Structure · one in each half of the brain
Choroid plexus
Also called Plexus choroideus
The brain's fluid factory: frilly tissue that makes cerebrospinal fluid.
The choroid plexus is a frilly, blood-rich tissue that hangs inside the ventricles and makes most of the brain's cerebrospinal fluid. A single layer of special cells covers it, taking water and chosen substances from the blood and releasing them as a clear, carefully balanced fluid. These cells are sealed tightly together, forming the blood-CSF barrier, which keeps many harmful substances out of the brain's fluid. Most of the roughly 500 ml of fluid made each day comes from here.
Where it is
Inside all four ventricles. It runs along the floor of each lateral ventricle and hangs from the roof of the third and fourth ventricles.
What it does
Making fluid
It produces most of the brain's cerebrospinal fluid, around the clock.
Guarding the gate
Tight seals between its surface cells form the blood-CSF barrier, which controls what passes from the blood into the fluid.
Delivering supplies
It moves vitamins and other useful substances into the fluid, and makes a protein that carries thyroid hormone.
Clearing waste
It also pumps some waste products and drugs out of the fluid and back into the blood.
Immune checkpoint
It is one of the routes by which immune cells can enter the fluid around the brain, helping to keep watch for infection.
Think of it as a water treatment plant inside the brain, turning blood into a clean, carefully mixed fluid.
Works with
- Lateral ventriclesIts largest parts lie in the lateral ventricles, where most of the fluid is made.
- Third ventricleA strip of it hangs from the roof of the third ventricle.
- Fourth ventricleA strip in the roof of the fourth ventricle adds fluid close to where it leaves the ventricles.
- CapillaryIts tiny blood vessels are leaky, unlike most in the brain, so the barrier is formed by its surface cells instead.
- Ventricular systemIt is the fluid factory for the whole ventricular system.
When it goes wrong
Calcium spots
It often collects small calcium deposits with age. These are usually considered harmless and show up as bright spots on CT scans.
Cysts before birth
Small fluid-filled cysts in the choroid plexus are a fairly common finding on pregnancy ultrasounds. They usually disappear on their own and are usually harmless.
Papilloma
A rare, usually noncancerous tumor of the choroid plexus, seen mostly in young children, can make too much fluid and cause hydrocephalus. Surgery can often cure it.
For learning only, not medical advice. If you have a health concern, talk to a doctor.
Surprising facts
- Its surface is folded into countless tiny fronds, each covered in microscopic finger-like bumps, which gives it a huge surface for making fluid.
- It works so steadily that all the fluid around the brain and spinal cord is replaced several times a day.
- Because its tiny blood vessels are leaky, the real barrier sits in the layer of cells covering them, sealed together like tiles with waterproof grout.
By the numbers
Where the name comes from
"Choroid" comes from the Greek for "like the chorion", a thin membrane that surrounds an unborn baby. "Plexus" is Latin for "braid" or "network". Together they describe a braided, membrane-like web.
Learn it in a lesson
- Wiring and fluidWhite matter cables and the ventricles. A short guided lesson in 3D.
Quick quiz
3 questions. Your answers are saved and come back in your daily review.
Which of these is a job of the choroid plexus?
Show the answer
Making fluid. It produces most of the brain's cerebrospinal fluid, around the clock.
Making fluid. It produces most of the brain's cerebrospinal fluid, around the clock.
The choroid plexus is part of which larger structure?
Show the answer
Ventricular system. It belongs to the ventricular system.
Ventricular system. It belongs to the ventricular system.
Which part fits this description? "Like a water treatment plant inside the brain, turning blood into a clean, carefully mixed fluid."
Show the answer
Choroid plexus. It is the choroid plexus. The brain's fluid factory: frilly tissue that makes cerebrospinal fluid.
Choroid plexus. It is the choroid plexus. The brain's fluid factory: frilly tissue that makes cerebrospinal fluid.
These parts now come back in your daily review, just before you would forget them.
Practice it and its neighbors in 3DSources
- Neuroanatomy, Choroid Plexus, StatPearls, NCBI Bookshelf
- Physiology, Cerebral Spinal Fluid, StatPearls, NCBI Bookshelf
- Choroid plexus, Radiopaedia
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Explore the choroid plexus in 3D
Turn it around, zoom inside and see how it connects to the rest of the brain, then test yourself with quick quizzes.
Open it in 3D