Homeostasis and Water Balance

1
Homeostasis and Water Balance I. Selective
Forces Animals must maintain constant
internal environment ( homeostasis)
involves two main functions A.
Osmoregulation maintain appropriate amount of
water and solutes in tissues B. Elimination
of nitrogenous wastes often requires water
2
Homeostasis and Water Balance II.
Osmoregulation A. Terminology
1. osmotic pressure -- solute of a
solution -- ability of a solution to draw
water into itself across a membrane
3
Homeostasis and Water Balance II. Osmoregulaton
A. Terminology

• 2. isosmotic
• -- two solutions separated by membrane have
  same osmotic pressure
• -- solutesin solutesout

4
Homeostasis and Water Balance II.
Osmoregulation A. Terminology

• 3. hyperosmotic
• -- body fluids have solutes gt that of
  environment
• -- solutesin gt solutesout
• -- water diffuses into tissues salts
  diffuse out
• -- all freshwater organisms

salts
5
Homeostasis and Water Balance II.
Osmoregulation A. Terminology

• 4. hypoosmotic
• -- body fluids have solutes lt that of
  environment
• -- solutesin lt solutesout
• -- water diffuses out of tissues salts
  diffuse in

salts
6
Homeostasis and Water Balance II.
Osmoregulation A. Terminology
5. osmoconformer animal that maintains an
isosmotic condition a. Stenohaline can
tolerate a narrow range of salinity b.
Euryhaline can tolerate broad range of salinity
7
Homeostasis and Water Balance II.
Osmoregulation A. Terminology
6. osmoregulator expends energy to maintain
internal solute different from external
environment a. Hyperosmotic regulator
maintain internal solute gt external
environment b. Hypoosmotic regulator
maintain internal solute lt external environment
8
Homeostasis and Water Balance II.
Osmoregulation B. Osmoregulation in marine
environments

• Invertebrates of stable marine environments
• -- experience constant salinity levels
• -- many are stenohaline osmoconformers
• -- limited ability to osmoregulate
• Ex reef invertebrates

9
Homeostasis and Water Balance II.
Osmoregulation B. Osmoregulation in marine
environments
2. Estuarine invertebrates -- experience
wide fluctuations in salinity -- many are
euryhaline osmoconformers -- osmoregulate
under more extreme conditions Ex shore crab
10
Homeostasis and Water Balance II.
Osmoregulation B. Osmoregulation in marine
environments

• 2. Estuarine invertebrates shore crab
• Osmoconformer

11
Homeostasis and Water Balance II.
Osmoregulation B. Osmoregulation in marine
environments

• 2. Estuarine invertebrates shore crab
• salt in water
• -- gain water, lose salts
• -- Hyperosmotic regulator
• produces large amounts of dilute urine
• active transport of Na and Cl- across gills
  into body

12
Homeostasis and Water Balance II.
Osmoregulation B. Osmoregulation in marine
environments

• 2. Estuarine invertebrates shore crab
• salt in water
• lose water gain salt
• -- Hypoosmotic regulator
• produce concentrated urine
• active transport of Na and Cl- across
  gills out of body

13
Homeostasis and Water Balance II.
Osmoregulation B. Osmoregulation in marine
environments

• 3. Chondrichthyes hyperosmotic regulators

14
Homeostasis and Water Balance II.
Osmoregulation B. Osmoregulation in marine
environments
3. Chondrichthyes hyperosmotic regulators
-- solute tissues gt solute seawater
-- water diffuses into tissues do not drink
except incidentally when eating --
store urea in tissues -- trimethylamine
oxide to protect tissues -- urea
trimethylamine oxide increased solute
tissues -- excess salt through ingestion
eliminated by rectal gland
15
Homeostasis and Water Balance II.
Osmoregulation B. Osmoregulation in marine
environments
4. Marine osteichthyes hypoosmotic regulators
-- solute tissues lt solute seawater
about 1/3 that of seawater -- water
diffuses out of tissues salt diffuses across
gills -- must osmoregulate to prevent
dehydration
16
Homeostasis and Water Balance II.
Osmoregulation B. Osmoregulation in marine
environments
4. Marine osteichthyes hypoosmotic regulators
-- drink seawater -- excess salt
absorbed by gut ? blood ? gills pumped out by
Cl- secreting cells Na follows
passively -- kidneys produce concentrated
urine
17
Homeostasis and Water Balance II.
Osmoregulation C. Osmoregulation in
freshwater environments

• -- all freshwater organisms are hyperosmotic
  regulators constantly
• gain water and lose salts
• -- ex freshwater fishes
• Do not drink, except incidentally when feeding
• Have water impermeable surfaces
• Kidneys produce copious, dilute urine
• Gill have Cl- absorbing cells Na follows
  passively

18
Homeostasis and Water Balance II.
Osmoregulation D. Osmoregulation in
terrestrial environments
-- drink water -- utilize metabolic water -- waxy
and oily surfaces -- hidden respiratory
devices -- water-saving behaviors -- kidneys
19
Homeostasis and Water Balance III. Elminiation
of Nitrogenous Wastes A. Source of
nitrogenous wastes -- deamination
of amino acids, nucleic acids ? ammonia
20
Homeostasis and Water Balance III. Nitrogenous
Wastes B. Forms of nitrogenous wastes
1. ammonia -- animals that live in
aquatic environment (many aquatic
invertebrates) -- ammonotelic

21
Homeostasis and Water Balance III. Nitrogenous
Wastes B. Forms of nitrogenous wastes
2. urea -- produced in vertebrate
liver through ornithine cycle -- in
amphibians and mammals -- less toxic than
ammonia must still be diluted with water
-- ureotelic
2 NH3 CO2 ? NH2 C NH2
H2O
O
urea
22
Homeostasis and Water Balance III. Nitrogenous
Wastes B. Forms of nitrogenous wastes
3. uric acid -- in terrestrial snails,
insects, reptiles, birds -- nontoxic and
water insoluble excreted as paste -- 1 g
uric acid requires 1.5-3 ml H2O 1g urea requires
60 ml H2O -- uricotelic
23
Bird Dropping Mimics
24
Homeostasis and Water Balance III. Nitrogenous
Wastes B. Forms of nitrogenous wastes
3. uric acid Gout (metabolic arthritis)
overproduction of uric acid from purine
metabolism, resulting in deposition of sodium
urate crystals in the joints
25
Homeostasis and Water Balance III. Nitrogenous
Wastes B. Forms of nitrogenous wastes
4. guanine -- in some spiders similar
to uric acid -- nontoxic and water
insoluble excreted as paste --
guanotelic
26
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms A. Contractile
Vacuoles freshwater protozoa
27
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms B. Body
surface Porifera Cnidaria Echinodermata

Dermal branchia of echinoderms
28
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms C. Excretory
organs 3 functions -- filter body
fluids -- reabsorb needed substances from
filtrate -- secrete substances into
forming urine
29
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms C. Excretory
organs 1. Protonephridia (flame cells) of
Platyhelminthes a. structure

mesh
Collecting duct
30
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms C. Excretory
organs 1. Protonephridia (flame cells) of
Platyhelminthes b. function --
flagella create current -- fluid drawn
through mesh filtration
-- collecting tubule reabsorbs
secretes -- used mainly for
osmoregulation ammonia
eliminated through body
surface
31
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms C. Excretory
organs 2. Metanephridia of Annelids
a. structure
Schizocoelom (with coelomic fluid)
Nephric tubule w/ capillary network
nephrostome
nephridiopore
32
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms C. Excretory
organs 2. Metanephridia of Annelids
b. function -- blood forced through
capillaries fluid with
solutes squeezed out (pressure
filtration) -- filtrate
becomes part of coelomic
fluid -- coelomic fluid constantly
taken up by ciliated nephrostome
-- reabsorption secretion in
tubules capillaries -- primarily for
osmoregulation
ammonia diffuses across body surface
33
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms C. Excretory
organs 3. Malpighian Tubules/Hindgut System
of insects a. structure
Malpighian tubule
Hemocoel with hemolymph
Rectal glands (pads)
34
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms C. Excretory
organs 3. Malpighian Tubules/Hindgut System
of insects b. function 1)
filtration Malpighian tubules -- MT use
active transport to move K and Na
from hemolymph into tubule -- water and
solutes (with urates) follow
passively -- larger compounds cannot
cross tubule wall -- filtrate
moves into hindgut urates
converted to uric acid
precipitate out
35
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms C. Excretory
organs 3. Malpighian Tubules/Hindgut System
of insects b. function 2)
reabsorption secretion Hindgut
-- rectal glands use active transport to
move K and Na from rectum back into
hemolymph -- water and solutes follow
passively -- uric acid remains in rectum
and is expelled
36
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms C. Excretory
organs 3. Malpighian Tubules/Hindgut System
of insects b. function 3)
hormonal regulation -- diuretic hormone
decreases uptake of ions by rectal
glands less water is reabsorbed and
more is voided -- antidiuretic hormone
increases uptake of ions by rectal
glands more water is reabsorbed and
less voided -- proctolin speeds up
movement of hindgut and increases
voiding of contents
37
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms C. Excretory
organs 4. Vertebrate kidney a.
general structure



collecting ducts
cortex (contains nephrons)
medulla
ureter
(p. 656)
38
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms C. Excretory
organs 4. Vertebrate kidney b.
structure of nephron




proximal convoluted tubule

distal convoluted tubule
Bowmans capsule
Peritubular capillary network

glomerulus
ascending limb
descending limb
collecting duct
vasa recta
Loop of Henle
p. 656
39

cortex
Bowmans capsule
Glomerulus
medulla
glomeruli
40
proximal convoluted tubule
distal convoluted tubule
Bowmans capsule

Peritubular capillary network
cortex
Glomerulus
medulla
41
proximal convoluted tubule
distal convoluted tubule
Bowmans capsule

Peritubular capillary network
cortex
Glomerulus
medulla
descending limb
ascending limb
vasa recta
collecting duct
Loop of Henle
42
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms C. Excretory
organs 4. Vertebrate kidney b.
structure of nephron




proximal convoluted tubule

distal convoluted tubule
Bowmans capsule
Peritubular capillary network

glomerulus
ascending limb
descending limb
collecting duct
vasa recta
Loop of Henle
p. 656
43
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms C. Excretory
organs 4. Vertebrate kidney c.
function of nephron 1)
filtration -- pressure filtration --
blood forced through glomerulus under high
pressure -- fluid and solutes (ions,
glucose, urea) squeezed across walls of
glomerulus into Bowmans capsule large molecules
remain in blood -- humans produce
about 180 liters (ca. 50 gal.) of filtrate each
day reduced to about 1.2 liters/day of
urine via reabsorption
(p. 656)
44

• Homeostasis and Water Balance
• IV. Excretory and Osmoregulatory Mechanisms
• C. Excretory organs
• 4. Vertebrate kidney
• c. function of nephron
• 2) tubular reabsorption
• proximal convoluted tubule
• -- uses active transport to reabsorb ca. 60 of
  filtrate
• -- reabsorbs most all glucose and amino acids
  via active transport
• -- ion pumps used to reclaim electrolytes most
  filtered Na reabsorbed here water follows
  passively
• distal convoluted tubule
• -- also reabsorbs Na water follows passively

(p. 656)
45
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms C. Excretory
organs 4. Vertebrate kidney c.
function of nephron 3) tubular
secretion -- occurs primarily in distal
convoluted tubule -- adds to forming urine
K drugs and other foreign compounds --
uricotelic vertebrates (Reptilia Aves) secrete
uric acid into forming urine


(p. 656)
46
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms C. Excretory
organs 4. Vertebrate kidney c.
function of nephron 4) water
balance and formation of concentrated urine
General mechanism -- primary function
of nephron is to save water and form
concentrated urine (in land vertebrates and
marine Osteichthyes) -- Loop of
Henle creates osmotic gradient in medulla of
kidney that draws water from the Loop
of Henle and Collecting ducts

(p. 656)
47
c. function of nephron 4)
water balance and formation of concentrated
urine a) ascending limb of Loop of Henle
creates osmotic gradient -- thick portion is
impermeable to H20 (cannot diffuse across) --
uses active transport to pump Na into
medulla -- at bottom of Loop of Henle
osmotic pressure inside loop is 1200 mOsm --
as fluid travels upward, Na pumped out
osmotic pressure within limb decreases, but
surrounding medulla is always higher
because of continued export of Na -- results
in osmotic gradient in medulla


p. 600
(p. 656)
48

• c. function of nephron
• 4) water balance and formation of
  concentrated urine
• b) descending limb of Loop of Henle
• -- permeable to H20
• impermeable to Na, Cl-
• -- fluid entering descending
• limb is 300 mOsm
• -- as it flows downward, H20
• drawn out into medulla
• taken up by vasa recta
• -- at each step along the way,
• Na in medulla gt Na in
• limb, because of Na pumping
• by ascending limb
• -- thus at each step water diffuses
• out and osmotic pressure
• inside tubule increases until
• it reaches 1200 mOsm at bottom

p. 600
(p. 656)
49
c. function of nephron 4)
water balance and formation of concentrated
urine c) collecting duct -- at top of
ascending limb, osmotic pressure of fluid is
100 mOsm -- more Na absorbed water follows
passively -- as fluid flows down collecting
duct, passes through osmotic gradient in
medulla created by ascending limb more
water is drawn out of forming urine -- some
urea also exits collecting duct further
contributes to osmotic gradient in medulla --
length of Loop of Henle determines strength
of osmotic gradient and amt. of water
reabsorbed. Very long in desert vertebrates
short in aquatic vertebrates


p. 600
(p. 656)
50
Homeostasis and Water Balance IV. Excretory and
Osmoregulatory Mechanisms C. Excretory
organs 4. Vertebrate kidney d.
hormonal control of nephron 2 systems
1) Antidirutic hormone (ADH vasopressin)
produced by neurosecretory cells in hypothalamus
stored in posterior pituitary -- release
regulated by osmoreceptors in hypothalamus
respond to increased blood osmotic pressure
and decreased blood volume (indicate loss of
fluid) -- osmoreceptors stimulate posterior
pituitary to release ADH -- ADH increases
permeability of collecting ducts to water more
reabsorbed as fluid passes through osmotic
gradient in medulla. -- if dehydrated release
more ADH, reclaim more water from collecting
ducts urine becomes more concentrated -- if
too hydrated release less ADH, more water
remains in collecting duct produce larger
volume of more dilute urine


(p. 656)
51

• Homeostasis and Water Balance
• IV. Excretory and Osmoregulatory Mechanisms
• C. Excretory organs
• 4. Vertebrate kidney
• d. hormonal control of nephron 2
  systems
• 2) Juxtaglomerular apparatus (JGA)
• -- group of specialized cells at base of
• glomerulus
• -- responds to dropping Na levels in blood
• and/or drop in blood pressure
• releases renin
• -- enzyme activates plasma protein,
• angiotensin

(p. 656)
52

• Homeostasis and Water Balance
• IV. Excretory and Osmoregulatory Mechanisms
• C. Excretory organs
• 4. Vertebrate kidney
• d. hormonal control of nephron 2
  systems
• 2) Juxtaglomerular apparatus (JGA)
• angiotensin
• stimulates adrenal glands ?
• aldosterone causes increased
• uptake of Na by distal convoluted
• tubule
• stimulates posterior pituitary ?
• increased ADH release increased
• permeability of collecting ducts to
• water

(p. 656)
53

• Homeostasis and Water Balance
• IV. Excretory and Osmoregulatory Mechanisms
• C. Excretory organs
• 4. Vertebrate kidney
• e. Adaptations to different
  environments
• Loop of Henle
• Aquatic environments or wet terrestrial
• environments short Loops of Henle
• less water reabsorbed
• Drier terrestrial environments
• longer Loops of Henle greater
• water reabsorption

(p. 656)