SECTION III 

 THE PHYSIOLOGY OF MICTURITION 



THE urine as it is formed passes through the ureters to the bladder, 

 where it gradually accumulates, and is voided at intervals. 



The ureters are muscular tubes lined by transitional epithelium. 

 The muscular coat is composed of three layers of unstriated fibres, 

 a middle circular coat lying between external and internal longitudinal 

 coats. If the ureter be exposed in the living animal, contraction 

 waves are seen to pass along its muscular coat from the pelvis of the 

 kidney to the bladder, driving the contained fluid in front of them. 

 The frequency of the contractions is increased by warming the ureter, 

 and to a certain extent by distension, so that the waves are more 

 frequent when the secretion of urine is profuse. The ureters enter the 

 bladder at or near its base, at the two posterior angles of the region 

 known as the trigonum. Their entrance is oblique, so that a valvular 

 orifice is formed, which effectively prevents reflux of urine from bladder 

 to ureter. Rhythmic waves of contraction are observed also in the 

 excised ureters, when these are kept warm, in normal saline solution. 

 By Engelmann they were regarded as myogenic, since they were 

 present in the middle third of the ureter, which he imagined to be 

 entirely free from ganglion-cells. As a matter of fact ganglion-cells 

 are found throughout the ureter, though in larger numbers at its two 

 ends. The ureters are supplied with nerve fibres from the splanchnic 

 nerves by way of the renal plexus, and at their lower ends from the 

 hypogastric nerves. Stimulation of the latter as a rule increases the 

 rhythm of the contraction presented by the lower end of the ureter. 

 The splanchnic nerves have been stated to produce either acceleration 

 or inhibition of the contractions at the upper end ; their action is, 

 however, uncertain. It is by the rhythmic advancing waves of 

 contraction of the ureter that the urine is continuously passed on to 

 the bladder, so that the pelvis of the kidney is kept empty of fluid 

 whatever the position of the animal. 



The bladder is lined by transitional epithelium, closely adherent to 

 the underlying muscular coat. It is usual to describe in the latter 

 three layers of muscular fibres : 



(1) An outer layer composed of bundles running longitudinally 



from the neck of the bladder to the fundus, sometimes distinguished 



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