Spermatogenesis Flashcards
why do the testes sit outside the body?
thermoregulation
- spermatogenesis can be dramatically affected by heat
- sit outside body cavity as spermatogenesis needs to occur at a few degrees lower than body temp (~34 degrees)
what are the testes made up of?
- Leydig cells
- seminiferous tubules
what do leydig cells produce
- produce androgens - testosterone and DHT
what affects androgen production by Leydig cells
gonadotrophins - LH and FSH - from anterior pituitary
(GnRH from hypothalamus influence gonadotrophin release from AP)
- involves positive and negative feeback
what are androgens essential for the production of
sperm
what are seminferous tubules made up of
- sertolli cells
- spermatogonia stem cells
what do spermatogonia stem cells produce & what is a quality about them?
- produce sperm
- they are self-replacing (ie/ a stem cell)
what do sertolli cells do?
provide support for spermatogenesis
orchestrate spermatogenesis
[LONG] 3 main phases of spermatogenesis
- mitotic proliferation -> produce large numbers of cells (spermatogonia germ cells [located same as spermatogonia stem cells] -> primary spermatocytes (diploid) and spermatogonia germ cells & spermatogonia stem cells -> spermatogonia stem cells and spermatogonia germ cells)
- meiotic division I resulting in secondary spermatocytes (haploid) -> halves chromosome number & generates genetic diversity
- meiotic division II resulting in round haploid spermatids (haploid)
- spermiogenesis -> turning spermatocytes into sperm ie/ spermatids into spermatozoa
describe structure of seminferous tubules
- spermatogonia at base of seminiferous tubule
- Sertolli cells extend from bottom through to lumen (fluid filled cavity in centre)
- various cell types within which are different types of sperm cells that developing
- once sperm exits into lumen
3 main phases of spermatogenesis
- mitotic proliferation producing large number of cells
- meiotic division halving chromosomes and generating genetic diversity
- spermiogenesis turning spermatocyte into sperm
meiotic division halves chromosome number and generates genetic diversity
- primary spermatocytes undergo meiosis I to form 2 secondary spermatocytes (diploid -> haploid)with genetic diversity
- meiosis II to form spermatids
NOTE - chromosome from 2n to n & recombination
- 2 haploid spermatids per secondary spermatocyte
mitotic proliferation produces large number of cells
- spermatogonia stem cells are self-replacing (divide into themselves partially)
- spermatogonia (diploid) also differentiate into primary spermatocytes (diploid)
- spermatogonia -> type B spermatogonia -> intermediate spermatogonia -> primary spermatocyte
spermiogenesis
- shape of spermatid changes from round to elongated ie/ to spermatozoon - chromatin condenses and cytoplasm removed
- acrosome forms - containing enzymes for penetrating oocyte/egg membranes at fertilisation
- tail forms & mid piece forms
what does the mid piece in spermatozoa do?
subsequently, what is importance of tail?
- contains mitochondria -> providing energy necessary for whiplash motion of tail
- whiplash motion of tail (from structure) allows sperm cell to move efficiently toward egg during fertilisation
what does it mean for spermatogenesis to be continuous spatially
- see sperm at different stages of development simultaneously along seminiferous tubules
- allowing sperm to be produced continuously
what does it mean for spermatogenesis to be continuous temporally
production of sperm cells occurs continuously from puberty throughout man’s life
- ongoing generation of sperm cells (not finite number)
how long is a spermatogenic cycle
between 63-72 days
how much sperm being produced everyday?
about 300 million sperm
where do the spermatozoa go from seminiferous tubules
- exit the testes into epididymus
- where spend ~6 days undergoing further maturation
what is involved in the further maturation of spermatozoa in epididymus
- removal & addition of proteins
- gain ability to swim progressively
- gain potential to fertilise
It is androgen dependent
where does final maturation (capacitation) of spermatozoa occur?
in female reproductive tract
what is semen made up of
seminal plasma combine with spermatozoa at ejaculation
where is seminal plasma produced
in male accessory glands, particularly prostate and seminal vesicles
function of seminal plasma
list one negative
- fluid vehicle for sperm
- buffering (maintain pH env for viability of sperm), antioxidant, metabolic support for sperm
- contain immune cells
- ## important for establishment of implantation and pregnancy
- vehicle of transfer of infection eg/ HIV
how long is sperm viable for & how long is egg viable for
sperm ~2 days
egg ~1 day
characterisations of “normal” and “sub fertile” semen
at least list the characteristics
ejaculate values
NORMAL
volume: 2-5mL
sperm conc: 100-700 million sperm
sperm motility: greater than 50% progressive motility
abnormal sperm: greater than 30%
SUBFERTILE
volume: less than 1.5mL
sperm conc: 40 million sperm
sperm motility: less than 32% progressive motility
abnormal sperm: greater than 4%
around what age does sperm fertility / male fertility decline?
around 40 years of age
what is reduced sperm fertility characterised by
- reduced semen volume
- reduced sperm number
- increase in sperm abnormalities
(missing semen progressive motility)
what are factors that can negatively influence spermatogenesis temporarily and / or long-term
- infection
- temperature (hot bath)
- chemical exposure
- smoking
- alcohol
- obesity
how common is infertility (stats)
- 1 in 6 couples infertile globally
when is infertile diagnosis made
after 12 months of unprotected sex with absence of successful pregnancy (can include fertilisation occurrence but unsustained pregnancy)
proportion of which gender infertile
1/3 female, 1/3 male, 1/3 both / unknown
what is a problem with males and infertility
- males typically do not think / unaware that they’re infertile
