Systems Notes 2.:
Homeostasis Across Body Systems
Homeostasis
• Homeostasis is a steady, yet dynamic state. The
organism will attempt to maintain a steady state
(such as body temperature in endotherms), but may
have to change or make adjustments (dynamic) by
shivering in order to do so. In addition, the organism
may shift response entirely in specific situations
• Alteration in the mechanisms of feedback often
results in deleterious consequences
The Essentials
• Negative feedback mechanisms maintain dynamic
homeostasis for a particular condition by regulating
physiological processes, returning the changing
condition back to its target set point
• Positive feedback mechanism amplify responses
and processes in biological organisms
• Organisms respond to changes in their environment
through behavioral & physiological mechanisms
Homeostasis Connection
• Homeostatic mechanisms reflect both common
ancestry and divergence due to adaptation in
different environments
• Organisms have various mechanisms for obtaining
nutrients and eliminating wastes
• Homeostatic control systems in species of microbes,
plants and animals support common ancestry
Homeostasis Basics: Systems
Positive Feedback:
An increase in product results in increasing
the rate of synthesis of that product.
Homeostasis Basics: Systems
Negative Feedback: An increase in product results
in a decrease in synthesis of more product. This is
the mechanism by which levels of a substance
remain relatively constant continually.
Example: ABCD where the synthesis of D acts as an
allosteric inhibitor of the enzyme “AB-ase”
Connecting with the Curriculum Guide
Negative Feedback Model
hormone 1
lowers
body condition
gland
(return to set point)
high
sensor
specific body condition
sensor
raises
body condition
low
gland
(return to set point)
hormone 2
Negative Feedback
• How do the stimulus and the response
relate to each other?
Digestion: Hunger Control
Which 2 are the easiest for you to remember?
The Hypothalamus Essentials
• The portion of the brain that
maintains the body’s internal balance
(homeostasis).
• The hypothalamus is the link between
the endocrine and nervous systems.
• The hypothalamus produces releasing
and inhibiting hormones, which stop
and start the production of other
hormones throughout the body.
Feedback: Regulation of Blood Sugar
insulin
liver stores
glucose as
glycogen
body
cells take
up glucose
from blood
pancreas
high
liver
blood glucose level
(90 mg/100 mL blood)
low
triggers
hunger
liver
releases
glucose
liver
Pancreas
glucagon
reduces
appetite
Respiration: Gas Exchange
Different Strategies
Which do you see here?
–Skin
–Gills
–Spiracles/
trachea
–lungs
Gas Exchange
CO2 = acidic = lower pH
How will this be used to regulate breathing rate?
Gas Exchange
Strategies: Counter current
exchange system
Water carrying gas flows in one direction,
blood flows in opposite direction
How counter current exchange
works
70%
40%
100%
water
90%
15%
60%
30%
counter5%
current
front
blood
50% 70%
100%
50% 30%
concurrent
5%
water
blood
• Blood & water flow in opposite directions
– maintains diffusion gradient over whole length of
gill capillary
– maximizing O2 transfer from water to blood
back
Temperature
Why is regulating temperature so important?
• Denaturing proteins
Temperature
Why is regulating temperature so important?
The Q temperature coefficient
Metabolism rates (Q10)
is a measure of the rate of
10
t2 = higher temperature
t1 = lower temperature
k2 = metabolic rate at t2
k1 = metabolic rate at t1
Q10 = the factor by which the reaction
rate increases when the
temperature is raised by ten
degrees
Practice Problems
1. Determine the Q10 value for the heart rate in
Daphnia, the water flea.
Temperature (C) Average Heart Rate
(beats per minute)
10
62
15
100
change of a biological or
chemical system as a
consequence of increasing the
temperature by 10 °C.
Answer is:
Q10= 2.59
Normally Q10 is
between 2 and 3
Feedback Mechanisms in Thermoregulation
Temperature
Endotherm
vs
Ectotherm
What is the difference?
What are some examples of each type?
Temperature
Endotherms vs Ectotherms
Endotherms (warm blooded) are able to maintain a
steady body temperature regardless (to some
extent) of environmental temperature.
Ectotherms (cold-blooded) are at the mercy of
external temperature and must find other means to
regulate body temperature.
Temperature
Mechanisms – Ectotherm Summary
Temperature
• How do organisms actually maintain their
stable temperature range?
– Structural
• Insulation, thick fur, etc
• Longer ears (radiate heat)
Temperature
• How do organisms actually maintain their
stable temperature range?
– Evaporative cooling (sweat)
– Conduction, Convection
– Radiation
Temperature
• How do organisms actually maintain their
stable temperature range?
– Acclimation
• “antifreeze” proteins
Temperature
• How do organisms actually maintain their
stable temperature range?
– Structural
• Counter-current exchange
• Vasodilation; vasoconstriction
Temperature
How do organisms actually maintain their
stable temperature range?
– Structural
• Counter-current exchange
• Vasodilation; vasoconstriction
http://www.biology.ualberta.ca/facilities/multimedia/uploads/zoology/coun
ter%20current.html
Temperature management
blood from arteries warms blood in veins
36˚C core body
temperature
5˚C environmental
temperature
Counter-current
exchange system!
Warm blood
Veins
Artery
Veins
Cold blood
Capillary
bed
Temperature
• How do organisms actually maintain their
stable temperature range?
– Behavior
•
•
•
•
Migration
Basking
Move to shade
Put on a sweater
Connecting with the Curriculum
Taxis
change in direction
automatic movement toward or
away from a stimulus.
Phototaxis Chemotaxis
Kinesis
change in rate of
movement in
response to a stimulus
Bugs run when the light come
on!
Connecting with the Curriculum Guide
Water Balance: N-wastes
Why do we make this
waste?
What’s the problem
with them?
Toxic!!!
3 strategies 
Intracellular Waste
What waste products?
• proteins = CHON
Animals
poison themselves
from the inside
by digesting
proteins!
H| O
||
H
N–C– C–OH CO2 + H2O
|
H
R
NH2 =
ammonia
cellular digestion…
cellular waste
Nitrogenous waste disposal
• Ammonia (NH3)
– very toxic
• carcinogenic
– very soluble
• easily crosses membranes
– must dilute it & get rid of it… fast!
• How you get rid of nitrogenous wastes depends on
– who you are (evolutionary relationship)
– where you live (habitat)
aquatic
terrestrial
terrestrial egg layer
Nitrogen waste
 Aquatic organisms


can afford to lose water
ammonia
 most toxic
 Terrestrial


need to conserve
water
urea
 less toxic
 Terrestrial egg
layers



need to conserve water
need to protect
embryo in egg
uric acid
 least toxic
Water Balance: Osmoregulation
• What is the
trade-off?
Water Balance: Osmoregulation
• Marine vs freshwater
– Different problems…different solutions
hypotonic
Osmoregulation
• Water balance
– freshwater
• hypotonic
• water flow into cells & salt loss
– saltwater
• hypertonic
• water loss from cells
hypertonic
– land
• dry environment
• need to conserve water
• may also need to conserve salt
Why do all land animals have to conserve water?
 always lose water (breathing & waste)
 may lose life while searching for water
Water Balance: Osmoregulation
Terrestrial creatures
- Malpighian tubules
(insects)
- Kidneys
(vertebrates)
Water Balance: Osmoregulation
Terrestrial creatures
– Kidneys…nephrons
Blood Osmolarity
ADH
increased
water
reabsorption
pituitary
increase
thirst
nephron
high
blood osmolarity
blood pressure
JuxtaGlomerular
Apparatus (JGA)
low
adrenal
gland
increased
water & salt
reabsorption
nephron
renin
aldosterone
angiotensinogen
angiotensin
Water Balance: Osmoregulation
Which 2 are the easiest to remember?