Male Reproductive Processes - Lecture (without answers).pdf

MD1020 Reproduction – Week 3 Assoc. Prof. Damien Paris ([email protected])  Introduction to sexual reproduction  Testis & epididymis  Spermatogenesis:  meiosis  cytodifferentiation  endocrine control (Hypothalamic – Pituitary – Testicular Axis)  Accessory glands & semen  GLS Organiz...

MD1020 Reproduction – Week 3 Assoc. Prof. Damien Paris ([email protected])  Introduction to sexual reproduction  Testis & epididymis  Spermatogenesis:  meiosis  cytodifferentiation  endocrine control (Hypothalamic – Pituitary – Testicular Axis)  Accessory glands & semen  GLS Organization  Relate process of meiosis to gametogenesis (particularly spermatogenesis)  Describe the process of spermatogenesis & relate to the gross & histological features of the testis  Explain the role of the hypothalamic-pituitary-testicular axis in the endocrine regulation of spermatogenesis  Outline the role of the male accessory sex glands in providing constituents that contribute to semen allows genetic mixing ≈ ↑ offspring fitness Spermatogenesis different reproductive anatomy permits production & delivery of genes (via gametes) Testis, Epididymis & Accessory Glands  mixing of genes occurs via gametes:  specialized meiotic cells  spermatozoa (sperm) & oocytes (eggs)  different structure reflects different functions in reproductive process:  spermatozoa: compact, streamlined, highly-motile (delivery vessel for DNA)  oocytes: large, nutrient/protein-rich cells (facilitate embryo development)  Lie within the scrotum  ~4 cm long & 2.5 cm wide  Primary function:  produce sperm  produce steroids (androgens such as testosterone) Marieb & Hoehn 2010  Each testis is divided into lobules contains 1-4 tightly coiled seminiferous tubules (site of spermatogenesis)  Sperm pass from the seminiferous tubules through the rete testis & into the efferent ducts of the epididymis  In the epididymis, sperm undergo further maturation (acquire motility & fertilization ability) & storage until ejaculation Marieb & Hoehn 2010 Marieb & Hoehn 2010 Sertoli cell Leydig cells     Leydig (interstitial) cells: produce androgens (testosterone) Sertoli (sustentacular) cells: support spermatogenesis spermatogonia, spermatocyte & spermatid: form sperm myoid cells: contract to move sperm & fluid through tubules  Spermatogenesis requires a temperature ~4-6°C lower than body temperature  Complex venous network (pampiniform plexus) wraps around the testicular artery in the spermatic cord  Cools incoming arterial blood (37°C) before it enters the testis by heat exchange with outgoing venous blood (33°C) ram Senger 2005 Senger 2005  Regions:  caput (head)  corpus (body)  cauda (tail)  Structure:  highly coiled duct ~6 m  pseudo-stratified epithelia with stereocilia  Function: Marieb & Hoehn 2010  sperm maturation (acquisition of motility & fertilizing ability)  sperm storage in cauda possible for several months  sperm are ejaculated from the caudal epididymis not the testes  formation of gametes (sex cells):  spermatogenesis → testes  oogenesis → ovaries  involves halving of the chromosomes via meiosis:  avoids polyploidy → detrimental diploid adult (2n=46) haploid sperm (n=23) + ÷2= haploid egg (n=23) haploid gametes (n=23) = diploid zygote (2n=46)  The formation of sperm occurs in the seminiferous tubules of the testes & takes ~64 to 72 days Marieb & Hoehn 2010  Process involves both mitotic & meiotic cell divisions  Mitosis:  equal division to produce 2 identical daughter cells with same number of chromosomes (replenishes spermatogonial stem cell reserve)  Meiosis:  reducing division to produce 4 unique daughter cells with half the number of chromosomes (sperm for reproduction) ? ? What is the ploidy & DNA copy number of each meiotic cell indicated? ? ? 1 cycle ≈70 days Spermatogonium (stem cell) Type A daughter cell (remains at basal lamina as a stem cell) Mitosis Growth Meiosis I (enters adluminal compartment) Meiosis II Basal lamina Sustentacular cell nucleus Type B daughter cell Tight junction (between sustentacular cells) Primary spermatocyte Secondary spermatocytes Early spermatids Late spermatids Spermatozoa Marieb & Hoehn 2010 Cytoplasmic bridge Lumen of seminiferous tubule  Cytoplasmic remodelling of the spermatid is called spermiogenesis  Packages chromosomes for delivery  Spermatids change from round to elongated cells with an acrosome “cap” containing enzymes & a flagellum  When fully differentiated, spermatozoa released into lumen of seminiferous tubule (spermiation)  Golgi forms acrosomal vesicle  acrosomal vesicle spreads over nucleus & distal centriole forms early flagellum  nucleus & cytoplasm elongate  mitochondria form midpiece, cytoplasm is shed & principle piece (tail) matures Senger 2005 Marieb & Hoehn 2010 Gametogenesis is largely regulated by hormones → endocrine system  Gonadotrophin releasing hormone (GnRH):  stimulates secretion of LH & FSH  Luteinizing hormone (LH):  stimulates secretion of testosterone  Follicle stimulating hormone (FSH):  supports Sertoli cell function  Androgen Binding Protein (ABP)†:  sequesters T to site of spermatogenesis  Testosterone (T):  essential for initiation of spermatogenesis  stimulates primary & secondary sex characteristics  Inhibin:  regulates rate of spermatogenesis (~20 million/ml) by inhibiting FSH † not a true hormone inhibin specifically inhibits FSH Leydig (not GnRH) Sertoli Green = control Red = inhibin treated Evidence….. Inhibin specifically inhibits FSH Johnson 2007  Seminal vesicles  Prostate  Bulbourethral glands Produce the bulk of the seminal plasma Marieb & Hoehn 2010  Seminal Vesicles:  contracts during ejaculation  secrete yellow viscous alkaline fluid containing fructose, ascorbic acid, coagulating enzymes & prostaglandins (enhance sperm motility/fertilization)  approx. 70% of semen volume  Prostate:  contracts during ejaculation causing secretions to enter the urethra  secretes milky acidic fluid containing citrate, several enzymes & prostate specific antigen (activates sperm)  up to 30% of semen volume  Bulbourethral Glands:  secretes a thick clear alkaline mucus (neutralises traces of acidic urine in urethra prior to ejaculation)  Mixture of sperm, testicular fluid & accessory gland secretions  Function:  transport medium for sperm  provides nutrients & chemicals that protect & activate sperm  facilitate sperm movement  Components:  Prostaglandins: stimulate contraction in female tract (facilitates sperm uptake)  Relaxin: enhances sperm motility  Clotting factors: promote semen coagulation typical ejaculate is 2-5 ml of semen containing 15 – 150 x 106 sperm/ml  SIGN-IN SESSION!!  Activity A - Testicular Histology: 8:00 – 12:00 noon Microscopy Lab (DB046-103) 4 x 1h rotations according to Home Group (consult overview) ENCLOSED FOOTWARE COMPULSORY!!  Activity B – Spermatogenesis & Activity C - Endocrine Control of Spermatogenesis: 8:00 – 12:00 noon Quad Rooms (DB046-104/104A) 4 x 1h rotations according to Home Group (consult overview)