What does the phrase "closed system' mean as it relates to the cardiovascular system?  

Mucous membranes.. a. cover or line external surface of body. b. line internal body surfaces that are in contact with the environment. c. produce antibodies to combat infection. d. secrete sweat, which has antibacterial enzymes.

Describe how the above factors create barriers for maintaining your mental and emotional health what barriers do they create

All my life, i had been afraid of a book. an important book, in the bible. it's called revelation. often times i've avoided it because i felt that it was scary and i couldn't understand, i thought wow, this basically tells the scary part of the future, but today i realized that it's about what's happening now, right now. in the beginning of the book, it talks about the churches, how some churches have false teachers, or some need to repent, and i realized that this book portrays to the churches nowadays also. i know jesus is coming one day, and i know that he is light, he will prevail over the darkness and he can show you the way. all you have to do is trust and believe in him, and he will guide you the right way. i love god with all my heart, and i believe that whoever is reading this you should too! i'm sorry that i put this on it's not a question, and it's only a matter of minutes before this gets reported but, i wanted people to know, revelation isn't scary, in fact it's amazing! you for your time. i hope you accept jesus christ into your life!