Physiological Homeostasis

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1 Physiological Homeostasis Maintenance of the body s internal environment within certain tolerable limits despite changes in the external environment or changes in the body s rate of activity

2 Maintenance of tolerable limits In groups discuss why it is important to keep the following three factors within tolerable limits Body temperature Blood sugar level Body water concentration

3 Maintenance of tolerable limits Water concentration Prevent the body from suffering osmotic imbalances Blood sugar level Cells supplied with the energy to carry out functions (protein synthesis and muscle contraction) Body temperature Maintained at 37 o C Optimum conditions for enzymecontrolled metabolic processes

4 Negative feedback control Norm level changes detected by receptors nerve or hormonal messages effectors responses return to norm level. This corrective mechanism is known as negative feedback control.

5 Negative feedback control messages RECEPTORS EFFECTORS Increase in factor affecting internal environment Corrective response bringing about negative feedback control decrease in factor affecting internal environment Corrective response bringing about negative feedback control RECEPTORS messages EFFECTORS

6 What happens when animal cells are put into distilled (100%) water? What happens when animal cells are put into concentrated salt solution? Why do cells need a carbohydrate (for example glucose) food supply? What happens to proteins (for example enzymes or egg white) when they are subjected too high a temperature? Why are enzymes important to cells?

7 Osmoregulation Maintenance of concentration of water, salts and ions Receptors Osmoreceptors in the hypothalamus Message Anti-diuretic hormone (ADH) released from pituitary gland Effector Collecting duct of kidney nephron

8 Structure of a nephron

9 Water balance Decreasing water concentration Increase in sweating Lack of water Salty food Increasing water concentration Drinking too much water

10 Osmoregulation Negative feedback control

11 Control of blood sugar level Glucose is stored as glycogen in the liver Receptors Islets of Langerhans in the Pancreas Messengers insulin or glucagon Effector - liver Response Glucose glycogen Glycogen glucose

12 Control of blood glucose glucose insulin glucagon glycogen

13 Blood Glucose Levels Negative feedback control

14 Negative feedback control messages RECEPTORS EFFECTORS Increase in factor affecting internal environment Corrective response bringing about negative feedback control decrease in factor affecting internal environment Corrective response bringing about negative feedback control RECEPTORS messages EFFECTORS

15 Negative feedback control of blood glucose Detected by pancreas Food intake Glucose levels rise Pancreas secrete insulin Glucose glycogen In liver Glucose levels fall Normal blood glucose levels Glucose levels rise Glucose levels fall (exercise) Glycogen glucose In liver Pancreas secrete glucagon Detected by pancreas

16 Adrenaline Fight or flight hormone. Overrides normal homeostatic control of blood sugar levels

17 Diabetes mellitus Insulin-secreting pancreas cells are nonfunctioning Produce insufficient insulin Blood glucose rises above normal concentration Glomerular filtrate is so rich in glucose not all is reabsorbed and some is excreted in the urine Fat stores can become depleted leading to weight loss and wasting of tissues

18 The principle of negative feedback blood sugar

19 Alternative diagrams negative feedback controls RECEPTOR MESSAGE HIGH MESSAGE LOW EFFECTOR

20 COPY AND COMPLETE Hormone Endocrine gland from which hormone originates Effect of hormone Adrenaline Insulin ADH glucagon

21 Thermoregulation Watch the summary video on thermoregulation

22 Control of body temperature Ectotherm unable to regulate body temperature by physiological means invertebrates, fish, amphibians, reptiles Body temperature varies with external temperature Lizards can regulate body temperature by behaviour e.g. basking

23 Control of body temperature Endotherm able to maintain a constant body temperature birds and mammals high metabolic rate which generates heat energy Body temperature is under homeostatic control

24 Graph: effect of external on body temperature

25 Temperature Thermoreceptors in hypothalamus detect fluctuations in temperature The hypothalamus transmits nervous impulses to the skin which acts as an effector.

26 Correction of overheating Increase heat lost by radiation Vasodilation- dilation of arterioles under skin allow more heat to be lost by radiation. Nerve impulses from hypothalamus Arterioles become dilated Capillaries receive large volume of overheated blood Increased sweating- brings body temperature down as body heat is used to evaporate the sweat

27 Correction of overcooling Reduce heat lost by radiation Vasoconstriction - Constriction of arterioles under skin means less heat is lost by radiation. Nerve impulses from hypothalamus Arterioles become constricted Capillaries receive small volume of blood Decreased sweating means more body heat is conserved Contraction of hair erector muscles hairs rise allowing a layer of air to be trapped between the skin and external environment insulation

28 Other corrective mechanisms increase in shivering metabolic rate when the temperature drops. decrease in metabolic rate when the temperature rises.

29 Section C practice Qu 1 Write notes on the following : (i) endotherms and ectotherms (2) (ii) temperature regulation in mammals (8)

30 Endotherms and ectotherms Max 2 marks 1. endotherms can regulate/control/maintain their (body) temperature (physiologically) AND ectotherms cannot/ectotherms temperature is dependent on their environment/behaviour 2. endotherms derive (most body) heat from respiration/metabolism/chemical reactions 3. ectotherms derive/get (body) heat from surroundings/environment OR description of behaviour note Point 1 not heat for temperature Point 3 must be clear that the behaviour is of an ectotherm Point 3 not their body temperature varies with / changes with environment

31 Temperature regulation in humans max 8 marks temperature monitoring centre/thermoreceptors in hypothalamus OR information about temperature detected/received by hypothalamus nerve message/communication/impulse sent to skin/effectors vasodilation/widening of blood vessels to skin in response to increased temperature OR vasoconstriction/narrowing of blood vessels to skin in response to decreased temperature more/less blood to skin/extremities OR less/more blood in body core increased/more OR decreased/less heat radiated from skin/extremities increased temperature/body too hot leads to (increase in) sweat production OR converse increase in heat loss due to evaporation of (water in) sweat OR converse Decrease in temperature causes hair erector muscles to raise/erect hair traps (warm) air OR forms insulating layer Decrease in temperature causes muscle contraction/shivering which generates heat/raises body temperature temperature regulation involves/is an example of negative feedback Point 5 sent through blood negates Point 6 not blood vasodilates Point 7 not heat in body core Point 11 not converse Point 12 not traps heat Ignore references to metabolic rate

32 Section C practice qu 2 coherence and relevance Give an account of the principal of negative feedback with reference to the maintenance of blood sugar levels.

33 Principal of negative feedback Max 2 marks 1. Negative feedback maintains constant internal conditions in the body/homeostasis 2. A change from the normal level/set point is detected 3. A corrective mechanism is switched on/activated 4. When condition returns to its normal level/set point, corrective mechanism switched off.

34 Maintenance of blood sugar levels Max 6 marks 5. Blood sugar/glucose level (BSL) detected by the pancreas/islets of Langerhans 6. If BSL increases, (more) insulin is made 7. Insulin increases permeability of cells to glucose OR Insulin increases uptake of glucose by cells 8. Liver/Muscle cells convert glucose to glycogen OR Glucose converted to glycogen and stored in liver/muscle 9. BSL returns to normal/set point 10. If BSL decreases, (more) glucagon is made 11. Glucagon causes conversion of glycogen to glucose 12. Glucose released into blood 13. BSL returns to normal/set point (Note: ONE mark may be awarded for EITHER point 9 OR point 13 but NOT BOTH)

35 Coherence The writing must be under sub-headings or divided into paragraphs with a subheading/paragraph for each of Principle of negative feedback and Maintenance of blood sugar levels. Information on Principle of negative feedback should have at least one point given. AND Information on Maintenance of blood sugar levels should have at least four points given. Both must apply correctly to gain the Coherence mark.

36 relevance Must not give details of control of water balance or temperature regulation Must have given at least one relevant point from Principle of negative feedback and at least four relevant points from Maintenance of blood sugar levels. Both must apply correctly to gain the Relevance mark

Section 12.1 Principle of homeostasis

Section 12.1 Principle of homeostasis The maintenance of a constant internal environment By maintaining a relatively constant environment (of the tissue fluid) for their cells, organisms can limit the