Transcript Ch 44 Lecture

Ch. 44:
REGULATING THE
INTERNAL ENVIRONMENT
I. Introduction
A.Homeostasis:
1.Thermoregulation = Regulation of Body
Temperature
2.Osmoregulation = Regulation of solute
and water balance
3.Excretion = Control of Nitrogen containing
waste
B.Regulators v. Conformers:
1.Regulators: Maintain constant internal
environment
2.Conformers: Allow for internal environment
to change over a range of external
conditions.
II.Thermoregulation: Regulation of Body Temp.
A. Q10 Effect: The rate at which an enzymemediated chemical reactions increases for
every 10° C temperature increase.
Ex. Rate of glycogen hydrolysis in a frog is
2.5 time greater at 30° C than 20° C. It’s
Q10 for that reaction is 2.5.
B.Temperature has a great effect on an animal’s
ability to do work.
C.Four physical processes account for heat gain
or loss:
1.Conduction: direct transfer of thermal
motion (heat) between molecules of objects
in direct contact with each other, as when
an animal sits on a pool of cold water or on
a hot rock.
2.Convection: is the transfer of heat by the
movement of air or liquid past a surface.
3.Radiation: is the emission of electromagnetic waves by all objects warmer than
absolute zero, including an animal’s body,
the environment, and the sun.
Ex. Transfer of heat from animal’s body.
4.Evaporation: Loss of heat from liquid to
gas.
D.Sources of Body Heat:
1.Ectotherms: determined by the
surrounding environment.
2.Endotherms: determined by metabolic
rates.
E.Advantages of endothermy:
1.High level of cellular respiration; allows for
endotherms to perform vigorous activities
much longer than ectotherms.
2.Stable body temperature allows for an
endotherm to live in fluctuating temps, that
are characteristics of terrestrial landscape.
However, endothermy requires much more
energy intake than ectothermy.
Example: 20°C, a human at rest has a
metabolic rate of 1,300 to 1,800 kcal/day
and an American alligator, has a metabolic
rate of only about 60 kcal per day at 20°C.
F.Thermoregulation involves physiological and
behavioral adjustments that balance heat gain
and loss.
Four categories of adpations that help animals
thermoregulate:
1.Adjusting the rate of heat exchange
between the animal and its surroundings:
a.Insulation (hair, fur, feathers, fat)
reduces the flow of heat between an
animal and its environment.
b.Adaptations of the circulatory system:
Vasodilation: an increase in the
diameter superficial blood vessels,
increasing the transfer of body heat to a
cool environment by radiation, conduction,
and convection.
Vasoconstriction: Reduces blood flow
and heat transfer by decreasing the
diameter of superficial vessels.
Countercurrent heat exchanger: special
arrangement of blood vessels that help
trap heat in the body core; helps reduce
heat loss in many endotherms.
Heat from the body core in the arteries are
transferred to the veins.
2.Cooling by evaporative heat loss:
evaporation at skin and by breathing; as
water evaporates, it also removes the heat.
-Panting
-Sweating
-Bathing
3.Behavioral responses: Sun basking, lying
in shade, hibernation, and migration, etc.
4.Changing the rate of metabolic heat
production: greatly increase heat
production when exposed to cold (will be
discussed further in the next section)
-Applies only to endotherms
G.Endothermy: Mammals and Birds
1.Body temp range: mammals = 36-38° C
birds = 39-42° C
2.Must counteract the constant heat loss to
the environment by:
a.High metabolic rate
b.Shivering to produce heat
c.Certain hormones can cause mitochondria
to increase their metabolic activity and
produce heat instead of ATP. This is
called NST (Nonshivering
Thermogenesis). It takes place
throughout the body, and also in a
specialized region called “brown fat.”
d.Insulation: Hair, feathers, fat
e.Vasodilation/Vasoconstriction
f. Panting
g.Sweating/Spreading saliva on body
surfaces
H.Ectothermy: Amphibians and Reptile
1.Body temp range: 7° to 25° C.
2.Behavioral adaptations: Moving to shade
or sunny spots.
3.Galapagos Island Iguana: vasoconstrict
their superficial blood vessels to conserve
body heat.
4.Large Endothermic Reptiles: Female
pythons, incubating eggs, increase their
metabolic rates by shivering, generating
heat (Dinosaurs endothermic??).
I. Ectothermy: Fishes
1.Conformers: within 1-2° C of their
surroundings.
2.Specialized endothermic fishes: powerful
swimmers like bluefin tuna, swordfish, and
great white sharks, have circulatory
adaptations that retain metabolic heat in
the body.
-Endothermy in
great white sharks:
countercurrent heat
exchanger in its
swimming muscles.
J. Ectothermy: Invertebrates
1.Aquatic Invertebrates: conformers
2.Terrestrial Invertebrates are actually endothermic as they can elevate body temp by
moving their powerful flight muscles.
-Bees and moths (Ex. Hawk moth)
-Countercurrent heat exchanger at the
thorax
-Honeybee social behavior: huddle and
shiver together in cold weather
K.Feedback Mechanisms in Thermoregulation:
1.Nerve cells that regulate thermoregulation
is concentrated in the hypothalamus.
2.The hypothalamus is like a thermostat,
responding to changes in body temperature
above and below a set point by activating
mechanisms that promote heat loss or gain.
L.Adjusting to Changing Temperature:
1.Many animals adjust to a new range of
environmental temperatures over a period
of days or weeks. This is called
acclimatization.
a.Acclimatization in birds and mammals:
Adjust the amount of insulation (thicker
coat of fur in the winter, etc), adjust the
metabolic heat production.
b.Acclimatization in ectotherms: process of
compensating for changes in body
temperature through adjustments in
physiology and temperature tolerance.
Ex. Winter-acclimated catfish can only survive
temps as high as 28°C, but summer-acclimated
fish can survive temps to 36°C.
-Acclimation in ectotherms often include
adjustments at the cellular level:
 Variant enzymes are produced that
have the same function, but has a
different optimal temperature.
 Membranes can also change the
proportions of saturated and unsat.
lipids they contain, which helps keep
membranes fluid at different temps.
 Antifreeze chemical: prevents ice from
forming in cells. Ex. Cryoprotectants
 Stress-Induced proteins (i.e., heatshock proteins): help maintain the
integrity of other proteins that would
otherwise be destroyed by heat.
M.Torpor conserves energy during
environmental extremes.
1.Torpor: a physiological state in which
activity is low and metabolism decreases.
2.Hibernation: long-term torpor
a.Body temp declines
b.Low metabolic rate
 Allows for survival on limited supplies of
energy
 Belding squirrel:
hibernates for 8 months;
body temp during
hibernation is near
freezing; arouses for a
few hours every week
or two.
Body temp and metabolism during
Hibernation of Belding’s ground squirrel:
3.Estivation: Summer torpor; slow
metabolism and inactivity during high
temps and when water is scarce.
4.Daily torpor: Small endotherms; occurs
at night or during the day (during hours
when they cannot feed).
III.Water Balance and Waste Disposal
A.Osmoregulation: management of water
content and solute composition.
B.Water balance and waste depends on
transport epithelia.
1.Transport epithelium: layers of epithelial
cells that move specific solutes in controlled
amounts in particular directions.
C.An animal’s nitrogenous wastes are
correlated with is phylogeny and habitat.
-Nitrogenous waste is produced when macromolecules are broken down for energy.
-Nitrogen is removed in the form of
ammonia.
1.Ammonia: small and very toxic molecule
created when macromolecules are broken
down.
a.Can only be tolerated at low
concentrations  requires access to lots
of water.
b.Ammonia release is common in aquatic
species.
c.Released easily by diffusion to the
surrounding water.
-Marine invertebrates: Diffuses across
the entire body surface.
-Fish: lost as ammonium ions (NH4+)
across the epithelium of gills, while
the kidneys extract minor amounts of
nitrogenous wastes.
2.Urea: Made in the liver by combining
ammonia with carbon dioxide and excreted
by the kidneys.
a.Low toxicity  allows for animals to
store and transport urea safetly at high
concentrations.
b.Disadvantage: Requires energy to
convert ammonia into urea.
3.Uric Acid: Land snails, insects, birds, and
reptiles excrete uric acid.
a.Insoluble in water and can be excreted
as a semisolid paste with very little water
loss (advantage).
b.Disadvantage: Requires a considerable
amount of ATP to synthesize it from
ammonia.
D.Osmoregulation:
1.Osmoconformers: internal osmolarity is
the same as that of its environment.
Osmoconformers often live in water that
has a very stable composition.
2.Osmoregulator: animals that must
control their internal osmolarity.
3.Most animals are stenohalines (animals
that cannot tolerate substantial changes in
external osmolarity.
4.Euryhalines are animals that can survive
large fluctuations of external osmolarity.
Example: Salmon migrate back and forth
between fresh and salt water.
E.Maintaining water balance in the sea:
1.Most marine invertebrates are osmoconformers.
2.Marine fishes (Class Osteichthyes)
constantly lose water through their skin
and gills.
-gain water through food, and drinking
large volumes of water (with salt disposed
by active transport out of the gills)
-very little urine is produced
3.Cartilagenous fish, like sharks (Class
Chondrichthyes) do not have large water
loss due to high concentrations of urea in
their body fluids, along with trimethylamine
oxide (TMAO), which protects proteins from
the urea; body is hyperosmotic to seawater.
F.Maintaining osmotic balance in freshwater:
1.Since freshwater fish are hypotonic to their
surroundings, they are constantly gaining
water by osmosis.
2.Freshwater fish excrete large amounts of
very dilute urine and regain lost salts in
food.
3.Paramecium have
a contractile
vacuole to
pump water out:
4.Salmon must adjust to different environments as they migrate from freshwater to
saltwater.
Ocean: Salmon drink seawater and excrete
salt from their gills.
Freshwater: Salmon cease drinking, begin
to produce lots of dilute urine and their
gills take in salt from water.
Freshwater fish
are hypertonic to
their environment.
Saltwater fish are
hypotonic to their
environment.
G.Special Problems of Living in Temporary
Waters: Anhydrobiosis (“life without water”)
1.Example: Tardigrades, or water bears
-Tiny invertebrates
-Active, hydrated state (85%)
-Inactive, dehydrate state (2%); can
survive in this state for decades
Active State
Inactive State
H.Maintaining Water Balance On Land:
1.Loss of water = Largest problem for
terrestrial organisms
2.Adaptations:
-Waxy cuticle
-Skin
-Drinking water and eating moist food
IV.Excretory Systems
A. An Overview:
1.Urine is produced in two steps:
a. Body fluid is collected – Filtration
b. Reabsorbtion
2.Filtrate: water and
small solutes, such
as salts, sugars,
amino acids, and
nitrogenous wastes
After filtration, the
filtrate is modified in
the excretory tubule
as valuable substances
from the filtrate are
reabsorbed.
B.Diverse excretory systems:
1. Protonephridia: Flame-Bulb System
a.Network of dead-end tubules lacking
internal openings.
b.Tubes branch throughout body, capped by
a flame bulb.
c.Cilia draws water and solutes
into flame bulb.
d.Urine is moved
outwards through
the nephridiopores.
e.Urine = dilute
f. Most metabolic
waste diffuses out
across the body surface
or into body cavity and out through mouth
2.Metanephridia: tubular excretory system
-Internal openings that collect body fluid
-Ciliated funnel, the nephrostome, which
collects fluids from coelom
-Each body segment contains a pair of
metanephridia
3.Malpighian Tubules: In insects and
terrestrial arthropods
-Remove nitrogenous wastes and
osmoregulate
-Tubes open to digestive tract and the
tips are immersed in the hemolymph
-Epithelial lining the tubules secrete solutes
and nitrogen wastes
-Water follows the solutes into tubule
-Most solutes are pumped back into the
hemolymph
-Water follows the solutes, and nitrogen
waste (uric acid) is eliminated as dry matter
(conserves water!)
4.Vertebrate Kidneys:
-Functions: osmoregulation and excretion
-Compact, hightly organized tubules
-Associated with capillaries and ducts
-Mammals have a pair of kidneys:
 Bean shape
 Supplied with blood by the renal artery
and a renal vein
 Urine exits each kidney through a duct
called the ureter
 Each ureter drains into the bladder
 Urine is expelled through a tube called
the urethra
Female and Male urinary tracts
C.Structure and Function of the Nephron and
their Associated Structures:
1.Two distinct regions of the kidney:
a. Renal Cortex
b. Renal Medulla
2.Nephron = the
functional unit of
the kidney
3.A nephron is a long
tubule and a ball
of capillaries called
the glomerulus
4.Bowman’s capsule:
the end of the tubule
that surrounds the
glomerulus.
5.Average human
kidney has a million
nephrons, with a total
tubule length of 80 km.
6.Filtration of blood:
-Blood pressure forces fluid from blood in
the glomerulus into the lumen of
Bowman’s capsule
-Specialized cells called podocytes are
permeable to solutes and water
-Filtrate: salts, glucose, and vitamins; &
nitrogenous wastes
7.Pathway of the Filtrate - Passes through 3
regions of the nephron:
Proximal tubules  Loop of Henle 
Distal Tube (empties into collecting duct)
8.Two types
of nephrons:
-Cortical (reduced
or no loop of henle)
-Juxtamedullary
well-developed
loop of henle;
goes into renal
medulla)
9.Blood vessels associated with Nephrons:
Key:
1.Bowman's capsule
2.Glomerulus
3.Afferent arteriole
4.Efferent arteriole
5.Proximal convoluted tubule
6.Distal convoluted tubule
7.Collecting duct
8.Loop of Henle
9.Peritubular capillary
D.From Blood Filtrate to Urine:
1.Inside the
proximal
tubule:
-maintain pH by
secretion of H+,
& ammonia.
-HCO3- absorbed
-Drugs/poison
pass from the
peritubular
capillaries
-Absorption of nutrients from filtrate
-Reabsorption of NaCl and water
2.Inside the
descending limb
of the loops of
Henle:
-Water is
reabsorption
as the filtrate
moves down the
loop.
3.Inside the
Ascending limb
of the loop of
Henle:
-NaCl diffuses out
-Filtrate becomes
more dilute
4.Inside the distal
tube:
-K+ is secreted
into the filtrate
-NaCl is reabsorbed
-pH is regulated (H+ and HCO3-)
5.Inside the collecting duct:
-NaCl, Urea,
and H2O is
reabsorbed; the
filtrate is hyperosmotic.
E.The mammalian kidney’s ability to conserve
water is a key terrestrial adaptation:
The Two
Solute
Model:
Osmolarity
Of Interstitial
Fluid Increases
The cooperative action and precise arrangement of
the loops of Henle and the collecting ducts are largely
responsible for the osmotic gradients that
concentrates the urine.
F.Regulation of blood osmolarity is maintained
by hormonal control of the kidney by negative
feedback:
1.ADH (Antidiuretic Hormone): produced by
the hypothalamus and stored in and
released by the pituitary gland.
a.Osmoreceptors cells in the hypothalamus
monitor osmolarity of blood.
b.Osmolarity rises: more ADH is released
c.Increases permeability of the epithelium
to water  Water is absorbed at the
distal tubes so that water is retained
d.ADH also causes thirst
Alcohol disturbs water balance by
inhibiting the release of ADH, causing
excessive water loss and dehydration.
2.The Renin-Angiotensin-Aldosterone
System (RAAS):
a.A drop in blood pressure or low blood
volume triggers a release of renin from
the juxtaglomerular apparatus (JGA).
b.Renin converts Angiotensinogen into
Angiotensin II, which stimulates the
Adrenal glands (on kidneys)
to release Aldosterone.
This hormone causes
the distal tubes
to reabsorb NaCl and water.
c.Angiotensin II raises blood pressure and
blood volume by constricting arterioles.
It also stimulates the proximal tubes to
reabsorb NaCl and water.
3.ADH is released when the body is
dehydrated or when there is excessive
water loss.
4.RAAS will be stimulated when there is
excessive loss of salt and body fluids due
to an injury.
5.Atrial Natriuretic Factor (ANF): a
hormone that opposes the RAAS response.
-Atria of heart releases ANF in response to
an increase in blood volume and pressure
-ANF inhibits the release of renin and
also inhibits the reabsorption of NaCl
-Reduces aldosterone release
-Lowers blood volume and pressure
G.Diverse adaptations of the kidney:
1.Most mammals have a very long loop of
Henle so to conserve as much water as
possible.
2.Beavers have very short loops because they
do not face the problem of dehydration.
3.Birds have kidneys with specialized
juxtamedullary nephrons; shorter loop of
Henle, but their main way of water
conservation is by producing uric acid.
4.Reptiles have only cortical nephrons and
their urine is isoosmotic to body fluids.
However, their cloaca reabsorbs some water
from their feces and urine. Also, they
produce uric acid.
5.Freshwater fish produce very dilute urine.
They conserve salts by reabsorbing them
in the nephrons.
6.Amphibians in freshwater accumulate salts
by active transport; they excrete very dilute
urine. On land, they conserve water by
reabsorbing water across the epithelium of
their bladder.
7.Marine fish excrete very concentrated
urine.