Lecture 2 Regulation and Scaling 2023 PDF

Biology 2601 Organismal Physiology Physiological Regulation and Scaling The milieu intérieur A description of the internal environment of organisms as distinct from the external environment. Variables such as water (osmolarity) Ions (Na+, K+, Cl-), glucose, pH, temperature, gases (O2, CO2), N wast...

Biology 2601 Organismal Physiology Physiological Regulation and Scaling The milieu intérieur A description of the internal environment of organisms as distinct from the external environment. Variables such as water (osmolarity) Ions (Na+, K+, Cl-), glucose, pH, temperature, gases (O2, CO2), N wastes Blood glucose in mammals Strand 1983 Physiology Conformity vs Regulation Mixed Conformity and Regulation Pros and Cons of Regulation and Conformity Regulation: • Pro – cells experience constant conditions • Con – energetically costly Conformity: • Pro – energetically cheap • Con – cells must have mechanisms to cope with variability Regulation has limits (zone of tolerance) Homeostasis “The coordinated physiological processes which maintain most of the constant states in the organism.” - Walter Cannon (1871 – 1945) Homeostasis “The condition of a relatively stable internal physiological environment, usually involving extensive feedback mechanisms” Hopkins & Hüner (2009) Body Temperature (°C) Temperature homeostasis Water Temperature: 7 °C 0 4000 8000 Time spent foraging (s) How does homeostasis work? Compares value to set point Effectors Controlled variable Sensor e.g. Temperature e.g. Hypothalamus Negative feedback loop Negative feedback • Works to return the value to the setpoint • On/off vs proportional control Too hot? Too cold? Increase heat loss (e.g. vasodilate, pant) Decrease heat loss (e.g. vasoconstrict, shiver) Body cools toward setpoint Body heats toward setpoint How is homeostasis achieved? Hormonal • e.g. Insulin & glucagon from pancreas regulate mammalian blood sugar Neuronal • e.g. Vasoconstriction and vasodilation regulate heat loss in vertebrates Biochemical • e.g. Maintaining rates of reactions by altering pathways and enzymes (phosphorylation, amounts or isoforms of enzymes if chronic). Molecular • e.g. Activating/repressing cell-signalling pathways that regulate gene expression and cytoplasm composition Is fever homeostatic? Positive feedback • Control system reinforces deviations of a controlled variable from set point. • e.g. Voltage gated Na+ channel Scaling – the study of how structural, mechanical, and physiological properties change with changing size. As linear size doubles body mass increases 8 fold (23 = 8). Bones should get bulkier. Galileo’s bones in Schmidt Nielsen 1984. Scaling, Why is Animal Size So Important? Scaling – the study of how structural mechanical and physiological properties change with changing size. 1) Direct proportionality – isometric scaling + C, but C=0 so Y = aX1 Equation: Y = aX1Omsee or LogY = 1LogX + Loga de Scaling – the study of how structural mechanical and physiological properties change with changing size. 1) Direct proportionality – isometric scaling Equation: Y = aX1 + C, but C=0 so Y = aX1 or LogY = 1LogX + Loga 2) Proportionality changes with size (non-linear) = allometric scaling Y = aXb or LogY = bLogX + Loga Dependent Variable Log10 transformation can linearize non-linear data, making it much easier to understand and analyze. Peters 1983. The Ecological Implications of Body Size. Independent Variable (W) Schmidt Nielsen 1984. Scaling, Why is Animal Size So Important? Using scaling to understand physiology Summarizing huge data sets, predicting unknowns Karasov and Martinez del Rio 2007. Physiological Ecology Using scaling to understand physiology Log Metabolic Rate (W) Residual analysis – are species above or below an allometric line special? Negative residual = relatively low metabolism Log Body Mass (kg) Using scaling to understand physiology Residual analysis – are species above or below an allometric line special? Using scaling to understand physiology Comparing scaling exponents (slopes) or proportionality coefficients (intercepts). Mammal basal metabolic rate (BMR) scales to M0.75, VO2max scales to M0.86, Why? resting exercing Placental mammal BMR = 3.53M0.72 Marsupial mammal BMR = 2.49M0.74 3.53/2.49 = 1.4X greater, Why? Using scaling to understand physiology Using scaling to understand physiology Matching organ size and rates of activity to demand Using scaling to understand physiology Matching heart function to metabolic rate Heart mass = 0.0059 M0.98 M0.75/ M1.0 = M-0.25 Heart rate = 241 M-0.25 Schmidt Nielsen 2001. Animal Physiology Scaling applies to plants too Growth rate scales with mass raised to a ¾ power Niklas and Enquist 2001. PNAS 2922-2927