Male Reproductive Physiology

• Technically outside of peritoneum it is in an outfolding of two layers 

• Visceral layer of peritoneum fixed to tunica albuginea  

• Lumen of vaginal process is continuous with peritoneal cavity  

• Parietal layer of peritoneum fixed to scrotum  

• Shrinking gubernaculum becomes proper ligament of testis joining caudal pole of testis to tail of epididymis  

• Mediastinum testes: cord of connective tissue running through testis  

• Seminiferous tubules loop through the testis and connect to the rete testis

• Rete testis - collect sperm cells in center of testis

• Germ cells are covered by the Sertoli cells in the tubules  

• Sertoli cells

  • Sustentacular or nurse cells

  • Lie inside basement membrane of seminiferous tubules
  • Tight junctions between adjacent cells  -  forms part of blood testis barrier 
  • Hormones

• androgen binding protein (ABP)  
• inhibin  

• Leydig cells - interstitial cells  
  • Lie between seminiferous tubules  
  • Secrete testosterone in response to LH  
    • Testoserone is pulsatile (chronic LH makes testis refractory) 
• Basement membrane -  forms part of blood testis barrier  
• Myoid cells -  forms part of blood testis barrier  
• Tunica albuginea
  • Tough fibrous layer that forms capsule
  • Sends projections down to the mediastinum
  • Actually contracts to help 'pump' sperm cells through rete  
• Tunica vaginalis - peritoneal layer  

Epididymis  

• Caput (head)  
• Corpus (body)  
• Cauda (tail)  

Human testis above

Scrotum

• Skin
• Sweat glands
• Tunica dartos  
• Tunica parietalis  
• Cavity of vaginal process  
• Hydrocele vs Hematocele

• Why a scrotum?
  • Temperature regulation
  • Sperm production does not occur normally at body temperature
  • Sweat gland cool
  • Tunica Dartos contracts or relaxes to control the closeness of the testis to the body
  • Nerves are very sensitive to temperature changes

Spermatic cord 

• From the inguinal ring to the testis
• Consists of the 
  • Ductus Deferens - enters urethra at colliculus seminalis  
  • Testicular artery
  • Lymphatics
  • Cremaster muscle
    • Striated muscle from internal abdominal oblique
    • Can only sustain short periods of contractions (does not work well to pull up testis)
    • Primarily a pumping action on the pampiniform
  • Pampiniform plexus
    • Spermatic artery and vein
    • Artery and vein intertwined
    • Form countercurrent exchange system
      • Decreases temperature of blood
      • Decreased pulse pressure - function not known
      • Testosterone contercurrent exchange also

Endocrine control of spermiogenesis Spermiogenesis requires stimulation by FSH and LH, which are controlled by the pulsatile secretion of GnRH from hypothalamus   FSH interacts with Sertoli cells to cause: Production of ABP (Androgen Binding Protein) Conversion of testosterone to dihydrotestosterone and estrogen Stimulation of spermatocytogenesis Completion of sperm release Secretion of inhibin, which has a negative feedback action on FSH release, GnRH LH Results in hypertrophy of Leydig cells Stimulates production of testosterone by Leydigs Androgens Major action is on Sertoli cell Produced by Leydig Diffuses into Sertoli and is secreted into blood - has effects on brain, muscle, etc. Causes negative feedback at hypothalamus and pituitary which inhibits LH release If administer exogenous testosterone, increased systemic conc. will result in negative feedback, reducing LH and reducing endogenous testosterone production, thereby inhibiting spermatogenesis If administer LH (or hCG) or GnRH, stimulate endogenous testosterone production and don't upset balance of androgen within tubule:androgen outside Relatively high level of testosterone (compared to systemic circulation) required for spermatid migration ABP Role is not to concentrate testosterone in tubule Most likely role is to transport testosterone to head of epididymis Inhibin From Sertoli cell Paracrine, autocrine and endocrine action Negative action on FSH, GnRH Estrogen Produced in Sertoli cells by conersion of testosterone Paracrine, autocrine and endocrine action Negative action on FSH Positive action on LH

Spermatogenesis

Spermatogenesis

Mitosis of spermatogonia and meiosis with differentiation into sperm takes 5-7 weeks in most mammals Renewal of stem cells Five mitotic divisions produce 16 primary spermatocytes Two meiotic divisions produce 64 spermatids Spermiogenesis (spermateliosis) Spermatids differentiate from compact spherical cell into spermatozoa without cell division Golgi granules coalesce to form acrosome One centriole gives rise to flagellum, other gives rise to basal plate Nucleus moves to periphery and chromatin condenses Spermatid rotates so tail sticks out into lumen Mitochondria congregate around flagellum and become localized in midpiece Most of cytoplasmic mass is engulfed by Sertoli cells when spermatozoa are released into lumen of seminiferous tubule, small amount remains at neck (proximal cytoplasmic droplet) Proximal droplet moves to distal end of midpiece during epididymal passage Distal droplet is lost during storage in the epididymis or during ejaculation

Sperm cell First described approx. 300 yrs ago Realized essential for fertilization around 1830 Covered by plasma membrane Acrosome contains hydrolytic enxzymes (acrosin, hyaluronidase, etc.) Postacrosomal region is where attachment and fusion to oolemma takes place Tail Responsible for motility Midpiece (mitochondria) Principle piece End piece 9:2 arrangement of doublets Kartagener's syndrome - lack 9:2 arrangement; immotile cilia syndrome (infertility,respiratory infections, situs inversus)

Changes with time in the appearance of one section of a tubule; series of changes in a given area of seminiferous epithelium Based on cell associations of different stages of spermatogonia, spermatocyte, spermatid, spermatozoa within one section of a seminiferous tubule In any given area of a tubule, stem cells initiate series of mitotic divisions preceding meiosis at extremely regular intervals Time from spermatogonium to spermatozoa is remarkably constant, cannot speed up process Each step of spermatogenesis has a fixed and constant duration Before spermatozoa are fully formed as a result of one cycle, three new cycles have started, four different stages of cells are associated with each other in one section of tubule at any one time Spermatogenic wave (space) Sequential change in stage of cycle along the length of the tubule In each sequential segment of tubule, a sequential stage of the cycle is found Blood testis barrier Primary component is tight junctions between Sertoli cells which divide tubules into 2 compartments Basal compartment - contains spermatogonium and preleptotene spermatocytes (2n) Adluminal compartment - communicates with lumen of tubule and contains more advanced stages (1n) Demonstrates wide range of permeability from complete exclusion of some substances to nearly free transfer of others Not only excludes some substances (such as antibodies) but functions in retaining others (such as Androgen Binding Protein, inhibin) Functions in keeping haploid cells from initiating immune reaction Incomplete or partial barrier of myoid cells surrounding tubule also a component Fluid Sertoli cells secrete fluid which transports immotile sperm from tubules Rete apparently secretes fluid also (although some claim evidence is lacking) Sperm movement is by fluid secretion, cilia movement and contractile elements (myoid layer)   Sperm Maturation Epididymis Maturation and storage of sperm Head Not motile - swim in circular motion Not fertile Proximal droplet Low disulfide linkage Fluid absortion Body  First see some forward motility in body Some fertility Droplet moving down More disulfide linkage Binds oocytes Tail Normal motility Fertile Distal droplet Hiigh disulfide linkage Binds oocytes Transport takes 9-13 d depending on species - mandatory Control of this????       Sperm Delivery Accessory glands  Contributions not needed for fertility Coating of gland secretion removed during capacitaion Ampulla  - thickened glandular portion of ductus deferens as it connects with urethra   Large in stallion, bull   Present in dog but not always grossly visible   Absent in boar, tom   Vesicular glands (seminal vesicles) - sac like organs with lobulated surface   Provide volume, protein, sugars, salts   Generally fill before copulation and empty during ejaculation   Boar - store large volume of fluid   Bull - more a solid mass of tissue, produces only small volume of fluid   Absent in tom, dog   Stallion - fills during sexual stimulation   Prostate - solid tissue mass which secretes during copulation   Animals with extended copulation times (boar and dog) have high volume contribution from prostate   Secretion mainly ionic compounds (NaCl, Na citrate, and variety of enzymes)   Present in all domestic species Bull and boar - anterior mass is body of prostate, disseminated portion is pars disseminata   Bulbourethral (Cowper's) - small, except in boar; muscular gland associated with caudal pelvic urethra   Boar - large gland containing large volume of stored gel (sialic acid) which is emitted during ejaculation   Can differentiate castrated from cryptorchid pig on basis of rectal palpation. In ruminant and boar, ducts open into urethral recess, situated dorsally, which may prevent passage of catheter

Penis 

Penis 

• Root -right and left crura, crus penis  
• Corpus (body)
  • Shaft  
  • Glans penis ornamental tip, may refer to portion of penis distal to attachment of free prepuce
    • Richly supplied with sensory nerves which respond to heat and moisture; normal sensation necessary to locate vagina, make intromission and initiate ejaculation
  •   Corpus cavernosum penis
    •   Arises as pair of crura under ischiocavernosus m.  
    • Continues to tip as paired cavernous body  
• Corpus spongiosum penis - surrounds urethra  
  • Enlarged at ischial arch to form penile bulb which is covered by striated bulbospongiosum m.  
  • Corpus spongiosum glandis - erectile body of glans  
• Tunica albuginea
  • thick fibroblastic covering of the cavernous bodies, 
  • capable of withstanding very high internal pressures  
  • Species differences  
    • Fibroelastic - 
      • small volume, minimal increase in size - 
      • thick tunica albuginea, 
      • trabeculae contain large amount of supporting tissue with small cavernous spaces
      • high pressure sigmoid flexure straightens to elongate in bull, ram, buck  
      • temperature sensitive vaginal ejaculation  
      • raphe penis (surgical landmark)  
      • preputial frenulum - 
        • remnant of developmental attachment apical ligament - fibrous band, originates on tunica albuginea proximal to fornix, extends to level of glans where it inserts on tunica albuginea; 
        • supports penis during erection; 
        • if a bull becomes "hyper-erect" the apical ligament will pull the tip back into a spiral; this is considered normal after intromission but is a problem if it occurs before intromission  
        • buck, ram have long urethral process boar corkscrew tip preputial diverticulum pressure sensitive cervical ejaculation  
    • Vascular penis  
      • low pressure high volume - 
      • large cavernous spaces, 
      • little supporting tissue, 
      • large increase in size stallion  
      • "bell" - glans swells during ejaculation  
      • urethral process, 
      • urethral fossa, 
      • fossa glandis  
      • urethral sinus - 
      • dorsal diverticulum, 
      • bean - smegma  
      • pressure and temp sensitive  
      • fractions  
        • pre - bulbourethral  
        • sperm rich - ampullary  
        • post - seminal vesicles  
    • Vascular penis with os penis  

• Dog os penis (baculum) - extends from tip to bulbus glandis
• Bulbus glandis - proximal portion of penis - swells to 2-3 times the diameter of the shaft during copulation  

• Feline projects posteriorly small os penis spines on surface of penis  
• Retractor penis muscles - control length of penis in ruminants and swine by action on sigmoid flexure
• Ischiocavernosus m. - important in causing erection, pumps blood into corpus cavernosum penis by compressing dorsal vein against ischial arch
• Prepuce  - Non-haired skin, not mucous membrane
  •   Loosely arranged elastic layers which allow penis to extend  
• Sheath - externally visible container for prepuce and penis
  

Male sexual development

• Migration of primordial germ cells to gonadal ridge
• In presence of Y chromosome - formation of primary sex cords which become germinal epithelium of seminifreous tubules; in absence - cells form into medullary pattern
• Rete testis establishes connection between mesonephric (Wolffian) tubules and seminiferous tubules; mesonephric tubules form efferent ductules in head of epididymis and mesonephric duct forms rest of epididymis, ductus deferens and seminal vesicles
• Fetal androgen causes development of male reproductive tract
• Müllerian inhibiting substance suppresses development of paramesonephric (Müllerian) ducts
• Formation of vaginal process (a peritoneal sac extending through abdominal wall) - encloses inguinal ligament of testis which, along with diaphragmatic ligament together with mesorchium suspends fetal testes, inguinal ligament connects testis and mesonephric duct, distal to this it is called the gubernaculum testis and terminates in the region of the scrotal rudiments
• Descent of testes
• Secretion of "descendin" from normal testes results in selective growth of gubernaculum
• Gubernaculum outgrowth results in masculinization of inguinal canal
• Intraabdominal pressure transmitted to gubernaculum which in turn applies traction to testes to introduce it into ing. canal
• Descent of testis into and through ing. canal is interplay between intra-abdominal pressure transmitted by patent processus vaginalis and androgen induced gubernacular regression
• Androgens, under the control of intact fetal hypothalamic-pituitary axis, alter visco-elastic properties of gubernaculum; reductions in turgidity of gubernaculum allow intra-abdom. pressure to push testes into scrotum
• Intact hypoth-pit axis necessary for testicular descent
• Alterations in maternal-placental-gonadal axis may be responsible for abnormal male phenotype
• descendin stimulates, estrogen inhibits gubernac. growth
• Consequences of failure of descent
  • Cryptorchid - unilateral or bilateral
  • bilateral - normal sexual phenotype, libido, androgens, but sterile due to relatively high intraabdominal temp.
  • may not be sterile if testes in inguinal canal
• Mechanisms to maintain lower temp in testes
  • dartos muscle in scrotum
  • inc/dec surface area
  • inc/dec thickness of skin
  • cremaster muscle in spermatic cord - raises or lowers testes
  • pampiniform plexus - countercurrent mechanism
  • temperature receptors in scrotal skin can elicit responses that tend to lower whole body temp (sweating, panting)

• Determined at time of fertilization
• Presence of testis determining factor (TDF) of Y chromosome causes mesonephros to form sex cords; in absence of Y chromosome cells form into a medullary pattern
• H-Y antigen, once thought to be TDF is now considered a minor histocompatibility antigen in close proximity to the TDF

• Hormones produced by gonad depend on what gonad resembles, regardless of chromosomes
• Fetal testis grafted against ovary of female fetus -get Müllerian inhibition and Wolffian development on that side only (local effect)
• If use testosterone implant -get Müllerian and Wolffian development, lack Mullerian Inhibiting Factor from testis

• Pigs
• Usually XX
• Cause?

• Female pseudohemaphrodite (male phenotype with ovaries)
  • Inherited in Cockers, German Shorthair, Pug, Kerry Blue, Weimaraner
  • TdY transposes to autosome
  • Simple autosomal recessive
  • AA, AY develop normally
  • AA* and A*Y develop normally but are carriers
  • A*A* are affected, look like males
  • affected animals are HY antigen positive
  • usually have ovotestes or ovaries and ovotestes; rarely have testes and ovotestes
  • phenotype depends on amount of testicular tissue
  • possess Mullerian ducts (MIF receptors present, timing problem?)
• XX sex reversal (mice, goats, pigs, dogs)
  • Autosomal dominant gene (Sxr) acts like a Y chromosome
• Goats: autosomal gene with Y effect is on chromosome which controls polledness. 
  • Intersex and hornedness are recessive. 
  • Polled gene is dominant. 
  • Sexual differentiation of heterozygous polled goat is unaffected but homozygous are hermaphrodites.
  • Most polled intersex goats are male pseudohermaphrodites and genotypically female (XX).
  • Homozygous bucks tend to become sterile due to a blockage in the head of the epididymis, in older bucks the seminiferous tubules close to the rete testis degenerate or rupture leading to the formation of sperm granulomas
• Dogs: American Cocker Spaniel -autosomal recessive, XX males and XX true hermaphrodites have been described
• XY sex reversal (horses): 
  • autosomal, sex-linked dominant gene or Y chromosome mutation, 
  • affected individuals range from phenotypically normal but sterile mares with inactive ovaries and normal tubular genitalia to individuals with streak gonads or ovotestes and hypoplastic or aplastic tubular genitalia
• Androgen insensitivity - Testicular feminization (humans, mice, rats, cats, cattle, horses): 
  • XY genotype, 
  • possess testosterone producing testes but neither Müllerian or Mullerian duct systems; 
  • external genitalia female, 
  • deficiency of intracellular androgen receptors, 
  • sensitivity to MIF is retained and MIF is produced; 
  • horses are unique in that they retain male behavior patterns
• Persistent Müllerian duct syndrome (dogs):
  • XY males with testes and normal masculinization of internal and external genitalia but possess complete tubular female tract;
  • Autosomal recessive
  • thought to be due to receptor defect
  • Min. Schnauzer, Basset, cat
• Freemarttin
  • Heifer born twin to a bull
  • 11/12 sterile
  • Chimera of XX/XY from placental anastamoses
  • XY prevents uterine development
  • Males also have dec. fertility
• XO
  • Fetal ovaries form but XO oocytes undergo rapid atresia
  • No germ cells at birth
  • No estrogen
  • Humans - short, infertile; normal genitalia
  • Mares - documented but rare
• XXX, XXY - survive by inactivating X

• B = black (dominant), b = yellow (recessive), on X chromosome
• XB XB = black; XbXb = yellow; XB Xb = tortoise shell
• Male tortoise shell
• XB XbY - sterile
• XB Xb / XY chimera
• fertile
• most are of this type