29
Physiology, Homeostasis, and
Temperature Regulation
Homeostasis
• the maintenance of stable conditions in an internal
environment.
• Cells are specialized for maintaining the internal
environment
• such as temperature, pH, and ion
concentration.
• Specialized cells evolve into tissues, organs, and
physiological systems that serve specific functions to
maintain homeostasis
Concept 29.1 Multicellular Animals Require a Stable Internal
Environment
Multicellular organisms
need a stable fluid
environment
Intracellular fluid – within
the cells (mostly water)
extracellular fluid
•which includes blood
plasma and interstitial
fluid that bathes each cell.
Figure 29.1 The Internal Environment
Cells make up tissues
Four types of tissue:
• Epithelial
• Connective
• Nervous
• Muscle
Epithelial Tissue
•are sheets of tightly connected
epithelial cells that cover inner
and outer body surfaces.
•Some line blood vessels and
hollow organs.
•Some secrete substances
such as hormones or sweat, or
serve transport functions for
nutrients.
•Others serve sensory
functions of smell, taste, and
touch.
Connective Tissue
•are dispersed cells in a
secreted extracellular matrix.
•The composition of the matrix
differentiates the types of
connective tissues.
•Collagen and elastin provide
strength and elasticity to
cartilage.
•Bone matrix is mineralized for
strength while the matrix of
blood cells—plasma—is liquid.
•Adipose tissue, made of fat
cells, has little matrix.
Nervous Tissue
•contain two basic cell types—
neurons and glial cells.
•Neurons generate and conduct
electrical signals, or nerve
impulses, throughout the body.
• They are units of the central and
peripheral nervous systems and
communicate via chemicals,
neurotransmitters.
•Glial cells provide support for
neuronal function.
Muscle Tissues
•consist of elongated cells that generate force and cause
movement.
•Three types of muscle tissues:
• Skeletal—responsible for locomotion and movement
• Cardiac—makes up the heart and generates heartbeat and blood
flow
• Smooth—involved in movement and generation of forces in internal
organs
To maintain homeostasis:
Set point – a reference
Feedback – what is happening
Error Signal – any difference
between set pt. and feedback
Sensor
Effectors
Negative Feedback
Positive Feedback
Feedforward Information
Figure 29.3 Control, Regulation, and Feedback
Feed forward –
changes set point!
Concept 29.2 Physiological Regulation Achieves Homeostasis of
the Internal Environment
Regulatory systems:
• Obtain, integrate, and process information
• Issue commands to controlled systems
• Contain sensors to provide feedback
information that is compared to the set point
• Regulatory systems then issue commands to
effectors that effect changes in the internal
environment.
• Effectors are controlled systems because they
are controlled by regulatory systems.
Concept 29.2 Physiological Regulation Achieves Homeostasis of
the Internal Environment
Sensory information in regulatory systems
includes:
• Negative feedback
• Positive feedback
• Feedforward information
Concept 29.2 Physiological Regulation Achieves Homeostasis of
the Internal Environment
Negative feedback:
• Causes effectors to counteract the
influence that creates an error signal
• Results in a movement back to set point
• Example: driving too fast – causes you to
slow down!
Positive Feedback
Positive feedback:
• Amplifies a response
• Increases deviation from a set point
• Examples: sexual behavior – little
stimulation increases behavior response
Feedforward Information
Feedforward information:
• Anticipates internal changes and changes
the set point.
• Example: seeing deer changes set point
to lower speed
29.3 Living Systems are
Temperature Sensitive
Concept 29.3 Living Systems Are Temperature-Sensitive
Physiological processes are temperaturesensitive and increase their rate at higher
temperatures.
Q10 describes temperature-sensitivity as the
quotient of the rate of a reaction at one
temperature divided by the rate of the
same reaction at a lower temperature (10
degrees)
Q10 = RT/RT–10
Figure 29.4 Q10 and Reaction Rate
if Q10 < 1 the rate drops with an increase in T
if Q10 > 1 then the rx rate increases with temperature
• Calculate the Q10 for the following scenario
• A rate of an enzyme worked at a rate of 76 at
10 degrees Celsius and it worked at a rate of
145 at 20 degrees Celsius.
• 145/76 = 1.91 (the exponent cancels out 10/(20-10)
• The temperature for these calculations do NOT always
have to be 10 apart. See formula.
Animals
• Animals can acclimatize to seasonal
temperature changes
• Animals can regulate their body
temperature
• Ectotherms – depends on temperature
of environment
• Endotherms – maintain constant body
temperature independent of external
temperatures
Figure 29.5 Ectotherms and Endotherms React Differently to Environmental Temperatures (Part 1)
Figure 29.5 Ectotherms and Endotherms React Differently to Environmental Temperatures (Part 2)
In the thermoneutral
zone the metabolic
rate is low and
independent of
temperature.
The basal metabolic rate (BMR)
is the metabolic rate of a resting
animal at a temperature within
the thermoneutral zone.
Concept 29.4
Animals Control Body Temperature by
Altering Rates of Heat Gain and Loss
• Metabolism—conversion of ATP to do work
produces heat
• Radiation—warmer objects lose heat to cooler
objects by radiation
• Convection—heat is lost when wind is cooler
than body surface temperature
• Conduction—heat is transferred when objects of
different temperatures come into contact
• Evaporation—heat is lost and body is cooled
when water leaves the body
• Mammals and Birds (Endotherms) have
high rates of metabolic heat production
• expend most of their energy pumping ions
across membranes.
• Cells are “leakier” to ions than cells of
ectotherms.
• Endotherms spend more energy and
release more heat to maintain ion
concentration gradients.
Concept 29.4 Animals Control Body Temperature by Altering
Rates of Heat Gain and Loss
If environmental temperature (Ta) falls below
an endotherm’s lower critical temperature,
animal must produce heat or body
temperature (Tb) will fall.
Mammals produce heat in two ways:
Shivering —skeletal muscles contract and
release energy from ATP as heat.
Nonshivering heat production—in adipose
tissue called brown fat. –
*hibernation
Figure 29.7 Brown Fat
Brown fat has lots of
mitochondria and a rich
blood supply!
Concept 29.4 Animals Control Body Temperature by Altering
Rates of Heat Gain and Loss
The basal metabolic rate (BMR) is
correlated with body size and
environmental temperature.
The BMR per gram of tissue increases as
animals get smaller.
Example: A gram of mouse tissue uses
energy at a rate 20 times greater than a
gram of elephant tissue.
Concept 29.4 Animals Control Body Temperature by Altering
Rates of Heat Gain and Loss
Reducing heat loss is important in cold
climates.
Some cold-climate species have a smaller
surface area than warm-climate relatives.
Rounder body shapes and shorter
appendages reduce surface area-tovolume ratios.
Figure 29.9 Anatomical Adaptations to Climate (Part 1)
•Short Fur
•Limited body insulation
•Large ears and long limbs allow heat to
radiate out
Figure 29.9 Anatomical Adaptations to Climate (Part 2)
•Thick coat of insulating fur
•Small ears, short limbs, rounded body
shape give it a smaller surface area to
volume ratio – so less heat can be lost
Concept 29.4 Animals Control Body Temperature by Altering
Rates of Heat Gain and Loss
Other adaptations to reducing heat loss
include:
• Increased thermal insulation with fur,
feathers, or fat
• Ability to decrease blood flow to the skin
by constricting blood vessels
Concept 29.4 Animals Control Body Temperature by Altering
Rates of Heat Gain and Loss
Some ectotherms are able to raise their
body temperature by producing heat:
• Insects contract their flight muscles
• Honeybees regulate temperature as a
group, adjusting individual heat and
position in the cluster so that larvae are
kept warm
Concept 29.4 Animals Control Body Temperature by Altering
Rates of Heat Gain and Loss
Both endotherms and
ectotherms may use
behavioral regulation
to maintain body
temperature.
Examples: Lizard
moving into sun or
shade, or elephant
spraying itself with
water or dust
Thermostat in Mammals
In vertebrate brains, the hypothalamus is
the major center of the thermostat.
The temperature of the hypothalamus can
be the main feedback to the thermostat.
Concept 29.5 A Thermostat in the Brain Regulates Mammalian
Body Temperature
Cooling the hypothalamus can cause body
temperature to rise by:
• Constricting blood vessels to the skin
• Increasing metabolic rate
Warming the hypothalamus can lower body
temperature by:
• Dilating blood vessels to the skin
• Sweating or panting
Figure 29.13 The Hypothalmus Regulates Body Temperature (Part 1)
Concept 29.5 A Thermostat in the Brain Regulates Mammalian
Body Temperature
The temperature of the hypothalamus is a
negative feedback signal—variability from
its set point can trigger thermoregulatory
responses.
Other factors can change hypothalamic set
points:
• Change in skin temperature
• Wakefulness or sleep
• Circadian rhythm—a daily internal cycle
Concept 29.5 A Thermostat in the Brain Regulates Mammalian
Body Temperature
Fever is a an adaptive response to help fight
pathogens.
 The rise in body temperature is caused
by a rise in the set point for metabolic
heat production.
Some animals lower their temperature
during inactive periods to conserve
energy—daily torpor.
Long-lasting regulated hypothermia—
hibernation