47. Endocrine system. Thyroid and parathyroid glands. Embryonic development. Macroscopic, micro-scopic, ultramicroscopic and functional characteristics. Blood and nerve supply.

97 PINEAL GLAND

• Is a Small, Pinecone - shaped.
• Located deep within the brain, in the epithalamus, near the center of the brain between the two hemispheres.
• Lies between the habenular commissure and posterior commissure.
• About 10 mm long and weights about 160 mg.

Syntopy:

• 1 Pineal gland
• 2 Cranially: corpus callosum
• 3 Caudally: quadrigeminal plate
• 4 Rostrally: third ventricle
• 5 Dorsolaterally: quadrigeminal cistern
• 6 Dorsally: great cerebral vein

Histological structure

• 1 Pia mater – is located on the surface of the gland
• emits septa inside the gland, which contain vessels and unmyelinated nerve fibres
• 2 Pinealocytes – the melatonin secreting cells
• 3 Interstitial cells – specific astrocytes of the pineal gland
• → perivascular phagocyte cells.

Functions:

• Secreation melatonin, secreated primarily in darkness. → Regulate sleep - wake cycles
• Involved in the control of circadian rythum.

98 THYROID GLAND

• The largest endocrine gland.
• Site: in the lower part of the front of the neck, and extends to the sides of the neck. (it is in the visceral compartment of the neck). . around the trachea. (between C5-T1)
• It is H-shaped
• Develops from the epithelium of the floor of the mouth.
• It is dark brownish in colour.
• weight around 18 - 60 g in detailes.