2. Development and Histology
• Develops from roof of diencephalon (a dorsal
diverticulum)
• Composed of two cell types :
• 1) pinealocytes and 2) neuroglial –like
interstitial cells
• Pinealocytes secretes primarily melatonin
which is syn from trytophan via serotonin.
Melatonin is highest at night. Exposure to
light decreases melatonin syn. Hence, a
diurnal rhythm
• Has brain sand or corpora arenacea –
calcified concretions –ppt of CaPO4
3. Histology
• Melatonin secretion is regulated by
norepinephrine that is released from
postganglionic sympathetic nerves.
• Pinealocytes have long cytoplasmic
processes that terminate near capillaries
• Melatonin is secreted into blood vessels
whereas serotonin is taken up by presynatic
axon terminals.
4. Synthesis of hormones
• Light entering CNS via the eyes
stimulates postganglionic nerves thus
releasing norepinephrine which
increases serotonin.
• At night, 5-hydroxy indole O- methyl
transferase (only found in pineal)
increases and converts serotonin to
melatonin
5. Clinical Significance
• Seasonal affected disorder (SAD)
affects some people during winter. It is
a type of depression. Corrected by
exposure to bright light.
• Jet lag – adjusting to sudden changes in
day length
