The document presents a detailed overview of the mammalian pineal gland, its structure, and the significance of its hormone, melatonin, in regulating circadian rhythms, seasonal reproduction, and various physiological processes. It highlights the role of the pineal body as an endocrine gland that produces melatonin in response to light exposure and discusses its effects on sleep-wake cycles, immune modulation, and neuroprotection. Additionally, it addresses potential clinical applications of melatonin in treating sleep disorders and other health conditions.

1. PRESENTATION OF
ZOOLOGY
TOPIC :Structure of mammalian pineal body,
Functional significance of pineal hormones
SUBJECT : COMPARATIVE ENDOCRINOLOGY
(MZOO - 402)
SUBMITTED BY:
Name - Yogesh
Class - M.Sc. Zoology 4th Semester
Class Roll No. - 2256001
University Roll No. - 81221680020
SUBMITTED TO:
Assistant Professor
Dr. Asha Garg

2. INTRODUCTION
• It is an important endocrine
gland in higher vertebrates.
• Its name is derived from its
pinecone like structure.
• It is also known as 'third eye' as
this gland receives its stimuli
through vision.
• It was first discovered by
Herophilus about 2000 years ago.
• Embryologically derived from
neuroectoderm of diencephalic
roof.

3. • This gland produces melatonin which regulates sleep -
wake cycle and circadian rhythm.

4. Mammalian Pineal Body

5. • The pineal gland is a small reddish - grey gland.
• It is approximately 8mm long & 5-7mm wide.
• It is located in the epithalamus, a region of the brain
that connects to thalamus and the midbrain.
• Pineal gland is surrounded by a capsule of connective
tissue and contains many pinealocyoes which are
specialized cells that produce and secrete melatonin.
• Pineal gland is a circumventricular organ ( which are
specialized structures located in walls of 3rd & 4th
ventricle which lacks a blood - brain barrier) .

7. • These pinealocytes produce and secretes melatonin.

8. PHYSIOLOGY OF PINEAL BODY
• The pineal gland is controlled by the suprachiasmatic
nucleus which is located in the hypothalamus
• The suprachiasmatic nucleus is responsible for regulating
the circardian rhythm which is the internal biological clock
that regulate the sleep - wake cycle.
• Pineal gland produce and secretes melatonin in a
response to change in light exposure.
• When light levels are low such as night , pineal gland
produces more melatonin.
• When light levels are high such as during the day the
pineal gland produces less melatonin.

12. • Melatonin production is regulated by the hormone
norepinephrine which is the released from sympathhetic
nerve fibres that innervates Pineal gland.
• Norepinephrine stimulates the production of cyclic
adenosine monophosphate which in turn activates the
production of melatonin.
• Melatonin is N - acetylated product of serotonin.
• Synthesis of melatonin is initiated by the conversion of
tryptophan to serotonin which is then converted to
melatonin by the action of enzyme Arylalkylamine
N-acetyltransferase.

14. FUNCTIONAL SIGNIFICANCE OF PINEAL HORMONES
• Melatonin is the only known hormone synthesized by the pineal gland
and is released in response to darkness hence the name, “hormone of
darkness.
1) Regulation of Circadian Rhythms
• Sleep-Wake Cycle: Melatonin helps regulate the sleep-wake cycle by
promoting sleep during the night and wakefulness during the day.
• Synchronization with Light-Dark Cycle: Melatonin levels are influenced
by light exposure, helping align biological rhythms with environmental
light-dark cycles.
2) Seasonal Reproduction
• Photoperiodism: Melatonin regulates reproductive cycles in response to
changes in day length. It triggers breeding behaviors in long-day and
short-day breeders, ensuring that offspring are born in optimal conditions.
3) Antioxidant Protection
• Scavenging Free Radicals: Melatonin acts as a powerful antioxidant,

15. neutralizing free radicals and reducing oxidative stress.
•Enhancing Antioxidant Enzymes: It boosts the activity of enzymes that
protect cells from oxidative damage.
4) Immune Modulation
• Immune Cell Activity: Melatonin enhances the activity of various immune
cells, including T lymphocytes, natural killer cells, and macrophages.
• Cytokine Production: It influences the production of cytokines, which are
crucial for immune response regulation.
5) Neuroprotection
• Protection Against Neurodegeneration: Melatonin protects neurons from
damage caused by excitotoxicity, apoptosis, and neuroinflammation.
• Aging and Brain Health: Declining melatonin levels with age are linked to
neurodegenerative diseases, and supplementation may help mitigate
age-related neural decline
6) Metabolism and Weight Regulation

16. • Energy Balance: Melatonin affects lipid metabolism and adipogenesis,
helping regulate body weight and energy balance.
• Insulin Sensitivity and Glucose Homeostasis: It improves insulin
sensitivity and helps maintain stable blood glucose levels.
7) Regulation of Seasonal Behaviors
• Adaptation to Seasonal Changes: Melatonin influences behaviors such
as migration, hibernation, and changes in fur thickness or fat storage,
helping animals adapt to seasonal variations.
8) Clinical Applications
• Treatment for Sleep Disorders: Melatonin supplements are used to treat
insomnia, jet lag, and other sleep disorders.
• Potential Therapeutic Uses: Research suggests potential benefits for
conditions like seasonal affective disorder (SAD), certain cancers, and
cardiovascular diseases.

17. THANK YOU

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