9.4 WATER
BALANCE
• Humans cannot survive without water for
more than a few days (water reserves
depleted faster than food)
• Avg. adult loses 2 L of water/day (urine,
sweat, exhalation)
• A 1% drop in fluid (body mass) causes thirst,
5% drop causes extreme pain/collapse, 10%
drop causes death
Can you drink urine? What!?!?!
The body’s internal environment of extracellular
fluid (fluid that surrounds the cells/tissues
and plasma portion of blood) must remain at
a constant volume, solute content and
temperature.
Recall Osmosis….
• Hyperosmotic – solution on one side has a
high [solute] and low [water]
• Hypoosmotic – solution on one side has a
high [water] and low [solute]
• Isoosmotic – same solute and water [] on
either side. (ideal condition)
Osmoregulation & Excretion
• Osmosis is a crucial process in regulating
homeostasis
• Actively regulating osmotic pressure of bodily
fluids is known as osmoregulation.
• All organisms need to keep their intracellular
and extracellular fluids isoosmotic.
• Some species of marine animals do not need
to regulate their extracellular fluid as water
flows freely through them.
• To maintain homeostasis, cells need to
regulate their ionic balance, pH, and
[osmotic]
• Animals maintain this balance through the
process of excretion. Excretion is the
elimination of waste products and foreign
matter from the body
• In humans, the excretory system is used
When proteins are metabolized, the amino group
must be removed and discarded by the body. This
is called DEAMINATION.
The by-product of deamination is ammonia, which
is extremely toxic to the body. The liver takes one
molecule of ammonia and adds it to HCO3- to make
urea (water soluble) which is eliminated in the
urine.
Urea is 100 000 times less toxic than ammonia.
•Side note: ammonia (NH3), a water soluble gas, is quite toxic,
0.005 mg can kill a human. Fish are able to pass ammonia out
through their gills, but land animals cannot do this, they must store
ammonia and find a way to get rid of it.
Urine Output
Increased water
intake
Decreased water intake
or
Increased exercise
increased urine
output
Decreased urine output
ADH ~
ANTI DIURETIC HORMONE
• causes the kidneys to increase water
reabsorption
• produced by the hypothalamus and released
by the pituitary
• ADH controls reabsorption of the last 15% of
water that passes through the nephron in the
Loop of Henle and the distal tubule
ADH and the Nephron
• Descending loop of Henle is permeable to
water and ions, but ascending tubule is only
permeable to NaCl
• Without ADH the rest of the tubule remains
impermeable to water
• ADH makes upper part of distal tubule and
collecting duct permeable to water
• The remaining urine becomes more
concentrated
HOMEWORK:
Pg. 445 # 1-7, 9, 12
Ch. 9 Quiz will be
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