Слайд 1Chapter 44
Osmoregulation and Excretion
Слайд 2Overview: A Balancing Act
Physiological systems of animals operate in a
fluid environment.
Relative concentrations of water and solutes must be maintained
within fairly narrow limits.
Osmoregulation regulates solute concentrations and balances the gain and loss of water.
Слайд 3Freshwater animals show adaptations that reduce water uptake and conserve
solutes.
Desert and marine animals face desiccating environments that can quickly
deplete body water.
Excretion gets rid of nitrogenous metabolites and other waste products.
Слайд 4 How does an albatross drink saltwater without ill
effect?
Слайд 5Osmoregulation balances the uptake and loss of water and solutes
Osmoregulation
is based largely on controlled movement of solutes between internal
fluids and the external environment. Cells require a balance between osmotic gain and loss of water.
Osmolarity = the solute concentration of a solution, determines the movement of water across a selectively permeable membrane.
If two solutions are isoosmotic, the movement of water is equal in both directions.
If two solutions differ in osmolarity, the net flow of water is from the hypoosmotic to the hyperosmotic solution.
Слайд 6Solute concentration and osmosis
Selectively permeable
membrane
Net water flow
Hyperosmotic side
Hypoosmotic side
Water
Solutes
Слайд 7Osmotic Challenges
Osmoconformers, consisting only of some marine animals, are isoosmotic
with their surroundings and do not regulate their osmolarity.
Osmoregulators expend
energy to control water uptake in a hypoosmotic environment and loss in a hyperosmotic environment.
Слайд 8Most animals are stenohaline; they cannot tolerate substantial changes in
external osmolarity.
Euryhaline animals can survive large fluctuations in external osmolarity.
Слайд 9 Sockeye salmon = euryhaline osmoregulators
Слайд 10Marine Animals
Most marine invertebrates are osmoconformers.
Most marine vertebrates and some
invertebrates are osmoregulators.
Marine bony fishes are hypoosmotic to sea water.
They lose water by osmosis and gain salt by diffusion and from food.
They balance water loss by drinking seawater and excreting salts.
Слайд 11 Osmoregulation in marine and freshwater bony fishes:
a comparison:
drinking, gills, urine …
Excretion
of salt ions
from gills
Gain of water and
salt ions from food
Osmotic water
loss through gills
and other parts
of body surface
Uptake of water and
some ions in food
Uptake
of salt ions
by gills
Osmotic water
gain through gills
and other parts
of body surface
Excretion of large
amounts of water in
dilute urine from kidneys
Excretion of salt ions and
small amounts of water in
scanty urine from kidneys
Gain of water
and salt ions from
drinking seawater
Osmoregulation in a saltwater fish
Osmoregulation in a freshwater fish
Слайд 12Freshwater Animals
Freshwater animals constantly take in water by osmosis from
their hypoosmotic environment.
They lose salts by diffusion and maintain water
balance by excreting large amounts of dilute urine.
Salts lost by diffusion are replaced in foods and by uptake across the gills.
Слайд 13Animals That Live in Temporary Waters
Some aquatic invertebrates in temporary
ponds lose almost all their body water and survive in
a dormant state.
This adaptation is called anhydrobiosis.
Слайд 14Anhydrobiosis - adaptation… Hydrated = active state
dehydrated = dormant state.
(a) Hydrated tardigrade
(b) Dehydrated
tardigrade
100 µm
100 µm
Слайд 15Land Animals
Land animals manage water budgets by drinking and eating
moist foods and using metabolic water.
Desert animals get major water
savings from simple anatomical features and behaviors such as a nocturnal life style.
Слайд 16Water balance in two terrestrial mammals
Water
gain
(mL)
Water
loss
(mL)
Urine
(0.45)
Urine
(1,500)
Evaporation (1.46)
Evaporation (900)
Feces (0.09)
Feces (100)
Derived
from
metabolism (1.8)
Derived from
metabolism (250)
Ingested
in food (750)
Ingested
in food (0.2)
Ingested
in liquid (1,500)
Water
balance
in a
kangaroo rat
(2 mL/day)
Water
balance in
a human
(2,500 mL/day)
Слайд 17Energetics of Osmoregulation
Osmoregulators must expend energy to maintain osmotic gradients.
Animals regulate the composition of body fluid that bathes their
cells.
Transport epithelia are specialized epithelial cells that regulate solute movement.
They are essential components of osmotic regulation and metabolic waste disposal. They are arranged in complex tubular networks
An example is in salt glands of marine birds, which remove excess sodium chloride from the blood.
Слайд 18 How do seabirds eliminate excess salt from their
bodies?
Ducts
Nostril
with salt
secretions
Nasal salt
gland
EXPERIMENT
Слайд 19Countercurrent exchange in salt-excreting nasal glands
Salt gland
Secretory
cell
Capillary
Secretory tubule
Transport
epithelium
Direction of
salt movement
Central
duct
(a)
Blood
flow
(b)
Secretory
tubule
Artery
Vein
NaCl
NaCl
Salt secretion
Слайд 20An animal’s nitrogenous wastes reflect its
phylogeny and
habitat
The type and quantity of an animal’s waste products may greatly affect its water balance.
Among the most important wastes are nitrogenous breakdown products of proteins and nucleic acids.
Some animals convert toxic ammonia (NH3) to less toxic compounds prior to excretion.
Слайд 21Nitrogenous wastes
Many reptiles
(including birds),
insects, land snails
Ammonia
Very
toxic
Uric acid - not soluble
Urea - less toxic
Most aquatic
animals, including
most
bony fishes
Mammals, most
amphibians, sharks,
some bony fishes
Nitrogenous
bases
Amino
acids
Proteins
Nucleic acids
Amino groups
Слайд 22Animals Excrete Different Forms of Nitrogenous Wastes
Ammonia - needs lots
of water. Animals release ammonia across whole body surface or
through gills / aquatic animals.
Urea - The liver of mammals and most adult amphibians converts ammonia to less toxic urea. The circulatory system carries urea to kidneys, where it is excreted. Conversion of ammonia to urea is energetically expensive; uses less water than ammonia.
Слайд 23 Nitrogenous Wastes …
Uric Acid - Insects, land snails,
and many reptiles, including birds, mainly excrete uric acid. Uric
acid is largely insoluble in water; can be secreted as a paste with little water loss. Uric acid is more energetically expensive to produce than urea.
The kinds of nitrogenous wastes excreted depend on an animal’s evolutionary history and habitat.
The amount of nitrogenous waste is coupled to the animal’s energy budget.
Слайд 24Diverse excretory systems are variations on a tubular theme
Excretory systems
regulate solute movement between internal fluids and the external environment.
Most excretory systems produce urine by refining a filtrate derived from body fluids.
Key functions of most excretory systems:
Filtration: pressure-filtering of body fluids
Reabsorption: reclaiming valuable solutes
Secretion: adding toxins and other solutes from the body fluids to the filtrate
Excretion: removing the filtrate from the system.
Слайд 25Key functions of excretory systems:
an overview
Capillary
Excretion
Secretion
Reabsorption
Tubule --> blood
Excretory
tubule
Filtration
Blood -->
tubule
Filtrate
Urine
Слайд 26Survey of Excretory Systems
Systems that perform basic excretory functions vary
widely among animal groups. They usually involve a complex network
of tubules.
Protonephridia flame cells / planaria
Metanephridia earthworm / similar to nephrons
Malpighian Tubules insects
Nephrons = the function unit of the kidneys / humans.
Слайд 27Protonephridia
A protonephridium is a network of dead-end tubules connected to
external openings.
The smallest branches of the network are capped by
a cellular unit called a flame bulb.
These tubules excrete a dilute fluid and function in osmoregulation.
Слайд 28Protonephridia: the flame bulb system of a planarian
Tubule
Tubules of
protonephridia
Cilia
Interstitial
fluid flow
Opening
in
body wall
Nucleus
of cap cell
Flame
bulb
Tubule cell
Слайд 29Metanephridia
Each segment of an earthworm has a pair of open-ended
metanephridia.
Metanephridia consist of tubules that collect coelomic fluid and produce
dilute urine for excretion.
Слайд 30
Metanephridia of an earthworm
Capillary network
Components of
a metanephridium:
External opening
Coelom
Collecting tubule
Internal opening
Bladder
Слайд 31Malpighian Tubules
In insects and other terrestrial arthropods, Malpighian tubules remove
nitrogenous wastes from hemolymph and function in osmoregulation.
Insects produce a
relatively dry waste matter, an important adaptation to terrestrial life.
Слайд 32Malpighian tubules
of insects
Rectum
Digestive tract
Hindgut
Intestine
Malpighian
tubules
Rectum
Feces and urine
HEMOLYMPH
Reabsorption
Midgut
(stomach)
Salt, water, and
nitrogenous
wastes
Слайд 33 Kidneys : Nephrons = the Functional Unit
Kidneys =
excretory organs of vertebrates, function in both excretion and osmoregulation.
Mammalian excretory systems center on paired kidneys, which are also the principal site of water balance and salt regulation.
Each kidney is supplied with blood by a renal artery and drained by a renal vein.
Urine exits each kidney through a duct called the ureter.
Both ureters drain into a common urinary bladder, and urine is expelled through a urethra.
Слайд 34Overview: mammalian Excretory System
Posterior
vena cava
Renal artery
and vein
Urinary bladder
Ureter
Aorta
Urethra
Excretory organs
and major associated blood vessels
Kidney
Слайд 35The mammalian kidney has two distinct regions: an outer renal
cortex and an inner renal medulla
Kidney structure
Section of kidney
from a
rat
4 mm
Renal
cortex
Renal
medulla
Renal
pelvis
Ureter
Слайд 36 Nephron = the Functional Unit of
the Kidney
Cortical
nephron
Juxtamedullary
nephron
Collecting
duct
Nephron types
To
renal
pelvis
Renal
medulla
Renal
cortex
10 µm
Afferent arteriole
from
renal artery
Efferent
arteriole from
glomerulus
SEM
Branch of
renal vein
Descending
limb
Ascending
limb
Loop of
Henle
Filtrate and blood flow
Vasa
recta
Collecting
duct
Distal
tubule
Peritubular capillaries
Proximal tubule
Bowman’s capsule
Glomerulus
Слайд 37The nephron = the functional unit of the vertebrate kidney,
consists of a single long tubule and a ball of
capillaries called the glomerulus.
Bowman’s capsule surrounds and receives filtrate from the glomerulus capillaries.
Слайд 38Nephron
Functional Unit of the Kidney
Cortical
nephron
Juxtamedullary
nephron
Collecting
duct
Nephron types
To
renal
pelvis
Renal
medulla
Renal
cortex
Слайд 39Nephron
Afferent arteriole
from renal artery
Efferent
arteriole from
glomerulus
SEM
Branch of
renal vein
Descending
limb
Ascending
limb
Loop of Henle
Filtrate
and blood flow
Vasa
recta
Collecting
duct
Distal
tubule
Peritubular capillaries
Proximal tubule
Bowman’s capsule
Glomerulus
10 µm
Слайд 40 Filtration : Glomerulus --> Bowman’s Capsule
Filtration occurs as blood
pressure = hydrostatic pressure forces fluid from the blood in
the glomerulus to lumen of Bowman’s capsule.
Filtration of small molecules is nonselective.
The filtrate contains salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules.
Слайд 41Pathway of the Filtrate
From Bowman’s capsule, the filtrate passes through
three regions of the nephron: the proximal tubule --> loop
of Henle --> distal tubule…
Fluid from several nephrons flows into a collecting duct ---> renal pelvis ---> ureter.
Cortical nephrons are confined to the renal cortex, while juxtamedullary nephrons have loops of Henle that descend into the renal medulla.
Слайд 42Blood Vessels Associated with the Nephrons
Each nephron is supplied with
blood by an afferent arteriole = a branch of the
renal artery that divides into the capillaries.
The capillaries converge as they leave the glomerulus, forming an efferent arteriole.
The vessels divide again, forming the peritubular capillaries, which surround the proximal and distal tubules.
Слайд 43Vasa recta are capillaries that serve the loop of Henle.
The
vasa recta and the loop of Henle function as a
countercurrent system.
The mammalian kidney conserves water by producing urine that is much more concentrated than body fluids.
Слайд 44The nephron is organized for stepwise processing of blood filtrate
Proximal
Tubule
Reabsorption of ions, water, and nutrients takes place in the
proximal tubule.
Molecules are transported actively and passively from the filtrate into the interstitial fluid and then capillaries.
Some toxic materials are secreted into the filtrate.
The filtrate volume decreases.
Слайд 45Descending Limb of the Loop of Henle
Reabsorption of water continues
through channels formed by aquaporin proteins.
Movement is driven by the
high osmolarity of the interstitial fluid, which is hyperosmotic to the filtrate.
The filtrate becomes increasingly concentrated.
Ascending Limb of the Loop of Henle
In the ascending limb of the loop of Henle, salt but not water is able to diffuse from the tubule into the interstitial fluid.
The filtrate becomes increasingly dilute.
Слайд 46Distal Tubule
The distal tubule regulates the K+ and NaCl concentrations
of body fluids.
The controlled movement of ions contributes to pH
regulation.
Collecting Duct
The collecting duct carries filtrate through the medulla to the renal pelvis.
Water is lost as well as some salt and urea, and the filtrate becomes more concentrated.
Urine is hyperosmotic to body fluids.
Слайд 47The Nephron and
Collecting Duct:
regional functions of the transport
epithelium
Key
Active
transport
Passive
transport
INNER
MEDULLA
OUTER
MEDULLA
H2O
CORTEX
Filtrate
Loop of Henle
H2O
K+
HCO3–
H+
NH3
Proximal tubule
NaCl
Nutrients
Distal tubule
K+
H+
HCO3–
H2O
H2O
NaCl
NaCl
NaCl
NaCl
Urea
Collecting duct
NaCl
Слайд 48Solute Gradients and Water Conservation
Urine is much more concentrated than
blood.
Cooperative action + precise arrangement of the loops of Henle
and collecting ducts are largely responsible for the osmotic gradient that concentrates the urine.
NaCl and urea contribute to the osmolarity of the interstitial fluid, which causes reabsorption of water in the kidney and concentrates the urine.
Слайд 49The Two-Solute Model
In the proximal tubule, filtrate volume decreases, but
its osmolarity remains the same
The countercurrent multiplier system involving the
loop of Henle maintains a high salt concentration in the kidney.
This system allows the vasa recta to supply the kidney with nutrients, without interfering with the osmolarity gradient.
Considerable energy is expended to maintain the osmotic gradient between the medulla and cortex.
Слайд 50The collecting duct conducts filtrate through the 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.
Слайд 51Two Solute Model:
How the
kidney
concentrates
urine
Key
Active
transport
Passive
transport
INNER
MEDULLA
OUTER
MEDULLA
CORTEX
H2O
300
300
300
H2O
H2O
H2O
400
600
900
H2O
H2O
1,200
H2O
300
Osmolarity of
interstitial
fluid
(mOsm/L)
400
600
900
1,200
100
NaCl
100
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
200
400
700
1,200
300
400
600
H2O
H2O
H2O
H2O
H2O
H2O
H2O
NaCl
NaCl
Urea
Urea
Urea
Слайд 52Adaptations of the Vertebrate Kidney to Diverse Environments
The form and
function of nephrons in various vertebrate classes are related to
requirements for osmoregulation in the animal’s habitat.
Mammals
The juxtamedullary nephron contributes to water conservation in terrestrial animals.
Mammals that inhabit dry environments have long loops of Henle, while those in fresh water have relatively short loops.
Слайд 53Birds and Other Reptiles
Birds have shorter loops of Henle but
conserve water by excreting uric acid instead of urea.
Other
reptiles have only cortical nephrons but also excrete nitrogenous waste as uric acid.
Слайд 54Freshwater Fishes, Amphibians, Marine Bony Fishes
Freshwater fishes conserve salt in
their distal tubules and excrete large volumes of dilute urine.
Kidney
function in amphibians is similar to freshwater fishes. Amphibians conserve water on land by reabsorbing water from the urinary bladder.
Marine bony fishes are hypoosmotic compared with their environment and excrete very little urine.
Слайд 55Hormonal circuits link kidney function, water balance, and blood pressure
Mammals
control the volume and osmolarity of urine by nervous and
hormonal control of water and salt reabsorption in the kidneys.
Antidiuretic hormone = ADH increases water reabsorption in the distal tubules and collecting ducts of the kidney. An increase in osmolarity triggers the release of ADH, which helps to conserve water.
Mutation in ADH production causes severe dehydration and results in diabetes insipidus.
Alcohol is a diuretic - it inhibits the release of ADH.
Слайд 56Regulation of fluid retention by antidiuretic hormone = ADH
Thirst
Drinking reduces
blood
osmolarity
to set point.
Osmoreceptors in
hypothalamus trigger
release of ADH.
Increased
permeability
Pituitary
gland
ADH
Hypothalamus
Distal
tubule
H2O reab-
sorption helps
prevent
further
osmolarity
increase.
STIMULUS:
Increase in blood
osmolarity
Collecting duct
Homeostasis:
Blood osmolarity
(300 mOsm/L)
(a)
Exocytosis
(b)
Aquaporin
water
channels
H2O
H2O
Storage
vesicle
Second messenger
signaling molecule
cAMP
INTERSTITIAL
FLUID
ADH
receptor
ADH
COLLECTING
DUCT
LUMEN
COLLECTING
DUCT CELL
Слайд 57The Renin-Angiotensin-Aldosterone System
The renin-angiotensin-aldosterone system RAAS is part of a
complex feedback circuit that functions in homeostasis.
A drop in blood
pressure near the glomerulus causes the juxtaglomerular apparatus = JGA to release the enzyme renin.
Renin triggers the formation of the peptide angiotensin II.
Слайд 58Angiotensin II
Raises blood pressure and decreases blood flow to
the kidneys
Stimulates the release of the hormone aldosterone, which increases
blood volume and pressure.
Слайд 59Regulation of blood volume and pressure by
RAAS
The Renin-Angiotensin-Aldosterone System
Renin
Distal
tubule
Juxtaglomerular
apparatus (JGA)
STIMULUS:
Low blood volume
or low blood
pressure
Homeostasis:
Blood pressure,
volume
Liver
Angiotensinogen
Angiotensin I
ACE
Angiotensin II
Adrenal gland
Aldosterone
Arteriole
constriction
Increased Na+
and H2O reab-
sorption in
distal tubules
Слайд 60Homeostatic Regulation of the Kidney
ADH and RAAS both increase water
reabsorption, but only RAAS will respond to a decrease in
blood volume.
Another hormone, atrial natriuretic peptide ANP, opposes the RAAS.
ANP is released in response to an increase in blood volume and pressure and inhibits the release of renin.
Слайд 61Summary
Review
Animal
Freshwater
fish
Bony
marine
fish
Terrestrial
vertebrate
H2O and
salt out
Salt in
(by mouth)
Drinks water
Salt out - active
transport
by gills
Drinks water
Salt in
H2O out
Salt out
Salt in
H2O in
active transport
by gills
Does
not drink water
Inflow/Outflow
Urine
Large volume
of urine
Urine is less
concentrated
than body
fluids
Small volume
of urine
Urine is
slightly less
concentrated
than body
fluids
Moderate
volume
of urine
Urine is
more
concentrated
than body
fluids
Слайд 62You should now be able to:
Distinguish between the following terms:
isoosmotic, hyperosmotic, and hypoosmotic; osmoregulators and osmoconformers; stenohaline and euryhaline
animals.
Define osmoregulation, excretion, anhydrobiosis.
Compare the osmoregulatory challenges of freshwater and marine animals.
Describe some of the factors that affect the energetic cost of osmoregulation.
Слайд 63Describe and compare the protonephridial, metanephridial, and Malpighian tubule excretory
systems.
Using a diagram, identify and describe the function of each
region of the nephron.
Explain how the loop of Henle enhances water conservation.
Describe the nervous and hormonal controls involved in the regulation of kidney function.
