P5 M2 D2 ANATOMY AND PHYSIOLOGY !

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Explain the concept of homeostasis (P5) Discuss the probable homeostatic responses to changes in the internal environment during exercise (M2)

Homeostasis can be defined as the maintenance of a constant internal environment within the body. Sensors within our body monitor a number of things including breathing, heart rate, body temperature and also blood sugar levels. These can also be known as detectors, which send signals to the control centre when there is a change, or the value has deviated from the norm. This value will then be corrected so that the norm can be maintained (study.com, 2015). 

Negative feedback is important in homeostasis and it responds when certain conditions change. This therefore means that receptors and effectors, i.e. muscles or organs, carry out a reaction so that these conditions can remain. This may also be explained by saying that a change in variable is detected by the receptor and the information from this is sent along an afferent pathway to the control centre. The control centre then sends the information along an efferent pathway to the effector whereby it either opposes or enhances the stimulus (Bioserv, 2001).

In the medulla oblongata there are chemoreceptors which are adjacent to the respiratory centre. These chemoreceptors are sensitive to the changes of arterial PCO2, PO2 and also pH, and send information to the medulla, determining the nervous response depending on the changes of the variables (Bioserv, 2001). Nerve impulses are therefore then sent to the repiratory muscles controlling both the force and how often it contracts. Furthermore, this changes the rate and depth of breathing and also ventilation (UWE, 2015). The change in ventilation brings CO2, O2 and pH back to their norm. Nerve impulses are sent along the phrenic nerve towards the external intercostal muscles which stimulates muscle contraction for inspiration. Expiration occurs due to the elastic recoil of the lungs and chest wall. This nerve firing is what gives us our resting breathing rate of 12-15 breaths per minute. During exercise, the muscles have to metabolise faster as they require both more oxygen and nutrients. Due to this, the heart then pumps the blood harder and faster to keep up this demand, as the heart is doing more work to supply this blood. This means that more oxygen is required, meaning, the response given is breathing being increased so that oxygen is pumped to all cells quicker. Due to homeostasis, levels of oxygen in the blood are always being measured, ensuring oxygen, carbon dioxide and also pH levels return to their norm. Messages that are sent to the effectors informing them that the breathing rate has to be increased, however, will decrease again when all activity has been stopped.

Homeostasis also controls heart rate. The medulla which is located within the brain also controls heart rate. It sends information or messages normally in form of chemicals/hormones. When we are carrying out exercise the heart has to supply oxygenated blood to the rest of the body. There is information sent to the medulla from the muscles via the nervous system. This allows the release of chemicals, to travel to the sinus node. The sinus node then therefore stimulates the contractions of the heart, also increasing the force which in turn, increases heart rate. When you are at rest, or stop exercising, another message is sent to the medulla, which in turn releases acetylcholine, slowing the heart rate. When engaging in more intense exercise, epinephrine and norepinephrine is released, increasing heart rate to supply more oxygen to the body.

There are two pathways known as the autonomic nervous system and the parasympathetic nervous system. During exercise the sympathetic nervous system is activated and this increases heart rate and also the force of the contractions due to the nerve impulses being transmitted to the heart via the sympathetic nervous system (Cvphysiology, 2013). In comparison the parasympathetic nervous system decreases heart and rate and therefore it returns back to the norm and this system is activated when we are resting. The vagal nerve is what reduces heart rate.

The sinoatrial node (SA node) acts as the body’s pacemaker. The impulses initiate at the SA node moving a wave of electrical excitation across the atria, which respond by contracting. The ventricles are relaxed meaning that more blood is being pushed into them. The impulses are then passed to the atrioventricular node (AV node), however, the AV node delays the passage of impulses to the bundle of His and is then conducted to the purkinje fibres (Campton, 2010). The ventricle walls will contract from the apex working up, meaning that blood is ejected from the ventricles efficiently sending blood to the lungs and the rest of the body (Campton, 2010).

The level of glucose within the blood is also controlled by homeostasis. The maintenance of the level of glucose within the blood involves both the pancreas and the liver. Islets of Langerhans are cells located in the pancreas and these secrete two hormones known as insulin and glucagon. Blood sugar rises after we have ate a meal resulting in the stimulation of the pancreas cells, meaning b-cells of Langerhans are stimulated, releasing more insulin, enabling the sugar uptake by cells and also the storage of sugar within the liver and muscles. As a result, blood sugar levels are decreased (Tortora and Anagnostakos, 2003 recited in Nursing times, 2015). If however, blood glucose levels are low, the body will not be able to produce the sufficient amount of ATP needed for bodily functions. Alpha cells in the pancreas are then stimulated releasing glucagon into the blood. The liver then breaks this down into glucose which is then released into the blood. Glucose levels in the blood have now risen and there is no need for the release of glucagon (Bioserv, 2001). During exercise there is a demand for glucose due to the contraction of the muscles and more energy being required and so this causes an increased uptake of glucose to working skeletal muscles which is caused by an increase in the insulin. Normal blood glucose levels however, can be maintained during exercise by increased glucose production and the release through the stimulation of the breakdown of glycogen and glucose synthesis from other substances. This increase allows the maintenance of blood sugars. When we stop exercising, receptors send information to the liver telling it to slow down glucose production.

There are four different ways in which heat can be gained or lost from the body including radiation, evaporation, convection and conduction. Radiation is when heat from the body is given off into the atmosphere. Evaporation is when you sweat and the evaporation from the liquid generates heat, resulting in a cooling effect. Convection is the process of heat leaving the body via moving air flowing by the skin. Conduction is the transfer of heat from direct contact with another object (Beyondcoldwater, 2011)

The main control centre in the brain that controls body temperature is known as the thermoregulatory centre. When we exercise, body temperature will increase as the body is working hard in attempt to be able to have more oxygen in the blood which then can be delivered to the muscles providing them with energy. Change within the temperature in the blood is detected by thermoreceptors. There are also receptors which are in the skin and they detect changes in temperature within the environment. Homeostasis will occur due to the negative feedback triggering homeostatic mechanisms. The hypothalamus in the brain detects signals and sends impulses to both blood vessels and sweat glands. Firstly the hairs on the skin lie flat as the erector muscles are relaxed. This therefore increases the process of heat loss by conduction and radiation. Increased sweating also known as hyperhidrosis is due to the sweat glands releasing a salty liquid onto the skins surface, taking heat with it. Blood vessels can also dilate allowing more blood to flow through. The blood flows close to the body’s surface meaning that there is increased radiation. This is a process known as vasodilation. Also due to an increased body temperature there will also be increased sweating, and the need to drink due to thirst. When we become too cold however, the opposite of this happens and begin to shiver as a mechanism to rise body temperature. Heat loss will be reduced as the hairs on the skin stand so that they are able to trap a layer of air, acting as an insulator.

In conclusion, homeostasis is important as it maintains the appropriate levels within our body that our cells need to function properly and it allows us to adapt to environmental changes. It keeps the body at a norm, however, if conditions are at the extreme, the negative feedback mechanism will no longer work, resulting in death, if there is no medical help.

D2

Evaluate the importance of homeostasis in maintaining the healthy functioning of the body (D2).

Homeostasis is maintaining a constant internal balance within the body, which can adjust to extreme external conditions/factors. Cold blooded organisms for example are unable to maintain and regulate their internal body temperature, and so when they become too cold they are slow. Therefore, this means that ectotherms, rely on external factors such as the sun to regulate their temperature. On the other hand, warm blooded organisms are able to regulate and maintain their body temperature by carrying out exercise. Due to homeostasis, both the nervous and endocrine system will maintain a core body temperature, resulting in shivering when it is too cold at low temperatures or sweating if the temperature rises. During exercise, we can maintain body temperature as we sweat to cool down. To account for this loss in water, there will be a decrease in the production of urine. ATP is produced from the stores of glucose, therefore breathing becomes faster which will provide the body with more oxygen and also heart rate will increase meaning that blood can be pumped around the body at a faster rate.

The body is able to maintain our temperature, even if we are surrounded by extreme conditions e.g. a snow storm, or extreme heat, this is due to homeostasis. If we were in extreme heat, homeostasis would occur to ensure that we survive. The body would start to sweat and the process of vasodilation would occur, cooling down the body. The opposite would then happen if we were in a snow storm. The body would start to shiver, producing heat and also vasoconstriction would occur, rising body temperature. If however, homeostasis did not occur this would then start to cause problems as the body would be unable to recognise the changes within the environment and respond to them appropriately.

If we are in extremely hot conditions for a long period of time, the enzymes in the body will start to denature and this in turn results in the body cells dying (ABPI, 2015). This is known as hyperthermia. Due to this homeostatic mechanisms will stop working and so the hypothalamus can no longer function. If there is an excessive amount of sweating, too much salt may be lost from the body, making ions in the blood fall out of balance, leading to cramps in the muscles (ABPI, 2015). This extreme heat can also effect the messages from the brain to both the nerves and spinal cord slowing them down. Dehydration may also occur, meaning that the kidneys will hold on to urea and ammonium, however, this can be dangerous, as these toxins need to be removed (Campton, 2010). The heart may also start to beat faster as it needs to maintain blood pressure, therefore blood vessels will dilate (Bradfield, 2001)

On the other hand, if the body was exposed to extremely cold conditions, homeostasis still may not work. Hypothermia is define as when the core body temperature drops to below the norm for bodily functions to be carried out efficiently and so chances of survival would decrease. Shivering may occur however, this may not work and so when hypothermia gets more severe it will stop. Heart rate and breathing rate will decrease and there may also be an incontinence of urine due to the kidneys having a larger workload which also relates to the blood being shunted to the major organs (better health channel, 2015). If there was no action taken to support homeostasis then the body would eventually shut down, resulting in death.

A continuous supply of glucose is required by the body to carry out normal metabolism. This glucose is then converted to ATP. B-cells of Langerhans are stimulated, releasing insulin into the blood if the blood glucose levels rise, leading to a decrease in these levels. The opposite then happens if blood glucose levels fall. The a- cells of Langerhans, releases glucagon into the blood, rising blood glucose levels. In relation to blood glucose, if there was a homeostatic imbalance it could result in the development of type 1 diabetes. Type 1 diabetes is when beta cells in the pancreas are destroyed, therefore, preventing the body from producing enough insulin to regulate blood glucose levels (Diabetes.co.uk, 2015). This is also known as hyposecretion of insulin. If blood glucose levels get too low, then hypoglycaemia may occur (Diabete.co.uk, 2015). Diabetes can also lead to long term complications such as heart disease, stroke or kidney disease just to name a few. Diabetes is an example of what may happen if the homeostatic mechanism fails.

Homeostasis helps to control breathing rate. The respiratory centre and chemoreceptors regulate the breathing rate by sending information to the medulla. This in turn increases carbon dioxide levels in the blood, and nerve impulses are then sent to respiratory muscles. These muscles are then informed that they have to work harder, ensuring that there is a sufficient supply of oxygen in the blood (Campton, 2010). If the mechanism happened to fail, oxygen supplies in the blood would be insufficient, as there the blood would contain an increased amount of carbon dioxide. This may cause problems as the body needs oxygen for all body cells to work efficiently carrying out their bodily functions and without which, the body would shut down.

The medulla also controls heart rate as well as the sinus node. The sinus node receives information, responding accordingly, depending on the body’s needs. An example of this would be if the body isn’t receiving enough oxygen for the muscles to work efficiently during exercise, meaning the sinus node would then give instructions for the heart to work faster, pumping the blood around the body quicker and at a stronger force. If the homeostatic mechanism was not initiated due to problems with either the medulla or the sinus node, the body would become oxygen deprived and so would result in a heart attack, resulting in possible death if the body was to be left in this way for a period of time (Bradfield 2001

In conclusion, homeostatic mechanisms in the body are vital for survival and without such mechanism, it may result in heart failure and possibly even death, highlighting just how important it is.

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