LH- and FSH-producing gonadotroph-adenomas occur, but tend to result
in hypogonadism. Somatotropic tumors produce GH and cause giantism
(answer e).Prolactinomas are the most common form of pituitary ade-
noma resulting in infertility, galactorrhea (excessive production of milk),
and amenorrhea. Diabetes insipidus (answer c)is caused by absence of
vasopressin [arginine vasopressin (AVP)], leading to excretion of a large
quantity of dilute fluid (hypotonic polyuria). Overproduction of parathy-
roid hormone (PTH) leads to osteoporotic changes, but PTH is notregu-
lated by the anterior pituitary (answer d).The thyroid secretes T 3 and T 4
(answer b).
230.The answer is a. (Junqueira, pp 407–411. Guyton, pp 884–893.
Kumar, p 1207. Kasper, pp 2222, 2228.)A tumor of the glucagon secreting
alpha (α) or A cells delineated with the asterisks results in hyperglycemia
and diabetes. This photomicrograph shows both exocrine and endocrine
portions of the pancreas. Pancreatic exocrine tissue is found throughout
the pancreas with round aggregation of lighter staining cells forming the
islets of Langerhans. There are several endocrine cell types within the islets.
The more numerous (70% of total) B or βcells are centrally located and
secrete insulin that is secreted after a meal and results in a lowering of
blood sugar. The smaller population of A or αcells located at the periph-
ery of the islet (∗) secrete glucagon. Glucagon is secreted in response to low
blood sugar and raises blood sugar levels. A glucagonoma produces exces-
sive amounts of glucagon that results in hyperglycemia and diabetes. The
interaction of βandαcells is based on the blood supply. Blood entering the
islet initially bypasses the αcells. The result is that blood reaching the α
cells already contains insulin, which regulates glucagon production. The
absence of normal glucagon regulation by insulin is a further complication
in type I diabetes in which insulin is not produced. Other cell types [D (δ)
and F] are variable in location and secrete somatostatin and pancreatic
polypeptide, respectively. Somatostatin regulates insulin and glucagon
release, whereas pancreatic polypeptide appears to regulate exocrine pro-
tein and bicarbonate secretion. The exocrine portion of the pancreas con-
sists of acinar and ductal cells. The acinar cells are pyramidal in shape and
possess a very basophilic basal cytoplasm, indicating the presence of abun-
dant rough ER and an acidophilic apical cytoplasm due to the presence of
numerous secretory (zymogen) granules.
354 Anatomy, Histology, and Cell Biology