GLOMERULAR EPITHELIUM. 42 1 



cardiac or pulmonary disease the venous congestion thereby produced may bring 

 about the same result.] 



Glomerular Epithelium. The amount of urine secreted does not depend upon 

 the hydrostatic pressure alone, but it seems that the epithelial cells covering the 

 glomerulus also participate actively in the process of secretion. Besides the water, 

 a certain amount of the salts present in the urine is excreted through the glomeruli. 

 The serum-albumin of the hood, however, is prevented from passing through. With 

 regard to the secretory activity of these cells, the quantity of water must also 

 depend upon the amount of the urinary constituents and water present in the blood 

 (R. Heidenhain). 



Only when the vitality of the secretory cells is intact, is there independent activity of these 

 secretory cells [Heidenhain). When the renal artery is closed temporarily, their activity is 

 paralysed, so that the kidneys cease to secrete, and even after the compression is removed and 

 the circulation re-established, secretion does not take place for some time (Overbeck). 



That the secretion depends in part upon the blood-pressure is proved by the 

 following considerations : 



1. Increase of the total contents of the vascular system, so as to increase the blood- 

 pressure, increases the amount of water which filters through the glomeruli. The 

 injection of water into the blood-vessels, or drinking copious draughts of water, 

 acts partly in this way. If the blood-pressure rises above a certain height, albumin 

 may pass into the urine. The active participation of the cells of the glomeruli is 

 rendered probable by the fact that, after very copious drinking, the blood-pressure 

 is not always raised {Pawlow) ; further, after copious transfusion, the quantity of 

 urine is not increased. Conversely, the loss of water owing to profuse sweating or 

 diarrhoea, copious haemorrhage, or prolonged thirst, diminishes the secretion of 

 urine. 



2. Diminution of the capacity of the vascular system, provided the pressure 

 within the renal area be thereby increased, acts in a similar manner. This may be 

 produced by contraction of the cutaneous vessels, owing to the action of cold, 

 stimulation of the vaso-motor centre, or large vaso-motor nerves, ligature, or 

 compression of large arteries ( 85, e), or enveloping the extremities in tight 

 bandages. All these conditions cause an increase in the amount of urine, and of 

 course the opposite conditions bring about a diminution of urine, e.g., the action 

 of heat on the skin causing redness and dilatation of the cutaneous vessels, 

 weakening of the vaso-motor centre, or paralysis of a large number of vaso-motor 

 nerves. 



3. Increased action of the heart, whereby the tension and rapidity of the blood in 

 the arteries are increased ( 85, c), augments the amount of urine ; conversely, 

 feeble action of the heart (paralysis of motor cardiac nerves, disease of the cardiac 

 musculature, certain valvular lesions) diminishes the amount. Artificial stimulation 

 of the vagi in animals, so as to slow the action of the heart, and thus diminish the 

 mean blood-pressure from 130 to 100 mm. Hg, causes a diminution in the amount 

 of urine to the extent of one-fifth (Goll, CI. Bernard); when the pressure in the 

 aorta falls to 40 mm. the secretion of urine ceases. [If the medulla oblongata be 

 divided (dog), there is an immediate fall of the general blood-pressure, and although, 

 as a general rule, the secretion of urine is arrested when the pressure falls to 40 to 

 50 mm. Hg, yet secretion has been observed to take place with a lower pressure 

 than this.] 



4. The amount of urine secreted rises or falls according to the degree of fulness of 

 the renal artery {Ludwig, Max Hermann) ; even when this artery is moderately 

 constricted in animals, there is a decided diminution in the amount of urine. 



Pathological. In fever the renal vessels are less full and there is consecutive diminution of 

 urine {Mendelson). It is most important, in connection with certain renal diseases, to note 

 that ligature of the renal artery, even when it is obliterated for only two hours, causes necrosis 



