• This PP is also in the first part of the Nervous system section (probably better there).

HOMEOSTASIS

37C pH of 7.35

0.1% bloodsugar

• 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

• achieved by self adjustment (feedback)• death results when then balance can no longer be

maintained

dynamic equilibrium – a condition that remains stable with fluctuation limits

• achieved by self adjustment (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• 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

FEEDBACK

SYSTEMS

MAINTAIN

HOMEOSTASIS

Components:

1. Receptors

2. Control Center

3. Effectors

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 messengers

• 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)

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

• Most homeostatic control systems are negative feedback systems. These systems prevent small changes from becoming too large.

• This is a relationship in which the response is opposite to the stimulus. The body is therefore self correcting.

• Example: glucose and insulin, thermostat (pg. 336)

high glucose in blood

↑ insulin production

Response

No heatproduced

Roomtemperaturedecreases

Roomtemperature

increases

Set point

Toohot

Set point

Heaterturnedoff

Toocold

Set point

Control center:thermostat

Heaterturnedon

Response

Heatproduced

NEGATIVE

FEEDBACK

►decreases an action►stops when

return to normal

►most homeostatic control mechanisms are negative feedback

• Positive Feedback systems: process by which a small effect is amplified

• A relationship in which the response is the same as the stimulus

• Can lead to instability and possibly death

• There are some rare limited examples that work:

birthing process in humans: childbirth hormone oxytocin

POSITIVEFEEDBACK(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

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

↓ progesterone contractions & oxytocin

+

+

Do Section 7.1 p. 337, #1-5

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

River otter (endotherm)

Largemouth bass (ectotherm)

Ambient (environmental) temperature (°C)

010 20 30 40

40

Bo

dy

tem

per

atu

re (

°C)

30

20

10

Relationship between body temperature & Environmental temperature

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

Conduction: direct transfer heat between molecules in contact

Convection: transfer heat by mvt air

Radiation: radiate heat between objects not in contact.

B. Balancing Heat Loss and Gain

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

• 5 general adaptations:– Insulation– Circulatory adaptations– Cooling by evaporative heat loss– Behavioral responses– Adjusting metabolic heat production

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

• 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 an arrangement of blood vessels called counter current heat exchange which is

important for reducing heat loss

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

• 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• 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

• 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

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

Human thermostat = hypothalamus (control centre)

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

• P. 337 #1-5,8,9• P. 341 #1-7,10,11

Homework Questions