how does the trachea remain open like a hollow tube?

Answer 1

the doctors place a valve inside the hole to keep it open, when the valve is removed the hole "seals" itself.

Answer 2

The trachea remains open because it is composed of rings of cartilage.

From Wiki:http://en.wikipedia.org/wiki/Vertebrate_trachea

The trachea, or windpipe, is a tube extending from the larynx to the bronchi in mammals, and from the pharynx to the syrinx in birds, carrying air to the lungs. It is lined with ciliated cells which push particles out, and cartilage rings which reinforce the trachea and prevent it from collapsing on itself during breathing.

These numerous cartilaginous half-rings, located one above the other along the trachea, have open ends adjacent to the esophagus. The rings are connected by muscular and fibrous tissue, and they are lined inside with a ciliated mucous membrane.

The epiglottis is the flap that closes the trachea.


[edit] Clinical significance
In ill or injured persons, the natural airway formed by the trachea may be damaged or closed off.

Endotracheal intubation is the medical procedure of inserting an artificial tube into the trachea to provide a secure route for ventilating the lungs.

Tracheotomy is a surgical procedure of making an opening in the front of the neck that extends to the lumen of the trachea, a short tube called a tracheostomy tube is inserted through this opening, entering below the level of the larynx and vocal cords.