Section 1 The Endocrine System Section 2 The Male Reproductive System Section 3 The Female Reproductive System MediaWise Sexuality in Music Videos Building Health Skills Practicing Healthful, Behaviors Breast and Testicular Self-Exams Section 4 Heredity
Section 1 Objectives ~ Describe the general roles of the endocrine system. ~ dentify the glands of the endocrine system. Vocabulary endocrine gland hormone hypothalamus pituitary gland puberty : Health Stats What trends in growth rate does this graph : show? Average Height of American Teens 70...65. ~ ~ '-" ~ @ i. 55 ~ : 50 0 9 10 11 12 13 14 15 16 17 18 19 20 Age (years) ~Does your observation of classmates support the trends shown in the graph? Explain....~. What s the Endocrine System? How much have you grown in the past year? When will you reach your adult height? Your growth rate is one of the many functions controlled by your body's endocrine system. The endocrine system regulates longterm changes in the body such as growth and development. t also controls many of your body's daily activities. Two examples of daily activities include your body's use of energy from a meal and its response to stress. Endocrine Glands Your endocrine system is made up of a group of organs, called endocrine glands (EN duh krin). An endocrine gland produces and releases chemical substances that signal changes in other parts of the body. Some of your body's glands, such as sweat glands, release their chemicals into tiny tubes called ducts. The ducts carry the chemicals to the place where they will be used. Endocrine glands, on the other hand, do not have ducts. nstead, they release substances directly into the bloodstream. The blood then carries those substances throughout the body. 460 Chapter 18
[H!,ii 1 1!llilll Adrenaline directs your response to sudden stress or fear. Testosterone controls beard growth in males. Hormones A chemical substance produced by an endocrine gland is known as a hormone. You can think of a hormone as a chemical messenger. Each hormone has a specific function and specific "targets" in the body. Once released into the bloodstream, a hormone travels to its target cells, where it turns on, turns off, speeds up, or slows down the activities of those cells. For example, targets of the hormone adrenaline include cells in your heart, muscles, and brain. Adrenaline causes a faster heartbeat, tensing of the mu~cles, and increased alertness-your "fight-or-flight" response. The endocrine system is kept in balance by the coordinated action of various hormones. For example, a hormone from one gland may turn on the production of a different hormone by a second gland. n turn, the hormone from the second gland signals the first gland to stop releasing its hormone. By this system of checks and balances, the endocrine system keeps the body's activities functioning smoothly. FGURE 1 Hormones play many roles in the body. ~ Describe a time when you experienced a surge YOUR LlFE/ of adrenaline. Functions of Endocrine Glands Each of your endocrine glands plays a specific, important role in your body. The endocrine glands include the hypothalamus, pituitary gland, thyroid and parathyroid glands, thymus gland, adrenal glands, pancreas, and reproductive glands. Hypothalamus The hypothalamus (hy poh THAL uh mus), an endocrine gland located in the brain, is actually part of both the nervous and the endocrine systems. For example, nerve signals from the hypothalamus control body temperature and feelings of sleep and hunger, and hormones from the hypothalamus control the body's water levels. The hypothalamus also produces a class of hormones called "releasing hormones" that signal the release of hormones from another region of the brain. Reproduction and Heredity 461
The Endocrine System r Thyroid Gland The thyroid gland regulates the body's overall metabolic rate and controls calcium levels in the bloodstream. Parathyroid Glands Four tiny parathyroid glands regulate levels of calcium and phosphorus-minerals that are necessary for proper bone and tooth formation and for muscle and nerve activity. Thymus Gland Hormones released by the thymus gland help the immune system develop during childhood. By adolescence, this gland has shrunk considerably in size. Adrenal Glands These glands release several hormones. Adrenaline triggers the body's response to sudden stress. Other hormones affect salt and water balance in the kidneys and general metabolism. Pancreas The pancreas is a large gland, located behind the stomach, that controls sugar levels in the blood. l Ovaries The female reproductive glands release sex hormones that regulate egg maturation and control changes in a female's body at puberty. Testes The male reproductive glands release a sex hormone that regulates sperm production and controls changes in a male's body at puberty. FGURE 2 Each of the endocrine glands plays an important regulatory role in the body. nterpreting Diagrams Where are the adrenal glands located? What is their function? Female Male 462 Chapter 18
Pituitary Gland "Releasing hormones" from the hypothalamus signal the release of hormones from a pea-sized endocrine gland in the brain, called the pituitary gland (pih TOO ih tehr ee). The pituitary controls many of your body's functions. These functions include growth, reproduction, and metabolism. Metabolism is the process by which you obtain energy from food. Some pituitary hormones act as "on" switches for other endocrine glands. For example, one pituitary hormone signals the thyroid gland to release hormones essential for normal metabolism. Other pituitary hormones control body activities directly. For example, growth hormone released by the pituitary gland regulates growth throughout your body from infancy to adulthood. For: More on endocrine glands Visit: PHSchool.com Web Code: ctd-6181 '1111, Other Endocrine Glands Endocrine glands are found throughout the body, as shown in Figure 2. Notice the range of body functions that your endocrine system controls-from your blood sugar level over the course of a day to the long-term as a teen. changes in your body that you experience The reproductive glands are an important part of the endocrine system. n males, the reproductive glands consist of two testes, and in females, two ovaries. The reproductive glands work at low levels in both boys and girls until about the age of ten, when puberty typically begins. Puberty is the period of sexual development during which a person becom~s sexually mature and physically able to reproduce. Puberty starts when the hypothalamus signals the pituitary gland to begin producing two hormones. Those hormones in turn signal the reproductive glands to produce sex hormones. Sex hormones activate several changes in your outward appearance during pu.berty. Sex hormones also control reproductive functions inside your body. You will learn more about the reproductive glands and their hormones in the next two sections. Section 1 Review Key deas and Vocabulary 1. What roles does the endocrine system play in the body? 2. What is a hormone? Explain how hormones reach the cells where they have their effect. 3. Listthe glands of the endocrine system. 4. What is the hypothalamus? How does it interact with the pituitary gland? Critical Thinking S. Relating Cause and Effect How is the onset of puberty related to the endocrine system? Health at Adrenaline in Action nterview a musician or an athlete at your school about the role that adrenaline might play during a performance or game. Find out the conditions under which they have noticed this response and whether it helped their performance. Write a transcript of your interview. ~ 6. Applying Concepts A driver brakes suddenly when a dog darts out in front of her car. How did the endocrine system aid her quick response? Reproduction and Heredity 463