Physiology of the Kidneys 615Lauren appeared to develop a nephrogenic diabetes
insipidus as a result of the lithium she took for her bipolar
disorder. The diabetes insipidus caused her to excrete
copious amounts of dilute urine, making her dehydrated.
As long as she continues to take lithium, she must drink
more water to prevent dehydration. Probenecid inhibits
the reabsorption of uric acid, so that Lauren’s kidneys
can clear uric acid from her blood more quickly as a
treatment for her gout. Probenecid also inhibits OATs and
thereby reduces the secretion of some antibiotics, which
would slow their excretion and increase their effective-
ness. Using Lauren’s plasma creatinine measurement
and her age, sex, and weight, a normal estimated GFR
was calculated and indicated that her kidneys were
healthy. However, she developed hypokalemia as a result
of taking hydrochlorothiazide, which promotes K^1 secre-
tion into the nephron tubules. She needs a diuretic to
treat her hypertension, and so the physician probably
prescribed a potassium-sparing diuretic, which blocks
K^1 secretion or aldosterone action, possibly in combina-
tion with hydrochlorothiazide.
See the additional chapter 17 Clinical Investigations on
Primary Aldosteronism and Acute Nephritic Syndrome in
the Connect site for this text.| CHECKPOINT Clinical Investigation SUMMARY
13a. List the different categories of clinical diuretics and
explain how each exerts its diuretic effect.
13b. Explain why most diuretics can cause excessive
loss of K^1. How is this prevented by the potassium-
sparing diuretics?- Define uremia and discuss the dangers associated
with this condition. Explain how uremia can be
corrected through the use of renal dialysis.
SUMMARY
through slits in the processes of the podocytes—the cells that
compose the inner layer of the glomerular (Bowman’s) capsule.
1. The glomerular ultrafiltrate, formed under the force of
blood pressure, has a low protein concentration.
2. The glomerular filtration rate (GFR) is the volume of
filtrate produced by both kidneys each minute. It ranges
from 115 to 125 ml/min.
B. The GFR can be regulated by constriction or dilation of the
afferent arterioles.
1. Sympathetic innervation causes constriction of the
afferent arterioles.
2. Intrinsic mechanisms help to autoregulate the rate of
renal blood flow and the GFR.17.3 Reabsorption of Salt and Water 590
A. Approximately 65% of the filtered salt and water is
reabsorbed across the proximal convoluted tubules.
1. Sodium is actively transported, chloride follows
passively by electrical attraction, and water follows the
salt out of the proximal tubule.
2. Salt transport in the proximal tubules is not under
hormonal regulation.17.1 Structure and Function of the Kidneys 582
A. The kidney is divided into an outer cortex and inner medulla.
- The medulla is composed of renal pyramids, separated
by renal columns. - The renal pyramids empty urine into the calyces that
drain into the renal pelvis. From there, urine flows into
the ureter and is transported to the bladder to be stored.
B. Each kidney contains more than a million microscopic
functional units called nephrons. Nephrons consist of
vascular and tubular components. - Filtration occurs in the glomerulus, which receives
blood from an afferent arteriole. - Glomerular blood is drained by an efferent arteriole,
which delivers blood to peritubular capillaries that
surround the nephron tubules. - The glomerular (Bowman’s) capsule and the proximal
and distal convoluted tubules are located in the cortex. - The loop of Henle is located in the medulla.
- Filtrate from the distal convoluted tubule is drained into
collecting ducts, which plunge through the medulla to
empty urine into the calyces.
17.2 Glomerular Filtration 587
A. A filtrate derived from plasma in the glomerulus must pass
through a basement membrane of the glomerular capillaries and