The Origin of the Pituitary. Disclosure 16
The current pituitary is a gland, located at the base of the skull, of complex anatomical structures, whose origin can be found in primitive annelid nodes existing at the Cambrian period, about 500 million years.
Although some descriptions consider the pituitary is formed by 4 cores called pars (distalis, tuberalis, intermediate and nervosa) we will use in this article, another description alleging that the pituitary is composed of three lobes (anterior,intermediate and later) to be more appropriate to describe the origin of this gland.
The anterior lobe has an endodermal origin and is formed from Rathke's pouch that is separated from the roof of the pharynx during embryo period. Although its is very important referring to the hormonal point of view it was no part of the original pituitary. It is found in the same position that the other lobes, but its appearance is later and is probably a specialization of the intermediate lobe to regulate latest features from the evolutionary point of view this gland.
On the other hand, intermediate and posterior lobes have ectodermal origin and are part of the original pituitary. The origin of both is the second ganglion pair of the "rope ladder" of annelids.
The posterior lobe consists of the terminal axons from the supraoptic nucleus, what relates it anatomically with the primitive first pair of ganglia " rope ladder "that led to the eyes, and stores hormones vasopressin and oxytocin produced by these axons. In this way, it regulates primitive functions such as water and minerals absorption and conservation and reproductive behaviors.
The intermediate lobe produces melanotropin, stimulating hormones of melanocytes, inducing to increase melanin cells the skin synthesis.
The pituitary is therefore a very small anatomical structure size, about 8 mm in the human, and in smaller percentage by relative weight of about 1 mg per kbw (0.0001% of body weight)
However, despite its small size, it regulates essential primitive aspects as epithelial reaction, feeding and reproduction since both lobes (second pair nodal "ladder of rope "of annelids) react in relation to light and hormonal information received from the eyes (first pair node of " rope ladder "of annelids) and define the behavior of skin and reproductive cycles of animals.
Its connection with the third pair of ganglia in rope ladder of annelids is very complex and lead us into the origin and central nervous system functionality.