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Bellwork
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What is the definition of osmosis?
If there is a membrane that is only permeable to water
and you add salt to one side, which way does the water
flow?
Excretory system
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Responsible for the disposal of nitrogen-containing
metabolites and other waste products.
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Note: this is different from the disposal of feces which is
food that has not been absorbed into the body.
Homeostasis and osmoregulation
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Organisms must control solute concentrations to balance
ions and water
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Ex. Salmon and albatross
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Osmoconformers – isoosmotic (same concentration of
solutes as its surroundings)
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Mainly marine invertebrates
Osmoregulator – controls its internal osmolarity
Osmoregulator: Adaptations to salt and
freshwater
Osmoregulator: Seabirds
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Ex. Countercurrent exchange
Osmolarity Adaptations to environment
Kidneys
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It is unknown why we have two kidneys. What hypothesis
could you come up with for why we have two?
Things to think about
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What is the path of waste through the excretory system?
What can be filter into the nephrons?
How does the inner medulla get hyperosmotic?
What is the purpose of the osmotic gradient in the
kidney?
Why don’t the vessels around the loop of Henle take
away the hyperosmotic gradients?
How does the kidney regulate osmolarity of blood?
Review of how the kidney works
Continued
A story of a vampire bat
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As it is lapping up blood, it
creates lots of very dilute
urine to decrease the
weight of the blood.
Once they get back to
their roost, their kidneys
change physiology and
create very little
concentrated urine.
Regulating urine concentration – ADH
(Antidiuretic Hormone)
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Hypothalamus monitors osmolarity of blood
ADH increases permeability of distal tubules and
collucting ducts – increasing intake of water
Ingest salty food or loose water through sweating triggers
ADH release
Ingesting a lot of water leads to decrease in ADH
Regulating Blood volume
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The Renin-Angiotensin-Aldosterone system (RAAS)
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Increases blood volume when there is a loss, such as diarrhea
or blood loss
Juxtaglomerular apparatus senses low blood volume releasing
renen, which then cleaves Angiotensinogen which then gives
rise to angiotesin I and then angiotesin II ⇨raises blood
pressure and stimulates Aldosterone ⇨increases
sodium and water reabsorption
Regulating Blood volume
Regulating blood volume
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Atrial natriuretic (ANP) peptide opposes RAAS.
Inhibits NaCl reapsorption