VET 313 Lecture Module: Male Reproductive System PDF

Lecture Module: The Male Reproductive System The male reproductive system consists of the paired testes suspended in the scrotal sacs, a continuous duct system for the storage and transport of the male gamete, the spermatozoon, and an ejaculatory organ, the penis. The accessory sex glands s...

Lecture Module: The Male Reproductive System The male reproductive system consists of the paired testes suspended in the scrotal sacs, a continuous duct system for the storage and transport of the male gamete, the spermatozoon, and an ejaculatory organ, the penis. The accessory sex glands secrete into the urethra and provide a suitable fluid medium to transport the spermatozoa during ejaculation and in the female reproductive tract. Objectives a) Recall and name the different organs comprising the male reproductive system of the body b) Identify and describe histologically the different organs and its associated structures belonging to male reproductive system c) Enumerate and recognize differences among organs among mammalian species d) Enumerate and recognize differences among organs in mammalian and avian species e) Relate structures present as to the functions of the organs. The male reproductive system is composed of organs that are involved in the production and transport of sperms and production and deposition of semen into the female vagina. The male reproductive system consists of the: o testes (sperm production), o epididymides (sperm maturation and transport), o deferent ducts (sperm transport), o accessory sex glands: ◼ terminal portion of the deferent ducts, ◼ prostate gland, ◼ vesicular glands, ◼ bulbourethral glands and penis. Not all accessory glands are present in all species. Accessory glands are absent in birds. VET 313 Lecture Module 2024 Mammalian Testis  An exocrine and endocrine gland.  Exocrine function: production of spermatozoa.  Endocrine function: secretion of the hormone testosterone by the interstitial cells of Leydig.  During the embryonic stage of life, is located near the kidneys and just before or immediately after birth it descends to a specialized pouch of skin, the scrotum in mammals.  Covered by the visceral layer of peritoneum, which blends with the capsule (tunica albuginea) of the testis.  Each testis is an ovoid parenchymatous organ composed of the following parts Fig. 210:  Capsule (tunica albuginea)  Irregular DWFCT.  Connects with the interlobular loose CT septa (septuli testis) of the testis.  Several septuli testis converge in the mediastinum testis.  Dogs and pigs: the septuli testes are complete while in other species they are just strands of loose CT.  Stratum vasculare  Vascular area located superficial to the tunica albuginea in dog and ram or beneath the tunica albuginea in stallion and boar.  Stroma  Septuli testis and mediastinum testis.  Septuli testes Divide the parenchyma into lobules. Each lobule contains the seminiferous tubules or tubuli seminiferi convoluti and tubuli recti, which are supported by the interstitial or intertubular loose CT.  In birds the interstitial connective tissue is scanty.  The intertubular loose CT presents clumps of interstitial endocrine (Leydig) cells.  Interstitial endocrine cells  Large polyhedral acidophilic cells with large spherical nucleus.  Most abundant in boar (20% - 30% of testicular volume) then in bull (5%), ram (1%) and few in birds. VET 313 Lecture Module 2024   Secrete testosterone and in boars, also large amounts of estrogen. Converge in the mediastinum testis.  Mediastinum testis An island of loose CT into which the septuli testes converge. Presents a network of short tubules, the rete testis. Horse, cat and rodents: mediastinum testis is small and located superficial to the testis.  Parenchyma  Composed of lobules called lobuli testis.  Inside each lobule are tiny (150 to 300 urn diameter), long, coiled two- ended loops of tubules called seminiferous tubules or tubule seminiferi convoluti, which radiate peripherally from the mediastinum testis to the tunica albuginea.  Seminiferous tubules Total length in the adult bovine testis is approximately 5000 m. Separated by the interstitial loose CT. Enclosed by a thin basal lamina on which the spermatogonia rest. Wall is a stratified special epithelium made up of spermatogenic cells and sustentacular (Sertoli) cells.  Spermatogenic cells represent the developmental stages of the male gametes and from the outside inward are the spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids and spermatozoa. Spermatogonia o Small round cells that that rest on basal lamina and form the basal layer of the tubular wall. o Present large, round vesicular nuclei and eccentrically located nucleoli. o Divide to form daughter spermatogonia or differentiate into primary spermatocytes. Primary spermatocytes o Occupy the 2nd to 4th cellular layers of the wall. VET 313 Lecture Module 2024  o Largest cells in the tubule. o Often seen in the prophase stage of meiosis, they present condensed chromosomes in the nucleus. o Divide to form secondary spermatocytes. Secondary spermatocytes o Difficult to find in tissue section because as soon as they are formed from the primary spermatocytes they immediately divide to form spermatids. Spermatids o The most numerous cell type o Two types of spermatids are usually seen in the tubule: early and late spermatids. o Early spermatids ▪ Small round cells with centrally located nuclei. o Late spermatids ▪ Ovoid with dense ovoid nuclei and short tails and are embedded in the cytoplasm of Sertoli cells for nourishment. ▪ Undergo morphogenesis to become spermatozoa. Spermatozoa o Mature male gametes that form clumps in the lumen of seminiferous tubule. o Like tadpoles with a head, neck and tail. ▪ Sustentacular or Sertoli cells Nourish, protect and support the developing spermatogenic cells and phagocytize degenerating spermatogenic cells. Occur at regular intervals in between spermatogenic cells in the wall of seminiferous tubule. Embryologically produces the antiparamesonephric hormone, a glycoprotein that suppresses the development of the female genital ducts in the male. In the adult: tall columnar with a broad base lying against the basal lamina and an apex reaching the lumen of the seminiferous tubule. VET 313 Lecture Module 2024  The basal cytoplasm contains an ovoid nucleus with a large nucleolus. The apical cytoplasm is dented by the "burrowing" spermatids. Mediate the action of testosterone and FSH on germ cells and produce the constituents of intratubular fluid such as transferrin, testosterone-binding protein and inhibin. o Inhibin exerts negative feedback on hypophyseal FSH secretion. Modulate the activity of interstitial cells through paracrine signals. Sustentacular cell tumors may produce large amounts of estrogen resulting in feminization of the animal. Seminiferous tubules form loops, the ends of which connect with tubuli recti. Tubuli recti Short straight tubules lined by simple squamous, cuboidal or columnar epithelium. Connect with the rete testis in the mediastinum testis. Rete testis A network of short tubules lined by simple squamous, cuboidal or columnar epithelium. Gives off several ductuli efferentes (efferent ducts). Avian Testes Retain the retroperitoneal location after birth. Surrounded by a thin tunica albuginea. Septuli testis and lobuli testis are not distinct. Other features are similar to those in mammals. Excretory or Genital Ducts Ducts that transport the spermatozoa from the rete testis to the outside. Include the ductuli efferentes, ductus epididymis, ductus deferens or vas deferens and urethra. VET 313 Lecture Module 2024  ❖ Ductuli efferentes (Efferent ducts) o Six to 20 coiled ductules that connect the rete testis with the ductus epididymis and collectively enclosed by tunica albuginea. o Appear as round or oval profiles in tissue sections embedded in the interductal CT. o Wall is atypical because it is composed only of a thin t. mucosa that is not folded. ▪ T. mucosa - pseudostratilied columnar intermittently ciliated (kinocilia) lining epithelium that rests on a basal lamina and a few circularly arranged smooth muscle cells beneath the basal lamina. The nonciliated cells are secretory with lighter cytoplasm and mucoid secretion. ▪ T. serosa is replaced by t. albuginea. ▪ Other layers of the wall are replaced by the interductal tissue. ❖ Ductus epididymis o A single coiled tubular duct that connects the ductuli efferentes at one end and the vas deferens at the other end. o Appears in tissue section as various profiles of ducts embedded in the interductal CT. o Could be mistaken for the testis due to the presence of round or oval ductules. o Unlike the testis which is lined by a stratified epithelium, the epididymis is lined by pseudostratified epithelium. o Consists of the head, body and tail. o Wall is similar to that of ductuli efferentis except that the: ▪ Larger profiles and lumen generally filled with spermatozoa. ▪ Head and body are lined by pseudostratified columnar epithelium with stereocilia. The tall columnar cells of the epithelium present lipid droplets and mucoid granules in the basal cytoplasm. ▪ Interductal CT (lamina propria), is thin (26-27 um). ▪ Tail has a folded t. mucosa and the interductal tissue is the thickest (59-63 um). ▪ Beneath the basal lamina is a thin layer of fine collagen fibers and beneath the latter is a thick layer of smooth muscle tissue. VET 313 Lecture Module 2024  ❖ Vas deferens or ductus deferens o A long duct that connects with the tail of the epididymis proximally and the pelvic urethra (or cloaca in birds) distally. o Mammals: opens into the pelvic urethra through all portion called the ejaculatory duct where the semen is collected prior to ejaculation. ▪ Horse and ox: Shortly before the urethra, the ductus deferens merges with the ductus excretorius of the vesicular glands to form the ductus ejaculatorius. ▪ Pig: The ductus deferens and ductus excretorius open separately into the urethra. ▪ Carnivores: The ductus deferens opens into the urethra independently as there are no vesicular glands. o Birds: the ejaculatory duct opens into the urodeum of the cloaca. o Has a narrow irregular lumen due to the longitudinal folds of the t. mucosa and a thick wall. o In transverse section, appears similar to the ureter except that its lining epithelium is pseudostratified columnar ciliated in contrast to the ureter which is transitional. o Wall consists of the following: ▪ T. mucosa - presents longitudinal fold. The lining epithelium is pseudostratified columnar ciliated. In the rat the tall columnar cells may present lipid droplets in the basal cytoplasm. The lamina propria is scanty and blends with the t. submucosa. The M.M. is absent ▪ T. submucosa - blends with the lamina propria of t. mucosa VET 313 Lecture Module 2024  ▪ T muscularis - well developed and very thick. It consists of three layers: inner and outer longitudinal muscle layers and a thick middle circular muscle layer. ▪ T. adventitia - typical. ❖ Urethra o A short tubular structure that connects proximally with the vas deferens and opens freely through the penis. o A common duct for urine and semen in mammals while it is absent in birds. o Two parts: pelvic and penile urethra. ▪ Pelvic urethra Located in the pelvic cavity where it is closely associated with the accessory glands. In the portion associated with the pars dessiminata of prostate, the urethral lumen is V-shaped, with the apex of the V pointing dorsad; the ventral wall of urethra bulges dorsally and termed the urethral crest; the two arms of the V-shaped lumen that pass laterally and ventrad constitute the urethral sinuses. Less extensive erectile tissue and more glands than the penile urethra. VET 313 Lecture Module 2024  Wall presents the following features: o T. mucosa —lined by transitional epithelium. LP presents erectile tissue and branched tubular mucous urethral glands or glands of Littre. MM absent. o T. submucosa - erectile tissue and pars dessiminata of prostate gland. o T. muscularis - three layers of smooth muscle fibers in the neck of the bladder but is rapidly replaced by striated or skeletal urethral muscle. Beyond the neck of the bladder, the t. muscularis becomes two- layered. o T. serosa - typical. ▪ Penile urethra Embedded in the ventral portion of fibrous penis or in the center of vascular penis but separated from the corpus cavernosum penis by tunica albuginea with circularly oriented smooth muscle tissue. Wall presents the following features: o T. mucosa - is lined by transitional epithelium that may change to stratified squamous at the urethral opening. The L. P. consists of erectile tissue, the corpus cavernosum urethrae or corpus spongiosum that presents urethral glands in stallion and boar. The M.M. is absent. o T. submucosa - blends with lamina propria and also contains erectile tissue o T. muscularis - is represented by the inner circular layer of smooth muscle cells of the t. albuginea o T. adventitia - represented by the t. albuginea VET 313 Lecture Module 2024 Accessory Glands  Exocrine glands that secrete substances that contribute to the formation of semen  Four male accessory glands: Ampullary gland, Vesicular gland or seminal vesicle, prostate gland and Bulbourethral or Cowper's gland.  Not all glands are present in all species of domestic animals.  The bull and stallion possess the full set of accessory glands.  The boar has vesicular, prostate and bulbourethral glands.  In the cat, the ampullary, prostate and the bulbourethral glands are present, while in the dog only the ampullary and the prostate glands are present. ❖ Ampullary gland o Located in the wall of the ampulla, the enlarged terminal portion of the ductus deferens (Fig. 218c,d). o Present in ruminant, horse and dog, not well developed in pig and absent in cat. o Branched, tubuloalveolar serous gland with sac-like dilatations; no excretory duct. o Secretory acini present simple columnar secretory epithelium ❖ Seminal vesicle o Absent in dog. o In ruminant and swine it is compact without a central duct. o In horse, it's a sac-like gland with a central or main excretory duct that opens into the pelvic urethra near its junction with the vas deferens. o Main excretory duct is lined by stratified columnar epithelium. o Secretes seminal fluid to transport spermatozoa and its large quantities of fructose is an energy source for the ejaculated spermatozoa. o Wall presents the following features: ▪ T. mucosa - presents intricate folds that may branch to form branching secretory acini that radiate from a central duct. The lining epithelium of the acini is simple or pseudostratified columnar. In the bull, the epithelial cells may present infranuclear lipid droplets, which appear as tiny vacuoles in tissue section. The L. P. consists of loose connective tissue interspersed between secretory acini. The M. M. is absent. ▪ T. submucosa - blends with the lamina propria of t. mucosa and made up of loose connective tissue ▪ T. muscularis - thin and consists of inner circular and outer longitudinal smooth muscle layers or intermingled smooth muscle cells. ▪ T. adventitia or t. serosa - may be present depending on the location of the gland: t. adventitia if outside the pelvic cavity and t. serosa if inside the pelvic. VET 313 Lecture Module 2024  ❖ Prostate gland o Present in all domestic species. ▪ Horse: The corpus prostatae consists of two lateral lobes joined dorsally by the isthmus prostatae. A pars disseminata is lacking. The tubular glandular segments are typically dilated and filled with secretion. Smooth muscle cells are widespread throughout the connective tissue capsule and stroma. ▪ Ox and pig: A flattened corpus prostatae lies dorsal to the urethra. Together with the m. urethralis, the distinct pars disseminata forms a sleeve around the urethra. The tubular components of the pars disseminata are arranged radially. ▪ Small ruminants: Only the pars disseminata is present in the ram and billy goat. It contains numerous expanded secretion-filled chambers. ▪ Carnivores: The corpus prostatae is particularly prominent, while the pars disseminata is scant. o Associated with the wall of pelvic (or prostatic) urethra. o Consists of pars disseminata or disseminate part and corpus prostate or body of Prostate. ▪ Pars disseminate Well developed in bull and boar. Compound tubuloalveolar serous gland located in the lamina propria-t. submucosa of the pelvic urethra. Well developed in the dorsal wall of pelvic urethra and extends laterad and ventrad to totally encircle the urethral lumen. Secretory acini are lined by simple cuboidal or simple columnar epithelium with secretory cells that present apical blebs. o Cytoplasm of secretory cell contains acidophilic granules and lipid droplets that appear as vacuoles in paraffin section. o Lumen of the secretory acinus may contain prostatic concretion, a stored secretion of the prostate gland. Lining epithelium of the duct is transitional at the entrance to the urethra lumen. ▪ Corpus prostate Well developed in carnivores and horses but not distinct in rams. Located outside of the pelvic urethra. VET 313 Lecture Module 2024  DWFCT capsule. Has a pseudostratified lining epithelium ❖ Bulbourethral or Cowper's gland o Paired and located in the dorsolateral aspect of the pelvic urethra. o DWFCT capsule continues as interlobular CT septa. o Compound tubuloalveolar mucous gland in boar, tomcat and billy goat. o Compound tubular mucous gland in stallion, ram and bull. o Horse: The gland is surrounded by striated muscle (m. bulboglandularis); six to eight ductus glandulae bulbourethrales open into the urethra. o Ox and sheep: Short intermediate segments connect expanded collecting ducts with secretory end pieces. o Pig: The glandula bulbourethralis is particularly well developed. The m. bulboglandularis forms a cuff around the cylindrical gland. o Cat: The ducts are expanded into sinus-like chambers. These are connected by short, unbranched portions to the glandular end pieces. Due to its high glycogen content, the glandular secretion (pre-ejaculate) may act as a source of energy for the spermatozoa (fructoseproducing vesicular glands are absent in the tomcat). o Absent in dogs. o Secretory units lined by simple columnar or pyramidal epithelium with mucous secretory cells (light cytoplasm, flattened basal nuclei). o Ducts are lined by simple or pseudostratified columnar or transitional epithelium. VET 313 Lecture Module 2024  Structural features of the accessory glands of the male reproductive system of mammals. Organ Structure Cells Features Pars Simple branched, tubular Pseudostratified Acts as storage area glandularis of glands in the lamina propria; columnar where maturation the ductus ampulla (ampulla ductus epithelium with processes occur at the deferens deferentis) present in spherical basally surface membrane of stallion, bull and dog, absent located nuclei; spermatozoa; presence in tomcat and boar; smooth apocrine mode of of basal cells muscle in stallion and bull secretion; expanded containing coalesced glandular lumen fat droplets (bulls) Vesicular gland Compound tubulo-alveolar Pseudostratified Energy source for (glandula within lamina propria; columnar spermatozoa; stallion – vesicularis) tubular portions expanded epithelium with markedly vesicular into collecting ducts; organelles morphology and collagenous connective indicative of expanded excretory tissue septa divide the gland secretory activity; duct lined with into lobules apocrine mode of cuboidal epithelium; secretion; fructose- bull – central excretory and citric acid-rich duct, lipid droplets and secretory products peroxisomes in promote motility of secretory epithelium; spermatozoa high secretory activity Prostate gland Compound tubulo-alveolar Cuboidal to The usually mixed (glandula gland composed of two columnar secretion includes prostatica) layers: an outer portion epithelium with electrolytes, citric acid (corpus prostatae) and an principal cells that and glucuronic acid, inner portion (pars produce a serous to which promote disseminata); the glandular seromucous motility of tissue is divided into distinct secretion (released spermatozoa and lobules by connective tissue by apocrine mode) initiate forward septa in the lamina propria progression of and tunica submucosa; a ejaculated stratum myoelasticum is spermatozoa; secretion present in the glandular is weakly alkaline, tissue, the capsule consists high fructose content of a stratum musculare and a in bull; pars stratum fibrosum; the disseminate absent in excretory ducts are typically stallion dilated and contain secretion Bulbourethral Compound tubular gland in Simple epithelium, The stringy, mucous the tomcat, boar and billy usually columnar, secretion acts as a gland (glandula goat, branched tubulo- with spherical preejaculate (not in bulbourethralis) alveolar in the stallion, bull basally located pigs), serving to and ram. Expanded nucleus; mucous neutralize the internal VET 313 Lecture Module 2024  collecting ducts are secretion; in the urethral environment surrounded by smooth excretory duct and moisten the muscle cells and fibro- system the vagina; particularly elastic tissue; skeletal epithelium well developed in the muscle present peripherally gradually boar; in the cat, in transforms into which vesicular glands pseudostratified, are absent, the becoming secretory product transitional at the contains glycogen as end of the an energy source; 6–8 bulbourethral duct excretory ducts open into the urethra in the stallion External Genitalia  The male external genitalia consist of the penis and scrotum or scrotal sac. ❖ Penis o Copulatory organ of the male species. o Encloses in its ventral portion, the penile urethra. o Consists of the root, body and glans (tip). ▪ Body - covered by skin with hairs superficially. In most sections the skin is no longer included. May contain erectile tissue, bone (Os penis), cartilage or DWFCT. ▪ Glans penis - well developed in primates, stallion and dog. Covered by the prepuce, a reflection of the skin without hairs. o Beneath the dermis of the skin is the tunica albuginea (DWFCT capsule of the penis). o The t. albuginea surrounds two cylindrical bodies of erectile tissue (collagen elastic fibers and blood sinuses) called corpora cavernosa penis, arranged side by side in the dorsal half of the penis. o Erectile tissue when engorged with blood causes penile erection. o Ventral to the corpora cavernosa is an erectile tissue called corpus cavernosum urethrae or corpus spongiosum, which has its own thin t. albuginea. o The corpus spongiosum surrounds the penile urethra. o Two types of penis: vascular and fibrous. ▪ Vascular penis (Musculocavernous) Thin tunica albuginea and less extensive corpora carvenosa penis. Found in horse, carnivore and man. The arrangement of connective tissue fibres permits limited expansion of the tunica albuginea during erection. The erect penis is firm and elastic. The well-developed erectile tissue of the glans penis is continuous with the corpus spongiosum (via deep veins of the glans in the dog). The loose connective tissue between the vascular spaces contains numerous elastic fibres and smooth muscle cells. ▪ Fibrous penis (Fibroelastic) Thicker tunica albuginea and more extensive corpora cavernosa penis. VET 313 Lecture Module 2024  Found in pig and ruminant. Elongation of the penis results primarily from straightening of the sigmoid flexure. The tissue between the vascular spaces consists mainly of fibro- elastic networks with few smooth muscle cells. The glans penis contains a modestly developed subepithelial stratum cavernosum that does not bring about enlargement of the glans o Horse: The fibres of the connective tissue sheaths are arranged in a lattice, surrounded by bundles of fibres. The erectile tissue is composed largely of longitudinally oriented smooth muscle. In the non-erect penis, the muscle reduces the cavernous spaces to narrow slits. Connective tissue in the erectile body is relatively sparse. o Carnivores: The erectile tissue is surrounded by smooth muscle; connective tissue is relatively meagre. An os penis is present. o Ox: The outer collagen fibre bundles have a mainly longitudinal orientation. They send trabeculae and septa into the erectile body. o Birds: ▪ In birds with a protrusible phallus, the penis arises as the basis phalli in the ventral wall of the cloaca, where it rests in a trough-like plate of fibrocartilage, the corpus fibrocartilagineum. ▪ It incorporates a lymphatic cistern that is partly divided into left and right components. The cistern continues as a narrow chamber that extend around the cutaneous and glandular phallic sacs. ▪ These sacs form the hollow interior of the body (corpus) of the phallus. ▪ The more proximal cutaneous sac leads into the glandular sac. ▪ In the non-tumescent phallus, the body is completely invaginated and the junction between the cutaneous and glandular phallic sacs, the flexura phalli, is curved. ▪ During intumescence, lymph derived from the vascular body of the phallus (see below) fills the lymphatic cisterns to bring about erection. ▪ This results in eversion of the cutaneous phallic sac. The glandular sac is not everted (it comes to lie within the cutaneous sac). ▪ As a result, the exteriorised flexura phalli becomes the tip (apex) of the erect phallus. A phallic sulcus (sulcus phalli) spirals around the free part of the erect phallus. ▪ In species with a non-protrusible phallus, erection also occurs due to engorgement with lymph, although in these species the erect phallus protrudes only slightly, if at all, from the cloaca. VET 313 Lecture Module 2024 References: Aughey, E. and Frye, F.L. 2001. Comparative Veterinary Histology with Clinical Correlates. Manson Publishing Ltd Bacha, W.J. and Bacha, L.M. 2012. Color Atlas of Veterinary Histology, 3rd Edition. John Wiley & Sons, Ltd. Banks, W.J. 1993. Applied Veterinary Histology. 3rd Edition. Mosby Inc. Caceci, T. 2015. Doctor C's On-Line Histology. https://www.doctorc.net/ De Ocampo, G.D. 2008. Lecture Notes in Veterinary Histology. 6th Ed. UPCVM, UPLB Dellman, H.D. and Eurell, J.A. 1998. Textbook of Veterinary Histology. 5th Ed. Baltimore: Lippincott, Williams and Wilkins Eurell, J.A. 2004. Quick Look Series in Veterinary Medicine: Veterinary Histology. Tenton NewMedia Eurell, J.A. and Frappier, B.L. 2006. Dellmann’s Textbook of Veterinary Histology. 6th Edition. Blackwell Publishing Liebich, H.G. 2019. Veterinary Histology of Domestic Mammals and Birds. 5th Edition. 5m Publishing VET 313 Lecture Module 2024