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Homeostasishomeostasis – constant physiological adjustments of

the body in response to external environment changes

also known as dynamic equilibrium

What happens to your body when you exercise?

body temperature increases

O2 levels being used up

increased cellular metabolism

evaporation of sweat to cool off

heart rate increases to increase blood flow (to get O2 levels back up)

pancreas signals breaking down of biomolecules to get energy needed to exercise

Exercise and Homeostasis

Homeostatic Control System1. Receptor – organs that detect changes or sense

when conditions are not within “normal” range

2. Control Centre – organs which process information it receives from the receptor and send signals to another part of the body

3. Effector – coordinating centre sends signals to an organ / tissue which will normalize the original organ

dynamic equilibrium

AnalogyResponse

No heatproduced

Roomtemperaturedecreases

Heaterturnedoff

Set point

Toohot

Setpoint

Control center:thermostat

Roomtemperatureincreases

Heaterturnedon

Toocold

Response

Heatproduced

Setpoint

dynamic equilibrium

Feedback Systemsnegative feedback system - buildup of the end product of

the system shuts the system off

blood pressure drops

brain nerve pathwayblood pressure

rises

heart rate increases

arteries constrict

The response counteracts further change in the same direction

Feedback Systemspositive feedback (feed-forward) system - a change in

some variable that triggers mechanisms that amplify the change progesterone

decrease

uterus endocrine system

oxytocin

increased contractions

ThermoregulationProcess by which animals maintain an internal

temperature within a tolerable range.

Critical to survival because biochemical and physiological processes are sensitive to changes in temperature.Enzymatic reactionsProperties of membranes

Modes of Heat ExchangeRadiation is the emission of electromagnetic waves by all objects warmer than absolute zero. Radiation can transfer heat between objects that are not in direct contact, as when a lizard absorbs heat radiating from the sun.

Evaporation is the removal of heat from the surface of aliquid that is losing some of its molecules as gas. Evaporation of water from a lizard’s moist surfaces that are exposed to the environment has a strong cooling effect.

Convection is the transfer of heat by the movement of air or liquid past a surface, as when a breeze contributes to heat loss from a lizard’s dry skin, or blood moves heat from the body core to the extremities.

Conduction is the direct transfer of thermal motion (heat) between molecules of objects in direct contact with each other, as when a lizard sits on a hot rock.

Balancing Heat Loss and Gain1. Insulation

2. Circulatory Adaptations

3. Cooling by Evaporative Heat Loss

4. Adjusting Metabolic Heat Production

InsulationFeathers, hair or fat layersReduces the flow of heat between an animal and

its environmentLowers the energy cost of keeping warm

In mammals, the insulating material is associated with the integumentary system (skin, hair and nails)

Hair

Sweatpore

Muscle

Nerve

Sweatgland

Oil glandBlood vessels

Adipose tissue

Hypodermis

Dermis

Epidermis

Most land animals and birds react to cold by raising their fur or feathersTraps a thicker layer of airIncreasing its insulating power (the more still air = the

better!)

GoosebumpsRaise hair on our bodyInherited from our furry

ancestorsWe rely more on a layer

of fat just beneath the skin

Circulatory AdaptationsWe can alter the amount of blood (and hence heat)

flowing between the body core and the skin.

Vasodilation

Muscles in superficial blood vessels relax

Increases the diameter of vessels = more blood

Increases heat transfer, warming the skin

VasoconstrictionMuscles in superficial blood vessels contractSmaller diameter of blood vessels = less bloodReduces heat transfer, preventing heat lossKeeps blood (and heat) in interior of body where it is

needed

Evaporative Heat LossWhen environmental temperatures are above body

temperature weSweat, pant, bathe, spread saliva over body surfacesHeat is carried away with water molecules as they

change into a gas

Adjusting Metabolic Heat ProductionShivering and Moving - Heat

production is increased by muscle activity

Non-shivering Thermogenesis (NST) - Certain hormones can cause mitochondria to increase their metabolic activity and produce heat instead of ATP

Brown Fat – Specialized tissue for rapid heat production (has higher conc’n of mitochondria)

What regulates our temperature?Hypothalamus - contains a group of nerve cells

that function as a thermostat

Body temperaturedecreases;thermostat

shuts off coolingmechanisms.

Increased bodytemperature (suchas when exercising

or in hotsurroundings)

Homeostasis:Internal body temperatureof approximately 36–38°C

Body temperatureincreases;thermostat

shuts off warmingmechanisms.

Decreased bodytemperature

Vasoconstriction, divertingblood from skin to deeper tissuesand reducing heat lossfrom skin surface.

Skeletal musclesrapidly contract,causing shivering,which generatesheat.

Thermostat inhypothalamusactivateswarmingmechanisms.

Cold Response

Thermostat inhypothalamusactivates coolingmechanisms.

Sweat glands secrete sweat that evaporates, cooling the body.

Vasodilation,Blood vessels relax and fillwith warm blood;heat radiates fromskin surface.

Body temperaturedecreases;thermostat

shuts off coolingmechanisms.

Increased bodytemperature

Homeostasis:Internal body temperatureof approximately 36–38°C

Heat Response

Extreme ColdWhy does your body allow you to get frost bite?

Why is hypothermia such a concern?

Classwork/HomeworkSection 7.1 – Pg. 337 #1-5, 7-9Section 7.2 – Pg. 341 # 1-9,11