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Reproductive System > Lecture 3 - The neuroendocrine timing of puberty. > Flashcards

Lecture 3 - The neuroendocrine timing of puberty. Flashcards

1
Q

What are the secondary sexual characteristics in girls?

A
  • puberty starts between 9-13 years.
  • –> development of breast buds (thelarche)
  • –> There is pubic hair growth.
  • growth spurt
  • onset of menstruation.

as an adult you get:

  • pubic hair
  • breasts
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2
Q

What are the secondary sexual characteristics in males?

A
  • puberty starts between 10-14 years.
  • –> there is genital development –> increase in testicular volume and penis length.
  • It begins with:
  • –> pubic hair growth
  • –> spermatogenesis
  • It is then followed by:
  • –> growth spurt
  • –> Genitalia adult
  • –> Pubic hair adult.
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3
Q

What does somatic grown depend on in both sexes?

A

Depends on growth hormone +IGF-1 and sex steroids in both sexes.

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4
Q

What is the differences in somatic growth between the sexes and why?

A
  • In females it is earlier and shorter.
  • In males it is larger and longer and faster.
  • —> this is because it depends on testosterone and boys have more testosterone.
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5
Q

What ends somatic growth in both sexes and what does this mean?

A

It is ended in both sexes by epiphyseal fusion.

—> Oestrogen closes epiphyses earlier in girls.

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6
Q

What is the critical weight for puberty to begin in girls?

A
  • 47 kg

- If there is significant weight loss, the reproductive cycles ceases.

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7
Q

Describe the HPG axis (hypothalamic- pituitary - gonadal axis)

A
  1. puberty is initiated by the brain - In the hypothalamus.
  2. Nocturnal GnRH is released in pulses. –> This precedes phenotypic changes by several years.
  3. The phenotypic changes that occur are breast buds/ testicular enlargement.
  4. The pituitary gland secretes more LH and FSH, which indicates the onset of puberty.
  5. Then gonad secretes androgens and oestrogen.
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8
Q

Briefly state the steps of the HPG axis.

A
  1. Hypothalamus secretes GnRH.
  2. Which goes to the pituitary, causing the pituitary gland to secrete LH and FSH.
  3. This signals to the Gonad to secrete androgens and oestrogen.
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9
Q

Why do most parts of the reproductive system not work before the normal age of puberty?

A

This is because hormone levels are too low due to low GnRH secretion.

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10
Q

What is precocious puberty?

A

This is puberty that comes too early due to the inappropriate release of GnRH.

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11
Q

What are the characteristics of GnRH?

A
  1. secretion in pulses are tied to internal biological clock..
    - —> there are synchronised external signals such as secreted by light.
  2. It acts on specific membrane receptors.
  3. It transduces signals via second messengers.
  4. They stimulate the release of stored pituitary hormones.
  5. They stimulate synthesis of pituitary hormones.
  6. It stimulates hyperplasia and hypertrophy of target cells.
  7. It regulates its own receptor.
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12
Q

What are the environmental influences that affect puberty?

A
  • triggered by changes in day length.
  • there is the involvement of pineal gland.
  • –> Puberty has sensitivity to light which feeds in through the pineal gland, so one of the first indications of puberty is at night when light levels are low, as at night there is an increase of LH.
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13
Q

Where is the GnRH-1 gene expressed?

A

It is exclusively expressed in a discrete population of neurons in the hypothalamus..

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14
Q

What happens if GnRH is blocked?

A

It results in the lack of gonadotrophin synthesis and secretion and reproductive development.

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15
Q

What happens if infertile HPG-mice are treated with synthetic GnRH?

A
  • In male HPG-mice —> Induces spermatogenesis.

- In female HPG-mice —> causes ovarian maturation and can lead to established pregnancy.

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16
Q

Describe the type of release GnRH does?

A
  • The release is pulsatile.
  • Every 1-3 hours
  • GnRH travels to the pituitary in the hypophyseal portal system.
  • The intensity of GnRH stimulus is affected by:
  • –> frequency of release.
  • –> Intensity of release.
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17
Q

Describe the composition of GnRH.

A

GnRH is a 10 amino acid peptide.

18
Q

What is the anterior pituitary gland and what is it connected by?

A
  • It is an amalgam of hormone producing glandular cells.

- Blood supply connects the anterior pituitary to the hypothalamus by the superior hypophyseal artery.

19
Q

What six peptide hormones does the anterior pituitary gland produce?

A
  1. prolactin - reproduction
  2. FSH - reproduction
  3. LH - reproduction
  4. Growth hormone - somatic growth
  5. Thyroid stimulating hormone - metabolism
  6. ACTH
20
Q

What is the relationship between sleep and LH?

A
  1. In adolescent boys, the sleep related LH increases.
  2. This stimulates a nocturnal rise of testosterone.
  3. Androgen levels also increase, which could account for some of the early pubertal changes seen in males.
  4. There is a similar pattern for women with an increase in oestrogen.
21
Q

Describe the androgen production in males?

A
  1. LH stimulates Leydig cells in testis.
  2. These produces the steroid hormone testosterone from cholesterol.
  3. The greatest amount of testosterone is produced from the testis.
22
Q

What affects the androgen production in males?

A
  • circadian rhythm –> Androgen production is highest early in the morning.
  • effects of environmental stimuli –> are both driven by the brain.
23
Q

Describe the structure of the Testes.

A
  • Each lobule contains 1-4 tightly coiled tubules called seminiferous tubules.
  • —> Each seminiferous tubule is around 60cm long.
  • In between the lobules, there is loose connective tissue and blood vessels.
  • The interstitial tissue contains leydig cells.
24
Q

What happens in the seminiferous tubules in the testes?

A
  • This is where there is 90% of the testicular volume.

- This is the location for spermatogenesis.

25
Q

What is the relationship between leydig cells and seminiferous tubules?

A
  • Leydig cells can function independently from the seminiferous tubules.
  • The seminferous tubules need functioning Leydig cells to function.
26
Q

What do the Leydig cells do?

A

They produce testosterone.

27
Q

Describe the structure of the seminiferous tubule cells.

A

they are lined by complex epithelium that is made up of two cells

  • –> supporting cells (Sertoli. cells)
  • –> Spermatogenic cells/ germ cells.
28
Q

What do Sertoli cells do?

A
  • provide nutrition and hormonal support to germ cells allowing sperm formation.
  • They are sensitive to FSH –> they increase sperm production.
  • There is inhibit secreted which does negative feedback on the anterior pituitary and FSH.
29
Q

What is the function of tight junctions between the Sertoli cells?

A
  • They act as a barrier to make sure the internal environment of the testes remain constant.
  • They also make sure that no small fragments of sperm get out.
30
Q

How do FSH and LH typically work in females?

A
  • they act primarily on gonads via Gas and then undergo PCR and interact with adenylate cyclase.
31
Q

What target cells do FSH and LH in women act on and what do these do?

A
  1. granulosa cells
  2. Theca interna
  • They stimulate sex hormone synthesis which is called steroidgenesis.
  • —> It does this by releasing oestrogen, progesterone, inhibit etc.
  • They control gamete production
  • —> folliculogenesis
  • —> Ovulation
32
Q

What do Granulosa cells respond to?

A

FSH

33
Q

What do Theca cells respond to?

A

LH

34
Q

What is the effect of oestrogen on GnRH in women?

A
  1. modern titres of Oestrogen reduces GnRH secretion
    - –> negative feedback.
  2. High titres of Oestrogen promotes GnRH secretion
    - –> positive feedback
    - –> LH surge
  3. Oestrogen reduces GnRH per pulse.
35
Q

What is the effect of progesterone on GnRH in women?

A
  1. progesterone increases the inhibitory effects of moderate oestrogen.
  2. progesterone prevents positive feedback of high oestrogen so no LH surge.
  3. Progesterone dictates the frequencies of pulses.
36
Q

What is the effect of Inhibin on FSH?

A
  • Inhibits the secretion of FSH.

- It has a small inhibitory effect on LH.

37
Q

Where is Inhibin from?

A
  • It is from granulosa cells of the corpus luteum.
38
Q

What does Growth hormone do when it is secreted from the pituitary gland?

A
  • increases TSH
  • increases metabolic rate
  • promotes tissue growth
  • increases androgens, which results in the retention of minerals in the body to support bone and muscle growth.
  • ultimately results in a growth spurt.
39
Q

what is leptin?

A
  • It is an adipocyte-derived protein hormone.
40
Q

What does leptin do?

A
  1. It signals information about energy stores to the CNS.
  2. it has an important role in regulating neuroendocrine function.
  3. Leptin has pulsatile release pattern that is associated with the variations in LH.
  4. Leptin can regulate GnRH levels and its secretion may be influenced by gonadal steroids but appear to be independent of LH control.
41
Q

How does leptin regulate neuroendocrine function?

A
  • leptin deficiency can lead to reproductive dysfunction.

- leptin can accelerate the onset of reproductive function.

Reproductive System (8 decks)

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