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AP Biology
Unit Four
Maintaining Homeostasis
• Endothermic – maintains a constant
body temperature (birds, mammals)
• Ectothermic – temp of environment
• BIG IDEA 2: Biological systems utilize
energy and molecular building blocks to
grow, to reproduce, and to maintain
homeostasis.
• BIG IDEA 3: Living systems store,
retrieve, transmit, and respond to
information essential to life processes.
• BIG IDEA 4: Biological systems
interact, and these interactions possess
complex properties.
We will cover…..
• Feedback control AGAIN!
• Evolutionary development of animal
organ systems to control homeostasis
with the environment
• Cellular signaling
• Specific systems: endocrine, nervous,
immune
• Developmental stages and timing
• Plants – homeostatic mechanisms and
how they respond
Organism Organization
•
•
•
•
Cells
Tissues
Organs
Organ Systems (not technically in
plants)
• Organism
The structure of a component of an
organism underlies its function.
Homeostasis
• occurs in ALL organisms
• Involves all levels (except unicellular
organisms): cells, organs, organisms
• Reflects continuity and change
• Shaped by evolution
• Affected by disruptions
• Defenses evolved to maintain
Remember….
• Body systems coordinate their
activities to maintain homeostasis.
• Boseman videos are helpful!
• bit.ly/homeoprezi
http://www.youtube.com/watch?v=TeSKSPPZ6Ik
https://youtu.be/CLv3SkF_Eag
HOMEOSTASIS
behavior
Timing and
control
control
disruption
Feedback
loops
response
environment
Shaped by
evolution
HOMEOSTASIS
physiological
abiotic
defenses
development
biotic
acclimatization
• An animal’s normal range of
homeostasis may change as the animal
adjusts to external environmental
changes
Video on Feedback Loops
• As you watch, take notes on the basic
diagram of a negative feedback loop
• What are the component parts
• Use two biological examples
https://youtu.be/CLv3SkF_Eag
http://www.youtube.com/watch?v=q_e6tNCW-uk
Negative Feedback Loops
RECEPTOR
STIMULUS
EFFECTOR
RESPONSE
Thermoregulation
RECEPTOR hypothalamus
STIMULUS body temp
drops/rises
EFFECTOR sweat glands in
skin, blood capillaries,
muscles in skin
RESPONSE blood vessels
dilate (high)or constrict
(low); sweating (high)
shivering (low)
Blood capillaries dilate
Sweat glands active
High
Temp
Drop Temp
HYPOTHALAMUS
Raise Temp
Low
Temp
Blood capillaries constrict
Sweat glands inactive
Shivering
• In mammals, a group of neurons in
the hypothalamus functions as a
thermostat
• Fever as a response to infection can
reset the hypothalamus set point.
Biological Examples of Negative
Feedback Loops
• Thermoregulation
• Blood Sugar Levels
Negative feedback: control of
sugar in the blood
Blood Glucose Regulation
RECEPTOR pancreas
receptor cells
STIMULUS blood glucose
drops/ rises
EFFECTOR – alpha and beta
cells in pancreas
RESPONSE
Alpha cells secrete glucagon
– adds glucose
Beta cells secrete insulin –
removes glucose
Glycogen is broken
down in the liver to
produce glucose.
Islets of Langerhans
Positive feedback:
oxytocin to induce childbirth
Ethylene in fruit ripening
Has anyone told you to put a banana in the bag with your apples or pears
them ripen?
Platelet formation
Thermoregulation in Animals
maintaining an internal temperature within a
tolerable range
Sources of heat
1) Internal metabolism
2) External environment
• Endothermic animals warmed mostly by
internal metabolism
- ex – mammals, birds, some fish,
many insects, a few nonavian
reptiles
• Ectothermic animals gain most of their
heat from outside sources
- ex – reptiles, fish, amphibians, most
Regulation of Body Temperature
• Why do physiological reactions
proceed more slowly when the
temperature decreases?
• How do biochemical reactions speed
up as temperature increases but then
cease to operate at high temps?
• Movement of molecules (kinetic
energy)
• Metabolism decreases/increases
• If too high, proteins (enzymes) can
become denatured and metabolic
reactions cease
Regulator or conformer?
• Regulators – control internal
fluctuations – more expensive
(ex – temp in us)
• Conformers – allow internal conditions
to vary with environmental changes
(ex - temp in ectotherms)
• Thermoregulators (homeotherms)
- their body temp stay constant but
metabolic rate varies with temp
- over relatively mild temps, metabolic
rate stays constant (thermoneutral zone
TNZ)
- as temp drops below TNZ or above the
TNZ, what happens to the metabolic rate?
Thermoconformers (poikilotherms or
ectotherms) Poikilo means variable.
• Their metabolic rate and temperature
varies exponentially with the rise
and fall of external temp.
• ectothermic
• Ex – reptiles, fish, amphibians, most
invertebrates
• Low temps slow metabolic reactions
As temp warms up,
metabolism slows down
since not as much energy
needed to heat the body.
As temp rises, more energy
Needed to cool the body.
Metabolic rate follows temp.
Balancing heat loss and gain
• Organism exchange heat with their
environment by: conduction, convection,
radiation, and evaporation
Behavioral Thermoregulatory mechanisms
Ectotherms:
1. Seek warm or cool places
2. Certain body postures
3. Huddling in groups
Endotherms:
1. Seek warm or cool places
2. Also postures
3. Us - clothing
Other thermoregulatory mechanisms
• Insulation
• Evaporative heat loss
• Regulation of metabolic heat
- endotherms use metabolic heat to
maintain their body temp
- ectotherm gain heat mostly from
environment
Raising temp metabolically
• Mammals and birds regulate rate of
metabolic heat production through
activity and shivering.
• Some mammals generate heat through
nonshivering thermogenesis, rise in
metabolic rate produces heat instead of
ATP.
• Some mammals have brown fat for
rapid heat production.
Circulatory adjustments:
Countercurrent exchange in temp regulation
• Common in marine mammals and birds
• the heat in the arterial blood leaving the
body core is transferred to the venous
blood
Acclimatization in thermoregulation
• Adjusting amount of insulation (fur) in
endotherms
• Changing amount of enzymes and
saturated/unsaturated lipids in cell
membranes used at various
temperatures
• Producing antifreeze compounds
Q10 – a method to describe the
temp sensitivity or process in
numerical terms
•R1 is the measured
reaction rate at
temperature T1 (where
T1 < T2). Note that R1
and R2 must have the
same unit.
•R2 is the measured
reaction rate at
temperature T2 (where
T2 > T1).
•T1 is the temperature
at which the reaction
rate R1 is measured
(where T1 < T2). T1 and
T2 do not need to be
exactly 10 degrees
apart but they need to
be in C or K, not F.
• If not sensitive Q10 is 1. Most biological
systems are between 2 and 3.
• At Q10 of 2, means the rate of a reaction
or process doubles as temp increases
by 10oC; Q10 of 3, rate triples.
For example, if a cricket respires 20 molecules of CO2/min @ 25° C
and 40 molecules/min @ 35° C, what is the Q10?
Q10 = (40/20)(10/(35-25)) = 2, so for every 10° C
increase in temperature, the rate would double. Thus, the cricket would respire
10 molecules/min @ 15° C and 80 molecules/min @ 45° C
(if the cricket could withstand that temperature).
• If a katydid breathes 6 times per minute
at 20° C, and 14 times per minute at
30° C, then what is Q10 for that
process?
Homeostatic mechanisms and organ
systems are shaped by evolution.
• Excretory systems deal with
osmoregulation (water balance) and
excretion of nitrogenous wastes
Remember…..
Balancing water amount is in
reality balancing solute
concentration.
osmoregulation
Prokaryotes respond via altered gene
expression to changes in the osmotic
environment
Protists: Many have contractile vacuoles
Osmoconformers
• Conform to the surrounding
environment as far as solute and water
are concerned
• Marine animals are usually
osmoconformers, while freshwater
species are generally osmoregulators.
• The sharks’ bodies are particularly high
in urea and trimethylamine N-oxide.
In Fish
• Freshwater Fish: Water will diffuse into
the fish, so it excretes a very hypotonic
(dilute) urine to expel all the excess
water. Gills uptake lost salt
• A marine fish has an internal osmotic
concentration lower than that of the
surrounding seawater, so it tends to
lose water and gain salt. It actively
excretes salt out from the gills.
Most animals are osmoregulators
dealing with nitrogenous wastes
The excretory system in vertebrates:
- maintains water, salt, and pH balance
- removes nitrogenous wastes (from
breakdown of protein and nucleic
acids) by filtering the blood
- nitrogenous waste type depends on
environment
Evolution of a tubular excretory system
Excretory system in flatworms
Excretory system in earthworms
In humans
• The kidney works closely with the
circulatory system in that the salt
content, pH, and water balance of the
blood is controlled by the kidneys.
Within the kidney, fluid and dissolved substances are
filtered from the blood and pass through nephrons
where some of the water and dissolved substances
(nutrients) are reabsorbed. The remaining liquid
(including toxins) and wastes form urine.
Increasing salt
concentration
draws water out of
tubule.
What homeostatic mechanisms
work here?
Concentrated blood (too much salt, too
little water) signal receptors in the
hypothalamus to stimulate release of
ADH (AntiDiuretic Hormone) by the
pituitary gland which influences kidney
to reabsorbs water, making blood more
dilute.
Antidiuretic – anti pee
https://www.youtube.com/watch?v=0wL4sYhfm3c
• If, on the other hand, a person drinks an
excess of water, the sodium in the blood
becomes more dilute and the release of
ADH is inhibited.
• The lack of ADH causes the nephrons to
become practically impermeable to water,
and little or no water is reabsorbed from
them back into the blood.
• Consequently, the kidneys excrete more
watery urine until the water concentration
of the body fluids returns to normal.
•
A song……
https://www.youtube.com/watch?v=cNklMCeAHv4
• Alcohol inhibits the release of ADH,
causing the kidneys to produce dilute
urine.
It’s really a salt thing!
Osmoregulation
RECEPTOR
STIMULUS
EFFECTOR
RESPONSE
Development of respiratory
systems
The Respiratory System
• The respiratory system:
• - delivers oxygen to and removes CO2
from the circulatory system and
eventually the tissues
• - in humans, this occurs in the alveoli
of the lungs which are covered in
capillaries
• The respiratory system works closely
with the circulatory system.
Exchange of gases in alveoli
Aquatic organisms such as
fish: respiratory system
Less Oxygen in
water….
Design of gills important….
Countercurrent exchange
How are lungs perfected for
terrestrial living?
lungfish
Transition…..both.
How does structure correlate with the function of the parts?
What homeostatic mechanisms
are at work here?
• Breathing is controlled by the medulla of the
brainstem. It repeatedly triggers contraction
of the diaphragm initiating inspiration.
• The rate of breathing changes with activity
level in response to carbon dioxide levels,
and to a lesser extent, oxygen levels, in the
blood. Carbon dioxide lowers the pH of the
blood (water and CO2 make carbonic acid
H2CO3).
• Hemoglobin carries oxygen and also can
carry bicarbonate ions (form of CO2)..
•
There are chemosensors in the carotid
artery and the arch of the aorta . The
sensors of the aortal are sensitive to the
level of oxygen in the blood. Sensors near
the medulla are sensitive to the level of
carbon dioxide in the blood.
• If oxygen level falls or carbon dioxide
levels vary too greatly from the set point,
a negative feedback mechanism
increases respiratory rate.
Mammals are most sensitive to
carbon dioxide levels because the
amount of CO2 varies most in
respiration in response to
different metabolic and
environmental conditions.
Oxygen-hemoglobin dissociation curves
• Hemoglobin carries oxygen and releases it to
the tissues. Look at the hemoglobin-oxygen
dissociation curve above. At which pH is the
hemoglobin least saturated with oxygen?
_____________ What has happened to the
oxygen and why? Think about when CO2 is in
the tissues, the pH drops due to the formation
of carbonic acid.
• CO2 + H2O
H2CO3 (carbonic acid)
At lower pH, the
Hemoglobin is
less saturated
because it has
given up its oxygen
to the tissues to
compensate for the
low pH due to CO2
concentration.
Muscles also needs oxygen particularly in times of exercise. A
special protein in muscles called ___myoglobin____
(myo – muscle) has more affinity for oxygen than hemoglobin.
Notice the graph below.
Fetal vs normal hemoglobin
Fetal
hemoglobin
has a
higher
affinity for
oxygen.
Respiration Regulation
RECEPTOR chemoreceptors
in the brainstem medulla
(CO2) and carotid artery and
aorta (O2)
STIMULUS – amount of CO2,
O2 and pH
EFFECTOR – diaphragm
muscles
RESPONSE breathing rate
Circulatory System
• Function – moving substances around:
nutrients (from digestion), wastes (from
excretion), O2 and CO2 (from
respiration), hormones (endocrine),
immune substances, and lymph fluid.
• Closely tied to the digestive, excretory,
respiratory, endocrine, immune, and
lymphatic system.
Types:
• Open – blood mixes with internal
organs directly (insects, arthropods,
mollusks)
• Closed – blood stays in vessels
(earthworms, some mollusks such as
octopi, vertebrates
Structures vary for types of animals:
• Fish – one ventricle, one atrium, gill
capillaries, single loop
• Amphibian – one v, 2 a, lung and skin
capillaries, double circulation (one to
body, one to lungs)
• Reptiles – partially divided v, 2 a, other
same as amphibs
• Mammal, Birds – 2 v, 2 a, lung
capillaries, double circulation
The ventricle is the
most muscular.
Flow of blood in Mammalian Heart:
right, right, lungs, left, left, body
(right side unoxygenated traveling
to lungs
the pulmonary artery (arteries –
away, veins – toward heart).
R R lungs L L body
1 –body – 10,11 – 2 – 4 (valve) – 3 – 5 (valve) – 6 –
lungs - 7 – 8 – 12 (valve) - 9 – 1.
Beating of the heart controlled when cardiac
muscles transfers an electrical signal via the SA
(sinoatrial) node or “pacemaker” (in top right
atrium) to the AV (atrioventricular) node between
the right a and v.
Blood Pressure
Force of blood against an artery.
Measured as Systolic (Super Top
Most….when ventricles are contracting)
over Diastolic (down, minimum, when
ventricles fill with blood); normal 120/80
Homeostatic mechanisms to regulate
blood pressure
• A negative feedback loop
• An increase in blood pressure is
detected by receptors in the blood
vessels that sense the resistance of
blood flow against the vessel walls.
• The receptors relay a message to the
brain, which in turn sends a message o
the effectors, the heart and blood
vessels.
Response
• The heart rate decreases and blood
vessels increase in diameter which
causes the blood pressure to fall back
within the normal range or set point.
• Conversely, if blood pressure
decreases, the receptors relay a
message to the brain, which in turn
causes the heart rate to increase and
the blood vessels to decrease in
diameter.
Circulatory (BP) Regulation
RECEPTOR pressure
receptors in blood vessels
STIMULUS – resistance of
flow in vessels
EFFECTOR – heart and blood
vessels
RESPONSE heart rate change,
diameter of vessels changes
Development of Digestive Systems
• Intracellular Digestion – ex amoeba
• Extracellular Digestion – bacteria, us
Digestive Systems in Animals
• One opening – sac (cnidarians,
flatworms)
• Tube – roundworms and on
Why more advantageous?
The Digestive System in Humans
• Ingestion, mechanical and chemical
breakdown of food, absorption of
nutrients, elimination of wastes
Pathway
• Oral Cavity – only carbs broken down
here! Mechanical digestion - teeth
• Esophagus – just a muscular tube,
peristalsis pushed food down
• Stomach – only protein broken down
here! (low pH due to secretion of gastric
juice), lots of churning in another
muscular organ
The Big Boys…..small intestines
and accessory glands
• Carbs, proteins, and lipids broken
down here.
• Most digestion and absorption here!
• Pancreatic enzymes and bile (for fat)
from the liver via the gallbladder
released in this area.
• Microvilli extend the surface area.
Microvilli in the small intestine
Finishing up…
• Large intestine (colon)- no digestion,
just reabsorbs water and creates feces
Can you live without your…How?
• Stomach?
• Small Intestine?
• Large intestine?
• How does the homeostatic evolution
of these systems reflect:
• Continuity
• Divergence
What about dehydration?
And other issues affecting
homeostasis?
http://www.youtube.com/watch?v=zrme9a_GMD
8&list=PLFCE4D99C4124A27A&index=27
Boseman
Case Study
• The story of Darlene Etienne and her
miraculous homeostatic mechanisms!
http://www.reuters.com/article/video/idUSTRE60O29A20100128?videoId=34511738
• "We cannot really explain this because that's just
(against) biological facts," Lambert told a news
conference. "We are very surprised by the fact that
she's alive. ... She's saying that she has been under
the ground since the very beginning on the 12th of
January so it may have really happened — but we
cannot explain that."
• Authorities say it is rare for anyone to survive more
than 72 hours without water, let alone 15 days. But
Etienne may have had some access to water from a
bathroom of the wrecked house, and rescuers said
she mumbled something about having a little CocaCola with her in the rubble.
• Fuilla said Etienne did not suffer a broken leg, as first
reported, but that both legs were trapped under
debris. "Both legs are very sore," he said.
Rescuers said the 16-year-old, who was severely
dehydrated and covered in dust, possibly survived
by drinking bathwater but could not have lasted
much longer.
Earthquake survival stories
http://news.bbc.co.uk/2/hi/americas/8459090.stm