Biology 2672a: Comparative Animal Physiology

1. Biology 2672a: Comparative Animal Physiology Kidneys and tubules

2. 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

3. Glomerular filtration Porous walls + high pressure Pressure maintained by vasoconstriction of efferent vessels Bowman’s capsule Water and solutes <10kDa 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

4. An Amphibian nephron

6. Water reabsorption modulated here Reabsorption of salts Concentrated Urine (permeable distal tubule) -antidiuresis Dilute Urine (impermeable distal tubule) -diuresis

7. 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

8. The nephron – not quite a one-way journey… Fig. 27.6

9. Bowman’s 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

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

11. Concentration gradient in kidney Fig. 27.13

12. 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

13. 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

14. Changing concentration of definitive urine Fig. 27.14

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

16. 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

17. 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

18. Cortex • Medullary thickness is a measure of the length of the loops of Henle • Medullar + Pelvis = good measure of concentrating power Medulla Renal Pelvis Medulla Fig. 27.6a

19. Medullary thickness is positively correlated to maximum urine concentration Fig. 27.8

20. Medullary thickness is related to body size and habitat Fig. 27.9

21. Microvasculature of kidneys Sand Rat Lab Rat Fig. 27.10a,c

22. Interspecific variation in urine concentration correlates with habitat in large mammals, too Mesic Xeric Table 28.2

23. Insects • Highly efficient (most successful terrestrial animals) • Open circulatory system • No high pressure filtering • Malpighian tubules Marcello Malpighi (1628-1694)

24. Malpighian tubules Foregut & Midgut Hindgut

25. 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

26. Malpighian tubules • No high pressure filtration • Active transport-driven formation of dilute urine

27. Cells Haemolymph Lumen Fig 27.21

28. Haemolymph Principal cell Stellate cell Mitochondria packed into evaginations Lumen

29. Proton pump generates electrochemical gradient Requires ATP K+ follows via electrogenic transporter Haemolymph K+ Channel V-ATPase (H+ pump) Lumen

30. Cl- follows K+ gradient Water follows osmotic gradient into tubule lumen Haemolymph Cl- Channel Aquaporin V-ATPase (H+ pump) Lumen

31. 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.

32. 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

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