The components of negative feedback in homeostasis

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Homeostasis is a process which enables an organism to maintain optimal conditions within the internal environment and compensate for environmental changes to ensure the organism remains compatible with life. In response to changing conditions, the body’s equilibrium can shift between points within a narrow range.

Homeostasis is extremely important for an organism’s survival. Without homeostasis the body would be unable to maintain the correct body conditions such as body temperature, glucose levels, blood pH and osmolality and the individual could die if deviations occured. For instance in winter, cold weather would cause the body to become extremely cold and without homeostasis the body would be unable heat up again. This would cause the enzymes in our body, which are temperature sensitive, to degrade and the organism would die. Therefore homeostasis allows adaptability within an environment so organism’s can survive in a range of climates.

Another example showing the importance of homeostasis is blood pH needs to be between a range of 7.35 -7.45. If the pH is below this range this condition is called acidosis and above the optimum pH this causes alkalosis. Both of these conditions are life threatening therefore homeostasis plays a vital role in ensuring blood pH stays within this optimum range.

Homeostasis occurs through a process known as negative feedback. Negative feedback is a mechanism in which the system responds in an opposite direction to their current level. For example if the blood pH becomes too high this will be detected by chemoreceptors in the body and negative feedback will begin to lower the blood pH back to within a normal range through increasing carbon dioxide levels and retaining hydrogen. Positive feedback is another feedback mechanism which strengthens or reinforces a change within a body’s controlled conditions, for instance breast feeding or labour contractions.

Negative feedback has at least three interdependent components for the variable being regulated. Firstly the receptor is the sensing component which monitors changes in body conditions. There are many types of receptors such as Peripheral receptors which are found within the skin and central receptors found within organs in the body. If receptors in the body sense a change in conditions, a signal is sent to the integrating center (within the brain) via the afferent pathway. The integrating center then determines an appropriate response to the received stimulus. The integrating center then sends this response via the efferent pathway to an effector in order to bring the internal conditions back to within a normal range. The effector is muscles or glands or other structures which are able to receive signals. In the example of the body temperature lowering, this would be detected by thermoreceptors which send an impulse to the integrating center to send out signals to increase heat production. This would involve shivering to produce heat as a by-product and vasodilation will also occur so the veins and arteries move away from the surface of the skin so heat loss is reduced. Piloerection will also occur where hairs stand up on end in order to trap a layer of air around the body to insulate the body. This response should be adequate to return the body temperature to within a normal range. (35.8-37.8°C is the optimum core temperature range)

Reference:

Biology Online. 2014. Homeostastis. [Online]. [Accessed 7th October 2014]. Available from: http://www.biology-online.org/dictionary/Homeostasis

Boundless. 2014. Homeostatic Contol. [Online]. Accessed 8th October 2014]. Available from:www.boundless.com/physiology/

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Tortora G. and Derrickson B. 2011. Principles of Anatomy and Physiology, United States: Wiley

Turrigiano G. 2007. Homeostatic signalling: the positive side of negative feedback. Current opinion in Neurobiology. 17 (3): pp.318-324

2. Asthma is a common long-term condition that causes breathlessness, wheezing, bronchospasm and coughing. Asthma causes irritation of the airways, causing the muscles in the airways to become inflamed narrowing the airway and causing breathlessness. Excess mucus is produced which can narrow the airway further and cause coughing as a way of clearing the airway.

Bronchospasm is a condition involving the abnormal contraction of the bronchi’s smooth muscle, leading to the narrowing and obstruction of the airway. The narrowing of the bronchi is caused by the muscles in the lung walls and lining contracting. During bronchospasm the mucosa becomes inflamed and swollen further narrowing the airway. Excess mucus is also produced which causes irritation leading to coughing. Therefore these factors make breathing much harder than usual.

Salbutamol is a drug prescribed to asthma sufferers and works to relieve asthma symptoms by relaxing muscles in the bronchi to allow the airway to open and make it easier to breathe. Salbutamol works by stimulating the B2 adrenergic receptors which are found in the bronchial smooth muscles within the lings. The stimulation of these receptors causes activation of adenyl cyclase which then forms cyclic AMP (adenosine-mono-phosphate). The increased levels of cyclic AMP cause the bronchial smooth muscle to relax and decreases airway resistance due to lowering the concentrations of calcium. Lowered calcium levels cause relaxation of the smooth muscle in the airway and leads to bronchodilation. Increased levels of cyclic AMP also work to inhibit the release of bronchoconstrictors such as histamine. Overall these responses ease breathing and reduce narrowing of the airway therefore reducing asthma/bronchospasm symptoms.

Bibliography:

Asthma UK. 2014. What is asthma? [Online]. [Accessed 15th October 2014]. Available from: www.asthma.org.uk/advice-what-is-asthma

Drug Bank. 2013. Salbutamol. [Online]. [Accessed 15th October 2014]. Available from: www.drugbank.ca/drugs/

NHS Choices. 2014. Asthma. [Online]. [Accessed 15th October 2014]. Available from: www.nhs.uk/Conditions/

NHS Choices. 2014. Easyhaler Salbutamol, [Online]. [Accessed 11th October 2014]. Available from: www.nhs.uk/medicine-guides/

Salbutamol Organisation. 2014. Salbutamol. [Online]. [Accessed 15th October 2014]. Available from: http://salbutamol.org

Walters E. Gibson P. Lasserson T. and Walters J. 2007. Long-acting beta2-agonists for chronic asthma in adults and children where background therapy contains varied or no inhaled corticosteroid, The Cochrane Library, 1: pp.1-50

3. Cancer is a disease caused by the uncontrolled division of abnormal cells which invade surrounding tissues. A multifactorial disorder is caused by a combination of genetic material, lifestyle factors and the environment. An example of this is cancer.

An individual’s genetics can increase the chances of developing certain cancers, for instance women carrying the faulty genes BRCA1 and BRCA2 have an increased chance of developing breast cancer. Furthermore genetic mutations can also increase the chance of developing cancer. The mutated gene can then be inherited by following generations leading to whole families at risk of cancer.

Individuals with a weakened immune system are more likely to develop certain cancers. This includes people with organ transplants and HIV/AIDS. Bacterial factors have also been linked with cancer for instance helicobacter pylori; which causes stomach lining inflammation increasing the risk of stomach cancer.

Viruses have also been found to cause some cancers. This is due to the virus causing genetic mutations leading to cancer. Examples of these viruses include the human papilloma virus (HPV), which increases the chance of cervical cancer onset and Hepatitis B and C, which increases the chance of liver cancer.

Lifestyle and environmental choices can increase susceptibility to cancer. These include increased sun exposure, which damages genetic information and causes skin cancer. Smoking is another factor, as tobacco smoke is a carcinogen which can cause lung cancer, however some peoples lungs may be more susceptible to damage than others so this could affect whether the individual develops cancer or not. Other lifestyle choices include alcohol consumption and poor diet. Age has also been linked with cancer, as the older you get the more genetic damage and mutations you have therefore increasing the chance of developing cancer. Other environmental factors include exposure to radiation and asbestos, which causes genetic damage leading to uncontrolled cell replication. Therefore as cancer has a range of genetic and environmental causes it is classed as a multifactorial disorder.

Reference:

Cancer Research. 2014. What causes cancer? [Online]. [Accessed 16th October 2014]. Available from: www.cancerresearchuk.org/about-cancer/

Craig,J.2008.Complex diseases: Research and applications.Nature Education1: pp:184

Willett W. 2002. Balancing Life-Style and Genomics Research for Disease Prevention, Science, 296 (5568) pp:695-698

4. A translocation is an exchange of genetic information from one chromosome to another homologous chromosome. No genetic information is lost in this process. A balanced translocation is when the exchange of material is balanced so the individual has the necessary genetic information to live a normal life and they will have no symptoms.

Unbalanced deletion is the deletion of a section of one of the chromosomes from a homologous pair meaning one chromosome is missing important genetic information. The seriousness of the disease depends on the size of the deletion and which sections of the chromosome are missing.

Stables D. and Rankin J. 2010. Physiology in Childbearing with Anatomy and Related Biosciences, United Kingdom: Elsevier Health Sciences

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