These molecules cannot readily pass across the lipid bilayer that forms the plasma membrane. These molecules have too large an electrical charge to cross the plasma membrane. The concentration of these hormones in the blood is so low that it takes too long for these molecules to diffuse into the cell. The two hormones that interact to keep blood glucose levels stable are insulin and glycogen. Negative feedback operates in many of the body's systems to keep conditions within a range compatible with normal function.
Negative feedback maintains homeostasis.
A home furnace that uses a thermostat provides a physical model of a biological system that uses negative feedback. Click here for answers to Lecture 19 Practice Questions Click here to move on to Lecture 20 Questions. Click here to return to the Biology 104 home page.