dilate
Meaning of dilate: The same word covers a vessel relaxing on its own, a pupil widening in the dark, and a balloon forcing a narrowed passage open.
Definition of dilate
To dilate is to widen or open a hollow structure beyond its usual resting size. The word covers changes the body makes itself, such as blood vessels relaxing to let more blood through or the pupil opening in dim light, and changes made deliberately, such as a balloon stretching a narrowed passage open. Its opposite is constriction.
What dilates, and why?
| Structure | What widening does |
|---|---|
| Blood vessel | Muscle in the wall relaxes, so more blood reaches the tissue and pressure within the vessel falls |
| Pupil | Opens in dim light, when the sympathetic nervous system is active, and in response to certain eye drops |
| Cervix | Opens gradually through labor to let the baby pass |
| Airway | Widens as the muscle wrapped around it relaxes, easing airflow |
| Bile duct or ureter | Swells upstream of a blockage, which is a warning sign rather than a useful change |
Two very different things share the word. Most of the entries above are active, controlled by muscle in the wall of the structure and adjusted moment to moment by nerves and circulating chemicals. The last is passive: a tube swells because something downstream is obstructing it. A dilated duct on a scan is therefore read as evidence of a blockage rather than as a normal adjustment, and the distinction matters when reading a report, since dilated skin vessels after exercise are expected while a dilated bile duct is not.
What happens when a procedure dilates something?
A narrowed passage can be stretched mechanically. A balloon on the tip of a catheter is inflated inside a narrowed artery, and a narrowed esophagus is opened either with a balloon or with a series of graduated dilators passed through it. The cervix is opened with tapered rods before some gynecological procedures. The principle is the same in each case: the narrowing is stretched or split rather than removed, so the passage can close in again and the procedure may be repeated. A stent is sometimes left behind to hold the widened channel open.
Is it dilation or dilatation?
Both forms are in use and both are correct. Dilatation is the older word and still appears in anatomical description and radiology reporting, as in dilatation of the aorta. Dilation is more common in everyday clinical speech and in obstetrics. Neither implies anything different about the process itself. What does change the meaning is whether the word describes a state or an action, since a pupil found dilated on examination is a finding, while a pupil dilated with drops is a deliberate step taken before an eye examination.
Used in a sentence
The pupils were noted to be equally dilated on neurologic examination.
Good to know
Dilation of a blood vessel and dilation of the cervix describe the same general widening process occurring in very different structures for very different physiological purposes.
Word origin
Where “dilate” comes from
Formed from Latin dilatare, meaning to spread out or make wider, from dis-, meaning apart, and latus, meaning wide.