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The pineal gland is present in almost all vertebrates, but is absent in protochordates in which there is a simple pineal homologue. The hagfish , archaic vertebrates, lack a pineal gland. [ 7 ] In some species of amphibians and reptiles, the gland is linked to a light-sensing organ, variously called the parietal eye , the pineal eye or the ...
As an elusive and unique part of the brain, the pineal gland has the longest history among the body organs as a structure of unknown function – it took almost two millennia to discover its biological roles. [1] Until the 20th century, it was recognised with a mixture of mysticism and scientific conjectures as to its possible nature. [2] [3]
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]
In humans, the major endocrine glands are the thyroid, parathyroid, pituitary, pineal, and adrenal glands, and the (male) testis and (female) ovaries. The hypothalamus, pancreas, and thymus also function as endocrine glands, among other functions. (The hypothalamus and pituitary glands are organs of the neuroendocrine system.
According to this belief, humans had in far ancient times an actual third eye in the back of the head with a physical and spiritual function. Over time, as humans evolved, this eye atrophied and sunk into what today is known as the pineal gland. [9]
The epithalamus is a tiny structure that comprises the habenular trigone, the pineal gland, and the habenular commissure. It is wired with the limbic system and basal ganglia . Species that possess a photoreceptive parapineal organ show asymmetry in the epithalamus at the habenula, to the left (dorsal).
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 .
The pineal gland starts to develop during the second month of gestation. In the average adult, the dimensions are as follow: 5-9mm in length, 1-5mm in width and 3-5mm in thickness. Its average weight is 100–180 mg. [40] The pineal gland consists of a central core made up of small lobes and a cortex that possesses a diffuse distribution of ...