ADH stimulation increases collecting duct permeability to water, allowing
the production of hyperosmotic urine. Without ADH, the urine leaving the
kidney would be hypo-osmotic. The collecting duct principal cells are the
ADH responsive cells and contain fewer mitochondria and basal infoldings
than occur in the cells of the distal convoluted tubule. Aldosterone (answer c)
also acts on the principal cells and secondarily on the thick ascending limb
of Henle to increase reabsorption of Nacl.
258.The answer is b.(Kierszenbaum, pp 526–527. Junqueira, pp 373, 375,
377–380.)The arrows on the scanning electron micrograph illustrate a
podocyte. The podocytes surround the glomerular capillaries. The spaces
between the foot processes (pedicels) form the filtration slits, an important
part of the filtration barrier of the kidney. The macula densa is a portion of the
distal tubule that is specialized for determination of distal tubular osmolarity.
259.The answer is e.(Kasper, pp 1688–1689. Kumar, pp 990–992.
Kierszenbaum, pp 370–373. Junqueira, pp 373–374, 379.)In patients who
have suffered from diabetes mellitus for many years glycation (nonenzy-
matic addition of sugar to proteins and other molecules) occurs in response
to high blood glucose levels. The critical renal changes are the thickening
of the glomerular basement membrane, elimination of the separation of
laminae rarae and densa, loss of anionic repulsion of sugar groups, and
obliteration of the filtration slits. These renal changes are known as
nephrotic syndrome and lead to loss of selectivity of the filtration barrier
(answer a)and increased permeability to proteins (answer b).This causes
the loss of protein from the blood to the urine (proteinuria). The liver
adjusts to the proteinuria by producing more proteins (e.g., albumin). After
continued proteinuria, the liver is unable to produce sufficient protein,
which results in hypoalbuminemia leading to an overall decrease in
osmotic pressure. Edema then occurs as fluid leaves the vasculature to
enter the tissues. The movement of fluid from the vasculature to the tissues
results in reduced plasma volume and decreased glomerular filtration rate
[GFR(answer c)]. The overall effect is further edema because of compen-
satory release of aldosterone (answer d)coupled with reduced GFR and
the already existing edema.
Glycation results in the production of advanced glycation end-products
(AGE, see figure on the next page), which alters the properties of the
glomerular basement membrane. The cellular receptor for AGE is called
RAGE and is a multiligand member of the immunoglobulin superfamily of
394 Anatomy, Histology, and Cell Biology