Osmoregulation

Chapter 44

Osmoregulation

Balance of water & solute concentrationIntracellular & extracellularIons (solutes)Na+1, Cl-1

Osmolarity

HyperosmoticHypoosmoticIsoosmoticNormal saline (0.9%)5% dextrose

Solutes Water

Selectively permeablemembrane

Net water flow

Hypoosmotic side:• Lower solute

concentration• Higher free H2O

concentration

Hyperosmotic side:• Higher solute

concentration• Lower free H2O

concentration

Osmoregulation

OsmocomfomersBody fluids have same concentration as environmentOcean invertebratesOsmoregulatorsConstant blood osmolarityVertebrates

Osmoregulation

(a) Hydrated tardigrade (b) Dehydrated tardigrade

50 µm

Nitrogenous wastes

Proteins, DNA & RNA contain nitrogenBreak downs-waste (NH2)

Aquatic animalsNH3

Mammals, amphibiansUreaBirds, reptiles, insects Uric acid

Nitrogenous wastes

Urea

Uric acid

Nitrogen wastes

Many reptiles(including birds),insects, land snails

Ammonia Uric acidUrea

Most aquaticanimals, includingmost bony fishes

Mammals, mostamphibians, sharks,some bony fishes

Excretory process

Excretory systemsRegulate solute concentrationsProduce urineRefine filtrate from body fluids

Excretory process

FiltrationBlood (body fluids) is filtered Forms filtrate (urine)ReabsorptionIons & nutrients are recoveredReturned to body from filtrate

Excretory process

SecretionWastes/water from capillaries to filtrate (urine)ExcretionRelease filtrate (urine) from bodyRelease nitrogenous metabolites

Excretion

Capillary

Excretion

Secretion

Reabsorption

Excretorytubule

Filtration

Filtrate

Urin

e

Figure 44.12a

Posteriorvena cava

Renalcortex

Excretory Organs Kidney Structure Nephron Types

Renalmedulla

Renalartery

Renalvein

Ureter

Renal pelvis

Renalmedulla

Renalcortex

Corticalnephron

Juxtamedullarynephron

Renal arteryand vein

Aorta

Ureter

Urethra

Urinarybladder

Kidney

Anatomy

KidneyUreterBladderUrethraRenal artery/vein Blood supply of kidney

Anatomy

Renal cortexOutside of kidneyRenal medullaInside of kidney (hypertonic)Renal pelvisFunnel shapedUreter meets kidney

Kidney

Anatomy

Nephron:Functioning unit of kidney1 million in each kidneyGlomerulusBowman’s capsuleProximal (convoluted) tubuleLoop of henleDistal (convoluted) tubule

Nephron

Kidney

Kidney

Pathway

Pathway through kidney

Blood forced into glomerulusBed of capillariesBlood cells & proteins are too largePlasma goes through with minerals & waterFiltrateEnters Bowman’s capsuleProximal tubuleLocated in renal cortex

Pathway through kidney

Enters loop of HenleIn the loop goes deep in the renal medulla Fluid returnsDistal tubule Drains into collecting ductGoes into renal pelvis (urine)Ureter

Pathway through kidney

Nephron

Corticalnephron

Juxtamedullarynephron

Collectingduct

(c) Nephron types

Torenalpelvis

Renalmedulla

Renalcortex

Nephron

Pathway through kidney

Capillaries surround the loopReabsorb water & ions

NephronAfferent arteriolefrom renal artery

Efferentarteriole fromglomerulus

SEM

Branch ofrenal vein

Descendinglimb

Ascendinglimb

Loop ofHenle

(d) Filtrate and blood flow

Vasarecta

Collectingduct

Distaltubule

Peritubular capillaries

Proximal tubule

Bowman’s capsuleGlomerulus

10 µm

Pathway through kidney

1000-2000L of blood flow through a day180 L of water a dayUrinate only 1.5 L per dayReabsorb glucose, aa, vitamins & water Excrete wastes, harmful substances, H+ & waterMaintain homeostasis (blood volume, pH electrolytes & BP)

Regulation diagram

Closer look

Proximal tubuleMost nutrients reabsorbed to blood NaCl, H2O, HCO3

-1 reabsorbed to bloodNH3, H+1 secreted into the tubule from blood

Bowman’s Capsule and Proximal Tubule

Closer look

Loop of HenleDescending loop water is reabsorbedAscending loop NaCl is reabsorbedLonger loop-more NaCl is absorbed

Closer look

Distal tubuleRegulation of K+1 & NaCl here Depends on body’s needsK+ is secreted into tubuleNaCl reabsorbed into tubule

Loop of Henle and Distal Tubule

Closer look

Collecting ductNaCl can be reabsorbed hereSome urea diffuses out of tubeRemaining filtrate passes as urine

Collecting Duct

Regulation diagram

Transport

Key

ActivetransportPassivetransport

INNERMEDULLA

OUTERMEDULLA

H2O

CORTEX

Filtrate

Loop ofHenle

H2O K+HCO3–

H+ NH3

Proximal tubule

NaCl Nutrients

Distal tubule

K+ H+

HCO3–

H2O

H2O

NaCl

NaCl

NaCl

NaCl

Urea

Collectingduct

NaCl

Regulation of kidney

ADH (antidiurectic hormone)VasopressinReleased by posterior pituitary glandReleased in response to increased solute concentration in plasmaDehydrated or eating salty foodsDistal tubule/collecting duct become more permeable to waterDecreases the amount of water in urine Reabsorbs more water

ADH

Thirst

Drinking reducesblood osmolarity

to set point.

Increasedpermeability

Pituitarygland

ADH

Hypothalamus

Distaltubule

H2O reab-sorption helpsprevent further

osmolarityincrease.

STIMULUS:Increase in blood

osmolarity

Collecting duct

Homeostasis:Blood osmolarity

(300 mOsm/L)

(a)

Osmoreceptors inhypothalamus trigger

release of ADH.

ADH

ADHreceptor

ADH

cAMP Secondmessenger

COLLECTINGDUCT CELL

LUMENCollectingduct

Proteinkinase A

Storagevesicle

Aquaporinwaterchannel

Exocytosis

H2O

H2O

Effect of ADH

Regulation of kidney

Low blood volumeJuxtaglomerular apparatus Tissue located near artery supplies blood to glomerulusSecretes renin (enzyme)Angiotensinogen to angiotensin IAngiotensin I to angiotension IICauses blood vessels to constrictCauses release of aldosterone

Regulation of kidney

AldosteroneReleased by the adrenal cortexDue to low sodium levelsDue to low blood volumeStimulates distal tubules/collecting ducts to reabsorb sodium Chlorine & water followStimulates potassium to be excreted

Regulation of kidney

AldosteroneIncreases serum sodium levelsIncreases water (blood volume)Decreases serum potassium levelsACE inhibitor Blood pressure medicationBlocks the affects of aldosterone

Aldosterone

Renin

Distaltubule

Juxtaglomerularapparatus (JGA)

STIMULUS:Low blood volumeor blood pressure

Homeostasis:Blood pressure,

volume

Liver

Angiotensinogen

Angiotensin I

ACE

Angiotensin II

Adrenal gland

Aldosterone

Arterioleconstriction

Increased Na+

and H2O reab-sorption in

distal tubules

Regulation of kidney

ANH (atrial natriuretic homone)Secreted by right atriumDue to increased blood volumeCauses sodium/water to be released Lowers blood volumeOpposes aldosterone

Problems

Diabetes insipidusLacks ADHPituitary problemIncreased urinationLeads to dehydration & low BPAlcohol consumptionBlocks ADH