: blood stream (Toole and Toole, 2004). Liver cells

: Negative feedback mechanisms inhibit the original stimuli (Springhouse, 2013). A feedback mechanism regulates hormones production and secretions to maintain the bodyâ??s equilibrium (Springhouse, 2013). This mechanism uses hormones, metabolites, blood chemicals and the nervous system to regulate the endocrine system. (Springhouse, 2013). Homeostasis includes two negative feedback loops (Khan Academy, 2018), these neutralize change of any system that strays away from there set equilibrium either increasing or decreasing (Khan Academy, 2018). There is no set strict equilibrium there is a point, rather the system sets on which is an acceptable range either side it varies for each mechanism (Khan Academy, 2018). The regulation of glucose concentration in the blood shows how homeostasis is maintained by negative feedback (Toole and Toole, 2004). The cells of the islets of Langerhans reacts to a drop-in blood glucose levels by secreting a hormone called glucagon straight into the blood stream (Toole and Toole, 2004). Liver cells are the only cells that have the ability to bind to glucagon (Toole and Toole, 2004), causes liver cells to produce the enzyme phosphorylase (Toole and Toole, 2004).Phosphorylases purpose is to convert glycogen to glucose (Toole and Toole, 2004) by increasing the conversion of amino acids along with glycerol into glucose (Toole and Toole, 2004).Gluconeogenesis is to increase the amount of glucose in the blood and taking it back to its normal level (Toole and Toole, 2004).This increasing of blood glucose level makes the cells to minimalize the secretion of glucagon (Toole and Toole, 2004).Adrenaline is a hormone which can also increase blood glucose (Toole and Toole, 2004). When a human is stressed or excited the adrenal gland makes adrenaline (Toole and Toole, 2004). Adrenaline enables the breakdown of glycogen in the liver (Toole and Toole, 2004) this increasing the blood glucose level (Toole and Toole, 2004). If the glycogen supply in the liver becomes drained, cortisol is produced by the adrenal gland (Toole and Toole, 2004), enabling the liver to convert amino acids and glycerol into glucose (Toole and Toole, 2004). Insulin and glucagon perform in opposite directions this is shown in Figure 1 (Toole and Toole, 2004). Insulinâ??s job is to lower blood glucose (Toole and Toole, 2004), whereas glucagons is to increase it (Toole and Toole, 2004). This system is self-regulating (Toole and Toole, 2004) the amount of glucose in the blood determines the amount of glucagon and insulin produced (Toole and Toole, 2004). Fluctuation of glucose levels occur around a set point (Toole and Toole, 2004). The negative feedback process takes effect only when blood glucose levels drop below the set point, then the insulin secretion lowers (Toole and Toole, 2004), resulting in a rise in blood glucose (Toole and Toole, 2004). It the same for when levels go above the set point, (Toole and Toole, 2004), glucagon secretion lowers (Toole and Toole, 2004).. The normal levels of blood glucose are 90mg in every 100cm of blood (Allott, 2001). Dysfunction of insulin production and secretion can lead to a condition known as diabetes (Betts et al., 2013). An increase in blood pressure is identified by receptors in the blood vessels that sense the resistance of blood flow against the vessel walls (Pocock, Richards and Richards, 2013). Receptors then transmit a message to the brain (Pocock, Richards and Richards, 2013), next sending the message to the effectors the heart and the blood vessels (Pocock, Richards and Richards, 2013).As a result the heart rate slows down whilst blood vessels enlarge in diameter (Pocock, Richards and Richards, 2013), this enabling the blood pressure to return back to its normal range (Pocock, Richards and Richards, 2013).Alternatively if blood pressure lowers the brain obtains a message from the receptors, causing the heart rate to increase and blood vessels to decrease in diameter (Pocock, Richards and Richards, 2013), also known as vasoconstriction (Pocock, Richards and Richards, 2013). Whilst undertaking exercise our blood pressure usually increases (Pocock, Richards and Richards, 2013), shown in figure 2, this is our bodies way of reacting to the increased need of oxygen by our muscle tissue (Pocock, Richards and Richards, 2013). In this instance the body reacts by increasing the blood flow to muscle tissues (Pocock, Richards and Richards, 2013). This process of resetting the normal homeostatic range is required to meet the expanded need of oxygen by muscles (Pocock, Richards and Richards, 2013). Equally when you deny your body of food or starve yourself, the set point of the metabolic rate can be reset to a lower than normal value (Pocock, Richards and Richards, 2013). Figure 2: An illustration of factors that increase blood pressure. Sv= stroke volume, HR=heart rate (Marieb, 2006). The normal range for blood pressure is 120 over 80 (120/80) to 140 over 90 (140/90) (Bloodpressureuk.org, 2018), anything higher than this is called hypertension and can cause stroke or heart failure (Bloodpressureuk.org, 2018). Anything lower than the range is called hypotension (Bloodpressureuk.org, 2018) this can cause you to faint or feel dizzy (Bloodpressureuk.org, 2018): Thermoregulation is whatâ??s known as the process in which the human body which maintains its core temperature (Khan Academy, 2018), your hypothalamus is the part of your brain that controls this (Khan Academy, 2018). A negative feedback loop will enable your bodyâ??s temperature to be brought back down towards the set point of 37 °C if it is too high or too low (Khan Academy, 2018). To enable metabolism to be sustained it is crucial a constant temperature is maintained, the heat we generate should be equal to the heat we lose (BBC.co.uk, 2018). Within our skin are temperature receptors, these detect alterations in external temperature (BBC.co.uk, 2018). This information travels on to the hypothalamus, also known as the brains processing centre (BBC.co.uk, 2018). Within our skin are temperature receptors, these detect alterations in external temperature (BBC.co.uk, 2018). This information then travels to the hypothalamus known as the brains processing centre (BBC.co.uk, 2018). Temperature receptors are also in the hypothalamus, their job is to detect deviations in the blood temperature (BBC.co.uk, 2018). The hypothalamus is then responsible for instantly initiating changes to the sweat glands and muscles to keep the body temperature on its equilibrium (Bbc.co.uk, 2018). Figure 3: An image showing the four parts involved in a negative feedback loop, showing an example of how body temperature is regulated by the negative feedback process (Khan Academy, 2018). Pick one example of negative feedback and analyse the mechanisms involved. There are many organs involved in body temperature control; the skin, the autonomic nervous system, the skeleton system, the circulatory system, the endocrine system and the brain (hypothalamus) (BBC.co.uk, 2018). If your body temperature increases the hypothalamus is activated, which stimulates the sweat glands shown in Figure 4 (Khan Academy, 2018). The sweat glands are one of the bodyâ??s cooling systems (Khan Academy, 2018). Glands within the skin secrete sweat to reduce the bodyâ??s temperature (Khan Academy, 2018). On completion of the temperature being decreased and restored to its normal range (Khan Academy, 2018), a message is sent via a negative feedback loop to notify the hypothalamus that it can stop activating sweat glands (Khan Academy, 2018). Figure 4 below shows a summary of the process when temperature is increased and decreased and the outcome which is a never-ending cycle of a healthy person (Khan Academy, 2018). Figure 4: Showing the bodyâ??s ability to regulate temperature in response to signals from the nervous system. (Khan Academy, 2018). If you are fit and well your body temperature should range between 36.5â??37.5 °C (Khan Academy, 2018). If your temperature goes outside of these ranges it could be fatal (Khan Academy, 2018). If your body temperate decreases too much it will result in hypothermia (Khan Academy, 2018) and all metabolic processes begin to slow. If it increases outside its range it will result in hyperthermia (Khan Academy, 2018) shown in Figure 5.A fever can be the result of an infection or virus (McCallum, Higgins, 2012), the bodies automatic defence mechanism is to get rid of these attacking organisms (Rosenzweig, Leiman and Breedlove, 2003), heat stroke is another good example of hyperthermia (Rosenzweig, Leiman and Breedlove, 2003). Dilation of cutaneous blood vessels (radiation) Hypothalamic heat loss centre activated Trigger â?² body temperature ( due to hot environment) Trigger â?¼ body temperature due to cool ( climate) Hypothalamic heat promotion centre activated Additional heat produced by skeletal muscles twitching (shivering) Vasoconstriction of cutaneous blood vessels causing blood to be shunted to deeper-lying organs to â?¼ heat loss to the environment Activation of sweat glands ) evaporation ( Body temperature â?¼ to normal range Body temperature â?² to normal range Normal range body temperature 35.6 o C-38.2 o C Dilation of cutaneous blood vessels (radiation) Hypothalamic heat loss centre activated Trigger â?² body temperature ( due to hot environment) Trigger â?¼ body temperature due to cool ( climate) Hypothalamic heat promotion centre activated Additional heat produced by skeletal muscles twitching (shivering) Vasoconstriction of cutaneous blood vessels causing blood to be shunted to deeper-lying organs to â?¼ heat loss to the environment Activation of sweat glands ) evaporation ( Body temperature â?¼ to normal range Body temperature â?² to normal range Normal range body temperature 35.6 o C-38.2 o C Figure 5: Outlines the autonomic physiological mechanisms that are activated through the thermoregulatory centre to keep body temperature within the normal range (McCallum, Higgins, 2012). Responsible for controlling responses to cold is the posterior hypothalamus (McCallum, Higgins, 2012). Alternatively, the anterior hypothalamus controls responses to heat (McCallum, Higgins, 2012). The Hypothalamus in the brain has thermoreceptors that identify the decrease in temperature of the blood (McCallum, Higgins, 2012), along with receiving impulses from the skin to identify it (McCallum, Higgins, 2012). Electro-chemical nerve impulses are then transmitted to the skin to increase sweat secretion (Rosenzweig, Leiman and Breedlove, 2003). If your body temperature decreases the blood flow also decreases (McCallum, Higgins, 2012). Shivering is a way in which the body tries to generate heart from your muscles (Khan Academy, 2018). Goose-bumps is also another way the body tries to increase heat production (Khan Academy, 2018). When goose-bumps happen it is, your hairs standing on end, this traps air between the skin and hair which increases a heat production hormone (Khan Academy, 2018). Another response to low temperature is; the thyroid glands secrete adrenaline and thyroxine together (Rosenzweig, Leiman and Breedlove, 2003), which increases the metabolic rate in different tissues, especially the liver, this generating heat (Rosenzweig, Leiman and Breedlove, 2003). Chemicals called pyrogens are dispensed by white blood cells (Rosenzweig, Leiman and Breedlove, 2003), these increase the thermoregulatory centreâ??s set point resulting in a body temperature increase (Rosenzweig, Leiman and Breedlove, 2003). The hormone estrogens can encourage vasodilation, heat dissipation, lower body temperature (Pocock, Richards and Richards, 2013) and progesterone can have the conflicting effect (Pocock, Richards and Richards, 2013). Temperature is measured with a thermometer and can be taken by oral, rectal, ear or forehead (NHS.uk, 2018).Positive feedback mechanisms enhance the original stimuli, they move the system away from its equilibrium (Khan Academy, 2018).A good example of a vital body function controlled by positive feedback is the process of blood clotting (Marieb and Hoehn, 2007).This is a normal response to a tear in the lining of a blood vessel.n the event of a blood vessel wall breaking a chain of events occurs to complete homeostasis, the stoppage of the blood flow (Marieb, 2006).This reaction is quick and localised including lots of substances that are in plasma (Marieb, 2006), along with others that are released by platelets and damaged tissue cells (Marieb, 2006).When vessels get damaged platelets instantly start to cling to the injured location (Marieb, 2006) see figure 6, whilst doing so release chemicals that draw more platelets (Marieb, 2006). Consequently, a final clot is made from this quick growing pile up of platelets (Marieb, 2006). Figure 6: A summary of the impact positive feedback has on regulating blood clotting. (Marieb and Hoehn, 2007). Due to the response following on to an even greater response as opposed to closing off the stimulus (Marieb, 2006), it involves positive feedback. When the clot binds the break in the vessel the cascade ends (Marieb, 2006). If a penetration wound occurs the initial threat is major blood loss (Betts et al., 2013), less blood circulating leads to decreased blood pressure and reduced perfusion to the vital organs and the brain (Betts et al., 2013). Second example of positive feedback: A good explanation of another positive feedback loop is child birth (Betts et al., 2013). In the process of labour a hormone named oxytocin is discharged (Betts et al., 2013), this exacerbates and accelerates contractions (Betts et al., 2013). The rise in contractions enable more oxytocin to be released (Betts et al., 2013), this cycle continues until the birth of the baby (Betts et al., 2013) shown in figure 7. Thus, the positive feedback mechanism ending when the birth ends the releasing of oxytocin (Betts et al., 2013). Figure 7: A positive feedback loop of a childbirth resulting in a change in the bodyâ??s status, rather than a return to homeostasis (Betts et al., 2013).. Child birth and the bodyâ??s reaction to blood loss, are both examples of positive feedback loops, (Betts et al., 2013) thus only taking effect when required (Betts et al., 2013). Full term child birth is an example in which the sustaining of the current body state is not wanted (Betts et al., 2013). Considerable changes in the motherâ??s body are necessary to push out the baby at the end of the pregnancy (Betts et al., 2013). The hormones, corticotropin-releasing hormone (CRH) and cortisol, increase within the last few days and weeks of gestation (MoÌ?ckel, 2008). The increase in stress hormones triggers an increase in the steroid hormone estriol (MoÌ?ckel, 2008). Estriol is a type of estrogen that is dominating whilst in labor (MoÌ?ckel, 2008). As estriol increases, it inhibits the synthesis of progesterone via the placenta whilst equipping the smooth muscles of the uterus for labour (MoÌ?ckel, 2008). Estriol and different estrogens rise the affectability of smooth muscles in the uterine wall to the hormones that will trigger uterine contractions (MoÌ?ckel, 2008). This additionally arranges uterine contractions (MoÌ?ckel, 2008). As estrogen initiates to stimulate uterine contractions, (MoÌ?ckel, 2008) the uterus likewise creates hormones called prostaglandins. These additionally add to a decline in progesterone levels (MoÌ?ckel, 2008). Once child birth has started, is must advance quickly to avoid risk to the mother and babyâ??s life (Betts et al., 2013). The intense muscular work of labour along with delivery are the consequence of a positive feedback system see figure 7 (Betts et al., 2013). The first contraction of labour is the stimuli (Betts et al., 2013), this pushes the body down towards the cervix, which is the bottom area of the uterus (Betts et al., 2013). Within the cervix is a stretch-sensitive nerve cells (Betts et al., 2013), theses observe the extent of stretching (Betts et al., 2013). Messages are sent to the brain from these nerve cells (Betts et al., 2013), this leads the pituitary gland at the bottom of the brain (Betts et al., 2013), to discharge the hormone oxytocin into the circulatory system (Betts et al., 2013).In the uterus, stronger contractions of the smooth muscle are made by oxytocin (Betts et al., 2013), pushing the baby further down the birth canal (Betts et al., 2013).As a result this brings about the cervix being greater stretched (Betts et al., 2013).Once the baby is born the cycle of stretching, oxytocin release and rapidly more stronger contractions stops (Betts et al., 2013). The discharge of oxytocin holts when the extension of the cervix holts (Betts et al., 2013).