Most multicellular organisms have organized tissue and organs with specialized functions (an exception would be the sponges). In order to coordinate the activities of these organs cells must be able to communicate with one another. The nervous system and the endocrine system play the central role in that communication. The nervous and endocrine systems regulate the metabolic activities of organs, control the organism's response to changes in the environment (external and internal), and modulate the timing of developmental changes over time. In this unit you will focus on the endocrine system in humans. In unit 17 you will study the functions of plant and insect hormones. We will study the nervous system in another unit.
Learning Objectives: The successful student will be able to ...
- name and describe examples of the major human hormones, their endocrine glands, target tissues/organs, and actions.
- distinguish between protein/amino acid based hormones and steroid hormones, give examples of each, and describe in detail their mode of action in target cells.
- describe in detail the endocrine control of blood sugar and blood calcium levels including the endocrine glands, hormones, and target tissues/organs involved.
- use the control of calcium and glucose levels as examples of negative feed back systems of homeostasis as well as the action of antagonistic control mechanisms.
- describe in detail the response of the adrenal cortical and medullary hormones to stress as part of the "fight or flight" response.
- name and describe several examples of medical conditions resulting from diseases of the endocrine system including diabetes, Cushing's desease, hypocalcemia, and Addison's disease.
Lesson One: Introduction To Hormones And Their Cellular Mechanisms.
Read the first four sections from this section of the Online Biology text. Appreciate the different types of hormones (protein/peptide/amino acids and steroids). Be able to name several examples of each and the general function. Be sure you understand the difference between an endocrine gland and the target tissue and their relation to the actual hormone. Most hormones function through a negative feedback system where the activity of the starting point is regulated by the end point. Use the production of the hormone thyroxine as an example. Notice that several organs are involved (brain/hypothalamus, the anterior pituitary, and the thyroid gland). The important point here is the activity of the initial point (e.g. the release of thyrotropin by the anterior pituitary) is regulated by the amount of thyroxine. This negative feedback mechanism is an almost universal feature of hormone regulation.
Finally, study the two models for the action of peptide and steroid hormones at the cellular level. Look for similarities and important differences in the manner that these two types of hormones initially interact with their receptors, the role of "second messengers," and how metabolic activity and/or DNA activity is influenced by the hormones. Kimball has a good summary of this material as well as a table listing the major hormones, and a good diagram of the major endocrine organs. Don't be mislead by this diagram; many organs that have a more obvious function also produce important hormones (e.g. stomach, kidneys, intestines, placenta, etc.). Here is another McGraw Hill tutorial on this subject; select the link to "Types of Hormones."
Homework, Due . Email the answers to the following questions using your Fontbonne account.
- List three hormones that are either proteins, peptides, or amino acids produced by three different endocrine glands. Name their target tissue and briefly describe their function.
- List three steroid hormones produced by three different endocrine glands. Name their target tissue and briefly describe their function.
Now go to this McGraw Hill Publishing site of animations and scroll down to Chapter 47. Run the three animations listed there.
- What type of hormones are thyroxine and epinephrine; steroids or amino acid derivatives? Explain. You may need the table from Kimball for help.
- For each hormone, thyroxine and epinephrine list the various proteins associated with its action on the target cell and briefly describe the protein's function.
- Which of these two hormones, thyroxine or epinephrine has a mode of action more similar to the typical steroid? Explain.
Lesson Two: Control Of Blood Calcium Levels.
You know that calcium is an important dietary mineral that supports the development of bones. However, the role of calcium goes far beyond building strong bones. It is critical for the proper function of skeletal muscles, heart muscles, and nerves. In fact these functions are so important, you body will dissolve calcium from your bones to maintain critical calcium levels for muscle and nerve function.
Go to this McGraw Hill tutorial and read about some of the basic organs and tissues involved in the maintenance of blood calcium levels. Select the links to "integration & coordination" then to "endocrine system" and finally to parathyroid and thyroid glands. Be sure you can name the glands involved, the hormones they produce, their target organs, and their effect. Notice that the control of blood calcium levels is accomplished by a double feed back mechanism. You will find another summary of this material here at Kimball.
Homework, Due . Email the answers to the following questions using your Fontbonne account.
- The contraction of the biceps and triceps muscles move your forearm in opposite directions; these muscles are said to be antagonistic. Antagonistic systems are very common in biology. Using blood calcium levels, describe two different antagonistic systems involved in this control system (one involving bone cells, the other the action of hormones).
- Do some research and find the medical terms for conditions resulting in an abnormally low and abnormally high level of blood calcium. Describe the symptoms and treatments for these conditions.
Lesson Three: Control Of Blood Sugar Levels.
From your study of cell respiration, you know that the sugar glucose plays a critical role in the production of the energy molecule, ATP. After the carbohydrates in your food are digested into glucose, this sugar is transported to the cells of the body via the circulatory system. In this unit you will study how the concentration of blood glucose levels is maintained and how the movement of glucose from the blood into the cells is regulated.
The pancreas is an organ located near the junction of the stomach and small intestine. It is a good example of an organ with several different functions; it produces a wide variety of digestive enzymes that are dumped into the small intestine and it produces several hormones critical for regulating the level of blood glucose and its movement into cells. Read the section from Kimball. Appreciate the antagonistic relationship between the hormones insulin and glucagon and the wide ranging actions of these hormones on various tissue and organs in the body. Understand the difference between diabetes I and II. This McGraw Hill tutorial has a good summary and excellent diagrams (go to the links for "integration & coordination" and then the "endocrine system" and "pancreas").
Homework, Due . Email the answers to the following questions using your Fontbonne account.
- Both insulin and glucagon are produced in the pancreas; is it correct to say that they are produced by the same type of cells? Explain and be specific.
- Are insulin and glucagon the only hormones produced by the pancreas? If not, what is the relationship of the other hormones to insulin and glucagon in terms of their target tissues/organs and action.
- Explain why diabetics are often encouraged to eat many small meals throughout the day rather than the typical three main meals. Use your knowledge of the pancreas to detail your answer.
- Why are injections of insulin only affective for some diabetics? Explain.
Lesson Four: The Biology Of Stress.
We all experience stress. Sometimes it is brief (falling down the stairs) and sometimes it is prolonged (taking AP Biology). In both cases, you react with a complex but predictable response that includes all of the major organs of your body. This lesson focuses on the role of the endocrine system in the response to stress, sometimes called the "fight or flight" response.
Although several endocrine glands respond to stress, none is more important than the adrenal gland. The adrenal glands, located on top of the kidneys, are actually two different glands in one, the outer adrenal cortex and the inner adrenal medulla. Go to Kimball and read the section on the adrenal gland and its hormones. For the cortex focus on the corticosteroid hormones; the others are not involved as much in the stress response. You will also find a good summary at the McGraw Hill tutorial. Appreciate that the medulla has a direct nerve connection from the brain and therefore responds very quickly to stress. The cortex, on the other hand, is controlled by the release of ACTH for the pituitary and takes a longer time to respond (but also has a longer lasting response). Notice the similarity of the action of the adrenal hormones to those of the pancreas.
Homework, Due . Email the answers to the following questions using your Fontbonne account.
- Injections of the adrenal medullary hormone, epinephrine, are often give to patients suffering from an asthma or severe allergic reaction. Explain why this would be the drug of choice? Be specific.
- Chronic stress is dangerous and unhealthy due, in part, to the prolonged exposure to hormones from the adrenal cortex. Explain how these hormones can have a damaging effect on the body in situations of long term stress.
- Name and describe two diseases involving malfunction of the adrenal cortex.
- How does the action of cortisol compare with the actions of the pancreatic hormones insulin and glucagon in terms of the movement of glucose into or out of the cells? Be specific.
The Scream by Edvard Munch
