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