Ch 26: Urinary System
Objectives
Identify and describe
the components of the
urinary system and
their function
Describe the
(histological)
organization of the
nephron
Identify the blood vessels that supply blood to the nephrons
Describe the blood flow through and around the nephron
Functions of Urinary System
(Kidneys):
● Regulate fluid balance (fluid
volume) of the body
● Excrete organic waste products
and conserve nutrients, etc
Stabilize pH
Regulate ion concentrations in
the blood
Kidney
Location
Lateral to vertebral
column high on body
wall, under floating
ribs
in retro-peritoneal
position
Surface
Anatomy
Size of bar of soap
Bean shaped
Hilus – indentation
Three layers
 Renal fascia – fibrous tunic
 Adipose capsule – protects kidney
 Renal capsule – anchors kidney to body wall,
continuous with peritoneum
Sectional Anatomy
Cortex: outer layer, light
reddish brow, granular
appearance (due to many
capillaries)
Medulla: darker striped
appearance (due to
tubules) Subdivided into
distinct renal pyramids,
terminating with a papilla.
Separated by renal
columns from the cortex.
Fig 26-3
Urine collection:
Ducts within each renal
papilla release urine
into minor calyx
major calyx
renal pelvis
ureter
Renal Circulation
Renal Artery
Segmental arteries
Interlobar arteries
Arcuate arteries
Interlobular arteries
Afferent arterioles
Glomerulus
Efferent arterioles
Peritubular capillaries
Renal Vein
Segmental veins
Interlobar veins
Arcuate veins
Interlobular veins
Venules
Fig 26-4
Functional unit: Nephron
(>mio/kidney)

Renal corpuscle:
Fig 26-8
» Glomerulus
» Bowman’s capsule

Tubular passageways with
associated blood vessels:
»
»
»
»
PCT
LOH
DCT
CD
Fig 26-6
Filtration: Passage across Three
Barriers
Fig 26-8
Capillary endothelium
Fenestrated
What gets through?
Basement membrane
Glomerular epithelium (= visceral layer of
Bowman’s capsule)
slit pores between pedicels of podocyte
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
Juxtaglomerular Apparatus
Macula densa
+
Juxtaglomerular cells
(smooth muscle fibers from
afferent arteriole)
= Juxtaglomerular
Apparatus
= Endocrine
system structure
(renin and EPO)
Urine Transport, Storage, and
Elimination

Trace drop of urine from
kidneys to outside world

Lining of these parts?

Nephroptosis (= floating
kidneys)

Nephrolithiasis
Nephrolithiasis
Occurs when
urine
becomes too
concentrated
and
substances
crystalize.
Symptoms
arise when
stones begin
to move down
ureter causing
intense pain.
Kidney stones may form in the pelvis or
calyces of the kidney or in the ureter.
Anatomy of Urinary Bladder




Retroperitoneal, behind pubis
Internal folds - rugae - permit expansion (max.
holding capacity ~ 1L)
Trigone - area at base delineated by openings of
ureters and urethra - without muscle
Internal urethral sphincter - involuntary sphincter
Histology
1. transitional epithelium
2. detrusor muscle – smooth muscle
Fig 26.10
Urethra
External urethral sphincters – voluntary at pelvic
floor
Female - short – from base of bladder to vestibule
Male
1. prostatic urethra – from base of bladder through
prostate gland
2. membranous urethra – between prostate gland &
base of penis
3. penile (spongy) urethra – traverses penis to orifice
Male versus Female
UTIs (esp. E.coli)
The End
Manneken Pis
Fountain
Brussels, 1619

Kidneys may
sustain 90% loss
of nephrons and
still not show
apparent
symptoms!!!

2-4 % of
population only
have 1 kidney!