Pineal Gland Study Guide
 

Where is the pineal located and what is another name for this gland?

The pineal is connected to the caudal end of the diencephalon by a small stalk.  It has also been called the "epiphysis".

 What are its principal cell types?

Pinealocytes: are like neurons.  They are stellate (star shaped) and arranged in clusters.  They may have numerous microtubules, extensive smooth-surfaced endoplasmic reticulum and a few small granules.  Cells are sensitive to light and innervated by the sympathetic and parasympathetic nervous sytems.  They receive signals via the retina of the eye. Thus, nerve endings are also seen in the pineal.  The nuclei of the pinealocytes are usually pale.

Glial cells: represent the other cell type.  They are elongated and run between nests of pinealocytes. Often the nuclei are more dense and ovoid. One can differentiate the glial cells from the pinealocytes by their dense nuclei.  Also you can see the rich vascular supply marked by red blood cells.

With age, the pineal accumulates large calcium-rich particles called "brain sand".  This is used to identify the pineal in radiographs and hence serves as a midline landmark.

What is the function of the pineal? What hormone mediates this function? How does the environment affect pineal function?

Pinealocytes produce melatonin which is derived from serotonin.  They induce rhythmic changes in the body in response to light.  Melatonin levels rise at night and make us sleepy.    Melatonin plays a role in our light-dark cycles and its secretion (or lack thereof) is one basis for our feelings associated with jet lag. 

How might the pineal be involved with precocious puberty? How is the pineal involved in seasonal breeders?

Melatonin also inhibits  the stimulation of gonadotropin (LH) activity before puberty (antigonadotropic).  It therefore prevents onset of puberty before the appropriate age. Children who experience precocious puberty may have a brain tumor that destroyed the pineal gland. 

Seasonal breeders are regulated by the length of day (signaled by sunlight).  Long days inhibit melatonin and stimulate gonadal activity.  Shorter days stimulate melatonin which causes gonadal atrophy (via the hypothalamus and pituitary).

Gwen V. Childs, Ph.D.
University of Arkansas for Medical Sciences
Shorey 9/32; (501) 686-7020
For questions or comments:  childsgwenv@uams.edu

visitors since 10/23/2000