Gonads (1) 10 Flashcards
What are the functions of the gonads?
1) gametogenesis
2) steroidogenesis
What is atresia?
When germ cells degenerate and die
What is the order in spermatogenesis?
1) Germ cell
2) Spermatogonia
3) Primary spermatocytes
4) Secondary spermatocytes (haploid)
5) Spermatids
6) Spermatozoa
Spermatogonesis background:
- 70 days
- occurs after puberty when FSH is first released
- high numbers throughout life
Describe Sequence of Oogenesis
1) Germ cell
2) oogonia
3) Primary oocytes
4) Secondary oocyte + polar body (haploid)
5) Ovum + 2nd Polar body
Oogenesis background:
- Primary oocytes are formed before birth (2 million)
- meiosis completed during ovulation
- by puberty there is only 0.5million
What steroids to the testes produce?
Mainly androgens
small amounts of oestrogen and progesterones
What steroids do the ovaries produce?
Mainly oestrogens and progesterones
small amounts of androgens
Where does spermatogenesis take place in the testes?
Semineferous tubules
What is the pathway after spermatogenesis?
1) Seminiferous tubules
2) Rete Testis
3) Vasa efferentia
4) Vas deferens
5) urethra
Where are the spermatozoa stored?
Epididymis
Where do the testes develop?
In the abdomen and descend into the scrotum just before birth
What is the function of Sertoli cells in the seiniferous tubules?
They are connected together via tight junctions that keep a blood-testis barrier to keep out large proteins such as antibodies. Therefore, spermatozoa are protected from immune reactions.
How do spermacytes move from behind the Sertoli cells to the tubule?
Spermatogonia are engulfed and enclosed within the cytoplasm where the rest of spermatogenesis actually occurs. The sertoli cells provide structural and metabolic support
What is the function of Leydig cells?
These are steroidogenic cells that contain enzymes allowing synthesis and excytosis of testosterone. testosterone is needed for spermatogenesis to occur.
What are the differences between Sertoli and Leydig cells?
Sertoli:
- synthesis FSH and androgen receptors. In response to FSH, they produce Inhibin that has -ve feedback on FSH production.
Leydig:
- synthesis LH receptors and produce androgens (testosterone) in response to LH
Describe the structure of the Graffarian Follicle
Ovum surrounded by follicular fluid surrounded by granulosa cells surrounded by thecal cells
Ovaries and atresia use?
In the ovaries, there are follicles at various stages of development and atresia at all times.
What are steroids synthesised from?
Cholesterol
What is the follicle developed into after ovulation?
Corpus luteum
What steroids are formed in the gonads?
- Progestogens (C21)
- Androgens (C19)
- Oestrogens (C18)
Common development between gonads and adrenals?
The first four reactions from cholesterol to form steroid hormones
What are the gonadal end products of steroid formation?
- porgesterone
- 17beta-oestradiol
- testosterone and subsequently dihydrotestosterone
How long does the menstrual cycle take?
28 days with ovulation occurring at day 14
What are the two events in the menstrual cycle?
- Ovarian cycle and endometrial cycle
Occurrences in ovarian cycle:
1) follicular phase
2) ovulation
3) luteal phase
Occurrences in endometrial cycle:
1) proliferative phase
2) secretory phase
What are the layers of the endometrium?
Superificial epithelial layer and a deeper stromal layer
Which hormones and when do they cause the link between the ovarian and the endometrial cycles?
17b-oestrodiol from the follicular phase causes the proliferative phase.
Then, 17b-oestrodiol and progesterone from the luteal phase cause the secretory phase in the endometrial phase
What is the split of the ovarian cycle?
1st 14 days = follicular phase
2nd 14 days = luteal phase
Describe the hormone level variations in the menstrual cycle:
1) FSH levels slightly raised at start to encourage development
2) As follicles start growing, 17b-oestrodiol is produced. this has a -ve feedback on gondaotrophin release (LH/FSH)
3) As the follicles grow, one becomes dominant and the others undergo atresia. This follicle then produces lots of oestrogen
4) If oestrogens are high enough for >36 hours, there is a switch from the -ve to the +ve feedback. this induces a surge of gonadotrophins (LH/FSH)
5) This surge induces ovulation
6) after ovulation, follicle forms corpus luteum which continues to form 17b-oestrodiol and progesterone in large quantities
7) progesterone and oestrogen have a -ve feedback on gondatrophins
8) if ovum is not fertilised, oestrogens/progesterones start to fall causing menstration of the endometrium
9) There is less -ve feedback so LH/FSH levels start to rise
10) as gonadotrophins rise, may be a small surge of 17-hydroxyprogesterone which adds to =ve feedback of oestrogen
11) an increase in body temperature can be measured after ovulation
Describe follicle sequence of events:
1) Pre-antral follicle (containing ovum)
2) Early-antral follcile (containing ovum/thecal/granulosa)
3) Late-antral follicle (containing ovum/thecal/granulosa but larger)
4) Graffarian follicle (see above with follicular fluid)
5) ovum (after ovulation) and corpus luteum
What stimulates ovum to complete first meiosis?
Surge of LH
Difference between thecal and granulosa cells?
Thecal cells (outer) have LH receptors
Granulosa cells (inner) have FSH receptors. Granulosa cells contain aromatase which converts androgens into 17b-oestrodiol
What is the difference between Proliferative and Secretory phases?
Proliferative - oestrogen is the dominant influence
Secretoy - progesterone is the dominant influence
