10 - The Gonads I

Question 1

What the primary germ cells?

Answer 1

spermatogonia and oogonia

Question 2

What are the Sertoli cells?

Answer 2

support cells

Question 3

What are the Leydig cells?

Answer 3

steroidogenic cells

Question 4

What is gametogenesis?

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

Answer 4

production of the gametes

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

Question 5

What is steroidogenesis?

What are produced in males and females?

Answer 5

production of steroid hormones

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

Question 6

What are the gonads?

Answer 6

the ovaries or testes

Question 7

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

Answer 7

primordial germ cells, Sertoli cells and leydig cells

Question 8

What causes the differentiation of the gonads?

Answer 8

the presence of the SRY gene

Question 9

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

Answer 9

remains the same (6-7 million)

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

Question 10

Give the steps of spermatogenesis

Answer 10

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

Question 11

Give the steps of oogenesis

Answer 11

• 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

Question 12

Why are polar bodies produced during meiosis in oogenesis?

What happens to the polar bodies?

Answer 12

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

Question 13

Where does spermatogenesis take place?

Answer 13

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

Question 14

Give a brief overview of the development of the testes

Answer 14

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

Question 15

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

Answer 15

2-3º cooler than core temp

this is critical for spermatogenesis

Question 16

What is the structure of the seminiferous tubules?

Answer 16

• 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

Question 17

When looking at the ovaries, what will you see?

Answer 17

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)

Question 18

What is a Graffian follicle?

Answer 18

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

Question 19

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

Answer 19

ovulation - day 14

Question 20

What are the 2 cycles of the menstrual cycle?

Answer 20

ovarian cycle
endometrial cycle (uterus)

Question 21

What are the phases of the ovarian cycle?

Answer 21

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

Question 22

What are the phases of the endometrial cycle?

Answer 22

proliferative phase

secretory phase

Question 23

What are the 2 layers of the endometrium?

Answer 23

superficial epithelial layer

deeper stromal layer

Question 24

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

Answer 24

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

Question 25

What hormones are produced in the luteal phase?

What effect do these have?

Answer 25

progesterone and 17β-oestradiol

they induce the secretory phase

Question 26

What are the effects of progesterone compared to oestrogen?

Answer 26

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

Question 27

Give an outline of the menstrual cycle

Answer 27

• 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

Question 28

When do the levels of oestrogen increase?

Answer 28

just before ovulation and and during the luteal phase

Question 29

When do the levels of progesterone increase?

Answer 29

in the luteal phase - it becomes the dominant hormones

Question 30

When do the levels go gonadotrophins increase?

Answer 30

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

Question 31

What are the graffian follicles made up of?

Answer 31

Thecal cells - the outer layers of the follicle

Granulosa cells - the inner layer

Question 32

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

Answer 32

• 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

Question 33

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

Answer 33

thecal (outer) - LH receptos

granulosa (inner) - FSH receptors

Question 34

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

Answer 34

• 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

Question 35

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

Answer 35

oestrodiol - causes proliferation of the endometrium

Question 36

During the secretory phase, what is the dominant hormone?

Answer 36

progesterone