Urinary System
Functions of Urinary System
• Filter Blood
• Regulation of Blood Volume/Pressure
[renin]
• Regulation of the solute concentration
of the Blood: Na+, Cl-, K+, Ca+2, HPO4-2
• pH regulation of extracellular fluid
• Regulation of RBC synthesis
[erythropoietin]
• Vitamin D activation
Anatomy of the Urinary System
Kidneys
• Primary organs of the urinary system
• Located between the 12th thoracic and 3rd
lumbar vertebrae. Right is usually lower due
to liver.
• Lie in shallow depressions against the
posterior abdominal wall and behind the
parietal peritoneum – retroperitoneal
• Held in place by connective tissue [renal
fascia] and surrounded by thick layer of
adipose [perirenal fat]
• Each kidney is
approx. 3 cm thick,
6 cm wide and 12
cm long
• Indentation on
medial aspect =
hilus – where renal
vessels and ureter
transverse
• Pyramids
• Papillae
• Calyces –
major/minor
• Columns
Nephrons
•Each kidney contains over
a million nephrons
[functional structure]
Blood enters the nephron from a
network that begins with the
renal artery. This artery
branches into smaller and smaller
vessels –and enters each nephron
as an afferent arteriole. The
afferent arteriole ends in a
specialized capillary called the
Glomerulus. Each kidney has a
glomerulus contained in Bowman’s
Capsule. Any cells that are too
large to pass into the nephron are
returned to the venous blood
supply via the efferent arteriole.
The efferent arteriole will
divides to become the peritubular
capillaries.
Nephron
• Proximal Convoluted Tubule [PCT] – H2O,
Na+, Cl-, glucose, amino acids, Ca+, Mg+,
K+, micronutrients [, zn,cu,fe]
• Descending Loop – H2O, Cl-, Na+
• Ascending Loop – Cl-, Na+ [ not
permeable to H2O]
• Distal Convoluted Tubule [DCT] – H20,
Na+, Cl-, HCO3-
URINE FORMATION
At least 500 mL (17 oz) of
urine must be eliminated
every day because this
amount of fluid is needed
to remove potential toxic
materials from the body
to maintain homeostasis.
Urine flows from the nephron
to the collecting ducts, which
extend to the tips of the
pyramids, and empty into the
calyces. All the urine will leave
the kidney via the ureters.
A normal adult eliminates
from 1.5 L (1.6 qt) to 2.3 L
(2.4 qt) of Urine a DAY,
depending on the amount
of water taken in and the
amount of water lost
through Respiration and
Perspiration.
Juxtaglomerular Apparatus
• Monitors blood pressure and secretes renin,
is formed from modified cells in the afferent
arteriole and the ascending loop of the
nephron
• The cells of the arteriole are called
juxtaglomerular cells and the cells of the loop
are called macula densa. The macular densa
cells monitor NaCl in the urine, and the
juxtaglomerular cells produce renin
Renin-Angiotensin-Aldosterone
• Renin: secreted by juxtaglomerular cells
if blood pressure in afferent arteriole
is low, or [Na+] of urine decreases as it
passes the macula densa cells.
• Renin: enters the gen’l circulation via
peritubular capillaries and activates
angiotensinogen to angiotensin I.
Angiotensin I  angiotensin II via a
converting enzyme found in the plasma.
• Angiotensin II is a vasoconstrictor, acts
on the hypothalamus causing the
sensation of thirst, salt appetite and
ADH secretion. It also causes the
secretion of aldosterone from the
adrenal cortex.
• Aldosterone [ a steroid hormone] acts
on the cells of the nephron [ esp. those
of the ascending loop and DCT] to
reabsorb more Na+.
ureters
Each ureter is about 25 cm long and carries
urine from the renal pelvis to the urinary
bladder via peristaltic waves.
.
The wall of the ureter consists of three layers.
The outermost is a fibrous coat, middle layer is
muscular [ circular & longitudinal] and the
innermost layer is called the mucosa, a
transitional epithelium that is continuous with
the lining of the renal pelvis and bladder, also
secretes a protective mucus.
The Urinary Bladder is a
‘temporary storage’ reservoir
for urine. When empty it
resides in the pelvis, when
full will rise above the
symphysis pubis.
A triangular region, called the
trigone, is formed by three
openings in the floor of the
bladder. Two are from the
ureters, and third from the
urethra. There are flaps of
mucosa covering the
openings of the ureters and
act as valves.
A band of muscles
encircles the opening to
the urethra forming the
internal urethral
sphincter.
The innermost lining of the urinary bladder is a
mucous membrane layer, continuous with the
ureters. This layer covers the transitional
epithelium. When empty, the mucosa forms folds
called rugae.
The second layer is called the submucosa. It
contains elastic connective tissue fibers.
The third layer is the muscularis: this collection of
smooth muscle is known as the detrusor muscle.
Contraction of this muscle expels urine from the
bladder.
The outermost layer is dense connective tissue.
Urethra
thin walled tube – conveys urine from bladder to
external environment.
Similar structure to ureter
Sphincters: internal urethral [involuntary] & external
urethral [ voluntary]
• Male Urethra
• 20 cm long [7-8 in]
• Transports both urine
& semen
Eternal urethral orifice
opens at tip of penis
• Female Urethra
• 3-4 cm long [1.5 in]
• External urethral
orifice opens just
anterior to the vaginal
opening
Kidney Stones
Kidney stones affect more than a million Americans each year. Twelve
to 24 million Americans will develop stones in their lifetime and the
incidence rate has increased dramatically over the last 20 years with
approximately 350,000 new stone cases reported each year.
In the United States, 7 to 10 of every 1,000 hospital admissions are due
to kidney stones.
Kidney stones are solid masses of mineral salt deposits
that are normally filtered through the kidney and voided
in urine. Urine naturally contains substances that dissolve
the waste materials that form these solids or calculi.
However, when the amounts of these salts are excessive,
the urine may be unable to dissolve them all, leaving
crystals that accumulate in the kidney and gradually
increase in size.
The stones can be as small as
a grain of sand or as large as a
golf ball. The size, shape, and
location of the stone can
cause many different
symptoms.
Most renal calculi are so small they are passed through
the urinary tract without any symptoms. Larger calculi
can obstruct the renal ducts, or become lodged in the
ureters. These larger obstructions cause sharp, severe
pain in the sides and back as they move through the
urinary tract. In medical parlance, this condition is called
renal colic.
Well, I guess you don’t
have kidney stones after
all.