Excretory System (pg 378)
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Maintain equilibrium by eliminating waste
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Lungs-CO2, H2O, heat (breath)
Skin-H2O, salt, heat (sweat)
Large intestines- indigestible materials (feces)
Liver-toxins, heavy metals (urine)
Kidneys- urea, uric acid (urine)
Urinary System

Maintains water balance, ion balance and
eliminates metabolic wastes
 Metabolic wastes are byproducts of cellular
respiration that have been converted to toxins by
the liver
 Ammonia (NH3) VERY TOXIC must convert to urea
 Urea (blood to kidneys)
 Uric acid (blood to kidneys)

Regulates the composition of blood
Principle Structures
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Renal Artery/Renal Vein
Ureter
Urinary Bladder
Urethra
Kidneys
Nephron
Renal Artery/Renal Vein
Renal Artery-Branches from the aorta to
carry blood to kidneys to be cleaned
 Renal Vein-Joins with inferior vena cava
to carry cleaned blood back to heart

Ureter
Tubes which carry urine from kidneys to
urinary bladder
 Lined with cells that secrete mucus to
protect walls
 Outside walls are smooth muscle for
peristalsis
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Urinary Bladder

Temporary storage of urine by muscular
organ behind pubic bone
 Empty looks like a deflated balloon
 Full about the size of a pear

2 rings of muscle at junction
 Internal sphincter-involuntary
 External sphincter- voluntary
200-400ml max vol over 600ml control is
lost
 1.5 L empties in 24 hours
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Urethra

Tube from bladder to exterior of body
 Longer in males
 Shorter in females
Kidneys (pg 379)
2 half kilogram fist sized on either side of
the spine on the back wall of the ab.
cavity
 May hold up to ¼ of body’s blood
 Filters waste from blood and produces
urine
 3 layers
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 Outer connective tissue-renal cortex
 Inner connective tissue-renal medulla
 Inner hollow chamber –renal pelvis
Nephron
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Functional part of the kidney
Approx 1 million slender tubules partly in
cortex and partly in medulla
Parts of the Nephron that carry
blood
Renal Artery
Afferent arterioles
Glomerulus
Efferent arterioles
Peritubular capillaries-wrap around the
kidney tubule
 Renal vein
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Parts that carry “urine”
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Bowman’s capsule
Proximal tubule
Loop of henle
Distal tubule
Collecting ducts
Nephron Functional Regions
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A Filter
A Tubule
A Duct
A Filter
Filtration structure at top of each nephron
is Bowman’s capsule
 Renal artery enters and splits into
glomerulus
 Walls of glomerulus act as a filter

 impermeable to proteins, large molecules and red
blood cells
 Permeable to water, small molecules, ions and urea

Filtered fluid that leaves glomerulus and
enters Bowmans capsule is called filtrate
A Tubule
Bowman’s capsule connects to small long
narrow tube that is twisted back on itself
to form a loop
 This loop is a reabsorption device and has
three sections: proximal (nearby)
tubule, loop of Henle, distal (distant)
tubule
 Tubule absorbs substances that are useful
to body (glucose, ions) from filtrate and
secretes substances into surrounding
tissue
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A Duct
Tubule empties into larger channel called
the collecting duct
 Collecting duct reclaims water from filtrate
 Filtrate that remains in collecting duct is
now called urine
 Solids and water reclaimed during
reabsorption returned to body via renal
veins
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Formation of Urine
Glomerular filtration
1.

Movement of water and solutes from blood into
nephron
Tubular reabsorption
2.
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Transfer essential solutes from nephron back into
blood
Tubular secretion
3.
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Transport of additional waste materials from blood
into nephron filtrate
Water reabsorption
4.

Removes water from filtrate and returns it to
blood
Glomerular Filtration
Process that forces waste from blood
plasma into Bowman’s capsule
 Filtrate is identical to blood plasma minus
proteins and blood cells

 Plasma protein, blood cells, platelets are too large
to move through
 Water, sodium chloride, glucose, amino acids, H
ions, urea are small enough to move through
Tubular Reabsorption
Proximal Tubule
 Mitochondria in walls use ATP for active
transport of nutrients (Na+, glucose,
amino acids, K+) back into blood
 Negatively charged ions (Cl-) tag along
passively, attracted by electrical charge
on transported ions
 Water follows by osmosis
Tubular Reabsorption
Loop of Henle
 Reabsorb water and ions from filtrate
 Permeability of loop changes and water is
reabsorbed on the descending side and
sodium ions reabsorbed on the ascending
side
Tubular Reabsorption &
Secretion
Distal Tubule (under control of hormones)
 Active reabsorption of sodium depends on
needs of body
 Passive reabsorption of negative ions like
chloride because of attraction
 Decreases concentration of filtrate so
water reabsorbed by osmosis
 Potassium and hydrogen (pH regulation)
is actively secreted back into nephron
 Other substances not normally part of
body also secreted
Water Reabsorption
Collecting Duct
 Filtrate still contains lots of water
 Passive reabsorption of water from filtrate
by osmosis
 Permeability to water will depend on body
conditions
 Filtrate is 4x more concentrated by the
time it leaves duct and is approx 1% of
original filtrate volume now its called urine
Maintaining the
Excretory system
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Water regulation (osmoregulation)
Blood pressure regulation
Water regulation
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Decrease of H2O in blood
More H2O moves from cells to blood increasing
the osmotic pressure
Cells shrink
Osmoreceptors located detect pressure change in
blood
Triggers thirst and the release of ADH
ADH (antidiuretic hormone)moves to distal tubule
and collecting duct to make them more
permeable to water which will increase
reabsorption into blood
More water in blood means more water to the
cells returning the osmotic pressure to normal
Negative feedback loop
Drinking
Change in
osmotic
pressure
Cells shrink
Release of ADH
to encourage
reabsorption
Blood Pressure Regulation
Blood volume influences blood pressure
Kidneys also play a role by adjusting blood
volume
 Blood pressure receptors near glomerulus called
detect low pressure
 Release enzyme rennin which activates
angiotensin
 Angiotensin constricts blood vessels and initiates
release of aldosterone produced in adrenal gland
above kidney travels to kidney to act on distal
tube and collecting duct to increase sodium
transport which causes fluid level to increase
 Increase fluid level means higher blood voluem
therefore pressure change
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Negative Feedback loop
Constrict blood
vessels
Change in blood
pressure
Renin initiates
activation of
Angiotensin
Release of
Aldosterone
Increase in NaCl
reabsorption
and
Fluid level in
body increases
Disorders of Urinary System
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Diabetes mellitus
Diabetes insipidus
Bright’s Disease
Kidney Stones
Gout
Nephrosis
Toxemia