Sentence:  When it's digested, its long amino-acid chains are first broken down into smaller fragments, or <WSD>peptides</WSD>. It turns out that many hormones and drugs are also <WSD>peptides</WSD>, and a number of casein <WSD>peptides</WSD> do affect the body in hormone-like ways. 
Meaning of the word marked with <WSD> tags:  Any of a class of organic compounds consisting of various numbers of amino acids in which the amine of one is reacted with the carboxylic acid of the next to form an amide bond.