Module 2

1. Module 2

1.15. Page 4

Lesson 2

Module 2—The Endocrine System

The photo shows children measuring the increase in their height as a result of hGH causing the growth of the long bones in their bodies.

Human Growth Hormone

The anterior pituitary regulates growth, muscle development, and fat metabolism through the production of human growth hormone (hGH), which ultimately affects every part of your body. Some athletes are interested in using human growth hormone to improve performance because it stimulates protein synthesis and subsequent muscle development as well as toning of muscles. Some overweight people are interested in using this hormone to fight obesity because it inhibits the storage of fat and encourages its use for cellular respiration. At the same time, hGH inhibits use of carbohydrates such as glucose. Some older people are also interested in using hGH. As one ages, the levels of this hormone decrease—fat is harder to keep off and muscles become flabby. Testimonials by aging stars, such as Sylvester Stallone, are prominent in advertisements for hGH. You will examine some of these ideas in “Thought Lab: Evaluating Potential Uses for Human Growth Hormone.”

The photo illustrates how excess hGH can cause the hands and feet to widen and enlarge.

Nearly everyone is interested being tall. Fairytales often contain stories of maidens being saved by “tall, dark, and handsome” heroes. Human growth hormone stimulates the growth plates at the end of the long bones and causes these bones to lengthen and increase a person’s height. Too much hGH during childhood causes gigantism. Today (early 2009), Leonid Stadnyk is the tallest living person, at a height of 2.57 m or 8 feet 5.5 inches. Too little hGH during childhood results in pituitary dwarfism. Thapa Magar, the shortest living person, is only 50.8 cm or 20 inches tall.

Emily, who you met earlier, had some very small tumours develop in the anterior pituitary several years after her final growth spurt. Instead of gigantism, she shows the symptoms of acromegaly. Because her growth plates have sealed, she cannot grow in height. Instead, her jaw has thickened, as have her ribs; and her fingers, toes, and nose have become enlarged. This type of growth results from excessive production of hGH during adulthood.

gigantism: a condition where a person produces excess hGH during childhood, resulting in a height of 8 feet or more

pituitary dwarfism: a condition where a person does not produce enough hGH during childhood, resulting in short stature

acromegaly: a condition brought about by excessive secretion of human growth hormone in an adult; hands, feet, and nose widen and enlarge; jaw protrudes; voice becomes husky; barrel chest may develop; sweat glands enlarge; heart enlarges; high blood pressure may develop; enlarged tissues press on nerves, especially optic nerves, causing loss of vision, particularly in the outer fields; and pressure on the brain causes severe headaches

There is an increased likelihood of developing diabetes mellitus.

Read

To learn more about human growth hormone, and to summarize the functions and effects of this important hormone, you may wish to review pages 444 to 446 in your textbook. “Figure 13.11,” on page 444, and “Figure 13.15,” on page 446, are good summaries that you may want to copy and include in your course folder.