Where it is
- There is a choroid plexus in each of the four ventricles of the brain. [1]
- In each lateral ventricle it is one continuous strip running through the body, the atrium (trigone) and the inferior (temporal) horn; it does not reach into the front (anterior) or back (posterior) horn. [1]
- The plexus in the roof of the third ventricle is continuous with that of the lateral ventricles through the interventricular foramina, and another plexus lies in the back part of the roof of the fourth ventricle. [1]
- In each lateral ventricle its edges are attached along the C-shaped choroid fissure, which runs between the fornix and the thalamus in the body of the ventricle and between the stria terminalis and the fimbria of the hippocampus in the inferior horn. [4]
What it does
- Its cells make most of the cerebrospinal fluid, about two-thirds to 80% of it, and most of that is made in the two lateral ventricles. The brain makes roughly 500 mL a day, about 20 mL an hour, while only 125–150 mL is present at any one time. [2]
- It makes the fluid in two steps: first a filtered form of blood plasma moves out of its fenestrated (leaky) capillaries into the tissue around them; then its lining cells actively move sodium, potassium, chloride and bicarbonate into the ventricle, and water follows by osmosis, helped by water channels (aquaporins). [2]
- Tight junctions between its lining cells, on the side facing the ventricle, form the blood–CSF barrier: they keep most blood-borne substances out of the fluid while letting chosen ones, such as nutrients, through. [1]
- It is also a major source of transferrin, a protein that plays a part in balancing iron in the brain. [1]
- In 1914 Harvey Cushing published conclusive evidence that the fluid is secreted by the choroid plexus. [2]
- Honest limit: its share is given as a range because the cells lining the ventricles and the brain tissue add fluid too, and one hypothesis holds that most of the fluid is made by water filtering through capillary walls throughout the CSF system, not mainly by the choroid plexus. [2]
Connections
- Blood reaches the plexus of each lateral ventricle through the anterior choroidal artery; the plexus of the fourth ventricle is fed by the anterior inferior, posterior inferior and superior cerebellar arteries. [2]
- The fluid it makes flows from the lateral ventricles through the interventricular foramina into the third ventricle, through the cerebral aqueduct to the fourth ventricle, and out into the space around the brain and spinal cord; it returns to the blood through the arachnoid granulations into the dural venous sinuses. [2]
- The autonomic nervous system tunes its output: sympathetic activity lowers secretion and parasympathetic activity raises it. Higher fluid pressure also slows it, by shrinking the pressure difference between its capillary blood and the fluid. [2]
Inside it
- A single layer of cube-shaped (cuboidal) epithelial cells, continuous with the ependyma that lines the ventricles, wrapped around a core of capillaries and loose connective tissue. [1]
- It is folded into finger-like villi around each capillary, and its cells carry a brush border of microvilli; both greatly increase its surface area. [1]
- It grows from the tela choroidea, a thin, blood-rich layer of pia mater stuck to the ventricle lining. [4]
Other names
- Also called the plica choroidea. The name comes from the Latin plexus chorioides: “choroid” joins the Greek chorion (membrane) and -oid (like), and a plexus is a network, here of blood vessels. [1]
Size
- On this model the left choroid plexus (lateral ventricles) measures about 43 mm front to back, 34 mm top to bottom and 37 mm side to side (the box it fits in, not its volume); the right one is its mirror image. [3]
- Centre of the left choroid plexus (lateral ventricles) compared with the centre of the left thalamus: 5 mm further back, 6 mm further from the midline; 7 mm apart in a straight line. [3]
- Centre of the left choroid plexus (lateral ventricles) compared with the centre of the left fornix: 8 mm further back, 6 mm further from the midline; 10 mm apart in a straight line. [3]