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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 ...
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 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 neurons. The principal cell type of the pineal is the pinealocyte sensu stricto.
The adult human brain weighs on average about 1.2–1.4 kg (2.6–3.1 lb) which is about 2% of the total body weight, [2] [3] with a volume of around 1260 cm 3 in men and 1130 cm 3 in women. [4] There is substantial individual variation, [ 4 ] with the standard reference range for men being 1,180–1,620 g (2.60–3.57 lb) [ 5 ] and for women ...
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 .
Another theory is that the cause may be related to melatonin, which is produced in dim light and darkness by the pineal gland, [23] since there are direct connections, via the retinohypothalamic tract and the suprachiasmatic nucleus, between the retina and the pineal gland.
Greek physician Galen was the first to give written description about the pineal gland in the 2nd century CE. [8] He indicated that the structure as an part of the brain was already known to earlier Greek scholars, crediting Herophilus (325–280 BCE) as the first to have described the possible role of the gland. [9]
The pineal gland produces melatonin when signaled by the SCN to help maintain circadian rhythms. Melatonin supplementation can be administered to older adults as their natural hormonal production decreases over time.