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The Urinary System
Glen Hookey
Eric Kolker
Justin Loeb
Michael Ross
Uston—Period 5
Overview
Animals and Waste
• Filter body fluid for toxins and unnecessary
substances
• Kidneys (bp, activation of vitamin D,
erythropoietin, wastes)
• Nitrogenous waste
Transport Epithelium
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Manage solute levels
Line many channels inside the body
Comprised of special epithelial cells
Can move solutes against gradient
Nitrogenous Wastes
• Three types: Ammonia, Urea, Uric Acid
• Ammonia
– Highly toxic, diluted with large supplies of water
• Urea
– Low toxicity, energy cost (used by mammals)
• Uric Acid
– Low toxicity, water insoluble, excreted as a paste
Excretory Processes
• Filtration
– One layer of transport epithelium (large molecules removed);
filtrate
• Reabsorption
– Active transport (glucose, amino acids, etc.)
• Secretion
– Materials added to excretory tubule
• Excretion
– Expelled as urine
Filtrate/Urine Pathway
Kidney
• Filters substances
form blood
• Adjusts filtrate’s
composition
• Returns most
substances to blood
Nephron
• Functional unit
• Packed tubules
• Surrounded by
capillaries
• Filters blood
Bowman’s Capsule
• Start of Nephron
• Glomerulus
• Filtration into
lumen:
– Water, salts
bicarbonate,
hydrogen ions,
urea, glucose,
amino acids
Proximal Tubule
• pH maintained
• Reabsorption
• Reabsorbs Na+ 
osmosis
Loop of Henle
• Descending
– Water
• Ascending
– Thin & Thick
– Passive & Active
Distal Tubule
• pH regulation
• Sodium, calcium,
potassium
Collecting Duct
• Subject to hormonal
controls
• Diseases
• Concentration of
filtrate
Urine Composition
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Excess water and solutes
Ions
Urea
Neurotransmitters
Histamine
Drugs/toxins
Osmoregulation
• Solute gradient
• Bends in nephron
• Membrane selective
permeability
• Diffusion
• Active transport
• Salt
Solute Gradient
• Membrane selective
permeability
• Interstitial fluid
• Filtrate
• Active transport
• Diffusion
Nephron Overview
Proximal
Tubule
Distal
Tubule
Descending
Loop of the
henle
Ascending
Loop of the
henle
Collecting
duct
Gradient Overview
Gradient #1: Proximal tubule
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Blood
– ~300 mosm/L
Interstitial fluid:
– ~300 mosm/L
Filtrate:
– ~300 mosm/L
– In:
• Hydrogen ions
• Ammonia
– Out:
• Bicarbonate
• Salt
• Water
• Nutrients
• Potassium ions
In cortex
Volume decreased
Osmolarity stays constant
Gradient #2: Descending Loop of
the Henle
– Interstitial fluid
• 300 - 1200 mosm/L
– Filtrate
• 300 - 1200 mosm/L
• In
– N/A
• Out
– Water
– Membrane permeable only
to water
– Salt concentration increases
– Water diffuses out
Gradient #3: Ascending Loop of
the Henle
• Ascending loop
– Interstitial fluid
• 1200 - 300 mosm/L
– Filtrate
• 1200 - 200 mosm/L
• In
– N/A
• Out
– Salt
– Membrane permeable only
to Salt
– Salt concentration decreases
– Filtrate osmolarity lowered
to increase osmolarity of
interstitial fluid
Gradient #4: Distal tubule
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Interstitial fluid
– 300 mosm/L
•
Filtrate
– 100 mosm/L
– In
• Potassium ions
• Hydrogen ions
– Out
• Salt
• Water
• Bicarbonate
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Filtrate at lowest osmolarity
Key role in determination of pH of
urine
Gradient #5: Collection duct
• Interstitial fluid
– 300 - 1200 mosm/L
• Filtrate
– 300 - 1200 mosm/L
– In
• N/A
– Out
• Salt
• Urea
• Water
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Final stage
Controls final salt output
Low salt
Water diffuses
Concentrated filtrate
Regulation #1: ADH
• Antidiuretic hormone
• Hormone
• Activated by
hypothalamus at high
blood osmolarity
• Decreases water loss
– More permeability to
water
Regulation #2: RAAS
• Renin-angiotensinaldosterone system
• Angiotensin II
• Activated at low blood
pressure/volume
• Decreases water loss
– Constricts capillaries
– More reabsorption of
salt
Regulation #3: ANF
• Atrial natriuretic factor
• Opposite of ADH and
RAAS
– Triggered by high blood
pressure/volume
– Inhibits NaCl absorption
– Increased water loss
through urine
• Disables ADH
Ureter
• Lining of ureter
• Smooth-muscle
cells contractions
• Ureter crosses
bladder wall
• Ureter in
Micturition
Urinary Bladder
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Storage organ
Bladder in micturition
Brain cells
Structure
Urethra
• Function and
location
• Cells of
Urethra
• External
Meatus
Abnormalities of the Renal System
• Acute
• Chronic
• Congenital
Congenital Problems
• Horseshoe kidneys
– Functions as one kidney
• Has to be cautious of rigorous activity
Acute Problems
• Usually reversible
• Examples: stones, infections, tumors,
inflammation, acute renal failure
• Detected by urinalysis or by pain and fever
Urinary Tract Infection (UTI)
• Occurs anywhere along the urinary tract
(kidneys, bladder)
• Women more prone than men; shorter
urethra
• Pain and fever
• Treated with antibiotics
Tumors and Stones
• Most tumors in kidneys
and bladder are
malignant
• Smokers are prone to
bladder tumors
• Stones- intensely painful
• Can be passed but some
require surgery or
ultrasound
Trauma
• Kidneys damaged by physical trauma
• People with one kidney have to avoid
potentially dangerous activities
• Blood in urine
Chronic Kidney Failure
• Dialysis (3 days a week; 4 hours)
– Cleans blood
• Only cure is
transplantation