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HOMEOSTASIS

HOMEOSTASIS. Ability of the body to maintain a relatively constant internal environment necessary for life. Overview: Temperature Regulation. Cyclic representation. Linear representation. Temperature Regulation. Allows humans to cope with a wide range of environments.

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HOMEOSTASIS

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  1. HOMEOSTASIS Ability of the body to maintain a relatively constant internal environment necessary for life.

  2. Overview: Temperature Regulation Cyclic representation Linear representation

  3. Temperature Regulation Allows humans to cope with a wide range of environments

  4. Temperature Regulation Mammals are endothermic homeotherms, which is a very precise way of saying they regulate their own body temperature. It is worth noting that not all organisms do so because it would in fact be disadvantageous for some to do so. Furthermore some organisms regulate their body temperature solely through behavioural methods.

  5. Temperature Regulation In humans it is the core body temperature which is maintained by homeostasis.

  6. Components

  7. Hypothalamus (of a sheep)

  8. Hypothalamus (of a sheep)

  9. Hypothalamus

  10. Skin based effectors

  11. Skin based effectors

  12. Skin based effectors

  13. Skin based effectors – responding to heat gain

  14. Skin based effectors – responding to heat loss

  15. Effectors

  16. Shivering

  17. Metabolic changes

  18. Responding to vigorous exercise • ·stimulus is the increase in blood temperature • ·this is caused by exercise/increased respiration/muscle contraction • ·the increase blood temperature is detected by receptors in the hypothalamus • ·the hypothalamus also acts as the co-ordinator • ·the effectors are muscles of arterioles • ·and sweat glands • ·response to arteriole muscles stimulation is vasodilation • ·which causes increased blood flow to the skin capillaries • ·which causes increased heat loss by radiation • ·response to sweat gland stimulation is increased sweating • ·which causes increased heat loss by the latent heat of evaporation

  19. Exam questions 1. All living organisms exist in changing external environments and many are able to control their internal environments. (a) Explain how the body of a mammal may respond to a rise in the environmental temperature. (8marks)

  20. Exam answers • Thermoreceptors in skin; nervous impulse;to hypothalamus; blood temperature monitored;heat loss centre involved; vasodilation / dilation of arterioles;more blood to skin surface; more heat lost by radiation;piloerector muscles relax; hairs flatten on skin surface;less insulation; sweating initiated / increased;panting / licking; evaporation removes latent heat; • thinner fur; migration; drop in metabolic rate / use less brown fat;accept long term changes such as less fat deposition;accept one behavioural process; • max. 8

  21. Exam questions 2. Size matters for marathon runners. Big athletes produce more heat and find it harder to keep cool. Shape matters too - a tall, thin runner has fewer problems keeping cool than a short, tubby runner of the same body mass. A 65 kg athlete running a marathon in 2 hours 10 minutes in reasonably dry conditions can avoid overheating at air temperatures up to 37 °C, but in humid conditions the same level of performance is possible only at temperatures below about 17 °C. (a) Explain how athletes produce heat when they run. (2) (b) Why does a ‘tall, thin runner have fewer problems keeping cool than a short, tubby runner of the same body mass’? (2) (c) Explain why runners are more likely to overheat in humid conditions. (3) (d) Describe how the body responds to a rise in core body temperature. (5) (Total 12 marks)

  22. Exam answers 2. (a) Respiration for muscular activity; (energy ‘needed/used’ for respiration’etc, disqualifies)respiration inefficient / releases waste heat / all energy ‘ends up as ‘heat’ 2 (b) Larger surface area: volume ratio, or less fat under skin;more rapid / more heat loss from body surface. 2 (c) Humidity reduces diffusion gradient / less difference in water potential;less evaporation of sweat;less cooling due to use of heat energy for evaporation of sweat. 3 (d) Temperature receptors stimulated in; (in skin disqualifies)hypothalamus;heat loss centre stimulated;nerve impulses to sweat glands;increase rate of / start sweat production;nerve impulses to skin arterioles;vasodilation (ref to vessels moving disqualifies) max 5 [12]

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