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Male Reproductive Physiology. Jeremy Johnson D.O. November 26, 2008. Male Reproductive Physiology. Male Reproductive Axis Testis Epididymis Spermatozoa Vas Deferens. Male Reproductive Axis. 3 tiers of organization: Hypothalamus, Pituitary gland, Testis

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male reproductive physiology

Male Reproductive Physiology

Jeremy Johnson D.O.

November 26, 2008

male reproductive physiology2
Male Reproductive Physiology
  • Male Reproductive Axis
  • Testis
  • Epididymis
  • Spermatozoa
  • Vas Deferens
male reproductive axis
Male Reproductive Axis
  • 3 tiers of organization: Hypothalamus, Pituitary gland, Testis
  • Hypothalamus: GnRH (gonadotropin-releasing hormone)
  • Pituitary gland: LH (luteinizing hormone), FSH (follicle-stimulating hormone)
    • LH: stimulates Testosterone production by Leydig cells in interstitium
    • FSH: supports spermatogenesis by stimulating Sertoli cells in the seminiferous epithelium
    • Inhibin: secreted by Sertoli cells, suppresses FSH secretion by gonadotropes; ? Use of Inhibin B as marker for impaired testicular function
    • Activin: secreted by Sertoli cells, stimulate transcription of FSH B subunit
male reproductive axis5
Male Reproductive Axis
  • Hypothalamus:
  • GnRH - 3 types of rhythmicity
    • Seasonal (in months) – peaks in Spring
    • Circadian (in hours) – highest Testosterone levels in AM
    • Pulsatile (in minutes) – peaks occur every 90 - 120 minutes

Melatonin: modifies seasonal & circadian rhythms from inputs from pineal gland (seasonal) & neural connections (circadian) from suprachiasmatic nucleus (mammalian 24-hr clock)

Precursors of GnRH neurons migrate to hypothalamus from olfactory placode during development

Kallman’s Syndrome: congenital hypogonadotropic hypogonadism, failure of normal migration of GnRH neurons -> hypothalamus unable to secrete GnRH; anosmia/other midline defects + hypogonadism is diagnostic

male reproductive axis6
Pituitary gland

Anterior Pituitary (Adenohypophysis) – regulated by bloodborne factors

Gonadotropes (secrete LH & FSH)*

Corticotropes (secrete ACTH)?

Lactotropes (secrete PRL)*

Somatotropes (secrete GH)*

Thyrotropes (secrete TSH)

*significant effects on male reproductive function

?unknown effects on male reproductive function

Posterior Pituitary (Neurohypophysis) – regulated by neural stimuli


Vasopressin (ADH)

Male Reproductive Axis
male reproductive axis8
Male Reproductive Axis
  • Steroid Feedback
    • Testosterone exerts negative feedback suppression on the release of GnRH at the level of hypothalamic neurons & pituitary; T is not the only active steroid in the target cells
    • Testosterone –(aromatase) Estradiol
    • Testosterone –(5 alpha reductase)  DHT
    • Testosterone acts primarily to feedback at the hypothalamus; Estrogens primarily feedback to the pituitary gland
    • In males:
      • LH secretion is regulated primarily by Testosterone
      • FSH secretion is regulated primarily by Estradiol
male reproductive axis9
Development of male reproductive axis

7 weeks gestation: 1st identifiable step differentiating ovarian from testicular pathways is movement of primordial germ cells into medullary cords

SRY (Sex-Determining Region on Y c’some) controls early testis differentiation

SRY gene product (a TF) acts w/ other TFs (WT-1, SOX-9, DAX-1) to initiate male sexual differentiation

10% of 46 XX males have no identifiable SRY gene

Sertoli Cells: secrete MIS (Mullerian Inhibiting Substanceaka: Anti-Mullerian Hormone); causes female reproductive structures to regress

Leydig Cells: secrete Testosterone which induces differentiation of the Wolffian duct system (epididymis, vas deferens, sex accessory glands)

Male Reproductive Axis
male reproductive axis11
Endocrinology of Testis

Leydig cell differentiation

1st wave - 7 weeks gestation: stimulated by hCG from placenta; androgens appear in circulation

2nd wave - 2-3 months after birth: stimulated by gonadotropin production from neonate’s pituitary; briefly elevates Testosterone

Androgens produced during first 2-6 months of life are thought to hormonally imprint hypothalamus, liver, prostate, phallus & scrotum

Leydig cells of infants then regress & testes are dormant until puberty


Hypothalamus generates pulses of GnRH around 12th year of life

Onset of GnRH pulses typically occurs at night, due in part to gradual decrease in nocturnal melatonin secretion from pineal gland

Also influenced by nutritional status of body and growth rate

GH & IGF-1 stimulate reproductive function

Leptin determines size of fat stores in body - ? Role in puberty

Male Reproductive Axis
male reproductive axis12
Aging of Hypothalamic/Pituitary Axis

Testosterone: levels decline at > 50 years of age

LH: basal levels increase in older men; LH pulsatility is blunted

Leydig cells: steroidogenic capacity decreases

Spermatogenesis: lower fecundity at > 40 years, 50% lower probability of achieving pregnancy w/in 1 yr compared to men < 25 years of age

Male Reproductive Axis
  • Gross structure & vascularization
    • Volume: 15 - 25 ml
    • Longitudinal length: 4.5 - 5.1 cm
    • 3 layers of capsule: outer visceral layer of tunica vaginalis, tunica albuginea, innermost layer of tunica vasculosa
    • Tunica albuginea contains smooth muscle; smooth mm. provides contractile capability to testis as well as affects blood flow into testis
    • Testicular arteries penetrate tunica albuginea & travel inferiorly on post. surface w/ branches passing anteriorly; also major branches present on inferior pole (potential for injury during orchiopexy/biopsy); medial and lateral midsection of testis have fewer vessels
    • Capsule separated by septa; between septa are seminiferous tubules & interstitial tissue
    • Seminiferous tubules: developing germinal elements & supporting cells (Sertoli cells)
    • Interstitial tissue: Leydig cells, mast cells, macrophages, nerves, blood/lymph vessels (20 – 30 % of total testicular volume

No somatic innervation

Autonomic innervation from intermesenteric nn. & renal plexus; travel along testicular artery

Arterial supply:

Internal spermatic testicular

Deferential vasal

External spermatic (cremasteric)

Countercurrent exchange of heat between pampiniform plexus & arteries

Intratesticular temps 3 – 4 degrees C lower than rectal temps

Variability in # of arteries entering testis exists

1 artery: 56%; 2 arteries: 31%; 3 or more arteries: 31%

  • Cryoarchitecture & Function
  • Interstitium: blood/lymph vessels, fibroblastic supporting cells, macrophages, mast cells & Leydig cells
  • Leydig cells: responsible for steroid production; Testosterone is synthesized from cholesterol & is principle steroid produced in human testis
  • 3 sources for cholesterol: external (bloodborne), de novo (acetate), stored cholesterol esters
  • LH: regulates Testosterone production; generates cAMP & initiates transport of cholesterol into mitochondria
  • Testosterone peaks:
    • 12-18 wks gestation
    • 2 months of age
    • 3rd decade of life (max concentration)
  • Seminiferous tubules – germinal elements & supporting cells
  • Germinal elements: spermatozoa
  • Supporting cells: sustentacular cells (basement membrane) & Sertoli cells
  • Sertoli cell functions:
    • Creates specialized microenvironment of adluminal compartment of seminiferous epithelium
    • Supports germ cells through gap junctions between Sertoli & germ cells
    • Facilitates migration of differentiating germ cells into seminiferous tubule
  • Blood-Testes Barrier
  • 3 levels:
    • 1.) Tight junctions between Sertoli cells & spermatogonia from other germ cells
    • 2.) Endothelial cells in capillaries
    • 3.) Peritubular myoid cells
    • Spermatogonia & young spermatocytes are outside blood-testes barrier in basal compartment; mature spermatocytes & spermatids are above barrier in adluminal compartment
    • Blood-Testes Barrier functionally develops at onset of spermatogenesis
  • Germinal Epithelium – 123 x 106 spermatozoa/day (21 – 374 x 106)
  • Phases of spermatogenesis
    • Proliferative: spermatogonia divide to replace their numbers; or produce daughter cells committed to becoming spermatocytes
      • Type A spermatogonia; Ad (dark) – stem cell renewal; Ap (pale) – produce daughter cells
    • Meiotic: reduction division resulting in haploid spermatids
      • Type B spermatogonia
    • Spermiogenic: spermatids undergo changes to form mature spermatozoa
      • Round Sa spermatid
      • Entire process requires 64 days (Ap spermatogonium  spermatozoon)
Hormonal Regulation of Spermatogenesis

Intratesticular Testosterone levels are 100 x greater than serum levels

Testosterone will initiate & qualitatively maintain spermatogenesis in humans

Genetic Basis of Spermatogenesis

AZF (azoospermia factor) region on long arm of Y c’some implicated in deletions resulting in azoospermia

Paternal centromere: appears to organize embryonic mitotic activity; viable embryo cannot be produced w/out this contribution

  • Gross structures:
  • Tubule: 3-4 meters in length
  • 3 regions: Caput, Corpus, Cauda
  • Contractile tissue (myofilaments)
  • Innervation: intermediate spermatic nerves (hypogastric plexus); inferior spermatic nerves (pelvic plexus); sympathetic fibers increase in # proximally
  • Vascularization: Testicular artery (Caput & Corpus), Deferential artery (Cauda); collateral circulation exists from Deferential & Cremasteric aa
  • Histology:
    • Ciliated cells
    • Principal cells: absorptive/secretive processes
    • Basal cells
  • Function
  • Sperm transport: 2 -12 days; transport time influenced by daily testicular sperm production; 2 days in men w/ high sperm counts vs 6 days in men w/ low sperm counts; recent emission reduces transit time thru Cauda by 68%; principal mechanism for moving spermatozoa thru epididymis is probably due to spontaneous rhythmic contractions of cells surrounding epididymal tract
  • Sperm storage: 50% of total # of epididymal spermatozoa are stored in Cauda (capable of undergoing motility & have capacity to fertilize); fate of unejaculated spermatozoa is unknown
  • Function
  • Sperm motility maturation: increase motility observed during transit
    • Efferent ducts: 0%
    • Caput: 3%
    • Proximal Corpus: 12%
    • Distal Corpus: 30%
    • Cauda: 60%
  • Function
  • Sperm fertility maturation:
  • Testicular spermatozoa are incapable of fertilizing eggs (unless injected)
  • Maturation is achieved at level of distal Corpus or proximal Cauda
  • Biochemical changes:
  • Increased capacity for glycolysis
  • Changes in intracellular pH & calcium content
  • Modification of adenylate cyclase activity
  • Alterations in cellular phospholipid & phospholipid-like fatty acid content
  • Mature spermatozoa stored in Cauda epididymis & Ductus deferens
  • 60 micrometers in length
  • Head: measures 4.5 micrometers in length & 3 micrometers in width
  • Oval sperm head: consists mostly of a nucleus which contains highly compacted chromatin material & an acrosome which contains enzymes necessary for penetration of outer membrane of female egg
  • Middle piece: helically arranged mitochondria surrounding a set of fibers & characteristic 9 + 2 microtubular structure of axoneme
  • Mitochondria contains enzymes required for oxidative metabolism & production of ATP (primary energy source for cell)
  • Axoneme contains enzymes & structural proteins necessary for transduction of ATP into mechanical movement resulting in motility
  • Outer dense fibers are rich in disulfide bonds & thought to provide sperm tail; fibers surround middle & principal piece, terminate at end piece
  • Plasma membrane envelops spermatozoan (except at end piece); regulates transmembrane movement of ions & other moleculs; at head, specialized proteins in membrane participate in sperm-egg interactions during early stages of fertilization
  • Effects of Sex Accessory Gland Secretions on Spermatozoal Function
    • Human ejaculate maintains an ability to coagulate initially & is liquefied by proteases from prostate (specifically PSA)
    • Unknown as to whether or not coagulum provides to maintain spermatozoa w/in vagina
    • Spermatozoa must traverse cervical mucus into uterus & finally into oviduct where fertilization occurs
    • Uterine transport in woman takes 5 – 68 minutes
    • Spermatozoa must undergo capacitation prior to oocyte fertilization ; capacitation occurs at different rates for each spermatozoan
    • Many changes occur during capacitation; most notably, the acrosome reaction & development of hyperactivatedmotility occurs
    • Unknown as to whether or not prostatic or seminal vesical secretions contribute to capacitation
    • Ejaculate:
      • Fructose – produced in seminal vesicle, provides energy for spermatozoa
      • Albumin – supports & stimulates spermatozoa
      • Antioxidants – enzymes (Glutathione peroxidase, Superoxide dismutase, Catalase), molecules (Taurine, Hypotaurine, Tyrosine) all provide anti-oxidant protection for sperm; oxidative effects on sperm include lower sperm motility & increased damage to sperm DNA
ductus vas deferens
Derived from Mesonephric (Wolffian) duct

30 – 35 cm in length

Begins at Cauda epididymis & terminates at ejaculatory duct near prostate gland

Outer diameter: 2 -3 mm; Lumen diameter: 300 – 500 micrometers

5 portions

Sheathless epididymal portion w/in tunica vaginalis

Scrotal portion

Inguinal division

Retroperitoneal (pelvic) portion


Outer adventitia (blood vessels, small nerves)

Muscular coat (middle circular, inner/outer longitudinal)

Mucosal inner layer (epithelial lining)

Ductus Vas Deferens
ductus vas deferens32
Ductus Vas Deferens
  • Vascularization & Innervation
  • Blood supply: Deferential artery via Inferior vesicle artery
  • Nervous supply: sympathetic & parasympathetic inputs
    • Parasympathetic (cholinergic) is of minor importance in motor activity of vas deferens
    • Sympathetic (adrenergic) nerves provide rich supply to vas deferens; sympathetics derived from Hypogastric nerves via Presacral nerve; vas deferens also receive a special type of short adrenergic nerve which are present in all 3 layers of the muscle layers of vas deferens (greatest concentration of these nerves are present in outer longitudinal layer)
ductus vas deferens33
Ductus Vas Deferens
  • Cryoarchitecture of Ductus Deferens
  • Lined by pseudostratified epithelium
  • Height of epithelium decreases along the length of ductus
  • Longitudinal folds of epithelium are simple in proximal region & more complex at distal segments
  • Muscle thickness gradually decreases along the length of the ductus
  • Pseudostratified epithelium is composed of basal cells & 3 types of columnar cells (Principal cells, Pencil cells & Mitochondrian-rich cells)
  • Columnar cells all show steriocilia & irregular convoluted nuclei
  • Principal cells more prominent in proximal portion of ductus
  • Pencil & Mitochondrian-rich cells more prominent in distal portion of ductus
ductus vas deferens34
Ductus Vas Deferens
  • Spermatozoal transport
  • Ductus exhibits spontaneous motility, has capacity to respond when stretched & contents of ductus can be propelled into urethra by strong peristaltic contractions elicited by stimulation of hypogastric nerve or adrenergic neurotransmitters
  • Immediately before emission, rapid & effective transport of spermatozoa from distal epididymis & proximal vas deferens occurs (apparently related to sympathetic stimulation)
  • This efficient transport of spermatozoa has revealed that the ductus deferens has the greatest muscle-lumen ratio (10:1) of any hollow viscus in the human body
  • Epididymal spermatozoal reserves: 182 million (26% caput, 23% corpus, 52% cauda); transit times in days (0.7 caput, 0.7 corpus, 1.8 cauda)
  • Ductus spermatozoal reserves: 130 million; storage site for spermatozoa
ductus vas deferens35
Ductus Vas Deferens
  • Spermatozoal transport
  • “During the sexual rest, epididymal contents were transported distally through the vas deferens into the urethra in small amounts and at irregular intervals”
  • Urethral disposal is a mechanism for ridding the epididymis of excess spermatozoa
  • After sexual stimulation and/or ejaculation: contents of ductus can be propelled towards proximal ductus & cauda epididymis because distal portion had increased contractility compared to proximal portion of ductus
  • Refluxing was noted to reverse w/ sexual rest
ductus vas deferens36
Ductus Vas Deferens
  • Absorption & Secretion
  • Suggested that ductus deferens may have absorptive & secretory functions
  • Principal cells have characteristics typical of cells that are capable of synthesizing & secreting glycoproteins
  • Stereocilia, apical blebbing, primary & secondary lysosomes of Principal cells are characteristic of cells involved in absorptive functions
  • Rat models have shown that terminal region of ductus possesses the ability to phagocytose & absorb spermatozoa; unknown if significant portion of human ductus deferens possesses sufficient spermiophagy
  • Structure & function of ductus deferens probably depends on androgen stimulation
    • Human ductus deferens converts Testosterone to DHT
    • Castration causes atrophy of ductus deferens; Testosterone treatment causes restoration of ductus deferens
    • Castration and/or Testosterone treatment alters adrenergic contractions of ductus