Biological Chemistry - Berezov, T. T., Korovkin, B. F. 1998

Nervous tissue
Cerebrospinal fluid

The total volume of CEREBROSPINAL FLUID in a healthy adult is normally about 125 mL, and it is completely renewed every 3–4 hours. Cerebrospinal fluid is sometimes considered a primary transudate or a plasma ultrafiltrate. Its composition differs significantly from that of Blood Plasma (see Table 17.1), which suggests that the vascular endothelium plays a major role in the barrier function of The Nervous system. Water accounts for 99% of the cerebrospinal fluid, with dry residue making up about 1% (Table 19.5).

Class="center">Table 19.5. Chemical composition of cerebrospinal fluid

The protein content in cerebrospinal fluid is low (0.15–0.40 g/L), with an albumin-to-globulin ratio of 4:1; lipid levels are hundreds of times lower than those in blood plasma. It is even possible that plasma Lipids are entirely absent from cerebrospinal fluid. The total content of low-molecular-weight nitrogenous substances, particularly Amino Acids, is 2–2.5 times lower than in blood. As noted earlier, Brain tissue contains a high amount of free amino acids, significantly exceeding their concentration in blood and, even more so, in cerebrospinal fluid. Studies have shown that Certain amino acids (e.g., glutamic acid) practically do not cross the blood-brain barrier. At the same time, amino acid amides (particularly glutamine) readily cross this barrier. The glucose content in cerebrospinal fluid is relatively high (2.50–4.16 mmol/L), though slightly lower than in blood, and its concentration in the cerebrospinal fluid may increase or decrease in response to changes in blood glucose levels.

In terms of K⁺ and Na⁺ ion content, cerebrospinal fluid is virtually identical to blood plasma. Ca²⁺ ion levels are nearly half as low as those in blood plasma. The concentration of Cl^- ions is markedly higher, while the bicarbonate ion concentration is somewhat lower in cerebrospinal fluid than in plasma. Thus, the mineral composition of cerebrospinal fluid has distinct features that set it apart from blood plasma. All this provides grounds to believe that the Transport of substances across the vascular endothelial membrane of the nervous system is an active biochemical process. The energy for Active Transport is derived primarily from AEROBIC GLUCOSE OXIDATION, with Glycolysis playing only a minor role.

The analysis of cerebrospinal fluid in pathological conditions is of great clinical importance. It has been established that in acute Purulent meningitis, its protein content can increase dramatically (reaching 5–20 g/L compared to the normal 0.15–0.40 g/L). Glucose concentrations also change significantly. Hypoglycorrhachia (decreased glucose levels in cerebrospinal fluid) is characteristic of meningitis, whereas hyperglycorrhachia (increased glucose levels in cerebrospinal fluid) is observed in encephalitis, diabetes, etc. Characteristic features include a decrease in cerebrospinal fluid chloride concentration during meningitis and an elevated level during encephalitis. Furthermore, it has been shown that the activities of AST, LDH, and several Other Enzymes are elevated in the cerebrospinal fluid in cases of meningitis, strokes, Brain Tumors, and trauma.