Chapter 26 - Urinary System
Urine Production
1-2 L a day for normal healthy adult
 Filtration:
The movement of fluid across the filtration membrane as a result of
pressure difference. The fluid that is pulled from the blood
becomes the filtrate.
21% of the total blood is the Renal fraction from the total cardiac
output which is the blood that leaves the heart.
The filtration barrier is composed of the __________________
epithelium of the capillaries that compose the glomerulus, the
basement membrane of that epithelium, and the podocytes (specialized
cells).
The capillaries of the glomerulus are 100-1000 times more permeable
than normal capillaries. It works to prevent all blood cells and
vital proteins from leaving the capillaries, but lets all the waste
out.
Smooth muscle in the efferent and afferent arterioles allow the
pressure to be changed when needed by enlarging or constricting the
diameter of the blood vessels.
 Reabsorption: Defined: The movement of substances from the filtrate
back into the blood.
The filtrate leaves the Bowman's capsule and flows through the PCT,
DCT, to the Collecting duct - tubular reabsorption takes place here.
Inorganic salts, organic molecules, and about 99% of the filtrate
volume leave into the interstitial fluid from the lumen of the
nephron. Which epithelium do you think would be most effective at
this role of tubular reabsorption? _________________________
Amino acids, glucose, potassium, and chloride ions are actively
transported via K/Na Pumps and carrier molecules in the PCT. By the
end of the PCT 65% of the filtrate is reabsorbed.
Other things like fructose, sodium, calcium and bicarbonate ions are
moved into the interstitial space via cotransport or secondary
active transport.
Passive movement of some organics occurs in the loop of Henle via
the ______________________ epithelium (hint: think diffusion).
The permeability of H2O is greatly reduced in the DCT and collecting
duct and is under hormonal control -(ADH) Antidiuretic hormone. It
makes the walls more permeable to H20.
 Secretion: Defined: The active transport of substances into the
nephron.
Some substances (by-products of metabolism) become toxic in high
concentrations, and some drugs and other molecules not produced by
the body are removed by the nephron.
Tubular secretion can be active or passive.
Ammonia is synthesized in the epithelium of the nephron and diffuses
into the lumen.
Other substances that are actively secreted by the cuboidal cells
include: Hydrogen ions, potassium ions, penicillin, and paraaminohippuric acid.