2.1 osmoregulation mnr

8/16/2019 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

2.1 osmoregulation mnr

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