25
The Urinary System
Kidney Anatomy
(pp. 955–963)
Location and External Anatomy
(pp. 955–956)
Internal Gross Anatomy (pp. 956–957)
Blood and Nerve Supply (pp. 957–958)
Nephrons (pp. 958–963)
Kidney Physiology: Mechanisms
of Urine Formation
(pp. 963–977)
Urine Formation, Step 1: Glomerular
Filtration (pp. 965–968)
Urine Formation, Step 2: Tubular
Reabsorption (pp. 968–972)
Urine Formation, Step 3: Tubular
Secretion (pp. 972–973)
Regulation of Urine Concentration
and Volume (pp. 973–977)
Clinical Evaluation of Kidney
Function
(pp. 977–979)
Renal Clearance (p. 978)
Urine (pp. 978–979)
Urine Transport, Storage,
and Elimination
(pp. 979–982)
Ureters (pp. 979–980)
Urinary Bladder (pp. 980–981)
Urethra (pp. 981–982)
Micturition (p. 982)
Developmental Aspects of the Urinary
System
(pp. 982–985)
954
E
very day the kidneys filter nearly 200 liters of fluid
from our blood-
stream, allowing toxins, metabolic wastes, and excess ions to leave the body in
urine while returning needed substances to the blood. Much like a water purifica-
tion plant that keeps a city’s water drinkable and disposes of its wastes, the kidneys are
usually unappreciated until they malfunction and body fluids become contaminated.
Te kidneys perform a chemical balancing act that would be tricky even for the best
chemical engineer. Tey maintain the body’s internal environment by:
Regulating the total volume of water in the body and the total concentration of solutes
in that water (osmolality).
Regulating the concentrations of the various ions in the extracellular fluids. (Even
relatively small changes in some ion concentrations such as K
1
can be fatal.)
Ensuring long-term acid-base balance.
Excreting metabolic wastes and foreign substances such as drugs or toxins.
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