2. Homeostasis What is homeostasis?
The maintenance of a constant internal environment within a living organism
What makes up the feedback circuit?
receptor
coordinator
effector

3. Homeostasis
What is negative feedback?
What is positive feedback?

5. Temperature and Life
Life can exist at almost all of the temperatures on Earth
This is because it is the internal not external temperature that is important to organsisms.

6. Temperature Change
Within thermal limits, temp change can cause problems
Most metabolic reactions are temperature sensitive
Although enzymes tend to denature above 45º C it is thought that death from excess heat is due to metabolic imbalance as some enzymes work faster than others so allowing intermediate chemicals to build up.
Q10 is a measure of temp sensitivity

8. Temperature Maintenance
Homeotherm
Poikilotherm
Endotherm
Maintain a stable core temperature using physiological and behavioural means examples?
Birds and Mammals
Ectotherm
Can control their body temperature only by changing their behaviour examples?
All other animals
Hometherm = consrtant temp warm blooded
Poikilotherm = changeable temp cold blooded
Hererotherm =

11. Thermoregulation and Behavior

12. Endotherm thermoregulation
Behavioural regulation
Wearing more or less clothes
Building shelters and fires
Curling up into a ball when cold
Stretching out when hot

13. Endotherm Thermoregulation
Adjust metabolic rate response to environmental temperature changes
Metabolic reactions product produce heat as a by product

14. Endotherm Thermoregulation
General body plan modifications
hair
feathers
shorter appendages
rounder body shapes
Humans and Heat
Humans have a thin covering of insulating fat and body hair is sparse
We are one of only a few animals to be covered in sweat glands

15. Thermoregulation and Skin Perfusion

16. How is heat produced and lost?
Heat can be gained or lost in four ways:
Conduction
Convection
Radiation
Evaporation
Conduction involves the transfer of heat between two objects that are in contact with oine anohter, heat is always conducted from a higher to lower temp e.g. when you sit on a cold chair heat is conducted from your body to the chair
Air has a lower thermal conductivity so heat loss to water is much greater
Convection is heat transfer due to currents of air or water, our clother reduce heat lost by convection by trapping a layer of air next to the skin
Radiation is the loss of inf red heat to the surroundings - most heat loss is due to radiation
Evaporation is the change of stae from liquis to gas and it has a cooling effect as energy id used to vapourise the liquid

17. Internal Regulation
In Humans the basic mechanism that underlies thermoregulation involves the hypothalamus
This part of the brain monitors the temperature of the blood and uses feedback to control internal body temperatures
Any increase in heat production is proportional to the temperature the hypothalamus is cooled below the set point

18. Hypothalamus

20. Blood temperature falls Blood temperature rises
Controlling body temperature
Blood temperature falls
Blood gets too hot
Brain switches
on cooling
mechanisms
Normal body
temperature
37ºC
Normal body
temperature
37ºC
Blood gets too cold
Blood temperature rises
Brain switches
on warming
mechanisms

21. The Skin
The skin is a large organ responsible for maintaining homeostasis through temperature regulation
It is also responsible for protection of underlying tissues, retardation of water loss, sensing environmental change, and housing cells of the immune system.

23. The Skin The skin consists of an outer epidermis
and a dermis, connected to underlying
tissue by the subcutaneous layer
(hypodermis).

25. Physiological Responses To Cold
There are 4 main responses when the hypothalamus detects a drop in temperature:
Shivering
Vasoconstriction
Piloerection
Increased metabolic rate

26. Shivering
Depends on contractile machinery of skeletal muscles to consume ATP
Tremor results
Conversion of ATP to ADP results in heat production

27. Piloerection Erection of hairs
The erection pili muscles in the skin pull our tiny hairs upright – producing goosepimples

28. Vasoconstriction
The arterioles that lead to the capillaries in the surface are of the skin constrict and so reduce blood flow to the skin
A shunt vessel by passes the surface capillaries

29. Increased metabolic rate
The body secretes the hormone adrenaline in response to cold.
This raises metabolic rate and therefore increases heat production.
People who live in cold conditions for a long time show a more permanent rise in metabolic rate due to the secretion of thyroxine.

30. When we are too cold

31. Physiological Responses To Heat
Sweating
Sweat is a salty solution made by sweat glands, evaporation of sweat from skin’s surface leads to cooling
Vasodilation
Arterioles that lead to skin capillaries dilate and shunt vessels are closed this leads to an increase in blood flow to the skin moer heat is lost by radiation

32. When we are too hot

33. Apocrine galds = water based sweat
Eccrine glands = oil based sweat – smelly bacteris

34. Fig. 49.03(TE Art) Perturbing factor Response Body temperature drops
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig (TE Art)
Perturbing factor
Response
Body temperature
drops
Sun
Effector
Negative feedback
Blood vessels
dilate
Glands release
sweat
Stimulus
To decrease
body temperature
Body temperature
rises
Integrating
center
Sensor
To increase
body temperature
Stimulus
Effector
Body temperature
drops
Negative feedback
Blood vessels
constrict
Skeletal muscles
contract, shiver
Perturbing factor
Response
Body temperature
rises
Snow and ice

35. Experiment where a naked man sits in a room where the temp around him is gradually raised or lowered. Btween 15 – 30 C the naked man can maintain a constant core temp, a point is reached where his sweating and vasodilation are no longer able to keep him cool he has reached the upper critical temp. After this him metabolic rate increases but the expeiment is always stopped , if it was not then positive feedback would take place and the enzymes would work faster and so increase metabolism and so heat at about 42 c the upper lethal tempo is reached and he would die
When temp is lowered the rrom gets so cold the bodt cannot maintain a constant core temp at the lower critical temp metabolic rate increase and generates heat, the exp0eriment is usually stopped at this point if continued a lower letahl temp would be reacheed and death

36. Problems in Temperature Regulation
Air can hold a limited amount of water vapor when air is saturated with water, sweat may fail to evaporate, and body temperature may remain elevated
Hypothermia is lowered body temperature, it causes shivering, mental confusion, lethargy, loss of reflexes & consciousness, and eventually major organ failure.

37. Non shivering Heat Production
Brown fat
Thermogenin uncouples proton movement from ATP production, so metabolic fuels are consumed without producing ATP
Heat is still released