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4/25/11
General
•  Exchanging materials
with environment happens at cellular level
via diffusion
•  Therefore aqueous
environment essential
–  easy in aquatic,
unicellular or simple
multicellular animals
–  simple diffusion
inadequate for larger
animals
Transport of internal fluids &
Gas Exchange
•  Not differentiated in
many organisms
•  Highly interconnected in
all.
•  Circulatory system:
hemolymph, blood
•  Respiratory system:
transport of O2 and
CO2: body
⇔environment via gills
or lungs, trachea
systems on land
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Circulation
1.  Gastrovascular
cavity
–  Cnidarians,
Flatworms: few
cell layers, all
tissues bathed
directly
Circulation
2.  Open
–  Mollusks (except
cephalopods),
Arthropods
–  Hemolymph baths
internal organs
directly in sinuses
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Circulation
3.  Closed
–  Annelids,
Cephalopods,
vertebrates
–  blood confined to
vessels, and
transported to
tissues/cells
Basic structure of closed
system
1.  vessels: arteries
⇒arterioles ⇒
capillaries ⇒ tissues ⇒
venules ⇒ veins
2.  pump: muscular walls
of arteries (heart)
3.  Unidirectional: heart
⇒gills ⇒ systemic
circuit
4.  Double circulatory
system of tetrapods
–  pulmonary
–  systemic
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Basic structure of closed
system
4.  Double circulatory system of tetrapods
–  pulmonary
–  systemic
Heart - Tetrapod
•  Chambers
•  Atrium: receives
blood returning from
systemic &
pulmonary circuits
•  +O2 from pulmonary
•  -O2 from systemic
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Heart - Tetrapod
•  Ventricle: receives
blood from atrium,
contracts (very
muscular) to push
blood out
•  Pulmonary to lungs
back to atria
⇒ventricle ⇒
systemic
Heart - Tetrapod
•  Ventricle undivided in
amphibians (3
chambers)
•  partially divided in most
reptiles (3ish chambers)
•  completely divided in
birds & crocs, mammals
(i.e. four chambers, no
mixing of unoxygenated
and oxygenated blood)
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Heart - Tetrapod
•  Ventricle undivided in
amphibians (3
chambers)
•  partially divided in most
reptiles (3ish chambers)
•  completely divided in
birds & crocs, mammals
(i.e. four chambers, no
mixing of unoxygenated
and oxygenated blood)
Heart - Tetrapod
•  Ventricle undivided in
amphibians (3
chambers)
•  partially divided in most
reptiles (3ish chambers)
•  completely divided in
birds & crocs, mammals
–  (i.e. four chambers, no
mixing of unoxygenated
and oxygenated blood)
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Heart - Tetrapod
•  Valves: assure
one-way flow:
atrioventricular
(AV); semilunar
valves (base of
pulmonary artery,
aorta)
Cardiac cycle
1.  Heart beat:
•  Diastole: relaxation
of the heart muscles
(atria and ventricles
fill)
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Cardiac cycle
1.  Heart beat:
•  Diastole: relaxation
of the heart muscles
(atria and ventricles
fill)
•  contraction = systole
–  FIRST, atrial systole
–  lub - recoil of blood
against closed AV
valve
Cardiac cycle
1.  Heart beat:
•  Diastole: relaxation of
the heart muscles (atria
and ventricles fill)
•  contraction = systole
–  FIRST, atrial systole
–  lub - recoil of blood
against closed AV valve
• 
contraction = systole
–  SECOND, ventricular
systole
–  “dub - recoil against
semilunar valve
• 
cycle ca 0.8 sec. in
human at rest
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Cardiac cycle
2.  Heart rate = beats/min
–  affected by oxygen debt, temperature,
hormones etc.
3.  Stroke volume = the amount of
blood pumped in a single
contraction
4.  Cardiac output = vol blood/min by left
ventricle (rate & vol/beat dependent)
Cardiac cycle
5.  SA node (pacemaker) in wall of right atrium sets
pumping rhythm
•  AV node acts as relay
• 
Pacemaker
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Blood flow
1.  Obeys laws of fluid
dynamics; flows under
pressure, faster in
larger vessels, slowest
in capillaries
2.  Elastic quality of
arteriole walls helps
smooth out pressure
3.  Blood pressure:
peripheral resistance of
arterial walls,
measured in mm
mercury
Blood flow
•  The critical exchange of
substances between the
blood and interstitial fluid
takes place across the
thin endothelial walls of
the capillaries
•  The difference between
blood pressure and
osmotic pressure drives
fluids out of capillaries at
the arteriole end and into
capillaries at the venule
end
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Lymphatic System
•  Collects blood lost through capillary
action (ca. 1%)
•  Collects interstitial fluid (lymph)
•  Lymph vessels drain into veinous
circulation near the neck
•  Lymph nodes filter lymph
Blood
•  Connective tissue:
cells in a liquid
matrix “plasma ,
•  solutes (salts,
electrolytes for
osmotic balance)
dissolved in water
(90%)
•  Average human 4-6
liters
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Blood
• 
• 
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• 
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RBCs - Erythrocytes
most numerous
mammal RBC lack nuclei
all RBCs lack
mitochondria
major function: O2
transport via hemoglobin,
an iron carrying protein
that binds O2, also nitric
oxide (NO)
Formed in red marrow of
bone (esp. ribs, vertebrae)
Blood
WBCs - Leukocytes
•  travel in interstitial fluid to
fight infections
•  5 kinds:
–  Monocytes: migrate &
differentiate as part of
immune response
–  Neutrophils: first defense
against microbes
–  Basophils: allergic reactions
(anticoagulant & vasodilator)
–  Eosinophils: allergic
reactions & parasites
–  Lymphocytes: vertebrate
adaptive immune response
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Blood
Platelets
•  chips of cells (pinched off cytoplasm from marrow
cells)
•  function: clotting; fibrinogen a plasma protein seals
leaks in vessels; multiple clotting factors
RESPIRATION
•  Mitochondrial respiration consumes O2 and
produces CO2.
•  Animals need to exchange gasesà
respiration
•  Animals that are larger than a few cells
cannot rely on diffusion (remember this
occurs slowly over long distances)
•  Animals rely on bulk flow then diffusion: there
is an intimate relationship between the
circulatory system and the respiratory system.
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Structure
•  Only requires a thin, moist
simple squamous
epithelium w/rich blood
supply, interfaces with
medium (air or water)
•  Many animals have
specialized respiratory
organs with large surface
areas (to maximize gas
exchange): gills (outpocketings, water)
or lungs (infolding, air)
•  Remember the skin is also
an important gas exchange
surface for some animals
(cutaneous gas exchange).
Gills
•  External extensions
of pharynx, feathery,
delicate
•  Advantages: water
keeps gills
constantly moist
•  Disadvantages: [O2]
in water is low
compared to air
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Air
•  high [O2] , easier to ventilate
•  but respiratory surface looses H2O
through evaporation
•  air utilized via invaginating respiratory
surface into body
Tracheae - Insects
•  tiny air tubes via spiracles
•  carry gases directly to tissues, do not use
circulatory system
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Lungs
•  vascularized mantel
of land snails
•  booklungs - spiders
•  air sacs of terrestrial
vertebrates
Mammalian Lung
•  Paired invaginations
restricted to single
location, circ system
must bridge gap to
other parts of body
•  Trachea, bronchus,
bronchiole, alveoli
•  Ventilation: negative
pressure breathing rib cage and
diaphragm
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Birds
•  anterior and posterior air sacs
•  two cycles inhalation and exhalation required
Temperature and Thermal
Environment
•  Temperature: a measure of the amount of
heat energy present.
–  Organisms are largely governed by the response
of water to temperature.
•  Macroclimate: The climate at the level of
biomes.
•  Microclimate: The climate that an organism
experiences: can vary considerably over short
distances.
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Microclimate
• 
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Altitude
Aspect
Vegetation
Color of ground
Exposure
Topography
Strategies for responding to thermal
environments
•  Some confusing
terminology…
– 
– 
– 
– 
– 
– 
– 
– 
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Endotherm
Ectotherm
Poikilotherm
Warm-blooded
Cold-blooded
Homeotherm
Heterotherm*
Stenotherm*
Eurytherm*
* terms not used in your textbook
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Strategies for responding to thermal
environments
Classic distinctions
•  Poikilothermy: body
temperature fluctuates with
environment.
•  Homeothermy: body
temperature remains
constant
•  Ectothermy: body
temperature regulated by
external sources.
•  Endothermy: body
temperature regulated by
internal metabolic sources.
• 
Poikilothermy/Homeothermy &
ectothermy/endothermy vary on
a continuum.
Strategies for responding to thermal
environments
More distinctions
• 
• 
Homeothermy: Body temperature
remains constant.
Heterothermy: Body temperature
varies.
• 
Note that endothermy & ectothermy
are distinguished by source of heat,
not body temperature.
• 
Organisms can be poikilothermic
homeotherms. How?
• 
Organisms can be endothermic
heterotherms. How?
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Strategies for responding to thermal
environments
More terminology
• 
• 
Eurythermic: wide tolerance range.
Stenothermic: narrow tolerance range.
• 
Examples: Tropical vs. Arctic terrestrial
animals.
• 
Examples: Polar fish vs. intertidal fish.
Antarctic Ice Fish thermal tolerance
range 6 ºC (-1.8º to 4ºC)
Intertidal goby thermal tolerance
range >30 ºC (8º to 40ºC)
Acclimation
•  Changes in
physiological or
biochemical processes
in response to some
environmental factor.
•  Permits organisms to
tolerate temperatures
one season that would
be fatal or sub-optimal
in another.
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Acclimation
•  Involves biochemical or
physiological adjustments.
•  Changes are relatively short
term and are reversible.
•  Not all organisms can
acclimate.
–  Depends on the amount of
variation in the environment.
–  In what environments/
organisms would you expect
to see acclimation?
Hibernation & Estivation
•  State of reduced metabolism
that may last several
months.
•  To avoid cold: hibernation.
•  To avoid heat: estivation.
•  Must rely on stored energy
reserves.
•  Lower metabolic rate
reduces loss of these
reserves.
Hibernating ground squirrels may have core temperatures as low as -2ºC
Estivating lungfishes seal themselves in a mud/mucus ball as lake beds begin to dry up
Check out this website on frozen frogs! It s very, very cool
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Why thermoregulate?
•  Biochemistry.
•  Maintain a metabolically active
temperature when external
temperatures vary.
•  Why would thermoregulation evolve?
(Later)
Why thermoregulate?
• 
• 
• 
• 
Biochemistry
Increased rate of many chemical reactions.
Affects solubility.
Too high temperatures denatures proteins.
Too low temperatures result in freezing.
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Why thermoregulate?
• 
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Thermal neutral zone
The range of environmental
temperatures over which the
metabolic rate of a
homeothermic animal does not
change.
Not a problem for poikilothermic
homeotherms (external
environment does not vary).
Big problem when external
environment varies
considerably.
Permits endothermic
homeotherms to live in
environments with higher
temperature fluctuations.
Thermoregulation
•  Regulation of body temperature.
•  Must manipulate heat gain and loss.
•  Via energy transfer processes:
Hs = Hm ± Hcd ± Hcv ± Hr - He
•  What are these variables?
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Hs = Hm ± Hcd ± Hcv ± Hr - He
•  Hs: Heat stored in the body (this is what is being
thermoregulated!)
•  Hm: Metabolic heat (heat gain through cellular
respiration)
•  Hcd: Conduction (transfer of heat between two
objects).
•  Hcv: Convection (transfer of heat between solid and
liquid or air).
•  Hr: Radiation (transfer through electromagnetic
radiation).
•  He: Evaporation (heat loss due to evaporation).
Temperature regulation in
ectotherms
•  Temperature dependent upon external
environment.
–  What variables of Hs = Hm ± Hcd ± Hcv ± Hr - He
can we ignore?
•  How then, do they thermoregulate?
–  Which variables can they manipulate?
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Temperature regulation in ectotherms
•  Can manipulate
conduction,
convection, and
radiation.
•  Behavioral patterns
–  Habitat selection
–  Posture
•  Color
•  Growth form
Temperature regulation in ectotherms
•  When it is too cold
the problem is to
increase heat
storage (maximize
the + aspect of
the equation;
minimize the aspect).
Hs = Hm ± Hcd ± Hcv ± Hr - He
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Temperature regulation in ectotherms
•  When it is too hot
the problem is to
keep heat storage
low (minimize the
+ aspect of the
equation; maximize
the - aspect).
Hs = Hm ± Hcd ± Hcv ± Hr - He
Temperature regulation in
endotherms
•  Endotherms can maintain body temperatures using
cellular respiration.
•  This is energetically expensive (high metabolic
costs).
•  Can mitigate this using other mechanisms that have
negligible metabolic costs.
–  Behavioral & Physiological
–  These manipulate Hcd, Hcv, and Hr.
•  Can mitigate this using strategies that decrease Hm
and He.
Hs = Hm ± Hcd ± Hcv ± Hr - He
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Negligible metabolic costs
• 
• 
• 
• 
Vasomotor responses
Postural changes
Insulation adjustments
Microclimate choices
How can conductance and
convection change?
•  Insulation
–  Pilomotor response
(goosebumps)
–  Seasonal fur
–  Fat/blubber
•  Vasoconstriction &
vasodilation
•  Burrow or huddle (can
also decrease Hr)
•  Counter-current
exchange.
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How can conductance and
convection change?
•  Insulation
–  Pilomotor response
(goosebumps)
–  Seasonal fur
–  Fat/blubber
•  Vasoconstriction &
vasodilation
•  Burrow or huddle (can
also decrease Hr)
•  Counter-current
exchange.
Decreasing metabolic costs
•  Avoidance and
habitat selection
•  Nocturnal activity
•  Hibernation or
estivation
•  Torpor
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Decreasing metabolic costs
•  Avoidance and
habitat selection
•  Nocturnal activity
•  Hibernation or
estivation
•  Torpor
Decreasing metabolic costs
•  Avoidance and
habitat selection
•  Nocturnal activity
•  Hibernation or
estivation
•  Torpor
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Decreasing metabolic costs
•  Avoidance and habitat
selection
•  Nocturnal activity
•  Hibernation or estivation
•  Torpor: Facultative
decrease of metabolic
rate.
–  Are hummingbirds
homeothermic???
Hummingbirds can have an active body temperature of 40ºC
(=104ºF). This is the highest body temperature of any bird.
During torpor they may lower this to 12ºC!
Manipulating He
•  Sweat (animals).
•  Breathing.
–  Panting.
•  All are tied in with
vasomotor control.
–  Evaporative surfaces
often heavily
vascularized.
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Why did endothermy evolve?
•  Metabolically
expensive--costs
involved.
–  Difficult if food is
scarce.
–  Metabolic costs
increase 10X--need
to eat more.
•  What are the
benefits?
Why did endothermy evolve?
•  Metabolically
expensive--costs
involved.
•  What are the benefits?
–  Increased locomotor
activity via increased
aerobic ability.
–  Increased
responsiveness in
varying environments.
–  Ability to exploit more
diverse environments.
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Summary
•  Animals and plants use numerous
mechanisms to cope with temperature
variation.
•  There is a broad continuum of
thermoregulatory strategies.
•  Thermoregulation can be accomplished
through numerous behavioral, morphological,
and physiological pathways.
Osmoregulation
•  Balances the uptake and loss of water
and solutes
•  Cells & tissues are bathed in internal
fluids, cannot tolerate dramatic changes
in osmotic content
–  Regardless of external environment:
–  Marine, freshwater, terrestrial; transitional,
fluctuating
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Osmolarity
•  Concentrations of solutes
in fluids
–  Measured in milliosmoles/
L
•  Hyperosmotic: higher
solute concentration
•  Hypoosmotic: lower
solute concentration
•  Isoosmotic: equal
osmolarity
Osmolarity
•  Water and salts will
move down their
concentration gradients
•  This presents different
challenges for marine,
freshwater, and
terrestrial organisms.
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Transport Epithelium
•  Is the specialized tissue
that regulates solute
movement.
•  Active transport of ions,
small molecules.
•  Controls permeability to
water.
Osmoconformers
•  Body fluids are
isoosmotic with
environment.
•  Most marine
invertebrates.
•  Any freshwater?
•  Do not lose or gain
water.
•  Are there costs to this?
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Osmoregulators
•  Adjust internal
osmolarity: body
fluids have different
osmolarity from
environment.
•  What they do
depends on habitat,
adaptation, and
phylogeny.
Tolerance
•  Most animals
(whether
osmoconformers or
osmoregulators)
cannot tolerate
broad changes in
external osmolarity:
Stenohaline (what
does this word
remind you of?)
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Tolerance
•  Euryhaline animals
can tolerate broad
changes.
•  Example: salmon
travel from
freshwater to
saltwater to
freshwater to breed
Osmoregulators: Chondrichtyes
•  Which animals are
these?
•  Where do they live
(for the most part)?
•  Sharks and relatives
are hyperosmotic
(gain water through
osmosis).
–  Because retain urea
dissolved in body
fluids
Urine gets rid of excess water.
Salt gland gets rid of excess
sodium.
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Osmoregulators:
Marine Osteichthyes
•  What kind of animals are
these?
•  Bony fishes evolved in
freshwater, maintain
ancestral freshwater
osmolarity
•  Are therefore strongly
hypoosmotic (lose water
through osmosis).
Drinking constantly.
Get rid of salts through chloride
cells in gills and urine
Osmoregulators:
Marine Reptiles
•  Have salt glands
•  Marine birds: nasal
salt glands
•  Crocodile tears
•  Marine turtles and
cloacal salt glands
•  Marine iguanas:
nasal salt glands
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Freshwater
animals
•  Problems are opposite to
marine
•  ALL animals are
hyperosmotic to
freshwater, so osmotically
take in water
•  Constantly urinating
•  Expend energy to
maintain salts
Terrestrial animals
•  Desiccation greatest
threat to life on land
•  Humans die if water
loss exceeds 12%
•  Helps explain why
so few colonizations
of terrestrial
environments
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Water balance in terrestrial
animals
•  Water balance is
acquisition vs loss
•  Acquisition
–  Wd = drinking
–  Wf = food
–  Wa = absorption
•  Loss
–  We = evaporation
–  Ws = secretions
•  Overall
–  Wia = Wd + Wf + Wa - We - Ws
Adaptations to terrestriality
involve maximizing acquisition
while minimizing loss
Water balance in terrestrial animals
•  Acquisition strategies
when water is limiting:
–  Condense fog.
–  Metabolic water from food
(oxidation of glucose).
•  Water conservation:
–  Prevent evaporation with
waterproofing cuticle.
–  Restrict time or place of
activity.
–  Concentrate urine or feces.
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Water balance in terrestrial animals
•  Acquisition strategies
when water is limiting:
–  Condense fog.
–  Metabolic water from food
(oxidation of glucose).
•  Water conservation:
–  Prevent evaporation with
waterproofing cuticle.
–  Restrict time or place of
activity.
–  Concentrate urine or feces.
Water balance in terrestrial animals
• 
Acquisition strategies
when water is limiting:
–  Condense fog.
–  Metabolic water from
food (oxidation of
glucose).
• 
Water conservation:
–  Prevent evaporation
with waterproofing
cuticle.
–  Minimize evaporation
through behavior or
morphological
structures.
–  Restrict time or place of
activity.
–  Concentrate urine or
feces.
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Water balance in terrestrial animals
•  Acquisition strategies when
water is limiting:
–  Condense fog.
–  Metabolic water from food
(oxidation of glucose).
•  Water conservation:
–  Prevent evaporation with
waterproofing cuticle.
–  Restrict time or place of
activity.
•  Estivation, nocturnality
–  Concentrate urine or feces.
Water balance in terrestrial animals
•  Acquisition strategies when
water is limiting:
–  Condense fog.
–  Metabolic water from food
(oxidation of glucose).
•  Water conservation:
–  Prevent evaporation with
waterproofing cuticle.
–  Minimize evaporation through
behavior or morphological
structures.
–  Restrict time or place of
activity.
–  Concentrate urine or feces.
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Nitrogenous wastes
•  Nitrogenous wastes
come from the
metabolic breakdown of
proteins or DNA.
•  Byproduct is ammonia,
which is highly toxic to
tissues.
•  Not a problem for
aquatic animals: simply
rid ammonia into
aqueous environment
Nitrogenous wastes
•  Terrestrial animals
cannot do this.
•  Expend energy to
convert ammonia into
less toxic form.
•  Mammals produce urea
–  Does not require dilution
by lots of water
–  Water soluble, removed
from fetus via placenta
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Nitrogenous wastes
•  Terrestrial animals cannot do
this.
•  Expend energy to convert
ammonia into less toxic form.
•  Why does this not work for
animals with shelled eggs?
•  Reptiles (including birds) and
insects produce uric acid
–  Precipitate, paste-like, not
water-soluble
–  Concentrations in pocket in
egg, does not contaminate
interstitial fluids
The Excretory System
• 
• 
These nitrogenous wastes are
removed from the bloodstream
by the excretory system
Four components:
1. 
2. 
3. 
4. 
Filtration: nonselective, water
and solutes
Reabsorption: returns valuable
substances to body fluids
Secretion: eliminates toxins
and excess salts
Excretion: altered filtrate
(urine) leaves body
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Excretory Systems
• 
• 
• 
• 
Varies widely across animal taxa
BUT similar theme where form meets function: network of tubules that provide
a large surface area for the exchange of water and solutes
Protonephridia in flatworms
Simple tubular system with flame bulb filtration
– 
Interstitial fluid ⇒ flame bulb filtration ⇒ external environment
Excretory systems
•  Metanephridia: most annelids
–  Excretory tubules with internal
opening.
–  Closed circulatory system:
metanephridia surrounded by
capillaries.
–  Metanephridia take in filtrate,
selectively reabsorb solutes.
–  Terrestrial & freshwater annelids
(?) live in hypoosmotic
environment, metanephridia
eliminate large amounts of
water.
–  Marine annelids isoosmotic,
eliminate ammonia wastes.
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Excretory systems
•  Malphighian Tubules:
Terrestrial arthropods
•  Open circulatory system
•  Dead end tips open into
hemolymph
•  Transport epithelium
secretes nitrogenous wastes
and solutes into tubules
(water follows, how?)
•  Transports to rectum, water
and solutes reabsorbed, uric
acid eliminated
Excretory systems
• 
• 
• 
• 
• 
Vertebrate kidney
Paired compact organs,
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
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Kidney
•  The mammalian kidney has two distinct
regions: an outer renal cortex and an
inner renal medulla
Kidney
•  The nephron is the functional unit of the kidney
–  Single long tubule and a ball of capillaries called the
glomerulus
–  Bowman s capsule surrounds and receives filtrate from the
glomerulus
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Kidney
• 
• 
• 
Filtration occurs as blood pressure forces fluid from the blood in the
glomerulus into the 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
Kidney
• 
• 
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, all of which
lead to the renal pelvis, which is drained by the ureter
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Kidney
•  Vasa recta are capillaries that serve the
loop of Henle
•  The vasa recta and the loop of Henle
function as a countercurrent system
Kidney
•  The mammalian kidney conserves water by producing urine that
is much more concentrated than body fluids
•  The cooperative action and 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
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Urine Concentration in the
Kidney
•  Loop of Henle
maintains interstitial
gradient of NaCl
–  Increases in the
descending limb
–  Decreases in the
ascending limb
–  Energy is expended
to maintain the
gradient between the
medulla and cortex
Urine Concentration in the
Kidney
•  Urea diffuses into the interstitial
fluid of the medulla from the
collecting duct
•  Filtrate makes three trips
between the cortex and medulla
•  As filtrate flows past interstitial
fluid of increasing osmolarity,
more water moves out by
osmosis, conserving water and
concentrating urine.
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Diversity of the Kidney
•  Reptiles tend to
have shorter loops
of Henle, conserve
by elimination of uric
acid (energetically
expensive)
•  Mammals in arid
environments have
extremely long loops
Hormonal control of the kidney
•  How are water and
solute levels
regulated?
•  Decision: conserve
or flush…
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Hormonal control of the kidney
•  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
Hormonal control of the kidney
•  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
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Hormonal control of the kidney
•  ADH binds to collecting
duct cells
•  Signals activation of
aquaporin water channels
•  Increases permeability of
cell wall to water
Hormonal control of the kidney
•  Why do caffeine
and alcohol make
us need to urinate
(or insert favorite
euphemism here)?
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Summary
•  Maintaining homeostasis in osmolarity
presents a challenge for all animals.
•  Habitat (marine, freshwater, terrestrial)
and phylogeny affect the solutions
found in the diversity of animals.
•  Homeostasis and excretion of waste are
intricately linked.
Neurons are excitable cells
•  A cell can rapidly alter its membrane
potential in response to an incoming
signal.
•  A change in membrane permeability to
certain ions causes the change in
membrane potential.
•  Neurons use this change in membrane
potential to carry electrical signals… often
across longggg distances.
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Motor Neurons
•  We ll first focus on
motor neuronsthese communicate
between the central
nervous system and
the skeletal
muscles.
Why do I keep saying neuron instead of nerve ?
•  A nerve is a bundle of
axons encased in sheath
found in peripheral nervous
system.
•  Nerves can have mixed
functions
–  May contain sensory
fibers as well as motor
fibers, for example.
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Neuron Structure
•  Neurons usually
receive signals at
one end and conduct
a signal in one
direction to the other
end, so they have a
certain polarity.
•  They receive signals
at the dendrites and
the cell body.
•  The signal is
converted into an
electrical signal and
passed to the cell
body.
Neuron Structure
•  Signal integration
occurs in a
specialized region
between the cell
body and the axon,
called the axon
hillock.
•  If the signal is
sufficiently large
(above a particular
threshold), an action
potential is initiated.
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Neuron Structure
•  The action potential
passes down the
axon which is
specialized for signal
conduction.
•  Axons may be very
short or VERY long.
•  Vertebrate axons are
wrapped with a
myelin sheath which
speeds up
conduction.
Neuron Structure
•  The action potential
passes down the axon to
the axon terminal where
the signal is transmitted to
the target cell (in the case
of motor neurons, this is
skeletal muscle).
•  The axon terminal forms a
synapse with the target
cell, and the electrical
signal is transduced into a
chemical signal
(neurotransmitter).
•  The neurotransmitter
diffuses across the
synapse and binds to
receptors on the muscle
cell membrane.
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Electrical Signals
•  Neurons can rapidly alter their membrane potential
in response to a signal.
•  Most neurons have a resting potential of -70mV.
•  This means that when the neuron is not involved in
sending signals, the inside of the cell membrane is
more negatively charged than the outside of the
membrane.
Electrical Signals
•  Depolarization occurs when the charge difference
between the inside and outside decreases and
becomes less negative.
•  This can happen when positively charged ions enter
the cell or negatively charged ions leave the cell.
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Electrical Signals
•  Hyperpolarization occurs when the
membrane potential becomes more negative.
•  Negative ions may enter the cell or positive
ions may leave.
Membrane Potential (Vm)
•  Only two factors are required to establish a
potential difference across a membrane: a
concentration gradient for an ion and a
membrane that is permeable to that ion (also
need to know the ion s charge).
Here we have more K+ inside, so it
would favor outward movement of K+.
And we have more Na+ outside, so this
would favor inward movement of Na+.
There is electroneutrality across the
membrane.
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Membrane Potential
•  To create a membrane potential, we insert K+
channels. This allows K+ to move out, but no
other ions may move across the membrane.
Membrane Potential
•  When K+ moves out, it creates a local region
of negativity on the inner surface of the
membrane and positivity on the outer surface.
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Membrane Potential
•  The negative charge inside generates an
electrical force that tends to draw positive
charges back inside.
•  So, the K+ is battling the force of its
concentration gradient as well as this
electrical gradient.
Membrane Potential
•  K+ ions continue to move across the
membrane, but their inward and outward
movements exactly balance each other.
•  The potential difference (voltage) under these
equilibrium conditions is called the equilibrium
potential.
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Membrane Potential
•  The actual number of ions needed to create
this membrane potential is VERY SMALL!
•  This is a local phenomenon right at the cell
membrane.
•  The ion movements we ll be talking about
(across the cell membrane) are not enough to
change the overall concentrations of these ions
inside the cytoplasm or in the extracellular fluid.
Membrane Potential
•  That example was SIMPLE, considering movement of K+
only.
•  In a neuron, resting Vm is determined by 2 factors:
1) Large chemical gradients for K+ and Na+ across plasma
membrane
Na+ / K+ ATPase is required to maintain this chemical gradient but does
NOT generate the resting electrical membrane potential
AND
2) Permeability of plasma membrane to ions
Membranes of resting cells are permeable to K+
K+ flux via passive (leaky) K+ channels is most important contributor to
Vm
Na+ flux also contributes to Vm
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Membrane Potential
•  Neurons depolarize or hyperpolarize by selectively altering the
permeability of their membranes to ions (by opening and closing
gated ion channels).
•  Dependent on the membrane permeability to an ion that is at
different concentrations on either side of the membrane.
Membrane Potential
•  Open Na+ channels and
Na+ flows IN due to
electrochemical gradient
until it reaches the
equilibrium potential.
•  Membrane depolarizes
due to + ions flowing in.
•  Open K+ channels and K+
flows OUT.
•  Membrane hyperpolarizes
due to + ions flowing out.
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So how do neurons communicate?
•  Remember the
different parts of the
neuron:
–  Signal reception
–  Signal integration
–  Signal conduction
–  Signal transmission
Our example: vertebrate motor neuron
•  Signal is a neurotransmitter
(remember in other
neurons, this can be
electrical, chemical,
mechanical, etc.)
•  Neurotransmitter must bind
to a receptor.
•  Receptor is a ligand-gated
ion channel.
•  These receptors are
concentrated on the
dendrites and cell body.
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Graded Potentials
•  The neurotransmitter
may be in high or low
concentrations resulting
in varying responses in
our neuron.
•  At low concentrations,
only a few channels will
open (permeability does
not change very much).
•  At high concentrations,
many channels open,
increasing ion
permeability a LOT… This is considered a graded potential
changing membrane because the membrane potential will vary
depending on the strength of the
potential.
incoming stimulus (the amount of NT).
Graded Potentials
•  NT binds to a ligand-gated Na
+ channel causing it to open.
•  Na+ flows into channel
causing depolarization.
•  That depolarization can
spread along the membrane,
but will decrease with distance
due to resistance within the
cell and current leakage
through the cell membrane.
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Graded Potentials
•  Graded potentials can be
excitatory or inhibitory.
•  HOW?
•  If a receptor is more likely to
depolarize the membrane it is
excitatory; if a receptor is
more likely to hyperpolarize
the membrane it is inhibitory.
•  Na+ and Ca2+ channels are
excitatory, K+ and Clchannels are inhibitory.
Graded Potentials and Action Potentials
•  Because these graded
potentials cannot be
transmitted across long
distances without degrading,
the cell needs another way to
transmit information across
distances of more than a
couple of mm.
•  Action potentials are triggered
at the axon hillock when the
voltage caused by graded
potentials is high enough
(above the threshold potential).
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Graded Potentials and Action Potentials
•  Threshold potential is ~ -55mV.
•  The axon hillock must depolarize 15mV from resting
potential in order to initiate an AP.
Graded Potentials and Action Potentials
• 
Graded potentials can result in action potentials in
numerous ways…
1)  A very strong graded potential may cause a large enough
depolarization to pass to the axon hillock and cause an
AP.
2)  Graded potentials from different sites can interact with
each other and add up to a large enough depolarization
at the axon hillock to cause an AP: spatial summation.
3)  Graded potentials can occur at two slightly different
times, but can combine to create a large enough
depolarization at the axon hillock to cause an AP:
temporal summation.
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Spatial Summation
Graded potentials from different sites can interact with each
other and add up to a large enough depolarization at the axon
hillock to cause an AP: spatial summation.
Temporal Summation
Graded potentials can occur at two slightly different times, but
can combine to create a large enough depolarization at the
axon hillock to cause an AP: temporal summation.
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Spatial and Temporal Summation
Of course these two phenomena are happening at the
same time!
Action Potentials
•  Action potentials
can be transmitted
across LONG
distances without
degrading… so
there s something
else going on
(compared to graded
potentials).
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Action Potentials
•  Three stages:
Depolarization
Repolarization
After-hyperpolarization or
undershoot
Neuron can generate a new
action potential only during
certain phases of the AP.
Absolute refractory period: NO
NEW AP
Relative refractory period: Need
a very large stimulus to
overcome the hyperpolarization.
Action Potentials
•  AP starts when threshold
potential is reached at the
axon hillock.
•  Voltage-gated Na+
channels open. These are
FAST opening.
•  Voltage-gated K+ channels
also open, but they are
SLOW… so we ll
concentrate on Na+ first.
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Action Potentials
•  Voltage-gated Na+
channels open and Na+
flows INTO the cell causing
the membrane to depolarize
(move toward the Na+
equilibrium potential).
•  As more Na+ flows in, the
membrane depolarizes
more, causing more
voltage-gated Na+ channels
to open, causing more Na+
to flow in… positive
feedback.
Voltage-gated Na+
channels
•  Na+ channels do not remain
open forever.
•  There are two gates on this
channel- an activation gate, and
an inactivation gate.
• At resting Vm, the activation gate
is closed, and the inactivation
gate is open.
•  As Vm increases, the activation
gate is more likely to be open,
allowing Na+ in, causing
depolarization, resulting in more
activation gates opening.
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Voltage-gated Na+
channels
•  The inactivation gate closes
after a certain amount of time
(this may be different for
different isoforms of the
channel).
•  This happens to coincide with
the Vm approaching +30mV
(but it is NOT voltage sensitive).
•  With the inactivation gate
closed, Na+ can no longer enter,
terminating the depolarization
phase of the AP.
•  Finally the channel returns to
its initial conformation.
Action Potentials
• Remember that the K+ channels
are also voltage sensitive, and
they opened as well (slowly)
when threshold was reached at
the axon hillock.
•  They start to open in large
numbers only shortly before the
Na+ channels start to close.
•  K+ leaves the cell, making the
inside more negative, causing
repolarization.
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Action Potentials
• The difference in opening and
closing kinetics of the Na+ and K
+ channels in response to a
threshold depolarization results
in repolarization occurring after
depolarization.
•  Because K+ channels close
slowly too, K+ ions continue to
move out of the cell until it
hyperpolarizes.
•  Na+/K+ ATPase pumps ions
back across the membrane to
restore Vm.
Refractory Periods
• Excitability
changes
across the AP.
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APs travel long distances
•  It is not actually individual APs that flow down the
axon.
•  Each AP triggers an AP in adjacent regions of the
axonal membrane… like a knocking over dominoes.
•  So, each AP is just as strong as the last one- no
degradation.
•  AP can theoretically move up or down the axon, but in
the organism, the AP is initiated at the axon hillock, so it
always moves from there to the axon terminal.
The Synapse
•  The neuron must transmit
the signal (AP) across the
synapse to the target cell.
•  Presynaptic cell,
postsynaptic cell, synaptic
cleft.
•  For a motor neuron, the
synapse is the
neuromuscular junction.
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The Synapse
•  When the AP reaches the
axon terminal, voltagegated Ca2+ channels
open.
•  Ca2+ flows into the cell.
•  Ca2+ is a signaling
molecule that causes
vesicles to bind with cell
membranes.
•  Synaptic vesicles contain
neurotransmitter.
•  Each vesicle contains a
certain amount of NT.
(NT is not released in a
smooth, graded fashion)
The Synapse
•  NT must diffuse across
the synaptic cleft.
•  Ca2+ is buffered in the
presynaptic cell, keeping
[Ca2+] low, limiting release
of NT.
•  If there are many APs
arriving, [Ca2+] rises,
providing a stronger signal
for exocytosis, and more
NT release.
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How is the signal terminated?
•  The neurotransmitter must
be removed from the
synaptic cleft, or it will
over-stimulate the
postsynaptic cell.
•  NT may diffuse away.
•  NT may be destroyed by
enzymes in the synaptic
cleft.
•  NT may be taken up by
the presynaptic cell and
other surrounding cells.
How can the signal be sped up?
•  Invertebrates use large diameter neurons.
•  With a large diameter, resistance decreases,
allowing faster currents (remember Ohm s law
V=IR)
•  Vertebrates insulate the neurons with myelin.
•  This has the advantage of allowing thinner axons
(not giant axons like inverts, so you can pack more
into small spaces); and energetic savings (without
the large volume of cytoplasm).
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Myelination
•  Myelin acts as
insulation, reducing
current loss through
leak channels.
•  AP jumps from
Nodes of Ranvier
(saltatory
conduction).
•  Placement of nodes
is critical for function
because current
carries AP from
node to node.
Why do animals need FAST axons?
•  Why have these two methods evolved: (large
diameter axons (giant fibers) and myelinated
neurons)?
•  Escape response in inverts
•  Vertebrates evolved very complex nervous
systems so in order to integrate all of that
information, rapid conduction is necessary.
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Functional organization of the
Nervous System
•  Most animals are bilaterally symmetrical
•  Allows for cephalization: concentration
of sense organs and nervous
integration centers at the anterior end of
the body.
•  Animals move in a particular direction.
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•  Vertebrate CNS (central
nervous system) is
encased in bone and
cartilage (brain and spinal
cord).
•  The rest is the peripheral
nervous system.
The brain and the
spinal cord are
made up of gray
matter (neuron cell
bodies and
dendrites) and
white matter
(bundles of axons
and associated
myelin sheaths).
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CNS development
•  The brain and spinal cord
develop from a hollow
tube (neural tube).
•  The posterior portion
forms the spinal cord and
the anterior portion
swells and forms 3
(basic) sections of brain.
•  The brain and spinal cord
are hollow (ventricles in
the brain) filled with
cerebrospinal fluid
(CSF).
Vertebrate Brains
•  Brain size and structure varies greatly
among vertebrates (birds and mammals
have much larger relative brain sizes
than other tetrapods).
•  Presumably this allows for more
complex integration.
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Vertebrate Brains
•  All vertebrates have the same basic
structure of the brain, no new
structures, just enlarged sections of
brain.
•  In birds and mammals, the forebrain is
enlarged.
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•  FOREBRAIN:
•  Telencephalon →cerebrum
•  Diencephalon
→hypothalamus,
thalamus, epithalamus.
•  FOREBRAIN:
•  Telencephalon →cerebrum
•  Specialized for
information processing,
perception, voluntary
movement, learning
•  Diencephalon
→hypothalamus,
thalamus, epithalamus.
•  Specialized for
processing and
integrating sensory
information,
coordinating behavior,
and maintaining
homeostasis.
Corpus callosum connects the two
hemispheres allowing them to communicate.
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MIDBRAIN is
greatly reduced in
mammals.
Important for some
coordination and
sensory
integration.
HINDBRAIN includes
the medulla oblongata15,
pons14 and
cerebellum25-29.
Often called the
primitive brain .
Supports vital body
functions (breathing,
circulation and
coordination of
movement).
Cerebellum integrates
sensory input from eyes,
ears and muscleà
coordination.
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The mammalian
cerebrum integrates
and interprets sensory
information and initiates
voluntary movements.
Highly folded- WHY?
Four Regions (based on
names of bones that
overlie them)
Frontal lobe:
reasoning, planning of
action and movement,
and some aspects of
speech.
Parietal lobe:
movement, orientation,
recognition and
perception of stimuli.
Occipital lobe: visual
processing
Temporal lobe:
perception and
recognition of auditory
stimuli, memory and
speech.
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Some regions of the
brain are organized
topographically
(homunculus).
The best examples of
these are the
somatosensory cortex
and the primary motor
cortex.
In these regions,
various parts of the
body are represented
by disproportionate
areas of the brain.
The size of the cortical region typically reflects the
number of sensory or motor neurons present in that
body part, rather than the size of that body part.
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Peripheral Nervous System
•  Afferent neurons- carry sensory
information to integrating centers.
•  Efferent neurons- carry signals from
integrating centers to govern
physiological responses and behaviors.
Peripheral Nervous System
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Autonomic Nervous System
•  Involuntary, homeostatic regulation of most
physiological functions.
•  Made up of sympathetic, parasympathetic
and enteric nervous systems.
•  Sympathetic: fight or flight , active during
stress or physical activity.
•  Parasympathetic: rest and digest , most
active during rest.
Autonomic Nervous System
•  Maintain homeostasis via:
–  Dual innervation: parasympathetic vs.
sympathetic
–  Creates antagonistic action (stimulate or
inhibit)
–  Basal tone: even at rest they produce
some action potentials so that increases
and decreases in AP frequency can alter
the response in the target organ.
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Autonomic Nervous System
•  All autonomic
pathways contain
two (2) neurons in
series:
–  Preganglionic (in
the central nervous
system)
–  Postganglionic
(efferent neuron in
the periphery)
Anatomical Differences
•  Cell bodies of
preganglionic
neurons are in
different regions of
the CNS
–  Sympathetic arise
in the thoracic
lumbar region
–  Parasympathetic
arise in the
hindbrain, cranial
and sacral regions.
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Anatomical Differences
•  Locations of
postganglionic
neurons are different:
–  Sympathetic: close to
spinal cord
–  Parasympathetic: close
to effector organ
•  So, sympathetic have
short preganglionic
and long
postganglionic
neurons, and vice
versa for
parasympathetic.
Anatomical Differences
•  Sympathetic
preganglionic
neurons synapse
with 10 or more
postganglionic
neuronsà
widespread effects
•  Parasympathetic
preganglionic
neurons synapse
with 3 or fewer
postganglionic
neuronsà more
localized effects.
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Neurotransmitters
•  For both systems, the
preganglionic
neurons release
stimulatory
neurotransmitter.
•  Postganglionic in
parasympathetic:
•  Inhibitory or
stimulatory, but
slower acting.
Neurotransmitters
•  Sympathetic:
postganglionic cell
typically releases
norepinephrine.
•  Results in flight or fight
response.
•  For instance, the heart
rate will increase and the
pupils will dilate, energy
will be mobilized, and
blood flow diverted from
other non-essential
organs to skeletal
muscle.
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Regulation
•  Autonomic NS regulates
primarily through reflex
arcs- simple neural
circuits that do not
involve the conscious
centers of the brain.
•  Sympathetic and
parasympathetic often
work antagonistically.
•  Ex: control of blood
pressure
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Somatic Motor Pathways
•  Control skeletal muscle.
•  Usually under conscious (voluntary)
control… a.k.a. voluntary nervous
system .
•  Can you think of an example when
muscle control is not under conscious
control?
•  Reflexes!
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Efferent Motor Pathways are
different from the Autonomic N.S.
•  Only control one type of effector organ:
skeletal muscle.
•  Cell bodies of motor neurons are located in
the CNS, never in ganglia outside of the CNS.
•  Monosynaptic- only one synapse between the
CNS and effector organ- can be LONG
neurons.
•  Neurotransmitter always excitatory.
Efferent Motor Pathways are
different from the Autonomic N.S.
•  Synapse at neuromuscular junction splits into a cluster of axon
terminals that branch out over the motor end plate. This allows the
neuron to contact more than one muscle fiber.
•  Synaptic cleft is very narrow- diffusion across of NT is very rapid.
•  All motor neurons release acetylcholine (ACh).
•  Effect of ACh on skeletal muscle is ALWAYS excitatory.
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Reflex
•  Patellar tendon (knee jerk) reflexmonosynaptic stretch reflex.
Communication: Nervous &
Endocrine Systems
•  Signaling in the body occurs in more ways
than just via neurons (direct signaling)
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Indirect Signaling
1.  Release chemical messenger
from signaling cell into
extracellular environment.
2.  Transport of the messenger to
the target cell.
3.  Communication of the message
to the target via receptor binding.
Endocrine Signaling
•  Usually slower than autocrine, paracrine
and nervous communication.
•  Any ideas why?
•  Hormones are transported through the
circulatory system- takes a while to get
around the whole body.
•  Hormones may be long-lived, increasing
the time they can have an effect.
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Secretory Cells of the Endocrine
System
•  Endocrine tissues are often grouped
into specific structures called glands.
•  Alternatively, hormones can be secreted
by cells within specific tissues (not
glands).
•  Hormones are not secreted only in
blood; they can be released into lymph
or extracellular fluids.
What is a hormone?
•  Hormones are chemical messengers that are
secreted by endocrine glands or cells.
•  They are transported to distant target tissues
where they bind to specific receptors and
exert effects at very low concentrations.
•  To maintain homeostasis, hormone action
must be terminated (regulated by negative
feedback loops).
•  All known hormones are either Peptides,
Steroids or Amines
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Hormones
•  Hormonal action is mediated via specific receptors
located on or within each target cell.
•  Many hormones have several different types of
receptors resulting in different physiological responses
to the same hormone.
•  Action depends on both the types of hormones and
the types of receptors.
Endocrine Control
•  Neuroendocrine System: Neurosecretory neurons
secrete neurohormones into blood or extracellular fluid
serving as a link between the nervous system and the
endocrine system.
•  Peripheral endocrine system: Non-neural tissues
secrete hormones into blood or extracellular fluid.
Secretion can be controlled by neurohormones, direct
innervation or by peripheral factors such as hormones,
nutrients, ions, temperature.
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Neuroendocrine Control
•  Hypothalamus important in
controlling body temperature,
thirst, hunger and many other
physiological processes, ALSO
regulates the function of the
pituitary.
•  Pituitary (a.k.a. Hypophysis):
Located ventral to the brain.
Attached to the brain by a stalk
(infundibulum).
– Anterior pituitary – true
endocrine gland.
– Posterior pituitary –
extension of neural tissue.
Posterior Pituitary
• 
• 
• 
• 
• 
Extension of neural tissue.
Hypothalamic neurohormones are
polypeptide hormones synthesized,
processed and packaged into secretory
vesicles in cell body of neurosecretory
neuron.
Transported to axon terminal at a
capillary bed at the posterior pituitary.
Hormones are carried in blood to target
tissues.
Releases non-tropic hormones
vasopressin and oxytocin.
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Anterior Pituitary
•  Neurohormones from the hypothalamus
control hormone secretion from anterior
pituitary (AP).
•  These neurohormones arrive at the AP via
a specialized microcirculation called the
hypothalamic-pituitary portal system. This
allows the signal from the hypothalamus to
arrive at the AP without being diluted
through the systemic circulation.
•  Hypothalamus secretes releasing or
inhibiting neurohormones, stimulating or
inhibiting release of AP hormones which
are released into the systemic circulation.
•  Produces polypeptide hormones some of
which serve as tropic hormones that
control growth, metabolism and
reproduction.
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•  Adrenal Gland (two parts)situated on top of your
kidneys
–  Medulla - adrenal
chromaffin tissue –
produces epinephrine.
Sympathetic Responses
–  Cortex - cortisol. Stress
Response.
–  Gonads - ovaries and testes;
Comprised of both endocrine
and gametogenic tissue.
Produce steroids for
reproduction, sexual
behavior, maintenance of
secondary sex
characteristics, brain
differentiation, production of
gametes.
–  Thyroid gland: Thyroxine
(T4) and Triiodothyronine
(T3) for Metabolism and
thermoregulation; Growth
and differentiation;
Reproduction
Pancreas - an exocrine
and endocrine organ.
Endocrine tissue referred
to as the Islets of
Langerhans is dispersed
among the exocrine
tissue.
β cells - insulin
α cells – glucagon
Gastrointestinal tract –
Secretes various
hormones involved in
digestion
Thymus – hormones for
lymphocyte development
(immune)
Pineal
Hypothalamus
Posterior Pituitary
Anterior Pituitary
Heart
Thyroid
Parathyroids
Stomach
Liver
Pancreas
Adrenal medulla
Adrenal cortex
Kidney
Testes
Pineal
Hypothalamus
Posterior Pituitary
Anterior Pituitary
Heart
Thyroid
Parathyroids
Stomach
Liver
Pancreas
Adrenal medulla
Adrenal cortex
Kidney
Testes
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Hormonal feedback
Nervous system
Feedback Regulation
provides many steps
for control
Neurohormonal
non-tropic feedback
Neurohormonal
tropic feedback
Regulation of Glucose
Metabolism
•  Remember that hormones play a role in
regulation of the majority of
physiological processes.
•  We will use glucose regulation as an
example.
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Regulation of Glucose
Metabolism
•  Mammals regulate glucose levels
precisely because the brain metabolizes
glucose primarily.
•  If glucose levels fall too low, the brain
cannot function.
•  If glucose levels are too high, the
osmolarity of your blood will be altered
affecting all of the cells in your body.
• 
Regulation of Glucose
Metabolism
The pancreas is the endocrine
gland that secretes the
hormones needed for regulation
of glucose metabolism.
•  The pancreas acts as an
exocrine gland (secreting
digestive enzymes) and an
endocrine gland.
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Regulation of Glucose
Metabolism
•  Islets of Langerhans are the
endocrine tissue in the
pancreas that contain α and
β cells.
•  β cells secrete insulin when
blood glucose levels rise.
•  With ↑ glucose, β cell
metabolism increases,
resulting in exocytosis of
vesicles containing insulin.
Regulation of Glucose
Metabolism
•  Insulin travels through the
blood to target tissues (liver,
muscle, adipose tissue).
•  Target tissues have receptor
which activates a signal
transduction cascade
ultimately causing the uptake
and storage of glucose.
•  This results in a decrease in
blood glucose levels.
•  Once blood glucose ↓, β
cells stop releasing insulin
and insulin levels in blood
decline. (negative feedback)
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Regulation of Glucose
Metabolism
•  Glucagon is secreted from α
cells in the islets of
Langerhans of the pancreas.
•  When blood glucose ↓,
glucagon is released into the
blood.
•  Target cells with glucagon
receptors release glucose in
response resulting in
increased blood glucose
levels.
•  Glucagon and insulin have
antagonistic (opposite)
effects on blood glucose
levels.
Summary
•  The nervous and endocrine systems are
intimately connected in order to
maintain homeostasis, regulate growth
and development, and affect behavior.
•  Nervous system: direct signaling, rapid
responses, short-term effectors.
•  Endocrine system: indirect signaling,
slow responses, long-term effectors.
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