The region labeled Ais the posterior pituitary that stores oxytocin and
vasopressin in dilated axonal terminals. Overall, the pituitary is derived
from the ectoderm of the oral cavity (Rathke’s pouch) and the floor of the
diencephalon. The anterior (C)and intermediate (H)lobes and pars tuber-
alis(G)are derived from the oral cavity, whereas the remainder of the pitu-
itary [pars nervosa (A)and the pituitary stalk (D)] is derived from a
neuroepithelial origin. The cleft of Rathke’s pouch (B)represents the lumen
of the structure formed originally from the oral cavity. The pars distalis (C)
contains acidophils and basophils regulated by stimulatory and inhibitory
hormones produced by the hypothalamus. In the pars nervosa (A),the
major cell type present is the pituicyte, a supportive glial cell. Axons that
originate in the supraoptic and paraventricular nuclei of the hypothalamus
descend into the pars nervosa. Oxytocin (regulating the milk ejection
reflex) and vasopressin [(AVP) also known as antidiuretic hormone (ADH)
regulates collecting duct permeability] are stored in dilated endings in the
pars nervosa called Herring bodies. Those secretions are, therefore, synthe-
sized in the hypothalamus and stored in the pars nervosa. Structure Eis the
median eminence; F represents the cavity of the third ventricle.
233.The answer is a.(Kasper, pp 2109–2111. Greenspan, pp 81, 91–92,
257–258. Kierszenbaum, p 504. Kumar, pp 1169–1171.)The patient is suffer-
ing from Hashimoto’s thyroiditis in which there is extensive infiltration of
the thyroid gland. Autoantibodies develop to thyroglobulin and thyroid
peroxidase, an iodine transporter and/or the TSH receptor. In cases where
there are autoantibodies to TSH receptor, the TSH receptor activity is
blocked, resulting in hypothyroidism compared to the hyperthyroidism,
which occurs in Graves’ disease (see question 227). The antibodies are to a
different site on the receptor, resulting in the different overall effect. CD8+
T cells are also directed against that site. T3 and T4 levels may be elevated
early in the disease (answer b)process due to disruption of the follicles
and release of hormones; however, the overall effect is hypothyroidism.
Destruction of thyroid hormone receptors (answer c)would lead to hyper-
thyroidism. Calcitonin is secreted by the C cells in the thyroid and is not
affected by the thyroiditis (answer d).Glucocorticoid levels are not ele-
vated(answer e).
234.The answer is b.(Kasper, pp 2104–2107. Kumar, p 1165.)T4 (thyroxine)
is the primary serum thyroid hormone and is produced only by the thyroid
Endocrine Glands Answers 357