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Arachnoid granulations (also arachnoid villi, and Pacchionian granulations or bodies) are small outpouchings of the arachnoid mater and subarachnoid space into the dural venous sinuses of the brain. The granulations are thought to mediate the draining of cerebrospinal fluid (CSF) from the subarachnoid space into the venous system .
Arachnoid villi are formed around the 35th week of development, with arachnoid granulations noted around the 39th, and continuing developing until 18 months of age. [3] The subcommissural organ secretes SCO-spondin, which forms Reissner's fiber within CSF assisting movement through the cerebral aqueduct. It is present in early intrauterine life ...
The ventral layer of arachnoid membrane, on the other hand, is a direct anterior extension of this arachnoid envelope that the dorsal layer forms over the pineal region. [4] [clarification needed] The arachnoid mater in the rat is composed of approximately 10 layers of fibroblast cells. [5]
The cerebrospinal fluid (CSF) within the skull and spine provides further protection and also buoyancy, and is found in the subarachnoid space between the pia mater and the arachnoid mater. [citation needed] The CSF that is produced in the ventricular system is also necessary for chemical stability, and the provision of nutrients needed by the ...
The walls of the dural venous sinuses are composed of dura mater lined with endothelium, a specialized layer of flattened cells found in blood and lymph vessels.They differ from other blood vessels in that they lack a full set of vessel layers (e.g. tunica media) characteristic of arteries and veins.
The majority of the CSF is formed in the choroid plexus and flows through the brain along a distinct pathway: moving through the cerebral ventricular system, into the subarachnoid space surrounding the brain, then draining into the systemic blood column via arachnoid granulations of the dural sinuses or to peripheral lymphatics along cranial ...
In a recent study, Go, et al., ~ using enzyme ultracnytochemistry, detected Na+/K + adenosine triphosphatase activity on cap cells of arachnoid villi; they proposed that this biochemical mechanism could contribute to CSF absorption. This assumption implies a "'secretory" component in CSF absorption along with the already widely accepted mechanisms.
In the early 20th century, the role of the arachnoid villi in absorbing cerebrospinal fluid was confirmed by Harvey Cushing. He recommended draining the fluid into the retroperitoneal space rather than the scalp. He was the first to attempt to create a shunt to the external jugular vein using a transplanted vein from the patient's father. [79]