2. 26-2
Urogenital System Functions
• Filtering of blood, Removal of wastes and
metabolites
• Regulation of
– blood volume and composition
– concentration of blood solutes
– pH of extracellular fluid
– blood cell synthesis
• Synthesis of Vitamin D
• Reproduction and sexual function
4. 26-4
Location and External Anatomy
of Kidneys
• Location
– Lie behind peritoneum on
posterior abdominal wall
on either side of vertebral
column
– Lumbar vertebrae and rib
cage partially protect
– Right kidney slightly lower
than left
• External Anatomy
– Renal capsule
• Surrounds each kidney
– Perirenal fat
• Engulfs renal capsule and acts as
cushioning and source of energy
– Renal fascia
• Anchors kidneys to abdominal
wall, separates from abdomen
– Hilum
• Renal artery and nerves enter and
renal vein and ureter exit kidneys
5. 26-5
Internal Anatomy of Kidneys
• Cortex: Outer area
– Renal columns
• Medulla: Inner area
– Renal pyramids
• Calyces
– Major: Converge to form
pelvis
– Minor: Papillae extend
• Nephron: Functional unit
of kidney
– Juxtamedullary
– Cortical
11. 26-11
Ureters and Urinary Bladder
• Ureters
– Tubes through which
urine flows from
kidneys to urinary
bladder
• Urinary bladder
– Stores urine
• Urethra
– Transports urine from
bladder to outside of
body
– Difference in length
between males and
females
– Sphincters
• Internal urinary
• External urinary
16. 26-16
Tubular Reabsorption
• Reabsorption almost 90%
takes place in Proximal
tubule via
– Passive transport
– Active transport
– Cotransport
• Specialization of tubule
segments
• Distal tubule and
collecting duct affected
by hormones like ADH &
Aldosterone
• Substances transported
– Active transport moves
Na+
across nephron
wall
– Other ions and
molecules moved by
cotransport
– Passive transport
moves water, urea,
lipid-soluble, nonpolar
compounds
20. 26-20
Tubular Secretion
• Substances enter proximal or distal tubules
and collecting ducts
• H+
, K+
and some substances not produced in
body are secreted by countertransport
mechanisms
22. 26-22
Urine Production
• In Proximal tubules
– Na+
and other substances
removed
– Water follows passively
– Filtrate volume reduced
• In descending limb of
loop of Henle
– Water exits passively,
solute enters
– Filtrate volume reduced
15%
• In ascending limb of
loop of Henle
– Na+
, Cl-
, K+
transported out of
filtrate
– Water remains
• In distal tubules and
collecting ducts
– Water movement out
regulated by ADH
• If absent, water not
reabsorbed and dilute urine
produced
• If ADH present, water moves
out, concentrated urine
produced
25. 26-25
Urine Concentration Mechanism
• When large volume of
water consumed
– Eliminate excess
without losing large
amounts of electrolytes
– Response is kidneys
produce large volume
of dilute urine
• When drinking water
not available
– Kidneys produce small
volume of concentrated
urine
– Removes waste and
prevents rapid
dehydration
27. 26-27
Hormonal Mechanisms
• ADH
– Secreted by posterior
pituitary
– Increases water
permeability in distal
tubules and collecting ducts
• Aldosterone
– Produced in adrenal cortex
– Affects Na+
and Cl-
transport in nephron and
collecting ducts
• Renin
– Produced by kidneys,
causes production of
angiotensin II
• Atrial natriuretic
hormone
– Produced by heart when
blood pressure increases
• Inhibits ADH production
• Reduces ability of kidney
to concentrate urine
30. 26-30
Autoregulation and
Sympathetic Stimulation
• Autoregulation
– Involves changes in
degree of constriction
in afferent arterioles
– As systemic BP
increased, afferent
arterioles constrict and
prevent increase in
renal blood flow
• Sympathetic stimulation
– Constricts small arteries
and afferent arterioles
– Decreases renal blood
flow
31. 26-31
Clearance and Tubular Load
• Plasma clearance
– Volume of plasma
cleared of a specific
substance each minute
– Used to estimate GFR
– Used to calculate renal
plasma flow
– Used to determine
which drugs or other
substances excreted by
kidney
• Tubular load
– Total amount of
substance that passes
through filtration
membrane into
nephrons each minute
– Normally glucose is
almost completed
reabsorbed
32. 26-32
Tubular Maximum
• Tubular maximum
– Maximum rate at
which a substance can
be actively absorbed
– Each substance has its
own tubular maximum
33. 26-33
Urine Flow and
Micturition Reflex
• Urine flow
– Hydrostatic pressure
forces urine through
nephron
– Peristalsis moves urine
through ureters
• Micturition reflex
– Stretch of urinary
bladder stimulates
reflex causing bladder
to contract, inhibiting
urinary sphincters
– Higher brain centers
can stimulate or inhibit
reflex
35. 26-35
Effects of Aging on Kidneys
• Gradual decrease in size of kidney
– Decrease in kidney size leads to decrease in
renal blood flow
• Decrease in number of functional nephrons
• Decrease in renin secretion and vitamin D
synthesis
• Decline in ability of nephron to secrete and
absorb
