Basic Female reproductive physiology Flashcards
What are the female reproductive organs?
Ovaries Uterus Vagina Fallopian tubes
Describe the structure of the ovaries
- Surface - connective tissue capsule covered with a simple layer of cuboidal epithelium
- Inside of the ovary is split into 2 parts:
- Cortex- peripheral part of the ovary, it holds the connective tissue containing ovarian follicles (one oocyte surrounded by single layer of cells-primordial follicles)
- Medulla- central part, connective tissue through which the blood vessels supplying the ovary run
What are the 2 main functions of the ovaries?
-
Oocyte production
- 1 mature egg per menstrual cycle, around 400 ovulated during reproductive lifespan
- Majority of eggs perish during the cycle
- Finite number, declines with increasing age
-
Steroid hormone production
- Oestrogen develops female secondary sexual characters i.e breasts, wider hips, pubic hair and armpit hair
- Progesterone prepares endometrium for implantation during every cycle
- 50% of testosterone produced by ovaries before menopause
Describe the process of Oogenesis from before birth to puberty
- Oogonium (Germ cell) undergoes mitosis in foetal life forming primary oocyte
- The primary oocyte cells begin meiosis 1 before birth (there are about 2 million primary oocytes at this stage) but are then arrested in prophase 1 of meiosis until puberty
- Once puberty is reached meiosis resumes due to a surge in hormone secretion - LH/FSH
- The primary oocyte undergoes first meiotic division to form secondary oocyte (dominant follicle goes on to ovulate) and 1 polar body (dies via apoptosis)
- The secondary oocyte then ruptures out of the follicle (ovulation) but at this stage it is then arrested in metaphase II until fertilisation occurs
- Meiosis completes when the sperm fertilises the egg
Describe the process of Oogenesis from after puberty to ovulation
- The primary oocyte grows dramatically whilst still being arrested in meiosis 1. Growth consits of Pre-antral and antral phases where the primary oocyte changes into a secondary follicle.
- In each monthly cycle one of these secondary follicles becomes dominant and develops further under the influence of FSH, LH and oestrogen.
- The LH surge (begins at puberty) induces this stage so meiosis I is now complete and meiosis II begins.
- Two haploid cells are formed within the follicle, but they are of unequal size. One of the daughter cells receives far less cytoplasm than the other and forms the first polar body, which will not go on to form an ovum.
- The other haploid cell is known as the secondary oocyte.
- Both daughter cells then undergo meiosis II, the first polar body will replicate to give two polar bodies but the secondary oocyte arrests in metaphase of meiosis II just before ovulation.
Describe the process of fertilisation
Secondary oocyte will only complete meiosis II following fertilisation.
Once meiosis II is complete:
- A third polar body is given off
- A fertilised egg is produced
If the egg is fertilised it moves to the uterus where it can implant into the edometrium
If fertilisation never occurs, the oocyte degenerates 24 hours after ovulation - period
How does Oogenesis differ from spermatogenesis?
Oogenesis differs from spermatogenesis in that it begins in the foetus prior to birth.
Pre-antral and antral phases of follicular development
- Primary follicle- oocyte surrounded by zona and cuboidal granulosa cells
- Secondary follicle- increased oocyte diameter and multiple layer of granulosa cells, resumption of first meiotic division
- Tertiary /Graffian follicle - mature - follicular fluid between the cells which coalesce to form antrum, completion of first meiotic division to form secondary oocyte and start of second meiotic division.
The hypothalamus releases which hormone that acts on the anterior pituitary gland to release gonadotropins?
Gonadotropin releasing hormone
What are the 2 types of gonadotropins?
- Luteinizing hormone (LH)
- Follicle stimulating hormone (FSH)
LH and FSH act on the ovary which then produces which 2 hormones?
- Oestrogen
- Progesterone
Oestrogen and progesterone act on the uterus to coordinate what?
The menstrual cycle
Explain the negative feedback loop created by Oestrogen and progesterone
As estrogen and progesterone levels increase they create a -ve feedback that signals the hypothalamus and the pituitary to reduce the amount of GnRH and gonadotropins that they release - this keeps hormones stable and at a level where the ovarian and menstrual cycles are coordinated within 1 month.
What is unique to female reproduction in terms of hormone production/regulation?
- A positive feedback loop
- This only happens mid-cycle (around day 12-14 of a 28 day cycle)
- Only the Oestrogen creates a +ve feedback to increase the GnRH and LH surge (FSH too but less) from the anterior pituitary which results in ovulation
What happens to the egg after ovulation in the luteal phase (last 2 weeks of cycle)?
- A corpus luteum forms - it is essential for conception to occur and for pregnancy to last.
- Second stage of hormones start getting secreted
- A rise in progesteron levels starts preparing the endometrial lining for pregnancy
What happens to the corpus luteum if the egg is not fertilised and a pregnancy has not resulted?
- The corpus luteum degenerates to form corpus albicans
- Oestrogen and progesterone levels drop
- The drop in hormone levels signals the start of a new cycle as it stops the –ve feedback inhibiting GnRH
- Increased secretion from the hypothalamus again
Ovarian cycle
2 phases – follicular and luteal – in a standard 28 day cycle
- Folliclular phase - follicle matures due to FSH and produces oestrogen
- Ovulation - Mid-cycle the LH surge happens - the follicle ruptures and releases the egg that is the secondary oocyte.
- Luteal phase - Ruptured follicle forms a corpus luteum and produces progesterone (and some oestrogen)
- At the end of the cycle (around day 28) if the pregnancy has not resulted the corpus luteum will shrink and regenerate into a structure called the corpus albicans.
- Estrogen and progesterone drop and a new ovarian cycle begins as when their levels drop, this removes the -ve feedback on the hypthalamus
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