ANATOMY OF PINEAL GLAND

Renee Descartes dubbed the pineal gland the “Seat of the Soul” because of its location in the brain’s center. The pineal gland’s primary function is to receive information about the state of the light-dark cycle from the environment and use that information to synthesize and secrete the hormone melatonin. Melatonin’s rhythmic production, which occurs solely during the dark hours of the day, is widely employed as a marker of the internal circadian clock’s phase. Melatonin is used to treat a variety of sleep disorders caused by irregular circadian rhythms, as well as to alleviate jet lag.

Melatonin has been linked to a variety of physiological functions, suggesting that it may have further therapeutic applications in the future. It has acute physiologic impacts at night or in the dark, as well as long-term consequences when melatonin levels are undetectable during the day. Melatonin is involved in cell protection, neuroprotection, and the reproductive system, among other tasks, particularly plays important roles in modulating the circadian rhythm and sleeping habits. Accidental and developmental defects include pineal tumors, craniopharyngiomas, injuries to the sympathetic innervation of the pineal gland, and uncommon congenital disorders that impact melatonin secretion can disrupt pineal gland function and melatonin release.

STRUCTURE OF PINEAL GLAND

The pineal gland is a single organ in the brain’s midline It gets its name from the shape of a pine cone. The form of the pinecone gives it its name. In humans, the gland is reddish-gray in color and around the size of a grain of rice (5–8 mm). The pineal gland, also known as the pineal body, is located between the laterally positioned thalamic bodies and behind the habenular commissure in the epithalamus. It can be found near the corpora quadrigemina in the quadrigeminal cistern. It is also placed behind the third ventricle and receives cerebrospinal fluid via a small pineal recess of the third ventricle that projects into the gland’s stalk. 

ANATOMY OF PINEAL GLAND

The pineal gland grows from the roof of the diencephalon, a brain region, and is placed behind the third cerebral ventricle in the midline of the brain (between the two cerebral hemispheres). Its name comes from the shape, which resembles that of a pinecone (Latin pinea). It is around 0.8 cm (0.3 inch) length and weighs about 0.1 gramme in adult people (0.004 ounce). 

The pineal gland contains a large number of adrenergic nerves (neurons that respond to the adrenal hormone epinephrine) that have a significant impact on its activity. The pineal gland is made up of pinealocytes (typical endocrine cells with extensions that mix with those of surrounding cells) and supporting cells that are comparable to astrocytes in the brain. The pineal body is frequently seen on X-rays in adults due to tiny calcium deposits. (In most people, the pineal gland becomes more or less calcified.)

The gland has a well-developed eyelike feature in several smaller animals. It works as a light receptor in others, even though it is not organized like an eye. 

PINEAL PHYSIOLOGY AND PATHOPHYSIOLOGY

Changes in the duration of the nightly melatonin plateau educate brain areas about environmental light-dark cycles and seasonality, as interpreted by circulating melatonin levels in vertebrates, which are generated from pineal melatonin release. These cues, in turn, aid in the entertainment of sleep (which is improved by darkness) and reproductive cycle events (increased with more seasonal lighting). Pinealectomy (removal of the pineal gland) inhibits reproduction in birds, rodents, and seasonally breeding mammals. Melatonin appears to increase the release of gonadotropin-inhibitory hormone in those species, which leads to the inhibition of gonadotropins (hormones that act on the ovaries or testes), which could explain the disruption in reproduction. 

Pineal tumors and cysts have been linked to both precocious and delayed puberty in humans. The pathophysiology of those disorders, however, is unknown, and mechanical and hormonal variables may be implicated. Although pure melatonin-secreting tumors have not been detected, there have been reports of positive connections between melatonin secretion and other hormones. There are no well-defined pineal hormone deficit or hormone excess syndromes, unlike other endocrine glands such as the pituitary, adrenal, or thyroid.

FUNCTION OF PINEAL GLAND

The pineal gland exerts most of its effects on bodily systems through the secretion of its major hormone melatonin. The hypothalamus and suprachiasmatic nucleus are the primary targets of this hormone, according to biochemical and electrophysiological studies, however the hippocampus and substantia nigra have also been implicated. Melatonin raises the levels of serotonin and catecholamines in several regions of the brain. Melatonin increases the concentration of biogenic amines, and biogenic amines are involved in many of the normal and abnormal functions of the central nervous system, such as mood and sleep disorders, so it’s likely that melatonin influences biogenic amine transmission in the central nervous system to exert some of its effects on bodily systems.

Melatonin mimics the light-dark cycle in the production of photoperiod dependent reactions when given in physiological amounts. The hormone serves as a carrier of photoperiodic data, which is read variable throughout the year. Hence in recent years studies on pineal gland function have focused mainly on seasonal cycles rather than on daily cycles. This claim is subject to some controversy.

CONCLUSION

The pineal gland, once thought to be a minor “neuroendocrine transducer” (a gland that converts a neural input into a hormonal output), has now been identified as a major “neuroendocrine transducer” (a gland that converts a neural input into a hormonal output) with specific effects on reproductive mechanisms, circadian organization, sleep mechanisms, and human mood control. The gland serves as a “general synchronizing, stabilizing, and regulating organ” for a variety of physiological processes (I), and the hormone melatonin is known as an “equilibrating hormone.”