Respuesta :

1: The endocrine system secretes hormones which essentially controls many body functions, from growth to food digestion.
2: Glands are organs which make and secrete Hormones. Hormones are specific chemicals made by the Endocrine glands, which are categorized as "Signaling Molecules" which as you guess, are like signals and instructions. 
3: Hormones travel via the blood stream.
5: A negative feedback system is a system which autocorrects itself through feedback. Lets take blood sugar from the liver as an example it has to know when to release glucose into the blood, and also when not to. The Hormones Glucagon and Insulin control this. One makes your liver excrete stored glucose, while the other halts it from doing so. The system is able to measure the blood sugar level, and release Glucagon and Insulin accordingly. 

Essentially, a negative feedback loop measures the levels of whatever, and releases hormones accordingly so the level stays at a healthy equilibrium.