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Anatomy & Physiology: The Urinary System
Transcript of Anatomy & Physiology: The Urinary System
loop of Henle ~ 15%
DCT and Collecting Duct ~ 19%
Important because secretion:
eliminates nitrogenous wastes: urea and uric acid (because they were reabsorbed)
rids the body of excess K+ (because it, too, was reabsorbed)
controls pH (by secreting more H+)
allows molecules too big to be filtered to leave the body (penicillin, example)
Slender, muscular tubes conveying urine into the bladder via peristalsis
~ 3-4 mm diameter proximal
~1.8-2.2 mm distal
The kidneys REGULATE:
blood pressure and volume
blood calcium concentration
red blood cell concentration
The kidneys are retroperitoneal
Protected by the floating ribs
Why is the right kidney lower?
The renal corpuscle
The renal tubules
proximal convoluted tubule (PCT)
loop of Henle (descending and ascending)
distal convoluted tubule (DCT)
Formation of Urine
substances forced out through glomerular fenestrations
Problem: Because of pressure, everything small enough
gets filtered through the glomerular fenestrations
(even the good stuff)
reclaiming the good stuff back into the blood stream
to blood stream
from blood stream
(positive pressure ~ 55 mmHg)
(negative pressure ~ 30 mmHg)
(negative pressure ~ 15 mmHg)
~ 10 mmHg
with a little ATP plus a lot
of diffusion and osmosis!
moving large, unfiltered and reabsorbed toxins back into the renal tubules
Problem: Diffusion and osmosis are not selective and some of the "bad" stuff is reabsorbed
Essentially the reverse of reabsorption
Composition of urine
mostly urea, uric acid and creatinine
ions: Na+, K+, phosphate and sulfate
pH ~ 6 (but may be as high as 8)
slightly aromatic (if left standing forms NH3) clear to deep yellow (due to urochrome)
NET FILTRATION PRESSURE (NFP)
What if pressures change?
Increased blood pressure?
Decreased osmotic pressure?
Increased capsular pressure?
Remember: Water follows
How fast this occurs is the glomerular filtration rate (GFR)
Ureters, Bladder, Urethra
Storage for urine
Drains urine from
(~ 8-9 mm diameter)
Aids in micturition
Internal urethral sphincter
External urethral sphincter
Region of most
Under low blood pressure situations:
juxtaglomerular cells do not stretch
(afferent arteriole does not fill as much)
blood flow slows in the glomerulus
(too much filtrate is reabsorbed)
Because they do not stretch, the JG cells release
from the lungs
a plasma protein
very powerful vasoconstrictor
In addition, adrenal glands release
which reabsorbs more sodium
Plus, the brain releases the
which increases the permeability of the
renal tubules to water
when blood pressure is
, the kidneys release
(to cause vasoconstriction), the adrenal glands
(to reclaim lots of sodium from filtrate)
and the brain releases the
(to reclaim lots of water).
All these actions will
Be sure you can:
Ureter diameter = 1.8 mm
macula densa cells