Title: Elements of human physiology
Identifier: elementsofhumanp05star (find matches)
Year: 1907 (1900s)
Authors: Starling, Ernest Henry, 1866-1927
Subjects: Physiology
Publisher: Chicago : W. T. Keener
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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FUXCTIONS OF THE KIDNEYS AM) SKIN 460 the bladder itself, the circulai- and longitudinal fibres both co-operate in straightening the vesico-urethral canal and forcing a tluid wedge into the beginning of the urethra. A recent investigation by Kalischer of the structures at the neck of the bladder has brought to light the existence of two distinct structures, both of which must play some part in the normal retention of urine. The first of these is a dense ring of unstriated muscular fibres, the sphincter frigonalis, which encircle the beginning of the urethra in an oblique direction, as indicated by the dotted line s s in Fig. 220, and are continuous with the muscle-fibres of the trigonum (the space between the openings of the ureters). These fibres are quite distinct from the circular fibres of the bladder. Besides this involuntary sphincter, Kalischer describes another, consisting of striated fibres which form a complete circle round the membranous portion of the urethra, and an incomplete ring round the anterior part of the prostate. This is the sphincter urogeniiaUa. Both structures, it will be observed, belong not to the bladder but to the urethra, of which the trigonum is genetically a part. We must now inquire into the mechanism of the act of expulsion. As the urine slowly trickles into the bladder, this viscus first relaxes to accommodate the fluid, so that its con- tents increase without a corresponding rise of intra-vesical Fig. 221.
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U, B. 20" ^ -VWl WAMWVAA,WA VW^UAAM\M/V\MMM/\\AMAAVv^\naAVv'vAAA/ Tracings of rhythmic contractions of urinary bladder. (Sherrington.) pressure. With increasing distension however the pressure in the bladder begins to rise, and this increased tension on the muscular walls has the ordinary excitatory effect on the muscle-fibre. Slow rhythmic contractions of the bladder make their appearance and increase in force with increasing tension on the muscular walls (Fig. 221). The exact point at which, with increasing pressure, this excitatory effect begins, depends largely on the rate at which the pressure is raised. A bladder which normally would hold 250 c.c. of fluid, will not hold more than 100 c.c. if injected rapidly by means of a syringe. In each case micturition would begin

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