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HOMEOSTASIS. pH of 7.35 . 37  C . 0.1% blood sugar . Homeostasis and Control Systems. Homeostasis – an equilibrium (steady state) between an organism’s various physiological functions, and between the organism and the environment.

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pH of



0.1% blood


Homeostasis and Control Systems

  • Homeostasis – an equilibrium (steady state) between an organism’s 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

Steady state
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.

Control systems
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






1. Receptors

2. Control Center

3. Effectors

Coordination of body functions
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

  • 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)

The endocrine system
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…..

Excreting waste urinary system formation of urine water balance 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.

Excreting Waste

Urinary System

Formation of Urine

Water Balance

Kidney Disease

  • 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.

high glucose in blood

↑ insulin production

  • 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)


No heat












Set point





Control center:














an action

►stops when return to normal

►most homeostatic control mechanisms are negative feedback

POSITIVE is amplified




an action

►must be turned off by outside event


an action

►could run away = death

* blood loss

- ↓ B.P.

- ↓ heart beat

- ↓ B.P.

* blood clotting

+ is amplified

↓ progesterone

contractions & oxytocin


  • Decrease in progesterone ---->increase in uterine contraction ----> release of oxytocin ---> increase in stronger contractions---->baby is expelled----->contraction stop--->release of oxytocin stops

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

Thermoregulation is amplified

  • 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 (37°C) regardless of environment. Respond to changes in environmental temp. by using energy to produce heat

Relationship between body temperature & Environmental temperature


River otter (endotherm)


Body temperature (°C)


Largemouth bass (ectotherm)







Ambient (environmental) temperature (°C)

B modes of heat exchange
B. Modes of Heat Exchange temperature

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

Radiation: radiate heat

between objects not in contact.

Evaporation: removal heat

from surface of liquid lost

as gas

Convection: transfer

heat by mvt air

Conduction: direct transfer

heat between molecules

in contact

B balancing heat loss and gain
B. Balancing Heat Loss and Gain temperature

In thermoregulation, physiological and behavioral adjustments balance heat loss and heat gain

5 general adaptations in animals’ thermoregulation:


Circulatory adaptations

Cooling by evaporative heat loss

Behavioral responses

Adjusting metabolic heat production

1 insulation
1. Insulation temperature

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

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

2. Circulatory Adaptations

Many marine mammals & birds have arrangement blood vessels called counter current heat exchanger which are

important for reducing heat loss

3 cooling by evaporative heat loss
3. Cooling by Evaporative Heat Loss called

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

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

4. Behavioral Responses

More extreme behavioral adaptations = hibernation or migration to more suitable climate

5 adjusting metabolic heat production
5. Adjusting Metabolic Heat Production control body temp

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

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

C. Feedback Mechanisms in Thermoregulation

Human thermostat = involving several organ systemshypothalamus (control centre)

Responses to heat stress: involving several organ systems (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