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CAMPBELL BIOLOGY IN FOCUS © 2014 Pearson Education, Inc. Urry Cain Wasserman Minorsky Jackson Reece Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge 32 Homeostasis and Endocrine Signaling
© 2014 Pearson Education, Inc. Multicellularity allows for cellular specialization with particular cells devoted to specific activities Specialization requires organization and results in an internal environment that differs from the external environment
© 2014 Pearson Education, Inc. Organisms must maintain homeostasis. Why are homeostasis and regulation essential life functions for living things?
© 2014 Pearson Education, Inc. Homeostasis Organisms use homeostasis to maintain a “steady state” or internal balance regardless of external environment In humans, body temperature, blood pH, and glucose concentration are each maintained at a constant level Regulation of room temperature by a thermostat is analogous to homeostasis
© 2014 Pearson Education, Inc. Figure 32.4 Sensor/ control center: Thermostat turns heater off. Sensor/ control center: Thermostat turns heater on. Stimulus: Room temperature increases. Stimulus: Room temperature decreases. Room temperature increases. Room temperature decreases. Set point: Room temperature at 20 C Response: Heating stops. Response: Heating starts.
© 2014 Pearson Education, Inc. Which body systems are responsible for maintaining homeostasis in animals? How are their modes of action different?
© 2014 Pearson Education, Inc. Coordination and Control Functions of the Endocrine and Nervous Systems In the endocrine system, signaling molecules released into the bloodstream by endocrine cells reach all locations in the body In the nervous system, neurons transmit signals along dedicated routes, connecting specific locations in the body
© 2014 Pearson Education, Inc. Figure 32.9 Cell body of neuron Response Hormone Nerve impulse Signal travels everywhere. Signal travels to a specific location. Response Stimulus Nerve impulse Blood vessel Endocrine cell (a) Signaling by hormones Axons Axon (b) Signaling by neurons
© 2014 Pearson Education, Inc. Regulating and Conforming Faced with environmental fluctuations, animals manage their internal environment by either regulating or conforming An animal that is a regulator uses internal mechanisms to control internal change despite external fluctuation An animal that is a conformer allows its internal condition to change in accordance with external changes
© 2014 Pearson Education, Inc. Interpret the following figure.
© 2014 Pearson Education, Inc. Figure 32.3 River otter (temperature regulator) 40 Largemouth bass (temperature conformer) Ambient (environmental) temperature ( C) Body temperature ( C)
© 2014 Pearson Education, Inc. An animal may regulate some internal conditions and not others For example, a fish may conform to surrounding temperature in the water, but it regulates solute concentrations in its blood and interstitial fluid (the fluid surrounding body cells)
© 2014 Pearson Education, Inc. How does an organism know if there is a disruption of homeostasis?
© 2014 Pearson Education, Inc. Animals achieve homeostasis by maintaining a variable at or near a particular value, or set point Fluctuations above or below the set point serve as a stimulus; these are detected by a sensor and trigger a response The response returns the variable to the set point
© 2014 Pearson Education, Inc. Homeostasis in animals relies largely on negative feedback, a control mechanism that reduces the stimulus Homeostasis moderates, but does not eliminate, changes in the internal environment Set points and normal ranges for homeostasis are usually stable, but certain regulated changes in the internal environment are essential
© 2014 Pearson Education, Inc. We need to know a few examples of how homeostasis is moderated for the AP exam. Let’s take a closer look…
© 2014 Pearson Education, Inc. Thermoregulation: A Closer Look Thermoregulation is the process by which animals maintain an internal temperature within a tolerable range
© 2014 Pearson Education, Inc. Describe the difference between endothermic and ectothermic organisms.
© 2014 Pearson Education, Inc. Endothermic animals generate heat by metabolism; birds and mammals are endotherms = “warm- blooded” Ectothermic animals gain heat from external sources; ectotherms include most invertebrates, fishes, amphibians, and nonavian reptiles = “cold- blooded” Endothermy and Ectothermy
© 2014 Pearson Education, Inc. Endotherms can maintain a stable body temperature in the face of large fluctuations in environmental temperature Ectotherms may regulate temperature by behavioral means Ectotherms generally need to consume less food than endotherms, because their heat source is largely environmental
© 2014 Pearson Education, Inc. How would you classify the following?
© 2014 Pearson Education, Inc. Figure 32.5a (a) A walrus, an endotherm
© 2014 Pearson Education, Inc. Figure 32.5b (b) A lizard, an ectotherm
© 2014 Pearson Education, Inc. Balancing Heat Loss and Gain Organisms exchange heat by four physical processes Radiation Evaporation Convection Conduction Heat is always transferred from an object of higher temperature to one of lower temperature
© 2014 Pearson Education, Inc. Generate definitions of each type of heat exchange from the figure.
© 2014 Pearson Education, Inc. Figure 32.6 Radiation Convection Evaporation Conduction
© 2014 Pearson Education, Inc. How might the circulatory system collaborate in this thermoregulation process?
© 2014 Pearson Education, Inc. In response to changes in environmental temperature, animals can alter blood (and heat) flow between their body core and their skin Vasodilation, the widening of the diameter of superficial blood vessels, promotes heat loss How? Vasoconstriction, the narrowing of the diameter of superficial blood vessels, reduces heat loss How? Circulatory Adaptations for Thermoregulation
© 2014 Pearson Education, Inc. In aquatic environments, we see adaptations for how thermoregulation takes place.
© 2014 Pearson Education, Inc. The arrangement of blood vessels in many marine mammals and birds allows for countercurrent exchange Countercurrent heat exchangers transfer heat between fluids flowing in opposite directions and reduce heat loss
© 2014 Pearson Education, Inc. Figure 32.7 Canada goose Blood flow Artery Vein Heat transfer Cool blood Warm blood Key 30 35 C 99 20 10 18 27 33 231
© 2014 Pearson Education, Inc. Other mechanisms for thermoregulation?
© 2014 Pearson Education, Inc. Birds and mammals can vary their insulation to acclimatize to seasonal temperature changes Acclimatization in ectotherms often includes adjustments at the cellular level Some ectotherms that experience subzero temperatures can produce “antifreeze” compounds to prevent ice formation in their cells Acclimatization in Thermoregulation
© 2014 Pearson Education, Inc. In mammals (FYI: we are mammals, in case you didn’t know)… where is the physiological thermostat for thermoregulation?
© 2014 Pearson Education, Inc. Physiological Thermostats and Fever Thermoregulation in mammals is controlled by a region of the brain called the hypothalamus The hypothalamus triggers heat loss or heat- generating mechanisms Fever is the result of a change to the set point for a biological thermostat Animation: Negative Feedback Animation: Positive Feedback
© 2014 Pearson Education, Inc. Figure 32.8a Sensor/control center: Thermostat in hypothalamus Body temperature decreases. Homeostasis: Internal body temperature of approximately 36–38 C Response: Blood vessels in skin dilate. Stimulus: Increased body temperature Response: Sweat
© 2014 Pearson Education, Inc. Figure 32.8b Stimulus: Decreased body temperature Body temperature increases. Homeostasis: Internal body temperature of approximately 36–38 C Response: Shivering Sensor/control center: Thermostat in hypothalamus Response: Blood vessels in skin constrict.
© 2014 Pearson Education, Inc. Hormones, released in the endocrine system, are released to moderate a series of feedback mechanisms in varying organ systems.
© 2014 Pearson Education, Inc. Hormones may have effects in a single location or throughout the body Only cells with receptors for a certain hormone can respond to it The endocrine system is well adapted for coordinating gradual changes that affect the entire body
© 2014 Pearson Education, Inc. We need to know a few examples of endocrine pathways within the mammalian system. Let’s take a closer look…
© 2014 Pearson Education, Inc. Simple Endocrine Pathways Digestive juices in the stomach are extremely acidic and must be neutralized before the remaining steps of digestion take place Coordination of pH control in the duodenum relies on an endocrine pathway
© 2014 Pearson Education, Inc. Figure Response Hormone Low pH in duodenum S cells of duodenum secrete the hormone secretin ( ). Pancreas Stimulus Blood vessel Endocrine cell Pathway Example Bicarbonate release Target cells Negative feedback
© 2014 Pearson Education, Inc. The release of acidic stomach contents into the duodenum stimulates endocrine cells there to secrete the hormone secretin This causes target cells in the pancreas to raise the pH in the duodenum The pancreas can act as an exocrine gland, secreting substances through a duct, Which substances??? or as an endocrine gland, secreting hormones directly into interstitial fluid Which hormones???
© 2014 Pearson Education, Inc. Neuroendocrine Pathways Hormone pathways that respond to stimuli from the external environment rely on a sensor in the nervous system In vertebrates, the hypothalamus integrates endocrine and nervous systems Signals from the hypothalamus travel to a gland located at its base, called the pituitary gland
© 2014 Pearson Education, Inc. Figure 32.11a Pancreas Insulin Glucagon Testes (in males) Androgens Parathyroid glands Parathyroid hormone (PTH) Ovaries (in females) Estrogens Progestins Thyroid gland Thyroid hormone (T 3 and T 4 ) Calcitonin Pineal gland Melatonin Major Endocrine Glands and Their Hormones Hypothalamus Pituitary gland Anterior pituitary Posterior pituitary Oxytocin Vasopressin (antidiuretic hormone, ADH) Adrenal glands (atop kidneys) Adrenal medulla Epinephrine and norepinephrine Adrenal cortex Glucocorticoids Mineralocorticoids
© 2014 Pearson Education, Inc. Figure 32.11b Posterior pituitary Neurosecretory cells of the hypothalamus Hypothalamic hormones Hypothalamus Testes or ovaries Portal vessels Pituitary hormones Anterior pituitary Endocrine cells Thyroid gland Adrenal cortex Mammary glands MelanocytesLiver, bones, other tissues HORMONE TARGET Prolactin FSHTSH ACTH MSH GH
© 2014 Pearson Education, Inc. Let’s consider another example…
© 2014 Pearson Education, Inc. Figure 32.11c TSH circulation throughout body Anterior pituitary Thyroid gland Stimulus Response Thyroid hormone Thyroid hormone circulation throughout body TSH − TRH Neurosecretory cell Negative feedback Hypothalamus − Sensory neuron
© 2014 Pearson Education, Inc. Figure 32.11d Thyroid scan Low level of iodine uptake High level of iodine uptake
© 2014 Pearson Education, Inc. Hormonal signals from the hypothalamus trigger synthesis and release of hormones from the anterior pituitary The posterior pituitary is an extension of the hypothalamus and secretes oxytocin, which regulates release of milk during nursing in mammals It also secretes antidiuretic hormone (ADH)
© 2014 Pearson Education, Inc. Another example…Oxytocin
© 2014 Pearson Education, Inc. Figure Pathway Sensory neuron Positive feedback Hypothalamus/ posterior pituitary Example SucklingStimulus Neuro- secretory cell Smooth muscle in breasts Neuro- hormone Blood vessel Target cells Response Milk release Posterior pituitary secretes the neurohormone oxytocin ( ).
© 2014 Pearson Education, Inc. Feedback Regulation in Endocrine Pathways A feedback loop links the response back to the original stimulus in an endocrine pathway While negative feedback dampens a stimulus, positive feedback reinforces a stimulus to increase the response
© 2014 Pearson Education, Inc. There are different types of hormones : water soluble or lipid soluble Their receptors are located in different places at their target cells. They also have very different modes of action.
© 2014 Pearson Education, Inc. Pathways of Water-Soluble and Lipid-Soluble Hormones The hormones discussed thus far are proteins that bind to cell-surface receptors and that trigger events leading to a cellular response The intracellular response is called signal transduction A signal transduction pathway typically has multiple steps
© 2014 Pearson Education, Inc. Lipid-soluble hormones have receptors inside cells When bound by the hormone, the hormone- receptor complex moves into the nucleus There, the receptor alters transcription of particular genes
© 2014 Pearson Education, Inc. Multiple Effects of Hormones Many hormones elicit more than one type of response For example, epinephrine is secreted by the adrenal glands and can raise blood glucose levels, increase blood flow to muscles, and decrease blood flow to the digestive system Target cells vary in their response to a hormone because they differ in their receptor types or in the molecules that produce the response
© 2014 Pearson Education, Inc. Figure Different cellular responses Same receptors but different intracellular proteins (not shown) Glycogen breaks down and glucose is released from cell. Different cellular responses Different receptors Glycogen deposits Vessel dilates. Vessel constricts. (c) Intestinal blood vessel (b) Skeletal muscle blood vessel (a) Liver cell Epinephrine receptor Epinephrine receptor Epinephrine receptor
© 2014 Pearson Education, Inc. Evolution of Hormone Function Over the course of evolution the function of a given hormone may diverge between species For example, thyroid hormone plays a role in metabolism across many lineages, but in frogs it has taken on a unique function: stimulating the resorption of the tadpole tail during metamorphosis Prolactin also has a broad range of activities in vertebrates
© 2014 Pearson Education, Inc. Figure Tadpole Adult frog
CAMPBELL BIOLOGY IN FOCUS © 2014 Pearson Education, Inc. Urry Cain Wasserman Minorsky Jackson Reece Lecture Presentations by Kathleen Fitzpatrick and Nicole.
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© 2014 Pearson Education, Inc. Figure © 2014 Pearson Education, Inc. Figure 32.2 Axons of neurons Skeletal muscle tissue Blood vessel Loose connective.
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