Homeostasis is the maintenance of a constant internal environment in organisms. It involves volume of blood and tissue fluid within restricted limits, it also maintains chemical makeup of the blood. Autonomic control systems throughout the body maintain temperature and water levels, which are required for cells to function properly. Although homeostasis maintains the internal environment it does not mean that there are no changes. There are continuous fluctuations brought about by variations in internal and external conditions such as temperature levels and the balance of alkalinity and acidity. The inability to maintain homeostasis could lead to disease or even possibly death, it can also lead to a condition known as homeostatic imbalance.
For instance when the negative feedback mechanisms become overwhelmed or destructive positive feedback mechanisms take over, heart failure can be a result. Other diseases which result from homeostatic imbalance include diabetes, dehydrations, hypoglycaemia, hyperglycaemia, gout and other diseases which are caused by the presence of toxins in the bloodstream. Homeostatic mechanism use negative feedback to maintain a constant level. Negative feedback means that changes have occurred in the body, which automatically causes a corrective mechanism to begin, this then reverses the original change and bring the system back towards the set point.
This also means that the bigger the change the larger the corrective mechanism is. Negative feedback also applies to biological systems, so in a system controlled by negative feedback the set level is never perfectly maintained but constantly is around the set point. When there is a significant time lag before the corrective mechanism is activated it mean that it has taken a bit longer for protein synthesis to commence, the hormone to diffuse into the bloodstream and for it to circulate around the body and take effect.
Symptoms and Explanation
If someone has mild hypothermia which is 32-35 degrees the symptoms are constant shivering, tiredness, low energy, cold or pale skin and fast breathing. Moderate hypothermia is 28-32 degrees and include not being able to think or pay attention, confusion, difficulty moving around and loss of co-ordination. Severe hypothermia which is 28 degrees has symptoms including unconsciousness, shallow to no breathing at all, an irregular pulse rate, dilated pupils, and they may appear to be dead but must be taken to the hospital to professionally determine whether they have died.
Symptoms of hyperthermia include heat stroke at a very severe rate – this occurs when the body is no longer able to regulate the internal temperature. Other symptoms include muscle cramps, fatigue, dizziness, headaches, nausea, vomiting and weakness. The heart rate may elevate and the skin may become redder, confusion and mental changes may begin to develop and seizures have been known to follow leading on to brain damage in the future.
Hypoglycaemia occurs when the level of glucose present in the blood falls below a set point which is 4mmol. The main symptoms of hypoglycaemia is sweating, fatigue, feeling dizzy and paleness. Symptoms can also include feeling weak and hungry, having a higher heart rate than usual, blurred vision, temporary loss of consciousness and confusion. In the most extreme cases a coma could potentially occur.
Hyperglycaemia is an extremely high blood glucose level. It is a sign of diabetes both type 1 and type 2. The main symptoms of hyperglycaemia are increased thirst and frequent need to urinate. Severely escalated hyperglycaemia can result in medical emergencies like diabetes cetaclosis. Insulin is the treatment choice for this if you have type 1 diabetes, type 2 must take multiple oral and injectable medicines to cure their diabetes.
When blood pressure in your arteries is abnormally low it is known as hypotension. If blood pressure drops too low it can restrict the amount of blood flow to the brain and other vital organs which can cause unsteadiness, dizziness and light headedness. Other symptoms include blurred vision, rapid or irregular heartbeat and feeling sick with general weakness,
Hypertension means that your blood pressure is continually high than the recommended level. High blood pressure can increase the risk of heart attack or a stokes and it is often referred to as a silent killer.
The way that control mechanisms is as follows:
Autonomic Nervous System
The autonomic nervous system regulated the functions of our internal organs, such as the heart, stomach and the intestines. It is a part of the peripheral nervous system and also controls some of the muscles within the body. Its functions are involuntary and reflexively which means we are often unaware of it. It has 1 divisions the sympathetic nervous system and the parasympathetic nervous system. Changes to the heart rate are controlled by a region of the brain called the medulla oblongata. This region of the brain has 2 centres which increase the heart rate which is link to the sinoatrial node by the sympathetic nervous system. A centre which decreases the heart rate which is linked to the sinoatrial node by the parasympathetic nervous stem.
The control of body temperature is fundamental in maintaining a constant internal environment and to help keep the internal body temperature suitable there are a variety of bodily responses for when it differs. For example, in warm conditions peripheral vasodilation and sweating is initiated by the body allowing heat to be released via the skins surface to maintain a constant core temperature. The thermoregulatory mechanisms play a very important role in maintaining homeostasis during rest and physical exercise. In humans body temperature is controlled by the thermoregulatory centre in the hypothalamus.
It receives input from two sets of thermoreceptors: Receptors in the hypothalamus itself which monitor the temperature of the blood as it passed through the brain and receptors in the skin which monitor the external temperature. Both receptors are important in allowing the body to then make the appropriate adjustments. The thermoregulatory centre sends impulses to several different effectors in order to adjust the body temperature. The thermoregulatory centre maintains the temperature of the body at a set point of 37.5 degrees.
However this set point can be altered by the following circumstance: Fever is when chemicals known as pyrogens are released by the white blood cells, raising the set point of the thermoregulatory centre enabling the whole body’s temperature to increase around 2-3 degrees. This allows bacteria to be killed and also explains the reason why you shiver even though you’re hot.
Response to low temperature
Response to high temperature during exercise
Smooth muscle in the arterioles of the skin
Vasoconstriction results from the muscles contracting. Less heat is transported from the core to the surface of the body, maintaining the core temperature. Frostbite can occur causing extremities to turn blue. Muscles relax causing vasodilation meaning more heat is carried from the core to the surface where it is lost by convection and radiation. Skin turning red is another response to the body becoming hot.
No sweat produced
The glands release sweat onto the surface of the skin where it then evaporates. Since water has high latent heat of evaporation it also heat in the body to be released. Erector pili muscle in the skin
Muscles contract raising the hair on the surface of the skin, tapping an insulating layer of still, warm air next to the skin. It is not the most effective method in humans it tend to generally cause goose bumps. Muscles relax lowering the hairs on the surface of the skin therefore allowing air to circulate over encouraging convection and evaporation.
Shivering which is when the muscles relax and contract repeatedly this generates heat by friction and from metabolic reactions: 60% of increased respiration generates heat.
Adrenal and thyroid glands
The glands release adrenaline, and thyroxin, respectively this increases the metabolic rate in a variety of tissues, specifically the liver therefore generating heat. Gland stop releasing adrenaline and thyroxin.
Heart rate and Breathing rate
Homeostasis is greatly involved with controlling the respiratory rate. In a normal individual they are not able to be conscious of their respiration as the act of respiration involuntary. Respiration is an involuntary control mechanism and is determined by an area of the brain known as the medulla. Within the medulla there is an area known as the breathing centre, this centre is composed of different section allowing each to take on an alternate aspect to respiration. There is a dorsal and a lateral area to the medulla and these both work to assist inspiration providing a stimulation for respiration. As well as this there is a ventral area which increases both the depth and the rate of respiration. This breathing centre is connected with the intercostal nerves and the phrenic nerves which lead onto the diaphragm.
These provide a communication system between the thorax, the respiratory system and the medulla. The medulla is the main component which maintains a constant rate of respiration, although both external and internal stimuli can change the rate of respiration, altering it to be higher or lower than the average rate. The most common influences to this is the level of carbon dioxide the bloodstreams, as if the concentration of carbon dioxide in the blood increase the chemoreceptors in the aortic bodies become activated. The activation of these chemoreceptors allows message to be sent to the medulla which then sends nerve impulses are sent back down the phrenic and intercostal never to the intercostal muscles and the diaphragm. This process allow them to contract and relax at a faster rate therefore increasing the breathing rate, this generally occur when doing exercise as the muscles require more oxygen to function more quickly.
This is an example of negative feedback processes and it introduces more oxygen to the bloodstream and order to bring back the equilibrium of both oxygen and carbon dioxide levels in the blood. As for the control of breathing rate, the medulla is also used in the process of controlling the heart rate. The process of regulation the heart rate is rather complex and is as follows. When an individual exercises, receptors in the muscles send impulses to the medulla, when these messages are received the medulla then secrete epinephrine and norepinephrine, these two combined proceed through pathways within the nervous system until that reach the Sino atrial node, and this is located in the myocardium. These chemicals also activate the Sino atrial node allowing it to produce more electrical energy thus making the heart rate increase.
On the other hand, once the exercise has stopped the muscle then send additional impulses to the medulla which activated the stimulation of the secretion of the hormone acetylcholine, this hormone is used to bring the heart rate down by slowing the electrical impulses from the Sino atrial node, therefore decreasing the heart rate. In addition to this, the medulla also has the ability to recognize other factors which can increase the heart rate. These factors include things such as emotional stress. In case of emotional stress the medulla also takes information from the thalamus, which informs the medulla of the location of the stressor, this comes with the initial information from the nervous system. The response would be triggered and the combination of the two pieces of information enable the process to occur.
Glucose is a carbohydrate which is used as a transport mechanism in animals and its concentration in the blood affects every cell the body. It concentration should be maintain within the range of 0.8 – 1g per dm3 of blood, and having very low levels which leads to hypoglycaemia or very high levels which leads to hyperglycaemia are both extremely serious and could lead to death. The concentration of glucose in the blood is controlled by the pancreas, as the pancreas has a glucose receptor cell which monitor the concentration of glucose in the blood and it also has endocrine which enable the secretion of hormones. The alpha cells in the system release the hormone glucagon, while the beta cells secrete the hormone insulin, these 2 hormones are known as antagonistic and have opposite effects on the blood glucose levels of the body: Insulin hormone stimulates the absorption of glucose by cells to be used in respiration and in the liver it stimulated the conversion of glucose to glycogen, this is a process known as glycogenesis.
This therefore decreases the blood glucose. Glucagon stimulate the breaking down of glycogen to glucose in the liver, this is a process known as glycogenosis, and in severe cases it can also stimulate the syntheses of glucose from pyruvate, therefore increasing the blood glucose levels. After a meal glucose is absorbed into the hepatic portal vein from the gut, increasing the blood glucose concentration. This absorption is detected by the pancreas which then in response secretes insulin from its beta cells. The job of the insulin is to cause glucose to be up taken by the liver and converted into glycogen, as this will reduce the blood glucose causing the pancreas to stop secreting insulin.
If the glucose levels of the blood fall to much then the pancreas also detects this change and releases glucagon from its alpha cells, the glucagon causes the liver to break down some of its glycogen store into glucose, which then enters the bloodstream through diffusion. This increases the blood glucose levels and signals to the pancreas that the body no long requires the production of glucagon. Glucagon and insulin cannot be produced at the same time and this is because blood glucose levels are able to differ from the set point by around 20% before any corrective mechanisms are activated therefore no 2 can be produced at the exact same time.
Diabetes is a disease cause by the failure of glucose homeostasis. There are 2 forms of the disease, type 1 and type 2. In type 1 diabetes due to an autoimmune reaction there is a severe insulin deficiency, killing of the beta cells which are relied upon to release the insulin. Type 1 diabetes is most commonly an inherited condition, potentially triggered by a virus in the body. As stated in this form of diabetes no insulin is produced. On the other hand type 2 diabetes insulin is still produced unlike type 1, but the receptors with detect the insulin the target cells no longer function correctly, so the insulin which is produced does not take effect on the body, giving off the same effect has type 1.
This is often a response to over production of insulin over multiple years cause by a high sugar diet. 40% of the UK on average are diabetic to some extent. In both cases with both type 1 and type 3 there is a very high blood glucose concentration after each meal and therefore the active transport pumps in the proximal convoluted tubule of the kidney can’t reabsorb it all from the kidney filtration, and the glucose required in the body is expelled via the urine. This leads to the symptoms of diabetes which are: High thirst due to osmosis of water from cells to the blood, which has a low water potential. Copious urine production due to excess water in blood.
Poor vision due to osmotic loss of water from the eye lens. Tiredness due to loss of glucose in urine and poor uptake of glucose by liver and muscle Cells. ‘Ketone breath’ caused by the body breaking down lipids to supply energy Muscle wasting due to gluconeogenesis caused by increased glucagon. Type 1 diabetes can be treated by multiple injections after each meal to supply insulin to the body to ensure that the blood glucose levels to not exceed the set point. Type 2 diabetes can be treated by a careful diet, or by tablets which stimulate the insulin production and the sensitivity of the liver cells to the hormone insulin, allowing it to become effective and reduce the blood sugar levels after each meal.
If the pH of the blood was to change chemoreceptors found in the walls of the carotid arteries and the aortic bodies would detect it. It is sensitive to changes in the pH of the blood that result from changes in the carbon dioxide levels. Ventilation levels behave as if they were regulated to maintain a constant level of carbon dioxide partial pressure and to ensure adequate oxygen levels in the arterial blood. The body responds by increased muscular/metabolic activity which means more carbon dioxide produced by tissues from more respiration, this lowers the ph. Chemical receptors in the carotid arteries increases the medulla oblongata frequency. The medulla oblongata speeds the heart rate through the SA node. Carbon dioxide levels return to normal.
Courtney from Study Moose