Homeostasis Chapter 28

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

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

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

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): https://www.youtube.com/watch?v=a73MCMDDBfs

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)

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

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: www.healthline.com

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.

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): http://www.youtube.com/watch?v=TSUCdLkI474

Review: Homeostasis of Blood Calcium

Review: Homeostasis of Blood Glucose

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

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

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).

Osmoconformers

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

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

Kidneys and Osmoregulation