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physiology - the reproductive system > 3- HPG Axis II > Flashcards

3- HPG Axis II Flashcards

1
Q

What is puberty?

A

The transition from a non-reproductive to a reproductive state

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2
Q

What happens during puberty?

A

1.Gonads produce mature gametes
- testis —-> spermatozoa
- ovaries —–> oocytes
2. Breast development in females , increased testicular volume of above 4ml in males
3. secondary characteristics develop
4. profound physical and psychological changes

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3
Q

What are the 2 endocrine events of puberty?

A

Adrenarche
Gonadarche

The two events are independently regulated

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4
Q

What is adrenarche?

A

Caused by the change in adrenal androgen secretion due to the cellular remodelling of the adrenal glands
Responsible for pubarche
- growth of pubic and axillary hairs
- growth in height

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5
Q

What is gonadarche?

A

Caused by the reactivation of the HPG axis
Activation of gonadal steroid production results in the production of viable gametes and the ability to reproduce
-results in LH/FSH release
LH- steroid synthesis —-> secondary sex characteristics
FSH- growth of testis (male)/ steroid synthesis and folliculogenesis (female)

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6
Q

What are the androgens that increase in secretion during adrenarche and where are they secreted from?

A

Dehydro- epiandosterone (DHEA)
Dehydro- epiandosterne sulphate (DHEAS)

They are secreted from the zona reticulatas of the adrenal cortex

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7
Q

What is pubarche?

A

The appearance of pubic and axillary hair resulting from adrenal androgens secretions
Triggered by adrenarche
Its associated with:
- increased sebum production = acne
- infection, abnormal keratinisation = acne

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8
Q

When is pubarche categorised as precocious?

A

Before 8 years in girls
Before 9 years in boys

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9
Q

When does gonadarche occur?

A

Several years after adrenarche (typically 11yrs)

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10
Q

What stimulates the onset of puberty?

A

There is a maturation event within the CNS
-GnRH maturation
-Environmental/genetic factors
-Body fat/nutrition
-Kisspeptin

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11
Q

How does nutrition and body fat have an effect on the onset of puberty?

A

There is a link between fat metabolism and reproduction

Anorexia nervosa/ intensive physical training
- reduced response to GnRH
- decrease gonadotropin levels
- amenorrhea (absence of menstrual periods)
- levels restored when nourished and exercise is stopped

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12
Q

What is the Frisch et al, body fat hypothesis?

A

Certain % body weight (17%) is necessary for menarche (first menstrual cycle) and (22%) to maintain female reproductive ability

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13
Q

What GI hormones affect the activity of kisspeptin?

A

Ghrelin
Leptin
The activity of these hormones in the hypothalamus influence the activity of kisspeptin and GnRH

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14
Q

How does kisspeptin affect onset puberty?

A

Experiments were done to see the effect of kisspeptin in puberty:

Inactivating mutations of KISS1R or the gene coding for kisspeptin:
- hypogonadism
- failure to enter puberty
- hypogonadotropic hypogonadism

Activating mutations of KISS1R:
- precocious puberty

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15
Q

What is consonance?

A

The completion of each stage of puberty in the correct order, as denoted by the Tanner Stages of Puberty, known as the ‘smooth ordered progression’. The time that individuals take to go through each stage may differ, but the order in which the stages are completed remains the same between individuals.

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16
Q

What are the Tanner stages of puberty?

A

Five stage scale of puberty, It describes the physical changes in breast development (females), hair development and external genitalia, with the first stage of puberty being breast budding in females, and an increase in testicular volume in males.

17
Q

What physical changes in puberty do the Tanner stages of puberty cover?

A
  1. Pubic and axillary hair growth (M/F)
  2. Testicular volume and penile growth (M)
  3. Breast development (F)
18
Q

What physical changes occur in females during puberty?

A
  1. Breast enlarge
    - thelarche: first outward sign of E2 (oestrogen) activity
  2. Pubic/axillary hair growth
  3. Uterus enlarges , cytology changes, secretions in response to oestrogen (E2)
  4. Uterine tubes - produce secretions
  5. Vagina - produce secretion
  6. Cervical changes - produce secretions
  7. Height
    - earlier onset than boys
  8. Body shape
  9. HPG axis
    - increase in ovarian size and follicular growth
  10. Menarche (first period)
    11.Fetrilarty
    - kicks in 1 year after menarche
19
Q

What physical changes occur in males during puberty?

A
  1. External genitalia
    - increase in testicular volume >4 ml
    - growth of penis, scrotum, scrotal skin changes
  2. Vas deferens
    - lumen increases
  3. Seminal vesicles & prostate (produce secretions)
  4. Facial/body hair
  5. Pubic / axillary hair
  6. Larynx –
    - androgens -> enlarge larynx, Adams apple (projection of thyroid cartilage), voice deepens
  7. Height
    - PHV =10.3 cm/y reached at 14 yrs
  8. Body shape
  9. Onset of fertility
    - testosterone from Leydig cells stimulates meiosis & spermatogenesis in Sertoli cells
    - boys fertile at the beginning of puberty
20
Q

What initiates a growth spurt?

A

A complex interaction between the growth hormone and oestrogen
It occurs earlier in girls

21
Q

What psychological changes occur in puberty?

A

1.Increasing need for independence

2.Increasing sexual awareness/interest

  1. Development of sexual personality

Later maturation = better adjustment

22
Q

What is the biphasic effect of oestrogen on epiphyseal growth?

A

Low levels:
- linear growth and bone maturation
High levels:
- epiphyseal fusion

23
Q

What are the effects of androgens on the differentiation of pilosebaceous units (PSUs)?

A

Sebaceous PCU, which secreted sebum, this can cause an infection and therefore acne

Vellous PCU, can differentiate into a terminal PSU (beard growth) or an APO PSU (pubic and auxiliary hair growth)

24
Q

What is the definition of precocious sexual development?

A

The development of any secondary sexual characteristics before the age of 8 in girls and before the age of 9/10 in boys

25
Q

What are the causes of precocious puberty?

A

Premature activation of the HPG axis
It can be gonadotropin dependent or independent

26
Q

What is gonadotropin dependant precocious puberty?

A

Excess GnRH secretion - can be idiopathic or secondary
Excess gonadotropin secretion - pituitary tumour
Consonance

27
Q

What is gonadotropin independent precocious puberty?

A

Loss of consonance
Testotoxicosis - activating mutation of LH receptor
Sex steroid secreting tumour or exogenous steroids

28
Q

How does McCune Albright Syndrome cause precocious puberty?

A

McCune Albright Syndrome is a result of an α G-subunit activating mutation. This is the hyperactivity of this signalling pathway, thus it will over-produce the hormones that work by this pathway.

LH and FSH work through this pathway, so we would get their overproduction, leading to precocious puberty.

29
Q

Define pubertal delay?

A

The absence of secondary sexual maturation by 13 years in girls (or the absence of menarche by 18) and by 14 in boys

30
Q

What is the cause of pubertal delay?

A

Delayed HPG axis activation

31
Q

In what ways can delaying of the HPG axis activation cause pubertal delay?

A
  1. Constitutional delay
    - affecting growth and puberty
    - 10 times more common in boys
    - secondary to chronic illness (eg. diabetes, cystic fibrosis)
  2. Hypogonadotrophic hypogonadism (low LH and FSH)
    - Kallman’s Syndrome (X-linked KAL1 gene, impaired GnRH migration)
    - other mutations causing defects in GnRH production
  3. Hypergonadotrophic hypogonadism (high LH and FSH)
    - gonadal dysgenesis and low sex steroid levels (can occur with normal karyotype, via viral infection eg. mumps)
32
Q

What are some chromosomal abnormalities that can cause gonadal dysgenesis?

A
  • Klinefelter’s Syndrome (an extra X chromosome, XXY)
    would have male genitalia, but also wide hips, long arms and legs, and some breast development
  • Turner’s Syndrome (missing an X chromosome, XO)
    are shorter than usual, have underdeveloped or ‘streak’ ovaries

physiology - the reproductive system (12 decks)

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