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Anatomy & Physiology: The Urinary System

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james donahue

on 3 May 2016

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Transcript of Anatomy & Physiology: The Urinary System

PCT ~ 65%
loop of Henle ~ 15%
DCT and Collecting Duct ~ 19%
~
99%
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+)
Ureters
Slender, muscular tubes conveying urine into the bladder via peristalsis
(~ 3-4 mm diameter)
Urinary
System

The kidneys REGULATE:
blood composition
blood pressure and volume
blood pH
blood calcium concentration
red blood cell concentration

Kidney
Ureter
Urinary
Bladder
Urethra
The kidneys are retroperitoneal
Cortex
Medulla
Pyramids
Pelvis
Calyces
Protected by the floating ribs
Why is the right kidney lower?
The Kidney
The Nephron
The renal corpuscle
Bowman's capsule
Glomerulus
The renal tubules
proximal convoluted tubule (PCT)
loop of Henle (descending and ascending)
distal convoluted tubule (DCT)
Hmmm...
Formation of Urine
Filtration
Reabsorption
Secretion
Filtration
substances forced out through glomerular fenestrations
How?
Problem: Because of pressure, everything small enough
gets filtered through the glomerular fenestrations
(even the good stuff)
Reabsorption
reclaiming the good stuff back into the blood stream
How?
Filtration
Reabsorption
Secretion
to bladder
to blood stream
now "clean"
afferent arteriole
efferent arteriole
peritubular capillary
from blood stream
"dirty blood"
still "dirty"
blood pressure
(positive pressure ~ 55 mmHg)
osmotic pressure
(negative pressure ~ 30 mmHg)
capsular pressure
(negative pressure ~ 15 mmHg)
~ 10 mmHg
pressure!
with a little ATP plus a lot
of diffusion and osmosis!
Secretion
moving large, unfiltered and reabsorbed toxins back into the renal tubules
How?
Problem: Diffusion and osmosis are not selective and some of the "bad" stuff is reabsorbed
Essentially the reverse of reabsorption
Composition of urine
95% water
5% solids
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)
NFP

=

bp
-

op

-

cp
NFP
=
55
-

30

-

15
What if pressures change?
Increased blood pressure?
Decreased osmotic pressure?
Increased capsular pressure?
Stress!
Starvation!
Renal calculi!
Remember: Water follows
salt
How fast this occurs is the glomerular filtration rate (GFR)
Ureters, Bladder, Urethra
Urinary Bladder
Storage for urine
Urethra
Drains urine from
the bladder
(~ 8-9 mm diameter)
Detrusor muscle
Aids in micturition
Internal urethral sphincter
Involuntary
External urethral sphincter
Voluntary
Trigone
Region of most
bacterial infections
Regulating blood pressure
afferent arteriole
efferent arteriole
DCT
PCT
juxtaglomerular cells
Bowman's capsule
Under low blood pressure situations,
juxtaglomerular cells do not stretch
(the afferent arteriole does not fill)
Because they do not stretch, the JG cells release
renin
angiotensinogen
angiotensin

I

angiotensin II
renin
angiotensin
converting
enzyme

from the lungs
a plasma protein
very powerful vasoconstrictor
In addition, adrenal glands release
aldosterone
which reabsorbs more sodium

Plus, the brain releases the
antidiuretic hormone
which increases the permeability of the
renal tubules to water
In conclusion,
when blood pressure is
too low
, the kidneys release
renin

(to cause vasoconstriction), the adrenal glands
release
aldosterone
(to reclaim lots of sodium from filtrate)
and the brain releases the
antidiuretic hormone
(to reclaim lots of water).
All these actions will
raise
blood pressure.
Be sure you can:
Renal
Calculus
Full transcript