Oogenesis and Menstruation

Question 1

What are primordial germ cells?

Answer 1

Earliest undifferentiated sex cells

Question 2

Describe the embryology of the primordial germ cell?

Answer 2

1. Originate in epiblast
2. 3rd week - migrate to yolk sack close to allantois
3. 4th week - travel along dorsal mesentery of hindgut
4. 5th week - Arrive at primitive gonads
5. 6th week - invade genital ridges

Question 3

What is oogenesis?

Answer 3

Primordial germ cells in ovaries differentiate into Oogonia

- Begins shortly after arrival in ovary

Question 4

Describe oogenesis?

Answer 4

1. Begins in the embryo when primordial germ cells undergo mitotic divisions to produce diploid oogonia.
2. Each oogonium will develop into primary oocyte by the time of birth of the female, resulting in all potential ova being present in the ovaries at birth (production of oogonia stops and never resumes)
3. Between birth and puberty, primary oocytes enlarge and their surrounding follicles grow: They replicate their DNA and enter Prophase and remain there until activated by hormones (Puberty)
4. After puberty during each ovarian cycle, FSH stimulates a follicle to enlarge and the primary oocyte completes meiosis I
5. LH triggers ovulation and the secondary oocyte is released from the follicle and is arrested in metaphase I until fertilization
6. If the sperm cell penetrates the secondary oocytes membrane, meiosis II will occur

Question 5

How many oogonia are present by 5 months of gestation?

Answer 5

6 – 7 million

Question 6

How many primary oocytes are present at birth?

Answer 6

About 700 000 – 2 million primary Oocytes

Question 7

How many primary oocytes are present at puberty?

Answer 7

400,000

Question 8

How many primary oocytes are ovulated?

Answer 8

<500

Question 9

How many primary oocytes are fertilized?

Answer 9

<15

Question 10

What is an ovarian follicle?

Answer 10

primary oocytes surrounded by epithelial cells (follicular cells)
- right before birth

Question 11

Describe ovarian follicles?

Answer 11

• Follicle occur in superficial ovarian cortex

- Basal lamina surrounds follicular cells separating follicle & vascularized stroma

Question 12

What are primordial follicles?

Answer 12

follicles formed during fetal life

Question 13

What stimulates the follicular growth of primordial follicles?

Answer 13

FSH

Question 14

Follicular growth of primordial follicles involves?

Answer 14

1. Oocyte growth
2. Follicular cells proliferation
3. Differentiation of stromal fibroblasts around follicle
4. Selection of dominant follicle

Question 15

What are the 2 sexual cycles in females?

Answer 15

1. ovarian cycle

2. uterine (menstrual) cycle

Question 16

Name the phases of the Ovarian cycle?

Answer 16

1. folicular phase

2. luteal phase

Question 17

Name the phases of the menstrual cycle?

Answer 17

1. Menstrual phase
2. Proliferative phase
3. Secretory phase

Question 18

What is the ovarian cycle?

Answer 18

Monthly series of events associated with maturation of egg
1. Follicular Phase - Follicular growth (day 1 - 14)
2. Luteal phase - Corpus luteum activity
(days 14 - 28)

Question 19

Describe the primordial follicle?

Answer 19

Has single layer of flattened follicle cells

– fetal period

Question 20

Describe the formation of unilaminar primary follicle?

Answer 20

Follicular cells undergo mitosis and form a simple cuboidal epithelium around growing oocyte

Question 21

Describe the formation of multilaminar primary follicles?

Answer 21

• Follicular cells continue to proliferate forming a stratified follicular epithelium called GRANULOSA
• Oocyte produces zona pellucida between oocyte and first layer of granulosa cells (surrounds the oocyte)
• follicular theca forms from differentiation of stromal cells (immediate cells outside each growing primary follicle)

Question 22

What is the zona pellucida?

Answer 22

a thick matrix composed of 4 glycoproteins
(ZP1 - ZP4)
- ZP3 & ZP4 serves as receptors for sperm

Question 23

Describe the differentiation of follicular theca?

Answer 23

further differentiates into

1. theca interna - well vascularized endocrine tissue
2. theca externa - fibroblasts & smooth muscle

Question 24

Describe the formation of the secondary follicle?

Answer 24

Move deeper in cortex, follicular fluid accumulates between cells
- an antrum forms (all cavities unite to form a large one)

Question 25

What is the other name for secondary follicle?

Answer 25

Antral or Vesicular Follicle

Question 26

Describe the formation of a mature (Graafian after 90 days) follicle?

Answer 26

Cumulus oophorus (small hill-like or elevated thickening structure formed by granulosa cells) protrudes into growing antrum - corona radiate forms from granulosa cells immediately surrounding zona pellucida Note: Corona radiate accompanies oocyte as it is ovulated

Question 27

When does ovulation occur?

Answer 27

midway through the menstrual cycle, around day 14

Question 28

Describe what happens just before ovulation to oocytes?

Answer 28

1. Oocyte complete meiosis I - One Daughter cell retains almost all the cytoplasm & becomes Secondary Oocyte. - The other becomes the first polar body (a small nonviable cell) 2. Oocyte begin Meiosis II but arrests at Metaphase II

Question 29

What is the luteal phase?

Answer 29

Post-ovulation, ruptured follicle becomes corpus luteum

Question 30

Corpus luteum secretes what hormones?

Answer 30

progesterone and estrogen

Question 31

What happens to the corpus luteum if pregnancy fails?

Answer 31

corpus luteum degenerates & the remnant is corpus albicans (scar)

Question 32

What happens to the corpus luteum if pregnancy succeds?

Answer 32

corpus luteum persists until placenta is ready to take hormonal duties

Question 33

Name the hormones that regulate the ovarian cycle?

Answer 33

1. Gonadotropin-releasing hormone (GnRH) 2. Pituitary gonadotropins (FSH, LH) 3. ovarian Estrogen & Progesterone

Question 34

Follicular development depends on which hormones?

Answer 34

FSH from pituitary grand whose secretion is stimulated by GnRH

Question 35

Granulosa cells produce?

Answer 35

Inhibin | - hormone responsible for negative feedback of Estrogen & Progesterone

Question 36

Which hormone assists in the development of vesicular follicles?

Answer 36

estrogen

Question 37

What is the uterine cycle?

Answer 37

Series of cyclic monthly endometrium changes - Responds to changes in ovarian hormonal levels in blood

Question 38

Describe the proliferative (Estrogenic or Follicular) phase?

Answer 38

1. Endometrium rebuilds itself 2. Under influence of rising estrogen levels; endometrium generates new functional layer 3. Endometrium becomes thick & well vascularized - Ovulation occurs at end of this stage (day 14) in response to LH surge

Question 39

Function of estrogen in the proliferative phase?

Answer 39

1. induces synthesis of progesterone receptors in endometrial cells 2. cause thick & sticky cervical mucus to become thin to facilitate sperm passage

Question 40

When does the proliferative phase take place?

Answer 40

days 6 - 14

Question 41

Describe the secretory (progestational) phase?

Answer 41

- Endometrium prepares for implantation of embryo - Rising levels of progesterone converts functional layer of endometrium to a secretory mucosa and inhibits LH release by anterior pituitary - Uterine glands secrete nutritious glycoproteins into the uterine cavity to sustain embryo until it has implanted

Question 42

What happens in the secretory phase if fertilization has not occured?

Answer 42

- corpus luteum begins to degenerate toward the end of secretory phase as LH levels decline - Progesterone levels fall, depriving endometrium hormonal support, hence, menstruation begins on day 28

Question 43

What happens in the secretory phase if fertilization takes place?

Answer 43

human chorionic gonadotropin from embryo prevents corpus luteum degeneration until 4th month when placenta takes over progesterone production

Question 44

When does the menstrual cycle start again?

Answer 44

the first day of menstrual flow

Question 45

What does does the secretory phase occur?

Answer 45

days 15 - 28

Question 46

Describe the menstrual phase?

Answer 46

- Uterus sheds its functional endometrium layer - Ovarian hormone levels decreases, endometrium enters ischemic phase. - Functional layer of endometrium detaches from uterine wall accompanied by bleeding for 3-5 days - Detatched tissue & blood pass out as menstrual flow which marks beginning of new cycle

Question 47

What is amenorrhea?

Answer 47

absence of menstrual periods

Question 48

What is dysmenorrhea?

Answer 48

Painful menstrual periods due to uterine contractions

Question 49

What is menorrhagia?

Answer 49

heavy or prolonged periods

Question 50

What is infertility?

Answer 50

not getting pregnant despite having carefully timed unprotected sex for one year

Question 51

What are assisted reproduction techniques?

Answer 51

hormones like FSH administered to induce multi-follicular growth in females or inducing sertoli cells function in males