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Reproductive Physiology Of The Male (Functional Anatomy (The Male…
Reproductive Physiology Of The Male
Functional Anatomy
The Male Reproductive system Consists Of Many Individual Organs Acting In Concert To Produce Spermatozoa And Deliver Them To The Female's Reproductive Tract.
Genital organs are testes, scrotum,spermatic cord, external cremaster muscle,epididymis, deferent ducts, accessory glands, and penis.
Scrotum, cremsater muscle and testicular artery and vein → thermoregulates the testes.
Scrotum made from subcutaneous fibroelastic and muscular layer called “tunica dartos”.
Testicular artery arranged in “ pampiniform plexus” → conutercurrent heat exchange for thermoregulations.
Horse testes have many sweat and subaceous gland for thermoregulation purpose.
Testis carry out steroidogenesis→ androgen production( Leydig cell) and generation of haploid germ cells by spermatogenesis ( seminiferous tubules).
3 compartment of testes ;-(1) Interstitial tissue compartment [ Leydig cells bath in testeosterone rich fluid];-(2) Basal compartment [ sperm undergo mitosis];-(3) Adluminal compartment [ spem undergo meiosis].
Sertoli cells nourish germ cells, extending from basal to adluminal compartment.
Sertoli tight-junction complex → blood-testeis barrier.(prevent compound from the blood and interstitial fluid enter the adluminal compartment).
Spermatogenesis require lower temperature than the core body temperature.
Failure of testes to descend from inguinal canal→ cryptorchidsm ( if bilateral- sterile).
Epididymis is where spermatozoa are concentrated, undergo maturition ,and acquire fertilizing capacity.
Sperm in caput(head of epididymis) are immotile and incapable of fertilization.
Sperm from caput to corpus are motile and capable of fertilization.
Mature sperm are stored from cauda to deferen duct.
Bull and stallion have prominent ampullae as extra sperm storage depot.
Dog have prominent prostate gland, but no bulbourethral and seminal vessicles.
Cat have prominent bulbourethral, but no seminal vessicles.
Llama have small bulbourethral and prostate gland,but lack seminal vessicles.
Penis = thick fibrous capsule ( tunica albuginea), Cavernous spaces ( Corpus Cavernosum), Corpus Spongiosum
Erection = ischiocavernosus muscle contract, corpus cavernosum and corpus spongiosum parasympathetically relax, cavernous space ↑, blood filled in→ penis elongated and turgid.
Emission Is The Release Of Spermatozoa And Accessary Gland Fluids Into The Pelvic Urethra, Whereas Ejaculation Is The Forceful Expulsion Of Semen From The Urethra.
Emission caused by contraction of ductus deferens and accessory gland.
Ejaculation caused by rhythmic contraction of bulbouspongiosus, ischiocavernosus and urethralis muscles.
After ejaculation, cavernous space ↑, blood outflow ↑, contraction of penis muscle withdraw penis back to prepuce.
Spermatogenesis
Spermatogenesis Is A Lengthy Orchestrated Process In which Diploid Stem Cells Divide By Mitosis To Maintain Their Own Numbers And Cyclically Produce Progeny That Undergo Meiotic Division And Differentiation Into Haploid Germ Cells.
3 stage of spermatogenesis ;-(1) spermatocytogenesis,;-(2) meiosis;-(3) spermiogenesis.
Spermatocytogenesis- (a) type A spermatogonia meiotic division→maintain population of stem cells.(b) type A spermatogonia mitosis→type B spermatogonia→spermatocytes.
Spermiogenesis = formation of acrosome, flagellum and extensive shedding of cytoplasm, forming the head, middle piece and tail.
Head- contain acrosome hydrolytic enzyme to penetrate oocyte.
Middle piece- contain mitochondria provide energy.
Tail - flagellum movement.
Spermatogenesis take about 60-70 days.
Potential sperm production loss, degenerating during spermatogenesis.
3.Hypothalamus-Pituitary-Testicular Axis
The Reproductive System Of The Male Is Regulated By The Hypothalamus, Which Is Normally Linked To The Anterior Pituitary And Testes By LH And FSH.
Hypothalamus secrete GnRH in pulsatile → adenohypophysis→ secrete gonadotropin(FSH & LH).
FSH and LH have same α-subunit but different specific β-subunit.
Low-amplitude GnRH pulse→FSH release.
High- frequency GnRH pulse→LH release.
LH bind to Leydig cell membrane receptor→ convert cholesterol to testosterone.
Androgen diffuse into blood and lymph and bound to “androgen- binding protein”(ABP), produced by Sertoli cells.
[androgen]↑ promote spermatogenesis.
ABP accumulates testosterone and dihydrotestosterone in high concentration.
Testosterone target on peritubular myoid cells and Sertoli cells.
ABP facillitates androgen transport from testis to epididymis.
FSH target Sertoli cells receptors.
FSH and testosterone stimulate Sertoli cell to synthesize ABP, inhibin, activin, estrogen, transferrin.
Sertoli and Leydig cell interact in paracrine manner.
FSH direct Sertoli →inhibin →Leydig to produce steroids (steroidogenesis).
Inhibin stimulates steroidogenesis of Leydig.
Inhibin & testosterone = complex feedback regulation of pituitary function.
Gonadal steroid suppress FSH secretion.
Inhibin also suppress FSH release.
FSH and LH promote spermatogenesis.
4.Puberty
Puberty Is Not Synonymous With Sexual Maturity
Puberty = when male able to produce sufficient number of sperm to impregnate a female.
10% of sperm are motile.
Puberty Results From A Continuous Process Of Endocrine Changes That Are Initiated Shortly After Birth.
Target organ= pituitary gland, gonads , steroid-dependent tissue.
Hypothalamus initiate puberty.
Puberty happen when hypothalamus-pituitary complex become desensitized to feedback inhibition of gonadal steroids.
Desensitized→↑[GnRH] release, ↑ FSH and LH → initiate puberty.
Puberty factor -breed, energy intake , season of birth.
Prepubertal children secrete low concentration of FSH and LH, thus indicate normal functional hypothalamic- pituitary- gonadal axis.
Sex steroid lower down the low concentration of FSH and LH.
5.Anabolic Steriods
Anabolic Steriods are Androgen Derivatives That Exert Negative Feedback On The Hypothalamic- Pituitary-Testicular Axis
Anabolic steroid improve perfomance by ↑ mental attitude,↑ stamina, ↑ physical strength.
Anabolic steroid is androgen derivatives, function same to testosterone.
Anabolic steroid affect pituitary function and cause long lasting impairment of testicular endocrine function.
Small and soft testical.
“Stanozolol” and “boldenone undecyclenate” are 2 common horse anabolic steriod.
Anabolic steriod ↓ sperm concentration, motility, number of sperm per ejaculation.
Testicular degeneration= shrunken Leydig cell and spermatid phagocytosis.
Using ↑ dose of testosterone/ anabolic steroid= “hypogonadotropic hypogonadism”
Reduced fertility= sterile.
Clinical Correlations
Infertility In A Stallion
Clinical Examination
A stallion mated with 10 mares but only 1 mare is pregnant.The stallion is normal and not under any medication. The stallion was given steroids to improve performance.The stallion have normal libido and ejaculate 2 times in 1 hour. The semen samples show poor spermatozoa concentration,low sperm number, many abnormal spermatozoa and immature germ cells. The steroid given have same function as testosterone, which in high dosage, it will cause negative feedback effect to reduced spermatogenesis and may lead to permanent infertility. The stallion has small and soft testes.
Treatment
Other than time, there is no treatment to erase the negative feedback effect of anabolic steroid. Maybe after a certain period of time, when the steroid effect wear weaken or totally off, the stallion just can breed with small number or mares with artificial insemination. The stallion need to be reexamined in several month to see any improvement in sperm morphology.