3 The Endocrine System

Transcription

1 CHAPTER 25 3 The Endocrine System SECTION Communication and Control BEFORE YOU READ After you read this section, you should be able to answer these questions: Why is the endocrine system important? How do feedback systems work? What are common hormone imbalances? National Science Education Standards LS 1a, 1d, 1e What Is the Endocrine System? The endocrine system controls body functions using chemicals made by endocrine glands. A gland is a group of cells that makes special chemicals for your body. The chemicals made by endocrine glands are called hormones. A hormone is a chemical messenger. It is made in one cell or tissue and causes a change in another cell or tissue. Hormones flow through the bloodstream to all parts of the body. Glands and Organs of the Endocrine System The pituitary gland makes hormones that affect other glands and organs. The thyroid gland increases the rate at which you use energy. STUDY TIP Describe As you read, fill in the chart at the end of the section to name the major endocrine glands and what each one does. READING CHECK 1. Explain How do hormones move from one part of the body to another? The parathyroid gland controls calcium levels in the blood. The adrenal glands help the body respond to danger. The thymus gland helps control your immune system, which helps your body fight disease. The pancreas controls glucose levels in the blood. The ovaries (in females) produce hormones needed for reproduction. 2. Identify What two structures produce hormones needed for reproduction? The testes (in males) produce hormones needed for reproduction. 3. Identify Which gland makes hormones that affect organs and other glands? Interactive Textbook 407 Communication and Control

2 SECTION 3 The Endocrine System continued Critical Thinking 4. Infer Why do you think increasing your breathing rate helps prepare you to fight or run away? ADRENAL GLANDS Endocrine glands may affect many organs at one time. For example, the adrenal glands release the hormone epinephrine, sometimes called adrenaline. Epinephrine increases your heartbeat and breathing rate. This response is called the fight-or-flight response. When you are scared, angry, or excited, the fight-or-flight response prepares you either to fight the danger or to run from it. How Do Feedback Systems Work? Recall how feedback mechanisms work in the nervous system. Feedback mechanisms are cycles in which information from one step controls another step in the cycle. In the endocrine system, endocrine glands control similar feedback mechanisms. The pancreas has specialized cells that make two different hormones, insulin and glucagon. These two hormones control the level of glucose in the blood. 5. Explain How could you raise your blood-glucose level without involving hormones? 5 Glucagon tells the liver to break down glycogen and release glucose into the blood. Pancreas When the blood-glucose 4 level is too low, the pancreas releases the hormone glucagon instead of insulin. Glucose is fuel for your 1body. Glucose is absorbed into the bloodstream from the small intestine. When the glucose level 2 in the blood is high, such as after a meal, the pancreas releases the hormone insulin into the blood. Pancreas 6. Identify Which hormone tells the liver to release glucose into the blood? Liver 3 Insulin signals the liver to take glucose from the blood and store it in the liver as glycogen. Interactive Textbook 408 Communication and Control

3 SECTION 3 The Endocrine System continued What Is a Hormone Imbalance? Sometimes, an endocrine gland makes too much or not enough of a hormone. For example, a person s body may not make enough insulin or be able use it properly. This is a condition called diabetes mellitus. A person who has diabetes may need daily injections of insulin. These injections help keep his or her blood-glucose levels within safe limits. Some patients get their insulin automatically from a small machine worn on the body. READING CHECK 7. Define What is a hormone inbalance? This woman has diabetes. She is wearing a device that delivers insulin to her body. Another hormone imbalance is when a child s pituitary gland doesn t make enough growth hormone. As a result, the child does not grow as quickly or as much as he or she should. If the problem is found early in childhood, a doctor can prescribe growth hormone. In some cases, the pituitary gland may make too much growth hormone. This may cause a child to grow taller than expected. Endocrine gland Function Pituitary increases the rate at which you use energy 8. Summarize Use this chart to help you summarize the major endocrine glands and their functions. Interactive Textbook 409 Communication and Control

4 Section 3 Review NSES LS 1a, 1d, 1e SECTION VOCABULARY endocrine system a collection of glands and groups of cells that secrete hormones that regulate growth, development, and homeostasis; includes the pituitary, thyroid, parathyroid, and adrenal glands, the hypothalamus, the pineal body, and the gonads gland a group of cells that make special chemicals for the body hormone a substance that is made in one cell or tissue and that causes a change in another cell or tissue in a different part of the body 1. Explain What is the function of the endocrine system? 2. Compare How are the thymus and thyroid gland similar? How are they different? 3. Identify Relationships How do the circulatory system and the endocrine system work together? 4. Explain What does insulin do? 5. Apply Concepts Many organs in the body are part of more than one organ system. List three examples from this section of organs that are part of both the endocrine system and another organ system. 6. Infer Glucose is a source of energy. Epinephrine quickly raises your bloodglucose level when you are excited or scared. Why is epinephrine important during these times? Interactive Textbook 410 Communication and Control

5 Life Science Answer Key continued 5. Sense Receptors What the receptors respond to Touch many different kinds pressure, temperature, vibration Sight photoreceptors light Hearing neurons in the sound waves cochlea Taste taste cells dissolved molecules Smell olfactory cells molecules in the air SECTION 3 THE ENDOCRINE SYSTEM 1. They move through the bloodstream. 2. ovaries in females and testes in males 3. pituitary gland 4. Your muscles need a lot of oxygen to fight or to run, and they produce a lot of waste. Increasing breathing rate helps you take in more oxygen and get rid of carbon dioxide quickly. 5. by eating something 6. glucagon 7. when an endocrine gland makes too much or not enough of a hormone 8. Endocrine gland Function Pituitary makes hormones that affect other organs Parathyroid controls calcium levels in the blood Thyroid increases the rate at which you use energy Thymus controls the immune system, which helps fight disease Adrenal helps the body respond to danger Review 1. to produce hormones that regulate the body 2. They are both hormone-producing glands found in the neck and chest area. The thyroid regulates energy use. The thymus is part of the immune system. 3. The endocrine system produces hormones that are transported through the body by the circulatory system. 4. Insulin decreases blood sugar levels. It signals the liver to convert glucose into glycogen or to store glycogen. 5. Ovaries: endocrine and reproductive Testes: endocrine and reproductive Pancreas: endocrine and digestive 6. Your cells need glucose for energy during fight-or-flight. Epinephrine helps keep the blood glucose level up so that your cells can get the glucose they need. Chapter 26 Reproduction and Development SECTION 1 ANIMAL REPRODUCTION 1. budding, fragmentation, regeneration 2. regeneration 3. when a sperm and an egg join together to form a zygote 4. 1/4 5. Answers will vary but may include: oceans, streams, ponds, rivers 6. external 7. They reproduce sexually and feed their young with milk. Review 1. In budding, an offspring develops on the parent and then pinches off. In fragmentation, part of the parent breaks off and then develops into another organism. 2. All living things will eventually die. The members of a species must reproduce for the species to survive. 3. Meiosis makes sex cells with half the number of chromosomes in most body cells. That way, when sex cells join, the zygote will have the correct number of chromosomes. 4. asexual 5. External fertilization happens outside both parents bodies, while internal fertilization happens within one parent s body. 6. It allows the female to protect the developing zygote inside her body. 7. birds, mammals, reptiles SECTION 2 HUMAN REPRODUCTION 1. millions 2. Arrow should point to the testis eggs 4. The ovary should be circled. The uterus should have a square around it. 5. sexually transmitted diseases and cancer 6. Fertilization generally takes place in the fallopian tubes. If they are blocked, fertilization cannot take place. Interactive Textbook Answer Key 29 Life Science