Homeostasis and temperature regulation
Homeostasis and temperature regulation BIOL1082
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This 3 page Class Notes was uploaded by Paul Murdock on Sunday February 21, 2016. The Class Notes belongs to BIOL1082 at University of Cincinnati taught by Dr. Kinkle in Winter 2016. Since its upload, it has received 130 views. For similar materials see Biology II: Evolution, Physiology, and Ecology in Biology at University of Cincinnati.
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Date Created: 02/21/16
Homeostasis and temperature regulation Campbell Biology- Tenth Edition Chapters 40.2 & 40.3 February 22, 2016 Section 40.2 Regulator vs. Conformer Animals are regulators if they use internal mechanisms to control internal change in the face of external fluctuation, such as a hot shower or a cold swimming pool. In contrast, an animal is considered a conformer if it allows external conditions to change its internal conditions. Example: A bass conforms to the temperature of its surrounding waters, but regulates the solute concentration in its blood and interstitial fluid. Homeostasis The stable concentration of solutes in a freshwater bass is an example of homeostasis, which means “steady state” and refers to the maintenance of internal balance. In order to stay at homeostasis, an animal needs a set point, or a value in which an animal is aiming to maintain, such as 98.6 F which is considered a “normal” body temperature in humans. A fluctuation in the set point value serves as a stimulus which is detected by a sensor. When a signal is received, a control center generates an output which triggers a response, or a physiological activity that returns the variable to the set point. Feedback Control in Homeostasis Animals rely primarily on negative feedback, which is a control mechanism that reduces stimuli. Example: During rigorous exercise heat is produced and your body temperature is increased. This is regulated by your body producing sweat, cooling your body and reducing the stimulus. The opposite of negative feedback is positive feedback, which is a control mechanism that amplifies rather than reduces the stimulus. Example: In animals, positive feedback typically helps to drive processes to completion. During childbirth, the pressure of a baby’s head against sensors near the mother’s uterus stimulates the uterus to contract, causing greater pressure against the opening of the uterus and resulting in a baby being born. Section 40.3 Homeostatic thermoregulation Thermoregulation is a process where animals maintain their body temperature within a normal range. Body temperatures outside of the normal range can alter cellular membranes and potentially cause problems leading to death. - Sensors for thermoregulation are concentrated in the hypothalamus, the brain region responsible for circadian clock. A group of nerve cells functions as a thermostat, responding to body temperatures outside the normal range by activating mechanisms to promote heat loss or gain. Endothermy vs. Ectothermy Humans and birds are endothermic, meaning they can be warmed mostly by heat generated by metabolism. - Endotherms can also vary heat product, known as thermogenesis, to match the changing rates of heat loss. Thermogenesis is increased by muscle activity such as moving or shivering. In contrast, many fish and invertebrates are ectothermic, meaning they gain most of their heat from external sources. - Even though ectotherms do not generate heat sufficient for thermoregulation, many do so by behavioral means, such as seeking sunlight during cold days or going into the shade if it is hot. - In cold weather, honeybees also use a thermoregulatory mechanism that depends on social behavior, which involves them huddling together. Note: Endothermy and ectothermy are not exclusive, meaning an animal may portray both. Body Temperature Variation Animals whose body temperature varies with its environment is called a poikilotherm and a homeotherm has a constant body temperature. Not all ectotherms are poikilothermic and not all endotherms are homeothermic either. There is no fixed relationship between heat source and stability of body temperature; many ectothermic marine fish maintain more of a constant body temperature than some mammals and other endotherms do. Another misconception is that ectotherms are cold-blooded and endotherms are warm-blooded, which is also not always the case. In fact, these terms are often avoided in scientific communication because they are misleading. Heat Exchange An organism exchanges heat by radiation, evaporation, convection, and conduction. Heat is always transferred from an object of higher temperature to one of lower temperature. In mammals the most common mechanism for heat exchange involves the integumentary system, or the outer covering of the body such as hair or skin. Hair also provides insulation, which reduces the flow of heat between an animal and its environment. Circulatory adaptations have also shown to be a beneficial route for heat exchange between the interior and exterior of the body in some animals. - In response to changes in temperature, some animals alter the amount of blood, and thus heat, flowing between their body core and skin. - Vasodilation refers to widening the blood vessels and increasing blood flow in the skin. In endotherms this usually warms the skin and increases the transfer of body heat to the environment via radiation, conduction, and convection. - Vasoconstriction refers to the reverse process and reduces blood flow/heat transfer by decreasing the diameter of superficial blood vessels. - Reducing heat loss in many mammals relies on countercurrent exchange, or the transfer of heat between fluids flowing in opposite directions, primarily between arteries and veins that are located adjacent to each other.
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