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Let’s start our USMLE Review with Anatomy from the Gold Standard USMLE Step 1 Audio Review program.
Play USMLE Audio MP3 25 08 CSF Physical Characteristics Below
Begin 25 08 CSF Physical Characteristics Transcription
Now we’re going to look briefly at the physical characteristics of the cerebrospinal fluid. If this does not apply to your current studies you may wish to skip this section.
What is the normal appearance of the CSF?
- CSF is normally a crystal clear fluid.
In terms of osmolality, how does the CSF compare with serum?
- CSF normally is isotonic with serum.
And what is the normal pH of CSF?
- About 7.33.
How does the concentration of Na in CSF compared with serum?
- The Na concentration in CSF is about equal to that of serum.
What is the Na concentration in both serum and CSF about normally?
- 138 mEq/L.
Now the CSF does have a higher concentration of two electrolytes as compared to serum. Student doctor, what are these two electrolytes?
- Magnesium and chloride.
What other compound, which is a minor contributor to the acidity of serum, is also found in higher concentration in the CSF?
- This would be lactate.
CSF contain a lower concentration of three electrolytes as compared to serum. Student doctor, what are these three electrolytes?
- Potassium, Calcium, and Bicarbonate.
How does the concentrations of glucose and total protein in CSF compare to serum?
- The concentrations of both glucose and total protein are lower in CSF compared to serum.
What type of cell is normally found in CSF?
- Lymphocytes, or more specifically, monocytes.
What is the normal concentration of lymphocytes or monocytes in the CSF?
- About 0-4 lymphocytes/monocytes per mL.
What cells common to the blood are not found in the CSF?
- Red blood cells and polymorphonuclear leukocytes.
What is the normal range of pressure of the CSF in the lumbar cistern when the patient is in a supine position?
- About 60 to180 mm of water.
And what is the normal range of pressure of the CSF in the lumbar cistern when the patient is in a seated position?
- About 200-350 mm of water.
Student doctor, please pause and summarize the physical characteristics of Cerebrospinal fluid. Normal CSF is a clear fluid isotonic with serum, with a pH of about 7.33. The Na concentration in the CSF is about equal to that in serum, and is about 138 mEq/L. The CSF has higher concentrations of chloride and magnesium as compared to serum. Lactate is also found in higher concentration in the CSF as compared to serum. CSF contains lower concentration of three electrolytes as compared to serum: potassium, calcium, and bicarb. The concentration of glucose and total protein are also lower in the CSF. Normal CSF contains about 0-4 lymphocytes or monocytes per mL. Polymorphonuclear lymphocytes or red blood cells are not normally found in the CSF. The pressure of CSF in the lumbar cistern is normally in the supine position about 60-180mm of water. The pressure of CSF in the lumbar cistern when the patient is in a seated position is normally about 200-350mm of water.
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