The urethral striated sphincter in adult male rat

This study reports the morphology of the urethral sphincter in adult male rats, mainly the histological aspects, the features of the endplates, and the heavy myosin chain distribution in the striated fibres. First, the prostate is entirely out of the striated sphincter, which is surprising when compared to man. Second, the urethral striated sphincter consists of two lateral fascicles separated by an anterior and a posterior strip of connective tissue, which extend from the prostatic urethra (i.e. the part of the urethra which runs though the prostate) to the bulb of the penis. An additional third fascicle of striated muscle (SM) covers the caudal part of the anterior connective strip of the membranous urethra (i.e. the urethra which extends from its prostatic part to the bulb of the penis). In the membranous urethra, the striated sphincter surrounds directly the urethral lumen without intercalated smooth muscle. In urethral cross sections, the endplates detected by α-bungarotoxin, which binds to nicotinic receptors, are clustered in the postero-lateral part of the lateral fascicles. The cross-sectional area of the urethral striated fibres shows a bimodal distribution: the largest fibres are located at the periphery of the sphincter and these fibres express only fast myosin heavy chains (MHC) as shown by immunochemistry. The smallest fibres are less numerous and are situated near the lumen co-expressing fast and slow MHC. All the striated fibres express desmin and dystrophin as SM fibres do. Taken together, these results suggest that the urethral striated fibres in male rat present the same characteristics as those of the skeletal muscles. The predominance of fast fibres is consistent with phasic contractions playing a role not only during micturition and urinary continence but also probably during ejaculation.     

Morphological analysis of the urethral muscle of the male pig with relevance to urinary continence and micturition

To investigate whether the pig could be considered a suitable model to study lower urinary tract function and dysfunction, the pelvic urethra of 24 slaughtered male pigs were collected, and the associated muscles were macroscopically, histologically and histochemically analyzed. In cross‐sections of the urethra, a muscular complex composed of an inner layer of smooth muscle and an outer layer of striated muscle that are not separated by fascial planes was observed. A tunica muscularis, composed of differently oriented smooth muscle bundles, is only evident in the proximal part of the pelvic urethra while, in the remaining part, it contributes to form the prostatic fibromuscular stroma. The striated urethral muscle surrounds the pelvic urethra in a horseshoe‐like configuration with a dorsal longitudinal raphe, extending from the bladder neck to the central tendon of perineum. Proximally to the bladder, it is constituted of slow‐twitch and fast‐twitch myofibers of very small diameter, and embedded in an abundant collagen and elastic fiber net. Moving caudally it is gradually encircled and then completely substituted by larger and compact myofibers, principally presenting circular orientation and fast‐twitch histochemical characteristics. So, like in humans, the cranial tract of the muscular system surrounding the pelvic urethra is principally composed of smooth musculature. The striated component cranially may have a role in blocking retrograde ejaculation, while the middle and caudal tracts may facilitate urine and semen flow, and seem especially concerned with the rapid and forceful urethral closure during active continence. Some differences in the morphology and structure between pigs and humans seem due to the different morphology of the ‘secondary’ sexual organs that develop from the urethral wall and to the different effect of gravity on the mechanics of the urinary system in quadruped and bipedal mammals.     

Striated muscle and nerve fascicle distribution in the female raturethral sphincter

The anatomical basis for urinary continence depends on a thorough understanding of the tissues in the urethra. The objective of this study was to evaluate the morphology and neuroanatomy of urethral striated muscle, called the rhabdosphincter or external urethral sphincter, in normal female rats. Urethras from 12 female rats were dissected from the bladder, fixed, embedded in paraffin or epon, and sectioned every 1 mm. Striated muscle content was taken as the ratio of the striated muscle area to net urethral area. Nerve fascicles containing myelinated axons near the rhabdosphincter were counted and mapped. Both striated muscle content and number of nerve fascicles peak in the proximal third of the urethra, with a secondary peak at the distal end of the urethra. This secondary peak may correspond to an analog of the combined compressor urethrae/urethrovaginal sphincter located in the distal urethra in human. The rhabdosphincter has a variable distribution along the length of the urethra. In the middle and distal thirds of the urethra, the dorsal striated muscle fibers between the urethra and vagina become more sparse. The majority of nerve fascicles are contained in the lateral quadrants of the urethra, similar to the lateral distribution of somatic nerves in humans. In conclusion, this study demonstrates the normal distribution of the striated musculature and neuroanatomy in the urethra, with similarities to the human. It thus supports and extends the usefulness of the rat as an experimental model for studying urinary incontinence. Anat Rec 290:145–154, 2007. © 2007 Wiley‐Liss, Inc.     

Histology of the canine urethra. I. Morphometry of the female urethra

Urinary bladders and urethrae were collected from six adult and two juvenile female dogs. Five urethral regions and the neck and body of the bladder were sampled. Volume fractions for connective tissue including elastic fibers, smooth and striated muscle, and epithelium were obtained by projecting section images onto an array of points and computing the number of points overlying a tissue constituent per total points overlying the tissue section. Smooth muscle occupied approximately half the volume of the bladder wall, one-third the volume of the vesical neck, and one-fourth the volume of the proximal urethra. Striated muscle was present in the distal half of the urethra, where the total muscle coat occupied about one-third of the urethral wall volume. Smooth muscle was practically absent in the terminal urethra, where the striated urethralis muscle encircles urethra and vagina in common. Epithelial area and lumen perimeter were not significantly different along the length of the urethra except that urethral epithelium was significantly thicker adjacent to the vesical neck. In terms of histological proportions, the vesical neck was intermediate between the body of the bladder and the proximal urethra.     

Histology of the canine uretha II. Morphometry of the male pelvic urethra

Urinary bladders and pelvic urethrae were collected from six adult and two juvenile male dogs. Within two vesical and six urethral sampling regions, volume densities were estimated for smooth and striated muscle, connective tissue and elastic fibers, stratum cavernosum, luminal epithelium, and prostate. The neck had significantly less smooth muscle and more connective tissue than the body of the bladder. In the prostatic urethra, smooth muscle was associated principally with trabeculae surrounding prostate lobules. Smooth muscle was sparse superficially in the prostatic capsule and practically absent in relation to the mid-prostatic urethra. Thus there was no mechanism for active closure of the middle prostatic urethra, and elastic fiber density was correspondingly high in this region. The smooth muscle sphincter needed to maintain urinary continuence and prevent semen reflux was primarily the vesical neck. Caudal to the body of the prostate, striated muslce comprised more than 50% of the urethral wall. Juvenile and adult postprostatic urethrae were similar except for a decreased quantity of stratum cavernosum in the pups.     

Morphological and functional characteristics of the urogenital diaphragm in women

Macroscopical study of muscle layer of urogenital diaphragm in women has revealed two muscles situated between its superior and inferior fasciae--m. transversus perinei profundus (MTPP) and sphincter urethrae (SU),--which are separated by connective tissue. In females, SU is not ring-shaped, but is an arched structure situated in front of urethral lumen intertwining into urethral outer circular muscular layer. MTPP consists of three groups of bundles: anterior, medium and posterior. Anterior bundles of MTPP are periurethral and directly interlace with urethral muscular wall. Medium and posterior bundles of this muscle do not reach the urethral wall and act on the muscular wall of vagina. The study of histotopographic sections of urethral muscular wall made from the level of neck of the urinary bladder to the urogenital diaphragm, showed that the urethral outer circular muscular layer contains both bundles of smooth muscle cells and striated muscle fibers which ascend from urogenital diaphragm attaining an oblique-circular course. Major part of urethral striated muscle fibers, as well as SU and MTPP fibers belong to "red", slow-twitch, tonic fiber type.     

The Distribution of Muscles Fibers and Their Types in the Female Rat Urethra: Cytoarchitecture and Three‐Dimensional Reconstruction

An attempt to explore urethral cytoarchitecture including the distribution of smooth muscles and fast and slow striated muscles of adult female Sprague Dawley rat—a popular model in studying lower urinary tract function. Histological and immunohistochemical stainings were carried out to investigate the distribution of urethral muscle fibers and motor end plates. The urethral sphincter was furthermore three‐dimensionally reconstructed from serial histological sections. The mucosa at the distal urethra was significantly thicker than that of other segments. A prominent inner longitudinal and outer circular layer of smooth muscles covered the proximal end of urethra. Thick circular smooth muscles of the bladder neck region (urethral portion) decreased significantly distalward and longitudinal smooth muscles became 2‐ to 3‐fold thicker in the rest of the urethra. An additional layer of striated muscles appeared externally after neck region (urethra) and in association with motor end plates ran throughout the remaining urethra as the striated sphincter layer. Most striated muscles were fast fibers while relatively fewer slow fibers often concentrated at the periphery. A pair of extraneous striated muscles, resembling the human urethrovaginal sphincter muscles, connected both sides of mainly the distal vagina to the dorsal striated muscles in the wall of the middle urethra. The tension provided by this pair of muscles, and in conjunction with the striated sphincter of the urethral wall, was likely to function to suspend the middle urethra and facilitates its closure. Comprehensive morphological data of urethral sphincter offers solid basis for researchers conducting studies on dysfunction of bladder outlet. Anat Rec, 296:1640–1649, 2013. © 2013 Wiley Periodicals, Inc.     

The structure and innervation of the male urethra: histological and immunohistochemical studies with three-dimensional reconstruction

The structure of the striated urethral sphincter, the so-called rhabdosphincter, remains the subject of controversy. There are two main concepts regarding its structure: either it is a part of the urogenital diaphragm, or it extends from the base of the bladder up to the urogenital diaphragm and is an integral part of the urethra. It is also uncertain whether it possesses a somatic innervation or a mixed innervation (i.e. autonomic and somatic). The purpose of this study was to show the precise location of the nerves running to the urethra, and to try to determine their exact nature. Histology and immunohistochemistry were performed in the external urethral sphincter of ten male fetuses (114-342 mm crown-rump length, or between 14 and 40 weeks of gestation). A three-dimensional (3D) reconstruction of the urethral structure and its innervation was made from serial sections. The 3D reconstruction of the same section levels with different strains allowed us to identify the precise structure of the muscle layers (smooth and striated muscle fibres) and the nature of the nerve elements (myelinated and unmyelinated), their distributions and their relationship to the urethral wall, the prostate and the seminal vesicles. Histological and immunohistochemical 3D reconstruction of the anatomical elements of the urethral sphincter helps us to understand the 3D arrangement of the sphincter muscle layers. It also provides a better understanding of the origin and nature of the nerve elements that play a role in urinary continence.     

Motor units in cranial and caudal regions of the upper trapezius muscle have different discharge rates during brief static contractions

Aim: To compare the discharge patterns of motor unit populations from different locations within the upper trapezius muscle during brief submaximal constant‐force contractions. Methods: Intramuscular and surface electromyographic (EMG) signals were collected from three sites of the right upper trapezius muscle distributed along the cranial‐caudal direction in 11 volunteers during 10 s shoulder abduction at 25% of the maximum voluntary force. Results: A total of 38 motor units were identified at the cranial location, 36 from the middle location and 17 from the caudal location. Initial discharge rate was greatest at the caudal location (P < 0.05; mean ± SD, cranial: 16.7 ± 3.6 pps, middle: 16.9 ± 4.0 pps, caudal: 19.2 ± 3.3 pps). Discharge rate decreased during the contraction for the most caudal location only (P < 0.05). Initial estimates of surface EMG root mean square values were highest at the most caudal location (P < 0.05; cranial: 32.3 ± 20.9 μV, middle: 41.3 ± 21.0 μV, caudal: 51.6 ± 23.6 μV). Conclusion: This study demonstrates non‐uniformity of motor unit discharge within the upper trapezius muscle during a brief submaximal constant‐force contraction. Location‐dependent modulation of discharge rate may reflect spatial dependency in the control of motor units necessary for the development and maintenance of force output.     

On Structure-Function Relationships in the Female Human Urethra: A Finite Element Model Approach

Remarkably little is known about urethral striated and smooth muscle and vascular plexus contributions to maintaining continence or initiating micturition. We therefore developed a 3-D, multiphysics, finite element model, based on sequential MR images from a 23-year-old nulliparous heathy woman, to examine the effect of contracting one or more individual muscle layers on the urethral closure pressure (UCP). The lofted urethra turned out to be both curved and asymmetric. The model results led us to reject the current hypothesis that the striated and smooth muscles contribute equally to UCP. While a simulated contraction of the outer (circular) striated muscle increased closure pressure, a similar contraction of the large inner longitudinal smooth muscle both reduced closure pressure and shortened urethral length, suggesting a role in initiating micturition. When age-related atrophy of the posterior striated muscle was simulated, a reduced and asymmetric UCP distribution developed in the transverse plane. Lastly, a simple 2D axisymmetric model of the vascular plexus and lumen suggests arteriovenous pressure plays and important role in helping to maintain luminal closure in the proximal urethra and thereby functional urethral length. More work is needed to examine interindividual differences and validate such models in vivo.

     

Tissue alterations in urethral and vaginal walls related to multiparity in rabbits

In rodents, vaginal distention after delivery or experimental manipulation affects innervations as well as the amount of striated/smooth musculature or collagen in both the urethra and vagina. These changes are associated with modifications in excretory and reproductive processes. Although successive and consecutive vaginal deliveries (multiparity) affect the contractile and functional properties of the female lower urogenital tract (LUT), its impact on LUT morphometry, including persistency, has been barely studied. The caudal urethra (CU) and cranial (V1) and caudal (V2) pelvic vaginal regions were excised from young and adult nulliparous (YN and AN, respectively) and multiparous (YM and AM, respectively) rabbits. Tissues were histologically processed and stained with Masson's trichrome. The thickness of the tissue layers and areas covered by tissue components were measured and compared using two‐way ANOVA followed by Student‐Newmann‐Keuls tests to determine statistical differences (P ≤ 0.05). Compared to YN, YM, and AN tissues showed a reduction in the thickness of the epithelium, as well as in areas covered by striated musculature, collagen, and blood vessels of the LUT. In comparison with YM, only some morphometric changes were recovered in the AM group. Our study shows that multiparity and age can be associated with epithelial and muscular atrophy of urethral and vaginal walls. The morphometry of the LUT between young and adult female rabbits varies with multiparity. These findings may help to better understand the effects of multiparity on young and adult females and its correlation with the development of pelvic dysfunctions. Anat Rec, 297:1963–1970, 2014. © 2014 Wiley Periodicals, Inc.     

The connective tissue sheath of uterus and vagina in the human female fetus.

A morphological study concerning the development and arrangement of the connective tissue surrounding uterus and vagina was performed by investigating epoxy resin impregnated sections through the pelves of 9-37-week-old female fetuses, of newborn children and a three-year-old child. In order to study the histology of the connective tissue in detail paraffin, semithin and ultrathin sections were used. The organization of the pelvic connective tissue in female fetuses can best be studied in middle-aged fetuses (19-28 weeks of gestation). We here report that no supportive ligaments of the uterus are found in fetuses of that age group, but that the connective tissue covering uterus and vagina is part of the connective tissue sheaths of neighbouring structures. The fetal uterus is interposed between dense subperitoneal connective tissue circularly covering the vesico- and rectouterine pouch. Dorsally the subperitoneal tissue of the rectouterine pouch joins the circularly arranged connective tissue of the rectal adventitia. A triangularly-shaped plate of dense connective tissue is situated at each lateral border of the cervix uteri. Dorsally it is continuous with the circularly running fibres of the rectouterine pouch. Whereas the dorsal wall of the vagina is loosely connected with the rectal adventitia, fibrous connective tissue intimately fuses the muscular wall of the vagina with that of the neck of the bladder and of the urethra. No evidence is provided for the existence of smooth muscle cells and elastic material within the connective tissue covering the fetal uterus.     

Investigation of the female canine urethral vascular plexus using light and scanning electron microscopy: a contributing factor to urinary continence

The vascular system of the female canine urethra was investigated by means of serial histological sections, vascular corrosion casts and scanning electron microscopy. The urethral vascular plexus, located in the proprial connective tissue between the epithelium and the smooth musculature, consisted of sinusoids. It could be divided distally into two parts defined by a constriction in the transitory region between the third and fourth urethral quarters. The proximal segment of the plexus was composed of interconnected longitudinal tubes, whereas the distal part assumed a more net-like form and was continuous with the vestibular plexus. Small arteries usually ran alongside the sinusoidal vessels for a considerable distance before emptying either directly or through branches into the plexus. This vascular arrangement establishes the vascular plexus as a structure similar to an erectile tissue with an arterial inflow, thereby emphasizing the importance of the plexus as a major contributory component guaranteeing urinary continence.     

Histology and carbohydrate histochemistry of the prostate gland of the Brazilian four-eyed opossum (Philander opossum Linnaeus, 1758)

The histology as well as glycogen and mucosubstances were described in the cranial, middle and caudal segments of the disseminate prostate of the Philander opossum. The prostate tubuli show external, medium and internal zones. The stroma presents few thin colagenous fibers while the reticular fibers form a well developed network around the glands. The elastic fibers are scant and only observed amidst the excretory ducts (internal zones). The cranial segment is formed by the narrowest tubuli of the gland. The external and medium zones are formed by cubic or cuboidal epithelium with acidophilic granules in the cytoplasm. The internal zone is lined by slightly acidophilic columnar cells. Several excretory ducts join to each other, before emptying in the urethral lumen. The middle segment is formed by largest and longest tubuli of the gland. The secretory epithelium of the external zone shows 2 morphologically distinct types of cells. The medium zone is formed by cells showing strong acidophilia at basal part and slightly basophilia in the apical part. The caudal segment is formed by cuboidal acidophilic epithelium and show the largest lumen of the gland. The luminal secretion of the gland is constituted by acidophilic fluid and numerous globules. Neutral mucosubstances were demonstrated in epithelium and lumen secretion of the 3 prostatic segments; epithelial glycogen was not found in the medium zone of the middle segment. Sialomucins were detected in the cranial and middle segments. Sulfomucins were not found in the prostate of the Philander opossum.     

Microvascularisation of the male urethra in neonates and infants

The microvascularisation of the male urethra was studied in neonates and infants by injection of agarised China ink into the circulation. The purpose of this study was to specify the angioarchitecture of each tunic of the urethral wall. The disposition of the microvascularisation networks varies depending on the urethral parts considered: only the mucous membrane networks are uniform throughout the entire urethra. The sub-mucous networks are significantly increased in the spongy part. The muscular networks disappear in the spongy part.     

Contractile effects of endothelin-1 and localization of endothelin binding sites in rabbit lower urinary tract smooth muscle

In isolated rabbit bladder and urethral smooth muscle, endothelin-1 caused concentration-related, slowly developing contractions that were difficult to wash out. Relative to contractions induced by K+ (124 mM), contractions in bladder preparations reached a higher amplitude than in urethral preparations. There was a marked tachyphylaxis to the effects of the peptide. The endothelin-1-induced contractions were not significantly affected by phentolamine or indomethacin in the urethra, or by scopolamine or indomethacin in the bladder. Incubation for 30 min in a Ca2(+)-free solution abolished the endothelin-1-induced contractions. Nifedipine did not affect the actions of endothelin-1 in the urethra but had a marked inhibitory action on its effects in the bladder. In the presence of endothelin-1, Ca2(+)-induced contractions were significantly blocked by nifedipine in the bladder but not in the urethra. Urethral preparations at resting tension responded to electrical stimulation by tetrodotoxin-sensitive, frequency-dependent contractions sensitive to alpha-adrenoceptor blockade. Pretreatment with endothelin-1 (10(-9) M) produced a significant increase in the nerve-induced contractions but had no significant effect on contractions induced by exogenous noradrenaline. Endothelin-1 did not affect spontaneous or stimulation-induced efflux of 3H-labelled noradrenaline in urethral smooth muscle. Preparations contracted by endothelin-1 were frequency-dependently relaxed by electrical stimulation. The peptide had no significant effect on the responses induced by electrical stimulation in the bladder preparations. In both bladder and urethra, [125]endothelin-1 binding sites were found mainly in the outer longitudinal muscle layer, in vessels and in the submucosa. The highest density of binding sites appeared to be in vessels and the outer muscle layer in both types of muscle. The results suggest that in the rabbit both bladder and urethral smooth muscle contain binding sites for endothelin. The peptide has contractant effects dependent on extracellular calcium in both types of tissue, but voltage-operated calcium channels seem to involved in activation only of bladder smooth muscle. The functional importance of endothelin-1 in the rabbit lower urinary tract remains to be elucidated.     

The urethral sphincter muscle in the male

The male urethral sphincter is a striated muscle in contact with the urethra from the base of the bladder to the perineal membrane. The individual muscle fibers are 25 to 30% smaller than fibers of associated muscles and are embedded in connective tissue which obscures the visibility of the whole muscle. The muscle primordium is laid down around the urethra prior to the development of the prostate. Subsequently, the prostate develops as a diverticulum of the urethra and grows into the developing sphincter, thinning the overlying musculature. With the onset of puberty, accelerated growth of the prostate displaces the sphincter, with atrophy of the overlying muscle, resulting in what may appear to be isolated segments of the sphincter muscle distributed around the prostate. The prostate overgrows the anterior portion of the urethra and the associated sphincter muscle. There is no distinct superior fascia of the so-called urogenital diaphragm separating the sphincter muscle from the prostate. The fascia of the sphincter muscle is inseparable from the prostatic sheath, is oriented vertically, and passes through the urogenital hiatus to unite with the fascia of the pudendal canals at the isochiopubic rami. Thus, the sphincter muscle is a component of a bladder-urethra-prostate-sphincter unit which lies within the pelvis, in the urogenital hiatus, and rests upon the perineal membrane. The concept of a urogenital diaphragm is not borne out by this study.     

Contractile effects of endothelin-I and localization of endothelin binding sites in rabbit lower urinary tract smooth muscle

In isolated rabbit bladder and urethral smooth muscle, endothelin-1 caused concentration-related, slowly developing contractions that were difficult to wash out. Relative to contractions induced by K⁺ (124 mM), contractions in bladder preparations reached a higher amplitude than in urethral preparations. There was a marked tachyphylaxis to the effects of the peptide. The endothelin-l-induced contractions were not significantly affected by phentolamine or indomethacin in the urethra, or by scopolamine or indomethacin in the bladder. Incubation for 30 min in a Ca²⁺-free solution abolished the endothelin-l-induced contractions. Nifedipine did not affect the actions of endothelin-1 in the urethra but had a marked inhibitory action on its effects in the bladder. In the presence of endothelin-1, Ca²⁺-induced contractions were significantly blocked by nifedipine in the bladder but not in the urethra. Urethral preparations at resting tension responded to electrical stimulation by tetrodotoxin-sensitive, frequency-dependent contractions sensitive to α-adrenoceptor blockade. Pretreatment with endothelin-1 (10^-9′ M) produced a significant increase in the nerve-induced contractions but had no significant effect on contractions induced by exogenous noradrenaline. Endothelin-1 did not affect spontaneous or stimulation-induced efflux of ³H-labelled noradrenaline in urethral smooth muscle. Preparations contracted by endothelin-1 were frequency-dependently relaxed by electrical stimulation. The peptide had no significant effect on the responses induced by electrical stimulation in the bladder preparations. In both bladder and urethra, [¹²⁵]endothelin-l binding sites were found mainly in the outer longitudinal muscle layer, in vessels and in the submucosa. The highest density of binding sites appeared to be in vessels and the outer muscle layer in both types of muscle. The results suggest that in the rabbit both bladder and urethral smooth muscle contain binding sites for endothelin. The peptide has contractant effects dependent on extracellular calcium in both types of tissue, but voltage-operated calcium channels seem to involved in activation only of bladder smooth muscle. The functional importance of endothelin-1 in the rabbit lower urinary tract remains to be elucidated.     

The Anatomy of Caprine Female Urethra and Characteristics of Muscle and Bone Marrow Derived Caprine Cells for Autologous Cell Therapy Testing

Cell therapy is emerging as an alternative treatment of stress urinary incontinence. However, many aspects of the procedure require further optimization. A large animal model is needed to reliably test cell delivery methods. In this study, we aim to determine suitability of the goat as an experimental animal for testing intraurethral autologous cell transplantation in terms of urethral anatomy and cell culture parameters. The experiments were performed in 12 mature/aged female goats. Isolated caprine muscle derived cells (MDC) were myogenic in vitro and mesenchymal stem cells (MSC) population was able to differentiate into adipo‐, osteo‐ and chondrogenic lineages. The median yield of cells after 3 weeks of culture amounted 47 × 10(6) for MDC and 37 × 10(6) for MSC. Urethral pressure profile measurements revealed the mean functional urethral length of 3.75 ± 0.7 cm. The mean maximal urethral closure pressure amounted 63.5 ± 5.9 cmH₂O and the mean functional area was 123.3 ± 19.4 cm*cmH₂O. The omega‐ shaped striated urethral sphincter was well developed in the middle and distal third of the urethra and its mean thickness on cross section was 2.3 mm. In the proximal part of the urethra only loosely arranged smooth muscle fibers were identified. To conclude, presented data demonstrate that caprine MDC and MSC can be expanded in vitro in a repeatable manner even when mature or aged animals are cell donors. Results suggest that female caprine urethra has similar parameters to those reported in human and therefore the goat can be an appropriate experimental animal for testing intraurethral cell transplantation. Anat Rec, 00:000–000, 2016. © 2016 Wiley Periodicals, Inc. Anat Rec, 300:577–588, 2017. © 2016 Wiley Periodicals, Inc.