Pineal Gland: Definition, What It Is, Function, Disorders, Anatomy, Hormones

What Is the Pineal Gland?

Pineal gland is a small, pea-shaped endocrine gland. It is located deep within the brain, between two hemispheres where thalamic halves join. It is named because of its shape, resembling a pinecone.

It is also known as the “third eye” because of its light sensitivity and plays an important role in generating circadian rhythms and modulating the sleep-wake cycle by synthesizing the hormone melatonin.

Anatomy of the Pineal Gland

Anatomically, the pineal gland is a small organ.

Location in the Brain

• Situated in the epithalamus

• Above the midbrain and near the third ventricle.

Structure and Size

• About 5 to 8 millimetres in length.

• Pinecone-shaped.

• Composed of cells called pinealocytes that produce the melatonin

• Highly vascularized, second to the kidneys.

Functions of the Pineal Gland

The functions of pineal glands include:

Regulation of Circadian Rhythms

• Controls the circadian rhythms, natural internal processes that occur in living organisms

• 24-hour cycle which responds to light and darkness.

Melatonin Production

• Produces melatonin, a hormone released in response to darkness.

• Signals the body that it is night and time to sleep.

• This helps to create the proper sleep-wake cycle.

Sleep-Wake Cycle

• Melatonin influences the sleep-wake cycle through the induction of drowsiness

• Regulates the time of sleep and wakefulness.

Seasonal Biological Rhythms

• Participates in seasonal biological rhythms, like those linked to reproduction and mood

• Modulates melatonin production based on length of days from one season to another.

Regulation of Hormones

• Influences reproductive health and stress response.

• Pineal gland coordinates with that hypothalamus and pituitary gland.

Disorders Related to the Pineal Gland

There are disorders related to the pineal gland are:

Pineal Gland Dysfunction

• Circadian rhythm disturbance and sleeping disorders.

• Sleep disorders, like insomnia or somnambulism, due to the imbalance of melatonin production.

Pineal Tumors

• Rare, either benign or malignant.

• Symptoms include headaches and impaired vision, hydrocephalus

• Treatment by surgery, radiation therapy, or chemotherapy.

Calcification of the Pineal Gland

• Accelerates with advancing years.

• Extreme calcification inhibits melatonin production

• Leading to sleep disorders and neurodegenerative diseases.

Pineal Gland NEET MCQs (With Answers & Explanations)

Important questions asked in NEET from this topic are:

• Pineal gland hormones and their functions

• Disorders related to pineal gland

Practice Questions for NEET

Q1. Which gland is the 'Third eye'?

1. Pineal

2. Thyroid

3. Thymus

4. Adrenal

Correct answer: 4) Pineal

Explanation:

The gland known as the 'Third eye' is the pineal gland. The hormone melatonin which helps in regulating sleep-wake cycles is produced by the pineal gland which is situated deep within the brain. It is sometimes referred to as the "third eye" due to its light sensitivity and role in regulating circadian rhythms. Its function in reacting to light and controlling sleep has given it this appellation even though it lacks a true eye structure.

Hence, the correct answer is option 1)Pineal.

Q2. Pineal gland is located on the dorsal side of

1. Midbrain

2. Hindbrain

3. Pons

4. Forebrain

Correct answer: 4) Forebrain

Explanation:

The pineal gland is located on the dorsal side of the forebrain. The pineal gland is located on the dorsal side of the forebrain, between the two hemispheres, in a small groove where the two halves of the thalamus meet. It is a small, pea-shaped endocrine gland that is primarily responsible for the production of melatonin. Melatonin is a hormone that helps regulate sleep-wake cycles and circadian rhythms in response to light. The pineal gland also plays a role in regulating seasonal biological rhythms and may influence reproductive functions. Despite its small size, the pineal gland has significant effects on the body’s biological clock and overall health.

Hence, the correct answer is option 4) Forebrain.

Q3. A hormone responsible for normal sleep-wake cycle is

1. Epinephrine

2. Gastrin

3. Melatonin

4. Insulin

Correct answer: 3) Melatonin

Explanation:

The hormone melatonin is principally in charge of controlling the circadian rhythm, also known as the sleep-wake cycle. The pineal gland releases it in reaction to darkness. Melatonin promotes relaxation and tiredness by telling the body it's time to get ready for sleep. To keep the body's internal biological clock in sync with the natural day-night cycle, this hormone is very important.

Hence, the answer is the option 3) Melatonin.

Also Read:

• MCQs on Pineal Gland

• Mechanism of Hormone Action

• Parathyroid Gland

Recommended Video for Pineal Gland