The placenta can release metabolic products.
Microbes simply secrete digestive enzymes into their surroundings, while animals only secrete these enzymes from specialized cells in their guts, including the stomach and pancreas, and in salivary glands
 Metabolic reactions may be categorized as catabolic  the breaking down of compounds (for example, of glucose to pyruvate by cellular respiration); or anabolic  the building up (synthesis) of compounds (such as proteins, carbohydrates, lipids, and nucleic acids)

