spermatogenesis & oogenesis/ovulation Flashcards
How long does it take for a sperm to be produced?
64 days
What stimulation is required to initiate spermatogenesis?
Stimulation from testosterone and also Sertole Cells
What are the precursor cells used by the body to make sperm?
Spermatagonia
How are spermatogonia formed in the testes during embryological development?
Spermatogonia migrate from the yolk sac to the testes and remain dormant until puberty.
What are the 2 fates of spermatogonia when they undergo mitosis?
- Type A spermatogonia - will perpetually undergo mitosis and serve as stem cells
- Type B spermatogonia - will differentiate into diploid primary spermatocytes and from there become sperm
What is the process of spermatogenesis from spermatogonia to spermatozoa?
- spermatogonia form Type A and Type B spermatogonia via mitosis
- Type B differentitae into diploid pimary spermatocytes.
- These undergo meiosis 1 and product 2 haploid secondary spermatocytes
- These undergo meiosis 2 and each form 2 spermatids.
- The final 4 spermatids will undergo spermiogenesis to develop accessory structures to become spermatozoa
Which hormones are involved in the regulation of spermatogenesis?
GnRH, FSH, LH, testosterone, inhibin
What is the role of LH in spermatogenesis?
Stimulates Leydig cells to produce testosterone, which promotes spermatogenesis and male sex characteristics
What is the role of FSH in spermatogenesis?
FSH stimulates Sertoli cells to produce proteins important for nurturing sperm and maintaining fertility. FSH also acts directly on spermatogenic cells to promote spermatogenesis
What is oogenesis?
The process by which oogonia are transformed into mature ova
How are oogonia formed embryologically?
Primordial germ cells form in the embryo at 5-6 weeks and then migrate to the ovaries where they differentiate to form oogonia
What is the embryological process through which oogonia form primary oocytes, of which there is a fixed number at birh?
Oogonia undergo mitosis to produce diploid primary oocytes until the 3rd trimester. These then begin meiosis 1, until a block occurs causing arrest of cell division. This leaves a fixed number of cells arrested at meiosis 1 at birth. The next phase of division will resume at puberty.
How do oocytes sit in the ovaries?
They are surrounded by granulosa cells, forming primordial follicles and then developing further into primary and secondary follicles
What happens to secondary oocytes during the menstrual cycle?
Each cycle, one secondary oocyte in one ovary will develop into a Graafian/Antral Follicle (fully mature follicle). The other secondary follicles will die through atresia
What stimulates primary oocytes to complete meiosis 1 and become secondary oocytes?
A rise in LH and FSH,
What is the ovarian reserve?
The number of oocytes in primordial follicles that remain in the ovaries
What are the cells that make up an antral follicle?
Outer theca cells, and inner granulosa cells
What is the function of theca cells in follicle?
Produce androgens
What is the function of granulosa cells in an antral follicle?
Convert androgens produced by theca cells into oestrogen
When will meiosis II of an oocyte be completed?
Only when a secondary oocyte is fertilised by a sperm
What are the 4 products of male gametogenesis?
4 spermatozoa (so four gametes)
What are the 4 products of female gametogenesis?
1 oocyte (gamete), while the other 3 daughter cells become polar bodies
What are the 2 phases of the ovarian cycle?
Follicular phase, luteal phase
What days of the ovarian cycle make up the follicular phase?
Days 1-14
What days of the ovarian cycle make up the luteal phase?
days 15-28
Which day of the ovarian cycle does ovulation typically occur?
Day 14
What are the steps of the follicular phase of the menstrual cycle, including the hormonal changes at each stage?
- rising levels of FSH from the anterior pituitary encourage the development of a secondary follicle to an antral follicle.
- granulosa cells of the follicle secrete oestrogen, causing levels to rise and feedback to the pituitary to reduce FSH and LH secretion.
- when oestrogen levels get very high on day 13, feedback becomes positive, and instead stimulate LH and FSH release.
- the LH surge causes ovulation, as the follicle burst and the oocyte is released for uptake by the Fallopian tube
- oestrogen levels rapidly decline
What are the two sub-phases of the luteal phase?
Post-ovulatory phase, pre-menstrual phase
What drives the hormonal changes in the luteal phase?
Hormone release from the corpus luteum
What hormones are produced by the corpus luteum?
Progesterone, oestrogen, inhibin
What is the fate of the corpus luteum if fertilisation does not occur?
It will involute to become the corpus albicans, and progesterone and oestrogen levels will decline to stimulate menstruation
What is the fate of the corpus luteum if fertilisation occurs?
Corpus luteum will not degenerate and will continue to produce progesterone to support the pregnancy. After 3 months, the placenta will take over progesterone secretion.
What is the role of progesterone in early pregnancy?
Prepares the uterine wall for pregnancy, and prevents further follicular development and ovulation
What is the menstrual cycle?
A cycle of changes to the endometrium, which occurs simultaneous to the ovarian cycle
Which days of the menstrual cycle does menstruation occur?
Days 1-5 approx.
What are 2 key phases of the menstrual cycle?
The proliferative phase (days 1-14),
The secretory phase (days 15-28)
What triggers menstruation?
Low progesterone levels, as the corpus luteum involutes
What happens to the uterus during menstruation?
Endometrial arteries contract, and there is sloughing of tissue of the endometrium
What triggers the post-menstrual phase of the menstrual cycle (days 6-14)?
Rising oestrogen levels, which is released by the maturing follicle
What happens to the uterus during the post-menstrual phase?
Oestrogen stimulates thickening of the endometrium, and the development of glands and spiral arteries
What changes occur during the secretory phase of the menstrual cycle?
Progesterone secreted by the corpus luteum stimulates thickening of the endometrium and endometrial gland growth and secretion, in preparation for fertilisation and implantation.
