18.4 Pineal gland and Circadian Rhythms Flashcards
What is the pineal gland and what is its location
It is a small, pinecone-shaped structure located in the centre of the brain
What hormone does the pineal gland secrete?
Melatonin
What type of hormone is melatonin
It is an indoleamine hormone
What is the most widely accepted role of melatonin?
It regulates the body’s circadian rhythms, synchronizing them with the light-dark cycle
What nucleus controls the circadian rhythms of the body
The Suprachiasmatic Nucleus (SCN)
What is the Suprachiasmatic nucleus
A small group of neurons in the hypothalamus located above the optic chiasma
Why is SCN referred to as the master biological clock
Because it serves as a central timekeeper, coordinating many of the body’s daily functions, such as temperature regulation, feeding, metabolism and behaviour.
The SCN’s rhythm relies on ________________ regulated through autoregulatory feedback loops.
Clock proteins
What two transcription factors activate the production of the 2 clock proteins (PER and CRY)
CLOCK & BMAL-1
Just explain the molecular mechanism of the SCN’s circadian rhythms
CLOCK & BMAL-1 activate the production of PER and CRY proteins. As these proteins accumulate, they inhibit CLOCK & BMAL-1, halting further production of PER and CRY until they degrade, allowing the cycle to start again. This cycle takes approximately 25 hours and governs the rhythmic output of the SCN, influencing various functions, including cortisol secretion.
To maintain synchronization with the external environment, SCN must be adjusted by ?
External cues such as the light-dark cycle
What may result due to the body’s rhythms being desynchronised due to the absence of external cues
jet lag
What two things does the SCN work with to ensure that the body’s internal clock is aligned with the day-night cycle
Melatonin and Pineal gland
How is the daily variation in light intensity the primary environmental cue for adjusting SCN
Special melanopsin-containing photoreceptors in the retina detect light levels independently of rods and cones (which are responsible for vision). These photoreceptors send signals directly to the SCN, helping to keep the body’s internal clock aligned with external day-night cycles.
When are melatonin levels the highest?
during the night
