thermoregulation

why does thermoregulation matter

• most enzymes work optimally within a relatively narrow range if temp, include many which control life critical reactions

• above 40, enzymes lose function and start to denature

endotherms

• can maintain its own body temp within fairly strict limits, largely independently of external temp

• eg humans

ectotherms

• have a body temp which tends to fluctuate with external temp

• rely on external sources of heat to keep warm

• eg lizard

behavioural responses of ectotherms to keep warm

• bask in sun by lying flat=increase surface area

• bask for long periods of time

• insects spread wings in sun

• iguanas can contract muscles and vibrate= increase cellular metabolism which raises core temp

behavioural responses of ectotherms to cool down

• shelter to reduce heat

• press against cool rocks

• minimise movements

physiological responses of ecotherms’s to maintain core temp

• increase:

  • dark colours absorb more

  • some can alter hr to increase metabolic rate which warms up

  • some lizards can cut off blood supply to legs to reduce heat loss

• decrease:

  • some can alter hr to decrease metabolic rate which cools down

how do endotherms measure external temp

• have peripheral temp receptors in the skin

how are endotherms core temp monitored

• thermoregulatory centre in the hypothalamus in brain

• this monitors the temp of blood flowing through it

what do signals from extremities cause

• behavioural mechanisms

what do changes in core body temp trigger

• physiological mechanisms to maintain temp

physiological mechanisms to gain heat

• vasocontraction

• increased metabolic rate

• shivering

• hairs

• decreased sweating

• more fat below skin

vasoconstriction

• less blood to skin surface so you lose less heat by radiation

• muscle contracted, reduced blood flow to skin surface

• arteriole constricts

• more blood passes through shunt vessel

increased metabolic rate

• controlled by thyroxine and adrenaline

shivering

• increased muscle contraction leads to increased heat generation

hairs

• stan up on end (erector pili muscle contract)

physiological mechanisms the body uses to lose heat

• vasodilation

• decreased metabolic rate

• hairs flattened

• increased sweating

• less fat below skin

vasodilation

• more blood to skin surface so you lose more heat by radiation

• muscle relaxed increased blood flow to skin surface so arteriole widens

• little blood passes through shunt vessel

increased sweating

• heat removed as water evaporation

blood temp TOO HIGH

1. Stimulus: increased body temp eg exercising

2. blood warmer than hypothalamic set point

3. activates heaat loss center in hypothalamus

4. sweat glands activate- sweat is vapourised by body heat, helping cool the body

5. blood vessel dilate, heat radiates from skin

6. body temp decreases, hypothalamus heat loss centre shuts off

blood temp TOO LOW

1. stimulus: decreased body temp due to the cold

2. blood cooler than hypothalamic set point

3. activates heat promotor centre in the hypothalamus

4. blood vessels constrict to deeper in skin

5. skeletal muscles activates when more heat must be generated, shivering begins

6. body temp increases, blood temp rises and hypothalamus heat promoting centre shuts off