Structure and Function of the Urinary Bladder

THE JOURNAL OF UROLOGY

Vol. 84, No. 1, July 1960 Printed in U.S.A.

STRUCTURE AND FUNCTION OF THE URINARY BLADDER RUSSELL T. WOODBURNE From the Department of Anatomy, The University of Michigan Medical School, Ann Arbor, Mich.

Past and some current teaching concerning the urinary bladder has tended to reflect too closely the concepts found to be useful in the other hollow viscera of the body. Thus, the two or three layered muscular arrangement of the gastrointestinal tract has been ascribed to the bladder and it is assumed that such layers in the bladder are discrete and exhibit the usual circular and longitudinal· orientation. Since the urinary bladder is served, like the other viscera, by the two part autonomic nervous system, there has also been a strong tendency to relate these to the muscular parts of the urinary bladder in a logical but not necessarily valid manner. Thus, the musculature of the wall, the detrusor muscle in general, has been considered to be antagonistic to the internal urethral sphincter and the two visceral innervations have been made to match this antagonism~the parasympathetic innervation motor to the detrusor and at the same time inhibitory to the sphincter, and the sympathetic innervation motor to the sphincter and inhibitory to the detrusor. Physiological evidence has long denied such a "pat" description of structure and function in the urinary bladder. In 1933 Denny-Brown and Robertson' demonstrated that urination is a reflex act mediated through the centers in the sacral cord and in 1936 Evans 2 was unable to obtain satisfactory evidence that the sympathetic nerves play any part in vesical function. Langworthy, Kolb and Lewis 3 advanced the opinion that the detrusor muscle is devoid of sympathetic innervation. These findings have been documented by others, 4 and it is now certain that the emptying reflex of the urinary bladder is, like the rectum, completely under the control of the

parasympathetic nerves which reach it. The parasympathetic reflex arc controlling the bladder is completed by afferent neurons in the parasympathetic nerves which respond to stretch receptors within the mucosa and submucosa. 5 It has been established that the sympathetic innervation reaches only the representation of ureteral musculature in the trigone of the bladder; 3 it also conducts most of the pain afferents from the bladder. There is now general agreement on the role of the nerves of the urinary bladder and understanding of the effects of nerve injury and cord lesions in disturbances of micturition. It is clear that these well-known facts of neurophysiology are not projected into a satisfactory concept of the structure of the bladder. Is it composed of a nicely layered musculature? Is there a discrete and separate vesical (internal urethral) sphincter and if so, is it antagonistic to the detrusor? What mechanism keeps the vesical orifice closed as urine accumulates and what mechanism holds the orifice open as vesical pressure drops during micturition? To answer these and other questions, a study has been made of the structure of the bladder by a combination of gross and microscopic techniques, using canine and human bladders. Stimulation experiments were carried out in dogs and sections of embryonic specimens were also examined. The embryonic development of the bladder and urethra gives no justification for regarding them as having separate origins. 6 • 7 Both bladder and urethra develop from the urogenital portion of the cloaca, their distinction being based only on the spheroidal enlargement of the proximal part of the allantois which results in the urinary bladder. The constituents of their walls are the same and the musculature of the bladder extends without interruption as the muscular wall of the

Accepted for publication October 30, 1959. 1 Denny-Brown, D. and Robertson, E. G.: On the physiology of micturition. Brain, 56: 149, 1933. 2 Evans, J.P.: Observations on the nerves of supply to the bladder and urethra of the cat with a study of their action potentials. J. Physiol., 86: 396, 1936.

5 Langworthy, 0. R. and Murphy, E. L.: Nerve endings in the urinary bladder. J. Comp. Neurol.,

7: 177, 1957.

6 Arey, L. B.: Developmental Anatomy. Philadelphia: W. B. Saunders Co., 1934. 7 Patten, B. M.: Human Embryology. Philadelphia: The Blakiston Co., 1946.

71: 487, 1939.

3 Langworthy, 0. R., L. C. Kolb and L. G. Lewis: Physiology of Micturition. Baltimore: The Williams and Wilkins Co., 1940. 4 Bors, E.: Neurogenic bladder. Urol. Survey,

79

80

RUSSELL T. WOODBURNE

Fm. 1. Photomicrograph of stained section. Longitudinal section of bladder and urethra of an 86 mm. human embryo. l\!Iasson stain, X25. urethra (fig. 1). Nor do fetal stages show any specialization at the transition region which would form an internal urethral or vesical i:iphincter. All the tissues and layers at the bladder neck flo\\' smoothly and without modification into the urethra. Adult human and canine bladders, fixed in both distended and contracted conditions, were macerated to weaken their connective tissue substrate, am! their musculature was studied. Observation of the internal muscular arrangements was facilitated by removal of the mucous membrane after maceration. Such observations make it abundantly clear that the urinary bladder is a muscular meshwork. In any section layers can be defined; layers which appear to be more or less at right angles to adjacent ones. However, on tracing continuities there can be no doubt that the bundles of bladder muscle change their level and direction, decussate, and intermingle in a way which appears haphazard but which is essentially a meshwork (figs. 2 and 3). This was dearly stated in the early observations of Griffiths. 8 Hunter 9 noted that the apparently longitudinal surface bundles separate from one another, run deeper into the wall, and Griffiths, J.: Observations on the urinary bladder and urethra. J. Anat. and Physiol., 25: 549, 8

1891.

9 Hunter, DeW. T., Jr.: A new concept of urinary bladder nrnsculatnre. J. Urol., 71: 695, 1954.

decussate, as many as five decussations being made by some bundles. A minor accumulation of muscle bundles about the vesical orifice constitutes the so-called vesical or internal urethral sphincter. This term persists in the literature despite the denial of any sphincter of annular fibers at the neck of the bladder as early as 1883.10 It is abundantly clear that such a minor gathering is not a separate muscle. It is composed of the bundles of the detrusor muscle which arc past the vesical orifice and continue into the urethra. This continuity is apparent in both adult and developmental preparations. After study of the human prostatic urethra, Clegg 11 stated that the musculature of the proximal urethra is partly derived from and continuous with the anterior longitudinal muscle of the bladder. He concluded that there was no anatomical sphincter at the bladder neck. The continuous and identical charaeter of the urethral muscle bundles make it impossible to regard them as the antagonists of the same bundles in the bladder wall. The present study of the muscular arrangements at the vesical neck in the dog disclosed also that certain detrusor fascicles arc 10 LeGros Clark, E.: Some remarks on the anatomy and physiology of the urinary bladder and the sphincter of the rectum. J. Anat. and Physiol., 17: 442, 1883. 11 Clegg, E. J.: The musculature of the human prostatic urethra. J. Anat., 91: 345, 1959.

STRUCTURE AND FUl\CTIO:\ OF BLADDER

FrG. 2. :\Iusculature of human bladder: A, anterior view; B, posterior view; C, lateral view; ternal aspect of anterior half of bladder. Xote descending longitudinal bnndles collt.inning into urethra.

toward and then past and away from the neck, accounting in part for the local thickening recog nized as the "vesical sphincter." Earl)· investigutors12 noted the arcing of the muscle bundles here but con,;iclered that the bundles went most of the 12 Wesson, ;\I. B .. Anatomical, embryological and ph_rniological studies of the trigone and neck of the bbdder. J. Urol., 14: 278, HJ20.

way around. Thus anterior and posterior nrchcs or loops were conceived which would constril,t tli< vesieal orifice between them The presl-rnt evi. clence suggests that the bundles arc past and no! around the aperture and thus do not operate :1~ r> closing mechanism (fig. 3, D). A prominent feature of the neek of the hladckr is the accumulation and continuation of it,"

82

RUSSELL T. \VOODBURNE

FIG. 3. View of musculature of dog's bladder: A, anterior aspect; B, posterior aspect; C, vertical section of vesical neck and prostate gland; D, dissection of external musculature at plane of vesical neck.

musculature into the urethra (figs. 2, D and 3, C). Perhaps because of the expanded nature of the bladder the musculature of the urethra appears somewhat thicker and more strongly longitudinal in orientation. The surface bundles and also the deepest (or submucosal) bundles are longitudinal. These can act as an opening device. ,Vith a bladder globular from distention, such longitudi-

nal bundles pull radially and open thr vesical orifice by direct outward action. Several observers13 • 14 have noted cystoscopically that the 13 Scher, S.: Some observations on the anatomy of the bladder neck and posterior urethra with reference to prostatic obstruction. Brit. J. Urol., 22: 116, 1950. 14 Lapides, J.: Structure and function of the internal vesical sphincter. J. Urol., 80: 341, 1958.

STRCCTUHE A_,D FUNCTION OF Bl,,I_DDEH

normal bladder opclls by 1,·id;-,ning of the vesical rll'c-k and chnrkning of the urethra. Direct obscrnitiorn, in the dog uf electrirnl stimulaticm of the ,mrfac-e of the hladder han· been made by Lapidcs aml 1Yoocllrnrne arnl ,;hm,· that the longitndiual snrface musclr of the urethra contracts in concert witli tlw same muscle of the lilacldf'r and effects a shortening of the urethra. [t can be suggest1~d theu that tlw aecumulation at trtP bladder neck wliich \ms been regankcl as a n·sical or internal urethral sphincter does not actuall>· coJtstitutP u sphincter at all. The mu;;culaturc l1ere i,: uot separate, from the rest of the bladder musculature am{ it contracts with and not against the 1frtrurnr. It should he considered a~ ~en·ing in the 1,mptyi11g mc;clrnnism rm a ~pecial dn·ice to shorten the urethra and to aid in opening the vesical orifice. Thi~ iu'tion eouplecl 1Yith tht> hydrostatii: pressure being imposed hy the contraction of the detrnsor complex pro, ides for the initiation of micturition. Such a mecha nism ob,,iously docs not require an inhibiting ~)'Dlpatlwtic i1merYatio11 in the region of the neck of the bladder. The solution of the role of the musculature of the ,,esical 1wi:k and the un·thra ancl its correlation witb the detrusor muscle under the control of one innl'rvation (thr: paras:1·mpathetic) explains the actin· phase of micturition I.mt leaYPS obscurp the means wlHTeb)· the bladder retains a COD· siclernbk nilume of fluicl ,1·ithout leakage during its inactin pr;riods. [t i8 apparent that there mLrnt he sume mechaui8m for holdi11g the orifice of the Yesic-al neck closed aP the bladder expands ancl the rmrncular wall is stretclwd. Elastic tissm• could logically proYide an antagonism to the opening action of muscle and so combined elastic: and Posin stains ,wre applied to spetions of Yarious part.~ of the uriua1-_v bladder and urethra of both the 1log ancl man. Ela,;tic tissue has been found in tlie general bladckr wall in several locatious--clircctly under the transitional epithelium, scattered in the submucosa, and as a component of the binding tissue around and betwPcn the muscle fasciculi. In tlwsP locatiorrn it appearn to be some\\·hat more prominent than that 8l'CJI in ,wctimrn of human sigmoid colon and rectum but not striking!)· so. Howeyer, elastic fibern are n·rY prominent at, the n:sical neck and along th(' urethra in both male and fpmale ~pecimens. They are inerea~ecl markcclly in the snbmucosa and armmd aml between the muscle bundles, especially the more ct'ntral Ol!E' (fig.-!, .l 0

aucl B). In fact, muscle and elastic t.issw' are intermingled in the \·esirnl neck and along tiH-' urethra in a most intimate fashi011,---s11cl1 as 1m1,_,· be expressed in tlw littlP-used term n1Yo-<'lasfr tissm,. ,\hundant elastic tissue exists thnrngl101,t the lengtb of the female url'1Jira and througl1 the prostatic portion of the mah_, urethra. Seetim1° were not made at more· distal le,·els in tli1· nwJ,,. 1lodian1o stucliecl rnses of human hladdn ne1k obstruction. ,\nalyzing stained sections of blo1:h:,, of prnstatic un·thra in tl1esc: inst:rnces, lw noted striking preponderance of Plastic tissm· belP\Y th,-· lend of thr seminal colliculus. ffr ulso ohs1-T1-1·d an elongation of thC' proshtk and rnuelw.lt•d tlw1, an 8lougated filmwlastic prostate offer~ at1 obstructiou to urinary flow along the ,,-hole rn1m;e of the posterior urethra. LapirlesH discuss1·d ti ,e faetors contributing to continence in a p:iJH'r denitecl to the structure and fonctiou of t.l,,, internal vesical sphineter. He <·alled attentiou to Laplace's law which states that till' pn·ssm,· ( P) exerted on the wall of a tube its fluid cout,,•ut;, is directly proportional to the term ion (T) iJt tfw wall and inversely proportional tn the radius (t'I of tlw tube whC'n these fore1·s :ire in e
P = T /r. An analysis of Laplace's \11,1· as 1<; blood vessels has becu nrndc hy Bmton. 1 '1 1:-l, noted for such tubular structures that kusion the ,rnll (in d:nics per l'm. of lengtli) <'lmsists pf Plastic tensio11 due to dastic tissue aud th,_, elasticity of the other compom·nts of the wall active tcn8ion due to tlw contraction of' Hie smooth muscle, and interfacial tension n,pn·sentcd by surface tension in tl1e fluid. He note, that "maintenanni tension" in blood ve8scl8 i,,, 11TH correlatPd \Yith the presence and ammmt of elastie tissue in their walls, and that lnrg;,· and mediuni-sized ,·essels require good representat.iou of this material. H iR apparent that, like tlu· larger blood Vl'ssels, the lll'dhra utiliz<'s das1i<" tissuP to rnaintain a high T valuP .. \.s the ddrusoi lwcomes active and increasPs the pressure in thC' bladder aud the urethra and shortPning and funneling of the nrdlm1 occur, the P value rises well abo,·e the T/r rnlue nnd 15 Bodian, :\L: !Some observation, on t lrn pn thology of "congenital idiopnt hie bladder-rnick obstruction" (l\-forion', clisea,re\ Brit. ,i. {'rnl., 29: ;:)f)3, Hl57. . 16 Burton, A. C .. On the physi(:al ;-,qmlilirirnn of small blood vessek Am. J. l'h:rniol. 164: :i 19

1051.

84

RUSSELL T. vYOODBURNE

Fm. 4. Photomicrographs of stained sections. A, segment of a cross-section of proximal part of urethra in dog. Elastic tissue black. Weigert stain, X40. B, segment of cross-section of snbmucosal a.rea of urethra. in man. Elastic tissue black. Weigert stain, X50.

STRlJCTURE AND :B'U'\:C'l'TON OF BLADDER

voiding occurs. "ls soon, however, as the act is completed, pressure drops and the T/r quotient mounts well above the eritical value required by tlw equation. Closun' follows \Yith obliteration of the lumen. Complete obliteration is 1mturally hindered hy structural bulkiness or cornparatin-: rigidity of the tissues ancl it is likely that a certain length of urethrn is n,quirccl to produce complete closurG on this account, as Lapicles has shown to be the case in dogs. StudieP of human incontim,nct,17 clemonstnttc that there is a necessary length for the mdhra below which continence is not easy or is impossible. Clinical evidence supports the concept that the entire methra in thr, fcrnak, is the; sphincter of the blarlcler and that the prostatie and 111embranmrn urethrn serves the same purpose in the male. The role of the voluntary e:--:.ternal urdhral sphinC'tcr ('Omposerl of striated musculatmc does not app(,ar to require c:ssential revision. This component of the museular urogt:uital diaphragm is capable of the; abrupt stopping; of micturition and its normal tonic state rloubtless contribute, to tlw usual closed condition of thr, urethra.. _.I, special portion of this musrle :lrdws backward on either side of tlw membranous urethra to attach to tlw ischial rnmi wdl bd1ind the levC'I of the urcthrn. 18 Siner the urogenital diaphragm slopes obliquely downward and backward (in the erect position of the body) this musd('. not only compresses the urethra hut also elong;ates it, an action which nicrly opposes the shortening of 17 Lapides, J. · Further observations on the kinetics of the 1nethrovesical sphincter. ,J. Urol., 84: F:6, 1960. rn Oelrich, T. \I.· Unpublished observations.

the urcthrn which accornp:rnies micturition. This cffed, together with the dcvatiug action of the pelvic cliaphrngrn, increases tbe length of tl1(· urethra and aids in the maintenance of closun: of the urethral lumen. A number of rr1·isions are rr·quirrd iu Uw concepts of anatomists and clinicians with n,sp,-'(''G to tlie structure and function of tlw bladder and thr urethra. There is rvi(lcnce that no :wtun.J Ycsical or internal urethral e:-;ist.-, ,uH! that no sphincteric function is scrvc'd i11 tlw region of the neck of tlw hJ:idcler·. lt has lwen shown tlmt the entire 1irethra in till' Icmale ,me! the prostatic and membranous tll'(-'tbrn in the mak is the sphincter of thr hlu.dder ,wd that tl1i.o function clepenc!R, in p:ut, on normal retained in these parts. Closure of the un{hrn gn,a.tly assisted by the cle,ve/opnwnt of elastic: tissue at the bladclPr neck and along tlw length of the urethra, such da"hc tic~\tt· and interbeing most prominent mingled \1·ith the innermost rnusr:ll' lmndl('i l\ficturition is accomplishrcl the pn·.c,s111oc exerted by the cletrusor rnusde (tlw entire m11s1·ular eomplex of the blacldn) n~sistecl by it.s con tinuorn, ur<'thrnl nrnsculature. Tlw contribution of tlw rmrncle of tlw bl:lclcler rn'c·k and urethra to the opening mc'clmnirn1 is in shortrning; and widening tlw urethra and in opening the aperture of the Yesieal IH'c·k in ;: funnel-like widening. The control of micturition according to the concepts of strnctm·e outlit1ed abovr can be achiever) by a reflex. and the single (parnsympatheti(') innervation a,: lw~ been establfahrd in the of the organ.