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Reproductive System > Session 3 - Neuroendocrine timing of puberty + Gametogenesis > Flashcards

Session 3 - Neuroendocrine timing of puberty + Gametogenesis Flashcards

1
Q

What is puberty?

A

A stage in puberty when sexual maturation and growth are completed and result in ability to reproduce.

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2
Q

Which basic features change in puberty in boys and girls?

A
  • Accelerated somatic growth
  • Maturation of primary sexual characteristics (gonad/genitalia)
  • Appearance of secondary characteristics (pubic + axillary hair, female breast development, male voice changes)
  • Menstruation and Spermatogenesis begin.
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3
Q

What is the average age of menarche?

A

Menarche = First menstruation

<13 years old

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4
Q

What is the critical weight in girls?

A

Weight thought to be needed to achieve first menarche. Around 47kg

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5
Q

What can happen in a woman of reproductive age with significant weight loss?

A

Menstruation can stop, as reproductive cycles cease.

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6
Q

What is thelarche, and when does it occur?

A

Development of breast bud
9-13 years
First sign of puberty in girls

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7
Q

What is adrenarche?

A

Increased levels of androgens from adrenal cortex, causes growth spurt and onset of menstruation.

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8
Q

When does puberty begin in boys, when do various stages happen?

A

10-14 genital development.
Begins:
- pubic hair growth
- spermatogenesis

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9
Q

What is the tanner scale?

A 
A scale used to asses the stage a person is in puberty.
From I to V
Assesses:
- Genital size
- Pubic hair
- Testicular volume
- Breast size
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10
Q

Which hormone is responsible for pubic hair growth?

A

Testosterone - in both male and female.

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11
Q

What are the levels of oestrogen and testosterone in girls and boys before puberty?

A

Similar levels of both in Girls and Boys.

may be on average slightly more testosterone in boys, and vice versa

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12
Q

When does puberty start in girls, and boys?

A

Girls 9-13
Boys 10-14
Boys later

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13
Q

Why are men generally larger than women?

A

Boys start somatic growth phase later, but it is rapid, and achieve more growth each year.
The epiphyseal growth plates close later.

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14
Q

What is the first recognised sign that a boy has entered puberty?

A

Increased testicular volume.

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15
Q

What is the first recognised sign that a boy has entered puberty?

A

Increased testicular volume.

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16
Q

What is the duration of puberty for men and women, what features show this stage?

A

Men (3.2 +/- 1.8) years - Adult size of testis

Women (2.4 +/- 1.1) years - Menarche

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17
Q

What is the HPG axis, and its role in puberty?

A

Hypothalamo-pituitary-gonadal axis.
Gradual activation with release of GnRH from hypothalamus.
This is responsible for switching this axis on, and initiating puberty.

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18
Q

Which gene is important in initiating the cascade of hormones which control puberty?

A

GnRH- 1 gene

gonadotrophin releasing hormone

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19
Q

What are the characteristics of hypothalamic releasing hormones?

A
  • Secreted in pulses, tied to internal biological clock.
  • Act on specific membrane receptors.
  • Transduce signals via second messengers.
  • Stimulate release of stored pituitary hormones.
  • Stimulate synthesis of pituitary hormones
  • Stimulates hyperplasia + hypertrophy of target cells.
    regulates its own receptor
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20
Q

What does GnRH stimulate in the pituitary?

A

Stimulates anterior pituitary to secrete:
1) Luteinizing hormone LH
2) Follicle-stimulating hormone FSH
(both made in anterior pituitary)

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21
Q

Which factors in the body affect the release of GnRH in the hypothalamus?

A
  • Leptin (to do with fat levels)
    (enough body mass- sexually active life)
  • Photoperiod (time of light in day)
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22
Q

What are the properties of leptin? How does it affect puberty?

A
  • Adipose derived regulatory hormone
  • Important in onset of puberty (weight)
  • Can cause menstrual cycles to stop if underweight female.
  • Is a pulsatile hormone
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23
Q

How does growth hormone initiate the growth spurt?

A 
GH secretion from pituitary.
- Increases TSH
> Metabolic rate
> tissue growth
> Androgens = retention of minerals to support bone and muscle growth.

= Growth spurt

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24
Q

How is GnRH released?

A
  • Pulsatile
  • Every 2-3 hours (from hypothalamus)
    In portal system - to anterior pituitary
    Cause LH, FSH release.
25
Q

What is the anterior pituitary?

A

Hormone producing glandular tissue, connecting to hypothalamus by portal system (NOT neurone)

26
Q

Which hormones does the anterior pituitary produce?

A

6 Peptide hormones

  • Prolactin
  • Growth hormone
  • Thyroid stimulating hormone(TSH)
  • Adrenocorticotropic hormone (ACTH)
  • FSH
  • LH
27
Q

When does LH start to rise in males? what time?

A

Starts in the night.

- Initial pulsitility of LH. (follows GnRH pulses)

28
Q

Which other axes are there from the pituitary? What do they control?

A

HPT = thyroid
HTA = adrenal
HPG - gonadal

Growth, lactation, milk secretion, water metabolism

29
Q

How is testosterone signalled to be produced in males?

A

Hypothalmus > GnRH
Anterior pituitary > LH
LH stimulates leydig cells to produce steroid hormone testosterone.

30
Q

What are the leydig cells?

A
  • Cells in the interstitial tissue

- Produce testodterone (separate to seminiferous tubules)

31
Q

How is spermatogenesis controlled so that it is not constant/ too much?

A

Sertoli cells secrete inhibin in response to FSH, which negatively feedsback on the hypothalamus.

32
Q

How do levels of oestrogen affect GnRH from the hypothalamus?

A
  • Low levels oestrogen = reduce GnRH secretion

- High levels oestrogen = promote GnRH secretion

33
Q

How many gametes does a woman release over her lifetime?

A

Around 400.

1 per month x number of years in reproductive age

34
Q

How is genetic variation achieved in gametes?

A
  • Crossing over of regions of DNA between 2 homologous chromosomes.
  • Independent assortment - of each bivalent chromosome along the metaphase plate.
  • Random segregation - of alleles among the four gametes.
35
Q

Describe the basic process of spermatogenesis.

A
  • Produced in seminiferous tubules.
    (sertoli cells support developing spermatid to spermatozoa)
  • Travel down tubules to gather in Rete testis
  • Here they become condensed, and move to ductili efferentes, for further condesing.
  • Move through to head of epididymis (storage).
  • Upon ejaculation, move through epididymis, through vas deferens and through the urethra.
36
Q

Why is the blood testis barrier (sertoli barrier) important?

A

To ensure spermatid/ spermatozoa do not come into contact with blood, as they are genetically different and could be detected as non- self. This could cause immune response against it.

37
Q

What are spermatogonia?

A
  • Raw material for spermatogenesis (male germ cells)
38
Q

What is spermiation?

A

Process by which spermatids are released into seminiferous tubules from sertoli cells.

39
Q

What are the three types of spermatogonia in the testes?

A

Ad Spermatogonium - “Resting”: reserve stock

Ap Spermatogonium - “Active”: Maintain stock + from puberty onwards produce type B spermatogonia, which give rise to primary spermatocytes.

Ad - dark
Ap - pale

40
Q

What is spermiogenesis?

A

Differentiation/ maturation of the spermatids (4 daughter cells 1n) into spermatozoa.

41
Q

What is the spermatogenic cycle?

A

Defined as time taken for reappearance of the same stage within a given segment of tubule (~16 days).

42
Q

What is the spermatogenic wave?

A

The distance between the same stages of the spermatogenic cycle along the length of the seminiferous tubule.
(distance to a section in the same stage of development)

43
Q

What occurs in spermiogenesis?

A
  • Moved through seminiferous tubules to epididymis.
  • Secretions and perstalsis move them (non motile)
  • Remodel as they pass through, to finally become motile.
44
Q

What are the components of the ejaculate? Where do they come from?

A 
- Seminal vesicles (70%)
AA, citrate, fructose, prostaglandins
- Prostate (25%)
Proteolytic enzymes, zinc
- Sperm (via vas) (2-5%)
- Bulbourethral gland (<1%)
Mucoproteins = lubricate, neutralise acidic urine.
45
Q

What is sperm capacitation?

A
  • Final maturation step before sperm are fertile, happens in female genital tract.
  • Removal of glycoproteins and cholesterol from membrane.

Allow sperm to bind to zona pellucida of oocyte.

46
Q

How is sperm capacitation signalled to happen?

A

Signalling pathways, (involving soluble adenylyl cyclase and PKA)

47
Q

How do oogonia develop into oocytes in the female in development?

A
  • Oogonia from yolk sac, stud the cortex of ovary.
  • Rapidly proliferate through mitosis.
  • Some cells will enter meiosis, but arrest in meiosis 1 = Primary oocytes.
  • Maximum ~7 million germ cells made.
  • Cell death occurs, and many oogonia and oocytes degenerate.
  • All surviving ~2 million oocytes have entered meiosis 1, and are surrounded by flat epithelial cells

= Primordial Follice!

48
Q

What happens to the number of primordial follicles during childhood?

A
  • Most oocytes undergo atresia during childhood.

- Only ~40,000 remain by puberty.

49
Q

How many oocytes start to mature each month in the female?

A

Around 15 - 20

50
Q

What are the three stages of oocyte maturation?

A
  1. Preantral
  2. Antral
  3. Preovulatory
51
Q

What happens in the preantral stage of maturation?

A
  • Surrounding follicular cells become cuboidal in shape, and form a stratified epithelium of granulosa cells around the oocyte.
  • Secrete glycoprotein coat called Zona Pellucida. (around oocyte)
52
Q

What is the antral stage of maturation of oocyte?

A
  • Fluid filled spaces form between granulosa cells, and join forming an antrum.
  • Surrounding outer Thecal cells.
53
Q

How does LH affect theca cells?

A

Causes theca cells to secrete androgens, which the follicular cells convert to oestrogen.

54
Q

What is the preovulatory stage of the follicle?

A
  • Surge in LH induces growth phase, Meiosis 1 completes. (polar body too)
  • Cell enters meiosis II but arrests at metaphase.
    (complete if fertilised)
55
Q

What happens to the follicles after ovulation?

A

Becomes corpus luteum.
Remaining granulosa/theca cells become vascularised.
Change into lutein cells (yellowish).
Secrete oestrogen + progesterone to maintain uterine wall.

56
Q

What is the name of the follicle after growth, several days before ovulation?

A

Graafian follicle.

57
Q

How long does the corpus luteum remain for?

A

degrades after 14 days.

58
Q

What happens if the oocyte is not fertilised?

A
  • Breakdown of corpus luteum. (forms fibrotic scar mass called corpus albicans)
  • Less progesterone secreted
  • Menstrual bleeding occurs.
59
Q

What happens to the corpus luteum if fertilisation occurs?

A
  • Human chorionic gonadotropin is released by embryo.
  • Corpus luteum continues to grow: forms corpus luteum of pregnancy.
  • Cells secrete progesterone until 4 months. (placenta secretion then becomes adequate)

Reproductive System (6 decks)

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