Male Reproductive SystemANS 215Physiology and Anatomy of Domesticated - PDF document

Male Reproductive SystemANS 215Physiology and Anatomy of Domesticated AnimalsI.IntroductionA.Reproductive functions of the male include the formation of sperm anddeposition of sperm into the female reproductive tractB.This process is assisted by hormones and the autonomic nervous systemC.Production of sperm is continuous once puberty is established but rate ofsperm formation can vary with daylengthD.Sexual behavior leading to deposition of sperm into the female is alsoaffected by daylength in some species. II.Anatomy of the Male Reproductive Tract1 A.Testisi.Two testes produce spermatozoa and testosteroneB.Site of spermatogenesis is the seminiferous tubule.i.Convoluted and occupy greatest portion of each testicleC.Outer covering of the testicle is the tunica albugineaD.Connective tissue extensions from the tuni

ca albuginea provide supportfor the seminiferous tubule.2 E.Cell types in the seminiferous tubule include:i.Germ cells and developing spermatocytesii.Ledydig cells1.Produce testosteroneiii.Sertoli cells1.Act as nurse cells for developing sperma.Processes from sertoli cells surround spermatids andspermatocytes and provide nutritional support forall stages of spermatogenesis.b.Also called sustentacular (supporting) cellsc.Sertoli cells have their base at the periphery of theseminiferous tubule and extend toward the center.d.The basal junction (tight junction) with adjacentSertoli cells forms a blood-testis barrier that permitscontrol of the environment with the tubule.e.Sertoli cells divide the seminiferous tubules intotwo compartments.3 i.Basal compartment-communicates withinterstitial fluid and providesspace fo

r germinal epithelialcells.ii.Adluminal compartment-space between Sertoli cellsthat communicates centrallywith the lumen of the tubuleiii.Division of the germinalepithelial cell (spermatogonium) provides a replacement cell and another cell whichmoves through the Sertoli cell junction to enter the adluminalcompartment. iv.In the adluminalcompartment the stages ofspermatogenesis occur.v.The Sertoli cells secrete afluid into the adluminalcompartment which favorsthe ongoing process ofspermatogenesis.4 B.Epididymisa.Collection and storage location for the testis and site of maturation ofsperm.b.Begins at the pole of the testis in which blood vessels and nerves enter;also known as the headc.The head of the epididymis receives sperm and adluminal fluidthrough efferent ducts from the rete testis i.Rete testis-intrates

ticular network of straight tubules thatreceives content from the convoluted seminiferous tubules.d.Head of epididymis continues along one side of testis as bodye.Storage in the epididymis allows the spermatozoa to undergomaturation and to gain motilityf.Spermatozoa move to the epididymis by the flow of luid into thelumen of the seminiferous tubules from the adluminal spaces.g.Reabsorption of much of the seminiferous tubular fluid occurs in thehead of the epididymis.C.Ductus Deferens (vas deferens)a.Continuaiton of the duct system from the tail of the epididymis to thepelvic urethrab.As the vas deferens leaves the testis toward the abdomen it is enclosedalong with the testicular artery, vein,nerve,lymphatic vessels andinternal cremaster muscle within the visceral layer of the tunicavaginalis (also known as the

spermatic cord)5 c.After the spermatic cord passes through the internal and external Inguinal rings the vas deferens separates from the spermatic cord toproceed to the pelvic urethrad.The vas deferens terminates with an enlarged glandular area Known as the ampulla6 D.Scrotuma.Cutaneous sac containing the testesb.Contains a subcutaneous layer of smooth muscle fibers known as thetunica dartosi.Relaxes or contracts depending on environmental temperaturec.Scrotum is lined with the parietal layer of the tunica vaginalisE.Tunica Vaginalisa.During embryonic development the testis is intra-abdominal but isoutside the peritoneum.b.The testis is connected to the scrotum by a fibrous connection knownas the gubernaculums testis.c.As development and growth progress the gubernaculums testis pullsthe testis through the ingui

nal rings into the scrotum through a doublewalled tube of peritoneum, the vaginal process, which preceded thedescent of the testis.d.The testis,epididymis, vas deferens, internal cremaster muscle andtesticular vessels are enveloped by the inner tube of the peritoneumknown as the tunica vaginalis.e.The outer tube of peritoneum is known as the tunica vaginaliscommunis (parietal tunic) and it lines the scrotum.f.The testis and epididymis that are enveloped within the visceral tuniccompletely fill the scrotal cavity lined by the parietal tunic so that onlya narrow space remains between the two tunics (vaginal cavity).g.The vaginal cavity is continuous with the abdominal cavity at thevaginal ring (inguinal ring).7 h.If the vaginal ring is too large loops of small intestine may enter thevaginal cavity (inguinal hern

ia).i.Cryptorchid testis are those that fail to descendF.Accessory Sex Glands and Semena.Accessory sex glands provide secretions that empty into the pelvicurethra near their origin.b.They vary in size and shape among species and can be absent in somec.Comprised of:i.Ampullae of vas deferensii.Seminal vesicles1.empty into the pelvic urethraiii.Prostate gland1.encircles urethra2.Enlargement can block urine flowiv.Cowpers glands (bulbourethral glands)1.Most caudal of accessory sex glandsd.At the time of ejaculation the accessory gland secretions (collectively known as seminal plasma) are mixed with sperm to formsemen.e.Components of seminal plasma include fructose, prostaglandins, Electrolytes, vitamins8 G.Penisa.Male organ of copulation through which urine and semen pass by wayof the penile urethrab.Variations in

penile structure include a sigmoid flexure in the bull, ramand boar and the bulbus glandis at the caudal part of the glans in thedog.H.Prepucea.Invaginated fold of skin that surround the free extremity of the penisI.Muscles of Male Genitaliaa.External cremaster musclei.Formed by the caudal fibers of the internal abdominal obliquemuscle.ii.Passes through the inguinal canal and attaches to the outsideparietal layer of the tunica vaginalis.iii.The muscle regulates testis temperature by controllingdistance from body wall.iv.b.Internal cremaster muscle9 i.Smooth muscle fibers that help to hold spermatic cordstructures together.c.Urethralisi.Pelvic continuation from the smooth muscle wall of the urinarybladder.ii.Peristaltic action of this muscle assists in the transport of urineor semen through the pelvic urethrad.

Bulbospongiosus musclei.Striated muscle continuation of the urethralisii.Continues throughout the length of the penis in the horse butonly proceeds for a short distance along the penile urethra inother domestic animalsiii.Continues the action of the urethralis in emptying the urethrae.Ischiocavernosus musclesi.Paired striated muscles that converge on the body of the penisfrom the origins on the lateral sides of the ischial archii.When these muscles contract, they pull the penis upwardagainst the floor of the pelvisiii.Much of the venous drainage from the penis is obstructedbecause of the location of the veins on the dorsal surface of thepenis and erection is thereby assistedf.Retractor penis musclesi.Paired striated muscles that originate from the suspensoryligaments of the anus.ii.Continue forward and converge

caudal to the body of thepenis.10 iii.After they join on the underside of the penis they continueforward to the glans penisiv.The retractor penis muscles pull the flaccid penis back into theprepuce.J.Blood and Nerve Supplya.Blood to the testis is supplied by the testicular arteries.b.Testicular veins parallel the testicular arteries.c.Both artery and vein are enclosed within the spermatic cord.d.A short distance above the testicle, the testicular vein is convoluted(pampiniform plexus) and is in close association with the convolutedpart of the testicular artery.i.Blood entering the testis is cooled by the venous blood leavingthe testis.e.In addition to autonomic nerve fibers to the testis, penis and Accessory glands, the penis is supplied by a spinal nerve, the pudendalnerve.i.Sensory stimulation of the glans p

rovides the afferent side For reflexes associated with erection and ejaculation.ii.Reflex centers for erection and ejaculation are in the Lumbar region of the spinal cord.11 III.SpermatogenesisA.Term refers to the entire process involved in the transformation ofgerminal epithelial cells (stem cells) to spermatozoa.B.Both mitosis (cell division in which each new cell retains a diploid, or 2n,number of chromosomes) and meiosis (cell division in which each newcell has a haploid, n, number of chromosomes) occur in spermatogenesis.Spermatozoa are haploidC.Mitogenic divisions result in production of primary SpermatocytesD.Meiotic division results in production of spermatidsi.In the bull, 64 spermatids are formed from 1 type AspermatogoniumE.Maturation of spermatids occurs while they are still in the adluminal Compart

menti.Involves a series of nuclear and cytoplasmic changes called 12 Spermiogenesisii.During spermiogenesis the spermatid transforms from a non-Motile to a potentially motile cell with a flagellum.iii.During the final phase of spermiogenesis the spermatids areReleased into the lumen of the seminiferous tubules asspermatozoa.F.Epididymal Transporti.Fertilizing ability of the spermatozoa is attained progressivelyduring the transport of sperm through the epididymis. 1.unidirectional motility2.changes in nuclear chromatin3.changes in plasma membrane4.ii.Major site of sperm storage is the tail of the epididymis1.70% of sperm outside of seminiferous tubules and retetestis are stored in tail of epididymis.2.100% of fertile sperm are stored here.G.Spermatogenic Wavei.Spermatogenesis requires 64 days in the bull.ii.To

ensure a constant supply of sperm different parts of theseminiferous tubule have different stages of spermatogenesis.13 iii.Daily production of spermatozoa is 6,000,000,000 in the bull.H.Hormonal Control of Spermatogenesisi.Leydig and Sertoli cells are responsible for hormone productionwithin the testes.ii.Luteinizing hormone (LH) controls production of testosteronefrom leydig cells1.Testosterone maintains spermatogenesis by supportingmeiosis2.Testosterone maintains secondary sexual characteristicsand Libido3.Boar taint comes from other androgens produced in theBoar which cause off-flavor in meatiii.Androgen binding protein is produced by Sertoli cellsiv.Sertoli cells also produce inhibin and estrogen1.inhibin inhibits FSHs secretion which is not required tomaintain spermatogenesisIV.Physical ConsiderationsA.

Erectioni.Increase in turgidity of the penisii.Caused by an increase of blood pressure within the cavernosussinuses of the penisiii.Complete erection of the glans penis in the horse is delayedUntil after introduction of the penis into the vagina of the mareDue to compression of the prepuce and subsequent blockage ofvenous drainageiv.Parasympathetic stimulation causes increase in blood flow Erection.v.In animals with a sigmoid flexure, the filling of the cavernous Sinuses, coupled with relaxation of the retractor penis musclescauses the flexure to be eliminated and the penis to be straightened.14 B.Mounting and Intromissioni.Mounting is the stance assumed by the male to bring the penis intoapposition with the vulva of the femaleii.Introduction of the penis into the vagina and its maintenancewithin the vagina dur

ing coitus is termed intromission.iii.Duration of intromission among species varies1. shortest for the bull and ram and longest for the boarC.Emission and Ejaculationi.Emission precedes ejaculation1.Results from sympathetic innervation whereby sperm andfluids in the vas deferens and ampullae are emptied into theurethra along with accessory gland secretions2.Accomplished by peristaltic movementii.Once emission has been accomplished, reflex peristalsis of the Urethral muscles forces contents of the urethra to the exterior.This is termed ejaculation.V.Reproduction in the BirdA.Testis is located within the body cavity in the birdB.Internal structure of testis is similar to mammalsC.There is no pampiniform plexus in the male birdD.Instead of an epididymis as arranged in mammals, the sperm are stored inthe vas defere