Transcript Kidneys and Water Balance

Osmoregulation and
Excretion
A.P. Biology
Ch. 44
Rick L. Knowles
Liberty Senior High School
Osmoregulation
• Maintaining a balance of both water and
ions across a membrane/organism. Solute
and water homeostasis.
• Osmolarity – moles of total solute per liter
of water; usually in milliosmoles/L.
• Mechanism of homeostasis varies with the
environment in which they’ve adapted
(freshwater, saltwater, terrestrial).
Some Comparison
Freshwater
0.5 -15
0
Distilled,deionized
Water
300
Human
Plasma
1,000
Seawater
Milliosmoles/L
(mosm/L)
5,000
Dead
Sea
• Most animals are said to be stenohaline:
– And cannot tolerate substantial changes in external
osmolarity; both osmoconformers and
osmoregulators.
• Euryhaline animals:
– Can survive large fluctuations in external osmolarity.
Tilapia,
freshwater up to
2,000 mosm/L
Figure 44.2
Osmoregulation and
Nitrogenous Wastes
• Other waste solutes must be
removed from cells and
organisms.
• A waste product of metabolizing
amino acids and nucleic acids
(deamination)- ammonia.
• Concept 44.2: An animal’s nitrogenous
wastes reflect its phylogeny and habitat.
• The type and quantity of an animal’s waste
products:
– May have a large impact on its water balance.
Ammonia
• Direct by-product of
protein and nucleic acids
(deamination).
• Very toxic to cells.
• Highly soluble in water.
• Molecule of choice for
freshwater organisms;
eliminated easily through
kidneys, gill epithelia, etc.
• Downside: requires a lot
of water.
Urea
• Saltwater and
terrestrial mammals
convert ammonia into
urea.
• Less toxic; accumulate
more in tissue.
• Less soluble in water
than ammonia.
• Allows conservation
of water.
Uric Acid
• Birds and reptiles
accumulate waste in an
egg.
• Convert ammonia into
uric acid.
• Insoluble in water;
crystallizes.
• Semisolid paste-guano.
• Requires less water to
eliminate.
• Among the most important wastes
– Are the nitrogenous breakdown products of
proteins and nucleic acids
Nucleic acids
Proteins
Nitrogenous bases
Amino acids
–NH2
Amino groups
Most aquatic
animals, including
most bony fishes
Many reptiles
(including
birds), insects,
land snails
Mammals, most
amphibians, sharks,
some bony fishes
O
H
C
NH3
Figure 44.8
Ammonia
C
O
NH2
Urea
C
C
C
C
NH2
O
HN
N
N
H
N
H
Uric acid
O
Osmoconformers
• Most marine protists and
invertebrates.
• Are isoosmotic with marine
environment.
• Open channels and carriers for most
ion transport (Not all ions are in
equilibrium).
• Ex. Invertebrates like sea anemones,
jellyfish, and only vertebrate, Class
Agnatha- hagfish.
Class Agnatha- Hagfish
Show me a real hagfish!
Video: Discovery- Blue
Planet: Ocean World
Osmoregulators
• Maintain constant osmotic
concentration in body fluids and
cytoplasm despite external variations.
• Continuous regulation since
environment and intake (diet) changes.
• Evolved special mechanisms for
different environments.
• Ex. Most Vertebrates
The Problems
• Freshwater Vertebrates- are
hyperosmotic, water enters body, tend
to lose ions.
• Marine Vertebrates- are hypoosmotic,
water leaves body, tend to gain ions.
• Terrestrial Vertebrates- are
hypoosmotic, water leaves body
through respiration, perspiration, skin.
Freshwater Protists
• Problem: hyperosmotic; impossible to
become isoosmotic with dilute fresh
water; tend to gain water; lose ions; no
excretory organ.
• Solution: Contractile Vacuoles –
active transport of water out of cell;
less permeable to ions
• Downside: Active transport requires
energy.
Freshwater Invertebrates
• Water and wastes are passed into a
collecting vessel or primitive
excretory organ.
• Membrane retains proteins and
sugars and allows water and
dissolved wastes to leave-selectively
permeable.
• Ex. Freshwater jellyfish, etc,
• Concept 44.3: Diverse excretory
systems are variations on a
tubular theme.
• Excretory systems:
–Regulate solute movement
between internal fluids and the
external environment.
Excretory Processes
• Most excretory systems
– Produce urine by refining a filtrate derived from body
fluids
Capillary
Filtrate
Excretory
tubule
1 Filtration. The excretory tubule collects a filtrate from the blood.
Water and solutes are forced by blood pressure across the
selectively permeable membranes of a cluster of capillaries and
into the excretory tubule.
2 Reabsorption. The transport epithelium reclaims valuable substances
from the filtrate and returns them to the body fluids.
3 Secretion. Other substances, such as toxins and excess ions, are
extracted from body fluids and added to the contents of the excretory
tubule.
Urine
Figure 44.9
4 Excretion. The filtrate leaves the system and the body.
•
Protonephridia: Flame-Bulb
Systems
A protonephridium:
– Is a network of dead-end tubules lacking internal
Nucleus
of cap cell
openings.
Cilia
Interstitial fluid
filters through
membrane where
cap cell and tubule
cell interdigitate
(interlock)
Tubule cell
Flame
bulb
Protonephridia
(tubules)
Figure 44.10
Tubule
Nephridiopore
in body wall
• The tubules branch throughout the
body:
– And the smallest branches are
capped by a cellular unit called
a flame bulb.
• These tubules excrete a dilute
fluid:
– And function in
osmoregulation
Metanephridia
• Each segment of an earthworm
– Has a pair of open-ended metanephridia
Coelom
Capillary
network
Bladder
Collecting
tubule
Nephridiopore
Figure 44.11
Nephrostome
Metanephridia
• Metanephridia consist of tubules:
– That collect coelomic fluid and
produce dilute urine for
excretion.
Terrestrial Insects
• Problem: Must minimize water
loss.
• Solution: Use chitin as an
exoskeleton.
Malpighian Tubules
• In insects and other terrestrial arthropods,
malpighian tubules
– Remove nitrogenous wastes from hemolymph and
function in osmoregulation Digestive tract
Rectum
Intestine
Midgut
(stomach)
Salt, water, and
nitrogenous
wastes
Malpighian
tubules
Feces and urine
Malpighian
tubule
Rectum
Figure 44.12
HEMOLYMPH
Hindgut
Reabsorption of H2O,
ions, and valuable
organic molecules
Anus
Malpighian Tubules
K+
Hemolymph
Water and K+
K+
Water and waste
K+
Na+/K+-ATPase
Hindgut
Conc. Waste
Malpighian Tubules
• Use Malpighian tubules- blind end tubules that
extend into hemocoel (body cavity).
• Cells  waste and salts into hemolymphlumen
of tubule by diffusion and active transport.
• K+ are actively transported into lumen; set up a
gradient.
• Water and other ions leave the hemolymph and
follow into the lumen by passive diffusion.
• Empty into hindgut; water reabsorbed; urine is
concentrated.
• Na+/K+-ATPase moves ions from lumen of hindgut
into hemolymph.
Insects versus other
Vertebrates
• Insects use a gradient to pull water
through a membrane; open
circulatory system = low blood
pressure.
• Vertebrates- push water through a
membrane; closed circulatory
system = higher blood pressure.
More Complex
Organisms Need Another
Solution
Introducing the
Vertebrate Kidney!
Nephron (Tubule)
Gill Epithelia is Permeable
Hypotonic Env.
Hypertonic Cells
Water
Freshwater Bony Fishes
• Problems: Water enters cells from
environment, solutes leave cells.
• Solutions: Drink very little water;
excrete large amounts of dilute
(hypoosmotic) urine with large
kidneys; reabsorb ions in kidney
tubules (active transport) back into
blood; use chloride cells in gill
epithelium (active transport).
• Freshwater animals maintain water balance:
– By excreting large amounts of dilute urine.
• Salts lost by diffusion:
– Are replaced by foods and uptake across the gills.
Osmotic water gain
through gills and other parts
of body surface
Uptake of
water and some
ions in food
Uptake of
salt ions
by gills
Figure 44.3b
(b) Osmoregulation in a freshwater fish
Excretion of
large amounts of
water in dilute
urine from kidneys
Hypotonic Cells
Water
Hypertonic Env.
Saltwater Bony Fishes
• Problem: Tend to lose water, gain
ions, mostly at gills.
• Solutions: Drink large amount of
water; kidney retains water and
excretes ions (isoosmotic urine); use
chloride cells in gills to actively
transport some ions across gill
epithelium.
• Marine bony fishes are hypoosmotic to sea
water:
– Lose water by osmosis and gain salt by
both diffusion and from food they eat.
• These fishes balance water loss:
– By drinking seawater.
Gain of water and
salt ions from food
and by drinking
seawater
Osmotic water loss
through gills and other parts
of body surface
Excretion of
salt ions
from gills
Excretion of salt ions
and small amounts
of water in scanty
urine from kidneys
Figure 44.3a
(a) Osmoregulation in a saltwater fish
Cartilaginous Fishes
• Problem: Same as marine bony fishes.
• Solution: Reabsorb urea from nephron
tubule back into the blood; 100X blood
[urea] than mammals (special protective
solute,TMAO to protect
proteins)blood is slightly
hyperosmotic kidneys and gills do
not have to remove ions; do not have to
drink large volume of water.
Cartilaginous Fishes
• Problem: Still must remove excess
Na+ and Cl- that diffuse across gills,
diet, etc.
• Solution: Rectal Gland- uses
Na+/K+-ATPase pumps to actively
transport Na+ and Cl- out of blood
by setting up a gradient.
How the Rectal Gland Works
Na
+
K+
Extracellular Fluid
Na+
Cl-
Na+/K+-ATPase
Na+
Cotransporter
Cl
+
Na
Cl-
Chloride Channel
Lumen of Rectal Gland
Cl-
Na+
To Rectum
How could a marine
shark enter freshwater?
By controlling the amount of solutes!
Video: National Geographic
Presents: Attacks of the Mystery
Shark
Rectal Gland
• Very common mechanism for
removing salt in marine animals.
• Problem: Marine birds and reptiles
have freshwater kidneys designed
to reabsorb salt from urine into
blood.
• Use similar salt glands in nostrils
to excrete salt.
• An example of transport epithelia is found in the
salt glands of marine birds.
• Remove excess sodium chloride from the blood.
Nasal salt gland
(a) An albatross’s salt glands
empty via a duct into the
nostrils, and the salty solution
either drips off the tip of the
beak or is exhaled in a fine mist.
Nostril
with salt
secretions
Lumen of
secretory tubule
Vein
Capillary
Secretory
tubule
Artery
NaCl
Transport
epithelium
(b) One of several thousand
secretory tubules in a saltexcreting gland. Each tubule Direction
of salt
is lined by a transport
movement
epithelium surrounded by
capillaries, and drains into
a central duct.
Figure 44.7a, b
Bloo
d
flow
Central
duct
Secretory cell
of transport
epithelium
(c) The secretory cells actively
transport salt from the
blood into the tubules.
Blood flows counter to the
flow of salt secretion. By
maintaining a concentration
gradient of salt in the tubule
(aqua), this countercurrent
system enhances salt
transfer from the blood to
the lumen of the tubule.
Show me some marine
reptiles! Salt glands in
action!
Video: Corwin
Experience- Galapagos
Animals That Live in Temporary
Waters
• Some aquatic invertebrates living in temporary
ponds
– Can lose almost all their body water and survive in a
dormant state
• This adaptation is called anhydrobiosis.
100 µm
100 µm
Figure 44.4a, b
(a) Hydrated tardigrade
(b) Dehydrated tardigrade
• The nephron, the functional unit of the vertebrate
kidney
– Consists of a single long tubule and a ball of capillaries
called the glomerulus
JuxtaCortical
medullary nephron
nephron
Afferent
arteriole
from renal
artery
Glomerulus
Renal
cortex
Bowman’s capsule
Proximal tubule
Peritubular
capillaries
Collecting
duct
To
renal
pelvis
20 µm
Renal
medulla
SEM
Efferent
arteriole from
glomerulus
Loop
of
Henle
(c) Nephron
Figure 44.13c, d
Distal
tubule
Collecting
duct
Branch of
renal vein
Descending
limb
Ascending
limb
(d) Filtrate and
blood flow
Vasa
recta
Vertebrate Kidneys
• Four Functions:
1. Filtration
2. Reabsorption
3. Secretion
4. Excretion
1. Filtration
• Glomerulus- tightly-woven ball of
capillaries embedded in a cup-shaped
tubule- Bowman’s capsule.
• Slits/pores in capillaries and capsule
allow liquid/solutes through but
prevent cells and large proteins from
entering the nephron.
• Produces isoosmotic filtrate with blood
Filtration of the Blood
• Filtration occurs as blood
pressure:
– Forces fluid from the blood in
the glomerulus into the lumen of
Bowman’s capsule.
Pathway of the Filtrate
• From Bowman’s capsule, the filtrate
passes through three regions of the
nephron:
–The proximal tubule, the loop of
Henle, and the distal tubule
• Fluid from several nephrons:
–Flows into a collecting duct
Blood Vessels Associated with
the Nephrons
• Each nephron is supplied with blood by an afferent
arteriole:
– A branch of the renal artery that subdivides into the
capillaries
• The capillaries converge as they leave the glomerulus
– Forming an efferent arteriole.
• The vessels subdivide again:
– Forming the peritubular capillaries, which
surround the proximal and distal tubules.
From Blood Filtrate to Urine: A
Closer Look
• Filtrate becomes urine:
– As it flows through the mammalian nephron and
collecting duct.
1 Proximal tubule
NaCl Nutrients
HCO3 H2O
K+
H+
NH3
4 Distal tubule
H2O
NaCl
HCO3
K+
H+
CORTEX
Filtrate
H2O
Salts (NaCl and others)
HCO3–
H+
Urea
Glucose; amino acids
Some drugs
Key
Active transport
Passive transport
Figure 44.14
2 Descending limb
of loop of
Henle
OUTER
MEDULLA
H2O
3 Thick segment
of ascending
limb
NaCl
NaCl
3 Thin segment
of ascending
limb
NaCl
INNER
MEDULLA
5 Collecting
duct
Urea
H2O
Transport
Epithelium
2. Reabsorption
• Must return most of the water and
solutes to the blood. (2000 l of
blood 180 l water 1-2 l urine
daily).
• Reabsorb glucose, amino acids,
divalent cations in proximal tubule
by active transport carriers.
• If not reabsorbed, lost in the urine.
• Ex. Diabetes mellitus
3. Secretion
• Foreign molecules and wastes
(ammonia, urea) are secreted into
lower portions of tubule.
• Opposite direction as reabsorption
(CapillaryTubule).
• Ex. Antibiotics and other drugs,
bacterial debris
• Secretion and reabsorption in the
proximal tubule:
– Substantially alter the volume and
composition of filtrate
• Reabsorption of water continues:
– As the filtrate moves into the
descending limb of the loop of Henle
4. Excretion
• Urine is a solution of:
Harmful drugs, hormones,
nitrogenous wastes, and excess K+,
H+, water.
• Homeostasis of:
pH, electrolytes, blood volume and
pressure.
• As filtrate travels through the ascending
limb of the loop of Henle:
– Salt diffuses out of the permeable tubule
into the interstitial fluid.
• The distal tubule:
– Plays a key role in regulating the K+ and
NaCl concentration of body fluids.
• The collecting duct:
– Carries the filtrate through the medulla to
the renal pelvis and reabsorbs NaCl.
• Concept 44.5: The mammalian kidney’s
ability to conserve water is a key
terrestrial adaptation.
• The mammalian kidney:
– Can produce urine much more
concentrated than body fluids, thus
conserving water.
Solute Gradients and Water
Conservation
• In a mammalian kidney, the
cooperative action and precise
arrangement of the loops of Henle and
the collecting ducts:
– Are largely responsible for the
osmotic gradient that concentrates
the urine.
Two solutes, NaCl and urea, contribute to the osmolarity
of the interstitial fluid.
- Causes the reabsorption of water in the kidney and
concentrates the urine.
Osmolarity of
interstitial
fluid
(mosm/L)
300
300
100
300
100
CORTEX
Active
transport
Passive
transport
OUTER
MEDULLA
NaCl
H2O
H2O
400
200
H2O
NaCl
H2O
H2O
NaCl
NaCl
600
300
400
400
H2O
400
NaCl
H2O
300
H2O
H2O
600
600
H2O
Urea
H2O
INNER
MEDULLA
H2O
NaCl
700
900
NaCl
900
H2O
Urea
H2O
Urea
1200
1200
Figure 44.15
1200
• The countercurrent multiplier
system involving the loop of
Henle
– Maintains a high salt concentration in
the interior of the kidney, which enables
the kidney to form concentrated urine.
• The collecting duct, permeable to
water but not salt:
–Conducts the filtrate through the
kidney’s osmolarity gradient, and
more water exits the filtrate by
osmosis.
• Urea diffuses out of the collecting
duct:
–As it traverses the inner medulla
• Urea and NaCl:
–Form the osmotic gradient that
enables the kidney to produce urine
that is hyperosmotic to the blood.
• Antidiuretic Hormone (ADH)
– Increases water reabsorption in the distal tubules
and collecting ducts of the kidney
(a) Antidiuretic hormone (ADH)
enhances fluid retention by
making
the kidneys reclaim more
water.
Osmoreceptors
in hypothalamus
Hypothalamus
Thirst
Drinking reduces
blood osmolarity
to set point
ADH
Increased
permeability
Pituitary
gland
Distal
tubule
STIMULUS:
The release of ADH is
triggered when osmoreceptor cells in the
hypothalamus detect an
increase in the osmolarity
of the blood
Collecting duct
Homeostasis:
Blood osmolarity
Figure 44.16a
H2O reabsorption helps
prevent further
osmolarity
increase
• The Renin-Angiotensin-Aldosterone System
(RAAS)
– Is part of a complex feedback circuit that functions in
homeostasis
Homeostasis:
Blood pressure,
volume
Increased Na+
and H2O reabsorption in
distal tubules
STIMULUS:
The juxtaglomerular
apparatus (JGA) responds
to low blood volume or
blood pressure (such as due
to dehydration or loss of
blood)
Aldosterone
Arteriole
constriction
Adrenal gland
Angiotensin II
Distal
tubule
Angiotensinogen
JGA
Renin
production (b) The renin-angiotensin-aldosterone system (RAAS) leads to an increase
in blood volume and pressure.
Renin
Figure 44.16b
• The South American vampire bat, which
feeds on blood:
– Has a unique excretory system in which its
kidneys offload much of the water absorbed from
a meal by excreting large amounts of dilute urine.
Figure 44.17
• Concept 44.6: Diverse adaptations of
the vertebrate kidney have evolved in
different environments.
• The form and function of nephrons
in various vertebrate classes:
– Are related primarily to the
requirements for osmoregulation in
the animal’s habitat.
Terrestrial Animals
• Land animals manage their water budgets
– By drinking and eating moist foods and by using
metabolic water.
Water
balance in
a human
(2,500 mL/day
= 100%)
Water
balance in a
kangaroo rat
(2 mL/day
= 100%)
Ingested
in food (750)
Ingested
in food (0.2)
Ingested
in liquid
(1,500)
Water
gain
Derived from
metabolism (250)
Derived from
metabolism (1.8)
Feces (0.9)
Water
loss
Urine
(0.45)
Feces (100)
Urine
(1,500)
Figure 44.5
Evaporation (1.46)
Evaporation (900)
• Desert animals:
– Get major water savings from simple anatomical
features
Knut and Bodil Schmidt-Nielsen and their colleagues from Duke University observed that the
fur of camels exposed to full sun in the Sahara Desert could reach temperatures of over 70°C, while the
animals’ skin remained more than 30°C cooler. The Schmidt-Nielsens reasoned that insulation of the skin
by fur may substantially reduce the need for evaporative cooling by sweating. To test this hypothesis, they
compared the water loss rates of unclipped and clipped camels.
EXPERIMENT
RESULTS
Removing the fur of a camel increased the rate
of water loss through sweating by up to 50%.
Water lost per day
(L/100 kg body mass)
4
CONCLUSION
Figure 44.6
The fur of camels plays a critical role in
their conserving water in the hot desert
environments where they live.
3
2
1
0
Control group
(Unclipped fur)
Experimental group
(Clipped fur)
• Exploring environmental adaptations of the
vertebrate kidney
MAMMALS
Bannertail Kangaroo rat
(Dipodomys spectabilis)
Beaver (Castor canadensis)
BIRDS AND OTHER REPTILES
Roadrunner
(Geococcyx californianus)
Desert iguana
(Dipsosaurus dorsalis)
FRESHWATER FISHES AND AMPHIBIANS
MARINE BONY FISHES
Rainbow trout
(Oncorrhynchus mykiss)
Figure 44.18
Frog (Rana temporaria)
Northern bluefin tuna (Thunnus thynnus)