2.1 Osmoregulation MNR
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Transcript of 2.1 Osmoregulation MNR
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• The fact that cells are living in fluid. Cell
cannot live without fluid. Interstitial fluid.
– Must be maintained within fairly narrow limits
• Freshwater animals – Show adaptations that reduce water uptake
and conserve solutes
• Desert and marine animals facedesiccating environments – With the potential to quickly deplete the body
water
2 System in Animals
!" #omeostasis
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• $smoregulation
– %egulation of the osmotic pressure of body fluids by
controlling the amount of water &uptake and loss'
and(or solutes in the body &internal fluid'!
• )*cretion
– +ets rid of metabolic wastes
• Solutes: substance dissolve in a liquid (solvent
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• Most animals are said to be stenohaline – ,nd cannot tolerate substantial changes in e*ternal
osmolarity
– Stenohaline- organisms adaptable with a narrow rangeof salinity only!
• )uryhaline animals – .an survive large fluctuations in e*ternal osmolarity
– )uryhaline- organisms adaptable to a wide range ofsalinity!
!igure "".2
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#arine Animals• Most marine invertebrates are osmoconformers
– $smoconformer- organisms which does not regulate the osmotic concentration ofinternal fluid!
• Most marine vertebrates and some invertebrates areosmoregulators – $smoregulator- organisms which actively regulate the osmotic concentration of its
internal fluid!
• Marine bony fishes are hy$oosmotic to sea water – ,nd lose water by osmosis and gain salt by both diffusion and from food they eat
• /hese fishes balance water loss – 0y drinking seawater
!reshwater Animals• Freshwater animals
– .onstantly take in water from their hypoosmotic environment
– 1ose salts by diffusion
• Freshwater animals maintain water balance – 0y e*creting large amounts of dilute urine
• Salts lost by diffusion – ,re replaced by foods and uptake across the gills
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• 1and animals manage their water budgets
– 0y drinking and eating moist foods and by usingmetabolic water
• Desert animals – +et ma2or water savings from simple anatomical
features
– /ransport epithelia• ,re speciali3ed cells that regulate solute movement
• ,re essential components of osmotic regulation andmetabolic waste disposal
• ,re arranged into comple* tubular networks
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• ,n e*ample of transport epithelia is found inthe salt glands of marine birds
– Which remove e*cess sodium chloride from theblood
!igure "".%a& b
4asal salt gland
4ostril
with salt
secretions
1umen of
secretory tubule
4a.l
0lood
flowSecretory cell
of transport
epithelium
.entral
duct
Direction
of salt
movement
/ransport
epithelium
Secretory
tubule
.apillary
5ein
,rtery
(a ,n albatross6s salt glands
empty via a duct into the
nostrils7 and the salty solutioneither drips off the tip of the
beak or is e*haled in a fine mist!
(b $ne of several thousand
secretory tubules in a salt8
e*creting gland! )ach tubule
is lined by a transport
epithelium surrounded by
capillaries7 and drains into
a central duct!
(c /he secretory cells actively
transport salt from the
blood into the tubules!
0lood flows counter to theflow of salt secretion! 0y
maintaining a concentration
gradient of salt in the tubule
&aqua'7 this countercurrent
system enhances salt
transfer from the blood to
the lumen of the tubule!
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'AST• /he type and quantity of an animal6s waste $roducts
– May have a large impact on its water balance
– )g9 4itrogenous wastes are ,mmnia7 :rea and :ric acid!Ammonia
• ,nimals that e*crete nitrogenous wastes as ammonia – 4eed access to lots of water – %elease it across the whole body surface or through the gills
)rea• /he liver of mammals and most adult amphibians
– .onverts ammonia to less to*ic urea
• :rea is carried to the kidneys7 concentrated – ,nd e*creted with a minimal loss of water
)ric Acid• ;nsects7 land snails7 and many reptiles7 including birds
– )*crete uric acid as their ma2or nitrogenous waste
• :ric acid is largely insoluble in water – ,nd can be secreted as a paste with little water loss
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• ,cretory systems – %egulate solute movement between internal fluids
and the e*ternal environment
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)*cretory
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4ucleus
of cap cell
.ilia
;nterstitial fluid
filters through
membrane wherecap cell and tubule
cell interdigitate
&interlock'
/ubule cell
Flame
bulb
4ephridiopore
in body wall
/ubule
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Metanephridia
• )ach segment of an earthworm
– #as a pair of open8ended metanephridia
!igure "".// 4ephrostome Metanephridia
4ephridio8
pore
.ollecting
tubule
0ladder
.apillary
network
.oelom
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Digestive tract
Midgut
&stomach'
Malpighian
tubules
%ectum
;ntestine#indgut
Salt& water& and
nitrogenouswastes
Feces and urine ,nus
Malpighian
tubule
%ectum
eabsor$tion of 23&
ions& and valuable
organic molecules#)M$1>M
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Vertebrate Kidneys• ?idneys7 the e*cretory organs of vertebrates
– Function in both e*cretion and osmoregulation
• 4ephrons and associated blood vessels are
the functional unit of the mammalian kidney
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• )ach kidney
– ;s supplied with blood by a renal artery and drained by a renal vein
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(b 5idney structure
:reter
Section of kidney from a rat
%enal
medulla
%enal
corte*
%enal
pelvis
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@u*ta8
medullary
nephron
.ortical
nephron
.ollecting
duct
/o
renal
pelvis
%enal
corte*
%enal
medulla
A Bm
,fferent
arteriole
from renal
artery +lomerulus
0owman6s capsule
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• /wo solutes7 4a.l and urea7 contribute to the
osmolarity of the interstitial fluid
– Which causes the reabsorption of water in thekidney and concentrates the urine
!igure ""./6
#$
#$
#$
#$
#$
#$
#$
4a.l
4a.l
4a.l
4a.l
4a.l
4a.l
4a.l
=AA
=AA "AA
EAA
AA
GAA
"AA
HAA
EAA
AA
"AA
,ctive
transport
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Filtration of the blood • Filtration occurs as blood pressure
– Forces fluid from the blood in the glomerulus into the lumen of 0owman6s capsule
• Filtration of small molecules is nonselective – ,nd the filtrate in 0owman6s capsule is a mi*ture that mirrors the concentration of various
solutes in the blood plasma
• From 0owman6s capsule7 the filtrate passes through threeregions of the nephron – /he pro*imal tubule7 the loop of #enle7 and the distal tubule
• Fluid from several nephrons – Flows into a collecting duct
• Blood Vessels Associated with the
Nephrons – )ach nephron is supplied with blood by an afferent arteriole• , branch of the renal artery that subdivides into the capillaries
– /he capillaries converge as they leave the glomerulus – Forming an efferent arteriole – /he vessels subdivide again – Forming the peritubular capillaries7 which surround the pro*imal and distal tubules
S ti d b ti i th i l t b l
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• Secretion and reabsorption in the pro*imal tubule – Substantially alter the volume and composition of filtrate
• %eabsorption of water continues
– ,s the filtrate moves into the descending limb of theloop of #enle
• ,s filtrate travels through the ascending limb ofthe loop of #enle
– Salt diffuses out of the permeable tubule into theinterstitial fluid
• /he distal tubule –
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• /he collecting duct7 permeable to water but not
salt
– .onducts the filtrate through the kidney6s osmolaritygradient7 and more water e*its the filtrate by
osmosis
• :rea diffuses out of the collecting duct
– ,s it traverses the inner medulla
• :rea and 4a.l
– Form the osmotic gradient that enables the kidney
to produce urine that is hyperosmotic to the blood
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%egulation of ?idney Function
• /he osmolarity of the urine
– ;s regulated by nervous and hormonal control
of water and salt reabsorption in the kidneys
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• ,ntidiuretic hormone &,D#'
– ;ncreases water reabsorption in the distal
tubules and collecting ducts of the kidney
!igure ""./;a
$smoreceptors
in hypothalamus
Drinking reducesblood osmolarity
to set point
#$ reab8
sorption helps
prevent further osmolarity
increase
S/;M:1:S-/he release of ,D# is
triggered when osmo8
receptor cells in thehypothalamus detect an
increase in the osmolarity
of the blood
omeostasis:0lood osmolarity
#ypothalamus
,D#
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• /he renin8angiotensin8aldosterone system &%,,S'
– ;s part of a comple* feedback circuit that functions in
homeostasis
!igure ""./;b
;ncreased 4aC
and #$ reab8
sorption in
distal tubules
omeostasis:
0lood pressure7volume
S/;M:1:S-
/he 2u*taglomerular apparatus &@+,' responds
to low blood volume or
blood pressure &such as dueto dehydration or loss of
blood'
,ldosterone
,drenal gland
,ngiotensin ;;
,ngiotensinogen
%eninproduction
%enin
,rterioleconstriction
Distal
tubule
@+,
(b /he renin8angiotensin8aldosterone system &%,,S' leads to an increasein blood volume and pressure!
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• ,nother hormone7 atrial natriuretic factor
&,4F'
– $pposes the %,,S