Animal Homeostasis: Maintaining Internal Balance

1. 31 Homeostasis and the Organization of the Animal Body 0

2. Chapter 31 At a Glance • 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • 31.2 How Is the Animal Body Organized?

3. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • 1. Most of the cells of your body maintain an almost constant temperature • 2. Cells are bathed in a liquid called interstitial fluid（细胞间液）, which has an almost constant composition despite enormous differences in the water and salt content of the outside environment • French physiologist Claude Bernard现代实验生理学的创始人 recognized the “internal constancy”（内环境稳定）of animal bodies in the nineteenth century

4. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Walter Cannon coined the term homeostasis to describe the ability of an organism to maintain its internal environment within narrow limits that allow optimal cell functioning • Although “homeostasis” (meaning “to stay the same”) implies a static, unchanging state, the internal environment actually seethes with activity as the body continuously adjusts to varying internal and external conditions

5. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • The internal environment is maintained in a state of dynamic constancy • Homeostatic mechanisms regulate various conditions • Temperature • Water and salt concentrations in body fluids • Glucose concentrations • pH (acid-base balance) • Hormone secretion • Oxygen and carbon dioxide concentrations

6. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • The internal environment is maintained in a state of dynamic constancy (continued) • Why are cells so particular about their surroundings? • Animal cells are constantly generating and using large quantities of ATP to sustain life processes • Continuous supplies of high-energy molecules (primarily glucose) and O2 are required to carry out the reactions that generate ATP • Energy production helps explain the importance of glucose and oxygen levels

7. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • The internal environment is maintained in a state of dynamic constancy (continued) • Almost every biochemical reaction in a cell is catalyzed by a specific protein whose ability to function depends on its three-dimensional structure maintained by hydrogen bonds • These bonds can be disrupted by an environment that is too hot, too salty, too acidic, or too basic • The need to maintain hydrogen bonds and the protein function that depends on them helps explain the requirement for a narrow range of temperature, salt, and pH

8. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Animals vary in their homeostatic abilities • Birds and mammals are highly efficient at maintaining homeostasis for virtually all of their internal conditions • Some animals have reduced homeostasis for one or more aspects of their internal environment • For example, many marine invertebrates, including snails, crabs, and worms, cannot regulate the overall concentration of their body fluids

9. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Animals vary in their homeostatic abilities (continued) • Animals vary in how—and how well—they generate heat and regulate body temperature • Scientists classify animals according to their major source of body warmth • Ectotherms derive body heat from the environment • Reptiles, amphibians, most fish and invertebrates are ectotherms

10. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Animals vary in their homeostatic abilities (continued) • Animals vary in how—and how well—they generate heat and regulate body temperature (continued) • Scientists classify animals according to their major source of body warmth (continued) • Endotherms generate most of their heat through metabolic reactions • Birds and mammals are principal endotherms on Earth

11. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Animals vary in their homeostatic abilities (continued) • Animals vary in how—and how well—they generate heat and regulate body temperature (continued) • The body temperatures of most ectotherms vary quite a bit as the external temperature changes over the course of hours, days, or weeks • Through behavior or by occupying a very constant environment, some ectotherms can maintain quite stable body temperatures

12. Figure 31-1 Warm-blooded or cold-blooded? Ruby-throatedhummingbird Desert pupfish Iguana

13. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Animals vary in their homeostatic abilities (continued) • Animals vary in how—and how well—they generate heat and regulate body temperature (continued) • Insects and lizards, for example, often warm up by basking in the sun • The pupfish can tolerate water temperatures ranging from 36 F to 113 F, but can breed only within a narrow range of temperatures

14. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Animals vary in their homeostatic abilities (continued) • Animals vary in how—and how well—they generate heat and regulate body temperature (continued) • Most endotherms maintain a fairly constant body temperature between about 95 F and 106 F(35°C-41°C) • There are both benefits and costs to keeping this warm • A warm body usually can sense its environment better, respond more quickly, and move faster than a cold body

15. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Animals vary in their homeostatic abilities (continued) • Animals vary in how—and how well—they generate heat and regulate body temperature (continued) • There are both benefits and costs to keeping this warm (continued) • The major cost is the energy required to maintain a high body temperature • Many ectotherms cool down and become inactive at night, conserving energy

16. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Animals vary in their homeostatic abilities (continued) • Animals vary in how—and how well—they generate heat and regulate body temperature (continued) • The internal environment is maintained by mechanisms collectively know as feedback systems

17. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions • There are two types of feedback systems 1. Negative feedback systems, which counteract the effects of changes in the internal environment and are principally responsible for maintaining homeostasis 2. Positive feedback systems, which drive rapid, self-limiting changes, such as those that occur when a mother gives birth

18. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions (continued) • Negative feedback reverses the effects of changes • The most important mechanism governing homeostasis is negative feedback, in which a change causes responses that counteract the change • The overall result of negative feedback is a return of the system to its original condition

19. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions (continued) • Negative feedback reverses the effects of changes (continued) • All negative feedback systems contain principal components • A sensor • A control center • An effector

20. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions (continued) • Negative feedback reverses the effects of changes (continued) • The sensor detects the current condition • The control center compares that condition to a desired state called the set point • The effector produces an output that restores the desired condition

21. Animation: Homeostasis

22. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions (continued) • Negative feedback reverses the effects of changes (continued) • Heating your home is an example of negative feedback • The sensor is a thermometer（温度计）, the control center is a thermostat（恒温调节器）, and the effector is a heater（加热器）

23. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions (continued) • Negative feedback reverses the effects of changes (continued) • Heating your home is an example of negative feedback (continued) • The thermometer detects the room temperature and sends that information to the thermostat, where the actual temperature is compared to the set point of the desired temperature

24. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions (continued) • Negative feedback reverses the effects of changes (continued) • Heating your home is an example of negative feedback (continued) • If the actual temperature is below the set point, the thermostat signals the heater to turn on and generate heat • The heater warms the room, restoring the temperature to the set point, which causes the thermostat to turn off the heater

25. Animation: Negative Feedback

26. Figure 31-2a Controlling the temperature in a house during cold weather Stimulus (cold) Condition (roomtemperature) Produces an output(heat) that raises thetemperature,counteracting thedeviation from theset point Measured by Sensor(thermometer) Effector(heater) If the temperatureis lower than theset point, sends asignal to Sends themeasurement to Control center(thermostat withthe set point) Controlling the temperature in a house during cold weather

27. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions (continued) • Negative feedback reverses the effects of changes (continued) • Because none of these components is perfect or responds instantaneously, the room temperature actually gets a bit cooler than the set point before the thermostat turns on the heater, and a bit warmer than the set point before the heater stops

28. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions (continued) • Negative feedback reverses the effects of changes (continued) • Endothermic animals use negative feedback systems to maintain their internal temperature despite fluctuations in the temperature around them • In humans and mammals, the temperature control center is located in a part of the brain called the hypothalamus（下丘脑）

29. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions (continued) • Negative feedback reverses the effects of changes (continued) • Nerve endings in the abdomen, skin, large veins, and hypothalamus itself act as temperature sensors and transmit this information to the hypothalamus

30. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions (continued) • Negative feedback reverses the effects of changes (continued) • If the body temperature falls below the set point, the hypothalamus activates effector mechanisms that raise body temperature • These mechanisms include shivering, blood vessel constriction, and increased metabolic rate

31. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions (continued) • Negative feedback reverses the effects of changes (continued) • When body temperature is restored, the sensors signal the hypothalamus to switch off the actions that generate and conserve heat

32. Figure 31-2b Controlling body temperature during cold weather Stimulus (cold) Condition (bodytemperature) Generate heatthat raises thebody temperature Measured by Sensor(temperaturereceptors inthe body) Effectors (e.g.,skeletal muscles,fat stores) If the bodytemperature is lowerthan the set point, activates Sends themeasurement to Control center(hypothalamusin the brain) Controlling body temperature during cold weather

33. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions (continued) • Negative feedback reverses the effects of changes (continued) • The body’s temperature control system can also act to reduce body temperature, if it rises over the set point • The hypothalamus sends out signals that cause the blood vessels leading to the skin to dilate, allowing warm blood to flow to the skin, where some heat can be radiated out to the air

34. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions (continued) • Negative feedback reverses the effects of changes (continued) • The body’s temperature control system can also act to reduce body temperature, if it rises over the set point (continued) • Sweat glands secrete fluid, cooling the body by evaporating water from the skin • Fatigue and discomfort cause the body to slow down, so the body generates less heat

35. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions (continued) • Positive feedback enhances the effects of changes • In positive feedback, a change produces a response that intensifies the initial change • Positive feedback is relatively rare in biological systems, but occurs during childbirth • The early contractions of labor push the baby’s head against the cervix子宫颈to stretch and open

36. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions (continued) • Positive feedback enhances the effects of changes (continued) • Positive feedback is relatively rare in biological systems, but occurs during childbirth (continued) • Nerve cells in the cervix react to the stretching by signaling the hypothalamus • The hypothalamus responds by triggering the release of a hormone called oxytocin（催产素）

37. 31.1 Homeostasis: How Do Animals Regulate Their Internal Environment? • Feedback systems regulate internal conditions (continued) • Positive feedback enhances the effects of changes (continued) • Positive feedback is relatively rare in biological systems, but occurs during childbirth (continued) • Oxytocin stimulates more and stronger uterine contractions • Stronger contractions cause the baby’s head to stretch the cervix even more

38. 31.2 How Is the Animal Body Organized? • Animals maintain homeostasis by performing numerous functions simultaneously, coordinating the activity of thousands to trillions of cells • This coordination of complex body systems is based on a simple hierarchy of structures • cells  tissues  organs  organ systems • Cells are the fundamental units of all living organisms

39. 31.2 How Is the Animal Body Organized? • Animal tissues are composed of similar cells that perform a specific function • Organs are structures that perform complex functions and include two or more interacting tissue types • Organ systems consist of two or more interacting organs that function in a coordinated manner • For example, the digestive system is made up of the mouth, esophagus, stomach, small and large intestines, and other organs that allow us to digest food and absorb the nutrients from it

40. Figure 31-3 Cells, tissues, organs, and organ systems Tissues: connective epithelial Cells: Organ: epithelial cells stomach arteriole venule lymphaticvessel muscle stomach pancreas largeintestine mouth pharynx esophagus smallintestine liver gallbladder Organ system: digestive system

41. 31.2 How Is the Animal Body Organized? • Animal tissues are composed of similar cells that perform a specific function (continued) • A tissue consists of cells that are similar in structure and functions • A tissue may include extracellular components produced by its cells, as in the case of cartilage and bone

42. 31.2 How Is the Animal Body Organized? • Animal tissues are composed of similar cells that perform a specific function (continued) • There are four major categories of animal tissues 1. Epithelial tissue （上皮组织） 2. Connective tissue （结缔组织） 3. Muscle tissue （肌肉组织) 4. Nerve tissue (神经组织)

43. 31.2 How Is the Animal Body Organized? • Animal tissues are composed of similar cells that perform a specific function (continued) • Epithelial tissue covers the body, lines its cavities, and forms glands • The internal and external surfaces of the body—including the skin and the insides of the circulatory, digestive, respiratory, reproductive, and urinary systems—are covered by epithelial tissue

44. 31.2 How Is the Animal Body Organized? • Animal tissues are composed of similar cells that perform a specific function (continued) • Epithelial tissue covers the body, lines its cavities, and forms glands (continued) • Epithelial tissue consists of sheets of cells firmly attached to one another by connections such as desmosomes（桥粒）and tight junctions（紧密连接） • Sheets of epithelial tissue are attached to an underlying layer of fibrous proteins, called the basement membrane（基底膜）

45. 31.2 How Is the Animal Body Organized? • Animal tissues are composed of similar cells that perform a specific function (continued) • Epithelial tissue covers the body, lines its cavities, and forms glands (continued) • Some of these protein fibers are secreted by the epithelial cells themselves • Others are secreted by connective tissue cells • The basement membrane provides support, flexibility, and strength to the epithelial tissue

46. 31.2 How Is the Animal Body Organized? • Animal tissues are composed of similar cells that perform a specific function (continued) • Epithelial tissue covers the body, lines its cavities, and forms glands (continued) • Simple epithelium(单层上皮 ) is only one cell thick and lines most or all of the respiratory, urinary, reproductive, and circulatory systems

47. 31.2 How Is the Animal Body Organized? • Animal tissues are composed of similar cells that perform a specific function (continued) • Epithelial tissue covers the body, lines its cavities, and forms glands (continued) • Simple epithelia vary in structure depending on the organ and its function • The simple epithelium that lines the lungs consists of a layer of thin, flattened cells that allows rapid diffusion of gases between the lungs and the bloodstream

48. Figure 31-4a Lining of the lungs (simple epithelium) flattenedcells basementmembrane Lining of the lungs (simple epithelium)

49. Figure 31-4b Lining of the trachea (simple epithelium) cilia mucus basementmembrane mucus-producingcells Lining of the trachea (simple epithelium)

50. 31.2 How Is the Animal Body Organized? • Animal tissues are composed of similar cells that perform a specific function (continued) • Epithelial tissue covers the body, lines its cavities, and forms glands (continued) • Stratified epithelium（复层上皮）is several cells thick and can usually withstand considerable wear and tear • Stratified epithelium is mostly found in the skin and just inside body openings that are continuous with the skin, such as the mouth and anus