Essentials of Human Anatomy
Urinary System
Dr Fadel Naim
Ass. Prof. Faculty of Medicine
IUG
1
General Structure and Functions
of the Urinary System
• Organs of the Urinary System:
–
–
–
–
Kidneys
Ureters
Urinary Bladder
Urethra
• Primary organs: kidneys
– filter waste products from the bloodstream
– convert the filtrate into urine.
• The Urinary Tract:
– Includes:
• ureters
• urinary bladder
• urethra
– Because they transport the urine out of the body.
Functions of the Urinary System
• Removing waste products from the bloodstream.
• Storage of urine.
– the urinary bladder is an expandable, muscular sac
that can store as much as 1 liter of urine
• Excretion of urine.
• Blood volume regulation.
– the kidneys control the volume of interstitial fluid and
blood under the direction of certain hormones
• Regulation of erythrocyte production.
– as the kidneys filter the blood, they are also indirectly
measuring the oxygen level in the blood
– Erythropoietin (EPO): hormone produced by kidney
• Released if blood oxygen levels fall
• Stimulates RBC production in red bone marrow
Kidneys: Gross and Sectional Anatomy
• Retroperitoneal
– Anterior surface covered with peritoneum
– Posterior surface against posterior abdominal
wall
Kidneys: Gross and
Sectional Anatomy
• Superior pole: T-12
• Inferior pole: L-3
• Right kidney ~ 2cm lower
than left
• Adrenal gland on superior
pole
Kidneys: Gross and Sectional Anatomy
• Hilum: concave medial border
• Renal sinus: internal space
– Houses blood vessels, lymphatic vessels, nerves
– Houses renal pelvis, renal calyces
– Also fat
Kidneys: Gross and Sectional Anatomy
• Surrounding tissues, from deep to superficial:
– Fibrous capsule (renal capsule)
• Dense irregular CT
• Covers outer surface
– Perinephric fat (adipose capsule)
• Also called perirenal fat
• Completely surrounds kidney
• Cushioning and insulation
Kidneys: Gross and
Sectional Anatomy
• Surrounding tissues, from deep to superficial:
– Renal fascia
• Dense irregular CT
• Anchors kidney to posterior wall and peritoneum
– Paranephric fat
• Between renal fascia and peritoneum
Kidneys: Gross and Sectional Anatomy
• Sectioned on a coronal plane:
– Renal Cortex
• Renal arches
• Renal columns
– Renal Medulla
•
•
•
•
Divided into renal pyramids
8 to 15 per kidney
Base against cortex
Apex called renal papilla
Kidneys: Gross and Sectional Anatomy
• Minor calyx:
– Funnel shaped
– Receives renal papilla
– 8 to 15 per kidney, one per pyramid
• Major calyx
– Fusion of minor calyces
– 2 to 3 per kidney
• Major calyces merge to form renal pelvis
• Renal Lobe
– Pyramid plus some cortical tissue
– 8 to 15 per kidney
Nephrons
• The functional filtration unit in the kidney.
• Consists of the following:
– Renal corpuscle
• Glomerulus
• Glomerular capsule (Bowman’s capsule)
– Proximal convoluted tubule (PCT)
– Nephron loop (loop of Henle)
• Ascending loop of Henle
• Descending loop of Henle
– Distal convoluted tubule (DCT)
– collectively called the renal tubule
• In both kidneys: approximately 2.5 million
nephrons.
• Are microscopic: measure about 5 centimeters in
length.
Two Types of Nephrons
• Cortical nephrons (85%)
shorter, mostly in cortex
of kidney, produce
"standard" urine
• Juxtamedullary nephrons
(15%), "juxta-next-to" the
medulla - responsive to
ADH, can concentrate
urine
Renal Blood Vessels
Ureters
• 25 cm long
• extend downward posterior
to the parietal peritoneum
• parallel to vertebral column
• in pelvic cavity, join urinary
bladder
• wall of ureter
• mucous coat
• muscular coat
• fibrous coat
Urinary Bladder
• hollow, distensible, muscular organ located within the
pelvic cavity, posterior to the symphysis pubis and inferior
to the parietal peritoneum
Urinary Bladder
• the internal floor of the bladder includes a triangular area
called the trigone which has an opening at each of three
angles
Micturition (Urination)
• The expulsion of urine from the bladder.
• Initiated by a complex sequence of events called the
micturition reflex.
• The bladder is supplied by both parasympathetic and
sympathetic nerve fibers of the autonomic nervous
system.
Urethra
• Fibromuscular tube
– exits the urinary bladder through the urethral opening
– at anteroinferior surface
• conducts urine to the exterior of the body.
• Tunica mucosa: is a protective mucous membrane
– houses clusters of mucin-producing cells called urethral
glands.
• Tunica muscularis: primarily smooth muscle fibers
– help propel urine to the outside of the body.
• Two urethral sphincters:
– Internal urethral sphincter
• restrict the release of urine until the pressure within the urinary
bladder is high enough
– External urethral sphincter
• and voluntary activities needed to release the urine are
activated.
Urethra
• The internal urethral sphincter
– involuntary (smooth muscle)
– superior sphincter surrounding the neck of the bladder,
where the urethra originates.
– a circular thickening of the detrusor muscle
– controlled by the autonomic nervous system
• The external urethral sphincter
– inferior to the internal urethral sphincter
– formed by skeletal muscle fibers of the urogenital
diaphragm.
– a voluntary sphincter
– controlled by the somatic nervous system
– this is the muscle children learn to control when they
become “toilet-trained”
Female Urethra
• Has a single function:
– to transport urine from the urinary bladder to the vestibule, an
external space immediately internal to the labia minora
• 3 to 5 centimeters long
• opens to the outside of the body at the external urethral
orifice located in the female perineum.
Male Urethra
• Urinary and reproductive functions:
– passageway for both urine and semen
• Approximately 18 to 20 centimeters long.
• Partitioned into three segments:
– prostatic urethra is approximately 3 to 4 centimeters long and
is the most dilatable portion of the urethra
• extends through the prostate gland, immediately inferior to
the male bladder, where multiple small prostatic ducts enter it
– membranous urethra is the shortest and least dilatable portion
• extends from the inferior surface of the prostate gland
through the urogenital diaphragm
– spongy urethra is the longest part (15 centimeters)
• encased within a cylinder of erectile tissue in the penis called
the corpus spongiosum
• extends to the external urethral orifice
Male versus Female
UTIs (esp. E.coli)
Cross Section of Urethra
Elimination of Urine
1.
2.
3.
4.
5.
6.
7.
8.
9.
nephrons
collecting ducts
renal papillae
minor and major calyces
renal pelvis
ureters
urinary bladder
urethra
outside
Clinical Application
Glomerulonephritis
• inflammation of glomeruli
• may be acute or chronic
• acute glomerulonephritis usually occurs as an immune reaction
to a Streptococcus infection
• antigen-antibody complexes deposited in glomeruli and cause
inflammation
• most patients recover from acute glomerulonephritis
• chronic glomerulonephritis is a progressive disease and often
involves diseases other than that caused by Streptococcus
• renal failure may result from chronic glomerulonephritis
Nephrolithiasis
Occurs when
urine
becomes too
concentrated
and
substances
crystalize.
Symptoms
arise when
stones begin
to move down
ureter causing
intense pain.
• Kidneys may sustain 90% loss of
nephrons and still not show apparent
symptoms!!!
• 2-4 % of population only have 1 kidney!
THE END