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Excretion by the Kidney
Urea
-nitrogenous waste
-made by liver-excess amino acids in blood
-toxic
Why must nitrogenous waste be excreted?
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1 Filtration by the Kidney
Renal
artery
Ureter
Renal
vein
Supplied with blood
from renal artery
Inside it splits into
many fine capillaries
Each capillary
supplies blood to
hundreds of
thousands of tinyfiltration units called
nephrons
Lets have a
look at a
nephron!!!
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1. Glomerulus brings a largesurface area of bloodcapillaries in close contact
with Bowmans capsule
2. Liquid filtered from bloodunder pressure (filtration)
3. Glomerular filtrate producedcontaining:
-water
-glucose
-salts
-urea
(Protein molecules and red blood
cells do not pass into tubule as
they are TOO BIG!!!!)
Blood from
renal artery
enters wide
capillary
Blood travelthrough
narrow
capillary
towards ren
vein
Glomerularfiltrate
Filtration
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Think
Which feature of the glomerulus helps the
process of filtration?
Which 4 components of unfiltered blood
appear in the glomerular filtrate?
Why do blood cells and protein molecules
not appear in the glomerular filtrate?
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Key Words!!
Nephron: structure in the kidney that acts asa microscopic filtration unit
Glomerulus: dense mass of very fine
blood capillaries at thenephron that act as a filter
Bowmans capusle: cup-shaped part of thenephron that holds a
glomerulus and collects theproducts of filtration from it
Glomerular filtrate: liquid removed from the blood byfiltration in the kidney
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2 Reabsorption by the Kidney
Once the main components of glomerulur filtrate
enter the bloodstream
-they are no longer in bloodstream
If nothing more happened in the nephron then all
the useful stuff would be lost in the urine!
Therefore, glucose, water and some salts need
to be reabsorbed!
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Glucose
reabsorbed
Variable amounts of water
and salts reabsorbed and
filtrate gradually turning intourine
More water
reabsorbed
Final urine
containing:
-excess water
-unneeded salts
-waste urea
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Think.
Which three components of the glomerular
filtrate are reabsorbed?
Why is it important for these to be
reabsorbed?
Which substances are present in the final
urine?
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Summary of kidney function
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2 Controlling Water
Concentration Blood
-important part of internal environment
-constantly changing water concentration-e.g. exercising
drinking lots of water
The body uses negative feedback controlto regulate water content of the blood
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How does it work?
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Control of Water animation
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