Complex sentence: The primitive areas (brainstem and midbrain) develop during gestation and during the early months after birth, and these parts regulate bodily functions, such as respiration, heart rate, sleep cycles and appetite.
Split into simpler sentences: The primitive areas (brainstem and midbrain) develop during gestation and during the early months after birth. The brainstem and midbrain regulate bodily functions, such as respiration, heart rate, sleep cycles and appetite.