BRAINCAKEHomeostasis
Revision notes for Homeostasis in OCR Biology A (H420). Read the start of any lesson here, then sign in free for the whole lesson, the R.E.C.I.P.E. recall steps and the quiz.
- HomeostasisHomeostasis is the maintenance of a constant internal environment, maintaining a dynamic equilibrium with only small variations over a narrow range…
- Feedback SystemsThere are two types of feedback systems.
- Examples of Positive FeedbackWhen a blood vessel is damaged, blood platelets stick to the damaged region and release chemicals that attract more platelets to the region.
- Endotherms and EctothermsFish, reptiles and amphibians are ectotherms and use their surroundings to warm their bodies.
- Behavioural Responses in EctothermsWhen ectotherms need to warm up, they may bask in the sun, orient their bodies towards the sun to expose the greatest surface area, increase their…
- Physiological Responses in EctothermsPhysiological adaptations include colour.
- ThermoreceptorsThere are two types of thermoreceptors in mammals.
- The HypothalamusThere are two thermoregulatory centres in the hypothalamus: the heat loss centre and the heat gain centre.
- CoolingThe arteriole near the surface of the skin dilate and the arteriovenous shunt, which connects the arterioles and venules, constricts.
- Warming UpVasoconstriction occurs when the arteriovenous shunts dilate.
- ExcretionExcretion is the removal from the body of metabolic waste.
- The LiverThe liver is about 5% of body mass and is the largest internal organ in the body.
- Structure of the LiverThe liver is divided into lobes, which divide further into cylindrical lobules.
- Carbohydrate Metabolism in the LiverHepatocytes are target cells for insulin and glucagon, both hormones responsible for the regulation of blood glucose concentration.
- Transamination and DeaminationOf the twenty amino-acids required by the body nine cannot be synthesised by the body and must therefore be obtained from the diet.
- DetoxificationToxins are produced by many metabolic pathways.
- Production of Bile Salts, Bile Pigments and CholesterolThe liver synthesises red blood cells in the fetus.
- The KidneysThe kidneys are a pair of red-brown organs attached to the back of the abdominal cavity.
- Structure of the KidneyThe kidneys are covered by a thin, tough membranous capsule made of tough fibres of collagen and elastin.
- NephronsNephrons, the filtering units, consist of the:Bowman's capsule where ultrafiltration takes place proximal convoluted tubule where water and other…
- Bowman's CapsuleThis is a filtering unit that encloses a network of 'leaky' capillaries called the glomerulus.
- GlomerulusThe glomerulus is a network of capillaries with many gaps between the capillary endothelial cells.
- Proximal Convoluted TubuleSelective reabsorptiontakes place in the proximal convoluted tubule.
- Loop of HenléThe loop of Henlé is responsible for the reabsorption of water.
- Countercurrent MultiplierAt the top of the ascending loop of Henlé sodium and chloride ions are actively transported out of the Loop of Henlé into the interstitial tissue…
- Ultrafiltration, Selective Reabsorption and Osmoregulation.Blood is filtered under pressure in the Bowman's capsule.
- Distal Tubule and Collecting DuctFluid passes from the top of the ascending limb of loop of Henlé to a short distal convoluted tubule.
- ADHOsmoreceptors in the hypothalamus monitor the water potential of the blood.
- Kidney failureKidney failure can occur due to diabetes, high blood pressure, infection or other reasons.
- HaemodialysisIn haemodialysis, bolld is taken from a vein and passed through a machine than contains a dialysis membrane and dialysis fluid.
- Peritoneal DialysisIn peritoneal dialysis, the body's peritoneum or abdominal membrane is used as a filter.
- Pregnancy TestingOnce the human embryo has been fertilised, it becomes implanted into the uterus.
- Anabolic SteroidsAnabolic steroids can be used to gain muscle mass.