[Music] hello and welcome to the ninth video in the a-level biology series today we are going to be covering homeostasis which describes the body's self-regulating process to keep a stable internal environment in this video we will discuss how the body controls blood glucose concentration blood water potential and internal temperature as mentioned homeostasis is crucial for the maintenance of a stable internal environment or set points which is vital for keeping cells healthy and functioning optimal temperature and ph are essential for enzyme activity for metabolic reactions extreme changes in blood glucose water potential and temperature from their set points from the norm can have detrimental effects on our bodies and health here are some examples when temperature is too high or 40 degrees or higher enzymes denature metabolic reactions become less efficient and cells collapse when temperature is too low enzyme activity is reduced slowing metabolism ph being too high or too low can also cause enzymes to denature glucose is important for energy production in the cell if blood glucose is too high the water potential of blood is reduced leading water to leave the cells by osmosis leading to cell death if blood glucose is too low cells cannot carry out key activities as energy is required to drive most processes and reactions in the cell the optimal levels for temperature and ph in the body are ph 7 and temperature at 37 degrees the body's systems sense change and respond by negative feedback mechanisms key components of these systems are receptors a communication system and effectors receptors sense a change in the environment which is communicated via the nervous system or hormonal system to effectors effectors act to counteract this change and bring levels back to normal through negative feedback mechanisms a negative feedback loop is a self-regulating process the idea that increasing the output from the system inhibits future production by the system the mechanism acts to return the levels back to normal for example increasing or decreasing the levels of output from the system i will illustrate this point in more detail in the following examples firstly the control of blood glucose concentration as we have covered in the previous topic of respiration glucose is essential for all cells to have energy to work the usual blood glucose concentration is 90 milligrams per 100 milliliters of blood these levels vary at different points in the day so sticking to the overall model of control systems one the sensor the cells of the pancreas monitor blood glucose levels two communication the sensing of blood glucose levels results in the release of hormones in response two hormones control blood glucose called insulin and glucagon these hormones are secreted by clusters of cells in the pancreas called the islets of langerhans alpha cells secrete glucagon and beta cells secrete insulin and number three effectors the two hormones bind to target cells such as liver cells and muscle cells in order to counteract the change in glucose levels in the blood when blood glucose is too high high blood sugar is sensed by the pancreas this promotes the release of insulin from the beta cells insulin binds to receptors on liver and muscle cells insulin stimulates an increase in glucose uptake in the cells by activation of glute4 glucose transporter in the membrane of cells insulin in the liver stimulates the conversion of more glucose into glycogen for storage therefore insulin increases the rate of respiration in muscle cells and this overall acts to reduce blood sugar levels when blood glucose is too low the low blood sugar is sensed by the pancreas glucagon is released by the alpha cells glucagon binds to receptors on liver cells the glucagon activates enzymes involved in the breakdown of glycogen into glucose a process called glycogenolysis enzymes are activated in the formation of glucose from glycerol and amino acids in a process called gluconeogenesis glucagon reduces respiration in cells these actions help overall to increase blood glucose levels diabetes mellitus is a condition in which blood glucose levels are not controlled properly leading to high sugar levels in the blood which can have severe impacts on the body and there are two types type 1 is when the immune system attacks the beta cells inhibiting insulin production and secretion insulin therapy and reducing carbohydrates are key for controlling the conditions type 2 usually develops later in life risk factors include obesity family history lack of exercise age and a poor diet this is when beta cells do not produce enough insulin to control blood sugar levels now for controlling water potential water potential is essential to control in the body water is crucial for cell and body function and must be kept at stable levels to prevent damage to cells and their processes [Music] water potential is sensed in the hypothalamus and is controlled by hormones and the kidneys the kidneys are a pair of bean-shaped organs located on either side of your spine they are about four to five inches long the role of the kidneys is to filter the blood removing waste substances and controlling electrolyte and fluids balance in the body each kidney contains millions of filtering units called nephrons nephrons are made up of two key parts the glomerulus and a tubule blood from the renal artery enters small arterioles in the cortex or the outer layer of the kidney each arteriole splits into a glomerulus a glomerulus is a bunch of capillaries looped inside a hollow ball-like structure called bowman's capsule the blood contained in the glomerulus is under very high pressure the arterioles carrying blood into the glomerulus are called afferent arterioles efferent arterioles take blood away from the glomerulus the efferent arterioles are under higher pressure than afferent arterioles which forces small molecules and liquid out of the capillary into bowman's capsule this is known as ultrafiltration and produces glomerular filtrate after the glomerulus the filtrate enters into the tubule where useful substances are reabsorbed waste substances are excreted by flowing through the tubules into the collecting duct and through the ureter to the bladder to summarize the kidneys excrete waste substances and regulate blood water potential by ultrafiltration as blood passes through arterioles into the glomerulus small substances are filtered out into long tubules of the nephron selectively reabsorption useful substances such as glucose water and electrolytes are reabsorbed into the blood through the capillaries surrounding the tubules any unwanted substances pass through the bladder for excretion from bowman's capsule filtrate passes through the tubules beginning in the proximal convoluted tubule or pct the loop of henle the distal convoluted tubule or dct collecting duct and then into the ureter and the bladder the pct loop of henle and dct are the areas involved in selective reabsorption glucose is reabsorbed into the blood in the pct by active transport and facilitated diffusion water is reabsorbed by osmosis in all sections of the tubule this is because the water potential in the blood will be much lower than the filtrate the loop of henle controls the gradient of sodium and chloride ions this controls the water potential in the medulla controlling how much water is reabsorbed [Music] if iron concentration increases in the medulla the water potential will decrease causing water to move out of the collecting duct by osmosis and then into the blood water moves out of the dct by osmosis for reabsorption in the blood the volume of water reabsorbed into the capillaries is controlled by changing the permeability of the dct and the collecting duct the filtrate remaining leaves via the ureter into the bladder as urine urine contains water dissolved salts urea hormones and excess vitamins urine should not contain proteins blood cells and glucose water is essential for cell and body function therefore it is important to keep water levels constant for a healthy body the kidneys are crucial for regulating the water potential of the blood and this is known as osmoregulation the water potential of blood is monitored by specialized sensors called osmoreceptors found in the hypothalamus of the brain the hormone antidiuretic hormone or adh controls the extent to which water is reabsorbed into the blood by acting on the collecting duct walls increasing the permeability of the collecting duct to water if the concentration of blood is too high the osmo receptors or the sensor send impulses to the posterior pituitary gland for communication the posterior pituitary gland releases adh which is the effector when the water potential is normal the impulses will stop so during dehydration blood concentration is high and water potential is low the posterior pituitary releases adh the collecting duct becomes more permeable to water and more water diffuses into the medulla for reabsorption into the blood this produces a small volume of concentrated urine and less water gets excreted during hydration blood concentration is low so water potential is high less adh is produced the collecting duct is less permeable to water so less water gets reabsorbed into the blood more water passes through the collecting duct into the bladder this produces a larger volume of dilute urine as more water is lost as it is in excess in the blood now for temperature temperature is sensed in the hypothalamus and is controlled by the nervous system as mentioned earlier the optimal internal body temperature is 37 degrees this temperature is essential to keep metabolic reactions and other key reactions involving enzymes undisrupted temperatures lower than 27 degrees result in a change in metabolic rate enzyme activity starts to slow down so cells start to lose energy when the body's internal temperature falls lower than 27 degrees the patient is described as hypothermic and eventually this leads to death internal temperatures of 40 and over start to affect enzyme activity enzymes denature and become non-functional at higher temperatures with a severe impact on cellular reactions which will eventually result in death without treatment a patient with severely high temperature is described as hyperthermic when temperature is too high this is sensed by the hot center in the hypothalamus this results in vasodilation of surface blood vessels allowing heat to be lost to surroundings this vasodilation is why our faces get flushed red when exercising or feeling hot increased sweating results in evaporation of sweat from our skin making us feel cooler decreasing metabolic rate reduces the amount of heat produced in respiration these responses act to cool the body by increasing heat loss when temperature is too low this is sensed by the cold center in the hypothalamus resulting in vasoconstriction of surface blood vessels conserving heat in the body decreasing sweating and erection of hairs on the skin or goosebumps trapping a layer of insulating air against the skin to reduce heat loss shivering contraction of the muscles leading to generation of heat with cellular respiration increasing metabolic rate to generate more heat these processes lead to increasing the generation and conservation of heat in the body returning the body temperature back to normal so this concludes today's video on homeostasis thank you for watching today's video we hope to see you next week which will be about control and coordination [Music]