Lecture 29: Staying Warm & Cold - Thermoregulation

04/04/25

homeostasis

• maintaining internal environment at relatively constant conditions

• homeostatically controlled factors: temperature, pH, blood glucose, salinity

• is regulated by types of feedback (positive vs. negative)

importance of homeostasis

• maintains enzyme function

• helps with metabolic efficiency

• keeps structural integrity of cells + proteins

negative feedback

mechanism that detects deviation from desired set point and counteracts the change to bring body back to original state

positive feedback

intensifies a physiological change, increasing deviation from set point in a certain direction

negative feedback: glucose example

• blood glucose falls → pancreas produces glucagon → conversion of stored, complex carbohydrates into glucose → raises blood level of glucose

• blood glucose rises → pancreas produces insulin → absorbs glucose rather than distributing into bloodstream

regulators

• maintain internal condition regardless of external environment changes

• important for homeostatic processes

conformers

• as the external environment changes, so does the internal environment

• still have homeostatic processes but are more bound by certain limits

circadian rhythm

• daily cycle of physiological patterns

• temperature, blood pressure, sleep/wake cycles

• maintained with minimal cues (shown by blind mole rat experiments)

• disruptions such as jet lag harms our circadian rhythm and can cause metabolic change or weight gain

temperature regulation: ectotherms

• use external source to control body temperature

• reptiles, shark, fish

• very closely aligned with conformers

temperature regulation: endotherms

• rely on internal energy (metabolic heat) to control body temperature

• mammals with high metabolic needs

• very closely aligned with regulators

temperature regulation: poikilotherms

• body temperature varies with environment

• classic conformers

temperature regulation: homeotherms

• body temperature is relatively stable regardless of environment

• classic regulators

how body temperature changes: evaporation

loss of heat by evaporation of water

how body temperature changes: radiation

emission of electromagnetic radiation

how body temperature changes: convection

movement of air or water to remove radiated heat

how body temperature changes: conduction

direct transfer of heat by contact (does not include touching water)

energy expenditure in ectotherms vs. endotherms

• ectotherms: expend less to maintain a certain temperature

• endotherms: expend A LOT to maintain a certain temperature

effect of environmental conditions in ectotherms vs. endotherms

• ectotherms: inactive under poor conditions

• endotherms: remain active despite poor conditions

enzymes in ectotherms vs. endotherms

• ectotherms: enzymes function under a certain range of internal conditions

  • costly to maintain multiple enzymes

• endotherms: enzymes optimized for near constant internal conditions

  • efficient to have optimized enzymes