Anatomy

The bladder is a hollow muscular organ normally situated behind the pubic symphysis and covered superiorly and anteriorly by peritoneum. It is composed of a syn-cytium of smooth muscle fibres known as the detrusor. Contraction of this meshwork of fibres results in simultaneous reduction of the bladder in all its diameters. The smooth muscle cells within the detrusor contain significant amounts of acetylcholinesterase, representing their cholinergic parasympathetic nerve supply.

The trigone is easily distinguishable from the rest of the smooth muscle of the bladder as it is divided into two layers. The deep trigonal muscle is similar to that of the detrusor, whereas the superficial muscle of the trigone is thin with small muscle bundles; the cells are devoid of acetylcholinesterase and have a reduced cholinergic nerve

Pericardium

Yolk sac

Allantois

Primitive bladder

Urogenital

Pericardium

Yolk sac

Foregut

Midgut Hindgut

Allantois

Primitive bladder

Anorectal canal

Metanephros

Foregut

Midgut Hindgut

Trigonal Muscle

Urorectal septum dividing the cloaca

Hindgut

Allantois

Allantois

Allantois Urachus

Trigone

Bladder Urethra

Anorectal canal

Metanephros

Urorectal septum dividing the cloaca

Hindgut

Allantois Urachus

Trigone

Bladder Urethra

Trigonal Muscle

Ureter

Mesonephric duct

Ureter

Mesonephric duct

Fig. 49.1 Longitudinal section through (a) a 4-week embryo; (b) a 5-week embryo; (c) a 6-week embryo; (d) an 8-week embryo.

supply. This superficial trigonal muscle merges into the proximal urethra and into the ureteric smooth muscle. In women the smooth muscle of the bladder neck is also different from that of the detrusor with orientation of the muscle bundles obliquely or longitudinally; they do not form a sphincter in women. The smooth muscle fibres of the detrusor, trigone and urethra have been shown embry-onically to be distinct from one another. The urothelium lining the bladder is composed of two or three layers of transitional cells.

The normal adult female urethra is between 3 and 5 cm in length (Fig. 49.2). It is a hollow tubular structure joining the bladder to the exterior and is located under the pubic symphysis, piercing the pelvic diaphragm anterior to the vagina. It is lined with pseudo-stratified transitional cell epithelium in its proximal half and distally by non-keratinized stratified squamous epithelium. Beneath this is a rich vascular plexus which contributes up to one-third of the urethral pressure and which decreases with age. Beneath this there is longitudinally orientated smooth muscle which is continuous morphologically with the detrusor, but histochemically distinct. Contraction of this muscle layer leads to shortening and opening of the urethra. The main bulk of striated muscle is located in the middle third of the urethra and is orientated in bundles of circularly arranged fibres, thickest anteriorly, thinning laterally and almost totally deficient posteriorly. This is the rhabdosphincter urethrae, and has also been called the external sphincter or the intrinsic sphincter mechanism. The muscle fibres of the rhabdosphincter consist of small diameter slow twitch fibres which are rich in acid-stable myosin adenosine triphosphatase (ATPase) and possess a number of mitochondria. This muscle mass is responsible for urethral closure at rest.

The extrinsic sphincter mechanism consists of striated periurethral muscle (levator ani) which has no direct connection with the urethra and is situated at the junction of the middle and lower thirds of the urethra. This muscle consists of large diameter fibres, most of which are rich in alkaline-stable myosin ATPase characteristic of fast twitch muscle fibres. This extrinsic sphincter mechanism contributes an additional closure force at times of physical

Extrinsic T sphincters mechanism

Periurethral striated muscle

Intrinsic sphincter mechanism

Pubourethral ligament

Collagen

Urethral smooth muscle

Elastic tissue

Rhabdosphincter

Periurethral striated muscle

Rhabdsphincter

Rhabdosphincter

Detrusor

Detrusor

Fig. 49.2 The adult female urethra.

effort. Together the intrinsic and extrinsic sphincter mechanisms of the urethra produce a greater pressure within the urethra than in the bladder. This is known as the positive closure pressure and is partly responsible for the maintenance of continence.

The proximal urethra is supported by the pubourethral ligaments which attach the proximal urethra to the posterior aspect of the pubic symphysis. These were originally described by Zacharin [3]) as consisting of parallel collagen bundles and elastic connective tissue. However, his histological examinations were of cadaveric specimens and Wilson et al. [4] have shown in operative specimens that these ligaments contain large numbers of smooth muscle bundles. Gosling et al. [5] reported that the pubourethral suspensory ligaments are histo-chemically identical to the detrusor with an abundant supply of cholinergic nerve fibres. But Wilson et al. [4] failed to demonstrate acetylcholinesterase activity in these fibres, thus their origin remains unclear. DeLancey [6] has described two distinct entities: the pubourethral ligament composed of collagen and a pubovesical ligament containing muscle fibres.

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Getting Back Into Shape After The Pregnancy

Getting Back Into Shape After The Pregnancy

Once your pregnancy is over and done with, your baby is happily in your arms, and youre headed back home from the hospital, youll begin to realize that things have only just begun. Over the next few days, weeks, and months, youre going to increasingly notice that your entire life has changed in more ways than you could ever imagine.

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