Week 5 - C - Oogenesis, spermatogenesis, menstrual cycle and hormonal control

Question 1

When does oogenesis begin? What is the immature female reproductive cell that gives rise to primary oocytes by mitosis?

Answer 1

Begins in utero

Oogonium

Question 2

After the mitotic phase where the oogonium becomes a primary oocyte, what phase is the process of oogenesis suspended in until puberty where one oocyte is chosen per month to undergo ovulation?

Answer 2

Supsended in prophase 1

Question 3

Once meiosis continues prior to ovulation, what does the primary oocyte divide to form? What phase does the secodnary oocyte arrest in?

Answer 3

Primary oocyte divided to form secondary oocyte and first polar body

Secondary oocyte arrests in metaphase II

Question 4

Oogensis is completed at fertilization, what happens to the secondary oocyte?

Answer 4

If the secondary oocyte is fertilized, the cell continues through the metpahase II, completing meiosis, producing a second polar body and a fertilized egg containing all 46 chromosomes of a human being, half of them coming from the sperm.

Question 5

What does the presence of two polar bodies signify?

Answer 5

Presence of two polar bodies signifies sperm entry and the completion of 2nd meiotic division.

Question 6

What is the earliest recognisable female germinal cell? It is capable of mitosis

Answer 6

Primordial germ cell

Question 7

How long does the ovarian cycle last and what are the two stages?

Answer 7

Lasts approximately 28 days and the two phases are the follicular phase and the luteal phase

Question 8

How long does the process of spermatogenesis take? and when does the process begin?

Answer 8

Spermatogenesis takes around 72 days and begins at puberty

Question 9

Describe the process of spermatogenesis from spermatogonium to the formaton of sperm?

Answer 9

Spermatogonium(spermatogonia - plural) goes through mitosis to form primary spermatocyte

which goes through meiosis I to form secondary spermatocyte

which then goes through meiosis II to form a spermatid

which differentiates to form sperm

Question 10

Where does spermatogenesis occcur?

Answer 10

Spermatogenesis occurs in the wall of the seminiferous tubules , with stem cells at the periphery of the tube and the spermatozoa (sperm) at the lumen of the tube.

Immediately under the capsule of the tubule are diploid, undifferentiated cells.

These stem cells, called spermatogonia

Question 11

What happens during the follicular phase of the menstrual cycle? What signifies the end of the follicular phase?

Answer 11

During the follicular phase, mutartion of the egg takes place ready for ovulation

Ovulation signifies the end of the follicular phase

Question 12

What is the name for the degeneration of those ovarian follicles which do not ovulate during the menstrual cycle?

Answer 12

Atresia

After puberty about 400 will be ovulated, the rest (99.98%) will undergo the process known as atresia

Question 13

What happens during the second part of the menstrual cycle, the luteal phase?

Answer 13

• Development of corpus luteum – from the left behind follicular cells after ovulation

Question 14

What is the process of which the left behind follicular cells transform to becom the corpus luteum known as?

Answer 14

Process is known as luteinisation

Question 15

What hormone is secreted in the follicular phase and why and which is secreted in the luteal phase and why?

Answer 15

Oestradiol is secreted in the follicular phase to thicken the endometrium and in the luteal phase, the corpus luteum secretes progesterone to prepare the uterine lining for implantation of the egg - maintains the endometrium and maintains pregnancy

Question 16

After ovulation how long does the corpus luteum grow for? How long will the corpeus luteum survive after ovulation?

Answer 16

Corpeus luteum will grow for 8-9days after ovulation and will last less than 14 if fertilisation does not occur

Question 17

If there is no production of which hormone by day 12 from the embryo? this causes the corpus luteum to degenerate What does the corpus luteum become? (the hormone is also known as the pregnancy hormone)

Answer 17

If there is no production of - human chorionic gonadotropin – pregnancy hormone

The corpus luteum degnerates forming the corpus albicans

Question 18

In the hormonal control of the menstrual cycle, what does the hypothalamus secrete to act on the pituitary gland? What is then secreted by the pituitary gland?

Answer 18

Hypothalamus secreted gonadotropin releasing hormone (GnRH)

This acts on the anterior pituitary to release Lutienising hormone and Follicle stimulating hormone (LH and FSH)

Question 19

What does FSH act on the ovary to stimulate the development of?

Answer 19

Acts on ovary to stimulate the development of follicles - ovarian follicle is what contains the immature egg - the oocyte

Question 20

What does LH act on the ovary to stimulate? What hormone do both LH and FSH stimulate the secretion of?

Answer 20

Stimulates follicle maturation, ovulation and the development of the corpus luteum

Both hormones work to stimulate the secretion of oestradiol

Question 21

Following the release of the pituitary gonadotropins - up to 15 follicles are rescued and begin to mature – theca cells develop What do the theca cells cause and what is the function of the granulosa? What is the other name for the follicular cells?

Answer 21

The theca cells produce androgens which is converted by the enzyme aromatase to oestrogen

Follicular cells also known as granulosa

Question 22

How does the release of FSH cause the production of oestradiol?

Answer 22

The sex steroid production consists of follicle-stimulating hormone (FSH) stimulating granulosa cells to convert androgens (coming from the theca cells) to estradiol by aromatase during the follicular phase of the menstrual cycle.

Question 23

Oestrogen is secreted primarily by the ovaries, what other two organs secrete oestrogen?

Answer 23

The adrneal cortex and the placenta in pregancny

Question 24

What does the estrogen do to the cervical mucus? What effect does the feedback have on the pituitary hormones?

Answer 24

Eostrogen thins the cervical mucus so it is ready for fertilisation of egg

It has a negative feedback on FSH and prolactin however stimulates secretion of LH

Question 25

After pregnancy there is a low concentration of oestrogen, what does this stimulate the secretion of?

Answer 25

This stimulates the secretion of prolactin - hence milk from mmamnry lands

Question 26

As oestrogen is produced by the follicle, once the protective follicle is formed and ovulation occurs, what happens to the oestrogen levels? What happens to the LH and FSH levels during ovulation?

Answer 26

The oestrogen levels fall

Both LH and FSH levels also fall

Question 27

There is a surge in LH levels prior to ovulation, how long after this surge does ovulation take place? When can progesterone levels be measured after ovulation as it peaks due to the formation of the corpeus luteum? (stimulated by LH)

Answer 27

Takes place 36.5 hours after surge

Measure the progesterone levels at day 21

Question 28

What does a high FSH level signify?

What day of cycle would we measure progesterone to assess if ovulation has taken place?

How do we detect ovulation?

What day of the menstrual cycle does ovulation normally take place?

Answer 28

High FSH level signifies oovualtion is about to occur

Measure progesterone on day 21

Ovulation detected by LH levels

Ovulaton normally takes place on day 14

Question 29

Once sperm is produced, what is the route of release?

Answer 29

Seminiferous tubules to head of epididymis,

travels down the epididyis then up via the vas deferens

to reach the seminal vesicle which adds fluid (making it semen) ,

past the prostate gland and through the internal urethral sphincter to the external urethral sphincter

Question 30

What is the function of LH and FSH in males? They act on different cells

Answer 30

LH acts on the Leydig cells which regulates testosterone secretion

FSH acts on Sertoli cells to enhance spermatogenesis – essential for spermatid re-modelling

Question 31

Once LH acts on the Leydig cells to produce testosterone, what does the tesosterone act on?

Answer 31

Testosterone acts on the Sertoli cells to aid with spermatogenesis