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Endocrinology of the Testis Vas Efferentia Seminiferous Tubule 6-12 Tubules

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Endocrinology of the Testis Vas Efferentia Seminiferous Tubule 6-12 Tubules Structure of Spermatic Cord the Testis Vas Deferens Caput Epididymis Endocrinology of the Testis Vas Efferentia Seminiferous Tubule 6-12 tubules John Parrish Tunica Albuginea Corpus Epididymis References: Williams Textbook of Endocrinology Rete Testis (within the mediastinum) Cauda Epididymis Seminiferous Mediastinum Tubule Rete Testis Spermatogonia Primary Spermatocyte Seminiferous Tubule Sertoli Cells Myoid Cells »Support spermatogenesis Secondary Spermatocyte Leydig Cells »Testosterone Round Spermatids synthesis Spermatozoa Basement Membrane The Testis Capillary Sertoli Cell Germ Cell Migration Migration begins by the 4 week of gestation in cow and human. 1 Migration from endoderm through mesoderm. XY Male Y Chromosome Circulating Androgen SRY, SOX9 Testes develop • Sex Hormone Binding Globulin - 44% • Albumin - 54% (1000 fold less affinity than Leydig Cells Sertoli Cells SHBG) Differentiate Differentiate • Free - 2% SF-1 SF-1 5a-red Bioavailable Testosterone = free + albumin bound Testosterone DHT AMH AR AR SHBG is made in Liver Development of AMHR Development ABP is made in Sertoli Cells of Wollfian penis scrotum and Ducts Degeneration of accessory Both also bind estradiol Mullerian Duct sex glands Undifferentiated Gonad AMH AMH 2 Differentiated Reproductive Tracts Testicular Development Mesonephric Duct Mesonephric Tubules Female Male (Wolffian Duct) Rete Tubules Mullerian Duct Tunica Undifferentiated Albuginea Sex Chords Mesonephric Tubules Primary Sex Chords in Fetal Testis Rete Tubules Pre-Sertoli - AMH Wolffian Duct Leydig Cells - Testosterone Mullerian Duct Primary, Epithelial or Medullary Sex Chords Tunica • Primordial germ cells Gonocyte Albuginea (gonocytes) • Pre-Sertoli Cells FSH on Sertoli Cells Hypothalamus • estradiol GnRH • inhibin Negative Feedback • ABP • tight junctions • growth factors • Hypothalamus Ant. Pituitary Negative Feedback of » Testosterone conversion to Estradiol Estradiol and Inhibin » Androgen receptor is less important Negative To • Anterior Pituitary LH FSH Epid. Feedback of ABP » Adrogen receptor involved because DHT has Androgens + negative feedback as well testosterone E2 T Leydig » Aromatization of testosterone to estradiol also Cells Inhibin Sertoli occurs Cells T » Inhibin TJ Germ Cells ABP Seminiferous Tubule 3 Leydig Cell and Sertoli Cell Hypothalamus Interactions GnRH Ant. Pituitary Fetal Leydig E2 Cells Pre-Sertoli T Cells Gonocytes AMH Primary Sex Chord Testosterone Levels: Fetus - Adult Testicular Descent Fetal Neonatal Pubertal Adult Fusion of the tunica 5.0 albuginea and peritoneum to form the visceral tunica vaginalis 2.5 Adult Leydig Cells Fetal Leydig Cells Plasma Testosterone ng/ml Birth Rapid growth Cranial of Spermatic Artery Front View Spermatic Artery Suspensory gubernaculum Ligament Cranial Peritoneum (disappears) Suspensory Ligament Visceral Growth Visceral Growth Fusion of Peritoneum Inguinal Ring and Testis Testis Gubernaculum Peritoneum Gubernaculum Gubernaculum (rapid growth) Parietal Tunica Vaginalis Peritoneum Testis is pulled down Inguinal Ring Visceral Tunica to the inguinal Vaginalis ring. 4 Gubernaculum Spermatic Artery Spermatic Artery regresses Continued regression of Peritoneum Peritoneum Gubernaculum Visceral Growth Visceral Growth Testis pulled deeper Inguinal Canal Inguinal Canal into Scrotum Peritoneum Peritoneum Testis Vaginal Process Vaginal Vaginal Process attaches to Scrotum Process Gubernaculum (Regressing) Testis Parietal Tunica Space between Parietal Tunica Vaginalis Visceral and Parietal T.V. Vaginalis is continuous with Visceral Tunica Testis pulled into Visceral Tunica Peritoneum Vaginalis scrotum Vaginalis Gubernaculum (Fully Regressed) Testicular Descent Timing of Testicular Descent in Mammals Gonad Adominal Pause Transinguinal Inguinoscrotal • Cryptorchid - failure of descent to testis Translocation • Controlling mechanisms Testis in » Androgen dependent Cattle Scrotum » DHT supported Deer » Estrogen inhibits Human • Gene Expression Horse » INSL3 - insulin like growth factor 3 Pig – From leydig cells Dog » Great/LGR8 - receptor for INSL3 Rabbit – In gubernaculum Mouse 0 20 40 60 80 Birth 120 140 Interval After Conception (% of Gestation) Normal Dog Seminiferous Tubule Cryptorchid Dog Seminiferous Tubule Increased Chance of Testicular Cancer Sertoli Cells 5 Primary Sex Chord to Seminiferous Tubule Primary Sex Chord to Seminiferous Tubule Primodial Sertolic Primodial Sertolic Germ Cell Cell Germ Cell Cell (PGC) Precursor (PGC) Precursor Proliferate to form Spermatogonial Stem Cells Stem Cell Niche •Along basement membrane FSH on Sertoli Cells Primary Sex Chord to Seminiferous Tubule Hypothalamus • estradiol GnRH • inhibin • ABP Primodial Sertolic • tight junctions • growth factors Germ Cell Cell Ant. (PGC) Precursor Pituitary Negative Feedback of Estradiol and Inhibin Negative To PGC and Stem Cell Proliferate to LH FSH Epid. Spermatogonia form Feedback of ABP Spermatogonial Androgens + a a E2 T • Express 3-, 5-, Stem Cells Leydig aV-, b1-integrins Cells Inhibin Sertoli • Initially express c- T Cells kit receptor, then TJ Germ stop Stem Cell Niche Cells ABP Seminiferous •Along basement membrane Tubule Sertoli Cell Regulation Sertoli Cell Regulation (cont.) • Switch from FSH to Testosterone • FSH causes Sertoli cells to secret factors » FSH causes increase in cAMP that increase Leydig cell response to LH » at puberty, phosphodiesterase increases » at puberty or start of breeding season – FSH less effective – FSH increases first » Testosterone takes over regulation – Sertoli cells trigger the development of SER in Leydig • Germ cells effect ability of Sertoli cell to cells respond to testosterone 6 Hormonal Regulation of Spermatogenesis Hormonal Regulation of Spermatogenesis (Cont.) • Level of Testosterone • Why is testosterone so high in STF? » intratesticular testosterone is higher than in circulation » Does testosterone work by androgen receptor? IF 600 nM (Leydig cells here) – Yes, DHT is more effective than testosterone TV 250 nM » What is level of free testosterone in STF? SV 150 nM – Have not been able to measure PV 20 nM – ABP is produced by sertoli cells under influence of FSH It is usually 30 to 170 times that seen in PV and is present at 30 - 40 nM » Seminiferous Tubule Fluid (STF) testosterone • Certainly reduces free testosterone but there is still STF 170 nM excess testosterone » Androgen receptor Kd for testosterone » Artificial testosterone via implants found need 75 3 nM nM to maintain spermatogenesis Hormonal Regulation of Spermatogenesis (Cont.) Mitotic Divisions of Spermatogenesis • Level of testosterone in Sertoli cell As Apr Aal - stem cells, resting pool, slow dividing » Testosterone is converted to estrogen in sertoli cell A type spermatogonia (1 - 4 types ) » Has not been addressed • No good answer Intermediate spermatogonia B type spermatogonia Primary spermatocyte Mitotic Divisions of Spermatogenesis Meiotic Divisions of Spermatogenesis As Apr Aal - stem cells, resting pool, slow dividing Primary spermatocyte - long interval A type spermatogonia (1 - 4 types ) • preleptotene - DNA synthesis • leptotene - condensation of the chromatin Random Divisions Intermediate spermatogonia • zygotene - thickening of chromosomes and pairing • pachytene - RNA synthesis, thickening of chromosomes, crossing over B type spermatogonia • diplotene - chromosomes separate but remain attached at chiasma Stage Specific • diakinesis - cells separate and divide Primary spermatocyte Divisions 7 Meiotic Divisions (cont.) Sperm Chromatin Sturcture Primary spermatocyte Secondary spermatocyte - short lived and undergoes reduction division Round spermatid spermiogenesis Spermiation Cytoplasmic Elimination Phase and Spermiation Seminiferous Tubule • residual body loss • phagocytosis by sertoli cell • elong. sperm. influences sertoli cell –sem. tubual fluid –ABP –inhibin –interleukin 1 Amann 1983 Lumen Adluminal Spermatids 1° Spermatocyte Basal Sertoli Cell Spermatogonium Interstitial Leydig Cell Blood Vessel 8 Cytoplasmic Bridges Present Among Daughter Cells Over Population of Spermatogonia All develop Tight Junction surrounded by 1 Formation - FSH Sertoli cell ! Sertoli Sertoli Maintenance - T SG SG SG SG SG SG SG SG SG Basement Membrane Normal Apoptosis Inhibited PS Sertoli SG Sertoli PS Sertoli SG Sertoli AP AP SG SG SG SG SG AP SG AP SG SG SG SG SG SG Degenerating Spermatogonia (Apoptosis, as high as 75%) Basement Membrane Basement Membrane Spermatogenesis Every 13.5 Days sperm are released from this point Ap Spermatogonial Ad Renewal in the Spermatid Stem Cell FSH Primate Round Pool Spermatid Secondary Spermatocyte B Sertoli Cells Primary Spermatocyte P Spermatogonia Every 13.5 Days a new group of cells initiate the cycle Myoid Cells Stages Cycle • Specific cellular associations within a small • progression through sequence of all stages segment of a seminiferous tubule • stages are not the same length in time 9 Normal Apoptosis Effect of Hormone Withdrawal • Experimental Approaches » Hypox. – can’t restore with testosterone alone » GnRH agonist – Decreased FSH and LH release – Requires both FSH and Testosterone to get normal spematogenesis » Ethane dimethane sulfonate (destroys leydig cells) – get destruction of spermatogenesis – testosterone can overcome effects of EDS except does not prevent destruction of Leydig cells Essential Prevents Apoptosis Testosterone Effects 10 FSH Effects Prevents Apoptosis N-cadherin loss FSH + T N-cadherin N-cadherin SCF Activin SCF Activin SCF SCF B to P promoted FSH Receptors Highest Testosterone
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