BRAINCAKE

Homeostasis

Edexcel A-level BiologyTopic 13 of 1641 lessons

Revision notes for Homeostasis in Edexcel Biology (9BI0). 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.

  1. Controlling the Heart RateHeart rate must change to match the body's demands.
  2. Nervous Control of the HeartHeart rate is controlled by the cardiovascular control centre in the medulla oblongata.
  3. BaroreceptorsBaroreceptors are stretch receptors that detect changes in blood pressure.
  4. ChemoreceptorsChemoreceptors detect changes in the chemical composition of the blood, especially the carbon dioxide concentration and the pH.
  5. Hormonal Control of the HeartHeart rate is also affected by the hormone adrenaline.
  6. Additional ResponsesDuring exercise, raising the heart rate is only part of the body's response.
  7. Protein Homeostasis in the LiverThe body cannot store excess amino acids.
  8. OsmoregulationOsmoregulation is the control of the water potential of the body fluids, by regulating the amount of water and the concentration of solutes (such as…
  9. Osmoregulation in MammalsIn mammals the main organs of osmoregulation are the kidneys.
  10. Structure and Function of the KidneyHumans have two kidneys at the back of the abdomen.
  11. UltrafiltrationUltrafiltration is the filtration of blood under high pressure in the Bowman's capsule.
  12. Selective ReabsorptionThe glomerular filtrate contains many substances the body needs.
  13. Proximal Convoluted TubuleThe proximal convoluted tubule (PCT) is the first, coiled part of the nephron after the Bowman's capsule, in the cortex.
  14. Loop of HenleThe loop of Henle is a hairpin-shaped section of the nephron that dips from the cortex down into the medulla and back up again.
  15. Countercurrent MultiplierThe loop of Henle is a countercurrent multiplier. 'Countercurrent' means that the filtrate flows in opposite directions in the two limbs, which lie…
  16. Distal Convoluted TubuleThe distal convoluted tubule (DCT) is the coiled part of the nephron after the ascending limb of the loop of Henle, back in the cortex.
  17. Collecting DuctThe collecting duct receives filtrate from the distal convoluted tubules of several nephrons.
  18. UrineUrine is the fluid that leaves the collecting ducts and is stored in the bladder.
  19. AdaptationsMammals that live in different habitats have kidneys adapted to the amount of water available.
  20. Control of OsmoregulationThe water potential of the blood is kept within narrow limits by a homeostatic control system involving the hypothalamus, the posterior pituitary…
  21. ADHAntidiuretic hormone (ADH) increases the permeability of the collecting duct walls to water, so more water is reabsorbed and less urine is produced…
  22. Negative Feedback ControlNegative feedback is the process in which a change from the normal level (set point) of a factor is detected and causes responses that reverse the…
  23. Extra FeedbackADH is not the only way the body corrects its water balance.
  24. Diabetes InsipidusDiabetes insipidus is a condition in which the kidneys cannot conserve water, so the person produces very large volumes of dilute urine (up to about…
  25. ThermoregulationThermoregulation is the control of body temperature.
  26. Losing or Gaining HeatBody temperature stays constant when heat gain equals heat loss.
  27. Control of Body TemperatureMammals and birds keep their core body temperature (the temperature of the blood and the organs deep inside the body) within narrow limits.
  28. EndothermsAn endotherm is an animal that generates most of its body heat internally from metabolic reactions and keeps its core temperature fairly constant…
  29. EctothermsAn ectotherm is an animal that relies mainly on heat from its surroundings to warm its body.
  30. Thermoregulation in EndothermsThermoregulation is the control of core body temperature.
  31. The SkinThe skin is the main organ through which a mammal exchanges heat with its surroundings, so many thermoregulatory effectors are found there.
  32. Keeping CoolWhen core temperature rises above the norm, for example during exercise or on a hot day, the hypothalamus triggers responses that increase heat loss…
  33. Keeping WarmWhen core temperature falls below the norm, the hypothalamus triggers responses that reduce heat loss and increase heat production.
  34. Control of Core Body TemperatureCore body temperature is controlled by the thermoregulatory centre in the hypothalamus, a small region at the base of the brain.
  35. VasodilationVasodilation is the widening of the arterioles that supply the capillaries near the skin surface.
  36. VasoconstrictionVasoconstriction is the narrowing of the arterioles that supply the capillaries near the skin surface.
  37. Adaptations for Cold EnvironmentsAnimals living in polar regions or at high altitude have anatomical, physiological and behavioural adaptations that reduce heat loss.
  38. Adaptations for Hot EnvironmentsAnimals in hot deserts and the tropics need to lose heat and avoid gaining it, often while also conserving water.
  39. Cooling The BrainThe brain is very sensitive to temperature, and its neurones and enzymes can be damaged if it gets much hotter than normal.
  40. Behavioural Control of Body TemperatureBoth ectotherms and endotherms use behaviour to control body temperature.
  41. Cape Ground SquirrelThe Cape ground squirrel (Xerus inauris) lives in the hot, dry Kalahari region of southern Africa.

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