Homeostasis

We are learning to

• Identify what homeostasis is

• Describe what mechanisms can be used to maintain a constant body temperature.

• Describe how thermoregulation is controlled by negative feedback and the role of the hypothalamus and receptors.

I can

• Define the terms Homeostasis, ectotherm, endotherm and negative feedback.

• I can describe the mechanisms utilised to control body temperature and explain how they work to increase/reduce heat loss.

Homeostasis

• Homeostasis is the maintenance of the body's internal environment within limits despite the external environment

• Regulation requires energy and is under negative feedback control

Negative feedback control

• When a body’s internal environment deviates from ‘normal’ it is detected by receptors

• Receptors send hormonal or nervous impulses

• Effectors act to return the environment back to ‘normal’

Conditions in the body change from

set point

Change detected

(by receptors)

Corrective mechanism(s) activated (by nerves or

hormones)

Corrective mechanism(s) switched off

Conditions returned to set point (by effectors)

Thermoregulation

• Thermoregulation is the control of temperature in an organism.

Ectotherm

• An ectotherm cannot maintain its body temperature by physiological means.

• Absorb heat from environment

• E.g. Fish and reptiles

Endotherm

• An endotherm maintains its body temperature at a relatively constant level regardless of environment.

• E.g. All birds and mammals

Comparing thermoregulation

Using the graphs, describe the effect of temperature on endotherms and ectotherms. Identify which is the ectotherm/endotherm and then explain why.

Y is a ectotherm/conformer because • Internal has varied with external

Z is a endotherm/regulator because • Internal has remained the same

Role of the hypothalamus

• The hypothalamus is the temperature monitoring centre. It contains thermoreceptors and receives electrical impulses through nerves from receptors in the skin

• It also senses the temperature of blood

• The hypothalamus sends appropriate impulses to effectors to trigger corrective feedback

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Body core and shell

• The shell or periphery is more susceptible to cool temperature.

• The core is maintained at 37°C.

Why?

Correcting overheating

• Vasodilation

• Arterioles in the skin dilate

• This allows blood flow to surface

• Heat loss by radiation

• Sweating

• Evaporation of vapour from the skin has a cooling effect

Decreased metabolic rate

• Less heat produced

Correcting overcooling

• Vasoconstriction

• Arterioles in the skin constrict

• This shifts blood flow from surface

• Heat loss by radiation reduced

• Shivering

• Muscle contraction generates heat

• Hair erector muscle

• Muscles attached to

hair erect and an insulating layer

of air is trapped.

Increased metabolic rate –

• more heat produced

hair

Hair erector pili

muscle

Sweat gland

Body temp. normal

Body temp. normal

Rise in body temp.

Detected in hypothalamus

Nerve impulses

sent

skin

Sweating increases

Drop in body temp.

Nerve impulses

sent skin

Sweating decreases

Detected in hypothalamus

vasodilation

Hairs lowered

vasoconstriction

Hairs raised

Messages to other

effectors

Decrease in metabolic rate

Messages to other

effectors

Increase in metabolic rate

Importance of thermoregulation

• For optimum enzyme activity and high diffusion rates.

• Most enzymes work best at 35-400C.

• Animals that can maintain their body within this range possess an efficient and active metabolism

Quick questions Q1: Complete the table with the temperature responses listed.

Temperature responses: active sweat glands, decrease in metabolic rate, hair erector muscles contracted, hair erector muscles relaxed, inactive sweat glands, increase in metabolic rate, vasoconstriction, vasodilation.

Q2: Which part of the brain is responsible for regulating body temperature in mammals?

Q3: In which of the following ways does the body respond when its temperature falls?

a) Vasoconstriction and sweating

b) Contraction of hair erector muscles and vasodilation

c) Vasodilation and decreased rate of metabolism

d) Shivering and vasoconstriction

Q4: Why do you sweat and your skin become flushed during exercise?