Cerebrospinal Fluid (CSF)
Table of Contents
What Is CSF?
Cerebrospinal fluid (CSF) is the clear, colorless, and transparent fluid that circulates through the ventricles ofΒ brain, subarachnoid space, and central canal of the spinal cord. It is a part of extracellular fluid (ECF).
Properties
Volume :Β 0.15 L (100 mL to 200 mL)
Rate of formation: 0.3 mL per minute
Specific gravity: 1.005
Reaction: Alkaline
Composition Of CSF
Β CSF also contains some lymphocytes.Β Β
Β CSF Functions
Protective Function
CSF acts as fluid buffer and the protects brain from shock. Since the specific gravity of the brain and CSF is more or less the same, the brain floats in CSF.Β
Regulation of Cranial Content Volume
Regulation of cranial content volume is essential because the brain may be affected if the volume of cranial content increases. It happens inΒ brain tumors. An increase in cranial content volume is prevented by greater absorption of CSF to give space for the increasing cranial contents.
Medium of Exchange
CSF is the medium through which many substances, particularly nutritive substances and waste materials are exchanged between blood and brain tissues.
Cerebrospinal fluid circulation
Formation of CSF
CSF is secreted by Β within the ventricles of the brain, with the two lateral ventricles. ItΒ Β travel through the interventricular foramina to the third ventricle, through the cerebral aqueduct to the fourth ventricle, Β the subarachnoid space at the base of the brain. From here it start multidirectional flow that creates an equalization of composition throughout the CSF.
Collection of CSF
CSF is collected either by cisternal puncture or lumbar puncture. In a lumbar puncture, the lumbar puncture needle is introduced into the subarachnoid space in the lumbar region, between the third and fourth lumbar spines.
Uses of Lumbar Puncture
Lumbar puncture is used for:
1. Collecting CSF for diagnostic purposes
2. Injecting drugs (intrathecal injection) for spinalΒ anesthesia, analgesia and chemotherapy
3. Measuring the pressure exerted by CSF
The posture of Body for Lumbar Puncture
- The reclining body is bent forward,
- flexΒ vertebral column as far as possible.
- Then the body is brought near edge of a table.
- The highest point of the iliac crest is determined by palpation.
- A line is drawn on the back of the subject by joining the highest points of iliac crests on both sides.
- Opposite to the midplane, this line crosses fourth lumbar spine.
- After determining the area of the fourth lumbar spine, the third lumbar spine is palpated.
- Needle is introduced into subarachnoid space by passing through soft tissue space between two spines.
Reasons for selecting this site
1. Spinal cord will not be injured, because, it terminates below the lower border of the first
lumbar vertebra. Cauda equina may be damaged. But it is regenerated.
2. Subarachnoid space is wider in this site. It is because pia mater is reduced very much.
Pressure exerted by CSF
The pressure exerted by CSF in man varies in different positions, viz.
Lateral recumbent position: 10 to 18 cm of H2O.
Lying position: 13 cm of H2O
Sitting position: 30 cm of H2O
Certain events like coughing and crying increase pressure by decreasing absorption. Compression of internal jugular vein also raises the CSF pressure.
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