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Choroid plexus

Arachnoid granulations

Third ventricle

Blood Vessels Figures

Blood-filled dural space

Figure

Choroid plexuses in ventricle walls secrete cerebrospinal fluid. The fluid circulates through the ventricles and central canal, enters the subarachnoid space, and is reabsorbed into the blood of the dural sinuses through arachnoid granulations. (Spinal nerves are not shown.)

Blood-filled dural space

-Cerebral vein

-Pia mater

-Subarachnoid space

Arachnoid mater Dura mater

Figure

Choroid plexuses in ventricle walls secrete cerebrospinal fluid. The fluid circulates through the ventricles and central canal, enters the subarachnoid space, and is reabsorbed into the blood of the dural sinuses through arachnoid granulations. (Spinal nerves are not shown.)

and lesser concentrations of glucose and potassium than do other extracellular fluids. Its function is nutritive as well as protective. Cerebrospinal fluid helps maintain a stable ionic concentration in the central nervous system and provides a pathway to the blood for waste. The cerebrospinal fluid may also supply in formation about the internal environment to autonomic centers in the hypothalamus and brain stem, because the fluid forms from blood plasma and therefore its composition reflects changes in body fluids. Clinical Application 11.1 discusses the pressure that cere-brospinal fluid generates.

Cerebrospinal Fluid Pressure

Because cerebrospinal fluid (CSF) is secreted and reabsorbed continuously, the fluid pressure in the ventricles remains relatively constant. However, infection, a tumor, or a blood clot can interfere with the fluid's circulation, increasing pressure within the ventricles (intracranial pressure). This can collapse cerebral blood vessels, retarding blood flow. Brain tissues may be injured by being forced against the skull.

Spinal cord

Conus medullaris

Subarachnoid space

A lumbar puncture (spinal tap) measures CSF pressure. A physician inserts a fine, hollow needle into the subarachnoid space between the third and fourth or between the fourth and fifth lumbar vertebrae — below the end of the spinal cord (fig. 11A). An instrument called a manometer measures the pressure of the fluid, which is usually about

Third lumbar vertebra

Dura mater

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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