432 



MOVEMENT OF THE URINE. 



The blood-vessels supply the various coats, and form a capillary plexus under the epithelium. 

 The nerves are not very numerous, but they contain medullated (few) and non-medullated 

 fibres, with numerous ganglia scattered in their course. They are partly motor and supply the 

 muscular layers, and some pass towards the epithelium, and are sensory and cxcilo-rejlccc in func- 

 tion. These nerves are excited when a calculus passes along the ureter, and thus give rise to 



Fig. 290. 



severe pain. The ureter perforates the wall of the bladder obliquely. The inner opening is a 

 narrow slip in the mucous membrane, directed downwards and inwards, and provided with a 

 pointed valve-like process (fig. 291). 



Movement of the Urine. The urine is propelled along the ureter thus : (1) 

 The secretion, which is continually being formed under a high pressure in the 



kidney, propels the urine onwards in front of 

 it, as the urine is under a low pressure in the 

 ureter. (2) Gravity aids the passage of the 

 urine when the person is in the erect posture. 

 (3) The muscles of the ureter contract rhythmi- 

 cally and peristaltically, and so propel it towards 

 the bladder. This movement is reflex, and is 

 due to the presence of the urine in the ureter. 

 Every three-quarters of a minute several drops 

 Transitional epithdiunVfrom the bladder. <> f urine pass into the bladder. But the fibres 

 Many of the large cells lie upon the may also be excited directly. The contraction 

 summit of the columnar and caudate passes along the tube at the rate of 20 to 30 



undeVTurface reSSi US "* S6eU ^ ^^ mm ' per second > always from aboVe downwards. 



The greater the tension of the ureter due to 



the urine, the more rapid is the peristaltic movement. 



Local Stimulation. On applying a stimulus to the ureter directly, the contraction passes 



both upwards and downwards. Engelmann observed that the movements occur in parts of the 



ureter where neither nerves nor 

 ganglia were to be found, and 

 he concluded that the move- 

 ment was propagated by " mus- 

 cular conduction." If this be 

 so, then an impulse may be pro- 

 pagated from one non- striped 

 muscular cell to another without 

 the intervention of nerves (see 

 Heart, 58, I., 3). 



Prevention of Reflux. 



The urine is prevented 

 from exerting a backward 

 pressure towards the kid- 

 neys : (1) The urine which 

 collects in the pelvis of the 

 kidney is under a high 

 pressure, and thus tends 

 uniformly to compress the 

 pyramids, so that the urine 



Lower part of the human bladder laid open, showing clear part, n ? ot P ass t0 the mi U * e 

 or trigone, the slit-like openings of the ureters, the divided orifices of the urinary tub- 

 ureters, and vesiculre seminales ; the sinus prostatitis, and ules. (2) When there is a 

 on each side of it, the openings of the ejaculatory ducts, and considerable accumulation 

 below both numerous small apertures of the prostate ducts. Q f ur i ne i n a ure ter e.g. 



from the presence of an impacted calculus or other cause, there is also more energetic 

 peristalsis, and, at the same time, the circular muscular fibres round the apices of 

 pyramids compress the pyramids and prevent the reflux of urine through the 

 collecting tubules. The urine is prevented from passing back from the bladder 

 into the ureter, the wall of the bladder itself, and the part of the ureter which 



