Feedback Loops and Homeostasis

When blood Glucose is high:

Beta cells in pancreas stimulates insulin which triggers body cells to  take up more glucose and liver to store the glucose as glycogen. This results in lowering the blood sugar level.

When blood Glucose is low:

Alpha cells in pancreas stimulates glucagon which signals the liver to break down glycogen into glucose and release it into blood stream. This results the blood sugar level to increase and balanced. 

When Metabolism is high:

T3 and T4 are stimulated by thyroid that will stop hypothalamus which stops pituitary gland from producing TSH and eventually stop production of T3 and T4. This results in the lowering of metabolism.

When Metabolism is low:

hypothanlamus stimulates TSH and triggers the thyroid to produce T3 and T4. This results in increase heart rate, liver activity etc. Therefore increase the metabolism. 

When the calcium level is high:

The thyroid gland produces calcitonin that signals the bone to take up calcium and store it. As a result, the calcium level in blood lowers. 

When the calcium level is low:

The parathyroid produces PTH and signals the bone to release calcium that it stores. The kidney and intestines will also absorb more calcium. This results in calcium level rises back to normal.