Homeostasis

The way the body keeps its internal

environment constant How the body “maintains a steady state”

What internal conditions need to be maintained? Temperature Blood pH Water levels Blood Glucose Levels

What is Homeostasis?

General mechanism of nervous or

hormonal regulation in animals Triggered when the response to a

stimulus has an effect of some kind ( or ) on the original stimulus Type of response ( or ) determines

how we label feedback

Feedback Mechanisms

Negative feedback : When a change in

the system occurs, a corrective measure occurs to bring system back towards the set point.

Positive feedback : When a change in the system occurs, a corrective measure occurs to amplify the system, moving it away from its set point

Feedback Mechanisms: How do we label?

How does your body try to warm-

up when you feel cold? Hair’s stand on end Blood vessels near the surface

receive less blood Shivering Behavioral responses

Thermoregulation: Cold

Hair stands on end so

air currents do not get to the skin, traps an insulating layer of still, warm air next to skin

Blood vessels near the skin constrict (vasoconstriction) so less blood passes through them. This means less heat is lost by radiation.

hair

Bloodvessel

Thermoregulation:Cold

Shivering:

Your muscles contract involuntarily, generating heat

Behavior: Curl up, huddle, put on more

clothes, drink something warm

Thermoregulation: Cold

How does your body try to warm-up

when you feel cold? Sweating Blood vessels near the surface receive

more blood Hairs lie flat Behavioral responses

Thermoregulation: Hot

Sweat is produced by sweat glands. When this evaporates, it cools the skin.

Thermoregulation

Sweat gland

Hair lies flat so air currents get to the skin. Heat is lost by convection.

Blood vessels near the skin dilate (vasodilation) so more blood passes through them. This means more heat is lost by radiation.

Normal body temperature is restored

Normal body

temperature

VasodilationHairs lie flatBody sweats

Normal body temperature is restored

VasoconstrictionHairs stand on endBody doesn’t sweat

Shivering occurs

Normal body

temperature

The

hypothalamu

s detects a

fall in

temperature

Body

temperature

falls

Body

tem

pera

ture

rises

The

hypo

thal

am

us d

etec

ts a

rise

in

tem

pera

ture

Heat Stroke: a condition marked by

fever and often by unconsciousness, caused by failure of the body's temperature-regulating mechanism when exposed to excessively high temperatures.

Mark’s Case

Exit Ticket Think back about Mark’s Case and the video you

just watched on heat stroke and answer the following questions: Why is Mark weak, delirious, nauseous, and

disoriented (this is a straightforward answer!)? DESCRIBE how Mark’s body initially reacted to being in

extremely warm temperatures. Why couldn’t Mark produce anymore sweat once he had

been out in the sun for a long period of time? Why would his blood pressure drop and his heart rate increase?

Is thermoregulation an example of positive or negative feedback? WHY?

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