Module 2 Lesson 1 - 8
Lesson 1 — The Endocrine System
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Melatonin is a hormone produced at night by the tiny pineal gland located within the brain. It is involved in your sleep-wake cycle and is controlled by sunlight. When light hits the retina of the eye, it inhibits the secretion of melatonin through the hypothalamus and causes wakefulness. When light levels decrease, the melatonin secretion increases and causes drowsiness.
Many people experience tiredness, inability to concentrate, and irritability when they are not exposed to periods of sunshine. This condition is called Seasonal Affective Disorder (SAD).
Read "Light up Your Life!" on page 443 of your textbook and respond to the following two questions:
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Why might people living in northern countries such as Canada, parts of Russia, and the Scandinavian countries be more susceptible to Seasonal Affective Disorder (SAD) compared to people who live in regions that are more southern?
- How do innovative technologies such as "Litebook" contribute to society?
- People living in northern countries may be more susceptible to Seasonal Affective Disorder as the daylight hours shorten during winter months and people are not exposed to enough light to decrease melatonin secretion.
- Light therapy, such as Litebook, is a non-drug therapy to treat people with SAD. People affected by SAD are exposed to bright lighting to inhibit the production of melatonin and stimulate the production of serotonin, a hormone that makes people feel energized.
Lesson Summary
In this lesson, you investigated the following focusing question:
- How is the endocrine system organized, and how do its parts communicate with each other and with various parts of the body?
To answer this question, the major glands of the endocrine system including the hypothalamus/pituitary complex, the thyroid gland, the parathyroid glands, the adrenal glands, and the islet cells of the pancreas were introduced and studied. These glands secrete hormones that have unique effects on the body by interacting with target cells. Some of these hormones work opposite each other and are called antagonistic hormones. Other hormones, called tropic hormones, target other endocrine glands, causing them to secrete more hormones. Levels of hormonal secretions are regulated by negative feedback mechanisms. Negative feedback tends to stabilize a system because the response compensates for the change in the internal environment. This leads to the reestablishment of homeostasis. In contrast, positive feedback reinforces the change in the internal environment, which leads to instability and an imbalance or deviation from homeostasis.