Biology 2672a: Comparative Animal Physiology

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Biology 2672a Comparative Animal Physiology

• Kidneys and tubules

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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

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Glomerular filtration
Porous walls high pressure
Pressure maintained by vasoconstriction of
efferent vessels
Bowmans capsule
Water and solutes lt10kDa out
Water, sugars, salts, amino acids, Urea
(sometimes assisted by active transport)
Primary Urine Dilute, no proteins etc.
Large things (e.g. proteins) remain behind
Fig. 27.1b
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An Amphibian nephron
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Water reabsorption modulated here
Reabsorption of salts
Concentrated Urine (permeable distal
tubule) -antidiuresis
Dilute Urine (impermeable distal tubule) -diuresis
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Mammalian kidneys, the big picture
Cortex
Medulla
Renal Pelvis
Ureter
Urine Flow
Blood ? Tubules Tubules ? Collecting
tubes Filtration
Reabsorption, Cunning osmotic trickery
concentrates waste products
Fig. 27.6a
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The nephron not quite a one-way journey
Fig. 27.6
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Bowmans capsule Ultrafiltration, Production of
primary urine
Thick ascending loop of Henle
Salt Re-absorption
Thick segment of descending loop of Henle
Collecting Duct
Urine out, concentration of definitive Urine
Re-absorption of sugars, amino acids, water
Loop of Henle
Thin segment of descending loop of Henle
Thin ascending loop of Henle
Fig. 27.6
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Solute reabsorption

• In thick segment of descending limb of loop of
  Henle
• Glucose
• Amino Acids
• Water
• Also some in the thick ascending limb

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Concentration gradient in kidney
Fig. 27.13
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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
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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
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Changing concentration of definitive urine
Fig. 27.14
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Concentrating Urine

• Essential for water conservation on land
• Allows the selective removal of salts
• Expected to be particularly highly developed in
  desert mammals

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Reducing excretory water loss

• Efficient kidneys
• Get rid of a lot of salt and wastes per unit
  water
• Mammals, birds, insects
• Efficient re-absorption of water from gut
• Dry Faeces

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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

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Cortex
Medulla
Renal Pelvis

• Medullary thickness is a measure of the length of
  the loops of Henle
• Medullar Pelvis good measure of concentrating
  power

Medulla
Fig. 27.6a
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Medullary thickness is positively correlated to
maximum urine concentration
Fig. 27.8
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Medullary thickness is related to body size and
habitat
Fig. 27.9
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Microvasculature of kidneys
Sand Rat
Lab Rat
Fig. 27.10a,c
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Interspecific variation in urine concentration
correlates with habitat in large mammals, too
Mesic
Xeric
Table 28.2
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Insects

• Highly efficient (most successful terrestrial
  animals)
• Open circulatory system
• No high pressure filtering
• Malpighian tubules

Marcello Malpighi (1628-1694)
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Malpighian tubules
Foregut Midgut
Hindgut
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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

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Malpighian tubules

• No high pressure filtration
• Active transport-driven formation of dilute urine

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Cells
Haemolymph
Lumen
Fig 27.21
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Haemolymph
Stellate cell
Principal cell
Mitochondria packed into evaginations
Lumen
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Haemolymph
K Channel

• Proton pump generates electrochemical gradient
• Requires ATP
• K follows via electrogenic transporter

V-ATPase (H pump)
Lumen
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Haemolymph
Cl- Channel

• Cl- follows K gradient
• Water follows osmotic gradient into tubule lumen

Aquaporin
V-ATPase (H pump)
Lumen
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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.

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Water and solute reabsorption

• Urine from tubules is dilute and contains lots of
  things the insect doesnt want to lose
• Reabsorption of water and solutes in
  hindgut/rectum
• Determines final concentration of the urine

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Reading for Thursday

• Thursday Guest lecture (Dr. Scott
  MacDougall-Shackleton birdsong)
• Reading on OWL
• Tuesday Navigation
• Pp 454-465