Anatomy of the Urinary
System
Structures
• Kidneys:
• located under back muscles, behind
parietal peritoneum, above the waistline,
right slightly lower than left
• Internal structure:
• Cortex: outer layer
• Medulla: inner portion
• Pyramids: triangular sections of medulla
• Kidney…con’t
• Papilla: narrow
innermost end
of pyramid
• Pelvis:
expansion of
upper end of
ureter, inside
the kidney
• Calyces:
division of the
renal pelvis
Microscopic Structures
•
•
•
•
Nephron: functional unit of kidney
1. Renal Corpuscle:
Bowman’s capsule with glomerulus
Glomerulus: network of blood capilliaries
• 2. Renal Tubule:
• Proximal convoluted tubule: first segment
• Loop of Henle: extension of prox. Tubule;
consists of descending limb, loop and
ascending limb
Renal Tubule…con’t
• Distal convoluted tubule: extension of
ascending Loop of Henle
• Collecting Tubule: straight extension of
distal tubule
Ureters
• Long narrow tube with
expanded ends in the
kidney (renal pelvis)
• Lined with mucous
membrane
• Drains urine from
kidney to urinary
bladder
Urinary Bladder
• Elastic muscular organ, capable of great
expansion
• Lined with mucous membrane arranged
with rugae
• Stores urine before voiding
• Voiding
Urethra
• Narrow tube from urinary bladder to
exterior urinary meatus
• Lined with mucous membrane
• Passage for urine from bladder to meatus
• Passage of semen from the body
Functions
• 1. Producing and Excreting Urine
• 2. Regulates chemicals in the blood
– Electrolytes, acid base balance
• 3. maintains fluid balance
• 4. Regulate blood pressure through
secretion of renin
Formation of urine
• 3 processes:
• 1. Filtration: continually in renal corpuscle,
• glomerular blood pressure causes water
and dissolved substance to filter out of
glomeruli into bowman’s capsule,
• normal rate is 125 ml/min
• 2. Reabsorption: movement of
substances out of renal tubules into blood
in the peritubular capillaries;
• Water, nutrients, and ions are reabsorbed
• Water is reabsorbed by osmosis from
proximal tubules
• 3. Secretion: movement of substances
into urine in the distal and collecting
tubules
• Hydrogen ions, potassium ions, and
certain drugs are secreted by active
transport
• Ammonia is secreted by diffusion
Control of Urine Volume
• Posterior Pituitary hormone: ADH,
which decreases urine, by making
collecting tubules permeable to water
• If no ADH is present, collecting tubules are
practically impermeable to water
• Adrenal Cortex: aldosterone, important
in controlling reabsorbtion of sodium
Abnormal amounts of Urine
• Anuria: absence of urine
• Oliguria: scant amounts of urine
• Polyuria: excessive amounts of urine
Micturation
• Urination/Voiding
• Sphincter control:
• Internal urethral sphincter: involuntary,
located at the bladder exit
• External urethral sphincter: voluntary,
located just below the neck of the bladder
• Most learn voluntary control between 2
and 3 years of age
Emptying Reflex
•
•
•
•
Initiated by stretch reflex in bladder wall
Bladder wall contracts
Internal sphincter relaxes
External sphincter relaxes and bladder is
emptied
Disorders
• Urinary Retention: urine produced,
bladder wont empty
• Urinary Suppression: no urine produced,
but bladder will empty
• Incontinence: Voiding involuntarily
– Causes: spinal injury, stroke
– Retention may cause cystitis
Disorders con’t
• Obstructive Disorders
• Renal Calculi (kidney stones) block
ureters, intense pain, renal colic
• Neurogenic bladder: paralysis or abn
functioning of bladder, prevents normal
flow of urine out of the body
• Tumors: renal cell carcinoma & Bladder
cancer: Characterized by blood in urine
UTI’s
• Often caused by gram negative bacteria
• Escherichia coli (E. coli) causes about 80% of
UTIs in adults.
These bacteria are normally present in the colon
and may enter the urethral opening from the skin
around the anus and genitals. Women may be
more susceptible to UTI because their urethral
opening is near the source of bacteria (e.g.,
anus, vagina) and their urethra is shorter,
providing bacteria easier access to the bladder.
UTI’s con’t
• Other bacteria that cause urinary tract
infections include Staphylococcus
saprophyticus (5 to 15% of cases),
Chlamydia trachomatis, and Mycoplasma
hominis.
• Men and women infected with chlamydia
trachomatis or mycoplasma hominis can
transmit the bacteria to their partner during
sexual intercourse, causing UTI
• Uretritis: inflammation of the urethra
• Cystitis: inflammation or infection of the
bladder
• Pyelonephritis: inflammation of the renal
pelvis and connective tissues of the
kidney: acute(infectious) or chronic
(autoimmune)
Glomerular disorders
• Nephrotic syndrome:
• Proteinuria: protiens in urine
• Hypoalbuminemia: low plasma protiens
(albumin) levels
• Edema: tissue swelling caused by loss of
water from plasma as a result of
hypoalbuminemia
• Acute glomerulonephritis: caused by
delayed immune response to
streptococcal infection
Chronic Glomerulonephritis
• Slow inflammatory condition caused by
immune mechanisms and often leads to
renal failure.
Renal Failure
• Acute: abrupt reduction in kidney function
that is usually reversible
• Chronic: slow progressive loss of
nephrons, caused by a variety of
underlying diseases (BUN increases, GFR
decreases, creatinine increases
Chronic Renal Failure
• Stage 1: some nephrons lost
• Compensation by enlargement of
remaining
• BUN is kept normal
• GFR drops (up to 75%)
• Often asymptomatic, may last for years
Stage 2
• Renal insufficiency: Kidney no longer
compensates for loss of nephrons
• Remaining cant handle urea load
• BUN increases dramatically
• Kidneys ability to concentrate urine is
impaired: polyuria and dehydration occur
Stage 3
•
•
•
•
•
Called “uremia” or “uremic syndrome”
High blood urea
BUN very high
Caused by loss of kidney function
GFR low=oliguria: edema and
hypertension result
• Dialysis or kidney transplant required or
• Death occurs