amino acids. When iodide enters the follicular cells, it undergoes oxida-
tion. Thyroglobulin is iodinated while in the colloid, and iodinated thy-
roglobulin (not the thyroid hormones) is the storage product in the thyroid
colloid. The thyroid follicular cells process iodinated thyroglobulin, and
the activity of lysosomes breaks down the colloid to form thyroxine (T4),
triiodothyronine (T3), diiodotyrosine (DIT), and monoiodotyrosine (MIT).
Most of the secretion of the human thyroid gland is composed of thyrox-
ine, although triiodothyronine is more potent.
228.The answer is d.(Sadler, pp 300–301. Junqueira, pp 392–393.)The
neurohypophysis containing the Herring bodies is formed from neuroecto-
derm as an extension of the developing diencephalon. The pars nervosa
consists of pituicytes (supportive glia) and the Herring bodies, dilated
axons that originate in the supraoptic and paraventicular nuclei. These
nuclei produce oxytocin and vasopressin that are stored in the Herring
bodies.
Overall, the pituitary gland (hypophysis cerebri) is formed from two
types of ectoderm. An outgrowth of the oral ectoderm, Rathke’s pouch,
forms the structures that compose the adenohypophysis: pars distalis, pars
intermedia, and pars tuberalis. The pars distalis includes the classic histo-
logic cell types: chromophils (acidophils and basophils) and chromophobes
(acidophils and basophils that are depleted of secretory product). Aci-
dophils include: lactotrophs (prolactin), somatotrophs (growth hor-
mone); basophils include: corticotrophs (ACTH, α-lipotropin, β-MSH,
andα-endorphin), thyrotrophs (TSH), and gonadotrophs (FSH and LH).
The pars intermedia is also formed from the oral ectoderm, is rudimentary
in humans, and may produce preproopiomelanocortic peptide. The pars
tuberalis forms a collar around the pituitary stalk and is also derived from
the oral ectoderm. The pars nervosa (including Herring bodies) and the
remainder of the pituitary stalk (infundibular stem and median eminence)
are formed from a downgrowth of the diencephalon. The posterior pituitary
(pars nervosa and stalk) retains this close relationship with the brain (i.e.,
hypothalamus) throughout life.
229.The answer is a. (Junqueira, pp 394–399, 415–416. Kumar, pp
1156–1162.)Pituitary adenomas are anterior pituitary specific. A corticotroph-
adenoma would cause increased levels of ACTH and stimulate excessive
production of corticosteroids from the adrenal cortex (Cushing’s syndrome).
Endocrine Glands Answers 353