Human Urogenital System
26-1
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
26-2
Urinary System Anatomy
26-3
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
26-4
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
26-5
The Nephron
26-6
Histology of the Nephron
26-7
Internal Anatomy of Kidneys
• Renal corpuscle
– Bowman’s or Renal capsule
• Parietal layer
• Visceral layer
– Glomerulus
• Network of capillaries
goes into another capillary
bed called the peritubular
Capillaries
- Arterioles
– Afferent
• Tubules
– Proximal (convoluted)
tubule
– Loops of Henle
• Descending limb
• Ascending limb
– Distal (convoluted) tubules
• Collecting ducts
• Blood to glomerulus
– Efferent
• Drains not into veinule but
another arteriole
26-8
Renal Corpuscle
26-9
Kidney Blood Flow
26-10
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
26-11
Ureters and Urinary Bladder
26-12
Urine Formation
26-13
Filtration
• Filtration
– Renal filtrate
• Plasma minus blood
cells and blood proteins
• Most (99%) reabsorbed
• Filtration membrane
– Fenestrated
endothelium, basement
membrane and pores
formed by podocytes
• Filtration pressure
– Responsible for filtrate
formation
– Glomerular capillary
pressure (GCP) minus
capsule pressure (CP)
minus colloid osmotic
pressure (COP)
– Changes caused by
glomerular capillary
pressure
EFP = GCP – CP – COP
Where Effective filtration pressure = EFP
26-14
Filtration Pressure
26-15
Tubular Reabsorption
• Reabsorption almost 90%
takes place in Proximal
• Substances transported
tubule via
– Passive transport
– Active transport
– Cotransport
• Specialization of tubule
segments
• Distal tubule and
collecting duct affected
by hormones like ADH &
Aldosterone
– Active transport moves
Na+ across nephron
wall
– Other ions and
molecules moved by
cotransport
– Passive transport
moves water, urea,
lipid-soluble, nonpolar
compounds
26-16
Reabsorption in Proximal Nephron
26-17
Reabsorption in Loop of Henle
26-18
Reabsorption in Loop of Henle
26-19
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
26-20
Secretion of Hydrogen and
Potassium
26-21
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
26-22
Filtrate and Medullary
Concentration Gradient
26-23
Medullary Concentration and
Urea Cycling
26-24
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
26-25
Urine Concentrating Mechanism
26-26
Hormonal Mechanisms
• ADH
• Renin
– Secreted by posterior
– Produced by kidneys,
pituitary
causes production of
– Increases water
angiotensin II
permeability in distal
• Atrial natriuretic
tubules and collecting ducts
• Aldosterone
– Produced in adrenal cortex
– Affects Na+ and Cltransport in nephron and
collecting ducts
hormone
– Produced by heart when
blood pressure increases
• Inhibits ADH production
• Reduces ability of kidney
to concentrate urine
26-27
Effect of ADH on Nephron
26-28
Aldosterone Effect on Distal Tubule
26-29
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
26-30
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
26-31
Tubular Maximum
• Tubular maximum
– Maximum rate at
which a substance can
be actively absorbed
– Each substance has its
own tubular maximum
26-32
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
26-33
Micturition Reflex
26-34
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
26-35
Kidney Dialysis
26-36