The muscles in the back of your tongue help you make certain sounds, like the letters k and hard g (like in the word go). Try saying these letters slowly, and you'll feel how the back of your tongue moves against the top of your mouth to create the sounds. The back of your tongue is important for eating as well.
The most common cause is a benign tumor in your pituitary gland, which is located under your brain. This tumor is not cancer. Because of the tumor, your body makes too much growth hormone. Once in a while, tumors in the pancreas, liver, or parts of the brain can cause high levels of growth hormone. That leads to higher levels of another hormone, called insulin-like growth hormone, which causes the symptoms you see.
The pituitary gland has different types of pituitary cells, each producing special hormones released into the bloodstream that affect other organs in the body. Pituitary tumors originate from one of these specialized cells. If the tumor cells produce an excess of one or more hormones, it is called a functional adenoma. Examples of functional adenomas include: Prolactinoma, a tumor that overproduces prolactin.