In humans and many other animals, hydrochloric acid is a part of the gastric acid secreted within the stomach to help hydrolyze proteins and polysaccharides, as well as converting the inactive pro-enzyme, pepsinogen into the enzyme, pepsin.
ɪn hjˈuːmənz ænd mˈɛni ˈʌðɚɹ ˈænɪməlz, hˌaɪdɹəklˈoːɹɪk ˈæsɪd ɪz ɐ pˈɑːɹt ʌvðə ɡˈæstɹɪk ˈæsɪd sᵻkɹˈiːɾᵻd wɪðˌɪn ðə stˈʌmək tə hˈɛlp hˈaɪdɹəlˌaɪz pɹˈoʊtiːnz ænd pˌɑːlɪsˈækɑːɹɹˌaɪdz, æz wˈɛl æz kənvˈɜːɾɪŋ ðɪ ɪnˈæktɪv pɹˈoʊˈɛnzaɪm, pˈɛpsɪnədʒən ˌɪntʊ ðɪ ˈɛnzaɪm, pˈɛpsɪn.