1. Blood is distributed to various parts of the body through blood vessels known as _______.   Hint First letter clue   2. Food descends from the mouth to the stomach through a muscular tube known as _______.   First letter clue   3. _______ is a tubular structure through which urine is excreted out of the body.   First letter clue   4. _______ is a sac-like structure which stores urine.   First letter clue   5. _______ is the opening in the body through which feces are excreted.   First letter clue   6. _______ are the main respiratory organs.   First letter clue   7. Kidneys are the main _______ organs.   First letter clue