Homeostasis Objectives: 1. Significance of homeostasis 2. Positive and negative feedback

Disruption of Homeostasis

n Polycystic Kidney Disease

Disruption of Homeostasis

n Start here

Two ways to maintain homeostatis n Negative feedback n Positive feedback

Negative Feedback: example body temperature

Q1: compare response to original stimulus n Answer: –The response by the effectors is antagonistic (opposite) of the stimulus Stimulus = body temp Response = body temp

Q2: homeostasis restored? How do you know? n Answer –Yes, because the response counteracts the stimulus –Brings back balance

Positive Feedback: example labor contractions

Q3: compare response and stimulus in positive feedback n Answer –The response acts to heighten or increase the stimulus Stimulus = distortion of uterus Response= distortion and contraction of uterus

Q4: Is homeostasis restored in this example? How do you know? n Answer: –No, homeostasis is continually disrupted –This is a good thing in this case b/c returning to homeostasis would cause the birthing process to stop. –The positive feedback loop will continue until birth is complete.

Lots of examples of negative feedback loops, few positive loops n Blood glucose – pages ____ n Blood clotting – pages _____ n Blood calcium level – pages ______ n Female reproductive cycle – pages ____

About Drinking Water n One glass of water shuts down midnight hunger pangs for almost 100% of the dieters studied in a University study. n Lack of water is the #1 trigger of daytime fatigue. n 9-10 glasses of water a day could significantly ease back and joint pain for up to 80% of sufferers.

More water stuff n A mere 2% drop in body water can trigger fuzzy short-term memory, trouble with basic math, and difficulty focusing. n Drinking 5 glasses of water daily decreases the risk of colon cancer by 45%, breast cancer by 79% and one is 50% less likely to develop bladder cancer.

Cellular homeostasis Every level of organization within the body must maintain homeostasis Phospholipid Bilayer

Diffusion n Diffusion is the movement of molecules from a higher concentration to a lower concentration. n The difference in concentration of two solutions is called the concentration gradient n Demonstration: food coloring in water ttp://

Diffusion across membranes n Molecules that dissolve in lipids can cross the lipid bilayer through diffusion. Example: O 2 CO 2 H 2 O

Osmosis n Think back to solutions: solutes and solvents n Osmosis is the process by which water molecules diffuse across a cell membrane from an area of lower solute concentration to an area of higher solute concentration. n Direction of movement depends on relative concentrations of solutions.

Direction of movement into cells n Hypotonic to the cytosol –solution outside the cell is less concentrated than inside the cell –water moves into the cell n Hypertonic to the cytosol –solution outside the cell is more concentrated than inside the cell –water moves out of the cell n Isotonic –concentrations are equal n

What about the molecules that cant pass through the membrane freely? n Glucose, Na+, Ca+, K+ and lots of other molecules need to get into and out of the cell but cant get through the lipid bilayer n They must use the proteins embedded in the lipid bilayer – and this takes type of transport takes energy

Now apply this knowledge to come up with a logical conclusion for the homeostasis and sports drink lab n Putting it altogether: research how your body maintains homeostasis when you become dehydrated. Why do you feel thirsty?

Active Transport n Transport Notes Transport Notes n Active Transport Movie 1 Active Transport Movie 1 n Active Transport Movie 2 Active Transport Movie 2

Predicting water movement n _structure/ce/m3/s3/cem3s3_3.htm _structure/ce/m3/s3/cem3s3_3.htm