Other tumors of the islets of Langerhans include insulinomas in which
elevated levels of insulin are secreted into the bloodstream. The result is
hypoglycemia as blood sugar levels drop. Insulin removes sugar from the
blood and, in the liver, either stores it as glycogen or metabolizes it through
glycolysis. Insulin inhibits glycogen phosphorylase (which catalyzes the
breakdown of glycogen to form glucose) and activates glycogen synthase in
both muscle and liver resulting in increased storage of glycogen.
231.The answer is c.(Kasper, pp 2141–2143. Junqueira, pp 366, 389, 407.
Kumar, pp 1215–1216.)The woman in the scenario suffers from Addison’s
disease, in which there is a progressive destruction (hypotrophy) of the
adrenal cortex (zones A, B, and C). The result in the patient is asthenia
(lack of strength, overall weakness, and fatigue), anorexia, nausea, vom-
iting, weight loss, hypotension, and low blood sugar. The hyperpigmen-
tation results from elevated ACTH stimulation of melanocytes. The
photomicrographs show the histology of the adrenal gland [cortex (∗)
and medulla (–∗–)], which releases stress-related hormones [i.e., gluco-
corticoids and catecholamines (norepinephrine and epinephrine)]. The
adrenal cortex originates from the intermediate mesoderm, whereas the
adrenal medulla forms from neural crest. Adrenocortical cells are under
the influence of corticotrophs in the anterior pituitary. Adrenocortical
cells import cholesterol and acetate and produce the hormones shown in
the table below. The zona glomerulosa (A)is found immediately beneath
the capsule (E)and is followed by the zona fasciculata (B)and zona retic-
ularis(C)as one moves toward the medulla (D). However, in all zones
the cells do not store appreciable quantities of hormones, there is an
absence of secretory granules, and the steroid hormones are released by
diffusion through the plasma membrane without use of the exocytotic
process used by most glands, including the adrenal medulla. The cells of
the adrenal medulla (D)may be considered as modified postganglionic
sympathetic neurons. Adrenal medullary cells synthesize and secrete nor-
epinephrine, epinephrine, and enkephalins in response to stimulation of
preganglionic sympathetic fibers that travel through the abdomen in the
splanchnic nerves and innervate the gland. The adrenal cortical hor-
mones are viewed as essential for life because of their regulation of
metabolism.
Endocrine Glands Answers 355