immense risk to the body and its systems. Affecting both structure and function, the body's ability to maintain homeostasis is thrown out of balance, resulting in major health issues that will affect a person both in the short term and in the long term.

BIBLIOGRAPHY

Association, A.L., 2008. Lungs 101: How Does Smoking Hurt Your Lungs? [Online] Available at: http://www.lung.org/about-us/our-impact/top-stories/lungs-101-how-does-smoking.html [Accessed 16 June 2015].

Dr Ananya Mandal, M., 2014. What is Nicotine? [Online] Available at: http://www.news-medical.net/health/What-is-Nicotine.aspx [Accessed 10 July 2015].

Huxley, L. & Walter, M., 2005. Biology: AnAustralia Perspective. 2nd ed. Melbourne: Oxford University Press.

Metrohealth, Unknown. Nicotine Addiction & Smokeless Tobacco. [Online] Available at: http://www.metrohealth.org/nicotine-addiction-and-smokeless-tobacco [Accessed 23 July 2015].

Pietrangelo, A., 2014. The Effects of Smoking on the Body. [Online] Available at: http://www.healthline.com/health/smoking/effects-on-body [Accessed 10 July 2015].

Roberts, M. & Ingram, N., 2001. Smoking and Health. In Biology. 2nd ed. Cheltenham: Thomas Nelson and Sons LTD. p.142.

sciencemuseum.org, Unknown. What is Nicotine? [Online] Available at: http://www.sciencemuseum.org.uk/WhoAmI/FindOutMore/Yourbrain/Howdodrugsaffectyourbrain/Whatarestimulants/Whatisnicotine.aspx [Accessed 11 July 2015].

Staff, M.C., 2015. Stroke. [Online] Available at: http://www.mayoclinic.org/diseases-conditions/stroke/symptoms-causes/dxc-20117265 [Accessed 25 July 2015].