Describe epithelial tissues function as an external and internal barrier

Epithelial tissue covers body surfaces that are exposed to the environment and also secretes internal regulatory molecules

Explanation:

The epithelium is one of the four main classes of animal tissues (i.e., epithelial, muscle, connective and nervous tissues). The epithelial tissue covers both external and internal body surfaces such as, for example, the skin and the digestive tract, respectively. In the skin, this tissue is a protective layer that prevents water loss and damage by external environmental factors or by mechanical friction. Moreover, in the digestive tract, epithelial tissue plays critical roles for the absorption of nutrients, as well as during regulation and excretion of hormones.

a tetrad is the foursome during meiosis made by two homologous chromosomes that have each already replicated into a pair of sister chromatids.