Chapter 32 Homeostasis and the Organization of the Animal Body - BIOL160 PDF

BIOL160 Chapter 32 Homeostasis and the organization of the animal body 1 Chapter 32 At a Glance ⚫ 32.1 Homeostasis: How Do Animals Regulate Their Internal Environment? ⚫ 32.2 How Is the Animal Body Organized?...

BIOL160 Chapter 32 Homeostasis and the organization of the animal body 1 Chapter 32 At a Glance ⚫ 32.1 Homeostasis: How Do Animals Regulate Their Internal Environment? ⚫ 32.2 How Is the Animal Body Organized? 2 32.1 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, which has an almost constant composition despite enormous differences in the water and salt content of the outside environment Homeostasis 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 3 32.1 Homeostasis: How Do Animals Regulate Their Internal Environment? ⚫ 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 4 32.1 Homeostasis: How Do Animals Regulate Their Internal Environment? ⚫ 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 5 32.1 Homeostasis: How Do Animals Regulate Their Internal Environment? ⚫ 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 6 32.1 Homeostasis: How Do Animals Regulate Their Internal Environment? ⚫ 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 ⚫ Endotherms generate most of their heat through metabolic reactions - Birds and mammals are principal endotherms on Earth 7 32.1 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 create cycles in which changes amplify themselves, such as those that occur when a mother gives birth A feedback system uses one of the products of a pathway, usually the end product, to control the activity of the pathway and to regulate the amount of that product. 8 Feedback systems 9 32.1 Homeostasis: How Do Animals Regulate Their Internal Environment? ⚫ 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 ⚫ All negative feedback systems contain principal components A sensor A control center An effector 10 32.1 Homeostasis: How Do Animals Regulate Their Internal Environment? ⚫ 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 11 32.1 Homeostasis: How Do Animals Regulate Their Internal Environment? Heating your home is an example of negative feedback ⚫ The sensor is a thermometer, the control center is a thermostat, and the effector is a heater ⚫ 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 ⚫ 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 12 13 32.1 Homeostasis: How Do Animals Regulate Their Internal Environment? ⚫ 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 ⚫ Nerve endings in the abdomen, skin, large veins, and hypothalamus itself act as temperature sensors and transmit this information to the hypothalamus ⚫ 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 14 15 16 32.1 Homeostasis: How Do Animals Regulate Their Internal Environment? ⚫ 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 ⚫ 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 17 32.1 Homeostasis: How Do Animals Regulate Their Internal Environment? ⚫ 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 to stretch and open - 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 - Oxytocin stimulates more and stronger uterine contractions - Stronger contractions cause the baby’s head to stretch the cervix even more 18