CHAPTER LXXII 



Intracranial and intraocular fluids 



HUGH DAVSON Department of Physiology, University College, London, England 



CHAPTER CONTENTS 



Anatomical Aspects 



Cerebrospinal System 



Ocular System 

 Chemical Composition of Intracranial and Intraocular Fluids 

 Blood-Aqueous, Blood-Cerebrospinal Fluid and Blood-Brain 

 Barriers 



Blood-Aqueous Fluid Barrier 



Blood-Cerebrospinal Fluid Barrier 



Blood-Brain Barrier 



Penetration into Different Regions of Cerebrospinal System 



Breakdown of Barriers 



Rates of Flow of Cerebrospinal Fluid and Aqueous Humor 



Mechanism of Drainage 

 Fate of Material Injected into Subarachnoid Space 



Cerebrospinal Fluid-Brain Barrier 

 Special Features of Chemical Composition of Intracranial and 

 Intraocular Fluids 



Urea 



Glucose 



Phosphate 



Ascorbic Acid 



Sodium 



Chloride and Bicarbonate 

 Intracranial and Intraocular Fluid Pressures 



General Considerations 



Intraocular Pressure 



Nervous Influences 



Cerebrospinal Fluid Pressure 



the central nervous system develops from a fluid- 

 filled and fluid-surrounded neural tube. In spite of 

 the varied development of the different parts during 

 embryonic and fetal growth, the adult central nerv- 

 ous system retains this essential feature, the internal 

 cavity having become the ventricles and spinal 

 canal while the enveloping fluid-filled space has 

 become the subarachnoid space. The eye is an out- 

 growth of the central nervous system and it, too, is 



filled with fluid — the aqueous humor and the vitreous 

 body, the latter being essentially a dilute aqueous gel, 

 a state of matter best characterized as intermediate 

 between the solid and the liquid. The cerebrospinal 

 and ocular fluids are thus specialized cavity-filling 

 fluids; the one acts as a cushion for the central nerv- 

 ous system while the aqueous humor and vitreous 

 body constitute a part of the rcir.ic ling media of the 

 visual apparatus and by virtue of their pressure — the 

 intraocular pressure maintain a degree of rigidity 

 in the system that preserves the corneal curvature. 

 On these mechanical grounds it would not be sur- 

 prising to find that the physiology of the two fluids 

 had much in common. There is some reason to believe, 

 however, thai besides fulfilling these purely mechani- 

 cal roles, the two fluids are also concerned with the 

 nutrition of the tissues with which they come in 

 close relationship. In the eye this is certainly true, 

 since the lens is a living structure, constituted of a 

 tightly packed mass of transparent fibrous cells, and, 

 being avascular, its prime, if not its sole, source of 

 nutrition is the aqueous humor; to a lesser extent, 

 this fluid is also concerned in the nutrition of the 

 nervous tissue of the eye — the retina. The extent to 

 which the cerebrospinal fluid acts as a nutrient 

 medium for the parenchyma of the central nervous 

 system is still a matter of conjecture, and the problem 

 of the relationship between the cerebrospinal fluid 

 and the nervous tissue is one that will occupy us in 

 this chapter and in Chapter LXXYIII by Tschirgi. 



ANATOMICAL ASPECTS 



Cerebrospinal System 



The ventricles are illustrated in figure i ; the two 

 lateral ventricles connect, by the interventricular 



1 76 1 



