Thermoregulation

Thermoregulation

Maintenance of a relatively constant core body temp. to maintain optimum enzyme activity

Ways of losing heat

• Evaporation of water

  • latent heat lost from surface (mouth /sweat)

• Radiation to surroundings

  • IR from skin → surroundings absorb it

• Convection to surroundings

  • Convection currents form from skin (warm air rises, cooler air sinks)

• Conduction to surroundings

  • Passes thermal energy between particles as they vibrate more 

Ectotherms

• Use surroundings to warm bodies 

• Core body temp. heavily dependent on environment 

• Invertebrate animals 

  • Those in water don’t need to thermoregulate 

Why do ectotherms in water not need to thermoregulate 

Water has high heat capacity, temp doesn’t change much 

Ectotherm behavioural responses to increase temp (4)

• Bask in sun

• Orientate / Change bodies so that max. SA exposed to sun

• Press bodies against warm ground 

• Exothermic metabolic reactions (vibrate wings, contract muscles & vibrate)

Ectotherm behavioural response to decrease temp (4)

• Shelter from sun

• Press bodies against cool, shady surfaces

  • Move into water or mud

• Orientate bodies so minimum SA exposed to sun

• Minimise movement to reduce metabolic heat generated 

Ectotherm physiological responses

Darker coloured organisms tend to live in colder areas (absorb more radiation)

• Get warmer

Alter heart rate to increase or decrease metabolic rate & to affect warming or cooling across body surfaces 

Pros of being ectotherm

1. Require less food

   • Use less energy regulating their temps

   • Can survive in harsh habitats where food scarce

Con of ectotherms

Vulnerable to fluctuations in environment

Endo and Ecto metabolic rates

Endo metabolic rate 5x higher than ecto

• Endo need to consume more food to meet metabolic needs

• Ecto use less of their food in resp. , need to find less food, can last long w.out food

Endotherms

• Mammals and birds

• Rely on metabolic processes to warm up, usually maintain v. stable core 

• Use heat produced internally to maintain body temperature

In endotherms, what are ultimately the physiological adaptations to maintain core body temp? (4)

1. Peripheral temperature receptors in skin

2. Temp. receptors/ thermoregulatory centres of hypothalamus

3. Skin

4. Muscles

Endotherms behavioural responses to temp changes

1. Basking in Sun

2. Pressing against warm surfaces

3. Wallowing in water to cool down

4. Digging burrows to keep warm or cool

5. Hibernation

6. Wearing clothes, heated/cooling down of houses

How do mammals cool down? (3)

1. Vasodilation

2. Increased sweating

3. Reduced insulation effect of hairs/feathers

How does Vasodilation cool body?

Arterioles near surface of skin dilate when temp rises

1. Vessels that connect arterioles & venules constrict

2. Forces blood thru capillary networks close to skin surface

3. Heat lost to environment via RADIATION

4. If skin pressed against cool surfaces, conduction

How does increased sweating cool body?

As sweat EVAPORATES from skin surface, heat lost, cooling blood below skin surface

How does reducing insulating effect of hair cool us down?

1. Erector pili muscles relax

2. Hair lie flat to skin

3. Avoids trapping insulating layer of air

How do endotherms warm up physiologically? (4)

1. Vasoconstriction

2. Decreased sweating

3. Raising body hairs

4. Shivering

How does vasoconstriction warm up?

Arterioles near skin surface constrict

1. Shunt vessels dilate, little blood throws thru capillary networks to skin surface

2. Very little heat loss by radiation occurs

3. Warm blood kept well below skin surface

How does decreased sweating warm up?

Reduces cooling by evaporation of water from skin surface

How does raising of body hair warm up?

Erector pili muscles contract

• Hair on animals erect

• Traps insulating layer of air, reducing cooling thry skin

How does shivering warm up?

Metabolic heat from exothermic reactions (produced from rapid succession of contraction & relaxation of muscles) warms body

What is the heat loss centre

Centre activated when temp. of blood flowing thru hypothalamus is increased

• Sends impulses thru autonomic neurones to effectors in skin & muscles

  • Triggers responses that lower core temp

What is the heat gain centre?

Activated when temp of blood flowing thru hypothalamus is decreased.

• Sends impulses thru ANS to effectors in skin & muscles

  • Triggers responses to raise core temp

Hypothalamus and body temp

1. Receives info about temp from thermoreceptors

2. Thermoreceptors send impulses along sensory neurones to hypothalamus, sending impulses along motor neurones to effectors

   • E.g. skeletal muscles, sweat glands, erector pili muscles, smooth muscles of shunt vessels

Endotherms thermoregulation

Interaction of sensory receptors, ANS & effectors enables endotherms to maintain stable core body temp, regardless of activity levels or environmental conditions