duct
Meaning of duct: Glands make things the body needs, and ducts are the plumbing that delivers them without spilling into surrounding tissue.
Definition of duct
A duct is a narrow tube inside the body that carries fluid from the place that makes it to the place that uses or stores it. Ducts drain glands, so tears, saliva, sweat, bile and pancreatic juice all reach their destination through one. When a duct is blocked, fluid backs up behind it and the gland tends to swell.
Which ducts does a person hear about most?
Most ducts are named for the gland they drain or for the route they take.
| Duct | What it carries | To where |
|---|---|---|
| Bile ducts | Bile from the liver | The small intestine |
| Pancreatic duct | Digestive juice | The small intestine |
| Salivary ducts | Saliva | The mouth |
| Tear ducts | Tears | The nose |
| Milk ducts | Milk | The nipple |
How is a duct different from a blood vessel?
Both are tubes, but they are built for different work. Blood vessels form a closed loop: blood leaves the heart, travels around and comes back. A duct is one-way plumbing with an open end. Fluid enters at the gland and leaves into a cavity such as the gut, the mouth or the surface of the skin. Ducts also carry a much smaller volume, and the fluid inside them is usually thicker than blood. Some ducts are microscopic and merge into progressively larger ones, in the way small streams join a river. The collecting duct of the kidney works this way, gathering fluid from thousands of filtering units before it becomes urine.
What happens when one gets blocked?
Blockage is the main reason ducts turn up in a medical report. A stone, thick secretion, swelling or a growth narrows the channel, and the fluid behind it has nowhere to go. Pressure rises, the gland becomes tender and swollen, and the trapped fluid can become infected. Where the fluid is bile, it backs up into the blood instead and turns the skin and eyes yellow. A stone lodged in the cystic duct causes the classic gallbladder attack, while one that reaches the common bile duct blocks the main drainage line from the liver. Imaging is used to find the level of the blockage, because the site determines what is happening and what can be done about it.
Used in a sentence
Imaging showed a dilated duct proximal to the obstruction.
Good to know
A blocked duct produces symptoms from the pressure that builds behind the blockage, so the site of the obstruction often matters more than its cause for the pattern of illness.
Word origin
Where “duct” comes from
From the Latin ductus, meaning a leading or conveying, from ducere, to lead.