7. Coitus & fertilisation (lecture) Flashcards
what do spermatogonia (2n) mature to?
spermatozoa (sperm)
how long does it take spermatogonia to mature to spermatozoa?
up to 74 days
50 days in testis, 12-24 days in epididymis
where are spermatozoa produced?
in the seminiferous tubules of the testis
when does sperm production begin?
puberty and continues until death
how many sperm is produced per day?
200-300 million sperm
only 1/2 become viable sperm
where is sperm produced?
in testis (Sertoli cells of seminiferous tubules)
how does sperm production change with age?
slight decrease in quantity and quality with age
describe the process of spermatogenesis: spermatogonium to spermatocyte (step 1)
spermatogonium (2n) –(mitosis)–> primary spermatocyte (2 x 2n)
1 stays in basal lamina and continue to divide (type A)
type B: pushed towards lumen (primary spermatocyte)
describe the process of spermatogenesis: primary spermatocyte (step 2)
primary spermatocyte (2n) –(meiosis I)–> secondary spermatocyte (2 x 1n)
describe the process of spermatogenesis: secondary spermatocyte (step 3)
2 x secondary spermatocyte (1n) –(meiosis II)–> 4 x 1n spermatid
describe the process of spermatogenesis: spermatid (step 4)
4 x spermatid (1n) –(spermiogenesis)–> spermatozoa (4 sperm)
what happens as sperm matures through the seminiferous tubules?
it migrates from the periphery of the seminiferous tubule in towards the centre (lumen)
what are the hormones controlling spermatogenesis?
during puberty, hypothalamus triggered to release GnRH, stimulating anterior pituitary to release LH and FSH
how does release of LH trigger spermatogenesis?
LH (anterior pituitary) –> Leydig cells (testis) –> testosterone (steroidogenesis) –> spermatogenesis
(testosterone diffuse into seminiferous tubules to bind to ABP)
Leydig cells produce testosterone (steroidogenesis)
how does release of FSH trigger spermatogenesis?
FSH produced triggers Sertoli cells to release androgen binding protein (ABP) - which binds to testosterone (diffused in) and triggers sperm production (control gamete production)
(FSH maintains Sertoli cells sensitivity to testosterone via release of ABP, requires testosterone)
aside from ABP, what else do Sertoli cells release?
inhibin: negative feedback on FSH (Sertoli cells)
what effect does testosterone have on Sertoli cells?
positive feedback
if pituitary gland is removed, how can spermatogenesis be initiated?
with FSH and testosterone alone
LH was only to produce testosterone from Leydig cells, to bind to ABP released by FSH
what is the function of testosterone released from Leydig cells
increase sperm viability
effect of testosterone on the feedback loop? (HPG axis)
negative feedback on hypothalamus release GnRH and there ant pit release LH/FSH
structurally, what happens to the HEAD of the spermatid in order to mature to a spermatozoon (spermatozoa) in spermiogenesis?
nuclear condensation
structurally, what happens to the ACROSOME of the spermatid in order to mature to a spermatozoon (spermatozoa) in spermiogenesis?
(acrosome: covering on tip of sperm - degraded by female secretions)
contains golgi apparatus
lysoosome-like (hydrolytic enzymes released to breakdown coroner radiata of oocyte)
enable sperm to penetrate ovum
structurally, what happens to the BODY (midpiece) of the spermatid in order to mature to a spermatozoon (spermatozoa) in spermiogenesis?
mitochondria packed around contractile filaments
provide energy for the sperm to swim up the vaginal canal –> cervix –> uterus –> fallopian tube
structurally, what happens to the TAIL of the spermatid in order to mature to a spermatozoon (spermatozoa) in spermiogenesis?
flagellum produced by microtubules growing from centriole to form axoneme (flagellum made up of many microtubules)
(centrioles –> microtubules –> flagellum –> axoneme)
what happens to the spermatozoa under the influence of testosterone?
cytoplasm and organelles stripped
what happens to spermatozoa?
they are now mature, but still lack motility (infertile)
what is spermation?
spermatozoa released from Sertoli cells into lumen of seminiferous tubule
after the spermatozoa released into the lumen of seminiferous tubule, what happens?
transported to epididymis in testicular fluid (produced by Sertoli cells) by peristaltic contractions
what happens to the spermatozoa within the epididymis?
gain motility and become ‘fertile’ in epididymis
how long can spermatozoa be stored within the epididymis?
stored for several months, no loss of fertility
what does sexual arousal lead to?
contraction of epididymal wall muscle –> expels spermatozoa into ductus (vas) deferens
what happens to the spermatozoa eventually if it is not expelled into the vas deferens?
eventually phagocytosed by epididymal epithelial cells
