Biology 272b: Comparative Animal Physiology
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Transcript Biology 272b: Comparative Animal Physiology
Biology 2672a:
Comparative Animal
Physiology
Kidneys and tubules
Kidneys
Regulation
of salts and water in
body
Excretion of nitrogenous wastes
Production of Urine
More concentrated: conserving
water/ excreting more salts
More dilute: excreting more water
Glomerular filtration
Bowman’s capsule
Pressure
maintained by
vasoconstriction
of efferent
vessels
Primary Urine:
Dilute, no proteins etc.
Porous walls +
high pressure
Water and solutes
<10kDa out
Water, sugars, salts,
amino acids, Urea
(sometimes assisted by
active transport)
Large things (e.g. proteins) remain behind
Fig. 27.1b
An Amphibian nephron
Reabsorption of salts
Water reabsorption
modulated here
Concentrated
Urine
(permeable
distal tubule)
-antidiuresis
Dilute Urine
(impermeable
distal tubule)
-diuresis
Mammalian kidneys, the big
picture
Cortex
Medulla
Renal Pelvis
Ureter
Urine Flow
Blood Tubules
Tubules Collecting tubes Reabsorption,
Cunning osmotic
Filtration
trickery concentrates
waste products
Fig. 27.6a
The nephron – not quite a oneway journey…
Fig. 27.6
Thick ascending
loop of Henle
Salt Re-absorption
Collecting Duct
Urine out,
concentration
of definitive
Urine
Loop of Henle
Thin ascending loop
of Henle
Bowman’s capsule
Ultrafiltration,
Production of
primary urine
Thick
segment of
descending
loop of
Henle
Re-absorption of
sugars, amino
acids, water
Thin segment
of descending
loop of Henle
Fig. 27.6
Solute reabsorption
In
thick segment of
descending limb of
loop of Henle
Glucose
Amino Acids
Water
Also
some in the
thick ascending limb
Concentration gradient in kidney
Fig. 27.13
The concentration gradient
Established
by active transport of
salts in loop of Henle
Leads to a gradient of urea as
well
e.g. Fig. 27.12
Concentration of urine
Occurs in collecting
ducts
Driven by osmotic
gradient across
kidney
Both urea and salts
Can be manipulated
by altering
permeability of
collecting duct to
water
Fig. 27.14a
Changing concentration of
definitive urine
Fig. 27.14
Concentrating Urine
Essential
for water conservation
on land
Allows the selective removal of
salts
Expected to be particularly highly
developed in desert mammals…
Reducing excretory water loss
Efficient
kidneys
Get rid of a lot of salt and wastes
per unit water
Mammals, birds, insects
Efficient
from gut
re-absorption of water
Dry Faeces
Predictions about desert
mammal kidneys
Longer
loop of Henle = greater
concentration gradient
Expect desert mammals to have
longer loops of Henle and to
produce more concentrated urine
Cortex
Medulla
Medulla
Renal Pelvis
Medullary thickness is a
measure of the length
of the loops of Henle
Medullar + Pelvis =
good measure of
concentrating power
Fig. 27.6a
Medullary thickness is positively correlated
to maximum urine concentration
Fig. 27.8
Medullary thickness is related to
body size and habitat
Fig. 27.9
Microvasculature of kidneys
Lab Rat
Sand Rat
Fig. 27.10a,c
Interspecific variation in urine concentration
correlates with habitat in large mammals, too
Mesic
Xeric
Table 28.2
Insects
Highly
efficient (most successful
terrestrial animals)
Open circulatory system
No high pressure filtering
Malpighian
tubules
Marcello Malpighi (1628-1694)
Malpighian tubules
Foregut & Midgut
Hindgut
Malpighian tubules
Anywhere
from 2 to 200,
depending on species
A blind-ended tube with walls
exactly 1 cell thick
Float in haemolymph
Open into hindgut
Malpighian tubules
No
high pressure filtration
Active transport-driven formation of
dilute urine
Cells
Haemolymph
Lumen
Fig 27.21
Haemolymph
Principal cell
Mitochondria packed into
evaginations
Stellate cell
Lumen
Haemolymph
K+ Channel
Proton pump
generates
electrochemical
gradient
V-ATPase (H+ pump)
Lumen
Requires ATP
K+ follows via
electrogenic
transporter
Haemolymph
Cl- Channel
Cl- follows K+
gradient
Water follows
osmotic
gradient into
tubule lumen
Aquaporin
V-ATPase (H+ pump)
Lumen
Malpighian tubules summary
Active transport sets up ion gradients
Proton pump; K+, Cl-
Na+,K+-ATPase also involved
(breaking news!)
Water follows
Passive transport of nitrogenous
wastes, amino acids etc.
Active transport of large molecules
Alkaloids, proteins etc.
Water and solute reabsorption
Urine
from tubules is dilute and
contains lots of things the insect
doesn’t want to lose
Reabsorption of water and
solutes in hindgut/rectum
Determines final concentration of
the urine
Reading for Thursday
Thursday:
Guest lecture (Dr.
Scott MacDougall-Shackleton;
birdsong)
Reading on OWL
Tuesday:
Navigation
Pp 454-465