Transcript Lecture Presentation to accompany Principles of Life

40
Salt and Water Balance and
Nitrogen Excretion
Chapter 40 Salt and Water Balance and Nitrogen Excretion
Key Concepts
• 40.1 Excretory Systems Maintain
Homeostasis of the Extracellular Fluid
• 40.2 Excretory Systems Eliminate
Nitrogenous Wastes
• 40.3 Excretory Systems Produce Urine by
Filtration, Reabsorption, and Secretion
Chapter 40 Salt and Water Balance and Nitrogen Excretion
Key Concepts
• 40.4 The Mammalian Kidney Produces
Concentrated Urine
• 40.5 The Kidney Is Regulated to Maintain
Blood Pressure, Blood Volume, and Blood
Composition
Chapter 40 Opening Question
How do excretory systems of animals
maintain homeostasis of the interstitial
fluid in the face of extreme challenges?
Concept 40.1 Excretory Systems Maintain Homeostasis of the
Extracellular Fluid
Excretory systems control volume,
concentration, and composition of the
extracellular fluid and excrete wastes.
Four excretory functions:
• Regulate fluid volume in the body
• Regulate solute concentrations, or
osmolarity, of extracellular fluid
• Maintain individual solutes
• Eliminate nitrogenous wastes
Urine is the liquid waste product.
Concept 40.1 Excretory Systems Maintain Homeostasis of the
Extracellular Fluid
The osmolarity of a solution is the number
of osmoles of active solutes per liter of
solvent.
The osmolarity of the extracellular fluid must
be maintained for cellular water balance.
If the osmolarity of the extracellular fluid is
different than the cytoplasm, water will
move into or out of the cells via osmosis,
and cells may be damaged.
Concept 40.1 Excretory Systems Maintain Homeostasis of the
Extracellular Fluid
Animals in different environments face
different osmolarity problems.
On land, salt and water must be conserved.
Terrestrial animals are osmoregulators
and actively regulate the osmolarity of their
extracellular fluid.
Freshwater animals have to conserve salts
but excrete excess water, so are also
osmoregulators.
Concept 40.1 Excretory Systems Maintain Homeostasis of the
Extracellular Fluid
Marine animals are exposed to the high
osmolarity of the ocean:
Osmoconformers equilibrate their
osmolarity with seawater.
Artemia (brine shrimp) can survive in varied
environmental osmolarities:
• In high osmolarity, Cl– is actively
transported out through the gills, Na+ ions
follow.
• In low osmolarity, the transport of Cl– is
reversed.
Figure 40.1 Osmoconformity Has Limits
Concept 40.1 Excretory Systems Maintain Homeostasis of the
Extracellular Fluid
Most animals are ionic regulators,
conserving some ions and excreting others
to maintain ionic composition of
extracellular fluid.
Ionic conformers allow their ionic
composition, as well as their osmolarity, to
match the environment.
Commonly regulated ions are Na+, Cl–, K+,
Ca2+, H+, and HCO3– (bicarbonate).
Concept 40.1 Excretory Systems Maintain Homeostasis of the
Extracellular Fluid
H+ concentration, or pH, is closely
regulated—important to protein structure
and function.
A buffer is a substance that can absorb or
release hydrogen ions.
The major buffer in blood is bicarbonate
(HCO3–), which is formed from CO2.
Lungs eliminate CO2 from blood, and
kidneys reabsorb HCO3– and excrete H+ to
maintain pH.
Concept 40.2 Excretory Systems Eliminate Nitrogenous Wastes
Animals must eliminate metabolic waste
products:
• Carbohydrates and fat end up as water
and CO2 and are easily excreted
• Proteins and nucleic acids contain
nitrogen, so metabolism produces
nitrogenous waste
Ammonia (NH3) is the most common
nitrogenous waste.
Concept 40.2 Excretory Systems Eliminate Nitrogenous Wastes
Ammonia is soluble in water—aquatic
animals who secrete NH3 through gills are
ammonotelic.
Animals must convert NH3 to urea or uric
acid.
Ureotelic animals mostly excrete urea. It is
water-soluble but results in large water
loss.
Uricotelic animals mostly excrete uric acid.
It is insoluble in water and precipitates out
of the urine with little water loss.
Figure 40.2 Waste Products of Metabolism
Concept 40.2 Excretory Systems Eliminate Nitrogenous Wastes
Most species secrete more than one
nitrogenous waste.
Humans are ureotelic but also excrete:
• Uric acid—from metabolism of nucleic
acids and caffeine
• Ammonia—regulates pH of extracellular
fluid by buffering urine
Concept 40.3 Excretory Systems Produce Urine by Filtration,
Reabsorption, and Secretion
In most systems urine is produced by
filtering extracellular fluid.
The resulting fluid is a filtrate—similar to
blood plasma.
Filtrate flows through tubules and is
modified by reabsorption or secretion of
solutes.
The modified filtrate is excreted as urine.
Concept 40.3 Excretory Systems Produce Urine by Filtration,
Reabsorption, and Secretion
Annelids have segmented bodies, with a
coelom in each segment.
In earthworms, blood pumped under
pressure causes blood to filter across
capillary walls.
Water, small molecules, and some waste
products enter the coelom.
Concept 40.3 Excretory Systems Produce Urine by Filtration,
Reabsorption, and Secretion
Each earthworm segment contains a pair of
metanephridia.
A metanephridium begins as a
nephrostome, or opening, which leads into
a tubule.
The tubule ends in a nephridiopore.
Fluid enters through the nephrostomes, and
tubule cells reabsorb or secrete molecules
into it.
Figure 40.3 Metanephridia in Earthworms
Concept 40.3 Excretory Systems Produce Urine by Filtration,
Reabsorption, and Secretion
The insect excretory system consists of
Malpighian tubules—blind-ended tubules
that open into the gut.
Tubule cells actively transport uric acid, K+,
and Na+ into the tubules.
Water follows the solutes and moves
contents toward the gut.
Water and ions are recovered in the
hindgut, and uric acid and other waste are
excreted.
Figure 40.4 Malpighian Tubules in Insects (Part 1)
Figure 40.4 Malpighian Tubules in Insects (Part 2)
Concept 40.3 Excretory Systems Produce Urine by Filtration,
Reabsorption, and Secretion
Vertebrates are well-adapted to excrete
excess water.
Kidney—the main excretory organ
Nephron—the main functional unit of the
kidney, consisting of a renal tubule and
the surrounding blood vessels
Nephrons filter large volumes of blood and
achieve bulk reabsorption.
Figure 40.5 The Vertebrate Nephron
Concept 40.3 Excretory Systems Produce Urine by Filtration,
Reabsorption, and Secretion
A nephron begins with Bowman’s capsule,
which encloses the glomerulus.
Blood enters through the afferent arteriole
and leaves through the efferent arteriole.
The glomerulus is highly permeable to
water, ions, and small molecules, but
impermeable to cells and large molecules.
Figure 40.6 A Tour of the Nephron (Part 1)
Figure 40.6 A Tour of the Nephron (Part 2)
Concept 40.3 Excretory Systems Produce Urine by Filtration,
Reabsorption, and Secretion
Filtration occurs when blood pressure drives
water and solutes through fenestrations in
glomerular capillaries.
Filtration slits in Bowman’s capsule are
formed by podocytes—specialized cells
with projections that wrap around
capillaries.
Glomerular filtration rate is the rate of the
filtered fluid entering the capsule.
Concept 40.3 Excretory Systems Produce Urine by Filtration,
Reabsorption, and Secretion
The filtrate entering the capsule is similar to
blood plasma—its composition is adjusted
as it passes along the renal tubule
Peritubular capillaries transport substances
to and from the renal tubules.
Concept 40.3 Excretory Systems Produce Urine by Filtration,
Reabsorption, and Secretion
Marine bony fishes must conserve water in
their high osmolarity environment.
They minimize water loss by producing very
little urine.
Some ions are not absorbed in their gut—
NaCl is excreted through the gills.
Concept 40.3 Excretory Systems Produce Urine by Filtration,
Reabsorption, and Secretion
Cartilaginous fishes convert nitrogenous
wastes to compounds and retain large
amounts in the extracellular fluid.
The fluid is similar in osmolarity to seawater
so water is not lost by osmosis to the
environment.
Concept 40.3 Excretory Systems Produce Urine by Filtration,
Reabsorption, and Secretion
Amphibians in dry environments reduce
permeability of their skin to water.
Estivation is a state of low metabolic
activity and low water turnover.
Some frogs fill a large bladder with dilute
urine before estivation and gradually
reabsorb it into the blood.
Concept 40.3 Excretory Systems Produce Urine by Filtration,
Reabsorption, and Secretion
Reptiles are amniotes and have three major
adaptations that allow them to exist
outside of water:
• Amniotic reproduction, shelled eggs
• Scaled epidermis that retards water loss
• Excretion of nitrogenous wastes as uric
acid, with little water loss
Concept 40.3 Excretory Systems Produce Urine by Filtration,
Reabsorption, and Secretion
Mammals also have adapted to conserve
water:
• Skin covering to reduce water loss
• Amniotic reproduction
• Evolution of a kidney to produce
concentrated urine
Concept 40.4 The Mammalian Kidney Produces Concentrated
Urine
Mammals have kidneys that filter blood and
produce urine.
In each nephron, there is a specialized
feature: the loop of Henle.
Ion transport in this region creates an area
of high osmolarity, so that water is able to
be reabsorbed from the urine.
This concentrates the urine and reduces
water loss.
Concept 40.4 The Mammalian Kidney Produces Concentrated
Urine
Ureter—a duct from the kidney that leads to
the urinary bladder
Urethra—a tube for urine excretion leading
from the urinary bladder, where urine is
stored, to the outside of the body
The ureter, renal artery, and renal vein
enter the kidney on the concave side.
Figure 40.7 The Human Excretory System (Part 1)
Figure 40.7 The Human Excretory System (Part 2)
Concept 40.4 The Mammalian Kidney Produces Concentrated
Urine
Kidneys have an outer cortex that covers
the inner medulla.
The glomeruli and Bowman’s capsules are
in the cortex.
Proximal convoluted tubules—the initial,
twisted segments of the renal tubules,
located in the cortex
Figure 40.7 The Human Excretory System (Part 3)
Concept 40.4 The Mammalian Kidney Produces Concentrated
Urine
The renal tubule descends into the medulla
and forms the loop of Henle, which is
important for urine concentration.
After forming the loop, the tubule returns to
the cortex.
The loop of Henle leads to the distal
convoluted tubule.
The distal convoluted tubules join the
collecting duct in the cortex.
Collecting ducts empty into the pelvis, which
drains into the ureter.
Concept 40.4 The Mammalian Kidney Produces Concentrated
Urine
The vasa recta is a network of peritubular
capillaries parallel to the loops of Henle
and the collecting duct.
Blood plasma that does not enter Bowman’s
capsule goes via the efferent artery to the
peritubular capillaries.
These play an important role in secretion
and reabsorption and in maintaining the
high-osmolarity region.
Concept 40.4 The Mammalian Kidney Produces Concentrated
Urine
The proximal convoluted tubule (PCT) is
responsible for the reabsorption of water
and solutes—osmolarity does not change.
PCT cells actively transport Na+, glucose,
and amino acids.
Water follows the transport of solutes.
Next steps in urine processing:
• Reabsorb salts, leaving urea
• Set up conditions for hypertonic urine
production
Concept 40.4 The Mammalian Kidney Produces Concentrated
Urine
Concentration of urine is due to a
countercurrent multiplier mechanism in
the loops of Henle.
Tubule fluid flows in opposite directions in
the two limbs of a loop of Henle.
The loops increase osmolarity of
extracellular fluid in a graduated way.
Figure 40.8 Concentrating the Urine
Concept 40.4 The Mammalian Kidney Produces Concentrated
Urine
Loop of Henle segments:
• Thick ascending limb—actively transports
Na+ (Cl– follows) and raises its
concentration in the interstitial fluid
• Thin descending limb—loses water to the
neighboring interstitial fluid with high Na+
and Cl– concentration
Concept 40.4 The Mammalian Kidney Produces Concentrated
Urine
• Thin ascending limb—receives
concentrated fluid from descending limb
and allows diffusion of Na+ and Cl– into the
interstitial fluid
Fluid reaching the distal collecting duct is
less concentrated—solutes in the medulla
create a concentration gradient.
Concept 40.4 The Mammalian Kidney Produces Concentrated
Urine
The concentration gradient is preserved by
the vasa recta.
Blood flowing down the descending limb
loses water and gains solutes.
Concentrated blood flowing up the
ascending limb gains water and loses
solutes—water is thus returned to the
bloodstream.
Concept 40.4 The Mammalian Kidney Produces Concentrated
Urine
Water reabsorption and fine-tuning of ionic
composition begins in the distal convoluted
tubule.
Fluid that leaves the tubule and flows into
the collecting duct as urine has different
solute composition than blood plasma.
Concept 40.4 The Mammalian Kidney Produces Concentrated
Urine
In collecting duct the major solute in tubular
fluid is urea.
Fluid flows down collecting duct and loses
water to interstitial fluid because of
concentration gradient established by
loops of Henle.
Some urea also diffuses and adds to
osmotic force—recycling this urea
contributes to urine concentration.
Concept 40.4 The Mammalian Kidney Produces Concentrated
Urine
Renal failure results in:
• Salt and water retention (high blood
pressure)
• Urea retention (uremic poisoning)
• Decreasing pH (acidosis)
Dialysis treatment passes blood through
membrane channels bathed in a plasmalike solution to remove wastes.
Concept 40.5 The Kidney Is Regulated to Maintain Blood
Pressure, Blood Volume, and Blood Composition
A constant glomerular filtration rate (GFR)
requires blood supplied to the kidneys
under adequate pressure.
Autoregulatory mechanisms ensure blood
supply and blood pressure.
Hormones released by other organs also
help regulate the kidneys.
Concept 40.5 The Kidney Is Regulated to Maintain Blood
Pressure, Blood Volume, and Blood Composition
If GFR begins to fall, the first autoregulatory
response is dilation of afferent renal
arterioles—increases glomerular blood
pressure.
Kidney releases renin if GFR still falls, this
activates angiotensin.
Concept 40.5 The Kidney Is Regulated to Maintain Blood
Pressure, Blood Volume, and Blood Composition
Angiotensin:
• Constricts efferent renal arterioles
• Constricts peripheral blood vessels to
raise blood pressure in the body
• Stimulates release of aldosterone to
increase Na+ uptake
• Stimulates thirst to increase water
ingestion to raise blood volume and
pressure
Figure 40.9 Renin-Angiotensin-Aldosterone System Helps Regulate GFR
Concept 40.5 The Kidney Is Regulated to Maintain Blood
Pressure, Blood Volume, and Blood Composition
The hypothalamus can stimulate release of
antidiuretic hormone (ADH, also called
vasopressin).
ADH increases the permeability of
membranes to water.
Osmoreceptors that detect a rise in blood
osmolarity will stimulate ADH release.
Concept 40.5 The Kidney Is Regulated to Maintain Blood
Pressure, Blood Volume, and Blood Composition
ADH causes aquaporins, or water channels,
to be inserted in the membranes of cells in
the collecting duct.
More water is reabsorbed and urine is more
concentrated.
Alcohol inhibits release of ADH—excessive
alcohol intake can cause substantial
dehydration.
Concept 40.5 The Kidney Is Regulated to Maintain Blood
Pressure, Blood Volume, and Blood Composition
Atrial muscle fibers release atrial
natriuretic peptide (ANP) when blood
volume in the atria increases
ANP decreases the reabsorption of Na+ in
the kidney.
Increased loss of Na+ and water decreases
blood volume and pressure.
Figure 40.10 ADH Induces Insertion of Aquaporins into Plasma Membranes (Part 1)
Figure 40.10 ADH Induces Insertion of Aquaporins into Plasma Membranes (Part 2)
Answer to Opening Question
Excretory systems include active transport
of Na+, often with Cl–.
Ion transport creates osmotic concentration
gradients that move water across
membranes.
Depending on an animal’s environment, it
will direct the absorption or secretion of
solutes.
Sea birds ingest salt water and use a saltsecreting organ with special transporters
that take up NaCl and secrete it.
Figure 40.11 Salt Excretion in a Marine Bird