6- Spermatogenesis Flashcards
compare oogonia and spermatogonia
both are laid down in the foetus
oogonia begin meiosis to make oocytes before birth, remain in meiotic arrest until puberty. sperm begin meiosis to make spermatocytes after puberty.
spermatogonia can divide meiotically to make more spermatogonia. oogonia can’t make more once they’ve entered meiosis.
lifetime supply of spermatogonia. limited supply of oogonia.
one good quality egg is produced, many low quality sperm can be produced
how long does a cycle of spermatogenesis take?
approx. 74 days
what is unique about spermatogenesis?
each cell division from a spermatogonium is incomplete - spermatogonia are all connected by cytoplasmic bridges forming a syncytium
allows synchronous development, varying stages of development across the syncytium for a continuous supply of sperm
describe the sequence of events in spermatogenesis
- spermatogonia as the initial primary germ cells on the basement membrane undergo mitotic division = form diploid cells with a darker appearance called ad spermatogonia
- ad spermatogonia differentiate into ap spermatogonia - become paler as they’re going to differentiate and become primary spermatocytes
- primary spermatocytes form with 46XY chromosomes, move to the ad-luminal compartment - undergo meiosis I
- secondary spermatocytes form - 2 non-identical = 23X and 23Y - and undergo meiosis II
- 4 haploid spermatids form. spermatids have differentiated from a rounded to elongated structure.
- spermatids lose cytoplasm, condense their nucleus and grow an acrosome and tail = become mature sperm
this process occurs consecutively across the lumen - sperm in different stages of development are connected by cytoplasmic bridges forming a syncytium
allows the constant production of sperm
what happens to sperm that isn’t ejaculated?
reabsorbed
ejaculated during sleep involuntarily
the hormonal control of spermatogenesis
Leydig cells respond to LH - convert cholesterol into androgens
some androgens are circulated, some taken to Sertoli cells, some used to regulate HPO negative feedback
androgens stimulate Sertoli cells to start and control spermatogenesis
FSH also binds to Sertoli cells - help maintain a functional Sertoli population
mechanism/ nervous system control of erection
parasympathetic NS control
arteries leading into the penis dilate, veins for venous drainage constrict
ischiocavernous and bulbospongiosus muscles constrict to restrict venous drainage
spongy tissues of the corpus cavernosum and spongiosum fill with blood
cause an erection
mechanism/ nervous system control of ejaculation
sympathetic NS control, some somatic NS control
smooth muscle contractions move sperm from the epididymis, through vas deferens, seminal vesicles, prostate gland and to the urethra
glandular secretions expelled through ejaculation
perineal branch of the pudendal nerve (somatic nerve) involved in the final part of ejaculation
how does the bulbourethral gland contribute to ejaculate?
produces pre-ejaculate = clear, viscous, high salt secretion
fluid helps lubricate the urethra, neutralises urine and prevents friction burns with sperm as they move down the urethra
how do the seminal vesicles contribute to ejaculate?
its secretions comprise 50-70% ejaculate = contains proteins, enzymes, fructose, prostaglandins
fructose for energy
high pH protects against the acidic environment of the vagina
seminal vesicle fluid released by sympathetic smooth muscle contractions
how does the prostate (gland) contribute to ejaculate?
secretes milky white fluid - constitutes 30% of seminal fluid
includes proteolytic enzymes, phosphatase, prostatic acid, prostate-specific antigens = involved in liquefication
high zinc content = anti-bacterial
where are spermatogonia found within the seminiferous tubule?
on the basement membrane as primary germ cells
