Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Variables such as blood pH, carbon dioxide concentration, blood glucose levels, body temperature and water balance are typically maintained within certain limits by homeostatic mechanisms Mechanisms of Homeostasis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nervous system and endocrine system work together to maintain homeostasis Many homeostatic mechanisms are controlled by the autonomic nervous system

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A homeostatic control system has three functional components – A receptor, a control center, and an effector

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Most homeostatic control systems function by negative feedback –

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A second type of homeostatic control system is positive feedback – Which involves a change in some variable that triggers mechanisms that amplify the change

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The internal environment of vertebrates is called the interstitial fluid, and is very different from the external environment Homeostasis is a balance between external changes and the animal’s internal control mechanisms that oppose the changes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Regulating and conforming – Are two extremes in how animals cope with environmental fluctuations Regulating and Conforming

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An animal is said to be a regulator – If it uses internal control mechanisms to moderate internal change in the face of external, environmental fluctuation An animal is said to be a conformer –

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Thermoregulation contributes to homeostasis and involves anatomy, physiology, and behavior Thermoregulation –

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ectotherms – Include most invertebrates, fishes, amphibians, and non-bird reptiles Endotherms – Include birds and mammals Ectotherms and Endotherms

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Birds and mammals are mainly endothermic, meaning that – Their bodies are warmed mostly by heat generated by metabolism – They typically have higher metabolic rates – – Also called homeotherms which means that they keep their body temp relatively constant Endotherms

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ectotherms Amphibians and reptiles other than birds are ectothermic, meaning that – They gain their heat mostly from external sources – They have lower metabolic rates – Body temp fluctuates with environmental temperatures – – Also called poikilotherms

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In general, ectotherms – Tolerate greater variation in internal temperature than endotherms

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Endothermy is more energetically expensive than ectothermy – But buffers animals’ internal temperatures against external fluctuations –

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Modes of Heat Exchange Organisms exchange heat by four physical processes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Balancing Heat Loss and Gain Thermoregulation involves physiological and behavioral adjustments that balance heat gain and loss

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Endotherms and some ectotherms maintain a constant internal temperature as the external temperature fluctuates by changing the rate of heat production, or by changing the rate of heat gain or loss

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animals adjust rate of heat gain or loss through several adaptations – Hairs trap layer of air next to skin and insulate animal, also thick coats in winter and thinner coats in summer – – Countercurrent heat exchanger in some sharks

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Insulation Insulation, which is a major thermoregulatory adaptation in mammals and birds – Reduces the flow of heat between an animal and its environment –

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In mammals, the integumentary system – Acts as insulating material

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Many endotherms and some ectotherms – Can alter the amount of blood flowing between the body core and the skin Circulatory Adaptations

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In vasodilation – Blood flow in the skin increases, facilitating heat loss In vasoconstriction –

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Many marine mammals and birds – Have arrangements of blood vessels called countercurrent heat exchangers that are important for reducing heat loss

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some specialized bony fishes and sharks – Also possess countercurrent heat exchangers

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Many endothermic insects – Have countercurrent heat exchangers that help maintain a high temperature in the thorax

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cooling by Evaporative Heat Loss Many types of animals – Lose heat through the evaporation of water in sweat –

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bathing moistens the skin – Which helps to cool an animal down

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Both endotherms and ectotherms use a variety of behavioral responses to control body temperature Animals may increase or decrease body heat by relocating-migration to a more suitable climate, basking in sun, huddling together Reptiles move between warmer or cooler locations to keep body temperature fairly stable Behavioral Responses

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Torpor and Energy Conservation Torpor – Is an adaptation that enables animals to save energy while avoiding difficult and dangerous conditions – Is a physiological state in which activity is low and metabolism decreases (heart and respiratory rate slow down – Animals active in day undergo torpor at night –

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hibernation is long-term torpor – That is an adaptation to winter cold and food scarcity during which the animal’s body temperature declines

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Estivation, or summer torpor – Enables animals to survive long periods of high temperatures and scarce water supplies Daily torpor – Is exhibited by many small mammals and birds and seems to be adapted to their feeding patterns

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings They must lower metabolic rate and hibernate, which allows them to burn very little energy all winter Endotherms can remain active in severe weather, but must use a lot more energy on heat production

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Insulin and Glucagon: Control of Blood Glucose Two types of cells in the pancreas secrete insulin and glucagon, antagonistic hormones that help maintain glucose homeostasis and are found in clusters in the islets of Langerhans (pancreatic islets)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glucagon – Is produced by alpha cells of the islets of Langerhans Insulin –

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Maintenance of glucose homeostasis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Target Tissues for Insulin and Glucagon Insulin reduces blood glucose levels by – Promoting the cellular uptake of glucose – Liver and muscle cells take up glucose from blood and convert to glycogen for storage –

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glucagon increases blood glucose levels by – Stimulating the conversion of glycogen to glucose in the liver – Stimulating the breakdown of fat and protein into glucose Blood glucose levels are maintained around 90 mg/100 ml

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Diabetes Mellitus Diabetes mellitus, perhaps the best-known endocrine disorder – – Is caused by a deficiency of insulin or a decreased response to insulin in target tissues – Is marked by elevated blood glucose levels

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Type I diabetes mellitus (insulin-dependent diabetes) is an autoimmune disorder in which the immune system destroys the beta cells of the pancreas (develops before age 15, called juvenile onset diabetes) Type II diabetes mellitus (non-insulin-dependent diabetes) i s characterized either by a deficiency of insulin or, more commonly, by reduced responsiveness of target cells due to some change in insulin receptors (pancreas produces enough insulin, but cells fail to respond normally) – – 90 % of U.S. cases

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hypoglycemia or low blood glucose levels result from hyperactive beta cells producing too much insulin