homeostasis

• humans need to stay around 37 degrees Celsius, this is the temperature at which your enzymes work best. your skin temperature is able to vary a lot without problems but it is the temperature deep inside your body which must remain, this is the core body temperature.
• in the body, it is the thermoregulatory centre that is located in the hypothalamus of the brain that controls the core body temperature. this centre contains receptors that are sensitive to temperature changes in the blood flowing through the brain itself.
• extra information comes from the temperature receptors in the skin. these send impulses to the thermoregulatory centre, giving information about the skin temperature. these receptors are highly sensitive
• when the core body temperature begins to rise, impulses are sent from the thermoregulatory system to the body so more energy is transferred to the surroundings to cool you down
• when your core body temperature increases, some responses will include vasodilation of the blood vessels, allowing more blood flow through the capillaries. your skin will flush so you transfer more energy by radiation from your skin to the surroundings, cooling you down and warming the air around you.
• when your core body temperature increases, you produce more sweat from the sweat glands in your skin. this extra sweat cools your body down as water evaporates from your skin, transferring energy to the environment
• if you get too cold, the rate of enzyme controlled reaction in your cells decreases. if your core body temperature gets too low, receptors will send impulses to the thermoregulatory centre in the hypothalamus, this will cause impulses to be sent to the rest of the body to reduce the energy transfer to the environment
• when your core body temperature gets too low, vasoconstriction happens which reduces the blood flow through vessels so less energy is transferred through the skin by radiation. sweat production is also reduced/ stopped so less water from sweat evaporates so less energy is transferred to the environment
• when core body temp is too low your skeletal muscles contract and relax rapidly, causing you to shiver. these muscles contractions require energy from cells through respiration, an exothermic process. the energy transferred from these exothermic reactions raise your body temperature until your shivering stops.
• when cold, the hair on your skin will be pulled erect to trap the insulating layer of air. when hot these hairs will lie flat
• homeostasis is about maintaining a stable internal environment. the body needs certain conditions to function properly, it cant be too hot, too cold, too acidic, too alkaline and must have good supply of things like glucose and water
• homeostasis is the regulation of conditions inside the body to maintain a stable internal environment in response to both internal and external factors
• the body has automatic control systems. these include receptors which detect a stimulus, a coordination centre like the brain or the spine and effectors e.g. the muscles or glands.
• negative feedback will do the opposite of what the change was
• thermoregulation is the control of our internal body temperature
• if we fall too far below the optimum temperature of the body (37 degrees), enzyme activity will slow down, if the temperature is too high, the enzymes may denature and stop working all together
• the thermoregulatory centre is in the hypothalamus of the brain and acts as a thermostat for our body
• to warm up we need to conserve the heat we have, e.g. vasoconstriction so less heat energy is lost because less blood is near the surface, and our hairs will stand due to erectors muscles contracting. we also need to generate more heat like how we shiver, this is the muscles contracting and relaxing repeatedly, this requires lots of energy from respiration. all of these reactions will release heat energy as waste
• to cool us down our erector muscles will relax allowing the hairs to fall down, the blood vessels vasodilate allowing more heat energy to be transferred to the surroundings because blood is nearer the surface of the skin. we also sweat, as sweat evaporates heat energy is taken away with it from the body
• for the body to work properly, the conditions around the cells must stay as constant as possible although, everything we do changes things. for example as you move, you respire, warming the body, as you respire you produce waste and when you digest food, you take millions of molecules into your body
• the cells of your body are producing waste products, these are the products of the chemical reactions that take place in cells. the more extreme positions you put yourself in, the more waste products your cells make. the 2 main waste products made by the body are carbon dioxide and urea, these both can cause problems if their levels build up
• carbon dioxide as a waste product is produced by the body cells during respiration, it must be removed because dissolved carbon dioxide produces an acidic solution, this would affect the pH levels of the enzymes working in your body. carbon dioxide diffuses from the blood into the alveoli down a concentration gradient, the air containing this is removed from your body when you exhale
• urea as a waste products is produced by the breakdown of excess amino acids in the liver. the urea passes from the liver cells into your blood, it is then filtered out of your blood by your kidneys and is then passed out the body in the urine produced by the kidneys along with any excess water and salt
• your liver removes the amino group from the amino acids in a process called deamination, this forms ammonia which is very toxic. the ammonia is immediately converted into urea for safe excretion from the body
• we cant always control when waste products leave the body, for example when we sweat, water, mineral ions and urea are lost through the skin. we can control urea, excess water and excess mineral ions excreted in the urine
• your kidneys remove urea, excess water and mineral ions through urine. urine is produced constantly by by your kidneys and stored temporarily in your bladder.
• if you are short of water, your kidneys will conserve it. you will produce very little, very concentrated urine and water is saved for use in the body. if you have too much water in the body, you kidneys will get rid of it by producing lots of dilute urine to get rid of the excess
• your kidneys filter your blood, glucose, mineral ions, urea and water all move out of the blood into the kidney. the blood cells and large proteins are too big to leave the blood in the filtering process. urine trickles from your kidney to the bladder where it is stored
• all of the glucose filtered out of the blood in the kidney will be reabsorbed by diffusion and active transport. however, the amount of water and dissolved mineral ions that are reabsorbed varies, depending what is needed by the body. this is known as selective reabsorption
• kidneys can become damaged by infections and some people have genetic problems that means their kidney will fail. failure of both kidneys can lead to death, this is because toxins such as urea build up in the body and the mineral ion and water balance of the body is not maintained, this can cause cells to be damaged by osmosis
• if someone is having problems with their kidneys, they have two main options. the first is dialysis, this is an artificial kidney and the function of the kidney is done artificially or they can have a kidney transplant, where the damaged kidney will be replaced with a healthy one.
• a dialysis machine can carry out the function of the kidney, dialysis will clean the blood. in the machine, a persons blood will leave the body and flow between partially permeable membranes. on the other side of the membranes is the dialysis fluid. the fluid contains the same concentration of useful substances of a healthy person
• treatment by dialysis restores the concentration of urea and mineral ions down to a normal level but as you carry on with normal life, urea and waste substances build up again, so dialysis has to be repeated at regular intervals. it takes around 8 hours for dialysis to be complete so people with kidney failure have to remain attached to a dialysis machine for hours, several times a week. they also have to manage their diets carefully to keep their blood chemistry as stable as possible
• diseased kidneys can be replaced using a single healthy kidney from a donor, this is known as a kidney transplant
• the main problem with transplanting a kidney is that the new kidney comes from a different person. the antigens of the donor organs will be different to those of the recipient. there is a risk the the antibodies of the immune system will attack the unrecognized antigens on the kidney resulting in rejection and destruction of the donated kidney
• to avoid kidney rejection, we can ensure that the match between antigens of the donor and the recipient are as close as possible for example ensuring the peoples tissue type are similar. the recipient can also be given drugs to suppress their immune system for their life.this helps avoid rejection but it prevents patient from dealing with any other infections or diseases they get in their life
• dialysis or transplant?

  dialysis is much more readily available when the kidneys fail as it can take years to wait for a new kidney. however the patients are tied to a special diets and regular sessions on the machine. long-term dialysis is much more expensive than a transplant and eventually dialysis can cause serious damage to the body.
• dialysis or transplant?

  if you receive a transplant, you are free from the restrictions that come with dialysis and can live almost a completely normal life. although there is the risk for rejection and you have to take immunosuppressant drugs for the rest of your life. you need regular check ups in case there are any signs of rejection
• urea is the main waste product filtered by the blood, it is produced in the liver during the process of deamination. deamination is where excess amino acids are converted into fats and carbohydrates for storage
• the kidneys also regulate the level of ions and water. potassium and sodium are ions we get from our diet. ions are lost through the kidney filtering or sweating