1. Homeostasis Chapter 28

2. Objectives Explain the importance of homeostasis in humans
Understand the role of the hypothalamus in maintaining homeostasis
Explain the process of thermoregulation
Explain how the body maintains homeostasis of nutrient levels
Explain the process of osmoregulation

3. Homeostasis
Regulation of cell processes to maintain conditions necessary for life
Maintain relatively constant internal environment (ie. Interstitial fluid)
External conditions may fluctuate widely, but internal conditions only have small fluctuations
Internal fluctuations are within the narrow range where life’s metabolic processes occur

4. Homeostasis (2 min): https://www.youtube.com/watch?v=O0Rfa3F_AD8

5. Thermoregulation
Regulation of internal temperature independent of external fluctuations
Controlled by the hypothalamus
Biochemical reactions catalyzed by enzymes occur within a narrow temperature range (36°C to 38°C)
Below 35°C results in hypothermia
Above 42°C results in brain damage
Why 37 Degrees? (2.5 min):

6. Heat transfer
Conduction: transfer of heat from objects in direct contact (eg. Touching a hot stove)
Convection: movement of air or liquid past a surface (eg. Breeze blowing)
Radiation: emission of electromagnetic waves (eg. Heat from the sun’s radiation)
Evaporation: loss of heat from the surface of a liquid as it turns into gas (eg. Sweating)

8. Thermoregulation involves
Sensors in your central nervous system (CNS) sending messages to your hypothalamus that your internal temperature is increasing or decreasing too much.
Anterior hypothalamus sends messages to cool your body down
Posterior hypothalamus sends messages to heat your body up

9. If your body needs to cool down, these include:
Sweating: Sweating is one of the first methods your body will use to control your temperature. Sweat cools your skin as it evaporates. This helps lower your internal temperature.
Vasodilatation: Your CNS may instruct the capillaries under the surface of your skin to dilate, or open. Vasodilation, or enlarged capillaries, increases blood flow at the skin surface. This lets your body release heat through radiation. 
Source:

10. If your body needs to warm up, these include:
Stopping sweating: Your nervous system can lower sweat production to help maintain the heat your body generates.
Vasoconstriction: Your CNS may signal your capillaries to constrict. This decreases blood flow under the skin and reduces heat loss.
Goosebumps: Skin pores close to reduce heat loss and hair stands up to trap air and increase insulation.

11. Thermogenesis: Your body’s muscles, organs, and brain can produce heat when your internal temperature decreases. This process is called thermogenesis. Shivering is one way muscles generate heat.
Hormonal thermogenesis: Your body can activate the thyroid gland if you are getting too cold. This releases hormones that increase your metabolism to increase heat due to exothermic reactions.
Thermoregulation (5 min):

13. Review: Homeostasis of Blood Calcium

14. Review: Homeostasis of Blood Glucose

15. Osmoregulation Control of gain and loss of water and solutes
Regulation of solute concentration to control water balance
Main challenge for terrestrial animals is dehydration
Humans are 55% - 60% water

16. Review of Osmosis
Diffusion of water across a permeable membrane based on solute concentration (osmolarity)
Water will move from an area of lower osmolarity to an area of higher osmolarity

18. Osmoconformers
Have solute concentration equal to external environment (eg. Marine invertebrates)
Gain and lose water at approximately equal rates
No need to expend energy to maintain water balance
Unable to tolerate much fluctuation in environmental salinity (stenohalines).

19. Osmoconformers

20. Osmoregulators
Have internal solute concentration different from external environment
Must regulate water loss or gain

21. Terrestrial Animals
Cannot directly exchange water with the environment
Lose water through respiration, evaporation and excretion
Need adaptations to prevent dehydration (eg. Skin, scales, amniotic fluid)
Kidneys help conserve water and regulate ion balance

22. Kidneys and Osmoregulation