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Repro > Lecture 6 - Puberty and HPG axis > Flashcards

Lecture 6 - Puberty and HPG axis Flashcards

1
Q

Puberty

A

Sexual maturation and growth

Develop ability to reproduce

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2
Q

Factors affecting timing of puberty

A

Pineal gland - disorders can causes precocious puberty

Body weight - low body weight can cause cessation of menstruation

Nutrition

Leptin - released from adipose tissue

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3
Q

Secondary sexual characteristics in girls

A

9 - 13 yrs old :

  • thelarche
  • adult pubic hair growth
  • adrenarche: growth spurt
  • menarche : initiation of menstruation
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4
Q

thelarche

A

Breast buds develop - marks start of puberty

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5
Q

Adult pubic hair

A

Coarser
Wider distribution
Influenced by testosterone

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6
Q

Primary sexual characteristics

A

At birth before puberty

Anatomy of the internal and external genitalia

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7
Q

Male secondary sexual characteristics

A

10 - 14 yrs old

  • adult genital development - testicular volume enlargement
  • pubic hair growth (testosterone)
  • spermatogenesis
  • growth spurt
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8
Q

Why are boys normally taller?

A

Men have less oestrogen so growth spurt lasts longer and occurs later.

Oestrogen fuses the epiphyseal growth plates so less oestrogen means you grow taller.

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9
Q

What scale is used to measure puberty development?

A

Tanner

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10
Q

Growth spurt

A

Depends on:

  • GH
  • IGF1
  • Sex steroid hormones (testosterone and oestrogen)
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11
Q

Aromatisation

A

Converting androgens to oestrogen.

If testosterone levels are high in females can be converted to oestrogen in tissues such as adipose therefore fuses epiphyseal growth plates quicker

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12
Q

Critical weight for menstruation

A

47kg

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13
Q

What initiates puberty

A

Hypothalamus externally stimulated by e.g. weight, leptins and light in the median eminence

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14
Q

Leptin

A

Causes the pulsatile release of GnRH form the hypothalamus

Located in adipose tissue

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15
Q

HPG axis

A
  1. Nocturnal pulsatile release of GnRH from hypothalamus
  2. Anterior pituitary released FSH and LH
  3. Acts on the ovaries to release oestrogen and progesterone
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16
Q

GnRH release

A

Related to internal body clock - light

Acts on specific membrane receptors to transduse second messengers

Stimulates:

  • synthesis and release of FSH and LH
  • stimulates hyperplasia and hypertophy of target cells
  • regulates own receptor (negative feedback)
17
Q

Triggers of puberty

A

Changes of day length

Pineal gland - secretion of melatonin

18
Q

Anterior pituitary

A

No neural signalling

Synthesises and secretes substances e.g. FSH and LH

19
Q

Anterior pituitary hormones (6)

A
  1. FSH
  2. LH
  3. GH
  4. Thyroid stimulating hormone
  5. Prolactin
  6. Adrenocorticotrophic hormone (ACTH)
20
Q

How does GnRH travel to the pituitary gland?

A

Hypophyseal portal system

21
Q

FSH and LH on gonadal development

A

In young children the FSH and LH concenrations are insufficient to stimulate gonadal development.

Between 9- 12 yrs old, blood FSH and LH levels rise as amplitude of GnRH pulses rise especially during sleep.

High FSH and LH levels initiate gonadal development.

22
Q

Sleep

A

Increase pulsatile amplitude of GnRH release

Increases LH

Increases testosterone/oestrogen

23
Q

Male androgen production

A

LH stimulates Leydig cells in testes to produce testosterone

Affected by:

  • circadian rhythm (highest in early morning)
  • environmental stimuli
24
Q

Seminiferous tubule epithelial lining

A

2 cell types:

  • Sertoli cells - support sperm formation
  • Spermatogenic germ cells
25
Q

Sertoli cells

A

Sensitive to FSH

Provide nutrition and hormonal support to germ cells to produce sperm

Secrete inhibin which stimulates negative feedback on anterior pituitary FSH

26
Q

What does FSH and LH act on in the female

A

G- alpha protein coupled receptors (GPCR) which stimulate adenyl cyclase

  • Granulosa cells - produce oestrogen
  • Theca interna cells - produce androgens that can be aromatised to oestrogen
27
Q

Granulosa cells

A

Stimulated by FSH to produce oestrogen

28
Q

Theca interna cells

A

Stimulated by LH to produce androgens

29
Q

Feedback

A

Moderate oestrogen - negative feedback on GnRH

High oestrogen alon - Positive feedback (LH surge)

30
Q

Progesterone

A

Causes negative feedback on GnRH release with oestrogen and prevent high oestrogen positive feedback

GnRH - decreases frequency of GnRH pulses

Oestrogen - decreases GnRH per pulse (amplitude)

31
Q

Inhibin

A

From granulosa cells of the corpus luteum
Inhibits FSH secretion
Small inhibitory affect on LH

32
Q

Growth hormone

A
  • Increases TSH
  • Increases metabolic rate
  • Promotes tissue growth
  • Increased androgens
  • Retention of mineral in body to support bone and muscle growth
33
Q

Leptin

A

Signals info abut energy stores to CNS

  • regulates neuroendocrine function
  • pulsatile release

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