Module 2

Module 2—The Endocrine System

Endocrine Glands

In Module 1 you learned about the basic unit of the nervous system—the neuron—and how communication occurs through neural pathways. Now, you will learn about the major glands of the endocrine system and how communication through the use of special chemical messengers called hormones occurs.

Endocrine glands are ductless glands—they do not release their secretions into a duct as exocrine glands do. Instead, endocrine glands secrete their hormones directly into the blood, which acts as the transport medium. As the hormones pass cells, only those cells with special receptors will react to their presence. These cells are called target cells. Lipid-soluble hormones and water-soluble hormones activate their target cells very differently. Hormones interact together and, in many instances, one hormone counteracts the action of a second hormone. Hormones such as these are called antagonistic hormones. This type of action is illustrated in the figure on the right.

Some hormones, called tropic hormones, influence other endocrine glands. They are secreted by the hypothalamus-pituitary complex. These hormones are very important in the control and regulation of the endocrine system. An important example is the gonadotropic hormones, which affect the reproductive organs. You can view the regulatory pathway of tropic hormones in “Figure 13.10” on page 441 of your textbook. You may want to sketch a copy this pathway and store it in your course folder for later reference.

Read

To help you identify the main endocrine glands, read pages 436 to 441 in your textbook. Summarize your readings about the endocrine glands in a chart or concept map with the following sections: “endocrine gland,” “hormone produced by gland,” and “primary effect of the hormone.” Place this chart in your course folder for future reference.

Watch and Listen

To further explore and review these concepts visually, watch the following segments of “The Hypothalamus and Pituitary: The Master Complex”:

• “Endocrine System”
• “Hormones”

You may be required to enter a username and password to access these videos. Contact your teacher for this information.

Self-Check

SC 6. Complete either Choice A or Choice B.

Choice A

This interactive drag-and-drop exercise has two parts.

In the first part of the exercise, match the statement that describes a hormone or the function of a hormone with the appropriate endocrine gland.

In the second part of the interactive exercise, drag the name of the hormone to the gland that produces it.

Choice B

Practise labelling the endocrine glands, identifying the hormones they produce, and describing the main functions of the hormones in the exercise that follows. After you have completed the exercise and checked your answers, file it in your course folder for access when you are studying.

1. Label the major endocrine glands numbered 1 through 8 on the diagram.
   
   
2. List the hormones (the number of hormones to be identified is indicated in brackets) that each gland produces. The ovary and testis will be studied in Unit B. Although the thymus and pineal gland are part of the endocrine system, you are not responsible for studying them for this course.
   
   
3. Construct and complete a table with the following headings.