Melatonin and Epinephrine

circadian rhythmn and melatonin

• Circadian rhythms are the body’s physiological responses to the 24 hour day-night cycle.

• Melatonin is the hormone that plays a role in the control of circadian rhythms.

Mechanisms for melatonin

1. Retina

   1. Light-sensitive tissue lining the back of the retina send signals to the suprachiasmatic nucleus (SCN)^*.

2. Suprachiasmatic nucleus

   1. The suprachiasmatic nucleus acts as a “central pacemaker” that synchronizes the body with the external light-dark cycle. 

3. pineal gland

   1. The SCN signals the pineal gland to produce melatonin.

Describe the secretion and action of melatonin due to mechanisms

Melatonin is therefore secreted in response to periods of darkness, resulting in higher concentrations at night.

• (Daylight inhibits melatonin production)

Outline the mechanism that regulates melatonin secretion in response to the day-night cycle

• Melatonin secretion is suppressed by bright light (primarily blue wavelengths) and hence levels increase during the night.

• Over a prolonged period, melatonin secretion becomes entrained 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 (e.g. humans).

• Melatonin levels naturally decrease with age, leading to changes in sleeping patterns in the elderly.

State the main evolutionary function of epinephrine 

Epinephrine (aka adrenaline)  is both a neurotransmitter and  a hormone. It plays a key role in your body’s “fight-or-flight” response.

• (It’s also used as a medication to treat many life-threatening conditions.)

• Epinephrine’s effects are rapid but short-lived, designed to prepare the body for immediate physical exertion in response to a threat.

Epinephrine

Hormone

• made and released by your adrenal glands, which are hat-shaped glands that sit on top of each kidney.

Neurotransmitter

• released by nerve endings to stimulate other nerve cells, muscle cells or gland cells.

Outline the mechanism of action of epinephrine as a signaling molecule

• A potential threat is registered in the brain (primarily in the amygdala, which is responsible for processing emotions).

• Signals are then sent from the hypothalamus (also in the brain) to stimulate the adrenal glands to release both epinephrine and cortisol (another primary stress hormone). 

• Adrenaline is released into the bloodstream

Outline the effects of epinephrine on the body

• Breakdown of glycogen into glucose  

  • (to increase cellular respiration)

• Increase in blood pressure

  • (ensures adequate blood flow)

• Heart rate increase 

• Dilated pupils

  • (to focus on immediate threat) 

• Slow in digestion

  • (redirects blood for digestion to muscles, etc.)

• Increased breathing rate