What structures does the endoderm develop into during the embryonic period?

The endoderm is one of the three primary germ layers formed during embryonic development, and it primarily gives rise to the epithelial lining of various internal structures. Specifically, during the embryonic period, the endoderm develops into the epithelial lining of the respiratory tract, as well as other important structures such as the gastrointestinal tract and various glands associated with these systems.

The respiratory tract formation from the endoderm includes critical components like the trachea, bronchi, and alveoli, which are essential for the exchange of gases in the lungs. Understanding the role of the endoderm in this development is crucial for recognizing how various organ systems arise during embryogenesis.

The other options represent structures derived from different germ layers. Muscle tissue, including that of the limbs, is derived from the mesoderm. Reproductive organs also arise from the mesoderm, whereas the nervous system develops from the ectoderm. Recognizing how germ layers differentiate into specific tissues and organs is key in embryology and understanding normal development.