FMD002 Homeostasis 2024 PDF

FMD002 Homeostasis Vikram Sharma 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 1  Homeostasis There is a narrow range of physical and biochemical conditions under which the body functions optimally Chemical constitution...

FMD002 Homeostasis Vikram Sharma 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 1  Homeostasis There is a narrow range of physical and biochemical conditions under which the body functions optimally Chemical constitution glucose, ion levels, etc. Osmotic pressure relative amounts of water and solutes CO2 levels Temperature 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 2  Homeostasis “homios” same “statis” state The maintenance of a stable but dynamic (within set parameters), physiological state by auto-regulatory processes of the body 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 3  A model of homeostasis External environment Internal environment Large Small Homeostatic Internal external control fluctuations fluctuations systems Cells in the body 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 4  The internal environment Most cells of large animals have no contact with the external environment – Their needs must be met by a wholly internal environment – Cells bathed in fluid: absorbs waste, contains nutrients, provides a relatively stable environment for the cell E.g. humans: about 60% water About 60% of that is in cells Remaining is extracellular fluid: 20% plasma 80% interstitial fluid 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 5  The internal environment Makes it possible to occupy habitats that would kill its cells if they were directly exposed 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 6  General scheme of homeostatic control Corrective mechanism Negative feedback Excess detected Norm Norm set point set point Deficiency Negative detected Corrective mechanism feedback 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 7  Control of blood glucose Blood glucose levels must be kept constant Glucose → small intestine → blood stream → liver Liver can either do: 1. Cell respiration → water and carbon dioxide 2. Convert → glycogen → stored 3. Convert → fat → fat deposits 4. Pass → general circulation Which of these happens depends on the level of blood glucose, and is controlled by hormones 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 8  The control of blood glucose Maintenance of blood glucose homeostasis by Negative feedback insulin and glucagon Negative feedback 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 9  Temperature sensitivity Cells need to be kept between ~0°C and ~40°C Even within those limits, physiological processes are temperature sensitive Not all biochemical reactions change at the same rate with temperature 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 10  Control of body temperature Animals get their heat from: – The sun (solar energy) – Chemical energy from cell respiration 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 11  Control of body temperature ‘Warm blooded’ vs ‘cold blooded’ ‘Poikilothermic’ vs ‘homeothermic’ 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 12  Control of body temperature Ectothermic animals (Greek ‘Ecto’= outside) Gain heat from the environment – All animals except birds and mammals* Endothermic animals (Greek ‘Endo’= inside) Generate heat mainly within the body – Birds and mammals* 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 13 Relationship between environment and body T 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 14  Ectothermic animals Require less food than endotherms Have a lower metabolic rate Do not use energy to maintain body temperature Have no mechanisms for conserving heat Use behavioural means to control body temperatures Only active when the weather is warm enough 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 15  Endothermic animals Require large quantity of food Have a high metabolic rate Use energy to maintain body temperature Have mechanisms for conserving heat Use behavioural and physiological means to control body temperatures Can remain active day and night, winter and summer 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 16  Ectothermic animals Aquatic animals Water temperature doesn’t fluctuate much Body temperature is the same as the water temperature Not all fish behave like ectotherms – e.g. ‘hot’ fish 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 17  Ectothermic animals Land animals Air temperature quite variable Gain heat from sunlight and the ground so can be more active than aquatic animals Warming – Change orientation to the sun, basking Cooling – Seek shade, wallow in water, open mouths 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 18  Ectothermic animals Not all invertebrates behave like ectotherms – e.g. social insects, flying insects 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 19  Heat exchange in ectotherms 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 20  Endotherms Endotherms can respond to temperature change by changing their metabolic rate In the thermoneutral zone, the metabolic rate is low (and independent of temperature) The basal metabolic rate (BMR) is the metabolic rate of a resting animal in the thermoneutral zone 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 21  Endotherm BMR 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 22 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 23  Outside the thermoneutral zone Behavioral Warming – huddle together – seek shelter – (add clothing) Cooling – seek shade – wallow in water – (remove clothes) 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 24  Outside the thermoneutral zone Physiological Warming – vasoconstriction – hair erect (piloerection) – shivering – increased metabolic rate Cooling – sweating – hair lies flat – vasodilation – decreased metabolic rate 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 25  Vasodilation and vasoconstriction Vasoconstriction Vasodilation Blood flow directed away Increased blood flow to the from the skin surface skin surface 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 26  Negative feedback 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 27  Homeostasis ( Slide Credit: Dr. Michael 9/20/2024 28 Thom) Control of body temperature by –ve feedback Detector – hypothalamus and skin Effectors – nervous system and endocrine system: Somatic nervous system (voluntary) behavioral mechanisms Autonomic nervous system (involuntary) shivering, vasodilation, sweating etc. Endocrine system adrenaline, thyroxine - increased metabolism 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 29 Negative feedback Negative feedback Homeostasis ( Slide Credit: Dr. Michael 9/20/2024 30 Thom)  Summary Homeostasis – maintain ideal internal environment Two examples of control mechanisms – Control of blood glucose levels by hormones – Control of body temperatures by behavioral and physiological means Negative feedback maintains physiology within acceptable parameters https://www.youtube.com/watch?v=62e8IV-WT8c 9/20/2024 Homeostasis ( Slide Credit: Dr. Michael Thom) 31