Control & Regulation

1. Control & Regulation Physiological Homeostasis Mr G Davidson

2. Physiological Homeostasis • We like to keep our living conditions stable, e.g. in Autumn, we turn up the heating. • In some countries, in summer, air conditioning is used. • The aim is to keep indoors at the same temperature all the time. G Davidson

3. Physiological Homeostasis • Physiological homeostasis is the process of maintaining a steady state in the body so cells can function effectively. • Our bodies automatically maintain a steady state. G Davidson

4. Physiological Homeostasis • In order to do this, there must be detectors which detect any changes in state as well as a means of altering it. • Most systems work on a negative feedback basis. G Davidson

5. Detected by 3. Control centres 4. Corrective mechanism 5. Cause of Change 2. Normal conditions 1. Normal conditions 6. Corrective mechanism 5. Cause of Change 7. Detected by 8. Control centres 9. General negative feedback system G Davidson

6. Osmoregulation • This is the process of the body maintaining the water, salt and iron levels at a proper level. • Should these levels alter they are detected by the osmoreceptors in the hypothalamus in the brain. G Davidson

7. Osmoregulation • This stimulated the pituitary gland into either releasing more or less ADH (anti-diuretic hormone). • The ADH takes effect in the kidneys and either more or less water is reabsorbed by the kidneys. G Davidson

8. Osmoreceptors Pituitary gland Less water reabsorbed into blood Increase in water concentration of blood Normal conditions Normal conditions Decrease in water concentration of blood More water reabsorbed into blood Osmoreceptors Pituitary gland Osmoregulation G Davidson

9. Control of blood sugar levels • The blood sugar level is controlled in the same way as the water concentration. • If too much glucose is found in the blood, the cells in the Islets of Langerhans in the pancreas, produce the hormone insulin. G Davidson

10. Control of blood sugar levels • This hormone is transported to the liver where it brings about the conversion of glucose to glycogen, which is then stored in the liver. • If there is not enough glucose in the blood, the cells in the islets of Langerhans detect this and release another hormone glucagon. G Davidson

11. Control of blood sugar levels • This hormone is transported to the liver where it brings about the conversion of glycogen back to glucose. • In emergencies, the adrenal glands produce adrenaline which overrides the process in order to release glucose for energy to deal with the emergency. G Davidson

12. Mammalian body temperature • We are endotherms (warm blooded). • This means we can keep our body temperature constant, regardless of the external environment. G Davidson

13. Mammalian body temperature • We have various methods at our disposal for achieving this, e.g. move into or out of the sun, change behaviour, put on or remove clothes, open windows, turn up heaters etc. • We also have physiological mechanisms at our disposal, e.g. when we are too hot, we sweat. G Davidson

14. Mammalian body temperature • If we are cold, we shiver and our extremities may go “blue” or “white” as blood to them is reduced. • The skin can detect temperature changes and send information to thermoreceptors in the hypothalamus in the brain. G Davidson

15. Mammalian body temperature • The hypothalamus responds accordingly, • e.g. too hot • sweating • hairs lie flat • red skin (due to increased blood flow) • Too cold • shivering • goose pimples (hairs erect) • white skin due to decreased blood flow G Davidson

16. Mammalian body temperature • Vasodilation:- when we are too hot, the arterioles to the skin surface dilate, allowing blood to the surface to lose heat. • Vasoconstriction:- when we are too cold, the arterioles constrict and blood is diverted along a “shunt” which keeps most of the blood away from the surface. G Davidson

17. Much Heat Lost Environment skin Vasodilation G Davidson

18. Little Heat Lost Environment skin Vasoconstriction G Davidson

19. Ectotherm body temperature • In some animals, like fish, body temperature varies exactly as the environment varies, and there is no control of body temperature. • Others, like many reptiles and some insects, may use behavioural mechanisms to control their body temperature. • Both these groups are called ectotherms; “ecto” meaning outside. G Davidson

20. Body temperatures G Davidson

21. Energy uses at different temperatures • As enzyme activity depends on temperature, an animal which cannot control its body temperature will be inactive at low temperatures. • When the enzymes of the respiration reactions work slowly, an animal like a fly will have a low energy uptake and low food requirements. G Davidson

22. Energy uses at different temperatures • In contrast, a small mammal in a cold environment uses a lot of energy to keep warm. • It may eat extra food and it will use extra oxygen. • This extra respiration provides heat to maintain a constant body temperature. G Davidson

23. Energy uses at different temperatures • People used to eat more in winter. • Central heating now makes that unnecessary. • Some animals which need a lot of energy hibernate when conditions are difficult. • The body temperature drops, it is inactive and food stores in the body can last a long time. G Davidson