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Flashcards in SPR L5 Female Reproductive Function Deck (15):
1

Learning Outcomes - for general perusal

  • To elucidate the importance of Reproduction to the human
  • To contrast female gamete formation (maturation of pre existing gametes) with that of the male (creation of millions of new gametes per day)
  • To show how the adult female not only develops a gamete monthly, but also an endometrial environment capable of supporting said gamete if fertilisation occurs.
  • To outline female secondary sexual characteristics

Concepts and Learning Outcomes - for general perusal

  • Whereas in the male, millions of gametes are produced daily, the female is born with 1 – 2 million gametes which must last her reproductive life span.
  • Some (about 400 – 500 per lifespan) of these potential oocytes enter the ovarian cycle under the influence of hypothalamic and pituitary hormones and produce the oestrogen and progesterone that are responsible for the growth and maintenance of an endometrium that could potentially support a foetus.
  • The female hormones not only support the endometrial lining and gamete maturation, they also underlie many female secondary sexual characteristics.

2

Outline some of the main differences between male and female reproductive function

Whereas the post pubertal male produces millions of gametes daily, a female is born with a set number of gametes that reduces as she grows older.

In addition, as well as supporting the formation of gametes, female reproductive function is also concerned with the preparation of a uterine lining that could potentially support a foetus.

3

Female Reproductive Structures

  1. What is the female gonad?
  2. What does it produce?
  3. What is closely associated with the ovaries?
  4. How does an unfertilised egg exit?

  1. the ovary
  2. the gametes and the main female sex hormones (oestrogen and progesterone) that underlie the development of the gamete and the uterine wall.
  3. the fimbriae of the fallopian tubes trough which the egg can pass and become fertilised
  4. via the uterus, cervix and vagina.  

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4

Oogenesis

  1. What are female gametes called?
  2. What are the primitive progenitor cells called and when does their maturation begin?
  3. Outline this maturation until puberty?
  4. Outline the cells present at puberty.
  5. What may explain why older mothers are more at risk of giving birth to children with genetic abnormalities eg. Downs Syndrome?

  1. oocytes
  2. oogonia - before birth

3.

  • the oogonia undergo a mitotic division to multiply numbers of potential oocytes
  • then the first meiotic division before birth takes place, forming primary oocytes.  Thence all division stops until the female reaches puberty. 

4. At this point the first meiotic division is completed, giving 2 distinct cells. 

  • One is a haploid cell rich in cytoplasm and nutrient, the secondary (2o) oocyte.  This, although haploid with unpaired chromosomes, still has twice the amount of genetic material of the final gamete. 
  • The second smaller cell is called the polar body, consisting largely of chromosomal material.

 

5. all of the female gametes are formed at birth, and they age with the individual) 

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5

Ovarian Cycle - Follicular Phase (1)

  1. What are the two phases, and when are they?
  2. How many primary oocyes is the human female born with?
  3. What are the structures called that these are contained within?
  4. What is the most basic of these structures called, and describe it.
  5. What is the Zona Pellucida?
  6. How do the theca cells come about?

  1. Follicular Phase (Day 1-14), and Luteal Phase (Day 14 - 28)
  2. about 1 – 2 million
  3. follicles
  4. Primordial Follicle - consist of the primary oocyte surrounded by a single layer of cells, the granulosa cells, sitting upon a connective tissue basal lamina.
  5. The granulosa cells then multiply and create a layer of mucopolysaccharide around the ovum.
  6. A layer of cells outside the basal lamina differentiates and forms the theca cells

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6

Outline Oogenesis

  • 1 – 2 million oogonia at birth of which 4 – 5 hundred reach maturity
  • Mitosis
  • Then meiosis I before birth
  • Completed at puberty
  • 2 haploid cells
  • 2O oocyte (2 X genetic material)
  • First polar body
  • Meiosis II complete at fertilisation

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7

Ovarian Cycle - Follicular Phase (2)

  1. Outline what happens from the start of each ovarian cycle
  2. What is the remaining follicle called, how does it develop?
  3. What allows the follicle to rupture, and when?
  4. What happens in ovulation?

  1. several of these primordial follicles enlarge and a cavity becomes visible (called the antrum) filled with follicular fluid produced by the granulosa cells.  Only one of these follicles develops further, becoming the dominant follicle with the other ones regressing or becoming the corpus luteum. 
  2. the Graafian or antral follicle enlarges and the theca cells differentiate further, becoming the theca interna and theca externa. 
  3. At around 14 days, the follicle is so large that it distorts the surface of the ovary.  Fluid accumulation within the follicle and proteolytic enzyme activity combine to allow the follicle to rupture
  4. The follicle ruptures, releasing the ovum (secondary oocyte) to the awaiting fimbriae of the fallopian tube (ovulation).

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8

Ovarian Cycle - Luteal Phase

  1. When does this phase take place?
  2. Outline what happens after rupture of the follicle
  3. What happens to the granulosa and theca cells?
  4. Blood vessels infiltrate the follicle, what are they attracted by?
  5. What is the structure called now?
  6. What happens if fertilisation doesn't happen?

  1. Day 14-28
  2. the follicle fills with blood, becoming the corpus haemorrhagicum. Many women get some ovulatory pain (termed “Mittleschmerz”) thought to be due to a little irritation from some of this blood in the peritoneum.
  3. they swell up, become rich in yellow fatty deposits, and blood vessels infiltrate the follicle, facilitating it's important endocrine function.
  4. vascular endothelium growth factor (VEGF),
  5. the corpus luteum (yellow body).
  6. the corpus luteum degenerates after about 10 days, which precipitates the breakdown of the uterine wall (menses).

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9

Hormonal Control (1)

Not only must the human female produce gametes for fertilisation every month, she must also create an environment in her uterus that could potentially nourish a foetus. This is why hormonal control is more comlicated in females.

What are the two phases in the ovarian cycle?

Why are they named this way?

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there are 2 phases of approximately 2 weeks each in the ovarian cycle

  1. a preovulatory follicular phase
  2. a  postovulatory luteal phase

named according to the structure predominantly secreting sex steroids at the time

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10

Hormonal Control (2)

  1. What happens at the start of the cycle, what is released and where from?
  2. Where does this travel along and to, and what does it cause?
  3. What is the role of FSH?
  4. What is the role of LH?

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  1. Gonadotropin releasing hormone (GnRH) is secreted by the hypothalamus
  2. travels down the hypophyseal portal circulation and causes the release of Follicle Stimulating Hormone (FSH) and Luteinizing hormone (LH) from the anterior pituitary gland.  These hormones start the cycle by stimulating the development of primordial follicles.  
  3. encourages cell division and oestrogen secretion by the granulosa cells
  4. LH functioning in the formation of the luteal body later in the cycle.  LH also has a role in the early part of the cycle, stimulating androgen production by the theca cells, androgens which then diffuse into the granulosa cells to be converted into still more oestrogens.

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11

Hormonal Control (3)

  1. What are the gonadotrophins normally inhibited by?
    1. What happens by about day 10 instead, how is this relevant to day 14?
  2. What takes over hormone production after day 14? What does it produce?
  3. What do these hormone levels negatively feedback upon?
  4. What happens at around day 22-24?
    1. What is the effect on GnRH?

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  1. the rising concentrations of oestrogens
    1. oestrogen levels actually stimulate LH secretion, giving rise to a dramatic surge by day 14 which stimulates ovulation.
  2. The corpus luteum producing oestrogen and especially progesterone. 
  3. on FSH and LH, keeping them low.
  4. the corpus luteum undergoes a preprogrammed degeneration or atresia, causing a rapid falling off in hormone levels
    1. This removes the negative feedback effect on GnRH, causing its  level to rise again, repeating the cycle

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12

The Uterine Cycle (1)

  1. Which two hormones are vital in the development and release of the female gamete during the ovarian cycle, and are also responsible for the female secondary sexual characteristics that occur during puberty?
  2. What does oestrogen promote?
  3. What does progesterone stimuate?
  4. Give examples of other female specific characteristics mediated by oestrogen and progesterone.

  1. oestrogens and progesterones 
  2. deposition of fat around the breasts and hips and promotes mammary duct development
  3. the formation of secretory lobules in the breast.
  4. wide hips, maintenance of laryngeal size and high vocal range, a characteristic “flat top” profile of pubic hair (the female escutcheon) and more responsive uterine muscle.  Female specific behavioural characteristics may also be attributable to the actions of the female sex hormones.

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13

The Uterine Cycle (2)

  1. What is one of the most important functions of oestrogens and progesterones?
  2. What are the two layers of the endometrium called?
  3. What is the stratum B supplied by?
  4. What is the stratum F supplied by?
  5. What occurs at the beginning of the mesntrual cycle?
  6. The uterine lining thickens and proliferates under the influence of what?

  1. the proliferation and maintenance of the endometrial lining of the uterus, so that, by the time the ovum is released it could potentially serve to nourish a developing embryo.
  2. a deep layer that is not shed - stratum basale and a more superficial layer that alters during the menstrual cycle under the influence of the hormones from the ovaries- stratum functionale
  3. short straight basilar arteries 
  4. supplied by coiled spiral arteries 
  5. about two thirds of the thickness of the endometrial wall sloughs off, leaving just the deep stratum basale layers.
  6. oestrogens produced in the developing follicles 

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14

The Uterine Cycle (3)

  1. The uterine lining thickens and proliferates to form what?
  2. What is the predominant hormone after ovulation and what does it do?
  3. What happens to the glands?
  4. What happens if there is no fertilisation and accompanying implantation?

  1. many tube like glands
  2. progesterone - maintains the uterine lining.
  3. lengthen without a corresponding thickening of the uterine wall and so become tortuous and “saw toothed” in profile.  They become highly vascularised and fill up with secretions rich in glycogen, ideal for nourishing any potentially implanting embryo. 
  4. then the rapid fall in hormone levels coming from atresia of the corpus luteum at about day 24 causes ischaemia and infarction of the endometrium which subsequently sloughs off and is shed during the menstrual flow.

15

Summing Up - For General Perusal

  • The female gamete is created from a pre existing precursor, formed from birth.  This contrasts male gamete formation.
  • Alongside gamete formation, the ovaries also produce oestrogen and progesterone that develop and maintain an endometrial environment appropriate for potential implantation of a fertilised egg
  • The oestrogen and progesterone thus produced also effect the female secondary sexual characteristics.

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