IB Biology - 6.6 Melatonin

Light exposure and melatonin

- LIGHT exposure to the retina is relayed via the suprachiasmatic nucleus (in the hypothalamus) and INHIBITS melatonin SECRETION - Melatonin is therefore SECRETED in response to periods of DARKNESS, resulting in higher concentrations at night

Circadian rhythms

Are the body's physiological responses to the 24-hour day-night cycle, driven by an internal (endogenous) circadian clock, although they can be modulated by external factors Melatonin is responsible for synchronizing circadian rhythms and regulates the body's sleep schedule Melatonin secretion is suppressed by bright light (principally blue wavelengths) and hence levels increase during the night Over a prolonged period, melatonin secretion becomes trained to anticipate the onset of darkness and the approach of day Melatonin functions to promote activity in nocturnal animals and conversely promotes sleep in diurnal animals (like humans) During sleep, necessary physiological changes occur in body temperature, brain wave activity, and hormonal production Melatonin levels naturally decrease with age, leading to changes in sleeping patterns in the elderly

Jet lag

Is a physiological condition resulting from a change to the body's normal circadian rhythm - Caused by the body's inability to rapidly adjust to a new time zone following extended air travel ('jet' lag) - Pineal gland continues to secrete melatonin according to the old time zone so that the sleep schedule is not synchronized to the new timezone - Individuals suffering from jet lag will often experience symptoms associated with fatigue - Symptoms: headaches, lethargy, increased irritability and reduced cognitive function - Should only last a few days and symptoms should resolve as the body resynchronizes its circadian rhythm - Some health professionals recommend taking melatonin near the sleep time of the new time zone to help recalibrate the body - By artificially increasing melatonin levels at the new night time, the body can respond quicker to the new day-night schedule

Produced by the...

Pineal gland Within the brain in response to changes in light