Answer:
I believe the correct answer is mucus.
Step-by-step explanation:
In the respiratory tract, there exist hairs called cilia that ensure anything entering the tract is moved out through a wavelike movement. To assist them, mucus is produced in pits of specific cells called goblet cells.
Further Explanation:
The mucus traps dust and other large particles that might cause physical harm to the soft tissue of the linings of the respiratory tract. The mucus starts all the way from the mouth to the nasal cavities, the trachea, bronchi, bronchioles and the lungs. Goblet cells are just but specialized epithelial cells that are usually found in every hollow surface in the body and are non keratinized. These goblet cells are not only found in the respiratory tract but every surface of the gastrointestinal tract. In the stomach, they are very essential since they protect the stomach from corroding itself because it secretes hydrochloric acid that has a pH of 2.3 which is very acidic. It also lubricates the gastrointestinal tract to ensure the smooth movement of food from the mouth to the anus as it is being digested.