Module 2 The Endocrine System

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The Brain and the Pituitary Gland

The hypothalamus—an important part of the brain—is located just above the pituitary gland—an important part of the endocrine system. Information is transmitted to the hypothalamus through sensory pathways from the sense organs. Based on this information, the hypothalamus controls and integrates many basic physiological activities including the reflex activity of the autonomic nervous system, of which the sympathetic nervous system is a part. In the hypothalamus there are two groups of nerve centres. One is connected to the anterior lobe of the pituitary by blood vessels, and the other is connected to the posterior lobe by nerve cells. These centres send instructions to the two parts of the pituitary, telling them whether or not to release their hormones into the bloodstream. However, the nerve centres communicate with the two parts of the pituitary gland in different ways. Releasing hormones are secreted by one nerve centre and carried to the anterior pituitary through the blood vessels, where they regulate the secretions of the anterior pituitary. Can you recall an example of this that you have studied? A second nerve centre, connected to the posterior lobe by nerve cells, performs two functions: (1) it secretes hormones which are carried by the nerve cells to the posterior pituitary where they are stored in the axon terminals and (2) it sends nerve impulses to the posterior pituitary, stimulating the release of the stored hormones. Can you identify the two hormones that are stored in the posterior pituitary? A third centre in the hypothalamus is connected by sympathetic neurons to the adrenal gland. Can you remember which hormone is released by the adrenal gland when these neurons are stimulated? These examples illustrate the importance of the hypothalamus as an important command centre for coordinating the activity of the nervous and endocrine systems.

For further discussion:

Read page 437 and page 463 of your textbook and make notes on how the nervous and endocrine systems maintain homeostasis, how they are coordinated, and how they act together. Developing a flow chart may help you visualize these relationships. You may want to review your notes, particularly from Module 2 Lessons 1, 2, 3 and 4. File your summarized notes in your course folder for later reference.

OR

You can investigate the same concepts by watching and making notes on the following videos. File your notes in your course folder.

Nervous vs Endocrine Action

Try This

TR 2.

To help you apply your understanding of the concepts in this lesson, complete the following questions by answering in complete sentences. Check your answers and then file your work in your course folder. Consult with your instructor for clarification.

1. Using an example, explain how the nervous and endocrine systems work together to regulate a response in the body.
2. 1. Why has the pituitary gland often been called the “master gland”?
   2. Explain how the hypothalamus controls the pituitary gland.
   3. Is “master gland” a suitable name for the pituitary gland?
3. Explain how the anterior and posterior pituitary differ with respect to their relationships to the hypothalamus.
4. How are neurotransmitters and hormones similar and how are they different?
5. Using an example, explain how the hormones of the adrenal medulla complement the actions of the sympathetic branch of the autonomic nervous system.
6. Compare and contrast the role of the norepinephrine in the nervous system with its role in the endocrine system.
7. How is the hypothalamus involved in the release of epinephrine and norepinephrine by the adrenal gland?
8. How is the secretion of tropic hormones from the pituitary gland regulated?
9. Compare the anatomy of the pituitary gland and adrenal medulla.
10. Why is control of the adrenal medulla by the nervous system important?