Simplify the following text for a Grade 7 native English-speaking person.
Original: Because the glands are branched , and because the tubules forming the branches contain secretory cells , submandibular glands are classified as branched tubuloacinar glands . Further , because the secretory cells are of both serous and mucous types , the submandibular gland is a mixed gland , though it is mostly serous .
Simplified: The submandibular glands are salivary gland .