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The pineal gland (also known as the pineal body [1] or epiphysis cerebri) is a small endocrine gland in the brain of most vertebrates. It produces melatonin, a serotonin-derived hormone, which modulates sleep patterns following the diurnal cycles. [2] The shape of the gland resembles a pine cone, which gives it its name. [3]
The hormone melatonin was isolated in 1958 by Aaron B. Lerner, a dermatology professor, and his team at Yale University. Motivated by the possibility that a substance from the pineal gland could be beneficial in treating skin diseases, they extracted and identified melatonin from bovine pineal gland extracts. [64]
Melanocytes in skin make and secrete MSH in response to ultraviolet light, where it increases synthesis of melanin. [3]: 441 Some neurons in arcuate nucleus of the hypothalamus make and secrete α-MSH in response to leptin; [3]: 626 [4]: 419 α-MSH is also made and secreted in the anterior lobe of the pituitary gland. [5]: 1210
Endocrine glands are ductless glands of the endocrine system that secrete their products, hormones, directly into the blood. The major glands of the endocrine system include the pineal gland , pituitary gland , pancreas , ovaries , testicles , thyroid gland , parathyroid gland , hypothalamus and adrenal glands .
An abundance of cilia and centrioles has also been found in these Type 2 cells of the pineal gland. [7] Unique to the Type 2 is the presence of vacuoles containing 2 layers of membrane. [7] As Type 1 cells contain serotonin, Type 2 cells contain melatonin and are thought to have similar characteristics as endocrine and neuronal cells. [8]
The thyroid secretes thyroxine, the pituitary secretes growth hormone, the pineal secretes melatonin, the testis secretes testosterone, and the ovaries secrete estrogen and progesterone. [ 2 ] Glands that signal each other in sequence are often referred to as an axis, such as the hypothalamic–pituitary–adrenal axis .
The epithalamus is associated with sleep disorders like insomnia revolving around circadian rhythms of sleep wake cycles. The close connection of the epithalamus with the limbic system regulates the secretion of melatonin by the pineal gland and the regulation of motor pathways and emotions. [9] The secretion of melatonin happens in a cycle.
These hypophysiotropic hormones are stimulated by parvocellular neurosecretory cells located in the periventricular area of the hypothalamus. After their release into the capillaries of the third ventricle, the hypophysiotropic hormones travel through what is known as the hypothalamo-pituitary portal circulation.