HOMEOSTASIS

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HOMEOSTASIS
pH of 7.35
37?C
0.1 blood sugar
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Homeostasis and Control Systems

• Homeostasis an equilibrium (steady state)
  between an organisms various physiological
  functions, and between the organism and the
  environment.
• This is a balance in response to continually
  changing conditions in both the internal and
  external environments

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Steady State

• achieved by self adjustment (see feedback)
• death results when then balance can no longer be
  maintained
• dynamic equilibrium a condition that remains
  stable with fluctuation limits

There are many factors that we, as organisms,
must balance ? ex. blood glucose, water content
(osmotic balance), temperature, hormones, etc.
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Control Systems

• All homeostatic control systems have three
  components
• a monitor ? special sensors located in the organs
  of the body detect changes in homeostasis
• a coordinating centre, ? receives message from
  sensors and relays information to appropriate
  regulator (organ/tissue that will act to restore
  steady state) ? brain
• a regulator ? restores normal balance ? muscles
  and organs

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• FEEDBACK
• SYSTEMS
• MAINTAIN
• HOMEOSTASIS
• Components
• 1. Receptors
• 2. Control Center
• 3. Effectors

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Coordination of Body Functions

• The activity of various specialized parts of an
  animal are coordinated by the two major systems
  of internal communication
• the nervous system involved with high-speed
  messages
• the endocrine system involved in the
  production, release, and movement of chemical
  messangers

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• All animals exhibit some coordination by chemical
  signals
• hormones produced by the endocrine system
  convey information between organs of the body
• pheromones chemical signals used to communicate
  between different individuals
• neurotransmitters chemical signals between
  cells on a localized scale (over short distances
  between neurons)

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The Endocrine System

• Has several key components
• Hormones secreted by endocrine or
  neurosecretory cells, travel into body fluids to
  target cells where it elicits a specific response
• Target Cell cell equipped to respond to the
  given hormone
• Neurosecretory cells neuron that receives
  signals from other nerve cells and responds by
  releasing hormones into body fluids or into a
  storage organ from which they are later released.
• Endocrine gland ductless gland that secretes
  hormones into the body fluids for distribution
  through the body
• Note Exocrine gland glands that produce a
  variety of substances (e.g sweat, mucus,
  digestive enzymes) and deliver their produces via
  ducts, are NOT part of the endocrine system.
• More on the endocrine system in chapter 8..

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1. Excreting Waste
2. Urinary System
3. Formation of Urine
4. Water Balance
5. Kidney Disease

Example carbon dioxide levels ? Levels increased
during exercise Chemical receptors in brain are
stimulated Nerve cells from the brain carry
impulses to muscles that increase breathing rate.

• A group of arteries in the neck can detect low
  levels of oxygen in the blood and they send a
  message via a nerve to the brain, which then
  relays the message to the muscles that control
  breathing movements.

• Because we are constantly having to fix our
  levels so they stay within a range, we call it
  dynamic equilibrium.
• Mechanisms that make adjustments to bring the
  body back within its acceptable range are called
  negative feedback systems.

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• Most homeostatic control systems are negative
  feedback systems. These systems prevent small
  changes from becoming too large.
• A relationship in which the response is opposite
  to the stimulus (or impressed change)
• The body is self correcting by the use of
  negative feedback
• Example glucose and insulin, thermostat (pg.
  336)

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Response
No heat produced
Heater turned off
Room temperature decreases
Set point
Too hot
Set point
Set point
Too cold
Control center thermostat
Room temperature increases
Heater turned on
Response
Heat produced
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• NEGATIVE
• FEEDBACK
• ?decreases
• an action
• ?stops when return to normal
• ?most homeostatic control mechanisms are negative
  feedback

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• Positive Feedback systems process by which a
  small effect is amplified
• A relationship in which the response is the same
  as the stimulus
• Leads to instability and possibly death
• Some rare limited examples
• birthing process in humans childbirth ?
  hormone oxytocin

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• POSITIVE
• FEEDBACK
• (reinforces)
• ?increases
• an action
• ?must be turned off by outside event
• ?decreases
• an action
• ?could run away death

blood loss - ? B.P. - ? heart beat - ?
B.P. blood clotting
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• Decrease in progesterone ----gtincrease in uterine
  contraction ----gt release of oxytocin ---gt
  increase in stronger contractions----gtbaby is
  expelled-----gtcontraction stop---gtrelease of
  oxytocin stops

Section 7.1 Questions, pp. 337, 1-5
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Thermoregulation

• Thermoregulation the maintenance of body
  temperature within a range that enables cells to
  function efficiently.
• Ectotherms (reptiles etc.) rely on air
  temperature to regulate metabolic rates.
  Therefore activity is dependent on environment.
• ? adaptations seeking sun, shade
• Endotherms (mammals etc.) maintain constant body
  temp (37C) regardless of environment. Respond
  to changes in environmental temp. by using energy
  to produce heat

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Relationship between body temperature
Environmental temperature
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River otter (endotherm)
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Body temperature (C)
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Largemouth bass (ectotherm)
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10
20
30
40
0
Ambient (environmental) temperature (C)
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B. Modes of Heat Exchange

• Organisms exchange heat by four physical
  processes conduction, convection, radiation, and
  evaporation

Evaporation removal heat from surface of liquid
lost as gas
Radiation radiate heat between objects not in
contact.
Convection transfer heat by mvt air
Conduction direct transfer heat between
molecules in contact
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B. Balancing Heat Loss and Gain

• In thermoregulation, physiological and behavioral
  adjustments balance heat loss and heat gain
• 5 general adaptations in animals
  thermoregulation
• Insulation
• Circulatory adaptations
• Cooling by evaporative heat loss
• Behavioral responses
• Adjusting metabolic heat production

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1. Insulation

• Insulation is a major thermoregulatory adaptation
  in mammals and birds
• It reduces heat flow between an animal and its
  environment
• Examples are skin, feathers, fur, and blubber
• In mammals, the integumentary system acts as
  insulating material

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2. Circulatory Adaptations

• Many endotherms some ectotherms alter amount of
  blood flowing between the body core skin
• Vasodilatation ? blood flow in skin ? heat
  loss
• Vasoconstriction ? blood flow in skin
• ? heat loss

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• Many marine mammals birds have arrangement
  blood vessels called counter current heat
  exchanger which are
• important for reducing heat loss

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3. Cooling by Evaporative Heat Loss

• Many types of animals lose heat through
  evaporation of water in sweat
• Panting augments the cooling effect in birds and
  many mammals
• Bathing moistens the skin, helping to cool animal

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4. Behavioral Responses

• Both endotherms and ectotherms use behavioral
  responses to control body temp
• Some terrestrial invertebrates have postures that
  minimize or maximize absorb solar heat

More extreme behavioral adaptations hibernation
or migration to more suitable climate
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5. Adjusting Metabolic Heat Production

• Some animals can regulate body temperature by
  adjusting their rate of metabolic heat production
• Many species of flying insects use shivering to
  warm up before taking flight

Preflight warmup in hawkmoth shiver-like to
help muscles produce enough power to take off
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C. Feedback Mechanisms in Thermoregulation

• Mammals regulate body temperature by negative
  feedback involving several organ systems
• In humans, the hypothalamus (a part of the brain)
  contains nerve cells that function as a thermostat

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Stimulus Physiological Response Adjustment
Decreased environmental temperature Constriction of blood vessels in skin-hairs on body erect shivering Heat is conserved more heat is generated by increased metabolism
Increased environmental temperature Dilation of blood vessels of skin-sweating Heat is dissipated
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Human thermostat hypothalamus (control centre)
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• Responses to heat stress (nerve messages from
  sensor via hypothalamus)
• increase sweat (glands)
• vasodilatation (blood vessels)
• Responses to cold stress (nerve
• messages from sensor via hypothalamus)
• smooth muscles contract
• vasoconstriction (blood vessels)
• hair stands on end to trap warm air near skin
  (follicles) (goosebump muscle
• contraction in area of hair follicle)
• rhythmic skeletal muscle
• contraction shivering to generate heat
• Mammalian Diving Reflex
• Section 7.2 Questions, pp. 341, 1-7