The uterus keeps the trachea from collapsing in a fetal pig.
Its cytoplasm.
cytoplasm
hydrostatic
Dynamic equilibrium.
gravity maybe?
The trachea has a series of cartilage rings that prevent it from collapsing.
Like a camera has a case, the eye is surrounded by tissues and are filled with fluid called "humours" to keep it from collapsing.
The valve springs.
It closes and keeps the VALVES shut when needed.
The chordae tendinae and their attachments to the papillary muscles prevent the AV valves from collapsing backwards into the atria.
Valves