1 2 think about… 2.1 importance of regulating body temperature 2.2 the role of skin 2.3 other...

2

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

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Heatstroke (中暑 ) often occurs among marathon runners, especially on hot and humid days.

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They fail to lose heat efficiently and the body temperature may rise to as high as 43 .℃

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They feel dizzy and may become unconscious.

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Heatstroke can be deadly if not treated immediately.

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Why is heatstrokemore likely to occur under hot and humid conditions

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Why may deathresult when the body temperature is too high

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What are thetreatments and precautions for heatstroke

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How does the environmental temperature affect our body

temperature?

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hum

an b

ody

tem

pera

ture

(o C

)

environmental temperature (oC)10

10

20

20

30

30

40

400


body temperature kept at about 37oC

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• metabolic activities are controlled by enzymes

only work efficiently within a narrow range of temperatureonly work efficiently within a narrow range of temperature


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• metabolic activities are controlled by enzymes

keeps enzyme activity and metabolic rate steady

• stable body temperature

we stay active at all times


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Heat gainradiation from the sun

liver metabolismrespiration in cells

muscle contraction

conduction from hot sand

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Heat loss

exhalation

evaporation of sweat

convection due to air current

urination and defaecation

Radiation?

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Heat lossHeat gain =

stable body temperature

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• skin is the major organ involved in regulating body temperature


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1 A stable body temperature allowsenzymes


properly, so that the metabolic rate can be kept and we can stay active at all times.

in cells to function

steady

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, ,

2 Heat is transferred between the body and the environment by

radiation


conduction

convection and evaporation.

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epidermis(表皮 )

dermis(真皮 )

• two layers:

Structure and functions of skin

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Structure and functions of skin

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Skin on different parts of the body

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Skin

• two layers:

epidermis

dermis

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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

Scanning electron microscope (SEM) picture

of normal skin

E. coli on the surface of human skin.

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epidermis

dermis


1 Epidermis• three

layers:

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layers:i) Innermost layer• produces new cells

by mitotic cell divisionby mitotic cell division

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• contains melanin (黑素 )



layers:i) Innermost layer

absorbs UV lightabsorbs UV light

protects the bodyprotects the body

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• contains melanin (黑素 )




determines skin colourdetermines skin colour

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• produces vitamin D when exposed to sunlight




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• consists of living cells



layers:ii) Middle layer:

pushed towards surfacepushed towards surface

die and flattendie and flatten

outermost layeroutermost layer

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• consists of dead cells



layers:iii) Outermost layer

constantly worn away and replaced by new cells

constantly worn away and replaced by new cells

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reduce water lossreduce water loss


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protect from mechanical injury

protect from mechanical injury


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prevent entry of pathogens

prevent entry of pathogens


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i) Sensory receptors


2 Dermis

pain receptor

touch receptor

thermoreceptor

pressure receptor

• detect stimuli

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ii) Hair follicles (毛囊 )


2 Dermis

• new hair cells produced from the base

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2 Dermis

root of hair

• new hair cells produced from the base

ii) Hair follicles (毛囊 )

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iii) Erector muscles (豎毛肌 )


2 Dermis

and hairs

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2 Dermis

• erector muscle contracts

hair pulled upright• erector muscle relaxes

hair lies flat

and hairsiii) Erector muscles (豎毛

肌 )

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Goose bumps

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Goose bumps

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iv) Sweat glands (汗腺 )


2 Dermis

• form sweat

contains mainly water, salts, urea

and other metabolic waste

contains mainly water, salts, urea

and other metabolic waste

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2 Dermis

sweat duct (汗管 )

iv) Sweat glands (汗腺 )sweat pore (汗

孔 )

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2 Dermis

• sweat coming out to the skin surface sweating


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2 Dermis


for regulating body temperature

for regulating body temperature


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2 Dermis


for excretionfor excretion


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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…

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v) Blood vessels


2 Dermis

• circulation of blood

supplies oxygen and nutrients

supplies oxygen and nutrients

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v) Blood vessels


2 Dermis


removes wasteremoves waste

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v) Blood vessels


2 Dermis


distributes heatdistributes heat

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v) Blood vessels


2 Dermis

• vasoconstriction and vasodilation

‘vessel’

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v) Blood vessels


2 Dermis


regulate heat loss by controlling the amount of blood

flowing to the body surface

regulate heat loss by controlling the amount of blood

flowing to the body surface

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v) Blood vessels


2 Dermis


arteriole

capillary

venule

shunt vessel (分流血管 )

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v) Blood vessels


2 Dermis


1 arteriole constricts

2 less blood to capillary

3 more blood through shunt vessel

less heat is lost

Under cold conditionsUnder cold conditions

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v) Blood vessels


2 Dermis


1 arteriole dilates

2 more blood to capillary

3 less blood through shunt vessel

more heat is lost

Under hot conditionsUnder hot conditions

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Vasoconstriction and vasodilation occur in the capillaries.


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Capillaries cannot constrict or dilate because they have no muscle walls.

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It is the arterioles in the deeper part of the dermis that constrict or dilate.

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vi) Sebaceous glands


2 Dermis

• secrete sebum (皮脂 )

keeps hairs and skin supple and

waterproof

keeps hairs and skin supple and

waterproof

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vi) Sebaceous glands


2 Dermis

• secrete sebum (皮脂 )

a natural antiseptica natural antiseptic

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hair follicle

epidermissweat duct

sebaceous gland

mammalian skin (L.S)

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Pimples – inflamed

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• insulates the body to reduce heat loss


Subcutaneous fat

• as energy reserve

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2.1

Examination of the mammalian skin

1 Examine a prepared slide of mammalian skin or a skin model.


2 Identify the structures.

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Functions of structures of the skin:Epidermis:

1 Innermost layer• produces by mitotic

cell divisionnew cells

• contains which protects the body against ultraviolet light

melanin

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1 Innermost layer• produces vitamin D

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2 Middle layer• when pushed towards the

surface , cells die and formthe outermost layer

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3 Outermost layer• reduces by

evaporationwater loss

• protects the body frommechanical injury

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3 Outermost layer• prevents the entry of pathogens

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Functions of structures of the skin:Dermis:

1 Sensory receptors• detect stimuli

2 Hair follicles• produce new hairs

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3 Erector muscles and hairs• help regulate body temperature

4 Sweat glands• secrete for excretion and

body temperature regulationsweat

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5 Blood vessels• supply and to

skin cells and remove waste from them

nutrientsoxygen

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5 Blood vessels• help regulate body temperature

by andvasodilation

vasoconstriction

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6 Sebaceous glands• secrete that keeps the

hairs and skin supple and waterproof, and reduces the growth of harmful microorganisms

sebum

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Functions of structures of the skin:Subcutaneous fat:• acts as a layerheat insulating

• acts as reserveenergy

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How does skin regulate body temperature?


3D animation

• by controlling heat loss

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1 erector muscles contract to pull hairs upright


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2 sweating is reduced


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3 vasoconstriction


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4 layer of subcutaneous fat becomes


less heat is lost

thicker (long-term response)

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1 erector muscles relax and hairs lie flat

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2 sweating increases

3 vasodilation

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4 layer of subcutaneous fat becomesthinner (long-term

response)

more heat is lost

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Sweat is produced only when the body temperature increases.


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Sweat is produced most of the time to remove metabolic waste.

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StructureResponse under cold conditions

1 Erector muscles

2 Hairs

3 Sweat glands

Contract

Pulled upright


Secrete less sweat

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StructureResponse under cold conditions

4 Arterioles

5 Subcutaneous fat

Constrict (vasoconstriction

)


Becomes thicker (long-term)

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StructureResponse under hot conditions

1 Erector muscles

2 Hairs

3 Sweat glands

Relax

Lie flat


Secrete more sweat

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StructureResponse under hot conditions

4 Arterioles

5 Subcutaneous fat

Dilate (vasodilation)


Becomes thinner (long-term)

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Muscle contraction• metabolism in muscle cells generates heat• shivering (顫抖 ) - skeletal muscles contract

involuntarily

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Action of hormone2.3 Other mechanisms of body temperature regulation

• body temperature is also regulated by thyroxine (甲狀腺素 )

increases metabolic rate

generates heat to keep the body warm

increases metabolic rate

generates heat to keep the body warm

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thyroid gland

secretes


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• increased thryoxine secretion is a long-term response


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1 A decrease in blood temperature stimulates the hypothalamus to secrete TSH-releasing hormone (TRH).

hypothalamus TRH

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2 TRH stimulates the pituitary gland to secrete thyroid stimulating hormone (TSH).

hypothalamus TRH

pituitary gland

TSH

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3 TSH stimulates the thyroid gland to secrete thyroxine.

hypothalamus TRH

pituitary gland

TSH thyroxine

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4 Thyroxine increases the metabolic rate of body cells and more heat is generated.

hypothalamus TRH

pituitary gland

TSH thyroxine

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thyroxine inhibits secretions of TRH and TSH (negative feedback)

hypothalamus TRH

pituitary gland

TSH thyroxine

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Change of behaviour2.3 Other mechanisms of body temperature regulation

• voluntary behaviour also plays a part in regulating body temperature

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wear more clothes

turner on the heater

take in warm food/drinks

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wear fewer clothes

turner on the fan

take in cold food/drinks


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1 in muscle cells generates heat to maintain the bodytemperature.

Metabolism

also generates heat. Shivering provides extra amount of heat to keep us warm under cold conditions.

Muscle contraction


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2 increases the metabolic rate of most cells, so that more heat can be generated to keep the body warm. Increased thyroxine secretion is a response to a cold environment.

long-term

Thyroxine


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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 food and drinks.

3 Behavioural mechanisms that help regulate body temperature:


warm

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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 food and drinks.

3 Behavioural mechanisms that help regulate body temperature:


cold

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• 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

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heat loss centre

thermoregulatory centre in hypothalamus

normal body temp

thermo-receptors

rises

heat gain centre

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heat loss centre

normal body temp

thermo-receptors

rises

initiates mechanisms

normal body temp

falls

heat gain centre

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Mechanisms to promote heat loss and decrease heat gain:

• relaxation of erector muscles• increased sweating

• vasodilation• decreased secretion of thyroxine

(long-term)

Physiological

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• thinner layer of subcutaneous fat (long-term)

Structural

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• wear fewer clothes

Behavioural

• turn on the fan

• take in more cold food

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heat loss centre

heat gain centre

normal body temp

thermo-receptors

rises


normal body temp

falls

falls

thermo-receptors


rises

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Mechanisms to reduce heat loss and increase heat gain:

• contraction of erector muscles• reduced sweating

• vasoconstriction• shivering

Physiological

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• increased secretion of thyroxine (long-term)

Physiological

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• thicker layer of subcutaneous fat (long-term)

Structural

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• wear more clothes

Behavioural

• turn on the heater

• take in more warm food

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in skin detect changes in external temperature and send nerve impulses to the thermoregulatory centre in the .

Thermoreceptors

hypothalamus


1a

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Thermoreceptors in the hypothalamus detect changes in the temperature of passing through it.

blood


1b

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Skin or blood temperature rises

heat loss


2a

centre stimulatedmechanisms

• erector muscles and hairsrelax lie flat• sweating increases• occursvasodilation

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Skin or blood temperature rises

heat loss


2a


• thyroxine secretion decreases• subcutaneous fat becomes thinner• ,

e.g. wear fewer clothes, turn on the fanbehavioural mechanisms

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Skin or blood temperature falls

heat gain


2b


• erector muscles and hairs arecontractpulled upright

• sweating decreases• and shivering occurvasoconstriction

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• thyroxine secretion increases• subcutaneous fat becomes thicker• behavioural mechanisms, e.g. wear

more clothes, turn on the heater

Skin or blood temperature falls

heat gain

2b


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Why is heatstroke more likely tooccur under hot and humid conditions?1High humidity lowers the rate of evaporation of sweat, so the body cannot lose heat effectively and heatstroke is likely to occur.

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Why may death result when thebody temperature is too high?2When the body temperature is too high, enzymes cannot work properly and cells fail to function.

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What are the treatments andprecautions for heatstroke?3To treat heatstroke, we should move the person to shaded areas and wrap the body with cool wet towels.

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What are the treatments andprecautions for heatstroke?3To prevent heatstroke, we should avoid doing vigorous exercise in a hot environment.

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maintained by balancing

A stable body temperature

heat gain


controlled by

heat loss

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through mechanisms that involve

skin

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structures involvedskin

subcutaneous fat

erector muscles and hairs

sweat glands

blood vessels

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blood circulation

distribution of heat

controls vasoconstriction and vasodilation

by

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skeletal musclesunder cold conditions

production of more heat

leads toshiver

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thyroid glandsecretes

metabolic rateincreases

thyroxine

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cerebrumbrings about

behavioural mechanisms

1 2 think about… 2.1 importance of regulating body temperature 2.2 the role of skin 2.3 other...

Documents

body slide

stable body temperature

steady slide

functions of skin slide

o c slide

epidermis dermis slide

hot sand slide

narrow range of temperature