Download Chapter 23

Chapter 23: Water, solutes and
excretion
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-1
Waters and solutes
•
All organisms contain high levels of water
• + ions
– Na+, K+, Cl-, Ca2+, SO42-, PO43•
+ organic solutes
– glucose, amino acids, proteins
•
These substances are essential for life
– few animals can survive dehydration or freezing
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-2
Exchange with the environment
•
Water and solutes are exchanged continuously
between an organism and its environment
– intake of food and fluids
– respiration
– elimination of wastes
•
Aquatic animals also
– gain or lose water by osmosis
– gain or lose solutes by diffusion
•
Terrestrial animals also
– lose water from body surface by evaporation
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-3
Intracellular environment
•
Intracellular fluid must have same osmotic
concentration as extracellular fluid to prevent
movement of water from one to the other
– iso-osmotic
•
Solute composition differs from that of extracellular
fluid
– higher levels of K+
– lower levels of Na+ and Cl-
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-4
Tonicity
•
•
Cell volume is determined by solute content in
intracellular fluid
Solutes move along diffusion gradients
– movement of a solute across membranes depends on the
membrane’s permeability to that solute
– if solutes move across the membrane, water moves with
them
•
Isotonic solutions maintain solute and water
balance across a membrane
– cells maintain cell volume by changing concentration of
amino acids
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-5
Ionic and osmotic balance
•
Osmotic concentration of extracellular fluid of
osmoconformers is identical to that of the external
environment
• Osmoregulators regulate the osmotic
concentration
• Ion concentration in ionoconformers is identical to
that of the external environment
• Ionoregulators regulate the ion concentration
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-6
Living in sea water
•
Many marine invertebrates are osmoconformers
and ionoconformers
– no regulation of osmotic or ionic concentrations
– extracellular fluid varies with external environment
•
Almost all marine vertebrates
– osmoconform and ionoregulate

cartilaginous fish (sharks, rays, chimaeras), coelacanth
– osmoregulate and ionoregulate

most fish, amphibians, reptiles, birds, mammals
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-7
Fig. 23.3: Marine bony fish
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-8
Living in salt lakes
•
•
Hypersaline water has a greater salt concentration
than sea water
Animals that live in salt lakes must osmoregulate
and ionoregulate
– fish excrete excess ions through salt pumps (chloride
cells) on gills
– brine shrimp (Artemia) excrete excess ions through salt
pumps on appendages
•
Water lost by osmosis is increased by drinking
salty water
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-9
Living in fresh water
•
Because fresh water has a low solute
concentration, animals that live in it
– gain water by osmosis
– lose solutes by diffusion
•
Freshwater animals must osmoregulate and
ionoregulate
– water is excreted as dilute urine
– ions are absorbed from the gut or actively taken up
across the skin and gills
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-10
From sea to fresh water
•
Euryhaline animals move between salt and fresh
waters
– may change water balance strategies between different
environments
•
Even those species that osmoregulate and
ionoregulate in both environments must adjust
pattern from fresh to salt
– ‘freshwater’ hormone prolactin lowers water permeability
of skin, gills and gut and increases ion retention and
uptake
– ‘seawater' growth hormone and cortisol increase ion
excretion from gills
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-11
Living on land
•
Terrestrial animals face water loss through
– evaporation from lungs and skin surface
– excretion in urine and faeces
•
Water is usually replaced by drinking
– in arid areas, food and metabolic water are important
sources
– some invertebrates can absorb water directly from air
through skin of mouth or anus
•
Water loss is minimised by producing solid or
concentrated wastes
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-12
Excretion
•
Excretion regulates the internal environment by
– controlling body water
– maintaining solute composition
– excreting metabolic waste products and unwanted
substances
•
Excretion differs from elimination
– excretion removes substances that have been
metabolised
– elimination expels unabsorbed food
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-13
Nitrogenous wastes
•
•
Nitrogen produced by metabolism of protein must
be excreted from the body
Toxic ammonia (NH3) is the first product of protein
metabolism
– excreted by aquatic animals
•
Terrestrial organisms convert NH3 to a less toxic
form
– soluble urea (CON2H4) in invertebrates and mammals
– insoluble uric acid (C5H4O3N4) in reptiles and birds
– insoluble guanine (C5H5ON5) in spiders and scorpions
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-14
Nitrogenous wastes
•
•
Advantages and disadvantages associated with
different nitrogenous wastes
Ammonia (NH3)
– toxic, requires water for excretion, no energy expenditure
•
Urea (CON2H4)
– less toxic, less water required for excretion, some energy
expenditure
•
Uric acid (C5H4O3N4) and guanine (C5H5ON5)
– non-toxic, very little water required for excretion,
substantial energy expenditure
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-15
Excretory organs
•
•
•
Single-celled organisms and simple animals use
contractile vacuoles to excrete material
More complex animals possess two mechanisms
for excretion
Surface epithelial solute pumps
– regulate exchange of specific ions
•
Internal tubular excretory organs
– form liquid urine that contains a variety of materials
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23-16
Epithelial excretory organs
•
•
•
Ion pumps on epithelia take up or excrete ions
selectively
Epithelial salt glands of brine shrimp (Artemia)
actively excrete Cl- and passively excrete Na+
Ion pumps on gills of fish
– marine species excrete Cl- and Na+
– freshwater species absorbs Cl- and Na+
•
Movement of ions may result in passive transport
of water
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-17
Tubular excretory organs
•
Tubular excretory organs
–
–
–
–
•
•
form urine
reabsorb solutes and water
secrete solutes
change osmolarity
Excretory tubules form a filtrate of coelomic fluid or
blood
As the fluid passes along the tubule, solutes and
water are reabsorbed or solutes secreted to form
urine
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-18
Fig. 23.10: Tubular excretory organs
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23-19
Nephridia
•
Nephridia
– ingrowths of body surface
– coelomic fluid drawn into nephridia by cilia
– excreted at nephridiopore
•
Protonephridia
– blind-ending flame cells
– fluid enters through perforations in walls
•
Metanephridia
– ciliated funnel (nephridiostome) opens into coelomic
cavity
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-20
Malpighian tubules
•
Malpighian tubules
–
–
–
–
–
•
open into digestive tract at junction of midgut and hindgut
K+ is actively transported into lumen of tubule
water and solutes follow
ions selectively reabsorbed
urine formed in tubules is emptied into hindgut for further
modification
Malpighian tubules of insects and some spiders
produce dry wastes
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-21
Coelomoducts
•
Coelomoducts
– develop from coelomic lining
– coelomic fluid is filtrate from blood vessels
– cilia draw coelomic fluid into funnels (coelomostomes) in
coelom
– excreted at coelomopore
•
Present in many invertebrates, hagfishes and
lampreys
– blood vessels and coelomoducts combine into single
structure in higher vertebrates
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-22
Kidneys
•
•
•
Kidneys are principal excretory organs of
vertebrates
Each kidney is composed of nephrons (excretory
tubules)
Nephrons of higher vertebrates are modified
coelomoducts in which a cluster of capillaries
(glomerulus) is associated with the tubule
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-23
Fig. 23.18: Four functions of nephron
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23-24
Mammalian nephrons
•
At one end of a nephron tubule is an enlarged
double-walled cup
– outer wall forms renal or Bowman’s capsule
– inner wall of podocytes encloses glomerulus
•
Proximal convoluted tubule extends from
Bowman’s capsule
• Loop of Henle
• Distal convoluted tubule empties into collecting
duct
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-25
Filtration
•
Fluid is filtered through walls of glomerular
capillaries and podocytes into lumen of Bowman’s
capsule
• Erythrocytes and protein molecules are too large
to pass out of capillaries
• Otherwise filtrate has similar composition to blood
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-26
Reabsorption
•
Approximately 180 L of filtrate is produced each
day in an adult human
– 99 per cent of filtrate is reabsorbed
•
Proximal convoluted tubule reabsorbs most of the
–
–
–
–
•
water
NaCl
glucose
amino acids
Capillaries surrounding tubule returns materials to
circulation
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-27
Secretion
•
Peritubular capillaries secrete ions into renal
tubules
–
–
–
–
•
H+
K+
NH4+
specific organic molecules
H+ is secreted to regulate blood and urine pH
– buffering H+ with NH3 to form NH4+ prevents excessively
low pH
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-28
Osmoconcentration
•
•
•
All vertebrates produce iso-osmotic or hypoosmotic urine
Most mammals and some birds produce
hyperosmotic urine
Hyperosmotic urine formed in juxtamedullary
nephrons
– long loops of Henle in medulla
(cont.)
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-29
Osmoconcentration (cont.)
•
•
Osmotic concentration gradient established
between descending and ascending limbs of loop
of Henle
Countercurrent multiplication of solute and water
transport
– ascending limb actively removes Cl– Na+ follows passively
– water cannot pass out of ascending limb because
membrane is not permeable to it
(cont.)
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-30
Osmoconcentration (cont.)
•
•
•
Increased solute concentration draws water out of
the descending limb
Urea from the collecting duct increases osmotic
gradient
Medullary osmotic gradient draws water from fluid
as it passes through collecting duct
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-31
Fig. 23.22: Loop of Henle
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-32
Control of kidney function
•
Hormones control kidney function
– antidiuretic hormone (ADH) causes water retention
– renin, released in response to low blood pressure,
converts angiotensinogen into angiotensin II
– angiotensin II decreases blood flow to capillary beds and
stimulates reabsorption of water and NaCl from proximal
tubules
– Angiotensin II causes release of aldosterone, which
stimulates reabsorption of water and NaCl from distal
tubules
– atrial natriuretic factor (ANF) acts antagonistically to
these other hormones, inhibiting renin, aldosterone and
NaCl reabsorption
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-33
Salt glands
•
Many marine vertebrates possess salt glands that
secrete NaCl or KCl
– cartilaginous fish, coelacanth
– marine reptiles
– marine birds
•
•
Excreted salt solution more concentrated than sea
water
Salt glands allow marine vertebrates to drink salt
water
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
23-34