Compiled from lecture notes, this is a condense but detailed summary of the physiology of the male, including spermatogenesis. Containing an overview of all the content in a logical order, easy to search and use for revision.
Physiology of the male
• Testicular temperature should be 2C lower than core body temperature
• Tight underwear or too much hot bath water/sauna can reduce sperm count
• Prostate gets with bigger with age
• Enlarged prostate = urinary issues
o Higher frequency
o Can’t empty bladder
• Each seminiferous tubule is 0.5m long
• Epididymis is 6m long
• Spermatogenesis
o During embryogenesis, primordial germ cells
move to testes and form immature germ cells
(spermatogonia)
o Spermatogonia found in seminiferous tubules
o Spermatogonia undergo mitosis at puberty
o Spermatogenesis occurs inn testes and is
stimulated by FSH/LH at 13 years old
o Spermatogonia move towards lumen of tubule at puberty before maturation –
spermatogonia enlarge as they move towards lumen and form primary spermatocytes
o Primary spermatocytes undergo meiosis I and form secondary spermatocytes which divide
again to form spermatids
o Spermatids mature into spermatozoa (sperm) (haploid, 23 chromosomes)
o Takes 74 days in total (2-2.5 months)
o LH and FSH decrease at 60 years old s spermatogenesis decreases with age
o Male sperm has Y chromosome, female sperm have X chromosome
• Hormonal role in spermatogenesis
o Testosterone – produced by Leydig cells, needed for growth and division of germ cells
o LH – stimulates Leydig cells for testosterone production
o FSH – help spermatids mature to sperm
o Oestrogens – produced by Sertoli cells, made from testosterone with help of FSH
o Growth hormone – germ cell division (dwarfs are infertile)
• Testosterone levels and sperm production
o ‘Mini puberty’ at birth where testosterone level is high
o Low level of testosterone during childhood until puberty at 13 years old
o Testosterone remains high throughout adult life and starts to decrease at 50 years old
• Sertoli cells
o Large, glycogen-rich cells that extend all the way from the basement membrane to the
lumen inside seminiferous tubules
o Spermatogonia (germ cells) must stay in contact with Sertoli cells to survive, as there is no
direct blood supply – contact maintained by cytoplasmic bridges/envelopes
o Secrete
▪ Androgen-binding protein (ABP) – maintain stable supply of androgens
▪ Inhibin B – inhibits FSH secretion via negative feedback
▪ Activin – function is not clear, thought to stimulate FSH secretion
▪ Mullerian Inhibitory substance (MIS)
• Mullerian ducts form female reproductive tract
• MIS causes regression/degradation of Mullerian ducts to allow male
reproductive tract to grow
• Blood-testis barrier
o Allows easy passage of germ cells
, o Make tubular lumen fluid – poor in protein and glucose, rich in androgens, estrogen, K+ and
inositol
o Protects germ cells from blood-borne noxious agents
o Prevents autoimmunity of germ/sperm cells - own antibodies cannot cross
o Help establish osmotic gradient that moves fluid to lumen
• Sperm morphology
o Acrosome in sperm head has proteolytic and hyaluronidase enzyme to ‘eat’ through zona
pellucida of ovum
▪ Sperm must penetrate granulosa cells then zona pellucida for fertilisation
▪ Once zona pellucida penetrated, Ca2+ ions enter oocyte and cause exocytosis of
granules, which release substances that prevent further sperm penetration
o Sperm tail uses ATP from mitochondria to move
▪ Sperm leaving rete testes are incapable of movement and cannot fertilise egg
(energy conservation)
▪ Sperm leaving epididymis are capable of movement and fertilisation but don’t swim
until after ejaculation (energy conservation)
o Sperm swims at 1-4mm/minute (0.00015 km/h)
o Ion channels in flagellum
▪ CATSPER – Ca2+
▪ Hv1 (H+)
▪ KSper (Slo1/Slo3) – K+
▪ Unknown channel for Na2+
o 25% of sperm are abnormal and defective
▪ Tail too long/short
▪ 2 tails/heads
▪ Small/large head
▪ Small acrosome
▪ Curly tail
▪ Vacuoles in acrosome
▪ Thick/thin/asymmetrical midpieces
▪ Tapered head
▪ Cytoplasmic droplet in midpiece
o Most defective sperm cannot swim properly so don’t reach egg – ‘survival of the fittest’
o If defective sperm does fertilise egg (highly unlikely), foetus unlikely to make it full term
o Low sperm counts
▪ Recent studies show low sperm counts correlated with other health issues
• Body fat/higher BMI
• Bad cholesterol (LDL)
• Metabolic syndrome
▪ 12x more likely to have lower testosterone as well
o Motility
▪ To be motile, sperm need to be in epididymis for 18-24 hours
▪ Inhibitory proteins keep sperm immotile to reserve ATP
▪ Most sperm stored in vas deferens (120-400million/day), for at least 1 month
▪ After ejaculation, sperm increase their motility and can live for 1-2 days in female
genital tract
• Semen composition
o Fluid and sperm from vas deferens (10%)
o Fluid from seminal vesicle (60%) – secret a mucoid material containing
▪ Fructose (energy source)
▪ Citric acid
▪ Fibrinogen
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