Pineal Gland

interstitial (glial) cells

Constitute about 5% of the cells in the pineal gland. They have staining and ultrastructural features that closely resemble those of astrocytes and are reminiscent of the pituicytes of the posterior lobe of the pituitary gland.

Pineal gland and circadian rhythms

The pineal gland is a photosensitive organ and an important timekeeper and regulator of the day/night cycle (circadian rhythm). It obtains information about light and dark cycles from the retina via the **retinohypothalamic tract,** which connects in the **suprachiasmatic nucleus** with sympathetic neural tracts traveling into the pineal gland. During the day, light impulses inhibit the production of the major pineal gland hormone, melatonin. Production of gonadal steroids is decreased by the inhibitory action of melatonin on neurosecretory neurons located in the hypothalamus (arcuate nucleus) that produce GnRH. Inhibition of GnRH causes a decrease in the release of FSH and LH from the anterior lobe of the pituitary gland. tumors that destroy the pineal gland are associated with precocious (early-onset) puberty

corpora arenacea (brain sand)

calcified concretions that appear to be derived from precipitation of calcium phosphates and carbonates on carrier proteins that are released into the cytoplasm when the pineal secretions are exocytosed. The concretions are recognizable in childhood and increase in number with age. Because they are opaque to X-rays and located in the midline of the brain, they serve as convenient markers in radiographic and computed tomography (CT) studies.

function of pineal gland

secretes melatonin endocrine or neuroendocrine gland that regulates daily body rhythm.

pinealocytes

the chief cells of the pineal gland. They are arranged in clumps or cords within lobules formed by connective tissue septa that extend into the gland from the pia mater that covers its surface produce melatonin

Melatonin synthesis

detection of light inhibits the production of N- acetyltransferase due to downregulation of NE = inhibition of melatonin production during darkness, NE is free to stimulate pinealocytes to produce N- acetyltransferase which will convert serotonin to melatonin

development of the pineal gland

develops from neuroectoderm of the posterior portion of the roof of the diencephalon and remains attached to the brain by a short stalk.