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1 Think about… 2.1 Importance of regulating body temperature 2.2 The role of skin 2.3 Other mechanisms of body temperature regulation 2.4 The thermoregulatory centre Recall ‘Think about…’ Summary concept map 2 Heatstroke (中暑) often occurs among marathon runners, especially on hot and humid days. 3 They fail to lose heat efficiently and the body temperature may rise to as high as 43℃. 4 They feel dizzy and may become unconscious. 5 Heatstroke can be deadly if not treated immediately. 6 1 Why is heatstroke more likely to occur under hot and humid conditions 7 2 Why may death result when the body temperature is too high 8 3 What are the treatments and precautions for heatstroke 9 2.1 Importance of regulating body temperature How does the environmental temperature affect our body temperature? 10 human body temperature (oC) 2.1 Importance of regulating body temperature 40 30 20 body temperature kept at about 37oC 10 0 30 40 10 20 environmental temperature (oC) 11 2.1 Importance of regulating body temperature • metabolic activities are controlled by enzymes only work efficiently within a narrow range of temperature 12 2.1 Importance of regulating body temperature • metabolic activities are controlled by enzymes • stable body temperature keeps enzyme activity and metabolic rate steady we stay active at all times 13 2.1 Importance of regulating body temperature Heat gain radiation from the sun liver metabolism respiration in cells muscle contraction conduction from hot sand 14 2.1 Importance of regulating body temperature Heat loss Radiation? exhalation evaporation of sweat convection due to air current urination and defaecation 15 2.1 Importance of regulating body temperature Heat gain = Heat loss stable body temperature 16 2.1 Importance of regulating body temperature • skin is the major organ involved in regulating body temperature 17 2.1 Importance of regulating body temperature 1 A stable body temperature allows enzymes in cells to function properly, so that the metabolic rate can be kept steady and we can stay active at all times. 18 2.1 Importance of regulating body temperature 2 Heat is transferred between the body and the environment by radiation , conduction , convection and evaporation. 19 2.2 The role of skin Structure and functions of skin • two layers: epidermis (表皮) dermis (真皮) 20 2.2 The role of skin Structure and functions of skin 21 Skin on different parts of the body 22 Skin • two layers: epidermis dermis 23 Scanning electron microscope (SEM) picture of normal skin E. coli on the surface of human skin. Human hair and skin layers. scanning electron micrograph (SEM) of a section through human skin with a hair (upper centre) emerging from the surface. The skin layers, from top to bottom, are the stratum corneum (flaky, brown), composed of flattened, dead skin cells that form the surface of the skin. The dead cells from this layer are continuously being shed and replaced by cells from the living epidermal layer below (red, extending downwards around hair follicle). The lowest layer seen here is the dermis (grey-brown, lower centre). This is a thick layer of fibrous connective tissue that supports and nourishes the epidermis. Magnification: x100 24 25 2.2 The role of skin 1 Epidermis • three layers: epidermis dermis 26 2.2 The role of skin 1 Epidermis • three layers: i) Innermost layer • produces new cells by mitotic cell division 27 2.2 The role of skin 1 Epidermis • three layers: i) Innermost layer • contains melanin (黑素) absorbs UV light protects the body 28 2.2 The role of skin 1 Epidermis • three layers: i) Innermost layer • contains melanin (黑素) determines skin colour 29 2.2 The role of skin 1 Epidermis • three layers: i) Innermost layer • produces vitamin D when exposed to sunlight 30 2.2 The role of skin 1 Epidermis • three layers: ii) Middle layer: • consists of living cells pushed towards surface die and flatten outermost layer 31 2.2 The role of skin 1 Epidermis • three layers: iii) Outermost layer • consists of dead cells constantly worn away and replaced by new cells 32 2.2 The role of skin 1 Epidermis • three layers: iii) Outermost layer • consists of dead cells reduce water loss 33 2.2 The role of skin 1 Epidermis • three layers: iii) Outermost layer • consists of dead cells protect from mechanical injury 34 35 2.2 The role of skin 1 Epidermis • three layers: iii) Outermost layer • consists of dead cells prevent entry of pathogens 36 2.2 The role of skin 2 Dermis i) Sensory receptors • detect stimuli pain receptor touch receptor thermoreceptor pressure receptor 37 2.2 The role of skin 2 Dermis ii) Hair follicles (毛囊) • new hair cells produced from the base 38 2.2 The role of skin 2 Dermis ii) Hair follicles (毛囊) • new hair cells produced from the base root of hair 39 2.2 The role of skin 2 Dermis iii) Erector muscles (豎毛肌) and hairs 40 2.2 The role of skin 2 Dermis iii) Erector muscles (豎毛肌) and hairs • erector muscle contracts hair pulled upright • erector muscle relaxes hair lies flat 41 Goose bumps 42 Goose bumps 43 2.2 The role of skin 2 Dermis iv) Sweat glands (汗腺) • form sweat contains mainly water, salts, urea and other metabolic waste 44 2.2 The role of skin 2 Dermis iv) Sweat glands (汗腺) sweat pore (汗孔) sweat duct (汗管) 45 2.2 The role of skin 2 Dermis iv) Sweat glands (汗腺) • sweat coming out to the skin surface sweating 46 2.2 The role of skin 2 Dermis iv) Sweat glands (汗腺) • sweat coming out to the skin surface sweating for regulating body temperature 47 2.2 The role of skin 2 Dermis iv) Sweat glands (汗腺) • sweat coming out to the skin surface sweating for excretion 48 Male Sweat Boosts Women’s Hormone Levels ..Sweat has been the main focus of research on human pheromones, and in fact, male underarm sweat has been shown to improve women’s moods and affect their secretion of luteinizing hormone, which is normally involved in stimulating ovulation… 49 2.2 The role of skin 2 Dermis v) Blood vessels • circulation of blood supplies oxygen and nutrients 50 2.2 The role of skin 2 Dermis v) Blood vessels • circulation of blood removes waste 51 2.2 The role of skin 2 Dermis v) Blood vessels • circulation of blood distributes heat 52 2.2 The role of skin 2 Dermis v) Blood vessels • vasoconstriction and vasodilation ‘vessel’ 53 2.2 The role of skin 2 Dermis v) Blood vessels • vasoconstriction and vasodilation regulate heat loss by controlling the amount of blood flowing to the body surface 54 2.2 The role of skin 2 Dermis v) Blood vessels • vasoconstriction and vasodilation capillary arteriole venule shunt vessel (分流血管) 55 2.2 The role of skin 2 Dermis v) Blood vessels • vasoconstriction and vasodilation 2 less blood to capillary 1 arteriole constricts less heat is lost Under cold conditions 3 more blood through shunt vessel 56 2.2 The role of skin 2 Dermis v) Blood vessels • vasoconstriction and vasodilation 2 more blood to capillary 1 arteriole dilates more heat is lost Under hot conditions 3 less blood through shunt vessel 57 2.2 The role of skin Vasoconstriction and vasodilation occur in the capillaries. 58 2.2 The role of skin Capillaries cannot constrict or dilate because they have no muscle walls. 59 2.2 The role of skin It is the arterioles in the deeper part of the dermis that constrict or dilate. 60 2.2 The role of skin 2 Dermis vi) Sebaceous glands • secrete sebum (皮脂) keeps hairs and skin supple and waterproof 61 2.2 The role of skin 2 Dermis vi) Sebaceous glands • secrete sebum (皮脂) a natural antiseptic 62 2.2 The role of skin epidermis sweat duct hair follicle mammalian skin (L.S) sebaceous gland 63 Pimples – inflamed 64 2.2 The role of skin Subcutaneous fat • insulates the body to reduce heat loss • as energy reserve 65 2.2 The role of skin 2.1 Examination of the mammalian skin 1 Examine a prepared slide of mammalian skin or a skin model. 2 Identify the structures. 66 2.2 The role of skin Functions of structures of the skin: Epidermis: 1 Innermost layer • produces new cells by mitotic cell division • contains melanin which protects the body against ultraviolet light 67 2.2 The role of skin Functions of structures of the skin: Epidermis: 1 Innermost layer • produces vitamin D 68 2.2 The role of skin Functions of structures of the skin: Epidermis: 2 Middle layer • when pushed towards the surface , cells die and form the outermost layer 69 2.2 The role of skin Functions of structures of the skin: Epidermis: 3 Outermost layer • reduces water loss by evaporation • protects the body from mechanical injury 70 2.2 The role of skin Functions of structures of the skin: Epidermis: 3 Outermost layer • prevents the entry of pathogens 71 2.2 The role of skin Functions of structures of the skin: Dermis: 1 Sensory receptors • detect stimuli 2 Hair follicles • produce new hairs 72 2.2 The role of skin Functions of structures of the skin: Dermis: 3 Erector muscles and hairs • help regulate body temperature 4 Sweat glands • secrete sweat for excretion and body temperature regulation 73 2.2 The role of skin Functions of structures of the skin: Dermis: 5 Blood vessels • supply oxygen and nutrients to skin cells and remove waste from them 74 2.2 The role of skin Functions of structures of the skin: Dermis: 5 Blood vessels • help regulate body temperature by vasoconstriction and vasodilation 75 2.2 The role of skin Functions of structures of the skin: Dermis: 6 Sebaceous glands • secrete sebum that keeps the hairs and skin supple and waterproof, and reduces the growth of harmful microorganisms 76 2.2 The role of skin Functions of structures of the skin: Subcutaneous fat: • acts as a heat insulating layer • acts as energy reserve 77 2.2 The role of skin How does skin regulate body temperature? 3D animation • by controlling heat loss 78 2.2 The role of skin Under cold conditions 1 erector muscles contract to pull hairs upright 79 2.2 The role of skin Under cold conditions 2 sweating is reduced 80 2.2 The role of skin Under cold conditions 3 vasoconstriction 81 2.2 The role of skin Under cold conditions less heat is lost 4 layer of subcutaneous fat becomes thicker (long-term response) 82 2.2 The role of skin Under hot conditions 1 erector muscles relax and hairs lie flat 83 2.2 The role of skin Under hot conditions 2 sweating increases 3 vasodilation 84 2.2 The role of skin Under hot conditions more heat is lost 4 layer of subcutaneous fat becomes thinner (long-term response) 85 2.2 The role of skin Sweat is produced only when the body temperature increases. 86 2.2 The role of skin Sweat is produced most of the time to remove metabolic waste. 87 2.2 The role of skin Structure 1 Erector muscles 2 Hairs 3 Sweat glands Response under cold conditions Contract Pulled upright Secrete less sweat 88 2.2 The role of skin Response under Structure cold conditions Constrict 4 Arterioles (vasoconstriction) 5 Subcutaneous Becomes thicker (long-term) fat 89 2.2 The role of skin Structure 1 Erector muscles 2 Hairs 3 Sweat glands Response under hot conditions Relax Lie flat Secrete more sweat 90 2.2 The role of skin Structure 4 Arterioles 5 Subcutaneous fat Response under hot conditions Dilate (vasodilation) Becomes thinner (long-term) 91 2.3 Other mechanisms of body temperature regulation Muscle contraction • metabolism in muscle cells generates heat • shivering (顫抖) - skeletal muscles contract involuntarily 92 2.3 Other mechanisms of body temperature regulation Action of hormone • body temperature is also regulated by thyroxine (甲狀腺素) increases metabolic rate generates heat to keep the body warm 93 2.3 Other mechanisms of body temperature regulation Action of hormone • body temperature is also regulated by thyroxine (甲狀腺素) secretes thyroid gland 94 2.3 Other mechanisms of body temperature regulation Action of hormone • body temperature is also regulated by thyroxine (甲狀腺素) • increased thryoxine secretion is a long-term response 95 2.3 Other mechanisms of body temperature regulation Under cold conditions 1 A decrease in blood temperature stimulates the hypothalamus to secrete TSH-releasing hormone (TRH). hypothalamus TRH 96 2.3 Other mechanisms of body temperature regulation Under cold conditions 2 TRH stimulates the pituitary gland to secrete thyroid stimulating hormone (TSH). hypothalamus TRH pituitary gland TSH 97 2.3 Other mechanisms of body temperature regulation Under cold conditions 3 TSH stimulates the thyroid gland to secrete thyroxine. hypothalamus TRH pituitary gland TSH thyroxine 98 2.3 Other mechanisms of body temperature regulation Under cold conditions 4 Thyroxine increases the metabolic rate of body cells and more heat is generated. hypothalamus TRH pituitary gland TSH thyroxine 99 2.3 Other mechanisms of body temperature regulation Under cold conditions thyroxine inhibits secretions of TRH and TSH (negative feedback) hypothalamus TRH pituitary gland TSH thyroxine 100 2.3 Other mechanisms of body temperature regulation Change of behaviour • voluntary behaviour also plays a part in regulating body temperature 101 2.3 Other mechanisms of body temperature regulation Under cold conditions wear more clothes turner on the heater take in warm food/drinks 102 2.3 Other mechanisms of body temperature regulation Under hot conditions wear fewer clothes turner on the fan take in cold food/drinks 103 2.3 Other mechanisms of body temperature regulation 1 Metabolism in muscle cells generates heat to maintain the body temperature. Muscle contraction also generates heat. Shivering provides extra amount of heat to keep us warm under cold conditions. 104 2.3 Other mechanisms of body temperature regulation 2 Thyroxine increases the metabolic rate of most cells, so that more heat can be generated to keep the body warm. Increased thyroxine secretion is a long-term response to a cold environment. 105 2.3 Other mechanisms of body temperature regulation 3 Behavioural mechanisms that help regulate body temperature: a Under cold conditions, we can reduce heat loss and increase heat gain by means like wearing more clothes, turning on the heater and taking in more warm food and drinks. 106 2.3 Other mechanisms of body temperature regulation 3 Behavioural mechanisms that help regulate body temperature: b Under hot conditions, we can promote heat loss and reduce heat gain by means like wearing fewer clothes, turning on the fan and taking in more cold food and drinks. 107 2.4 The thermoregulatory centre • in hypothalamus • has thermoreceptors that detect the temperature of blood passing through it • receives nerve impulses about changes in external temperature from the thermoreceptors in the skin 108 2.4 The thermoregulatory centre thermoreceptors heat loss centre rises thermoregulatory centre in hypothalamus normal body temp heat gain centre 109 2.4 The thermoregulatory centre thermoreceptors heat loss centre rises initiates mechanisms falls normal body temp normal body temp heat gain centre 110 2.4 The thermoregulatory centre Mechanisms to promote heat loss and decrease heat gain: Physiological • relaxation of erector muscles • increased sweating • vasodilation • decreased secretion of thyroxine (long-term) 111 2.4 The thermoregulatory centre Mechanisms to promote heat loss and decrease heat gain: Structural • thinner layer of subcutaneous fat (long-term) 112 2.4 The thermoregulatory centre Mechanisms to promote heat loss and decrease heat gain: Behavioural • wear fewer clothes • turn on the fan • take in more cold food 113 2.4 The thermoregulatory centre thermoreceptors heat loss centre rises falls normal body temp normal body temp falls thermoreceptors initiates mechanisms rises heat gain centre initiates mechanisms 114 2.4 The thermoregulatory centre Mechanisms to reduce heat loss and increase heat gain: Physiological • contraction of erector muscles • reduced sweating • vasoconstriction • shivering 115 2.4 The thermoregulatory centre Mechanisms to reduce heat loss and increase heat gain: Physiological • increased secretion of thyroxine (long-term) 116 2.4 The thermoregulatory centre Mechanisms to reduce heat loss and increase heat gain: Structural • thicker layer of subcutaneous fat (long-term) 117 2.4 The thermoregulatory centre Mechanisms to reduce heat loss and increase heat gain: Behavioural • wear more clothes • turn on the heater • take in more warm food 118 2.4 The thermoregulatory centre 1a Thermoreceptors in skin detect changes in external temperature and send nerve impulses to the thermoregulatory centre in the hypothalamus . 119 2.4 The thermoregulatory centre 1b Thermoreceptors in the hypothalamus detect changes in the temperature of blood passing through it. 120 2.4 The thermoregulatory centre 2a Skin or blood temperature rises heat loss centre stimulated mechanisms • erector muscles relax and hairs lie flat • sweating increases • vasodilation occurs 121 2.4 The thermoregulatory centre 2a Skin or blood temperature rises heat loss centre stimulated mechanisms • thyroxine secretion decreases • subcutaneous fat becomes thinner • behavioural mechanisms , e.g. wear fewer clothes, turn on the fan 122 2.4 The thermoregulatory centre 2b Skin or blood temperature falls heat gain centre stimulated mechanisms • erector muscles contract and hairs are pulled upright • sweating decreases • vasoconstriction and shivering occur 123 2.4 The thermoregulatory centre 2b Skin or blood temperature falls heat gain centre stimulated mechanisms • thyroxine secretion increases • subcutaneous fat becomes thicker • behavioural mechanisms, e.g. wear more clothes, turn on the heater 124 1 Why is heatstroke more likely to occur under hot and humid conditions? High humidity lowers the rate of evaporation of sweat, so the body cannot lose heat effectively and heatstroke is likely to occur. 125 2 Why may death result when the body temperature is too high? When the body temperature is too high, enzymes cannot work properly and cells fail to function. 126 3 What are the treatments and precautions for heatstroke? To treat heatstroke, we should move the person to shaded areas and wrap the body with cool wet towels. 127 3 What are the treatments and precautions for heatstroke? To prevent heatstroke, we should avoid doing vigorous exercise in a hot environment. 128 A stable body temperature maintained by balancing heat loss heat gain controlled by thermoregulatory centre in hypothalamus 129 thermoregulatory centre in hypothalamus through mechanisms that involve skin 130 skin structures involved erector muscles and hairs sweat glands blood vessels subcutaneous fat 131 thermoregulatory centre in hypothalamus through mechanisms that involve blood circulation controls distribution by of heat vasoconstriction and vasodilation 132 thermoregulatory centre in hypothalamus through mechanisms that involve skeletal muscles under cold conditions shiver production of more heat leads to 133 thermoregulatory centre in hypothalamus through mechanisms that involve thyroid gland secretes thyroxine increases metabolic rate 134 thermoregulatory centre in hypothalamus through mechanisms that involve cerebrum brings about behavioural mechanisms 135