Kidney Structure
& Function
Removing Intracellular
Waste
Glucose
Amino
acids
H2O
Mg++ Ca++
H2O
H2O
Na+ ClH2O
Na+ ClH2O
H2O
Loop of Henle
AP Biology
Collecting
duct
Animal systems evolved to support
multicellular life
aa
O2
CH
single cell
CHO
CO2
aa
NH3
CHO
O2
O2
CH
aa
CO2
CO2
aa
NH3
CO2
NH3
CO2
O2
aa
CH
NH3
CO2
NH3
AP Biology
CO2
NH3
CO2
NH3
CO2
CO2
NH3
CO2
aa
intracellular
waste
O2
NH3
but what
if the
cells are
clustered?
CHO
Diffusion too slow!
extracellular
waste
for nutrients in & waste out
Overcoming limitations of diffusion
 Evolution of exchange systems for
distributing nutrients
 circulatory system
 removing wastes
 excretory system

aa
AP Biology
aa
CH
NH3
CO2
NH3
CO2
NH3
CO2
CO2
NH3
O2
NH3
NH3
CO2
O2
systems to support
multicellular organisms
CO2
CO2
NH3
CO2
CO2
NH3
CO2
aa
CHO
Osmoregulation
hypotonic
 Water balance vs. Habitat

freshwater
 hypotonic to body fluids
 water flow into cells & salt loss

saltwater
 hypertonic to body fluids
 water loss from cells

land
hypertonic
 dry environment
 need to conserve water
 may also need to conserve salt
Why do all land animals have to conserve water?
 always lose water (breathing & waste)
AP
may
lose life while searching for water
Biology
Intracellular Waste
 What waste products
Animals
poison themselves
from the inside
by digesting
proteins!
are made inside of cells?

what do we digest our food into…
 CO2 + H2O
 lipids = CHO  CO2 + H2O
 proteins = CHON CO2 + H2O + N
 carbohydrates = CHO
lots!
very
little
 nucleic acids = CHOPN CO2 + H2O + P + N
cellular digestion…
cellular waste
NH2 =
AP Biology
ammonia
H| O||
H
N –C–C–OH
|
H
R
CO2 + H2O
Nitrogenous waste disposal
 Ammonia (NH3)

very toxic
 carcinogenic

very soluble
 easily crosses membranes

must dilute it & get rid of it… fast!
 How you get rid of nitrogenous wastes depends on

who you are (evolutionary relationship)

where you live (habitat)
aquatic
AP Biology
terrestrial
terrestrial egg layer
Nitrogen waste
 Aquatic organisms


can afford to lose water
ammonia
 most toxic
 Terrestrial


need to conserve
water
urea
 less toxic
 Terrestrial egg
layers



need to conserve water
need to protect
embryo in egg
uric acid
AP Biology
 least toxic
Freshwater animals
 Hypotonic environment

water diffuses into cells
 Manage water & waste together

remove surplus water & waste
 use surplus water to dilute ammonia & excrete it
 also diffuse ammonia continuously through gills

overcome loss of salts
 reabsorb in kidneys or active transport across gills
AP Biology
H
Land animals
 Nitrogen waste disposal on land
H
H
H
need to conserve water
 must process ammonia so less toxic

N
C
N
 urea = larger molecule = less soluble = less toxic
 2NH2 + CO2 = urea
Urea
 produced in liver
costs energy

kidney
to synthesize,
but it’s worth it!
 filter solutes out of blood
 reabsorb H2O (+ any useful solutes)
 excrete waste
 urine = urea, salts, excess sugar & H2O

AP Biology

urine is very concentrated
concentrated NH3 would be too toxic
mammals
O
Egg-laying land animals
 Nitrogen waste disposal in egg
no place to get rid of waste in egg
 need even less soluble molecule

 uric acid = BIGGER = less soluble = less toxic

birds, reptiles, insects
itty bitty
living space!
AP Biology
Uric acid
 Polymerized urea
And that folks,
is why most
male birds don’t
have a penis!
large molecule
 precipitates out of solution

 doesn’t harm embryo in egg
 white dust in egg
 adults still excrete N waste as white paste
 no liquid waste
 uric acid = white bird “poop”!
O
H
H
N
N
O
O
N
N
AP Biology
H
H
Mammalian System
blood
 Filter solutes out of blood & reabsorb
filtrate
H2O + desirable solutes
 Key functions

filtration
 fluids (water & solutes) filtered out
of blood

reabsorption
 selectively reabsorb (diffusion) needed
water + solutes back to blood

secretion
 pump out any other unwanted solutes to
urine

excretion
 expel concentrated urine (N waste +
AP Biology
solutes + toxins) from body
concentrated
urine
Mammalian Kidney
inferior
vena cava
aorta
adrenal gland
kidney
nephron
ureter
bladder
urethra
AP Biology
renal vein
& artery
microvilli on
epithelial
cells
Nephron
 Functional units of kidney

1 million nephrons
per kidney
 Function


filter out urea & other
solutes (salt, sugar…)
blood plasma filtered
into nephron
 high pressure flow

selective reabsorption of
valuable solutes & H2O
back into bloodstream
AP Biology 
greater flexibility & control
why
selective reabsorption
& not selective
filtration?
“counter current
exchange system”
How can
different sections
allow the diffusion
of different
molecules?
Mammalian kidney
 Interaction of circulatory &
excretory systems
 Circulatory system

glomerulus =
ball of capillaries
Bowman’s
capsule
Proximal
tubule
Distal
tubule
Glomerulus
 Excretory system



nephron
Bowman’s capsule
loop of Henle





AP Biology
proximal tubule
descending limb
ascending limb
distal tubule
collecting duct
Glucose
Amino
acids
H2O
Mg++ Ca++
H2O
H2O
Na+ ClH2O
Na+ ClH2O
H2O
Loop of Henle
Collecting
duct
Nephron: Filtration
 At glomerulus

filtered out of blood
H2O
 H2O
 glucose
&
solutes
 salts / ions (Na+ / Cl–)
 urea

cells &
large
molecules
not filtered out
AP Biology
 cells
 proteins
high blood pressure in kidneys
force to push (filter) H2O & solutes
out of blood vessel
BIG problems when you start out
with high blood pressure in system
hypertension = kidney damage
Nephron: Re-absorption
 Proximal tubule

reabsorbed back into blood
 NaCl
 active transport
of Na+
 Cl– follows
by diffusion
 H2O
 glucose
 HCO3 bicarbonate
 buffer for
AP Biology
blood pH
Nephron: Re-absorption
 Loop of Henle
descending limb
 reabsorbed
 H2O
 structure

 many aquaporins in
cell membranes
 high permeability
to H2O
 no Na+ or Cl– channels
 impermeable
AP Biology to salt
structure fits
function!
Nephron: Re-absorption
 Loop of Henle
ascending limb
 reabsorbed
 Na+ & Cl–
 structure

 many Na+ / Cl– channels
in cell membranes
 high permeability
to Na+ & Cl–
 no aquaporins
 impermeable to H2O
AP Biology
structure fits
function!
Nephron: Re-absorption
 Distal tubule

reabsorbed
 salts
 H2O
 bicarbonate
 HCO3 regulate blood pH
AP Biology
Nephron: Reabsorption & Excretion
 Collecting duct

reabsorbed
 H2O = through
aquaporins

excretion
 concentrated urine
 to bladder
 impermeable lining
= no channels in
cell membranes
AP Biology
Osmotic control in nephron
 How is all this re-absorption achieved?
tight osmotic
control to reduce
the energy cost
of excretion
 use diffusion
instead of
active transport
wherever possible

the value of a
counter current
exchange system
AP Biology
Summary
 Not filtered out of blood


why
selective reabsorption
& not selective
filtration?
cells
◆ proteins
remain in blood (too big)
 Reabsorbed back to blood: active transport
Na+
◆ glucose

◆
amino acids
 Reabsorbed back to blood: diffusion

H2O
◆
Cl–
 Excreted out of body



AP Biology
urea
excess H2O
◆ excess solutes (glucose, salts)
toxins, drugs, “unknowns”
Any Questions?
AP Biology