Male Anatomy Spermatogenesis PDF

Male Reproductive System: General Anatomy Structure Function 1  Learning Objectives Understand the anatomy of the male reproductive system Understand the organization of the male reproductive tract and how the various parts/organs are interco...

Male Reproductive System: General Anatomy Structure Function 1  Learning Objectives Understand the anatomy of the male reproductive system Understand the organization of the male reproductive tract and how the various parts/organs are interconnected 2  Male Reproductive Organs Major function is to produce and deliver spermatozoa to the female 3 4 5  Temperature control is key! Testes need to be kept 4-6 C below temperature for spermatogenesis During late part of gestation or early life: testicular descent via the inguinal canal is required Later in life: temperature controlled by the veins of the “pampiniform plexus” (in the spermatic cord) forming a countercurrent heat exchanger 6 7  Outside the testes Testes are located in the scrotum = skin sac from the abdominal cavity with a layer of smooth muscle (tunica dartos) On the inside of the scrotum: layers of connective tissue (scrotal fascia and parietal vaginal tunic) Covering the testes is a layer of vascularized connective tissue (tunica albuginae + visceral vaginal tunic) that projects septa in the testis. Smooth muscle cover the septa (help moving immature sperms) 8 9 EH/T: epididymal head/tail; M:mediastinum; TP: testicular parenchyma10  Inside the testes 2 major parts: Seminiferous tubules (S.T.): site of sperm production. Ducts collect sperm to rete testis in the center = tubes that bring the sperm to the epididymis Interstitium (between S.T.): composed of connective tissue, nerve, blood vessels, and Leydig cells which produce testosterone 11 12 CT: connective tissue; ST: senimiferous tubule; BV: blood vessel; GC: germ cells (spermatogonia); LC: Leydig cells; F: Flagella; BM: Basal lamina 13 Boar reproductive tract 14  Boar reproductive tract Testis structure similar to bull – more pronounced interstitium [Leydig cells produce wider array of androgens, C16, C19 steroids (16- androstenes) plus estrogens] Testis location against the abdominal cavity reduces efficiency of heat exchange Large seminal vesicles = large volume Large bulbo-urethral glands = gel Copious ejaculate/prolonged ejaculation Smaller sperm “reserves” v/v bull 15 16 17 Spermatogenesis Spermiogenesis 18 Learning Objectives Explain the mechanisms occurring during the formation of spermatozoa Cell division (meiosis) Differentiation and maturation (spermatogonia to spermatozoa) 19 20 Spermatogenesis 21  Meiosis Interphase: replication of DNA (4c – 2n) Prophase I: Leptotene: condensation of chromatin Zygotene: pairing of homologues (forming a tetrade) Pachytene: crossing-over and recombination Diplotene: synaptonemal complexes dissociate Diakinesis: chiasma disappear and homologues begin to repel 22 23 Meiosis (continued) Metaphase I: homologue centromere binds to spindle fiber Anaphase I: homologous pairs separate and begin to move Telophase I: chromosomes migrate to each pole, cell division. 1 chromosome of pair in each cell = (2c – 1n) Prophase II: spindle fibers rearrange and chromosomes recondense Metaphase II: chromosomes align along spindle equator Anaphase II: sister chromatids separate and move to opposite poles Telophase II: daughter cell nucleus has one set of chromosomes (1c – 1n) 24 4c 2c 1c http://fig.cox.miami.edu/~cmallery/150/devel/c7.46.12.spermatogenesis.jp 25  Sertoli Cells Blood testis barrier Basal/luminal and adluminal compartments Provide nutrients and several factors to control spermatogenesis “Fluid pumping” during final maturation if sperm Produce androgen-binding protein and inhibin Express FSH receptors (regulated by FSH) 26  Spermiogenesis In contact with Sertoli cells Nuclear condensation Formation of the acrosomal cap (derived from Golgi) Development of a tail The distal centriole provides a template for accretion of cytoskeletal elements comprising the contractile lattice of the tail Mitochondria become concentrated into the sheath of the middle piece. 27 Reproduction in Mammals. CR Austin and RV Short 1982. 2nd edition, Cambridge University Press. 28  Leydig Cells Interstitial cells – located in the spaces between tubules Highly perfused (blood vessels/capillaries) Synthesize androgens – testosterone Express LH receptors 30 FYI: Spermatogenic Cycle (Time) Organized cellular associations Section of tubule will always have an identifiable stage Cycle = approximately 13.5 days Spermatogenic Wave (Spatial) Specific stages coordinated along a tubule in precise + repetitive manner Note: intercellular bridges between A1 spermatogonia) 31 FYI: FYI:  Proximal Epididymis: To Pelvic Head Urethra Immotile Dista (Caput) 8-25 l x 109 Infertile spermatozo a Acquisition of Ductus Body potential to Deferens (Corpus) 8- 25 x 109 be: Motile spermatozo Fertile a Proximal Tail (Cauda) Dista 10-50 x 109 Upon l spermatozo dilution: a Motile Spermatozoa in this region can be Fertile transported into an ejaculatory  Accessory Sex Glands Ampular gland (ampullae, absent in boar and dogs) = enlargement of the ductus defferent Vesicular (absent in dogs) secretes Fructose: sperm energy pack Vitamins and prostaglandins important for mobility and survival Proteins for coagulation Prostate: alkaline substance to enhance motility Bulbourethral: alkaline substances to neutralize acidity and mucus to lubricate vagina during copulation 35  Semen Characteristics Bull Boar Stallion Ejaculate volume (mL) 5-8 150-200 60- 100 Sperm/ejaculate (x109) 5-15 30-60 5- 515 Protein (g/100 mL) 6-8 3.7 1.0 Fructose (mg/100 mL) 460-600 9 2 Citric acid (mg/100 mL) 620-806 173 8-53 36 Production of Spermatozoa Function (bull) # of Days Spermatocytogenesis 47 (spermatogonia to spermatids) + Spermiogenesis ~14 (spermatid to spermatozoon) = Spermatogenesis 61 (4.5 cycles) Epididymal transit 10-12 37 Arousal Ejaculatory Process Innervation of the Male Genital System  Extender for cryopreservation Nutrient - Egg Yolk - Whole homogenized milk Buffer - Citrate - Sodium Phosphate Antimicrobials - Penicillin/Streptomycin (bacteria) - Minosin (mycoplasma) Cryoprotectant - 6 – 12% glycerol (if to be frozen) Most popular: “Egg yolk - citrate” (clear) “Whole Homogenized Milk” (opaque) 43 Endocrine Control In the Male 44