The definition of guts goes far beyond the literal meaning of "digestive tract." When you say a person has guts, you're saying that the person is determined, brave, and courageous. When you use guts to describe an object, you're suggesting that the object is one of substance or integrity.
Ex: It takes a lot of guts to get up and speak in front of a group of people the first time you do it. The first time I taught a class, I was queasy with worry. Once I was up there, though, everything was fine.
Ex: Mr. Wiley, the retiring social studies teacher, gave our commencement address at graduation this year, and his speech was great. It was very strongly worded, and had a lot of guts to it.
When you spill your guts, you are revealing something personal about yourself, especially about your problems or worries. You would usually only do this with a close friend. When you have a gut feeling, you are experiencing a strong feeling or belief about something that cannot be explained by logic or observation. A gut feeling is something you somehow "know" without any real reason.
Ex: When his son, Roger, came home and explained that the dent in the car was the result of a "hit and run" driver who "must have hit the car while it was parked," Frank had a gut feeling that the boy was lying to him.