What increases the heart rate and decreases the appetite?

The sympathetic division of the autonomic nervous system will do both plus many other things. It prepares the body for what is called the 'fight or flight' response. The body will try to get rid of anything that may slow you down. That includes the urge to urinate and defecate and even empty the stomach by throwing up. Your heart and blood pressure will increase and you will begin to sweat. You may have had this happen with a very scary event at one time or another.