Examine the posterior pituitary on slide 122 and identify parts of the microvasculature, non-myelinated axons, and the support cells called pituicytes (Fig. 20-11). The non-myelinated axons present are difficult to see without special stains.

Where are the two hormones synthesized which these axons secrete and how is the secretion controlled?

To what CNS cells are pituicytes of the neurohypophysis analogous?

Clinical note: Diabetes insipidus is a disorder in which the neurohypophysis fails to secrete vasopressin/antidiuretic hormone in response to normal stimuli. The disorder involves excessive thirst, excessive water intake, and excessive urination and can be treated by injection of vasopressin or similar drugs.

Pineal gland -- small neurosecretory organ in brain with axons communicating to other parts of the brain. The pineal is a photoreceptor organ in primitive vertebrates.

Examine pineal tissue on slide 106 or 107. Pineal tissue can be identified from surrounding brain tissue by the presence of pineal sand (Fig. 20-24), concretions of mineralized organic matrix of unknown significance. Note the abundant vasculature. Identify the small clumps of pinealocytes, with scant poorly stained cytoplasm and ovoid nuclei containing nucleoli. The fibrous material surrounding all the cells is primarily neuropil, not collagen.

What function is primarily associated with the pineal gland?

“Pineal sand’ has medical relevance because radiologists find that it is a good marker of the brain’s midline.

Next is the thyroid.