Lecture 4: Homeostasis - Biol 224.3 Animal Body Systems PDF

Biol 224.3 – Animal Body Systems Lecture 4: Homeostasis Dr Joan Forder Supplementary Textbook Reading: Textbook (5th Edition, Chapter 35, page 935- 941; Chapter 39, page 1043-1053)...

Biol 224.3 – Animal Body Systems Lecture 4: Homeostasis Dr Joan Forder Supplementary Textbook Reading: Textbook (5th Edition, Chapter 35, page 935- 941; Chapter 39, page 1043-1053) 1 Road Map for Today What is Homeostasis? Why is it necessary? Homeostasis Methods Thermoregulation  HOMEOSTASIS Definition: Regulation of the body’s internal environment at or near a stable level. external environment (large changes over time) homeostatic mechanism internal environment (small changes over time) See page 937 (35.4a) 3 Stability NOT Constancy! e.g. diurnal changes in human body temperature Source: Encyclopedia Britannica 11 ed, downloaded from Wikipedia 4  Why is Homeostasis Necessary? Temperature O2 Concentration Nutrient Concentration CO2 Concentration Concentration of waste chemicals Water and NaCl concentration pH Goal of Homeostasis? To allow organism to reach OPTIMAL PHYSIOLOGICAL PERFORMANCE! 5  Homeostatic Methods Homeostasis regulates a physiological variable within a narrow range around a set point Regulatory mechanisms may involve: Negative Feedback (Primary method) Positive Feedback Feedforward In most complex regulation, all three may be used. 6  Negative Feedback Variable rises above the set point. Negative Feedback mechanisms return the variable back towards the set point. i.e. minimizes difference between actual level and the set point) *NEGATIVE FEEDBACK MECHANISM KICKS IN variable Magnitude * * * * of Variable set point Time see Chapter 35 7  Positive Feedback Used to quickly increase (or decrease) a process Moves variable away from the set point. Amplification effect eventually i.e. amplifies difference between actual shut off by negative feedback. level and the set point *Positive Feedback kicks in Set Point Magnitude * of Variable Variable Time 8 Positive Feedback Example: Childbirth oxytocin 9 Positive Feedback Example: Membrane Potentials more about the Hodgkin-Huxley cycle in bioelectricity lectures. * *The rising phase of the nerve action potential 10 Feedforward Future needs are anticipated Physiology is adjusted in advance Often involves learning and complex behaviours! 11 Feedforward in Monarch Butterflies 12 Thermoregulation Key Terms Endoderms vs Ectoderms Homotherms vs Heterotherms Examples of Ectoderms Examples of Endoderms Use of Negative Feedback loops  Thermoregulation: Key Terms Endotherm vs Ectotherm Homeotherm vs Heterotherm Location of needed body heat Constant vs Variable body Endotherms: get heat from temperature internal physiological sources Homeotherms – maintains body Ectotherms: get heat from temp at a constant level/range. external environment E.g. mammals, birds, dinosaurs? Heterotherms – vary between self- regulating their body temperature Thermogenesis: heat production and allowing the surrounding through physiological processes environment to affect it. E.g. reptiles, amphibians  Endotherms vs Ectotherms Endotherms (e.g. mouse) As environmental temperature decreases, animal’s metabolic rate increases causing body temperature to increase Ectotherms (e.g. lizard) Body temperature decreases as environmental temperature decreases Causes biochemical and physiological processes to slow down Questions What are the advantages and disadvantages of being an Endotherm? What are the advantages and disadvantages of being an Ectotherm? Which one is superior?  Homotherms vs Heterotherms Temperature stable 17 Question Are all Endotherms Homotherms? Ectotherms in All Invertebrate Groups Most aquatic invertebrates are limited thermoregulators. But some use behavioural responses to regulate body temperature. Terrestrial invertebrates regulate body temperatures more closely. Some use a combination of behavioural and heat-generating physiological mechanisms. 19 The Flying Sphinx Moth  Most Fishes, Amphibians, and Reptiles are Ectotherms Fishes Body temperature of most fishes remains within one or two degrees of the aquatic environment. Many fishes use behavioural mechanisms to regulate temperature. Amphibians and reptiles Body temperatures closely match environmental temperature. Can move to different locations to regulate More pronounced among terrestrial reptiles 20  Endotherms: Birds & Mammals external environment (large changes over time) homeostatic mechanism internal environment (small changes over time) See page 937 (35.4a) 21 Endotherms Physiological and behavioural responses to changes in skin and core body temperature Fig. 39.23 22 Use of Negative Feedback Loops e.g. increased blood flow to skin; sweating; panting; cooling physiology others Maintains a balance stimulated; heating physiology inhibited between heat loss & temp increase heat gain. integrated by hypothalamus body temp rises above set point body temp falls below set point temp decrease e.g. decreased blood integrated by flow to skin; shivering heating physiology hypothalamus (skeletal muscle stimulated; cooling contractions); physiology inhibited erect hair or feathers; others 23 Negative Feedback Mechanisms Returns the condition to the set point if it has strayed away Detects a change in an external or internal condition Compares the detected change with a set point Fig. 35.11, p. 938 Temperature Homeostasis using Negative Feedback Fig. 35.13, p. 940