Homeostasis and Negative Feedback Loops

Review

So far we have learned about what molecules we need and what we use them for.

• • we eat food because it contains biomolecules (carbohydrates, proteins, lipids and nucleic acids)
  • we break down those biomolecules into their monomers in our digestive system (sugars, amino acids, fatty acids, nucleotides)
  • then we absorb them into our bloodstream to deliver to all the cells in our bodies
  • when those monomers arrive at a cell they are used either for
  • building new biomolecules for growth or repair of the cells
  • burning in cell respiration for energy in the form of ATP that is the fuel for the work in the cell.

Steady State = Homeostasis

Our cells need a regular supply (24/7) of these monomers (and other essentials like O2 and water), but we only eat food a couple of times a day. Our bodies and their cells crave what is called homeostasis. Homeostasis is a stable internal environment and you can think of it like a factory that is operating 24 hours a day, 7 days a week and therefore needs a consistent regular supply of materials, as well as a stable temperature in order to operate.

Homeostasis and Negative Feedback

This video shows different examples of homeostasis and introduces you to one of the main methods for achieving it; negative feedback loops . Watch the video and then look at the diagram below.

Negative Feedback Loops and Blood Glucose

Our bodies are trying to keep a stable level of ...everything! But let's focus on the concentration of sugar in our blood. This is often called Blood Glucose or BG since glucose is the most common form of sugar in our blood. In order to do this, our body needs the following pieces of the puzzle:

• • a stimulus= blood glucose levels
  • something to sense the stimulus = in this case the pancreas
  • something to control the action = in this case insulin and glucagon are molecules that controls blood glucose
  • something to take action = in this case it will be the liver to absorb extra glucose or release stored glucose
  • this results in a reduction of the stimulus= in this case the concentration of blood glucose falls.

This last step is why the process is called a negative feedback since the stimulus ultimately ends in a reduction of the amount of stimulus.

Text description of Negative Feedback Loops and Blood Glucose image (Word doc)Download Text description of Negative Feedback Loops and Blood Glucose image (Word doc)

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Take this short quiz to make sure you understand the basics of homeostasis and negative feedback loops.