Human Anatomy - Kotsan I. Ya. 2009

Endocrine Glands
Pineal gland — pineal body

The Pineal Gland (epiphysis cerebri) is a part of the epithalamus within the Diencephalon. It lies in a shallow groove that separates the superior colliculi of the Midbrain. The pineal gland is shaped like a pinecone, which gives rise to its alternative name, the pineal body (corpus pineale or glandula pinealis). The narrow end of the gland points downward and backward, while its expanded base is directed toward the third cerebral ventricle, featuring a small pineal recess at its base. In an adult, the pineal gland weighs no more than 0.2 g, with a length of 8—15 mm, a width of 6—10 mm, and a thickness of 4—6 mm. It reaches its maximum development during childhood. Starting around the age of 7, it undergoes involution, characterized by the proliferation of Connective Tissue and the deposition of salts (Brain sand). Some glandular Cells persist into old age.

Externally, the pineal gland is enveloped in a connective tissue capsule containing numerous anastomosing Blood Vessels. Connective tissue trabeculae extend from the capsule into the organ, dividing the glandular parenchyma into lobules. These lobules consist of two Cell types: glandular cells (pinealocytes), located in the center of the lobule, and glial cells (gliocytes), situated mainly at the periphery. The function of pinealocytes exhibits a distinct circadian rhythm, synthesizing melatonin at night and serotonin during the day.

The pineal gland influences numerous body Functions, particularly in early childhood. This is due to its connections with the diencephalon and its regulatory effect on the entire Endocrine System (including the Pituitary Gland, Thyroid Gland, adrenal cortex, and Thymus). Its primary action involves delaying sexual maturation and preventing precocious Puberty. The inhibitory effect on the Reproductive System—achieved by suppressing the secretion of gonadotropic Hormones in the adenohypophysis—is mediated not only by melatonin and serotonin but also by other BIOLOGICALLY ACTIVE SUBSTANCES produced by the pineal body. Through similar mechanisms, it suppresses The activity of The Thyroid Gland and the lymphoid tissue of the thymus. Furthermore, serotonin has been shown to be involved in the daily fluctuations of the hypothalamic-pituitary-adrenal axis, leading to the Conclusion that the pineal body plays a key role in regulating the body's biological clock.

The pineal body develops as a single midline outpocketing from the roof of the second cerebral vesicle. The cells of this protrusion form a compact mass invaded by mesoderm, which subsequently gives rise to the stroma of the pineal body. Together with blood vessels, the stroma divides the organ's parenchyma into lobules.

In a newborn, the pineal gland weighs approximately 7 mg, increasing to 100 mg During the first year of life. By the age of 10, the organ's weight nearly doubles, after which it remains virtually unchanged. However, because cysts and brain sand deposits can develop during adulthood and are particularly common in old age, the size and weight of the pineal body may significantly exceed these average figures.

The pineal gland receives its blood supply from Branches of the posterior cerebral and superior cerebellar Arteries. Venous blood drains into the great cerebral vein or its tributaries. Sympathetic nerve fibers accompany the blood vessels into the tissue of the organ, serving to innervate the vasculature.