Female reproduction system

Question 1

What is oogenesis?

Answer 1

The oogenesis is the process that terminates with the production of an ovum.
It begins before birth, reaches its peak at puberty and ends with menopause, and occur on a monthly basis as part of the ovarian cycle.

1. Mitosis: the oogonia undergo mitosis, producing two identical daughter
   cells.
   
   • one remain an oogonium
   • one differentiate in the diploid primary oocyte.
2. Meiosis I: the primary oocyte undergo meiosis I, producing two cells.
   
   • one will differentiate in a polar body
   • one will differentiate in the secondary oocyte
     This division occurs before birth and at the beginning of a woman’s life,
     but the meiosis I will stop at prophase and will continue its division only
     after puberty. This resting stage is called Diplotene stage.
3. Meiosis II: the secondary oocyte undergoes meiosis II, producing to
   haploid cells.
   
   • one will differentiate in a polar body
   • one will differentiate, eventually, into an ovum
     Meiosis II will be finished only if fertilisation occur, thus it remain
     immature until a spermatozoa penetrates it.

Every meiosis division does not produce two identical cells, but it produce a polar body (atretic cell) and a cell that will continue development: this process is asymmetric cytokinesis.

Question 2

What is the ovarian cycle?

Answer 2

The ovarian cycle is responsible for the oogenesis and release of the immature secondary oocyte.
The cycle has three phases:
1. Follicular/preovulatory/estrogenic phase: during this phase the ovarian follicle mature and estrogen is secreted. Under the effect of FSH hormone, many follicles grow at the same time in the ovaries, but only one reach maturation, while the others will undergo artesia. The maturation of the follicle secrete estrogen.
2. Ovulation: during this phase FSH is inhibited while LH is stimulated, resulting in the release of the immature ovum into the pelvic cavity from the mature primary follicle.
3. Luteal/postovulatory/progestational phase: during this phase the Corpus Luteum is formed. The corpus luteum is simply the cavity left by the ovum in the follicle. LH will stimulate the granulosa cells to invade and proliferate the corpus luteum. LH will also stimulate the corpus luteum to secrete progesterone, that will prepare the uterus and the whole body for a possible pregnancy. In case fertilization does not occur, the corpus luteum will become Corpus Albicans, a pale scar tissue caused by the invasion of the corpus luteum by fibroblasts.

The first phase of the ovarian cycle is the one that occur during the diplotene stage, thus there will be a resting phase right after it. Phase 2 and 3 will occur only after puberty, as the meiosis I will continue.

Question 3

What is the uterine cycle?

Answer 3

The uterine cycle, or menstrual cycle, is a repeating series of changes in the structure of the endometrium.

1. Menstrual phase: degeneration and sloughing of endometrial functional layer, which leads to menstruations/menses.
2. Proliferation phase: restoration of the uterine epithelium.
3. Secretory phase: secretion of progesterone and estrogen, to prepare the uterus for the next possible pregnancy.

Question 4

What is the relation between ovarian and uterine cycles?

Answer 4

Day 1-7:

• Ovarian cycle: follicular phase (the follicular is being prepared, oogenesis occur)
• Menstrual cycle: menses (no pregnancy occurred, thus degradation of uterus)

Day 8-13:

• Ovarian cycle: still follicular phase
• Menstrual cycle: proliferative phase (reconstruction of the uterus)

Day 14:
Ovulation (the secondary oocyte is released)

Day 15-30:

• Ovarian cycle: luteal phase (formation of corpus luteum, secretion of hormones that affect the uterus)
• Menstrual cycle: secretory phase

Question 5

Which hormones control and regulate the female reproductive system?

Answer 5

The hormones that are released in the reproductive tract are:

1. GnRH (gonadotropin-releasing hormone)
2. LH (luteinizing hormone)
3. FSH (follicle-stimulating hormone)
4. Estrogen
5. Inhibin
6. Progesterone

The organ that release this hormones are:

1. Hypothalamus
2. 3. Pituitary gland
3. 5. Ovaries

The hypothalamus release GnRH that stimulate the pituitary gland to produce LH, responsible for the maintain of the structure and secretory function of the corpus luteum, and to produce and secrete FSH, responsible for the stimulation of follicular development; FSH stimulate follicle development, which cause the secretion of inhibin, responsible for inhibition of FSH, and the secretion of estrogens, responsible for the stimulation of the pulse frequency of secretion by the hypothalamus, stimulation of the secretion of LH and, together with LH, the secretion of progesterone by the corpus lutem, responsible for the inhibition of the pulse frequency of secretion by the hypothalamus and stimulation of endometrial growth and secretion.

Estrogens are not only responsible for the influence of the reproductive tract, but they also:

• affect CNS
• stimulate bone and muscle growth
• establish and maintain female secondary sex characteristics
• maintain accessory glands and organs