Homeostasis Bioenergetics Thermoregulation Metabolic Rates Biology 1107 Lecture 16 Lecture 16 Overview 2 49 Regulators vs conformers 3 4 Homeostasis basics 5 12 Importance of internal maintenance 6 Role of epithelial tissue in homeostasis 7 How homeostasis works 8 12 Role of feedback mechanisms 10 11 Regulated changes in homeostasis 12 Thermoregulation 13 35 Endotherms vs ectotherms and tradeoffs 14 17 18 Homeotherms vs poikilotherms 15 Mechanisms of heat exchange 19 23 Thermoregulatory adaptations 24 32 Insulation 25 Circulatory adaptation and countercurrent exchangers 27 29 Evaporative heat loss 30 Behavioral responses 31 Acclimation 32 Homeostatic temperature regulation in endotherms 33 35 Bioenergetics 36 45 Metabolic rates and measurements 38 45 Minimum metabolic rate 40 Effect of size on metabolic rates 41 44 Maximum metabolic rate and activity 45 Maintaining Internal Environments When faced with environmental fluctuations animals manage their internal environment by either regulating or conforming 3 49 A regulator can use internal mechanisms to control internal changes in the face of external fluctuation A river otter mammal maintains a body temperature of about 38 C regardless of water temperature A conformer allows internal conditions to change in accordance with external changes for a particular environmental variable The body temperature of a largemouth bass closely matches that of the surrounding water 4 49 Maintaining Internal Environments Animals that conform all of their physiological mechanisms or regulate all of their physiological mechanisms are extremes along a continuum Most organisms use different strategies for different physiological systems and thus most are never complete conformers or regulators e g bass conform to the temperature of surrounding water but actively regulate blood solute concentrations so that they are different than the solute concentrations in the surrounding environment Complete Conformers Complete Regulators 5 49 Homeostasis Homeostasis steady state is the maintenance of a relatively constant internal environment Although external conditions may vary as an animal s environment changes internal chemical and physical states are kept within a tolerable range e g temperature regulation in sea otters and blood solute concentration regulation in bass Human homeostasis Maintenance of a fairly constant body temperature of 37 C 98 6 F Maintenance of a blood and interstitial fluid pH within 0 1 pH unit of 7 4 Maintenance of a blood glucose level in the bloodstream within the range of 70 110 mg glucose 100 ml blood Why Is Homeostasis Important 6 49 Temperature pH and other physical and chemical conditions have a dramatic effect on the structure and function of enzymes Most enzymes function best under a fairly narrow range of conditions i e optimal conditions Molecules cells tissues organs and organ systems function at an optimal level when homeostasis occurs The Role of Epithelial Tissue in Homeostasis 7 49 Epithelium plays a vital role in homeostasis Creates an internal environment that is dramatically different from the external environment Maintains physical and chemical conditions inside an animal that are relatively constant One of the most basic functions of epithelial tissue is to control the exchange of materials across its surfaces in a way that is consistent with homeostasis Tight junctions are used to maintain barriers such that controlled exchanges can occur Mechanisms of Homeostasis 8 49 The key to homeostasis is constant maintenance homeostasis requires monitoring regulating and feedback control The process is like temperature regulation in a room using a thermostat For any particular variable e g temperature pH There is a particular set point normal or target value e g pH 7 4 in human body fluids Some variables may have a normal range with an upper and lower limit rather Fluctuation around the set point serve as a stimulus which is detected than a set point by a receptor or sensor A signal from a sensor triggers a response by a control center a response is a physiological activity that helps return the variable to the set point Mechanisms of Homeostasis 9 49 Thermostat example a drop in temperature below the set point acts as a stimulus the thermostat serves as the sensor and the control center and the heater produces the response The Role of Feedback In Homeostasis 10 49 Homeostatic systems are based on negative feedback a control mechanism that reduces the stimulus In the thermostat example the heater produces a response to the stimulus of decreasing temperature by pumping out more heat this in effect reduces the original stimulus of less heat by increasing the temperature In humans vigorous exercise produces heat which increases body temperature The nervous system detects this increase and triggers sweating which helps cool the body reduces the stimulus and returns body temperature to the set point Negative vs Positive Feedback in Homeostasis 11 49 Unlike negative feedback positive feedback is a control mechanism that amplifies rather than reduces a stimulus Positive feedback loops in animals do not play a major role in homeostasis but instead help drive physiological processes to completion e g pressure during childbirth stimulates contractions of the uterus which increases pressure which increases contractions until the process is complete 12 49 Regulated Changes In Homeostasis The set points and normal ranges for homeostasis can change under various circumstances such regulated changes are essential to normal body functions Cyclical changes Variation in hormonal levels responsible for a woman s menstrual cycle Metabolic changes associated with circadian rhythms that occur in a 24 hour cycle Acclimatization acclimation Gradual adjustment to changes in external environment set points may be overshot or undershot until control centers can adjust the response to the environment Gradual increase in red blood cell production at high altitudes will ensure enough oxygen is being consumed for cellular respiration 13 49 How Do Animals Regulate Body Temperature Heat exchange is critical in animal physiology because individuals that get too hot or too cold may die Overheating can cause proteins to denature and cease functioning and can lead to dehydration Low body temperatures can slow down enzyme function and energy production For every 10 C 18 F decrease in temperature the rates of most enzyme mediated reactions decrease two to three