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Reproductive System > Session 3 - Gametogenesis > Flashcards

Session 3 - Gametogenesis Flashcards

1
Q

What are the differences in production of gametes in oogenesis and spermatogenesis?

A

Oogenesis:

  • very few gametes (~400 in lifetime)
  • intermittent production (~1/month)

Spermatogenesis:

  • huge number (~200 million/day)
  • continuous production
  • essentially ‘disposable’ cells
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2
Q

What are the two main functions of meiosis?

A

Reduce the chromosome number in the gamete to 23 (haploid)

Ensures that every gamete is genetically unique

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3
Q

How many daughter cells are produced by meiosis?

A

4 daughter cells

In female only one develops into a mature oocyte, others form polar bodies

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4
Q

How does genetic variation arise in meiosis?

A

Crossing over (exchange of regions of DNA between 2 homologous chromosomes)

Independent assortment (random orientation of each bivalent along the metaphase plate with respect to other bivalents)

Random segregation (random distribution of alleles among the four gametes)

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5
Q

Where does spermatogenesis occur?

A

Sertoli cells in the seminiferous tubules of the testes

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6
Q

What are spermatogonia?

A

Male germ cells

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7
Q

Male germ cells divide by MITOSIS to give rise to what cells?

A

Ad spermatogonium (‘Resting’, reserve stock)

Ap spermatogonium (‘Active’, maintain stock and from puberty onwards produce type B spermatogonia which give rise to primary spermatocytes)

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8
Q

What happens to the spermatocytes after primary spermatocytes have been produced?

A

Primary spermatocytes divide by meiosis giving rise to secondary spermatocytes and then spermatids (the four daughter cells)

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9
Q

Each primary spermatocyte forms how many spermatids?

A

4 haploid spermatids

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10
Q

What is spermiogenesis?

A

The differentiation of spermatids into spermatozoa as they pass from seminiferous tubules to the epididymis.

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11
Q

Are all stages of spermatogenesis visible in a single cross-section of seminiferous tubule?

A

No, cells tend to appear in groups with the same maturation stages. Each stage follows an orderly sequence along the length of the tubule.

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12
Q

What is the spermatogenic cycle defined as?

A

The time taken for the same stage of spermatogenesis to reappear in a give segment of seminiferous tubule (~16 days in humans)

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13
Q

What is the spermatogenic wave?

A

The distance along the seminiferous tubule between the same stage of spermatogenesis.

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14
Q

What is spermiation?

A

The release of spermatids into the lumen of the seminiferous tubule.

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15
Q

What happens to spermatids as they pass down the seminiferous tubule?

A

They are remodelled as they pass through the seminiferous tubules, through the rete testis and ductuli efferentes and into the epididymis to finally form spermatozoa.

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16
Q

Describe how the spermatids are transported through the lumen to the epididymis.

A

Non-motile transport. Transported via Sertoli cell secretions and assisted by peristaltic contractions until they reach the epididymis.

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17
Q

What is semen composed of?

A

Seminal vesicle secretions (~70%)
Secretions of the prostate (~25%)
Sperm (via the vas deferens) (2-5%)
Bulbourethral gland secretions (<1%)

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18
Q

What do the seminal vesicles secrete into semen?

A

Amino acids, citrate, fructose, prostaglandins

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19
Q

What does the prostate secrete into semen?

A

Proteolytic enzymes, zinc

20
Q

What do the bulbourethral (Cowper’s) glands secrete into semen?

A

Mucoproteins which help lubricate and neutralise acidic urine in distal urethra.

21
Q

What is sperm capacitation?

A

The physiological changes that occur in the final step of maturation of the spermatozoa. Must undergo these changes in order to have the ability to penetrate and fertilise an egg. Occurs in the female genital tract.

22
Q

What happens during sperm capacitation?

A

Conditions in female genital tract stimulate:

  • removal of glycoproteins and cholesterol from sperm membrane
  • activation of sperm signalling pathways

These allow sperm to bind to the zona pellucida of the oocyte and initiate the acrosome reaction.

23
Q

What must human sperm for in vitro fertilisation first go through so that it is able to fertilise the oocyte?

A

Must first be incubated in capacitation media

24
Q

When does maturation of oocytes begin?

A

Before birth

25
Q

When does oogenesis stop?

A

Menopause

26
Q

Primary oocyte have arrested in what phase of meiosis I?

A

Prophase

27
Q

What is a primordial follicle?

A

A primary oocyte that is surrounded by a layer of flat epithelial cells called follicular cells.

28
Q

What happens to the majority of oogonia and primary oocytes before birth and during childhood?

A

They undergo atresia

29
Q

From puberty onwards, ~15-20 oocytes will start to mature each month. What 3 stages do the oocytes have to pass through during their maturation?

A
  1. Preantral
  2. Antral
  3. Preovulatory
30
Q

What happens in the preantral stage of oocyte maturation?

A

Primordial follicle begins to grow. The follicular cells surrounding the oocyte change from flat to cuboidal and proliferate. This produces a stratified epithelium of granulosa cells.

31
Q

What is the function of granulosa cells?

A

Granulosa cells secrete layers of glycoprotein onto the oocyte creating the zone pellucida.

32
Q

What happens during the antral stage of oocyte maturation?

A

Fluid filled spaces appear between the granulosa cells.

These spaces join to create one large space, the antrum.

33
Q

What happens during the preovulatory stage of oocyte maturation?

A

LH surge induces the preovulatory growth stage.
Meiosis I is completed. This create two haploid daughter cells of unequal size (one receives most of the cytoplasm, the other becomes a polar body).
Secondary oocyte (and polar body) enters meiosis II but arrests i metaphase.
Meiosis II is only completed if the oocyte is fertilised, otherwise cell degenerates.

34
Q

What is the name of a fully mature follicle?

A

Graafian follicle

35
Q

What is the effect of LH on the wall of the ovary?

A

Increases collagenase activity.
Causes local muscular contractions of ovarian wall.
(Release of prostaglandins increases response to LH)

36
Q

What is the corpus luteum?

A

What remains of the follicle after ovulation.

Remaining granulosa and theca interna cells become vascularized and turn into lutein cells.

37
Q

What is the function of the corpus luteum?

A

Secrets oestrogen and progesterone. This stimulates the uterine mucosa to enter the secretory stage in preparation for embryo implantation.

38
Q

How is the oocyte transported from the ovary to the uterus?

A

Shortly before ovulation, fimbriae sweep over the surface of the ovary.
The uterine tube start to contract rhythmically.
The oocyte is carried into the Fallopian tube by the fimbriae and cilia.
Oocyte then propelled by peristaltic muscular contractions of the tube and cilia of the mucosa.

39
Q

What happens to the corpus luteum if fertilisation does not occur?

A

If fertilisation does not occur the corpus luteum degenerates.
Forms a mass of fibrotic scar tissue called the corpus albicans.
Progesterone production decreases (no longer secreted by corpus luteum), precipitating menstrual bleeding.

40
Q

What happens to the corpus luteum if fertilisation does occur?

A

Degeneration of the corpus luteum is prevented by the hormone human chorionic gonadotropin (secreted by the embryo).
The corpus luteum continues to grow and forms the corpus luteum graviditatis (corpus luteum of pregnancy).
Corpus luteum cells continue to secrete progesterone until ~4 months, beyond which progesterone secretions from the placenta are sufficient.

41
Q

Which hormone stimulate growth of follicles?

A

FSH

42
Q

Which hormones stimulate maturation of follicles?

A

FSH and LH

43
Q

Ovulation occurs on surge of what hormone?

A

LH

44
Q

How many polar bodies are formed in oogenesis?

A

3

45
Q

Where in the femal reproductive tract does the final stage of meiosis II occur?

A

Oviduct/Fallopian tube

Reproductive System (10 decks)

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