Urinary System
Urinary System Basic
Anatomy
• Kidneys -filter blood
•
•
•
of toxins, regulate
water, pH, salt content
of blood (also helps
regulate blood
pressure, produces
erythropoietin)
Ureters - carry urine
to bladder
Bladder - stores urine
Urethra - allows urine
to pass out of body
Kidneys
• Are located posterior
•
to digestive organs in
a retroperitoneal
position (behind
peritoneal membrane)
Covered by
transparent
membrane called the
renal capsule
Renal Blood Supply
• Renal artery carries
•
•
blood from aorta into
kidneys at the hilus
(see diagram)
Renal vein carries
blood from kidneys to
inferior vena cava
Blood vessels branch
into tiny capillaries
inside the kidneys
Cross-section of Kidney
• Cortex (outer portion
•
of kidney)
Medulla (inner portion
of kidney)
The Nephron
Nephron
Functional unit of kidney (1
million per kidney):
Composed of:
• Glomerulus: ball of
capillaries involved in
filtration of blood- keeps
large particles (blood
cells, large proteins) out
of the filtrate (filtrate
becomes urine)
• Renal tubules: involved
in reabsorption - (putting
needed substances back
into the blood) and
secretion (moving wastes
from blood to the filtrate
to be excreted in urine)
Components of a nephron
Areas of the Nephron
1) Glomerulus (surrounded
by Bowman’s capsule) filtration
2) Proximal convoluted
tubule (PCT) reabsorption
3) Loop of Henle (descending
and ascending limbs)
4) Distal convoluted tubule
(DCT) - secretion
* The filtrate drains into the
collecting duct (not part of
the nephron) and is carried
out of the kidneys to the
ureters
1
Bowman’s
capsule
2
4
3 3
A Nephron
Collecting
duct
The Nephron
Concentration of Urine
• ADH (antidiuretic
•
•
•
hormone - released
from pituitary gland)
enhances the
reabsorption of water in
the collecting ducts
Triggered when blood
pressure and volume
are low
Makes urine very
concentrated
Urine is dilute when
ADH is not present
No
With
ADH
ADH
ADH vs. No ADH
No ADH
ADH
present
Renin-Angiotensin System
• Renin – enzyme secreted by
juxtaglomerular cells in the
kidneys in response to low
blood pressure/volume
• Leads to a cascade of
reactions that results in
production of angiotensin II,
a vasoconstrictor
• Angiotensin II stimulates
aldosterone production from
adrenal glands
• Blood pressure increases
Aldosterone
• Released from the adrenal
•
•
glands on top of the
kidneys
Leads to conservation of
sodium (and sometimes
water) and the excretion of
potassium
Raises blood pressure by
increasing blood volume
Bladder
• Holds urine (made of
•
•
smooth muscle)
Stretch receptors in wall
of bladder trigger urge to
urinate (occurs after
about 200ml of urine
collect) - maximum
capacity is about
800-1000ml
Micturition (urination)
occurs when it is
“convenient” to go (see
animation)
Micturition Reflex
Urinary Tract Infections (UTIs)
• Infection of the urinary tract
•
•
•
(most commonly urethra) by
bacteria (usually E.coli from
digestive tract)
More common in women
(shorter urethra and proximity
of urethra to anus)
Infections could spread to
bladder (cystitis) or kidney
(pyelonephritis) if not treated
Risk increases if urine flow is
obstructed or if catheters are
used frequently
Kidney Stones