The urinary system consists of the kidneys, ureters, urinary bladder, and urethra. The kidneys filter waste from the blood to produce urine. The ureters carry urine from the kidneys to the urinary bladder, which stores urine temporarily. The urethra then carries urine from the bladder to exit the body. Together, these organs work to regulate fluid balance and remove waste via urine production and excretion.

1. Anatomy of the urinary
system
1
The urinary system consists of:
Two kidneys
Two ureters
One urinary bladder and
One urethra
FUNCTIONS OF THE URINARY SYSTEM
1. Kidneys regulate blood volume and composition; help regulate
blood pressure, pH, and glucose levels; produce two hormones
(calcitriol and erythropoietin); and excrete wastes in urine.
2. Ureters transport urine from kidneys to urinary bladder.
3. Urinary bladder stores urine and expels it into urethra.
4. Urethra discharges urine from body.
do the major work of the urinary system
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2. THE URINARY SYSTEM
The urinary system
consists of:
• The kidneys: which
excrete urine
• The ureters: convey
urine from the
kidneys to the
urinary bladder
• The urinary bladder:
stores urine
temporarily
• The urethra: carries
urine from the
bladder to the
exterior of the body 2
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3. Functions of the Kidneys
• Filters
useful
blood,
blood plasma, separates waste from
chemicals, returns useful substances
eliminates wastes
to
• Regulate blood volume and pressure by
eliminating or conserving water
• Regulate the osmolarity of the
controlling the relative amounts
solutes eliminated
Secretes enzyme, renin, which
body fluids by
of water and
• activates
hormonal mechanisms that control blood
pressure and electrolyte balance
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4. Functions of the Kidneys
• Secretes the hormone, erythropoietin, which
stimulates the production of red blood cells
Collaborate with the lungs to regulate the CO2
and acid–base balance of body fluids
Final step in synthesizing hormone, calcitriol,
which contributes to calcium homeostasis
Gluconeogenesis from amino acids in extreme
starvation
•
•
•
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5. Mnemonic for kidney functions
Just remember ' A WET BED', which stands for:
•Maintaining ACID-base balance
•Maintaining WATER balance
•ELECTROLYTE balance
•TOXIN removal
•BLOOD Pressure control
•Making ERYTHROPOIETIN
•Vitamin D metabolism
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6. Anatomy of the kidneys
• Are paired , bean-shaped
retroperitoneal organs in
the posterior abdominal
region
• Location: between T12-
L3 vertebrae but the right
kidney lies slightly inferior
in position to the left
kidney due to the Right
lobe of the Liver
6
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7. Shape and Measurements
• Shape: Bean shaped.
• Measurements:
• Length: 11 cm.
– (left kidney is slightly longer
and narrower).
• Width: 6 cm.
• Weight: 150 g in males; 135
g in females.
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8. HILUM
• The medial border (central part) of the kidney presents a
deep vertical slit called hilum.
• It transmits, from before backward, the following
structures
1. Renal vein.
2. Renal artery.
3. Renal pelvis.
4. Subsidiary branch of renal artery.
In addition to the above structures the hilum also transmits
lymphatics and nerves, the latter being sympathetic and
mainly vasomotor in nature.
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9. Relationship of structures passing through the
hilum of kidney
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10. CAPSULES (COVERINGS) OF KIDNEY
• From within outwards, the kidney is surrounded by four
capsules/coverings as follows
1. Fibrous capsule (true capsule): a thin membrane which closely
invests the kidney
2. Perirenal (perinephric) fat: a layer of adipose tissue, surrounding
the fibrous capsule
3. Renal fascia (false capsule): It is a fibroareolar sheath, which
surrounds the kidney and perirenal fat.
4. Outside the fascia is the most superficial layer – a layer of fat
tissue called the Paranephric fat.
This layer sits posteriorly and posterolaterally to each kidney and
separates it from the muscles of the abdominal wall.
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12. INTERNAL ANATOMY OF KIDNEYS
• Each kidney consists of an outer renal cortex and an
inner renal medulla
• The renal cortex is a continuous band of pale tissue
that completely surrounds the renal medulla
• The renal medulla consists of several cone-shaped
renal pyramids. The base (wider end) of each pyramid
faces the renal cortex, and its apex (narrower end),
called a renal papilla, points toward the renal hilum.
12
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13. • The kidneys are supplied by the renal arteries.
• Usually there is one renal artery for each kidney,
• The renal arteries arise directly from the abdominal aorta
just below the origin of the superior mesenteric artery
(i.e.,at the level of intervertebral disc between L1 and L2).
• The renal arteries have a blood flow in excess of 1
L/minute.
• Kidneys account for only 0.4% of body weight, they
• receive about 21% of the cardiac output (renal fraction)
Renal Circulation
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14. Renal Circulation
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Interlobular
artery and vein
Interlobar
artery and vein
Segmental
artery
Aorta Inferior vena cava
Renal a. Renal v.
Renal
medulla
Segmental a.
Renal
artery
and
vein
Interlobar a. Interlobar v.
Renal
cortex
Arcuate a. Arcuate v.
Interlobular v.
Interlobular a.
Arcuate
artery
and vein
Peritubular capillaries
Afferent arteriole Vasa recta
Efferent arteriole
Glomerulus
(a) (b)
Kidneys receive 21% of cardiac output
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15. NEPHRONS
Structural units of Kidneys
15
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16. Nephron
 Each kidney contains
1 - 1.4 million nephrons
 Each renal lobe contains
hundreds or thousands
of nephrons
 Each nephron originates
in the cortex, at the
renal corpuscle
associated with
glomerular capillaries
16
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17. 17
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18. Parts of a Nephron
A. Renal corpuscle – filters blood plasma
• Glomerulus: capillary network
• Glomerular (Bowman’s) capsule: double-walled
cup surrounding glomerulus
18
B. Renal tubule – filtered fluid passes into
• Proximal tubule
• Descending and ascending loop of Henle (nephron loop)
• Distal tubule
• Connecting tubule- connects the DT with the collecting
tubule
• Collecting tubules (are not part of nephron)
Components of renal corpuscle
Has three sections
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19. 19
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20. Renal Corpuscles
Bowman’s capsule: comprises outer parietal and
inner visceral layer
External parietal layer forms the outer surface of
the capsule consists of simple squamous
epithelium
Internal visceral layer is composed of complex
epithelial cells called podocytes
Space between the two capsular layer called
urinary or capsular space
20
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21. 21
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22. Filtration Barrier
3 layered components:
 Fenestrated glomerular endothelium
 Filtration slits between podocyte processes
 A common basal lamina
22
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23. Filtration slit
Pedicel of podocyte
Fenestration (pore) of
glomerular endothelial cell
Basal lamina
Lumen of glomerulus
(b) Filtration membrane
78,000x
(a) Details of filtration membrane
Filtration slit
Pedicel
23
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24. The Renal Tubule
• Renal (uriniferous) tubule—a duct that leads away from
the glomerular capsule and ends at the tip of the medullary
pyramid
Divided into four regions
– Proximal convoluted tubule, nephron loop, distal convoluted tubule:
parts of one nephron
– Collecting duct receives fluid from many nephrons
•
• Proximal convoluted tubule (PCT)—arises from
glomerular capsule
– Longest and most coiled region
– Simple cuboidal epithelium with prominent microvilli for
absorption
majority
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25. The Renal Tubule
Nephron loop (loop of Henle)—long U-shaped portion of renal
tubule
•
–
–
Descending limb and ascending limb
Thick segments have simple cuboidal epithelium
• Heavily engaged in the active transport of salts and have many
mitochondria
Thin segment has simple squamous epithelium
• Forms lower part of descending limb
• Cells very permeable to water
–
• Distal convoluted tubule (DCT)—begins
ascending limb reenters the cortex
shortly after the
–
–
–
Shorter and less coiled than PCT
Cuboidal epithelium without microvilli
DCT is the end of the nephron
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26. The Renal Tubule
Collecting duct—receives fluid from the DCTs
nephrons as it passes back into the medulla
• of several
•
Flow of fluid from the point where the glomerular filtrate is
formed to the point where urine leaves the body:
glomerular capsule → proximal convoluted tubule →
nephron loop → distal convoluted tubule → collecting duct
→ papillary duct → minor calyx → major calyx → renal
pelvis → ureter → urinary bladder → urethra
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Ureter

28. Intr
oduction
• The ureter is a narrow, thick•
walled, expansile muscular
tube.
Conveys urine from the kidney
to the urinary bladder.
The urine is propelled from the
•
•
kidney to the urinary bladder
by the peristaltic contractions
of the smooth muscle of the wall
of the ureter.
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29. Measurements
• Length: 25 cm (10 inches).
• Diameter: 3 mm.
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30. 30
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31. SITES OF ANATOMICAL
NARROWING CONSTRICTIO
NS
• The lumen of the ureter is not uniform throughout and presents three
constrictions at the following
At the pelviureteric junction
end of ureter. It is the upper
sites.
where the renal pelvis joins the upper
most constriction, found approximately
1.
5 cm away from the hilum of kidney.
At the pelvic brim where it crosses the common iliac artery.
At the uretero-vesical junction (i.e., where ureter enters into
the
bladder).
2.
3.
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33. The Ureters
– Three layers of ureter
• Adventitia—connective tissue layer
surrounding structures
that connects ureter to
• Muscularis—two layers of smooth muscle with third layer
in lower ureter
– Urine enters, it stretches and contracts in peristaltic wave
Mucosa—transitional epithelium
– Begins at minor calyces and extends through the bladder
•
– Lumen very narrow, easily obstructed kidney stones
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34. Clinical Anatomy
• Renal Stones (Calculi)
Malignant
• Tumors of the Kidney
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35. Urinary Bladder
• A hollow organ with strong
muscular walls
• Is characterized by its
distensibility
• Is a temporary reservoir
for urine
• Varies in size, shape,
position, and relationships
according to its content
and age of the person
35
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36. Urinary Bladder
• Anatomically, it has:
an apex, body,
fundus, and neck
• It also has four
surfaces superior,
two inferolateral,
and posterior
36
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37. Cont..
It plays two main roles:
• Temporary storage of urine – the bladder is a
hollow organ with distensible walls. It has a
folded internal lining (known as rugae), which
allows it to accommodate up to 400-600ml of
urine in healthy adults.
• Assists in the expulsion of urine – the
musculature of the bladder contracts during
micturition, with concomitant relaxation of the
sphincters.
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38. Musculature
• The musculature of the bladder plays a key role in the
storage and emptying of urine.
• The bladder wall contains specialized smooth muscle –
known as detrusor muscle.
• It receives innervation from both the sympathetic and
parasympathetic nervous systems.
• The fibers of the detrusor muscle often
become hypertrophic (presenting as prominent
trabeculae) in order to compensate for increased
workload of the bladder emptying.
• This is very common in conditions that obstruct the urine
outflow such as benign prostatic hyperplasia.
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39. Cont…
• There are also two muscular sphincters located in the
urethra:
• Internal urethral sphincter:
– Male – consists of circular smooth fibres, which are under
autonomic control. It is thought to prevent seminal
regurgitation during ejaculation.
– Females – thought to be a functional sphincter (i.e. no
sphincteric muscle present). It is formed by the anatomy of
the bladder neck and proximal urethra.
• External urethral sphincter – has the same structure in
both sexes. It is skeletal muscle, and under voluntary
control.
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40. Vasculature
1. The principal arteries supplying blood to the bladder are:
– superior and inferior vesical arteries which are the branches of
anterior division of internal iliac arteries.
2. The other arteries which make small contribution in
supplying the lower part of the bladder are:
(a) Obturator and inferior gluteal arteries.
(b) Uterine and vaginal arteries in the female.
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41. NERVE SUPPLY
Motor Innervation
• It is provided by the parasympathetic, sympathetic, and somatic
fibres.
1. Parasympathetic fibres (nervi erigentes) are derived from S2, S3, S4
(spinal micturition centre) segments of the spinal cord.
• They are motor to the detrusor muscle and inhibitory to the
sphincter vesicae (internal urethral sphincter).
2. Sympathetic fibres are derived from T11, T12 thoracic and L1, L2
lumbar segments of the spinal cord.
• They are inhibitory to the detrusor and motor to the
sphincter vesicae.
3. Somatic fibres (pudendal nerve) are derived from S2, S3, S4
spinal segments. They are motor to the external urethral
sphincter.
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42. Cont..
• The sympathetic innervation is responsible
for the filling of the bladder
• Parasympathetic innervation for the
emptying of the bladder.
• The somatic innervation is responsible for
voluntary control of micturition.
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44. Urethra
44
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45. The Urethra
• The urinary bladder is drained by a single tubular
urethra which communicates with the exterior
• The female urethra is short and wide but the male
one is long and forms the common pathway for urine
and semen
• The wall of the urethra is formed of mucous
membrane, elastic tissue and smooth muscle
45
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46. 46
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47. The Male Urethra
• Is a muscular tube (18 - 22 cm long) that conveys
urine from the internal urethral orifice of the urinary
bladder to the external urethral orifice, located at
the tip of the glans of penis in males
• The urethra also provides an exit for semen (sperms
and glandular secretions)
47
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48. 48
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49. Male Bladder and Urethra
• 18 cm long
• Internal urethral sphincter
• External urethral sphincter
• 3 regions
– prostatic urethra
• during orgasm receives semen
– membranous urethra
• passes through pelvic cavity(deep perineal
muscles
– penile urethra
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50. The Female Urethra
• Is 3 -5 cm long
• The musculature surrounding the internal urethral
orifice of the female bladder is not organized into an
internal sphincter
• In females, the external urethral orifice is located in
the vestibule, directly anterior to the vaginal orifice
• The urethra lies anterior to the vagina (forming an
elevation in the anterior vaginal wall)
50
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51. 51
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52. Female Urethra
• 3 to 5 cm long
• External urethral orifice
– between vaginal orifice and
clitoris
• Internal urethral sphincter
– detrusor muscle thickened,
smooth muscle, involuntary
control
• External urethral sphincter
– skeletal muscle, voluntary
control
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53. The Male vs Female Urethrae
• The female urethra is distensible because it contains
considerable elastic tissue, as well as smooth muscle
• It can be easily dilated without injury; consequently, the
passage of catheters or cystoscopes is easier in females
than in males
• Infections of the urethra, and especially the bladder, are
more common in women because the female urethra is
short, more distensible, and is open to the exterior
through the vestibule of the vagina
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