1、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,Pressure maintained by
2、vasoconstriction of efferent vessels,Bowmans capsule,Porous walls + high pressure,Fig. 27.1b,Water and solutes 10kDa out,Water, sugars, salts, amino acids, Urea (sometimes assisted by active transport),Large things (e.g. proteins) remain behind,Primary Urine: Dilute, no proteins etc.,An Amphibian ne
3、phron,Dilute Urine (impermeable distal tubule) -diuresis,Water reabsorption modulated here,Concentrated Urine (permeable distal tubule) -antidiuresis,Reabsorption of salts,Mammalian kidneys, the big picture,Cortex,Medulla,Renal Pelvis,Ureter,Blood Tubules Tubules Collecting tubes Filtration,Urine Fl
4、ow,Reabsorption, Cunning osmotic trickery concentrates waste products,Fig. 27.6a,The nephron not quite a one-way journey,Fig. 27.6,Bowmans capsule Ultrafiltration, Production of primary urine,Loop of Henle,Thick segment of descending loop of Henle,Re-absorption of sugars, amino acids, water,Thin seg
5、ment of descending loop of Henle,Thick ascending loop of Henle,Thin ascending loop of Henle,Collecting Duct,Urine out, concentration of definitive Urine,Salt Re-absorption,Fig. 27.6,Solute reabsorption,In thick segment of descending limb of loop of Henle Glucose Amino Acids Water Also some in the th
6、ick 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
7、 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 dese
8、rt mammals,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,Predictions about desert mammal kidneys,Longer loop of Henle = greater concentration gradient Expect desert mamma
9、ls to have longer loops of Henle and to produce more concentrated urine,Cortex,Medulla,Renal Pelvis,Fig. 27.6a,Medulla,Medullary thickness is a measure of the length of the loops of Henle Medullar + Pelvis = good measure of concentrating power,Medullary thickness is positively correlated to maximum
10、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,Table 28.2,Mesic,Xeric,Insects,Highly efficient (mos
11、t 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 i
12、n haemolymph Open into hindgut,Malpighian tubules,No high pressure filtration Active transport-driven formation of dilute urine,Fig 27.21,Haemolymph,Lumen,Cells,Haemolymph,Lumen,Stellate cell,Principal cell,Mitochondria packed into evaginations,Haemolymph,K+ Channel,Proton pump generates electrochem
13、ical gradient Requires ATP K+ follows via electrogenic transporter,Lumen,V-ATPase (H+ pump),Haemolymph,Cl- Channel,Lumen,V-ATPase (H+ pump),Cl- follows K+ gradient Water follows osmotic gradient into tubule lumen,Aquaporin,Malpighian tubules summary,Active transport sets up ion gradients Proton pump
14、 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 doesnt 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,
