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    Homeostasis: Feedback and Body Essay

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    Homeostasis is a simple term which holds a large significance in the functionality of the human body. This essay will discuss and define this term. Explanation as to why homeostasis is important to be maintained and two examples of homeostasis relevant to its control mechanism will be stated in this essay as well. The word homeostasis was first introduced by Walter B. Cannon, an American physiologist, to describe the body’s ability to maintain relative stability of its internal conditions even though there were constant changes in the surroundings outside. (Marieb & Hoehn, 2007).

    Thus, homeostasis is utterly defined as “the condition of equilibrium in the body’s internal environment due to the constant interaction of the body’s many regulatory processes”. (Tortora & Derrickson, 2009, p. 8). Homeostasis has a dynamic state of balance, in which the body’s internal condition may vary, but only within a narrow range that is compatible with maintaining life. (Marieb & Hoehn, 2007). The important concept here is that the body is continuously monitoring its internal state and takes action to rectify disruptions that threaten its normal functions. (Silverthorn, 2001)

    Humans are multicellular organism, which sits right at the top of the hierarchy of structural organization. The cell is the basic living unit of the body and each organ is a collective of many different cells held together by intercellular supporting structures. (Guyton & Hall, 2006). Each type of cells usually differs from one another in order to adapt and serve their functionality; but ironically all cells are comparatively similar in a particular way as they share certain basic characteristics. These similarities of theirs are fundamentally the reason why it is important to maintain homeostasis.

    An adult human body is 60% fluid. Although most of this fluid, called the intracellular fluid, is inside the cells, one third of it fills the narrow spaces outside the cells. That fluid is identified as the extracellular fluid. (Guyton & Hall, 2006). Extracellular fluid is always in constant motion, travelling throughout the body in the circulating blood. Ions and nutrients that make up the extracellular fluid are needed by cells to sustain cell life. Hence, all cells in essence live in the same environment – the extracellular fluid. In ddition, the proper functionality of body cells is also highly dependent on an accurate control of the composition of the extracellular fluid which surrounds them. (Guyton & Hall, 2006; Tortora & Dirrickson, 2009). For these reasons, the extracellular fluid is also known as the body’s internal environment. Extracellular fluid acts as a transition between the intracellular fluid inside cells and the organism’s exterior environment. As tolerances for much change is exceedingly low for cells of multicellular organisms, it therefore depends on the consistency of the extracellular fluid to maintain normal function.

    Because of extracellular fluid’s significant role, sophisticated physiological processes have been developed to keep its composition relatively stable. (Tortora & Dirrickson, 2009; Silverthorn, 2001). When the extracellular fluid composition has an abnormal range, compensatory mechanisms activate in order to return the fluid to normal state. Homeostasis is of such importance because it is the body’s platform of balance to maintain health and preserve life. An important aspect of homeostasis is communication within the body.

    Organ systems do not work solely by themselves; cooperation between them is essential to promote the well being of the body. (Marieb & Hoehn, 2007). The body’s regulating systems that can usually bring the internal environment back into balance is mainly done by the communication between the nervous and the endocrine system. These two regulating systems work either independently or together, using neural electrical impulses or blood- borne hormones respectively, as information carriers, to provide the needed corrective measures. (Tortora & Dirrickson, 2009; Marieb & Hoehn, 2007).

    A feedback cycle in relative to the regulating systems is used by the body as a homeostatic control mechanism. The feedback cycle comprises of three basic components – a receptor, a control center, and an effector. A monitored variable such as body temperature, blood volume and etc. is termed a controlled condition. A receptor’s job is to monitor changes in a controlled condition and sends input – usually in the form of nerve impulses or chemical signals – to a control center. The control center sets the range of values of a controlled condition (set point), and evaluates the input it receives from the receptors.

    Output commands, usually in the form of nerve impulses, or hormones, or other chemical signals are generated by it when needed. The body structure that receives output and produces a response or effect that changes the controlled condition is called an effector. A feedback system is therefore a group of receptors and effectors communicating with their control center to regulate a controlled condition in the body’s internal environment. (Tortora & Dirrickson, 2009). The feedback system is classified into two mechanisms which are the positive feedback and the negative feedback mechanism.

    Homeostatic control mechanisms are mostly negative feedback mechanisms. A negative feedback system reverses a change in a controlled condition, as in the output reduce its intensity or disable the original stimulus, returning it to its “ideal” state. Another way of putting it is that the variable changes in a direction opposite to that of the initial change, thus earning the title ‘negative’. (Marieb & Hoehn, 2007). The regulation of body temperature is one such mechanism to restore homeostasis. The human body temperature is controlled by the thermoregulatory centre in the hypothalamus which is located in the middle of the brain.

    Inputs are received form two sets of thermo-receptors. The first is the receptors in the hypothalamus itself which monitors the temperature of blood passing through the brain – the core temperature, and the second is the receptors in the skin which monitors external temperature. Both sets of the information are vital and are received alongside each other so that the appropriate adjustments can be made by the body. The thermoregulatory center sends impulses to several different effectors so body temperature can be adjusted swiftly. In the case of body temperature increasing (e. . exercising or hot weather), the heat loss centre in the hypothalamus is triggered. The thermostat in the hypothalamus activates cooling mechanisms. Output is send to the effectors such as the smooth muscles (arterioles in the skin), and the sweat glands. Muscles relax causing vasodilatation – skin blood vessels dilate. Additional heat is carried from the core to the surface, where it is dissipated by convection and radiation. That is why the skin has a reddish appearance to it. Glands secrete sweat onto surface of the skin, which later evaporates.

    As water have a high latent heat of evaporation, meaning that extra energy is needed to aid the process of evaporation, sweat absorbs heat from the body before it evaporates. The body temperature decreases and the hypothalamus halt the cooling mechanisms. This sequence of events returns the controlled condition – body temperature – to normal, and homeostasis is restored. (Marieb & Hoehn, 2007; Silverthorn, 2001). In positive feedback mechanisms, the result tends to enhance the original stimulus or reinforce the change in the body’s controlled condition.

    It is termed ‘positive’ because the change that takes place progresses in the same direction as the original stimulus. Positive feedback is typically known as a “vicious cycle” and is likely run out of control, causing a waterfall effect. Consequently, it is rarely used to promote the day-to-day well being of the body. ( Marieb & Hoehn, 2007; Guyton & Hall, 2006). Even though the positive feedback mechanism bears the role of a villain, in some instances, the positive feedback to some degree can be very useful to the body when take advantage of.

    An example of positive feedback as a homeostatic mechanism is blood clotting. When a blood vessel is damaged, a whole series of reaction is set in motion to achieve hemostasis, meaning the stopping of bleeding. Three steps occur in rapid sequence during hemostasis: (1) Vascular spasm – constriction of damaged blood vessel; (2) Platelet plug formation – platelets are element found in blood and have an imperative role in the clotting process. Platelets form a temporary plug that seals the break in the damaged vessel.

    They cling themselves to the injured site and releases chemicals, initiating the positive feedback cycle that attracts more platelets to the area, building up the platelet plug which further reduce blood loss. (3) Coagulation or blood clotting – blood changes from liquid to gel form involving multistep process. ( Marieb & Hoehn, 2007). Homeostasis is restored by which the blood volume is maintained with preventing blood loss. In conclusion, homeostasis means the maintenance of virtually steady conditions in the body’s internal environment. It is important to sustain life and keeping the body healthy.

    Efficiency of the regulating systems in correlation with the feedback system is essential for homeostatic control mechanism which is the negative and positive feedback mechanisms. Homeostasis can be witness not only in body temperature and blood volume maintenance but also in many other parts of the body. Homeostasis is of such importance that the disturbance of it and failure of compensation to restore it will result in illness or diseases. Word count: 1028 Bibliography Guyton, A. C. , & Hall, J. E. (2006). Textbook Of Medical Physiology. Pennsylvania: Elsevier Saunders. Marieb, E. N. , & Hoehn, K. 2007). Human Anatomy & Physiology. San Francisco: Pearson Benjamin Cummings. Silverthorn, D. U. (2001). Human Physiology: an integrated approach. Upper Saddle River: Prentice Hall. Tortora, G. J. , & Derrickson, B. (2009). Principles of Anatomy and Physiology. USA: John Wiley & Sons Inc. Homeostasis. (n. d. ). In Wikipedia: The Free Encyclopedia. Retrieved January 27, 2010, from http://en. wikipedia. org/wiki/Homeostasis DeRosnay, J. (1997, February 17). Homeostasis: resistance to change. Retrieved January 27, 2010, from Principia Cybertica Web: http://pespmc1. vub. ac. be/homeosta. html

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