Reproductive Physiology Part 2

Question 1

What is oogenesis?

Answer 1

The process of formation and maturation of the female gamete (ovum) in the ovaries.

Question 2

Where in the ovary does oogenesis occur?

Answer 2

In the ovarian cortex, within structures called follicles.

Question 3

What are oogonia?

Answer 3

The diploid germ cells that arise from primordial germ cells and undergo mitosis to increase their number before birth.

Question 4

Around what fetal age do oogonia peak in number, and roughly how many are there?

Answer 4

About the 5th month of fetal development, reaching ~6–7 million oogonia.

Question 5

Into what do oogonia differentiate, and at what meiotic stage do they arrest before birth?

Answer 5

They differentiate into primary oocytes and arrest in prophase I (dictyotene stage).

Question 6

What structure forms when a primary oocyte is surrounded by granulosa cells?

Answer 6

A primordial follicle.

Question 7

Which hormones stimulate follicle growth and trigger ovulation?

Answer 7

FSH (Follicle-Stimulating Hormone) stimulates growth; LH (Luteinizing Hormone) triggers ovulation and resumption of meiosis I.

Question 8

What are the products of the first meiotic division of a primary oocyte?

Answer 8

A large secondary oocyte (haploid) and a small first polar body.

Question 9

At what stage does the secondary oocyte arrest, and when is meiosis II completed?

Answer 9

It arrests at metaphase II and completes meiosis II only upon fertilization, yielding the mature ovum and a second polar body.

Question 10

Why are polar bodies formed during oogenesis?

Answer 10

To discard the extra haploid sets of chromosomes while retaining most cytoplasm in the single functional ovum.

Question 11

How many functional gametes result from one oogonium compared to one spermatogonium?

Answer 11

Oogenesis yields 1 ovum per oogonium; spermatogenesis yields 4 sperm per spermatogonium.

Question 12

Describe two key differences between oogenesis and spermatogenesis.

Answer 12

1. Timing: Oogenesis begins before birth and has long arrests; spermatogenesis begins at puberty and is continuous.
   
   2. Cytoplasmic division: Oogenesis is unequal (polar bodies); spermatogenesis is equal (four similar sperm).

Question 13

What is the Hypothalamic-Pituitary-Ovarian (HPO) axis?

Answer 13

It is the regulatory system involving the hypothalamus, anterior pituitary, and ovaries that controls oogenesis and the menstrual cycle.

Question 14

What hormone does the hypothalamus release to begin hormonal regulation of oogenesis?

Answer 14

GnRH (Gonadotropin-Releasing Hormone).

Question 15

What does GnRH stimulate the anterior pituitary to release?

Answer 15

FSH (Follicle-Stimulating Hormone) and LH (Luteinizing Hormone).

Question 16

What is the role of FSH in oogenesis?

Answer 16

FSH stimulates growth and maturation of ovarian follicles.

Question 17

Which ovarian cells does FSH act upon?

Answer 17

Granulosa cells of the developing follicles.

Question 18

What are two functions of granulosa cells under the influence of FSH?

Answer 18

1) Proliferate and support follicle growth, (2) Secrete estrogen.

Question 19

What does FSH induce on granulosa cells of the dominant follicle?

Answer 19

Expression of LH receptors.

Question 20

What is the role of LH in oogenesis?

Answer 20

LH triggers ovulation and resumption of meiosis I.

Question 21

What causes the LH surge?

Answer 21

Sustained high estrogen levels from the dominant follicle.

Question 22

What are the two main effects of the LH surge?

Answer 22

(1) Ovulation, (2) Completion of meiosis I (primary → secondary oocyte).

Question 23

What structure forms after ovulation due to LH action?

Answer 23

The corpus luteum.

Question 24

What does the corpus luteum secrete?

Answer 24

Progesterone (and some estrogen).

Question 25

What are the main roles of estrogen in the menstrual cycle?

Answer 25

(1) Thickens endometrium (proliferative phase), (2) Regulates FSH and LH through feedback.

Question 26

How does estrogen exert feedback on the pituitary?

Answer 26

• Low to moderate levels: Negative feedback (inhibits FSH/LH). • High sustained levels: Positive feedback (triggers LH surge).

Question 27

What phase of the uterus corresponds to high estrogen levels?

Answer 27

The proliferative phase – endometrial thickening.

Question 28

What are the main roles of progesterone?

Answer 28

1) Prepares and maintains endometrium (secretory phase), (2) Inhibits GnRH, FSH, and LH.

Question 29

What structure secretes progesterone and when?

Answer 29

The corpus luteum, after ovulation.

Question 30

What does progesterone do to the endometrium? .

Answer 30

Maintains and enhances it for potential implantation

Question 31

Why is progesterone important in preventing another ovulation during the same cycle?

Answer 31

It suppresses GnRH, FSH, and LH (negative feedback), preventing new follicle development.

Question 32

What happens hormonally if fertilization does not occur?

Answer 32

Corpus luteum degenerates → progesterone and estrogen drop → menstruation begins.

Question 33

What are the dominant hormones in the follicular phase of the cycle?

Answer 33

FSH and rising estrogen.

Question 34

What are the dominant hormonal events during ovulation?

Answer 34

LH surge and peak estrogen levels.

Question 35

What hormone dominates the luteal phase?

Answer 35

Progesterone (from the corpus luteum).

Question 36

What type of feedback does estrogen typically exert?

Answer 36

• Negative feedback at low levels • Positive feedback at high, sustained levels

Question 37

How do progesterone and estrogen together regulate the next menstrual cycle?

Answer 37

They suppress FSH and LH to prevent new follicle development unless fertilization fails.