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 con- 

 tractions 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 

 \>f muscular fibres : 



(1) An outer layer composed of bundles running longitudinally from 

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

 name of the detrusor urince. At the neck of the bladder these bundles send 

 some fibres to be attached to the pubes as the pubo-vesical muscles. On 



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