Homeostasis 1 2 Objectives Significance of homeostasis Positive

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

Disruption of Homeostasis

Disruption of Homeostasis n. Polycystic Kidney Disease

Disruption of Homeostasis

n. Start here

Two ways to maintain homeostatis n n Negative feedback Positive feedback

Negative Feedback: example body temperature

Q 1: compare response to original stimulus n Answer: – The response by the effectors is antagonistic (opposite) of the stimulus Stimulus = body temp ↑ Response = body temp ↓

Q 2: homeostasis restored? How do you know? n Answer – Yes, because the response counteracts the stimulus – Brings back balance

Positive Feedback: example labor contractions

Q 3: 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

Q 4: 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 n Blood glucose – pages __295__ Blood clotting – pages __314___ Blood calcium level – pages __287____ Female reproductive cycle – pages _508___

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

More water stuff n n A mere 2% drop in body water can trigger fuzzy short-term memory, trouble with basic math, and difficulty focusing. 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. The difference in concentration of two solutions is called the concentration gradient Demonstration: food coloring in water ttp: //www. biosci. ohiou. edu/introbioslab/Bios 170/diffusion/Diffusion. html

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 n n Think back to solutions: solutes and solvents 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. 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 http: //www. tvdsb. on. ca/westmin/science/sbi 3 a 1/Cells/Osmosis. htm

What about the molecules that can’t pass through the membrane freely? n n Glucose, Na+, Ca+, K+ and lots of other molecules need to get into and out of the cell but can’t get through the lipid bilayer 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 Putting it altogether: research how your body maintains homeostasis when you become dehydrated. Why do you feel thirsty? n