The Urinary System
Learning Outcomes
 Describe the structure, location, and functions of the
kidney.
 Define the term nephron and describe its structure.
 Explain how nephrons filter blood and form urine.
 Describe the locations, structures, and functions of the
ureters, bladder, and urethra.
 Explain how urination is controlled.
 Describe the causes, signs and symptoms, and treatments
of various diseases and disorders of the urinary system.
Introduction
Kidneys
Ureters
Bladder
Urethra
 System functions to remove waste products from the
blood
 Main functional units of the kidneys are the nephrons
 Nephrons filter the blood and form the urine
The Urinary System
 Paired kidneys
 A ureter for each kidney
 Urinary bladder
 Urethra
*
*
 Kidneys are retroperitoneal organs
 Superior lumbar region of posterior abdominal wall
 Lateral surface is convex
 Medial surface is concave
 Hilus* is cleft: vessels, ureters and nerves enter and leave
 Adrenal glands* lie superior to each kidney
Note layers of
adipose (fat),
capsule, fascia
Transverse sections
show
retroperitoneal
position of kidneys
Note also:
liver, aorta
muscles on CT
 Kidney has two regions
 Cortex: outer


Columns of cortex divide medulla into “pyramids”
Medulla: inner
Darker, cone-shaped medullary or renal pyramids
 Parallel bundles of urine-collecting tubules

 The human kidney has lobes
 Pyramid and cortical tissue surrounding it
 5-11 per kidney
 Renal pelvis (=basin)
 Expanded, funnel shaped, superior part of ureter
 Branches to form two or three major calices (seen best on right pic
below)
 Each of these divides again, minor calices: collect urine from papillae of
pyramids
Main Functions of Urinary System
 Kidneys filter blood to keep it pure
 Toxins
 Metabolic wastes
 Excess water
 Excess ions
 Dispose of nitrogenous wastes from blood
 Urea
 Uric acid
 Creatinine
 Regulate the balance of water and electrolytes,
acids and bases
The Kidneys (cont.)
 Renal sinus – concave depression of the surface of
the kidney
 Hilum – point of entry for the renal artery, renal
vein, and ureter
 Renal pelvis – expansion of the ureter that further
divides into calyces
The Kidneys (cont.)
 Renal cortex – outermost portion of the kidney that
covers the pyramids and dips down between them
 Renal medulla – middle portion that also divides
into renal pyramids
 Renal column – portion of the cortex between
pyramids
The Kidneys: Nephrons
 Removes waste products from the blood
 Each kidney contains about 1 million nephrons
 Made of a renal corpuscle and a renal tubule
Extend from the Bowman’s
capsule
Composed
of a group of capillaries
of a nephron
called of
a glomerulus
 Consist
three parts:
 Glomerulus
surrounded
by
 Proximal is
convoluted
tubule
Bowman’s
 Loop of capsule
Henle
 Blood
filtration
occurs
in corpuscle
 Distal
convoluted
tubule

Renal
Tubules
Corpuscles
The Nephron
glomerulus
efferent arteriole
proximal
convoluted
tubule
blood
distal
convolute
d tubule
blood
afferent arteriole
Loop of Henle
Previous
The Kidneys – Nephrons (cont.)
Afferent Arteriole
Glomerulus

Afferent arterioles deliver
blood to the glomeruli

Efferent arterioles carry
blood from the glomeruli to
peritubular capillaries
Efferent Arteriole
Peritubular Capillaries
Veins of the Kidney
The Arteries
Aorta gives off right and left renal arteries
Renal arteries divides into 5 segmental arteries as enters hilus
of kidney
Segmentals branch into
lobar arteries
Lobars divide into
interlobars
Interlobars into arcuate
in junction of medulla and
cortex
Arcuates send
interlobular arteries into
cortex
Cortical radiate arteries
give rise to glomerular
arterioles
Vasculature of the kidney
 The glomerular capillary bed is unusual in having
arterioles going both to it and away from it
(afferent and efferent), instead of a vein going
away as most
 It is also unusual in having two capillary beds in
series (one following the other)
Apply Your Knowledge
What are the functions of the kidney?
ANSWER: The kidney removes metabolic waste products from the blood,
secretes erythropoietin to help regulate RBC production, and secretes renin to
help regulate the BP.
Correct!
Urine Formation: Glomerular Filtration
 First process occurs in renal
corpuscles
 Fluid part of the blood is forced
from glomerulous into Bowman’s
capsule
 Becomes glomerular filtrate
To right is a single, generalized uriniferous tubule
More than a million of these tubules act together to form the
urine
Two major parts
1. A urine-forming nephron
2. A collecting duct which concentrates urine by removing water
from it
Urine Formation: Glomerular Filtration
(cont.)
 Factors affecting glomerular filtration
 Filtration pressure – amount of pressure
that forces filtrate from the glomerulus
into Bowman’s capsule.


Determined by blood pressure
Rate of filtration – sympathetic nervous
system control

Constriction of afferent arterioles decreases
filtration pressure
Urine Formation: Tubular Reabsorption
 Second process in urine formation
 Blood reabsorbs needed substances from the proximal
convoluted tubule
 Glomerular filtrate  proximal convoluted tubule
 Nutrients, water, and ions pass through the walls of the
renal tubule into the peritubular capillaries
 Water reabsorption depends on hormones
 Antidiuretic hormone (ADH)
 Aldosterone
 Both increase water reabsorption, which decreases urine
production
Urine Formation: Tubular Secretion
 Third process of
urine formation
 Substances move
from blood in the
peritubular
capillaries into the
renal tubules
 Secreted substances

Drugs

Hydrogen ions

Waste products
Tubular Reabsorption
Tubular Secretion
Understand at least this much:
Filtration
a. Fluid is squeezed out of
the glomerular capillary
bed
Resorption
b. Most nutrients, water ad
essential ions are
returned to the blood of
the peritubular
capillaries
Secretion
c. Moves additional
undesirable molecules
into tubule from blood
of peritubular capillaries
Helpful Sites to Checkout
 http://www.sumanasinc.com/webcontent/animatio
ns/content/kidney.html
 http://www.kidney.org.au/flash/kidney_animation/
kidneys.html
Urine Formation (cont.)
 Urine composition


Mostly water
Urea and uric acid


Formed by the breakdown of proteins and nucleic acids
Trace amounts of amino acids and various ions
 Secretion of waste products helps maintain the
acid-base balance
Apply Your Knowledge
Match the following:
ANSWER:
B Second process in urine formation
___
C
A. Glomerular filtration
___ Substances move from blood into renal tubules
B. Tubular reabsorption
A Depends on filtration pressure
___
C. Tubular secretion
C Third process of urine formation
___
A First process of urine formation
___
B Filtrate flows into the proximal convoluted tubule
___
Nice
Job!
Ureters, Urinary Bladder, and Urethra
 The Ureters





Long muscular tubes
Carry urine to the bladder
 Peristalsis – rhythmic
muscular contraction of
ureters
Slender tubes about 25 cm
(10 “) long leaving each
renal pelvis
One for each kidney
carrying urine to the
bladder
This oblique entry helps
prevent backflow of urine
Ureters, Urinary Bladder, and Urethra
(cont.)
 Urinary bladder






Expandable muscular organ
 Stores up to 600 ml urine on average
Stores and expels urine
Lies on pelvic floor posterior to pubic symphysis
 Males: anterior to rectum
 Females: just anterior to the vagina and uterus
Detrusor muscle – smooth muscle in wall of bladder
Trigone – triangle on internal floor of bladder formed by urethra
and ureters
Micturation
 Process of urination
 Stretching of bladder triggers process
 Approximately 150cc of urine
Ureters, Urinary Bladder, and Urethra
(cont.)
 Urination
 External
urethral
sphincter relaxes
 Micturation reflex –
impulses from pons
and hypothalamus
 Detrusor muscle
contracts
 Urine expelled
Ureters, Urinary Bladder, and Urethra
(cont.)
 Urethra
Tube that moves urine from the bladder to the outside
world
 Smooth muscle with inner mucosa

Changes from transitional through stages to stratified squamous
near end
 Drains urine out of the bladder and body

Male: about 20 cm (8”) long
 Female: 3-4 cm (1.5”) long


Short length is why females have more urinary tract infections
than males - ascending bacteria from stool contamination
 Urethral sphincters
 Internal: involuntary sphincter of smooth muscle
 External: skeletal muscle inhibits urination voluntarily
until proper time (levator anni muscle also helps
voluntary constriction)
Males: urethra has
three regions (see
right)
_________trigone
1. Prostatic urethra__________
2. Membranous urethra____
3. Spongy or penile urethra_____
female
Apply Your Knowledge
True or False:
ANSWER:
___
T Ureters move urine by peristalsis.
trigone
F The detrusor is formed by the openings of the ureters and urethra.
___
T The process of micturition is triggered when the bladder contains
___
about
150 ml urine.
ureters
F The urethra move urine from the kidney to the bladder.
___
males
F The urethra is longer in females.
___
T Contraction of the detrusor muscle pushes urine from the bladder.
___
Diseases and Disorders of the Urinary
System
Disease/Disorder
Acute renal failure
Description
Sudden loss of kidney function; may be
reversible with treatment
Chronic renal
Kidneys slowly use ability to function; not
failure
reversible
Cystitis
Urinary bladder infection; more common in
females
Glomerulonephritis Inflammation of the glomeruli of the kidney;
one cause of chronic renal failure
Incontinence
Inability to control urination
Diseases and Disorders of the Urinary
System
Disease/Disorder
Description
Polycystic kidney
disease
Enlargement of kidneys because of the
presence of many cysts within them; slow,
progressive disease
Complicated urinary tract infection; starts
with a bladder infection and spreads to both
kidneys; can be acute or chronic
Kidney stones; can become lodged in ducts
within kidneys or ureters
Pyelonephritis
Renal calculi
Apply Your Knowledge
Matching: ANSWER:
___
A Complicated urinary tract infection A. Pyelonephritis
___
C Inability to control urination
B. Glomerulonephritis
E Kidney stones
___
C. Incontinence
___
D Slow loss of kidney function
D. Chronic renal failure
F Bladder infection
___
E. Renal calculi
B Inflammation of the glomeruli
___
F. Cystitis
H Kidney enlargement due to cysts
___
G Sudden loss of kidney function
___
G. Acute renal failure
GO
O
D
JO
B!
H. Polycystic kidney disease
Breaching Homeostasis
1. Diabetic Kidney Disease
If glucose stays in the blood instead of breaking down, it
can act like a poison, damaging the nephrons.
2. High Blood Pressure
-can damage the small blood vessels in the kidneys so they
can’t filter wastes.
3. Glomerular Diseases
-attack the tiny blood vessels, glomeruli, within the kidney.
The first sign of a glomerular disease is often too much
protein in the urine. Another common sign is blood in the
urine. Glomerular diseases can slowly destroy kidney
function.
Breaching Homeostasis
4. Inherited and Congenital Kidney Diseases
Example: Polycystic kidney disease (PKD), for example, is
a genetic disorder in which many cysts grow in the kidneys.
5. Trauma, such as a direct and forceful blow to the kidneys,
can lead to kidney disease
6. Ingestions of poisons.
What happens when kidneys fail completely?
The body fills with extra water and waste
products (uremia). Hands or feet may swell.
A person will feel tired and weak because the
body needs clean blood to function properly.
2. Untreated uremia may lead to seizures or
coma and will ultimately result in death.
3. A person whose kidneys stop working
completely will need to undergo dialysis
or kidney transplantation.
1.
Treatment
 Dialysis
Home dialysis
 Transplant
Live Donor Transplant
In Summary
 The organs of the urinary system include the




kidneys, ureters, bladder, and urethra
The kidneys remove metabolic waste products
from the blood and secrete erythropoietin and
renin
Urine travels through the ureters to the bladder
Stretching of the bladder triggers micturition reflex
Urine travels from the bladder through the urethra
to the outside world
This too shall pass—
just like a kidney
stone.
~H. Madson