Homeostasis Objectives: 1. Significance of homeostasis 2. Positive and negative feedback
Mar 26, 2015
Homeostasis
Objectives:
1. Significance of homeostasis
2. Positive and negative feedback
Disruption of Homeostasis
Disruption of Homeostasis
Disruption of Homeostasis
Disruption of Homeostasis
Polycystic Kidney Disease
Disruption of Homeostasis
Start here
Two ways to maintain homeostatis
Negative feedback Positive feedback
Negative Feedback: example body temperature
Q1: compare response to original stimulus
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?
Answer– Yes, because the response counteracts
the stimulus– Brings back balance
Positive Feedback: example labor contractions
Q3: compare response and stimulus in positive feedback
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? 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
Blood glucose – pages ____ Blood clotting – pages _____ Blood calcium level – pages ______ Female reproductive cycle – pages ____
About Drinking Water
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 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
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/Bios170/diffusion/Diffusion.html
Diffusion across membranes
Molecules that dissolve in lipids can cross the lipid bilayer through diffusion. Example: O2 CO2 H2O
Osmosis
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
Hypotonic to the cytosol– solution outside the cell is less concentrated than inside the cell
– water moves into the cell
Hypertonic to the cytosol– solution outside the cell is more concentrated than inside the cell– water moves out of the cell
Isotonic– concentrations are equal
http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm
What about the molecules that can’t pass through the membrane freely?
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?
Active Transport
Transport Notes Active Transport Movie 1 Active Transport Movie 2
Predicting water movement
http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ce/m3/s3/cem3s3_3.htm