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L5 Functional Anatomy and Histology of Male Reproductive System

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L5 Functional Anatomy and Histology of Male Reproductive System L5 Functional Anatomy and Histology of Male Reproductive System A. Testis - Page 87 of 370 - Testes are housed in scrota outside body cavity □ Scrotum: two perineal pouches separated by perineal raphe □ Perineal raphe: a visible ridge of tissue extending from anus through the perineum (originating from fusion of urogenital folds) □ Significance: testis kept at lower temperature (~35.3oC) than rest of body → Sperm development requires lower temperature □ Control of testicular temperature achieved by contraction of Dartos and cremaster muscles to pull testis to body wall → Dartos: fascia lining both scrotum and penis → Cremaster muscles: a skeletal muscle lining scrotum → ↓temperature → contraction → ↓ surface area of scrotum → ↑temp Functions of testis: □ Exocrine glandular function: sperm production in seminiferous tubules □ Endocrine glandular function: secretion of testosterone by interstitial cells 1. Seminiferous Tubules Seminiferous tubules: site of sperm production in testis □ Spermatogenesis: production of spermatids from spermatogonia by meiosis □ Spermiogenesis: transformation from spermatid to a spermatozoon 1 testis → >100 lobules → 2-3 seminiferous tubules per lobule Epithelium lined by Sertoli cells to support spermatogenesis and spermiogenesis Myoid cells: smooth muscle cells surrounding Sertoli cells responsible for contraction to propel immotile sperms out of seminiferous tubules - Page 88 of 370 - a. Sertoli Cells Irregular nuclei with tripartite nucleoli (nucleoli divided into three segments) Basolateral junctional complex between adjacent Sertoli cells form blood-testis barrier → no immune response against mature sperms Functions of Sertoli cells: □ Supply nutrients and maintain hormone level to facilitate sperm production and maturation □ Formation of blood-testis barrier □ Release of sperms □ Steroidogenesis: conversion of testosterone into dihydrotestosterone (DHT) and oestrogen → DHT an even more potent androgen than testosterone □ Secretion of androgen-binding protein (ABP), inhibin, fluid, ions and anti-Müllerian hormone (in embryonic stage) → Androgen-binding protein (ABP): binds androgens to make them less lipophilic → ↑concentration in luminal fluid of seminiferous tubules → facilitate spermatogenesis and sperm maturation in epididymis → Inhibin inhibits FSH production → negative-feedback regulation → Anti-Müllerian hormone leads to degeneration of Müllerian ducts - Page 89 of 370 - b. Spermatogenesis Spermatogenesis: formation of spermatozoon from spermatogonia via meiosis Under control of GnRH via: □ FSH, stimulating primary spermatocytes to undergo meiosis I □ Testosterone, activating genes necessary for spermatogonia differentiation in Sertoli cells → Testosterone secretion by Leydig cells dependent on LH stimulation Process of spermatogenesis: 1) A spermatogonium (SG) divides by mitosis into a primary spermatocyte (PS) and another spermatogonium; 2) A primary spermatocyte divides by meiosis I into two secondary spermatocytes (SC); 3) A secondary spermatocyte divides by meiosis II into two spermatids (ST). Throughout the process, spermatocytes move progressively from base of Sertoli cells to the luminal side, where spermatids undergo spermiogenesis to become mature sperms - Page 90 of 370 - c. Spermiogenesis Spermiogenesis: morphological transformation from a spermatid to a spermatozoon Changes underwent by a spermatid: □ Condensation of nucleus □ Formation of acrosome cap in head with enzymes (eg. hyaluronidase) for sperm to penetrate ovum □ Formation of body with spiral mitochondria for energy for movement of tail □ Formation of a tail for motility (3mm/h) □ Re-organization of mitochondria to form a sheath in the tail Mature spermatozoon then released into the seminiferous tubules and ejaculated into female body via genital ducts and penis □ ~3mL (2.5-6) of semen ejaculated per ejaculation □ 100M sperm/mL semen → ~300M per ejaculate □ Oligospermia: insufficient sperm count → Sperm count <20M → sterility Note that sperms only develop motility and ability to fertilize ovum in the epididymis (full maturation) - Page 91 of 370 - 2. Interstitial Cells of Leydig Interstitial cells of Leydig: cells found in interstitium adjacent to seminiferous tubule responsible for testosterone secretion EM shows abundant smooth ER → steroid hormone production Functions of testosterone: □ Embryonic development of male genital system (incl. descent of testis)\ □ Required for sperm development □ Development of secondary sexual characteristics, including hypertrophy of larynx, facial hair growth and rougher, coarser skin □ Increase in melanin and sebum secretion □ Increase in metabolic rate, RBC count, protein synthesis and bone growth → Excess → early closure of epiphyseal plates Hormonal control of spermatogenesis and sexual organ development by hypothalamus-pituitary-gonadal axis: □ Prenatal: placental human chorionic gonadotrophin (hCG) stimulates fetal testes to secrete testosterone → development of genital system □ Birth to puberty: no testicular secretion of testosterone □ Puberty: GnRH stimulates FSH and LH production → LH stimulates testosterone and development of sex organs → FSH stimulates sperm development - Page 92 of 370 - B. Male Genital Ducts Tubuli recti: short straight tubes lined with Sertoli-like cells □ Simple cuboidal epithelium □ Connects seminiferous tubules to rete testis Rete testis: space in mediastinum testis lined by cuboidal cells Mediastinum testis: c.t. mass in back of testis continuous with tunica albuginea and internally with septula testis □ Tunica albuginea: fibrous external covering of testis □ Septula testis: fibrous c.t. between adjacent testis lobules 1. Ductus Efferentes Ductus efferentes (efferent ducts) found in head of epididymis Lined by: □ Simple columnar epithelium with ciliated and non-ciliated epithelial cells □ Fibroelastic connective tissues □ Smooth muscles - Page 93 of 370 - 2. Ductus Epididymis Ductus epididymis (or epididymis): a 20ft-long tube connecting a testicle to a vas deferens Lining: □ Pseudostratified columnar epithelium with stereocilia (long microvilli) → absorption of excessive fluid from seminiferous tubules (∵spermatozoa from seminiferous tubules non-motile → need large amounts of fluid for propelling as spermatozoa matures in epididymis, the fluid is no longer needed) □ Basal cells □ Basement membrane □ Connective tissue with smooth muscles Function: stores and nourishes sperms for maturation (for 1-2d) 3. Ductus Deferens Ductus deferens: continuation of ductus epididymis towards prostatic urethra Bilateral ductus deferentes join to form ejaculatory duct near prostate Lining: □ Pseudostratified columnar epithelium with stereocilia □ Muscular layer (inner longitudinal, middle circular, outer longitudinal) □ Adventitia: loose fibroelastic c.t. Easily palpable Clinical relevance: vasectomy in male contraception - Page 94 of 370 - C. Male Accessory Sex Glands 1. Seminal Vesicle Lining: □ Pseudostratified epithelium with basal cells □ Lamina propria □ Smooth muscle □ Adventitia Secretions responsible for 60% of semen and contain □ Fructose → nourishes sperms □ Fibrinogen → formation of sperm plug inside female genital tract → keeps sperms inside female body □ Alkaline secretion → neutralizes acidity in vagina Contracts during orgasm to contribute to semen ejaculation - Page 95 of 370 - 2. Prostate Gland About the size of a walnut Lining: □ Simple cuboidal to simple or pseudostratified columnar epithelium □ Fibromuscular stroma with c.t. and smooth muscle Acidic milky secretions responsible for 15-30% of semen and contains: □ Prostatic acid phosphatase (PAP) → prostate cancer marker (function unknown) □ Fibrinolysin → cleaves fibrin clot to maintain motility of sperms □ Citric acid → acidity to activate sperms □ Prostatic specific antigen (PSA) → liquefies semen for sperm motility + dissolution of cervical mucus + prostate cancer marker Prostatic concretions: small hyaline masses found in prostatic lumen (esp in older people) □ Arises from hardened secretions and degenerated cells □ Unknown significance but is a signature characteristic for microscopic identification of prostate tissue Clinical significance: □ Benign prostatic hyperplasia (BPH): a benign increase in size of prostate → Mainly derived from central zone □ Prostate cancer → Mainly derived from peripheral zone → Elevated PSA can serve as a marker for prostate cancer - Page 96 of 370 - 3. Bulbourethral Glands Also called Cowper’s glands About the size of a pea Lined by cuboidal to columnar epithelium Secretions responsible for 5% of semen □ Secretes a clear viscous fluid just before ejaculation □ Responsible for neutralization of acidity in urethra and female vagina and provide lubrication D. Penis Three erectile bodies: □ Two corpora cavernosa □ One corpus spongiosum □ Composed of trabeculae filled with coiled arteries covered by tunica albuginea Penile urethra enclosed by corpus spongiosum and opens at external urethral orifice on glans penis Root of penis formed by two crura of corpus cavernosus and a bulb of corpus spongiosum Glans penis: an engorgement of corpus spongiosum covered by prepuce (foreskin) □ Circumcision: surgical removal of prepuce - Page 97 of 370 - Function of penis: urination and ejaculation Ejaculation: expulsion of semen via penis into the female genital tract during copulation □ PN stimulation for arousal, SN stimulation for orgasm □ Arterial blood flow to fill cavernous bodies with blood □ Erection of penis blocks venous return from penis □ ~3mL of semen expelled per ejaculate, consisting of fluid secretions from the three accessory glands, mucus from bulbourethral gland and sperm Peyronie’s disease: fibrous plaques in tunica albuginea of penis → upward curvature of penis when erect □ Occurs in 1-4% of adult men - Page 98 of 370 - .
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