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Questions and Answers
What is the primary purpose of oogenesis?
What structure surrounds each primary oocyte during oogenesis?
At what stage does the oocyte maturation inhibitor play a crucial role?
How many primary follicles are typically present in a female's ovaries at birth?
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What happens to the majority of primary follicles after puberty?
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In which part of the female reproductive system does oogenesis occur?
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What does the term 'Graafian follicle' refer to?
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What occurs during ovulation?
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What is the role of the cumulus oophorus in the ovarian follicle?
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At what stage does oogenesis begin?
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How many haploid gametes are produced from a primary oocyte?
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What is the primary function of the corpus luteum?
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Which phase of the menstrual cycle involves the shedding of the endometrial lining?
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What triggers the formation of the corpus luteum?
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During which phase of the ovarian cycle does the follicular phase occur?
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Which hormone is primarily responsible for controlling the proliferative stage of the menstrual cycle?
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What results from the division of a primary oocyte during meiosis I?
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What is the fate of the 1st polar body after meiosis I?
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What occurs during ovulation?
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What does the corpus luteum secrete?
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What triggers the degradation of the secondary oocyte if fertilization does not occur?
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What happens to the corpus luteum if fertilization occurs?
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Which structure surrounds the zona pellucida?
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What initiates the formation of the corpus luteum after ovulation?
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Study Notes
Female Genital System
- Primary sex organs are two ovaries, attached to the back of broad ligaments on the sides of the uterus.
- Ovaries secrete female sex hormones (estrogen and progesterone) and produce an ovum each cycle after puberty.
- Secondary sex organs include fallopian (uterine) tubes, uterus, vagina, external genitalia, and mammary glands.
Oogenesis
- The goal of oogenesis is the formation of a mature, single, large, and haploid ovum.
- Oogenesis occurs in the ovary, where each ovary produces one ovum every 2 cycles.
- The process starts before birth and is arrested after birth until puberty.
- After puberty, it continues till menopause.
Steps of Oogenesis
- During early fetal life, oogonia (diploid = 44 + XX) divide by mitosis to create daughter oogonia.
- Daughter oogonia enlarge to form primary oocytes (diploid).
- Primary oocytes are surrounded by flat follicular cells (derived from ovarian tissue), forming a primordial follicle.
- Flat cells become cuboid, transforming the primordial follicle into a primary follicle.
- Further development is arrested until puberty due to oocyte maturation inhibitor secreted by follicular cells.
- A female is born with about 40,000 primary follicles in her ovaries, only about 500 of which will be ovulated.
- After puberty, 15-20 primary follicles grow each month, with all but one degenerating to form atretic follicles.
- The remaining follicle continues its development:
- Follicular cells multiply in the primary follicle, transforming it into a growing follicle.
- The primary oocyte inside the growing follicle divides by meiosis I, producing a secondary oocyte and a 1st polar body.
- The secondary oocyte is haploid (22 + X) and receives most of the cytoplasm.
- The 1st polar body is haploid (22 + X) and receives very little cytoplasm.
- Follicular cells around the secondary oocyte differentiate and together form the Graafian follicle.
- The 1st polar body may or may not divide by meiosis II, but eventually both polar bodies degenerate.
- If fertilization does not occur, the secondary oocyte degenerates after 24 hours without undergoing meiosis II.
Ovulation
- Ovulation is the rupture of the mature Graafian follicle, releasing the secondary oocyte (along with the zona pellucida and corona radiate) into the peritoneal cavity.
- The fimbriated end of the uterine tube catches the secondary oocyte.
- If fertilization occurs, the secondary oocyte undergoes meiosis II to produce a mature ovum and a second polar body.
- After ovulation, the remaining part of the Graafian follicle is invaded by lutein (a yellow pigment), forming a corpus luteum within 3 days.
- The corpus luteum secretes progesterone (mostly) and estrogen.
Fate of the Corpus Luteum
- If fertilization occurs, the corpus luteum becomes the corpus luteum of pregnancy, which continues secreting hormones for 3-4 months until the placenta takes over.
- If fertilization does not occur, the corpus luteum becomes the corpus luteum of menstruation, which secretes hormones for 9 days before gradually regressing until menstruation occurs.
- In either case, the corpus luteum eventually becomes fibrosed, forming a corpus albicans.
- Drugs that inhibit ovulation are used as contraceptives (containing estrogen and progesterone).
- Drugs that stimulate ovulation are used to treat infertility (e.g. parlodel), but may cause twins.
Structure of a Graafian Follicle
- The Graafian follicle is ½ cm in diameter.
- Inside is a secondary oocyte (120 microns in diameter) surrounded by:
- Vitelline membrane: the cell membrane of the secondary oocyte.
- Zona pellucida: a non-cellular glycoprotein coat separated from the vitelline membrane by the perivitelline space.
- Corona radiata: a single layer of cells surrounding the zona pellucida.
- Stratum granulosum: the outer wall of the follicle, made of follicular cells.
- Antrum: the cavity of the follicle, filled with liquor folliculi.
- Cumulus oophorus: a group of follicular cells attaching the secondary oocyte to one side of the follicle.
- The compressed ovarian stroma forms a capsule around the follicle called the Theca Folliculi, divided into:
- Theca interna: made of secretory cells.
- Theca externa: mostly fibrous.
Differences Between Spermatogenesis and Oogenesis
- Both processes produce haploid gametes. | Feature | Spermatogenesis | Oogenesis | |---|---|---| | Location | Testis | Ovary | | Commencement | After puberty | During fetal life | | Duration | Continues until death | Ends at menopause | | Primary Cell Outcome | Primary spermatocyte gives 4 equal sperm | Primary oocyte gives one large ovum | | Motility | Sperms are motile | Ova are non-motile |
Adult Female Cycles
- Occur every 28 days from puberty until menopause.
- Cycles include the ovarian cycle and the menstrual cycle.
Ovarian Cycle
- Located in the ovarian cortex and depends on pituitary hormones.
- 3 phases:
- Follicular phase (14 days): Under the effect of pituitary follicle stimulating hormone (FSH), 15-20 primordial follicles grow. This results in a single Graafian follicle (which secretes mainly estrogen) and several atretic follicles.
- Ovulation: Under the effects of FSH and pituitary leuteinizing hormone (LH), the secondary oocyte is released, and a corpus luteum is formed.
- Luteal phase (14 days): Under the effect of LH, the corpus luteum is formed (which secretes mainly progesterone). Eventually, the corpus luteum degenerates, forming a corpus albicans.
Menstrual Cycle
- Located in the endometrium of the uterus and depends on ovarian hormones.
- 4 stages:
- Menstrual stage (4 days): Shedding of the superficial layers of the endometrium leads to bleeding (50-60 cc of non-clotting blood). This shedding is caused by a lack of ovarian hormones.
- Repair (3 days): Healing of the raw endometrial surface from the epithelial cells at the bases of the glands.
- Proliferative stage (7 days): Thickening of the endometrium with straight glands. This and the next stage are controlled by estrogen from the follicular phase of the ovarian cycle.
- Secretory stage (14 days): Further thickening of the endometrium under control of progesterone from the luteal phase of the ovarian cycle. The endometrium differentiates into:
- Deep basal layer containing the straight basal parts of the glands.
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Description
This quiz covers the female genital system, focusing on the primary and secondary sex organs, as well as the process of oogenesis. Explore the stages of oogenesis from early fetal life to menopause, and understand the hormonal functions of the ovaries. Test your knowledge on female reproductive anatomy and physiology.
