one of the thin-walled projections outwards of the arachnoid membrane into the blood-filled sinuses of the dura, acting as a one-way valve for the flow of cerebrospinal fluid from the subarachnoid space into the bloodstream. Large villi, known as arachnoid granulations (or Pacchionian bodies), are found in the region of the superior sagittal sinus. They may be so distended as to cause pitting of the adjacent bone.
One of the minute processes thickly distributed upon the inner surface of the small INTESTINE, giving it, to the naked eye, a velvety appearance, and greatly assisting absorption of digested food. (See also DIGESTION; ABSORPTION; ASSIMILATION.)... villus
A method of diagnosing genetic abnormalities in a fetus using a small sample of tissue taken from the chorionic villi at edge of the placenta. Because the cells have the same chromosome makeup as those in the fetus, they can be used to detect genetic abnormalities. Chorionic villus sampling (CVS) is usually performed in the first 3 months of pregnancy in women who are at a higher-than-normal risk of having a child with a chromosomal disorder, such as Down’s syndrome, or a genetic disease, such as thalassaemia. Chromosome analysis of the villi cells takes place in the laboratory. CVS slightly increases the risk of miscarriage. choroid A layer of tissue at the back of the eye, behind the retina. The choroid contains many blood vessels that supply nutrients and oxygen to the retinal cells and to surrounding tissues in the eye. choroiditis Inflammation of the choroid. It is often caused by infections such as toxocariasis or toxoplasmosis, more rarely by sarcoidosis, syphilis, and histoplasmosis. It sometimes has no obvious cause. Treatment includes corticosteroid drugs for the inflammation, and antibiotic drugs for any causative infection.... chorionic villus sampling
(arachnoid mater) n. the middle of the three membranes covering the brain and spinal cord (see meninges), which has a fine, almost cobweb-like, texture. Between it and the pia mater within lies the subarachnoid space, containing cerebrospinal fluid and large blood vessels; the membrane itself has no blood supply.... arachnoid
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