What are Amino acids? How are they bound?

How does the nervous system affect the excretory system?

Which statement describes a way in which the digestive and excretory systems work together? a. the nephrons absorb nutrients from food going to the large intestine. b. the excretory system balances blood gases in the small intestine. c. the intestinal villi filter blood and send wastes to the bladder. d. the excretory system balances the salts and water obtained from digested food

This is a biological reaction due to a stimulus. i need this quickly !