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SA reproductive > S3) Puberty and HPG Axis > Flashcards

S3) Puberty and HPG Axis Flashcards

1
Q

What is puberty?

A

Puberty is a stage of human development when sexual maturation and growth are completed and result in ability to reproduce

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2
Q

Identify 3 forms of development that occur during puberty

A
  • Morphological development
  • Physiological development
  • Behavioural development
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3
Q

Identify the primary sexual characteristics

A
  • Gonads
  • Genitals
  • development of these sexual characteristics at birth
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4
Q

Identify 4 secondary sexual characteristics

A
  • Pubic hair
  • Axillary hair
  • Female breast development
  • Male voice changes
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5
Q

Briefly, describe the reproductive system before and after puberty

A
  • Primary sexual characteristics are established before birth
  • Reproductive system inactive until puberty
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6
Q

Identify 4 events that occur in puberty for males and females

A
  • Accelerated somatic growth
  • Maturation of primary sexual characteristics
  • Appearance of secondary sexual characteristics
  • Menstruation and spermatogenesis begin
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7
Q

Describe the involvement of the pineal gland in puberty

A
  • Triggered by changes in day length
  • Varies with secretion of melatonin
  • Pineal gland tumours influence puberty
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8
Q

Describe the variation in the menarche of puberty in western countries over the years

A
  • Average age of menarche = 17 years (C 1800)
  • Average age of menarche < 13 years (C 2000)
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9
Q

Explain how nutrition has a notable role in the onset of puberty

A
  • Body weight most important factor
  • Leptins may be involved in signalling
  • Significant weight loss = menstrual cycles stop
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10
Q

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

A

Weight = 47 kg

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11
Q

When does puberty begin in girls?

A

9 - 13 years

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12
Q

What is thelarche?

A

Thelarche is the onset of female breast development

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13
Q

What is pubarche?

A

Pubarche is the appearance of sexual hair

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14
Q

What is adrenarche?

A

Adrenarche is the onset of androgen-dependent body changes such as growth of axillary and pubic hair, body odor, and acne, awakening of the adrenal glands

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15
Q

Describe the sequence of events in female puberty

A

Breast bud growth → Pubic hair growth → Growth spurt → Onset of menstruation

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16
Q

Which hormones drive puberty in females?

A
  • Oestrogen
  • Testosterone
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17
Q

Describe the sequence of events in male puberty

A

Genital development → Pubic hair growth → Spermatogenesis → Growth spurt

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18
Q

Which hormone drives puberty in males?

A

Testosterone

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19
Q

Identify the stages of the following photos in the Tanner Scale:

A
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20
Q

Identify the stages of the following photos in the Tanner Scale:

A
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21
Q

Accelerated somatic growth occurs in both sexes. What drives this process?

A
  • Growth hormone
  • Sex steroids
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22
Q

What concludes the period of accelerated somatic growth in both sexes?

A

Epiphyseal fusion

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23
Q

If accelerated somatic growth occurs in both sexes, why are women generally smaller/shorter?

Provide 3 reasons

A
  • Growth spurt in girls is shorter and earlier
  • Growth spurt in boys is longer and slightly faster
  • Oestrogen closes epiphyses earlier in girls, oestrogen is responsible for fusing the growth plates in the bones
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24
Q

Compare and contrast puberty in males and females in terms of the following:

  • Onset
  • First sign of puberty
  • Growth velocity
  • Duration of puberty
A
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25
Q

Outline the HPG axis in females

A
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26
Q

Outline the HPG axis in males

A
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27
Q

Identify the 4 events which succeed increased stimulation of the hypothalamo-pituitary-gonadal axis

A
  • Gradual activation of GnRH
  • Increased frequency and amplitude of LH pulses
  • Stimulated secretion of sexual steroids
  • Extragonadal hormonal changes
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28
Q

GnRH -1 gene is primarily responsible for mammalian GnRH.

What happens when GnRH is blocked?

A
  • Lack of gonadotrophin synthesis and secretion
  • Lack reproductive development occurs
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29
Q

Identify 5 characteristic functions of hypothalamic releasing hormones

A
  • Act on specific membrane receptors
  • Transduce signals via second messengers
  • Stimulate release & synthesis of stored pituitary hormones
  • Stimulates hyperplasia & hypertrophy of target cells
  • Regulates its own receptor
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30
Q

How are hypothalamic releasing hormones secreted?

A

Secretion in pulses tied to internal biological clock

31
Q

GnRH stimulates the anterior pituitary gland gonadotrophs to secrete two gonadotropic hormones.

Identify them

A
  • Luteinising hormone (LH)
  • Follicular stimulating hormone (FSH)
32
Q

What is leptin and what is its broad function?

A
  • Leptin is an adipocyte-derived protein hormone
  • It signals information about energy stores to CNS
33
Q

Describe the release of leptin

A
  • Leptin has pulsatile release patterns significantly associated with the variations in LH
  • Its secretion may be influenced by gonadal steroids but appears to be independent of LH control
34
Q

What role does leptin have in reproductive function?

A
  • regulates menstral cycle

– puberty: the more leptin and fat the earlier someone will start menstruation

– fertility: low levels increase chance of infertility

– pregnancy: levels increase in pregnancy and help develop the placenta and fetal growth

35
Q

In four steps, explain how GH secretion from the pituitary gland leads to a growth spurt

A

⇒ Increased TSH

⇒ Increased metabolic rate

⇒ Promoted tissue growth

⇒ Increased androgens

36
Q

What effect does the increased production of androgens have?

A

It retains minerals in body to support bone and muscle growth

37
Q

How often is GnRH released?

A

Released every 1-3 hrs, don’t want it to be continuous otherwise the body becomes desensitise to it.

38
Q

Identify the two factors which affect the intensity of the GnRH stimulus

A
  • Frequency of release
  • Intensity of release
39
Q

Where is GnRH released into?

A

Travels to the anterior pituitary gland in the hypophyseal portal system, it stimulates the anterior pituitary gland to release LH and FSH

40
Q

How is the anterior pituitary connected to the hypothalamus?

A

Anterior pituitary is connected to the hypothalamus by the superior hypophyseal artery

41
Q

Identify the six peptide hormones found in the anterior pituitary

A
  • Prolactin
  • Growth hormone (GH)
  • Thyroid Stimulating Hormone (TSH)
  • Adrenocorticotropic Hormone (ACTH)
  • Follicle-Stimulating Hormone (FSH)
  • Luteinizing Hormone (LH)
42
Q

Most parts of the reproductive system can work before the normal age of puberty.

Why does puberty not occur earlier?

A

Puberty is under hormonal control:

  • LH and FSH levels insufficient to initiate gonadal function
  • Between 9-12 yrs, blood levels of LH & FSH increase to trigger puberty
43
Q

Which cells does LH act on in males?

A

Leydig cells: release testosterone

causes a negative feedback on hypothalamus and pituitary gland

44
Q

Where in the body is the most testosterone produced?

A

Testes

45
Q

Which factors affect the production of testosterone?

A
  • Circadian rhythm (highest early in morning)
  • Environmental stimuli
46
Q

Describe the structure of the testes

A
  • Each lobule contains 1-4 seminiferous tubules
  • Interstitial tissue contains Leydig cells
  • Contains loose connective tissue
  • Contains blood vessels
47
Q

Describe the structure and function of the seminiferous tubules

A
  • Structure:

I. Tightly coiled tubes

II. Composes 90% of testicular volume

  • Function: location for spermatogenesis
48
Q

Explain the relationship between leydig cells and seminiferous tubules

A
  • Leydig cells function independently of seminiferous tubules
  • Seminiferous tubules need functioning Leydig cells
49
Q

Identify the two cells found in the epithelium of the seminiferous tubules

A
  • Sertoli cells
  • Spermatogenic cells/germ cells
50
Q

What do Sertoli cells do?

A

Sertoli cells provide nutrition and hormonal support to germ cells allowing sperm formation

51
Q

Describe the hormonal control and release of Sertoli cells

A
  • Sensitive to FSH (increase sperm production)
  • Secrete inhibin (feedback on Anterior Pituitary to stop release of FSH)
52
Q

What do LH & FSH do in the female HPG axis?

A

They act primarily on gonads via Gαs PCR → adenylate cyclase

53
Q

Identify the target cells of FSH and LH in the female

A
  • Granulosa cells
  • Theca interna
54
Q

What are the roles of FSH and LH in the female HPG axis?

A
  • Stimulate sex hormone synthesis (steroidgenesis)
  • Control gamete production (folliculogenesis and ovulation)
55
Q

Identify some sex hormones in females

A
  • Oestrogen
  • Progesterone
  • Inhibin
56
Q

Describe the hormonal control of ovarian cells

A
  • Granulosa cells respond to FSH
  • Theca cells respond to LH
57
Q

Describe the control of oestrogen on GnRH secretion

A
  • Moderate titres of oestrogen reduce GnRH secretion (negative feedback)

- High titres of oestrogen alone promote GnRH secretion (positive feedback LH ‘surge’), only positive feedback during ovulation

58
Q

Describe the control of progesterone on GnRH

A
  • Progesterone increases inhibitory effects of moderate oestrogen
  • Progesterone prevents positive feedback of high oestrogen (no LH surge)
  • it prevents more eggs to mature and so reduces the frequency of GnRH production
  • it has the opposite effect of oestrogen
59
Q

Describe the function and location of inhibin secretion in females

A
  • Location: secreted from granulosa cells of corpus luteum
  • Function: inhibits the FSH secretion & small inhibitory effect on LH
  • stops more follicles being stimulated
60
Q

what is the definition of gonadarche

A
  • activation of the gonads
61
Q

what is the definition of menarche

A
  • onset of menstruation at puberty
62
Q

what age defines central precocious puberty in boys and girls and what is its relationship with GnRH

A

-GnRH → elevated GnRH levels, premature activation of HPA

boys - before 9

girls - before 8

  • in girls its more common to start puberty early whereas, with boys its more pathological
63
Q

causes for central precocious puberty

A
  • idiopathic
  • CNS lesion
  • `pituitary secreting GnRH tumours
  • obesity
64
Q

how can you test for precocious puberty

A
  • basal LH and FSH increased
  • girl will have high oestrogen
  • boy will have high testosterone
65
Q

what is peripheral precocious puberty

A
  • not to do with GnRH
  • high oestrogen and testosterone peripherally due to problems with ovaries, testicles, adrenal glands or pituitary gland
66
Q

causes of peripheral precocious puberty

A
  • increased androgen production due to cysts
  • increased oestrogen due to HCG germ cell tumours
  • increased HCG (pregnancy hormone) due ti hypothyroidism
67
Q

reasons for delayed puberty

A
  • constitutional growth delay
  • malnutrition
  • chronic disease
  • hypogonadism
68
Q

What products do the granulosa cells produce and the theca cells produce

A

granulosa: oestrogens
theca: androgens

69
Q

by what age should the earliest sign of puberty be observed in boys and girls

A

9

11

70
Q

does variation in the luteal phase account for varying duration of a woman’s menstrual period

A

no

71
Q

which cells are the primary site of actions for LH in males

A

leydig

72
Q

what are the functions progesterone

A
  1. inhibit FSH and LH
  2. initiation of the secretory phase
  3. increase basal body temp
73
Q

where is inhibit produced

A

Sertoli cells in the male

granulosa cells in the female

SA reproductive (22 decks)

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