10 - The Gonads I Flashcards by Saira C

What the primary germ cells?

spermatogonia and oogonia

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What are the Sertoli cells?

support cells

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What are the Leydig cells?

steroidogenic cells

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What is gametogenesis?

What are the processes called in males and females and what are the products of these called?

production of the gametes

males = spermatogenesis -----> mature spermatozoa 
females = oogenesis -----> ripe ova

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What is steroidogenesis?

What are produced in males and females?

production of steroid hormones

males = androgens (and small amounts of oestrogen and progesterone)
females = oestrogens and progesterone (and small amounts of androgens)

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What are the gonads?

the ovaries or testes

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6 weeks in utero, what are the gonads made up of?

primordial germ cells, Sertoli cells and leydig cells

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What causes the differentiation of the gonads?

the presence of the SRY gene

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What happens to the number of spermatogonia is males throughout life?

remains the same (6-7 million)

NOTE: during childhood, they have a dormant period and are not activated until puberty

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Give the steps of spermatogenesis

germ cells —–> spermtogonia (diploid) —–> 1º spermatocytes (diploid) —–> 2º spermatocytes (haploid) —–> spermatids —–> spermatozoa

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Give the steps of oogenesis

germ cells multiply to produce oogonia (diploid) —–> 1º oocytes (diploid)
the 1º oocyte enters straight into meiosis, but are halted at prophase
a layer of cells form around them

(all of this is before birth)
they are dormant for 12-50 years

at 12 years, some are rescued under the influence of FSH and development continues
at ovulation, thye first meiotic division is completed —–> 2º oocyte and a polar body
2º oocyte enter meiosis II (the division doesn’t complete until fertilisation) —–> 2º oocyte and a polar body

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Why are polar bodies produced during meiosis in oogenesis?

What happens to the polar bodies?

there is unequal distribution of the cytoplasm, the secondary oocyte or the ovum (depending on which meiotic division it is) retain all the cytoplasm. The polar body just contains the chromosomes.

These cells eventually die off

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Where does spermatogenesis take place?

in the Sertoli cells of the (coiled) seminiferous tubules of the testes

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Give a brief overview of the development of the testes

develop in the abdomen and descends into the scrotum just before birth

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What is the temperature in the scrotum and why is this important?

2-3º cooler than core temp

this is critical for spermatogenesis

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What is the structure of the seminiferous tubules?

on the outside, there is a sheath of connective tissue
underneath it is a layer of spermatogonia
under that is a layer of elongated Sertoli cells
the sertoli cells are connected by tight junctions (spermatogonia can get through this barrier)
there are leydig cells outside the seminiferous tubules

When looking at the ovaries, what will you see?

follicles at all different stages of development
some follicles undergoing atresia
remnants of the corpus luteum (a hormone-secreting structure that develops in the ovary but degenerates after a few days unless pregnancy has begun)

What is a Graffian follicle?

a follicle that has reached its maximum size and is now ready for ovulation

What is the most important reproductive event during the menstrual cycle and what day does it occur on?

ovulation - day 14

What are the 2 cycles of the menstrual cycle?

ovarian cycle
endometrial cycle (uterus)

What are the phases of the ovarian cycle?

follicular phase
ovulation
luteal phase
(both phases are equal in length - 14 days - with ovulation on day 14)

What are the phases of the endometrial cycle?

proliferative phase

secretory phase

What are the 2 layers of the endometrium?

superficial epithelial layer

deeper stromal layer

What causes the effects seen in the proliferative phase in the endometrial cycle?
How does it cause proliferation?

oestrogens
increase in mitosis
increase in the number of progesterone receptors and in oestrogen receptors

What hormones are produced in the luteal phase? | What effect do these have?

progesterone and 17β-oestradiol they induce the secretory phase

What are the effects of progesterone compared to oestrogen?

progesterone reverses the effects of oestrogen (it reduces the number of oestrogen receptors so reduces the proliferation that oestrogen causes) it also increases the secretory activity of the cells in the myometrium- the glands become wider and produce various substances which make the environment suitable for implantation

Give an outline of the menstrual cycle

- FSH levels slightly raised at the beginning - this causes dormant follicles to develop - developing follicles produce 17β-oestradiol (has negative feedback on GnRH) - dominant follicle is selected and the rest undergo atresia - dominant follicle releases high levels of 17β-oestradiol VERY HIGH LEVELS HAVE A POSITIVE FEEDBACK EFFECT - surge of gonadotrophins - stimulates ovulation - the empty follicle becomes a corpus luteum, and continues to produce high levels of 17β-oestradiol and produces progesterone - negative feedback on the gonadotrophins - no fertilisation= oestrogen and progesterone levels fall - causes changes in the endometrium that lead to menstruation - low progesterone and oestrogen = high LH and FSH

When do the levels of oestrogen increase?

just before ovulation and and during the luteal phase

When do the levels of progesterone increase?

in the luteal phase - it becomes the dominant hormones

When do the levels go gonadotrophins increase?

during ovulation and at the end/beginning of the cycle (FSH in particular)

What are the graffian follicles made up of?

Thecal cells - the outer layers of the follicle | Granulosa cells - the inner layer

Give the sequence of events that leads to ovulation (ovum release)?

- under the influence of FSH, the follicles get bigger until they eventually reach their maximum size - the follicle produces high levels of 17β-oestradiol, +ive feedback -----> stimulates GnTP - LH surge causes rupture of the follicle and release of the egg -

What are the receptors on the surface of thecal cells and granulosa cells?

thecal (outer) - LH receptos | granulosa (inner) - FSH receptors

How do the 2 cells of the follicles work together? What do they produce when the gonadotrophins bind?

- LH stimulation of thecal cells = steroid hormone synthesis and production of androgens - FSH stimulation of granulosa cells = aromatase enzyme - aromatase enzymes convert androgens into oestrodiol

During the proliferative phase, what is the dominant hormone? What does it cause?

oestrodiol - causes proliferation of the endometrium

During the secretory phase, what is the dominant hormone?

progesterone