Download Fluid Balance/ Nitrogen Excretion

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 modes
Figure 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 Forms
Figure 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 Planaria
Figure 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 earthworm
Figure 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 tubule
Figure 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 anatomy
Figure 51/8
renal filtration
Figure 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 contents
Figure 51.7
Vertebrate Excretory Systems
• nephron
– peritubular capillaries combines into a renal
venule
– the renal tubule delivers urine to a collecting
duct
fluid collection
Figure 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 anatomy
Figure 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
pyramid
Figure
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
water
Figure
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
water
Figure
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
function
Figure
51/14