Osmoregulation and Excretion
CHAPTER 44CHAPTER 44
WATER BALANCE
Osmolarity - total solute Osmolarity - total solute concentration (M) = moles of concentration (M) = moles of solute per litersolute per liter
Osmosis – water moves from Osmosis – water moves from hypoosmotic (less solute) to hypoosmotic (less solute) to hyperosmotic (greater solute)hyperosmotic (greater solute)
Figure 44.12 Salt-excreting glands in birds
Figure 44.14a Osmoregulation in a saltwater fish
Figure 44.14b Osmoregulation in a freshwater fish
OsmoconformerOsmoconformer - does not - does not actively adjust internal osmolarityactively adjust internal osmolaritySome saltwater fish, most Some saltwater fish, most
marine invertebratesmarine invertebrates
OsmoregulatorOsmoregulator – adjusts – adjusts internal osmolarityinternal osmolarityAll freshwater fish, some All freshwater fish, some
mammals, most marine mammals, most marine vertebratesvertebrates
Cost of regulation depends on Cost of regulation depends on environmentenvironment
AnhydrobiosisAnhydrobiosis – a few animals – a few animals can lose almost all of their body can lose almost all of their body water and survive in a dormant water and survive in a dormant statestateTardigrades (water bears)Tardigrades (water bears)Some nematodesSome nematodes
DesiccationDesiccation Humans die if lose 12% body Humans die if lose 12% body
waterwater
Figure 44.15 Anhydrobiosis: Hydrated tardigrade (left), dehydrated tardigrade (right)
EXCRETORY SYSTEMS
Balancing water loss and gains and Balancing water loss and gains and disposing of wastesdisposing of wastes
Transport epitheliumTransport epithelium – layer(s) of – layer(s) of epithelial cells the regulate solute epithelial cells the regulate solute movement (selectively permeable movement (selectively permeable membranes)membranes)
Most harmful wastes are Most harmful wastes are nitrogen nitrogen products from breakdown of proteins products from breakdown of proteins and nucleic acidsand nucleic acids
Figure 44.16 Water balance in two terrestrial mammals
Figure 44.13 Nitrogenous wastes
AMMONIA
Most waste is NHMost waste is NH33
Most aquatic animals secrete Most aquatic animals secrete nitrogenous wastes as nitrogenous wastes as ammonia or ammonium (NHammonia or ammonium (NH44
++))
Many animals convert NHMany animals convert NH33 to to
urea or uric acidurea or uric acid
UREA
Mammals, most amphibians, Mammals, most amphibians, sharks, some fishessharks, some fishes
100,000 times less toxic than 100,000 times less toxic than NHNH33
Produced in vertebrate liver by Produced in vertebrate liver by combining COcombining CO22 with NH with NH33
Urea is carried to kidneysUrea is carried to kidneys
URIC ACID
Land snails, birds, insects, many Land snails, birds, insects, many reptilesreptiles
Least soluble in waterLeast soluble in water Excreted in paste-like form so little Excreted in paste-like form so little
water losswater loss Can be stored within shelled egg Can be stored within shelled egg
without harming embryowithout harming embryo
Dispose wastesDispose wastes OverviewOverview
FiltrationFiltration – fluids filtered – fluids filtered through transport epitheliathrough transport epithelia
ReabsorptionReabsorption – some filtered – some filtered compounds are actively compounds are actively transported back to body fluidstransported back to body fluids
Secretion Secretion – removal of wastes – removal of wastes from bodyfrom body
Figure 44.17 Key functions of excretory systems: an overview
PLATYHELMINTHES (FLATWORMS)
ProtonephridiumProtonephridium – network of – network of closed tubules throughout closed tubules throughout body; branches end in flame body; branches end in flame bulbsbulbs
Cilia provide movement of fluid Cilia provide movement of fluid within tubuleswithin tubules
Functions mostly in Functions mostly in osmoregulationosmoregulation
Most metabolic waste diffuse Most metabolic waste diffuse outout
Figure 44.18 Protonephridia: the flame-bulb system of a planarian
ANNELIDS
MetanephridiumMetanephridium – tubular – tubular system with internal openings system with internal openings located in each segmentlocated in each segment
NephrostomeNephrostome – internal – internal opening where fluid entersopening where fluid enters
Most solutes reabsorbed into Most solutes reabsorbed into blood capillariesblood capillaries
Nitrogenous wastes exit via Nitrogenous wastes exit via nephridioporesnephridiopores
Figure 44.19 Metanephridia of an earthworm
INSECTS AND TERRESTRIAL ARTHROPODS Malpighian tubulesMalpighian tubules – remove – remove
nitrogenous wastes from nitrogenous wastes from hemolymphhemolymph
Empties into digestive tract and Empties into digestive tract and is eliminated in fecesis eliminated in feces
Figure 44.20 Malpighian tubules of insects
MAMMALIAN KIDNEY
Renal arteryRenal artery – blood enters – blood enters kidneykidney
Renal veinRenal vein – blood leave – blood leave kidneykidney
UreterUreter – tube that takes urine – tube that takes urine from kidney to bladderfrom kidney to bladder
Urinary bladderUrinary bladder – urine (from – urine (from ureters) is storedureters) is stored
UrethraUrethra – tube in which urine – tube in which urine leaves bladder and exits bodyleaves bladder and exits body
Renal cortexRenal cortex – outer region of – outer region of kidneykidney
Renal medullaRenal medulla – inner region of – inner region of kidneykidney
Renal pelvis Renal pelvis – area in center of – area in center of kidney where urine collectskidney where urine collects
NephronNephron – functional unit of kidney– functional unit of kidney GlomerulusGlomerulus – ball of capillaries of – ball of capillaries of
each nephroneach nephron Bowman’s CapsuleBowman’s Capsule – surrounds – surrounds
glomerulusglomerulus
Figure 44.21 The human excretory system at four size scales
Figure 44.22 The nephron and collecting duct: regional functions of the transport epithelium
FILTRATION OF BLOOD
Blood pressure sends anything Blood pressure sends anything small enough into Bowman’s small enough into Bowman’s capsulecapsuleFiltrate includes glucose, Filtrate includes glucose,
salts, nitrogenous wastes, salts, nitrogenous wastes, vitamins, but vitamins, but notnot cells cells
Filtrate passes through 3 regions Filtrate passes through 3 regions of nephron:of nephron:Proximal tubuleProximal tubuleLoop of HenleLoop of HenleDistal tubuleDistal tubule
Filtrate (urine) Empties in Filtrate (urine) Empties in collecting ductcollecting duct
Urine then empties into renal Urine then empties into renal pelvispelvis
Urine leaves kidneys via uretersUrine leaves kidneys via ureters
Blood vessels along nephronsBlood vessels along nephronsAfferent arterioleAfferent arteriole – blood to – blood to
glomerulusglomerulusEfferent arterioleEfferent arteriole – blood – blood
away from glomerulusaway from glomerulusDivides in capillaries that Divides in capillaries that supply proximal and distal supply proximal and distal tubule and loop of Henletubule and loop of Henle
SecretionSecretion – substances put – substances put into proximal and distal tubules into proximal and distal tubules from blood (selective process)from blood (selective process)
ReabsorptionReabsorption – substances – substances put back into bloodput back into bloodNearly all water, sugar, Nearly all water, sugar,
vitamins, and nutrients are vitamins, and nutrients are reabsorbedreabsorbed
Figure 44.23 How the human kidney concentrates urine: the two-solute model (Layer 1)
Figure 44.23 How the human kidney concentrates urine: the two-solute model (Layer 2)
Figure 44.23 How the human kidney concentrates urine: the two-solute model (Layer 3)
Filtration Proximal tubuleProximal tubule
HCOHCO33--, NaCl, H, NaCl, H22O, nutrients (ex. O, nutrients (ex.
glucose and amino acids), Kglucose and amino acids), K++ reabsorbed (some actively and some reabsorbed (some actively and some passively)passively)
HH++ and NH and NH33 secreted secreted Descending loop of HenleDescending loop of Henle
Cells permeable to water, but not Cells permeable to water, but not NaCl; water reabsorbed by osmosisNaCl; water reabsorbed by osmosis
Filtrate becomes more concentratedFiltrate becomes more concentrated
Ascending loop of HenleAscending loop of HenleCells permeable to NaCl, but not Cells permeable to NaCl, but not
water; NaCl reabsorbed by water; NaCl reabsorbed by passive and then active transportpassive and then active transport
Filtrate becomes more dilutedFiltrate becomes more diluted Distal TubuleDistal Tubule
HCOHCO33--, NaCl, and H, NaCl, and H22O reabsorbedO reabsorbed
HH++ and K and K++ secreted secreted
Collecting ductCollecting ductWater is reabsorbed passivelyWater is reabsorbed passivelyNaCl is actively reabsorbed (in outer NaCl is actively reabsorbed (in outer
medulla)medulla)Urea and HUrea and H22O are passively O are passively
reabsorbed (in inner medulla)reabsorbed (in inner medulla)Urine becomes more concentratedUrine becomes more concentrated
Making urine in humans
Approximately 1600 L of blood flows Approximately 1600 L of blood flows through a pair of kidneys and we make through a pair of kidneys and we make approximately 1.5 L of urine per dayapproximately 1.5 L of urine per day
Osmolarity of blood is about 300 Osmolarity of blood is about 300 mOsm/L and osmolarity of urine is mOsm/L and osmolarity of urine is about 1200 mOsm/Labout 1200 mOsm/L
Kidneys are water-conserving (involves Kidneys are water-conserving (involves lots of energy to move solutes actively)lots of energy to move solutes actively)
HORMONAL FEEDBACK
Hormones link kidney function, water Hormones link kidney function, water balance, and blood pressurebalance, and blood pressure
Antidiuretic hormone (ADH)Antidiuretic hormone (ADH)Made in hypothalamus and stored in Made in hypothalamus and stored in
pituitary glandpituitary glandSecreted when blood osmolarity risesSecreted when blood osmolarity risesMay be caused by excessive May be caused by excessive
sweating, diarrhea, or eating salty sweating, diarrhea, or eating salty foodsfoods
Increases water reabsorption in Increases water reabsorption in distal tubule and collecting duct distal tubule and collecting duct (makes membranes more (makes membranes more permeable to water)permeable to water)
Alcohol can inhibit ADH so Alcohol can inhibit ADH so excessive drinking causes excessive drinking causes dehydration (due to excessive dehydration (due to excessive urination)urination)
RAAS system of regulationRAAS system of regulation Juxtaglomerular apparatusJuxtaglomerular apparatus
Specialized tissue located near Specialized tissue located near afferent arteriole which supplies afferent arteriole which supplies blood to glomerulusblood to glomerulus
Responds to low blood pressure Responds to low blood pressure by secreting by secreting reninrenin
ReninRenin activates activates angiotensinogenangiotensinogen which which becomes becomes angiotension IIangiotension II
Angiotension IIAngiotension II increase blood increase blood pressure by:pressure by:Constricting arteriesConstricting arteriesSignals proximal tube to reabsorb Signals proximal tube to reabsorb more NaCl and watermore NaCl and water
Stimulates Stimulates adrenal glandadrenal gland to to secrete secrete aldosteronealdosterone
AldosteroneAldosterone increases the increases the reabsorption of sodium and water reabsorption of sodium and water in distal tubes, which increases in distal tubes, which increases blood volume and pressureblood volume and pressure
Hypertension and Kidneys
Hypertension is treated with drugs that Hypertension is treated with drugs that inhibit angiotensin II.inhibit angiotensin II.
Many hypertension drugs inhibit the Many hypertension drugs inhibit the ACE enzyme that takes Angiotensin I ACE enzyme that takes Angiotensin I and cleaves it to make Angiotensin IIand cleaves it to make Angiotensin II
DIVERSE ADAPTATIONS
Birds: shorter loops of Henle Birds: shorter loops of Henle so urine not as concentratedso urine not as concentrated
Freshwater fish: must Freshwater fish: must conserve salts so more conserve salts so more reabsorption of ionsreabsorption of ions
Marine fish – lack glomeruli and Marine fish – lack glomeruli and Bowman’s capsules so excrete Bowman’s capsules so excrete mostly divalent ions while gills mostly divalent ions while gills excrete monovalent ionsexcrete monovalent ions
Frogs: can reabsorb water from Frogs: can reabsorb water from bladderbladder
Figure 44.25 A vampire bat (Desmodus rotundas), a mammal with a unique excretory situation. While the bat feeds on a blood meal, its kidneys make dilute urine copiously. Thus shedding weight for the flight home. While the bat roosts during the day, the kidneys secrete small amounts of concentrated urine.
Top Related