Introduction Homeostasis 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

Homeostasis Homeostasis 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 Sugar You 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 Systems Feedback 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 Loops There 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 Loops A 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 Loop Regardless 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 onto A 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 warm Sensors in the brain detect our body is too warm They send a message to the hypothalamus saying it is too hot The hypothalamus sends a nerve impulse to: Sweat glands to begin sweating Blood 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 cold Thermoreceptors in the skin notice our body temperature is too cold and they send a message to the Hypothalamus, realizes the body is too cold and sends a nerve signal to: Blood vessels close to the skin to constrict Skeletal muscles to contract and cause shivering and teeth chattering Smooth 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!

Homework Read pages P. 337 #1, 2, 4, 5, 7 and 9 P. 341 #1-5, 7 and 10