WEBVTT 00:00:00.500 --> 00:00:03.975 Welcome to GCSE Edexcel Science revision. 00:00:04.125 --> 00:00:09.131 Unit C B 7: Animal coordination, control and homeostasis. 00:00:11.800 --> 00:00:15.858 The nervous system sends rapid electrical signals along neurones. 00:00:16.008 --> 00:00:23.259 Hormonal communication uses chemical messengers carried in the blood and is usually slower, with longer-lasting effects. 00:00:25.933 --> 00:00:29.674 Endocrine glands release hormones directly into the bloodstream. 00:00:29.824 --> 00:00:35.603 Blood carries a hormone around the body, but only target cells with suitable receptors respond to it. 00:00:38.267 --> 00:00:42.124 A target organ is an organ affected by a particular hormone. 00:00:42.274 --> 00:00:47.243 A hormone may affect several target tissues; it does not act on every cell it passes. 00:00:49.900 --> 00:00:52.865 The pituitary gland lies at the base of the brain. 00:00:53.015 --> 00:01:00.523 It releases F S H, L H and growth hormone, and hormones such as T S H that influence other endocrine glands. 00:01:03.200 --> 00:01:06.261 The thyroid gland in the neck produces thyroxine. 00:01:06.411 --> 00:01:11.957 The adrenal glands above the kidneys produce adrenalin; adrenaline is an alternative spelling. 00:01:14.633 --> 00:01:17.523 The pancreas produces insulin and glucagon. 00:01:17.673 --> 00:01:22.835 The ovaries produce oestrogen and progesterone; the testes produce testosterone. 00:01:22.985 --> 00:01:27.433 A hormone directory: target cells respond through suitable receptors. 00:01:32.100 --> 00:01:35.511 Growth hormone supports growth of bones and other tissues. 00:01:35.661 --> 00:01:46.422 Puberty involves changes in sex hormones and growth-hormone activity; it is an oversimplification to say that sex hormones alone directly make the pituitary release growth hormone. 00:01:49.100 --> 00:01:55.734 Homeostasis maintains a stable internal environment despite changes inside or outside the body. 00:01:55.884 --> 00:02:01.025 Examples include blood glucose concentration, body temperature and water balance. 00:02:03.700 --> 00:02:09.299 Stable does not mean perfectly unchanging: conditions fluctuate around suitable levels. 00:02:09.449 --> 00:02:13.750 Maintaining these levels helps cells and enzymes function effectively. 00:02:16.400 --> 00:02:19.939 Negative feedback reverses a change from the normal level. 00:02:20.089 --> 00:02:26.093 If a level rises too high, the response brings it down; if it falls too low, the response brings it up. 00:02:26.243 --> 00:02:29.917 The response gets smaller as the level returns towards normal. 00:02:32.567 --> 00:02:39.333 If a regulated level rises too far, feedback can reduce it; if it falls too far, feedback can raise it. 00:02:39.483 --> 00:02:43.167 The response must oppose the change, rather than amplify it. 00:02:45.833 --> 00:02:52.425 Negative feedback is a control mechanism, while homeostasis is the maintenance of the internal environment. 00:02:52.575 --> 00:02:56.196 The two terms are related but are not identical definitions. 00:02:58.867 --> 00:03:04.798 Thyroxine helps control metabolic rate: the rate at which chemical reactions occur in the body. 00:03:04.948 --> 00:03:07.487 It also supports growth and development. 00:03:10.167 --> 00:03:17.761 When blood thyroxine concentration is low, the hypothalamus releases more T R H, thyrotropin-releasing hormone. 00:03:20.433 --> 00:03:26.363 T R H stimulates the pituitary gland to release T S H, thyroid-stimulating hormone. 00:03:29.033 --> 00:03:34.473 T S H stimulates the thyroid gland to produce and release thyroxine into the blood. 00:03:37.133 --> 00:03:44.747 When thyroxine returns to a suitable level, it reduces (inhibits) further T R H release and T S H production. 00:03:44.897 --> 00:03:50.156 The thyroid receives less stimulation, so it does not keep producing too much thyroxine. 00:03:52.833 --> 00:03:58.647 This is negative feedback: the increase in thyroxine reduces the signals that caused its production. 00:03:58.797 --> 00:04:04.539 Do not confuse the thyroid, which makes thyroxine, with the pituitary, which makes T S H. 00:04:04.689 --> 00:04:09.904 Thyroxine inhibits its stimulating signals: an example of negative feedback. 00:04:14.567 --> 00:04:20.090 Adrenalin is released from the adrenal glands during frightening or exciting situations. 00:04:20.240 --> 00:04:23.567 It prepares the body for a rapid fight-or-flight response. 00:04:26.233 --> 00:04:31.448 It increases heart rate and blood pressure, and increases blood flow to skeletal muscles. 00:04:31.598 --> 00:04:35.137 This helps deliver more oxygen and glucose for respiration. 00:04:37.800 --> 00:04:43.707 Adrenalin stimulates the liver to break glycogen down into glucose and release glucose into the blood. 00:04:43.857 --> 00:04:48.584 Glycogen is a stored carbohydrate; glucose is the circulating sugar. 00:04:51.267 --> 00:04:59.277 Adrenalin changes where blood flows: vessels supplying skeletal muscles widen (dilate), while vessels in some other regions narrow. 00:04:59.427 --> 00:05:02.943 More blood reaches the muscles to support rapid activity. 00:05:05.600 --> 00:05:08.329 The nervous system and hormones can work together. 00:05:08.479 --> 00:05:16.095 An adrenalin response is a temporary preparation for activity, rather than the same long-term control pathway as thyroxine. 00:05:18.767 --> 00:05:22.687 The menstrual cycle prepares the uterus for a possible pregnancy. 00:05:22.837 --> 00:05:25.098 An egg matures and is released. 00:05:25.248 --> 00:05:31.541 Cycles start during puberty and stop at menopause; their length and the ages at which they start and stop vary. 00:05:34.200 --> 00:05:36.760 Day 1 is the first day of menstruation. 00:05:36.910 --> 00:05:42.807 The uterus lining is shed when hormone levels fall; menstruation is not simply the loss of an egg. 00:05:45.467 --> 00:05:50.886 After menstruation, the lining is repaired and thickens under the influence of oestrogen. 00:05:51.036 --> 00:05:54.576 It does not wait until a fixed day 11 to begin repairing. 00:05:57.233 --> 00:06:00.199 Ovulation is the release of an egg from an ovary. 00:06:00.349 --> 00:06:06.909 In a simplified 28-day cycle it occurs around day 14, but actual timing varies with the cycle. 00:06:09.567 --> 00:06:14.133 After ovulation, progesterone helps maintain the thickened uterus lining. 00:06:14.283 --> 00:06:20.052 If pregnancy does not occur, progesterone and oestrogen fall and another menstruation begins. 00:06:22.733 --> 00:06:26.199 Sperm can travel through the cervix and uterus to an oviduct. 00:06:26.349 --> 00:06:33.282 Fertilisation is the fusion of sperm and egg nuclei, usually in an oviduct, also called a fallopian tube. 00:06:35.933 --> 00:06:40.670 The fertilised egg divides to form an embryo as it moves towards the uterus. 00:06:40.820 --> 00:06:46.696 Implantation is the embryo attaching to the uterus lining; it is different from fertilisation. 00:06:49.367 --> 00:06:55.904 Fertilisation is associated with the time around ovulation, not a fixed day 17, 21 window. 00:06:56.054 --> 00:07:01.695 A textbook 28-day example cannot reliably predict an individual's fertile days. 00:07:04.367 --> 00:07:08.923 F S H, follicle-stimulating hormone, is released by the pituitary. 00:07:09.073 --> 00:07:15.375 It stimulates an ovarian follicle containing an egg to mature and encourages oestrogen production. 00:07:18.033 --> 00:07:20.764 The developing follicle produces oestrogen. 00:07:20.914 --> 00:07:26.588 Oestrogen repairs and thickens the uterus lining and inhibits F S H for much of the cycle. 00:07:29.267 --> 00:07:34.217 A high oestrogen level just before ovulation stimulates an L H surge. 00:07:34.367 --> 00:07:40.617 This is a change in its feedback effect; do not assume oestrogen always inhibits every pituitary hormone. 00:07:43.267 --> 00:07:46.813 The pituitary releases L H (luteinising hormone). 00:07:46.963 --> 00:07:49.779 A sharp rise in L H triggers ovulation. 00:07:49.929 --> 00:07:53.941 The emptied follicle then forms a structure called the corpus luteum. 00:07:56.600 --> 00:08:00.405 After ovulation, the corpus luteum produces progesterone. 00:08:00.555 --> 00:08:11.551 This maintains the uterus lining and reduces (inhibits) F S H and L H release, helping prevent another follicle maturing and another egg being released in the same cycle. 00:08:14.233 --> 00:08:20.408 If pregnancy does not occur, the corpus luteum breaks down and progesterone and oestrogen decrease. 00:08:20.558 --> 00:08:26.073 The lining is shed and reduced inhibition allows F S H to rise for the next cycle. 00:08:26.223 --> 00:08:31.120 Sequence if pregnancy does not occur; actual cycle lengths and timings vary. 00:08:35.800 --> 00:08:45.153 When interpreting a hormone graph, look for an oestrogen rise before ovulation, a sharp L H surge around ovulation and a progesterone rise afterwards. 00:08:45.303 --> 00:08:49.529 These are schematic patterns, not identical curves in every person. 00:08:52.200 --> 00:08:55.143 Contraception reduces the chance of pregnancy. 00:08:55.293 --> 00:09:02.641 Different methods act in different ways, so preventing ovulation and blocking sperm should not be described as the same mechanism. 00:09:05.300 --> 00:09:11.506 The combined contraceptive pill contains oestrogen and a progestogen, which acts like progesterone. 00:09:11.656 --> 00:09:16.743 These hormones suppress pituitary F S H and L H and prevent ovulation. 00:09:19.400 --> 00:09:24.551 Progestogen can also thicken cervical mucus, making it harder for sperm to pass. 00:09:24.701 --> 00:09:31.353 Hormonal methods can include pills, patches, injections and implants; their mechanisms and suitability vary. 00:09:34.033 --> 00:09:39.291 A condom is a barrier that prevents semen and sperm entering the vagina when used correctly. 00:09:39.441 --> 00:09:47.140 Condoms also reduce transmission of many sexually transmitted infections; hormonal contraception does not provide that protection. 00:09:49.800 --> 00:09:55.720 A diaphragm covers the cervix and is used with spermicide to reduce sperm entry into the uterus. 00:09:55.870 --> 00:09:58.611 It does not stop the ovaries releasing eggs. 00:10:01.267 --> 00:10:09.989 Evaluate a method using effectiveness, correct use, possible side effects, how long it lasts, reversibility and protection against infections. 00:10:10.139 --> 00:10:14.513 No method should be described as guaranteed to prevent every pregnancy. 00:10:17.167 --> 00:10:24.920 A daily pill requires consistent use; a long-acting method reduces that daily requirement but can need a healthcare procedure. 00:10:25.070 --> 00:10:30.232 Barrier methods avoid altering the menstrual hormones but also depend on correct use. 00:10:32.900 --> 00:10:38.275 Assisted reproductive technology, or ART, can help some people with fertility problems. 00:10:38.425 --> 00:10:43.215 The approach depends on the cause of the difficulty and does not guarantee a pregnancy. 00:10:45.867 --> 00:10:51.871 Clomifene is a fertility medicine that can encourage ovulation in people who do not ovulate regularly. 00:10:52.021 --> 00:10:58.345 It promotes pituitary release of F S H and L H by reducing the effect of oestrogen feedback. 00:11:01.000 --> 00:11:08.709 In I V F, in vitro fertilisation, fertility hormones such as F S H stimulate development of several follicles. 00:11:08.859 --> 00:11:14.501 A hormone trigger, often acting like L H, helps eggs complete maturation before collection. 00:11:17.167 --> 00:11:20.633 Eggs are collected and fertilised with sperm in a laboratory. 00:11:20.783 --> 00:11:25.871 Embryos are allowed to develop before a selected embryo is transferred into the uterus. 00:11:28.533 --> 00:11:33.727 Progesterone can be given to help support the uterus lining after embryo transfer. 00:11:33.877 --> 00:11:39.551 Laboratory fertilisation and transfer do not guarantee implantation or a live birth. 00:11:39.701 --> 00:11:44.820 IVF involves laboratory fertilisation followed by embryo transfer. 00:11:49.500 --> 00:11:54.459 Benefits include the possibility of pregnancy despite some fertility problems. 00:11:54.609 --> 00:12:04.239 Limitations include cost, physical and emotional demands, variable success and risks such as excessive ovarian stimulation or multiple pregnancy. 00:12:06.900 --> 00:12:13.022 Evaluate success using comparable data and the stated outcome, such as pregnancy or live birth. 00:12:13.172 --> 00:12:19.721 Age and the cause of infertility can affect success, so results from different groups are not automatically comparable. 00:12:22.400 --> 00:12:29.523 Blood glucose concentration rises after absorption of carbohydrate from food and can fall as cells use glucose. 00:12:29.673 --> 00:12:32.913 The pancreas monitors and responds to these changes. 00:12:35.567 --> 00:12:39.632 When blood glucose is high, the pancreas releases more insulin. 00:12:39.782 --> 00:12:46.991 Insulin promotes glucose uptake by body cells and promotes conversion of glucose into glycogen in the liver and muscles. 00:12:49.667 --> 00:12:54.712 As blood glucose returns towards a suitable level, insulin secretion decreases. 00:12:54.862 --> 00:12:58.507 This is a negative-feedback response to an increase in glucose. 00:13:01.167 --> 00:13:05.158 When blood glucose is low, the pancreas releases more glucagon. 00:13:05.308 --> 00:13:11.066 Glucagon stimulates the liver to break glycogen down into glucose and release it into the bloodstream. 00:13:13.733 --> 00:13:18.927 As blood glucose rises towards a suitable level, glucagon secretion decreases. 00:13:19.077 --> 00:13:23.449 Insulin and glucagon therefore have opposing effects on blood glucose. 00:13:23.599 --> 00:13:29.838 Insulin and glucagon have opposing effects; secretion decreases as glucose returns towards normal. 00:13:34.500 --> 00:13:44.759 Glucose and glycogen are not interchangeable names: glucose is a small sugar that circulates in blood, while glycogen is a storage carbohydrate made from glucose units. 00:13:47.433 --> 00:13:54.238 Glucagon and glycogen are also different: glucagon is a hormone, while glycogen is a stored carbohydrate. 00:13:54.388 --> 00:13:57.383 The liver can supply glucose to the blood between meals. 00:14:00.033 --> 00:14:08.586 In type 1 diabetes, the body's immune system destroys insulin-producing pancreatic cells, so little or no insulin is produced. 00:14:08.736 --> 00:14:10.933 Blood glucose can become too high. 00:14:13.600 --> 00:14:23.657 Type 1 diabetes is controlled with insulin delivered by injections or a pump, together with blood-glucose monitoring and appropriate management of food and activity. 00:14:23.807 --> 00:14:26.794 Diet alone cannot replace the missing insulin. 00:14:29.467 --> 00:14:37.466 In type 2 diabetes, cells respond less effectively to insulin, and the pancreas may also produce insufficient insulin. 00:14:37.616 --> 00:14:40.601 This is often described as insulin resistance. 00:14:43.267 --> 00:14:51.020 Type 2 diabetes may be managed with dietary changes, physical activity and medicines; some people also need insulin. 00:14:51.170 --> 00:14:55.525 It should not be described as always controlled by diet and exercise alone. 00:14:58.200 --> 00:15:07.703 A higher body mass and greater abdominal fat are associated with increased type 2 diabetes risk, but genetics, age and other factors also matter. 00:15:07.853 --> 00:15:11.010 Type 2 diabetes can occur without obesity. 00:15:13.667 --> 00:15:17.588 Glucose may appear in urine if blood glucose becomes high enough. 00:15:17.738 --> 00:15:23.347 This can be a sign of diabetes, but a urine result alone cannot confirm a diagnosis. 00:15:26.000 --> 00:15:36.427 Body mass index, B M I, is calculated as mass in kilograms divided by height in metres squared: B M I equals mass (kg) divided by [height (m)]squared. 00:15:39.100 --> 00:15:49.871 For a mass of eighty one kilograms and height of one point eight zero metres, body mass index equals eighty one divided by one point eight zero squared, which equals twenty five. 00:15:50.021 --> 00:15:54.365 Square the height before dividing, and convert centimetres to metres first. 00:15:57.033 --> 00:16:09.051 Common adult categories are below 18.5: underweight; 18.5 to below 25: healthy-weight range; 25 to below 30: overweight; 30 or above: obesity. 00:16:09.201 --> 00:16:15.493 These adult boundaries are not used directly to assess children and teenagers, whose age and sex are considered. 00:16:18.167 --> 00:16:22.940 Waist:hip ratio equals waist circumference divided by hip circumference. 00:16:23.090 --> 00:16:27.103 Use the same units for both measurements; the ratio has no unit. 00:16:29.767 --> 00:16:35.804 For a waist of 80 centimetres and hips of 100 centimetres, the ratio is 0.80. 00:16:35.954 --> 00:16:41.797 A greater proportion of abdominal fat is associated with increased type 2 diabetes risk. 00:16:44.467 --> 00:16:50.717 A positive correlation means that higher values of one variable tend to occur with higher values of another. 00:16:50.867 --> 00:16:58.705 A trend between B M I and diabetes risk is not proof that every person with a high B M I will develop diabetes. 00:17:01.367 --> 00:17:05.745 B M I does not distinguish muscle from fat or show where fat is stored. 00:17:05.895 --> 00:17:13.915 Waist:hip ratio provides different information, but neither measure alone describes an individual's complete health or proves causation. 00:17:16.567 --> 00:17:21.781 Compare diabetes risk using proportions or percentages when group sizes differ. 00:17:21.931 --> 00:17:29.504 Ten cases out of 100 people and ten cases out of 1,000 people are different rates despite the same case count. 00:17:32.167 --> 00:17:37.125 Percentage equals number in a group divided by total number times 100. 00:17:37.275 --> 00:17:44.195 For example, 12 cases in 200 people is 6 percent; state which population the percentage describes. 00:17:46.867 --> 00:17:52.838 Check whether differences in age, activity or other factors could affect a reported correlation. 00:17:52.988 --> 00:17:57.312 A large sample and comparable groups support a more reliable comparison. 00:17:59.967 --> 00:18:08.882 Benedict's test can investigate reducing sugars in simulated urine: add Benedict's reagent and warm in a hot-water bath under school instructions. 00:18:09.032 --> 00:18:14.985 A colour change from blue towards green, yellow, orange or brick-red indicates reducing sugar. 00:18:17.667 --> 00:18:21.712 Benedict's reagent detects reducing sugars, not only glucose. 00:18:21.862 --> 00:18:29.307 Use simulated samples, appropriate eye protection and controlled heating; compare with a known positive and a negative control. 00:18:31.967 --> 00:18:36.905 A colour test on a simulated sample illustrates the chemistry of sugar detection. 00:18:37.055 --> 00:18:41.483 It does not diagnose diabetes or replace blood-glucose monitoring. 00:18:44.133 --> 00:18:48.254 That completes Animal coordination, control and homeostasis. 00:18:48.404 --> 00:18:51.749 Revisit the notes and test yourself on the revision website.