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The lower respiratory tract development stages
The lung buds develop from the foregut's ventral wall, which subsequently gives rise to the trachea and bronchi.
During this stage, the epithelium, smooth muscles, and cartilage begin to form.
The respiratory bronchioles and alveolar ducts begin to form during the canalicular stage, which occurs between 16 to 26 weeks
The first alveoli, known as saccules, form, and surfactant production begins.
This stage begins shortly after birth and lasts until around the age of eight years.
The saccules continue to grow in number and size as they mature into mature alveoli.