The pineal gland is an endocrine structure of the diencephalon of the brain, and is located inferior and posterior to the thalamus. It is made up of pinealocytes. These cells produce and secrete the hormone melatonin in response to low light levels. High blood levels of melatonin induce drowsiness. Jet lag, caused by traveling across several time zones, occurs because melatonin synthesis takes several days to readjust to the light-dark patterns in the new environment.
melatonin
amino acid–derived hormone that is secreted in response to low light and causes drowsiness
pineal gland
endocrine gland that secretes melatonin, which is important in regulating the sleep-wake cycle
pinealocyte
cell of the pineal gland that produces and secretes the hormone melatonin
Visit this link to view an animation describing the function of the hormone melatonin. What should you avoid doing in the middle of your sleep cycle that would lower melatonin?
Turning on the lights.
1. What cells secrete melatonin?
A) melanocytes
B) pinealocytes
C) suprachiasmatic nucleus cells
D) retinal cells
B
2. The production of melatonin is inhibited by ________.
A) declining levels of light
B) exposure to bright light
C) the secretion of serotonin
D) the activity of pinealocytes
B
1. Seasonal affective disorder (SAD) is a mood disorder characterized by, among other symptoms, increased appetite, sluggishness, and increased sleepiness. It occurs most commonly during the winter months, especially in regions with long winter nights. Propose a role for melatonin in SAD and a possible non-drug therapy.
SAD is thought to occur in part because low levels and duration of sunlight allow excessive and prolonged secretion of melatonin. Light therapy—daytime exposure to very bright lighting—is one common therapy.
2. Retinitis pigmentosa (RP) is a disease that causes deterioration of the retinas of the eyes. Describe the impact RP would have on melatonin levels.
The retina is important for melatonin production because it senses light. Bright light inhibits the production of melatonin, whereas low light levels promote the production of melatonin. Therefore, deterioration of the retinas would most likely disturb the sleep-wake pattern because melatonin production would be elevated.