fluid balance/ nitrogen excretion kidney function
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Fluid Balance/Nitrogen Excretion
Kidney Function
Salt/Water Balance
• ionic composition of cytosol is maintained by osmotic interaction with intercellular fluid
• intercellular fluid is conditioned by osmotic interaction with capillary contents
• excretory organs control the osmotic composition of blood
– differentially excrete different compounds
– excrete nitrogenous wastes from terrestrial animals
Salt/Water Balance
• common mechanisms of excretory organs– filtration
• movement of water and solutes out of capillary under pressure
– secretion • active transport of additional molecules into filtrate
– resorption• active uptake of solutes from filtrate
Salt/Water Balance
• diverse challenges of different environments– osmotic potentials of aquatic environments
vary dramatically• marine: 1070 mosmol/L• fresh water: 1-10 mosmol/L
– physiological responses to different environmental osmolarities vary
Salt/Water Balance
• physiological responses to different environmental osmolarities
– osmoconformers do not regulate tissue fluid osmolarity
• ionic conformers
–same ionic composition as ambient
• ionic regulators
–modify ionic composition but not overall osmolarity
Salt/Water Balance• physiological responses to different
environmental osmolarities – osmoregulators maintain tissue fluid
osmolarity different from environmental• hypotonic osmoregulators
–marine organisms–excrete salt; conserve water
• hypertonic osmoregulators–fresh water organisms–excrete water; conserve salt
three osmoregulatory modesFigure 51.1
Salt/Water Balance• physiological responses to different
environmental osmolarities– terrestrial organisms conserve water & salt
Nitrogenous Wastes are Excreted• catabolism of amino acids & nucleotides
produces nitrogenous waste– ammonia (NH3) is quite toxic
• ammonotelic organisms lose NH3 to aqueous environment across gills
• ureotelic organisms convert NH3 to urea–highly water soluble
• uricotelic organisms covert NH3 to uric acid–slightly water soluble
Three N Excretion FormsFigure 51.3
Invertebrate Excretory Systems• protonephridia
– in flatworms– flame cell + tubule
• tissue fluid enters flame cell lumen• cilia drive fluid toward excretory pore• tubule cells modify fluid composition• urine is less concentrated than tissue fluid
protonephridia in PlanariaFigure 51.4
Invertebrate Excretory Systems• metanephridia
– annelid worms• fluid-filled coelom in each body segment• closed circulatory system
–filtration from blood into coelom–diffusion of waste products into coelom
circulatory/excretory interaction in earthwormFigure 51.5
Invertebrate Excretory Systems• metanephridia
– annelid worms• metanephridia occupy adjacent segments
–nephrostome collects coelomic fluid–tubule travels to adjacent segment–tubule cells resorb & secrete
compounds–dilute urine leaves a nephridiopore
Invertebrate Excretory Systems• Malpighian tubules - insects
– join gut between midgut & hindgut– extend into body tissues– actively transport uric acid, K+, Na+ from
hemolymph– take water into tubules by osmosis– muscular contractions propel toward gut– hindgut returns Na+, K+ to tissue fluid; water
follows– uric acid precipitates in rectum
Malpighian tubuleFigure 51.6
Vertebrate Excretory Systems
• nephron (functional unit of kidney)– an afferent arteriole branches into a dense
capillary bed = the glomerulus– the glomerulus is surrounded by Bowman’s
capsule (= renal corpuscle)– blood is filtered from the glomerulus
through podocyte “fingers” into Bowman’s capsule
nephron anatomyFigure 51/8
renal filtrationFigure 51.7
Vertebrate Excretory Systems
• nephron– glomerular capillaries combine into an
efferent arteriole – the efferent arteriole branches into a
peritubular capillary bed– the renal tubule modifies fluid composition
• resorption & secretion– peritubular capillaries
• deliver materials to be secreted into urine• take up resorbed materials
tubular modification of fluid contentsFigure 51.7
Vertebrate Excretory Systems
• nephron– peritubular capillaries combines into a renal
venule– the renal tubule delivers urine to a collecting
duct
fluid collectionFigure 51.7
vertebrate nephron
Figure 51/7
Vertebrate Excretory Systems
• nephrons of different vertebrates accomplish different tasks
– water excretion; salt conservation
– water conservation; salt excretion
Vertebrate Excretory Systems
• marine bony fishes
– secrete salts; conserve water
• hypotonic osmoregulation
• fewer glomeruli - limits volume of urine
• excrete Na+, Cl-, NH3, through renal tubules & gills
• do not absorb some ions from gut
Vertebrate Excretory Systems
• cartilaginous fishes– ionic regulating osmoconformers
• N waste retained as urea • special salt-secreting sites remove excess dietary NaCl
Vertebrate Excretory Systems
• amphibians– conserve salt; excrete water, OR– conserve both
• reduce skin permeability• estivate during hot dry periods
Vertebrate Excretory Systems
• reptiles & birds– conserve water & salt
• minimize skin evaporation• limit water loss by excreting uric acid
Vertebrate Excretory Systems
• mammals– conserve water, regulate ions
• excrete urine hypertonic to tissue fluids• kidney concentrates urine
human urinary system; kidney anatomyFigure 51.9
human kidney
• nephron components & arrangement - tubule– Bowman’s capsule - cortex– proximal convoluted tubule - cortex– loop of Henle - descending/ascending in
medulla– distal convoluted tubule - cortex– collecting duct - cortex => medulla
renal pyramidFigure 51.9
human kidney
• nephron components & arrangement - vessels– afferent arteriole supplies glomerulus– efferent arteriole branches into peritubular
capillaries– vasa recta capillary bed parallels loop of
Henle– peritubular capillaries join to form the
venule that empties into the renal vein– ~98% of filtrate leaves kidney in renal vein
human kidney
• nephron function– glomerulus filters plasma into Bowman’s
capsule– proximal convoluted tubule transports Na+,
glucose, amino acids, etc. into tissue fluid– water moves out of tubule by osmosis– peritubular venous capillaries take up water
and molecules– tubule contents enter loop of Henle at an
osmotic potential similar to plasma
human kidney• nephron function
– urine concentration in loop of Henle• thin descending limb
–permeable to water–impermeable to Na+, Cl-
thin descending
limb loses water, retains NaCl
Figure 51.10
thin ascending limb loses
NaCl, retains waterFigure 51.10
human kidney• nephron function
– urine concentration in loop of Henle• thin descending limb • thin ascending limb• thick ascending limb
–impermeable to water–actively transports Cl- out, Na+ follows
thick ascending
limb pumps out
NaCl, retains waterFigure 51.10
human kidney
• nephron function– thick ascending limb increases solute in
tissue fluid – thin ascending limb increases solute in
tissue fluid– thin descending limb contents become
increasingly concentrated– dilute fluid enters distal convoluted tubule– osmosis empties distal convoluted tubule
until osmotic potential is same as plasma
human kidney
• nephron function– the loop of Henle creates a concentration
gradient in the medulla – vasa recta removes water from medulla– collecting duct passes through the medulla
• water leaves the duct by osmosis• highly concentrated urine is produced
nephron function
in the human kidney
Figure 51.10
nephron function
• blood plasma is filtered into tubule
• ions are actively resorbed
• a concentration gradient is established in the medulla
• water is reclaimed by osmosis
Control & Regulation of Kidney Function• Glomerular Filtration Rate depends on blood
pressure and blood volume• autoregulatory renal responses
– reduced blood pressure causes afferent arteriole dilation
– continued low GFR causes release of renin which activates circulating angiotensin
Control & Regulation of Kidney Function• autoregulatory renal responses
– continued low GFR causes release of renin which activates circulating angiotensin• efferent arteriole constriction
• systemic peripheral vessel constriction
• release of aldosterone from adrenal cortex
–stimulates Na+ resorption ( & so H2O)
–stimulates thirst
Control & Regulation of Kidney Function
• Glomerular Filtration Rate depends on blood pressure and blood volume
• antidiuretic hormone (ADH) control– ADH release increases as aortic stretch
signals decrease or as osmolarity increases• increases permeability of collecting ducts to water
• increases blood volume• decreases osmolarity
control & regulation of kidney functionFigure 51/14
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