Download The Urinary System

Primary Functions
of the Urinary System
Excretion
-The removal of organic waste products from
body fluids
Elimination
-The discharge of excess water and waste
products
Homeostatic regulation of blood
-Regulating blood volume and pressure
-Regulating plasma ion concentrations
-Stabilizing blood pH
Urinary System Organs
• Kidneys - major excretory organs
• Ureters - transport urine from kidneys to
urinary bladder
• Urinary bladder - temporary storage
reservoir for urine
• Urethra transports urine out of body
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Figure 25.1 The urinary system.
Hepatic veins (cut)
Esophagus (cut)
Inferior vena cava
Adrenal gland
Renal artery
Renal hilum
Aorta
Renal vein
Kidney
Iliac crest
Ureter
Rectum (cut)
Uterus (part of female
reproductive system)
Urinary
bladder
Urethra
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Figure 25.2b Position of the kidneys against the posterior body wall.
12th rib
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Figure 25.2a Position of the kidneys against the posterior body wall.
Anterior
Inferior
vena cava
Aorta
Peritoneum
Peritoneal cavity
(organs removed)
Supportive
tissue layers
• Renal fascia
anterior
posterior
Renal
vein
Renal
artery
• Perirenal
fat capsule
• Fibrous
capsule
Body of
vertebra L2
Body wall
Posterior
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Figure 25.3 Internal anatomy of the kidney.
Renal
hilum
Renal cortex
Renal medulla
Major calyx
Papilla of
pyramid
Renal pelvis
Minor calyx
Ureter
Renal pyramid in
renal medulla
Renal column
Fibrous capsule
Photograph of right kidney, frontal section
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Diagrammatic view
Urinary System Organs:
the Kidneys
 About the size of your
fist, the kidneys are
bean shaped organs
located in the posterior
abdominal cavity.
Urinary System Organs:
the Kidneys cont.
 the kidneys' main role is to filter water soluble
waste products from the blood, and to regulate
the water volume in the blood.
Internal Anatomy
• Renal cortex
– Granular-appearing superficial region
• Renal medulla
– Composed of cone-shaped medullary (renal)
pyramids
– Pyramids separated by renal columns
• Inward extensions of cortical tissue
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The Kidney
 Blood enters each
kidney through
the renal artery
and branches into
arterioles and
capillaries which
encompass the
medulla.
The Kidney
cont.
 Capillaries then come
into contact with the
functional unit within
the kidney called the
nephron.
 A healthy kidney has
over one million
functional nephrons
The Nephron at a Glance…
The Kidney
cont.
 The filtering unit within the nephron is called the
glomerulus. It removes water and solutes from
the blood, which collect in the Bowman’s
Capsule.
The Kidney
cont.
 The filtrate (excess water
and solutes) then pass
through tubules.
 The tubules are lined with
specially designed cells
which process the filtrate,
allowing the reabsorbtion of
water and chemicals useful
to the body, while passing on
excess water and waste
products.
Juxtaglomerular Complex (JGC)
• One per nephron
• Involves modified portions of
– Distal portion of ascending limb of nephron
loop
– Afferent (sometimes efferent) arteriole
• Important in regulation of rate of filtrate
formation and blood pressure
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Reabsorbtion and ADH
 Via both active and passive
transport, specialized cells which
line the proximal/distal tubules
respond to ADH (from the pituitary)
and aldosterone (from the adrenal
glands) effectively regulating the
re-uptake of water, conservation of
Na+ ions, and secretion of K+ ions.
The Renin-AngiotensinAlderosterone System is
a hormone system that
regulates blood pressure
and fluid balance…
 This re-absorption capacity is
essential in homeostatic regulation
of the blood.
 Angiotensinogen is
generated by the
liver and becomes
Angiotensin when
activated by Renin
secretion (from the
juxtaglomerular
apparatus within the
kidneys).
 These hormones
ellicit a cascade of
responses among
multiple body
systems to maintain
homeostasis.
 Can you trace these
pathways?....
Did you know?
 kangaroo rats produce
the most concentrated
urine of all mammals,
and only pass a few
drops per day.
 the extended Loop of
Henle, which enables the
enhanced concentration
process.
Collecting Waste Material
•The excess filtrate leads
to the renal pelvis via
collecting ducts and
eventually to the ureter.
•What is “filtrate”
referred to as at this
point?
The Kidney
cont.
 Filtered “clean”
blood (now blue) recollects and returns
to the heart via the
renal vein.
What are the structures
labeled at X and Y?
Figure 25.10a The filtration membrane.
Efferent
arteriole
Glomerular
capsular space
Cytoplasmic extensions
of podocytes
Filtration slits
Podocyte
cell body
Afferent
arteriole
Glomerular
capillary covered by
podocytes that form
the visceral layer of
glomerular capsule
Proximal
convoluted
tubule
Parietal layer
Fenestrations
of glomerular
(pores)
capsule
Glomerular capillaries and the
visceral layer of the glomerular
capsule
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Glomerular
capillary endothelium
(podocyte covering
and basement
membrane removed)
Foot
processes
of podocyte
Figure 25.10b The filtration membrane.
Filtration slits
Podocyte
cell body
Foot
processes
Filtration slits between the podocyte foot processes
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Figure 25.10c The filtration membrane.
Capillary
Filtration membrane
• Capillary endothelium
• Basement membrane
• Foot processes of podocyte
of glomerular capsule
Filtration
slit
Plasma
Fenestration
(pore)
Filtrate
in capsular
space
Slit
diaphragm
Foot
processes
of podocyte
Three layers of the filtration membrane
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The Filtration Membrane
• Macromolecules "stuck" in filtration membrane
engulfed by glomerular mesangial cells
• Allows molecules smaller than 3 nm to pass
– Water, glucose, amino acids, nitrogenous wastes
• Plasma proteins remain in blood  maintains
colloid osmotic pressure  prevents loss of all
water to capsular space
– Proteins in filtrate indicate membrane problem
© 2013 Pearson Education, Inc.
Did you know…
 The kidneys take in and process 1.25
liters of blood per minute. That’s 25% of
your total blood volume!
Filtrate = Urine
 Urine is composed primarily of water, but also
contains:
-Urea/Uric Acid- Bi-product of protein metabolism
-Dissolved Materials- Sodium, Chloride,
potassium, bicarbonate, hydrogen Ions, and various
other water soluable components.
Did you Know?...
Biliruben, the
chemical that makes
urine yellow, is
generated in the
liver. The color of
your urine is a key
hydration indicator.
Normal
Hydration
dehydration
Glomerular Filtration Rate (GFR)
• Volume of filtrate formed per minute by
both kidneys (normal = 120–125 ml/min)
• GFR directly proportional to
- primary pressure is hydrostatic pressure in
glomerulus
– Total surface area available for filtration –
glomerular mesangial cells control by
contracting
– Filtration membrane permeability – much
more permeable than other capillaries
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Regulation of Glomerular Filtration
• Constant GFR allows kidneys to make
filtrate and maintain extracellular
homeostasis
– Goal of intrinsic controls - maintain GFR in
kidney
• GFR affects systemic blood pressure
–  GFR  urine output   blood pressure,
and vice versa
– Goal of extrinsic controls - maintain systemic
blood pressure
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The Ureters
 Urine collects in the
renal pelvis and
drains through long
muscular tubes
called ureters to
the bladder.
Ureters
• Three layers of ureter wall from inside out
– Mucosa - transitional epithelium
– Muscularis – smooth muscle sheets
• Contracts in response to stretch
• Propels urine into bladder
– Adventitia – outer fibrous connective tissue
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Figure 25.19 Cross-sectional view of the ureter wall (10x).
Lumen
Mucosa
• Transitional
epithelium
• Lamina
propria
Muscularis
• Longitudinal
Layer
• Circular
layer
Adventitia
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Homeostatic Imbalance
• Renal calculi - kidney stones in renal
pelvis
– Crystallized calcium, magnesium, or uric acid
salts
• Large stones block ureter  pressure &
pain
• May be due to chronic bacterial infection,
urine retention, Ca2+ in blood, pH of
urine
• Treatment - shock wave lithotripsy –
noninvasive; shock waves shatter calculi
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The Bladder
 The urinary bladder is a hollow muscular
pouch that sits on the floor of the pelvis.
Urine enters the bladder via the ureters and
exits via the urethra.
Urinary Bladder
• Muscular sac for temporary storage of
urine
• Retroperitoneal, on pelvic floor posterior to
pubic symphysis
– Males—prostate inferior to bladder neck
– Females—anterior to vagina and uterus
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Urinary Bladder
• Openings for ureters and urethra
• Trigone
– Smooth triangular area outlined by openings
for ureters and urethra
– Infections tend to persist in this region
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Urinary Bladder
• Layers of bladder wall
– Mucosa - transitional epithelial mucosa
– Thick detrusor - three layers of smooth
muscle
– Fibrous adventitia (peritoneum on superior
surface only)
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Urinary Bladder
• Collapses when empty; rugae appear
• Expands and rises superiorly during filling
without significant rise in internal pressure
• ~ Full bladder 12 cm long; holds ~ 500 ml
– Can hold ~ twice that if necessary
– Can burst if overdistended
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Figure 25.18 Pyelogram.
Kidney
Renal
pelvis
Ureter
Urinary
bladder
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Figure 25.20a Structure of the urinary bladder and urethra.
Peritoneum
Ureter
Rugae
Detrusor
Adventitia
Ureteric orifices
Trigone of bladder
Bladder neck
Internal urethral sphincter
Prostate
Prostatic urethra
Intermediate part of the urethra
External urethral sphincter
Urogenital diaphragm
Spongy urethra
Erectile tissue of penis
External urethral orifice
Male. The long male urethra has three regions:
prostatic, intermediate, and spongy.
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Figure 25.20b Structure of the urinary bladder and urethra.
Peritoneum
Ureter
Rugae
Detrusor
Ureteric orifices
Bladder neck
Internal urethral
sphincter
Trigone
External urethral
sphincter
Urogenital diaphragm
Urethra
External urethral
orifice
Female.
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Developmental Aspects
• Three sets of embryonic kidneys form in
succession
– Pronephros degenerates but pronephric
duct persists
– Mesonephros claims this duct; becomes
mesonephric duct
– Metanephros develop by fifth week, develops
into adult kidneys and ascends
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Figure 25.22a Development of the urinary system in the embryo.
Degenerating
pronephros
Developing
digestive tract
Urogenital
ridge
Duct to
yolk sac
Mesonephros
Allantois
Cloaca
Mesonephric duct
(initially, pronephric duct)
Hindgut
Week 5
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Ureteric bud
Figure 25.22b Development of the urinary system in the embryo.
Degenerating
pronephros
Duct to yolk sac
Allantois
Body stalk
Mesonephros
Mesonephric
duct
Week 6
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Urogenital sinus
Rectum
Ureteric bud
Metanephros
Developmental Aspects
• Metanephros develops as ureteric buds
that induce mesoderm of urogenital ridge
to form nephrons
– Distal ends of ureteric buds form renal pelves,
calyces, and collecting ducts
– Proximal ends become ureters
• Kidneys excrete urine into amniotic fluid by
third month
• Cloaca subdivides into rectum, anal canal,
and urogenital sinus
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Figure 25.22c Development of the urinary system in the embryo.
Gonad
Metanephros
(kidney)
Week 7
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Urogenital
sinus
(developing
urinary
bladder)
Rectum
Figure 25.22d Development of the urinary system in the embryo.
Urinary bladder
Gonad
Urethra
Kidney
Anus
Ureter
Week 8
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Rectum
Homeostatic Imbalance
• Three common congenital abnormalities
• Horseshoe kidney
– Two kidneys fuse across midline  single Ushaped kidney; usually asymptomatic
• Hypospadias
– Urethral orifice on ventral surface of penis
– Corrected surgically at ~ 12 months
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Homeostatic Imbalance
• Polycystic kidney disease
– Many fluid-filled cysts interfere with function
• Autosomal dominant form – less severe but more
common
• Autosomal recessive – more severe
– Cause unknown but involves defect in
signaling proteins
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Developmental Aspects
• Frequent micturition in infants due to small
bladders and less-concentrated urine
• Incontinence normal in infants: control of
voluntary urethral sphincter develops with
nervous system
• E. coli bacteria account for 80% of all urinary
tract infections
• Untreated childhood streptococcal infections
may cause long-term renal damage
• Sexually transmitted diseases can also inflame
urinary tract
© 2013 Pearson Education, Inc.
Developmental Aspects
• Most elderly people have abnormal
kidneys histologically
– Kidneys shrink; nephrons decrease in size
and number; tubule cells less efficient
– GFR ½ that of young adult by age 80
• Possibly from atherosclerosis of renal arteries
• Bladder shrinks; loss of bladder tone 
nocturia and incontinence
© 2013 Pearson Education, Inc.
Did You Know?
 The world famous
astronomer Tycho Brahe
died of a complication to
his bladder, when he did
not urinate from
politeness at a dinner in
Prague 1601, eleven days
before his death.
The Urethral Sphincter
 urethral sphincter muscles
are used to control the flow of
urine, or micturition from the
urinary bladder. These
muscles surround the
urethra, effectivley sealing
the urethra shut until relaxed.
Did you Know….
 Males have a 2nd urethral
sphincter at the base of the
prostate gland (it prevent reflux
of seminal fluids into the male
bladder during ejaculation)
which is not present in females.
 Females typically must urinate
more often than males due to
the bladder sharing space with
reproductive organs.
Challenge Question
 How much urine
can your bladder
hold?
Kidney Disease
 Sometime genetic and/or
environmental factors can lead
to a decline in kidney function
over time.
 When this happens one must
undergo regular dialysis
sessions, in which a machine (a
hemodiaizer) substitutes for
regular kidney function.
Kidney Stones
 Mineral crystals can
sometimes form in the renal
pelvis and are usually
passed without notice,
however, if they get large
enough, they’re referred to
as kidney stones.
 Passing a kidney stone is
remarkably painful!
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