Introduction to Homeostasis

IntroductionHomeostasis is the

maintenance of a relatively steady internal environment despite external conditions.

This conditions cannot be too extreme, especially for prolonged periods of time, else wise we would not survive.

Body Systems involved in Homeostasis

The three body systems that deal with homeostasis are: Nervous System Endocrine System Kidneys/Urinary System

HomeostasisHomeostasis is

dynamic.This means that our

body conditions fluctuate over time around a set norm.i.e. our body

temperature is not exactly 37 degrees Celsius, but rather averages out to that over the course of the day.

Example: Blood SugarYou have a normal

blood sugar level (dashed line).

After you eat, your blood sugar rises, especially if you are eating carbohydrates (i.e. pasta).

Your endocrine system kicks in and brings your blood sugar back to normal.

Feedback SystemsFeedback systems (or

feedback loops) are what monitor your internal environment, assess any changes and then provide the required response.

Variables monitored by feedback systems include: blood pH, blood sugar, body temperature, blood pressure, breathing rate…

Important to note that feedback systems are a response to stimulus.

Negative Feedback LoopsThere are two types of

feedback loops in the body: Positive and Negative.

A negative feedback loop recognizes a change and returns the change back to normal.

Examples: blood sugar, body temperature, blood pressure, calcium levels… the majority of the feedback loops in the body are negative.

This is one associated with metabolism.

Positive Feedback LoopsA positive feedback loop

recognizes a change and amplifies it further away from normal.

There are few positive feedback loops in the body.

Main one would be the blood clotting process.

Two other ones associated with females: uterine contraction (on right) and lactation.

Parts of a Feedback LoopRegardless of whether it is positive or

negative, each feedback loop contains three main parts:Sensors which detect changes in our internal

environment and pass that info ontoA control centre which sets the range for our

internal environment, decides what to do with the info from the sensors and sends signals to

Effectors (Regulators) which are told to respond to the change by the control centre.

Thermoregulation

When it is too warmSensors in the brain detect our body is too

warmThey send a message to the hypothalamus

saying it is too hotThe hypothalamus sends a nerve impulse to:

Sweat glands to begin sweatingBlood vessels close to the skin to dilate

Both of these things work to lower our body temperature back to within normal range.

This is an example of __________ feedback!

When it is too coldThermoreceptors in the skin notice our body

temperature is too cold and they send a message to theHypothalamus, realizes the body is too cold and sends a

nerve signal to:Blood vessels close to the skin to constrictSkeletal muscles to contract and cause shivering and teeth

chatteringSmooth muscles around body hair to contract causing

body hair to become erect and keep heat close to the body.All of these things cause our body temperature to rise

back to within normal range.This is an example of ____________ feedback!

HomeworkRead pages 334-341

P. 337 #1, 2, 4, 5, 7 and 9

P. 341 #1-5, 7 and 10