Presentation on theme: "Homeostasis and Endocrine Signaling"— Presentation transcript:
1 Homeostasis and Endocrine Signaling 32Homeostasis and Endocrine Signaling
2 Multicellularity allows for cellular specialization with particular cells devoted to specific activitiesSpecialization requires organization and results in an internal environment that differs from the external environment
3 Organisms must maintain homeostasis Organisms must maintain homeostasis. Why are homeostasis and regulation essential life functions for living things?
4 HomeostasisOrganisms use homeostasis to maintain a “steady state” or internal balance regardless of external environmentIn humans, body temperature, blood pH, and glucose concentration are each maintained at a constant levelRegulation of room temperature by a thermostat is analogous to homeostasis
5 Sensor/ control center: Thermostat turns heater off. Response: Figure 32.4Sensor/control center:Thermostatturns heater off.Response:Heating stops.Roomtemperaturedecreases.Stimulus:Roomtemperatureincreases.Set point:Room temperatureat 20CFigure 32.4 A nonliving example of temperature regulation: control of room temperatureStimulus:Roomtemperaturedecreases.Roomtemperatureincreases.Response:Heating starts.Sensor/control center:Thermostatturns heater on.5
6 Which body systems are responsible for maintaining homeostasis in animals? How are their modes of action different?
7 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 bodyIn the nervous system, neurons transmit signals along dedicated routes, connecting specific locations in the body7
8 Endocrine cell Cell body of neuron Figure 32.9(a) Signaling by hormones(b) Signaling by neuronsStimulusStimulusEndocrinecellCellbody ofneuronNerveimpulseAxonHormoneSignaltravelseverywhere.Signaltravels toa specificlocation.BloodvesselNerveimpulseFigure 32.9 Signaling in the endocrine and nervous systemsAxonsResponseResponse8
9 Regulating and Conforming Faced with environmental fluctuations, animals manage their internal environment by either regulating or conformingAn animal that is a regulator uses internal mechanisms to control internal change despite external fluctuationAn animal that is a conformer allows its internal condition to change in accordance with external changes
11 (temperature conformer) Figure 32.340River otter (temperature regulator)30Body temperature (C)20Largemouth bass(temperature conformer)10Figure 32.3 Regulating and conforming10203040Ambient (environmental) temperature (C)11
12 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)
13 How does an organism know if there is a disruption of homeostasis?
14 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 responseThe response returns the variable to the set point
15 Homeostasis in animals relies largely on negative feedback, a control mechanism that reduces the stimulusHomeostasis moderates, but does not eliminate, changes in the internal environmentSet points and normal ranges for homeostasis are usually stable, but certain regulated changes in the internal environment are essential
16 We need to know a few examples of how homeostasis is moderated for the AP exam. Let’s take a closer look…
17 Thermoregulation: A Closer Look Thermoregulation is the process by which animals maintain an internal temperature within a tolerable range
18 Describe the difference between endothermic and ectothermic organisms.
19 Endothermy and Ectothermy 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”
20 Endotherms can maintain a stable body temperature in the face of large fluctuations in environmental temperatureEctotherms may regulate temperature by behavioral meansEctotherms generally need to consume less food than endotherms, because their heat source is largely environmental
22 (a) A walrus, an endotherm Figure 32.5aFigure 32.5a Endothermy and ectothermy (part 1: endotherm)(a) A walrus, an endotherm22
23 (b) A lizard, an ectotherm Figure 32.5bFigure 32.5b Endothermy and ectothermy (part 2: ectotherm)(b) A lizard, an ectotherm23
24 Balancing Heat Loss and Gain Organisms exchange heat by four physical processesRadiationEvaporationConvectionConductionHeat is always transferred from an object of higher temperature to one of lower temperature
25 Generate definitions of each type of heat exchange from the figure.
26 Radiation Evaporation Convection Conduction Figure 32.6 Figure 32.6 Heat exchange between an organism and its environmentConvectionConduction26
27 How might the circulatory system collaborate in this thermoregulation process?
28 Circulatory Adaptations for Thermoregulation In response to changes in environmental temperature, animals can alter blood (and heat) flow between their body core and their skinVasodilation, the widening of the diameter of superficial blood vessels, promotes heat lossHow?Vasoconstriction, the narrowing of the diameter of superficial blood vessels, reduces heat loss28
29 In aquatic environments, we see adaptations for how thermoregulation takes place.
30 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 loss30
33 Acclimatization in Thermoregulation Birds and mammals can vary their insulation to acclimatize to seasonal temperature changesAcclimatization in ectotherms often includes adjustments at the cellular levelSome ectotherms that experience subzero temperatures can produce “antifreeze” compounds to prevent ice formation in their cells
34 In mammals (FYI: we are mammals, in case you didn’t know)… where is the physiological thermostat for thermoregulation?
35 Physiological Thermostats and Fever Thermoregulation in mammals is controlled by a region of the brain called the hypothalamusThe hypothalamus triggers heat loss or heat-generating mechanismsFever is the result of a change to the set point for a biological thermostatAnimation: Negative FeedbackAnimation: Positive Feedback
36 Sensor/control center: Thermostat in hypothalamus Response: Sweat Figure 32.8aSensor/control center: Thermostatin hypothalamusResponse: SweatResponse:Blood vesselsin skin dilate.Stimulus:Increased bodytemperatureBodytemperaturedecreases.Figure 32.8a The thermostatic function of the hypothalamus in human thermoregulation (part 1: increase)Homeostasis:Internal bodytemperature ofapproximately36–38C36
37 Sensor/control center: Thermostat in hypothalamus Response: Shivering Figure 32.8bHomeostasis:Internal bodytemperature ofapproximately36–38CBodytemperatureincreases.Stimulus:Decreased bodytemperatureResponse:Blood vesselsin skin constrict.Figure 32.8b The thermostatic function of the hypothalamus in human thermoregulation (part 2: decrease)Sensor/control center: Thermostatin hypothalamusResponse: Shivering37
38 Hormones, released in the endocrine system, are released to moderate a series of feedback mechanisms in varying organ systems.
39 Hormones may have effects in a single location or throughout the body Only cells with receptors for a certain hormone can respond to itThe endocrine system is well adapted for coordinating gradual changes that affect the entire body39
40 We need to know a few examples of endocrine pathways within the mammalian system. Let’s take a closer look…
41 Simple Endocrine Pathways Digestive juices in the stomach are extremely acidic and must be neutralized before the remaining steps of digestion take placeCoordination of pH control in the duodenum relies on an endocrine pathway41
42 Pathway Example Stimulus Low pH in duodenum S cells of duodenum Figure 32.10PathwayExampleStimulusLow pH induodenumS cells of duodenumsecrete the hormonesecretin ( ).EndocrinecellNegative feedbackHormoneBloodvesselFigure A simple endocrine pathwayTargetcellsPancreasResponseBicarbonate release42
43 The release of acidic stomach contents into the duodenum stimulates endocrine cells there to secrete the hormone secretinThis causes target cells in the pancreas to raise the pH in the duodenumThe pancreas can act as an exocrine gland, secreting substances through a duct,Which substances???or as an endocrine gland, secreting hormones directly into interstitial fluidWhich hormones???43
44 Neuroendocrine Pathways Hormone pathways that respond to stimuli from the external environment rely on a sensor in the nervous systemIn vertebrates, the hypothalamus integrates endocrine and nervous systemsSignals from the hypothalamus travel to a gland located at its base, called the pituitary gland44
45 Major Endocrine Glands and Their Hormones Hypothalamus Figure 32.11aMajor Endocrine Glandsand Their HormonesHypothalamusPituitary glandAnterior pituitaryPineal glandMelatoninPosterior pituitaryOxytocinVasopressin(antidiuretichormone, ADH)Thyroid glandThyroid hormone(T3 and T4)CalcitoninAdrenal glands(atop kidneys)Parathyroid glandsParathyroid hormone (PTH)Adrenal medullaEpinephrine andnorepinephrineOvaries (in females)EstrogensProgestinsFigure 32.11a Exploring the human endocrine system (part 1: glands and hormones)Adrenal cortexGlucocorticoidsMineralocorticoidsTestes(in males)AndrogensPancreasInsulinGlucagon45
46 Hypothalamus Anterior pituitary Neurosecretory cells of the Figure 32.11bHypothalamusNeurosecretorycells of thehypothalamusPortal vesselsHypothalamichormonesHORMONEPosteriorpituitaryAnterior pituitaryEndocrine cellsTARGETPituitary hormonesFigure 32.11b Exploring the human endocrine system (part 2: hypothalamus and pituitary)FSHTSHACTHProlactinMSHGHMammaryglandsTestes orovariesThyroidglandAdrenalcortexMelanocytesLiver, bones,other tissues46
48 Stimulus TSH circulation throughout body Sensory neuron Thyroid gland Figure 32.11cStimulusTSH circulationthroughout bodySensoryneuron−HypothalamusThyroidglandNeurosecretory cellTRHNegative feedbackThyroidhormoneThyroid hormonecirculationthroughoutbodyFigure 32.11c Exploring the human endocrine system (part 3: hormone cascade)−AnteriorpituitaryTSHResponse48
49 Low level of iodine uptake High level of iodine uptake Thyroid scan Figure 32.11dLow level ofiodine uptakeHigh level ofiodine uptakeFigure 32.11d Exploring the human endocrine system (part 4: thyroid scan)Thyroid scan49
50 It also secretes antidiuretic hormone (ADH) Hormonal signals from the hypothalamus trigger synthesis and release of hormones from the anterior pituitaryThe posterior pituitary is an extension of the hypothalamus and secretes oxytocin, which regulates release of milk during nursing in mammalsIt also secretes antidiuretic hormone (ADH)50
53 Feedback Regulation in Endocrine Pathways A feedback loop links the response back to the original stimulus in an endocrine pathwayWhile negative feedback dampens a stimulus, positive feedback reinforces a stimulus to increase the response53
54 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.
55 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 responseThe intracellular response is called signal transductionA signal transduction pathway typically has multiple steps55
56 Lipid-soluble hormones have receptors inside cells When bound by the hormone, the hormone-receptor complex moves into the nucleusThere, the receptor alters transcription of particular genes56
57 Multiple Effects of Hormones Many hormones elicit more than one type of responseFor 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 systemTarget cells vary in their response to a hormone because they differ in their receptor types or in the molecules that produce the response57
58 Same receptors but different intracellular proteins (not shown) Figure 32.13Same receptors but differentintracellular proteins (not shown)Different receptorsDifferent cellular responsesDifferent cellular responsesEpinephrineEpinephrineEpinephrine receptor receptor receptorGlycogendepositsFigure One hormone, different effectsVesseldilates.Vesselconstricts.Glycogenbreaks downand glucoseis releasedfrom cell.(a) Liver cell(b) Skeletal muscleblood vessel(c) Intestinal bloodvessel58
59 Evolution of Hormone Function Over the course of evolution the function of a given hormone may diverge between speciesFor 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 metamorphosisProlactin also has a broad range of activities in vertebrates59
60 Tadpole Adult frog Figure 32.14 Figure Specialized role of a hormone in frog metamorphosisAdult frog60
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