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Physiology 2 > Reproduction: Hypothalamic/Pituitary/Gonadal Axis II > Flashcards

Reproduction: Hypothalamic/Pituitary/Gonadal Axis II Flashcards

1
Q

What is puberty?

A

Transition from a non-reproductive to a reproductive state in both males and females

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2
Q

What is the clinical defintion of puberty in both males and females?

A
  • Clincal definition in females is breast development
  • Clinical defintion in males is increased testicular volume
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3
Q

What are the 2 endocrine events that contribute to puberty?

A
  • Adrenarche
  • Gonadarche
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4
Q

What event is induced once as a result of adrenarche?

A

Puberarche

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5
Q

What is Adrenarche?

A

A change in adrenal androgen secretion due to the remodelling of the adrenal gland

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6
Q

What are the main adrenal androgens that see an increase in secretion as a result of adrenarche?

A
  • Dehydro-epiandrosterone (DHEA)
  • Dehydro-epiandrosterone sulphate (DHEAS)
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7
Q

During adrenarche does the level of secretion in another other adrenal androgen change apart from DHEA and DHEAS?

A

No, only secretion of DHEA and DHEAS is changed (increased) durinf adrenarche

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8
Q

What area of the adrenal cortex are DHEA and DHEAS produced and secreted on?

A

Zona reticularis of adrenal cortex

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9
Q

What is puberarche?

A

The appearance of pubic hair/axillary hair due to the increase in adrenal androgen secretion durinf adrenarche

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10
Q

What process is puberarche associated with?

A

Increased sebum production which reults in acne

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11
Q

What other reasons are there for the acne seen during puberarche?

A
  • Infection
  • Abnormal keratinization of the skin
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12
Q

What is Gonadarche?

A
  • The reactivation of the HPG axis at puberty
  • Gradual increase in pulsatile release of GnRH which results in the production of viable gametes
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13
Q

Why does the HPG axis need to be reactivated as a result of Gonadarche?

A
  • HPG axis fist activates at 16th gestational week to ensure correct sexual differentiation
  • Remains active during first 2 postnatal years and then shuts down for about 10 years
  • HPG axis needs to be reactivated via maturation of GnRH neurons to ensure production of mature gametes
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14
Q

Why is LH used to study the behaviour of GnRH within the body rather than GnRH itself?

A
  • LH mimics behaviour of GnRH within the body
  • GnRH only released into hypophyseal portal circulation so incredibly difficult to take GnRH samples directly
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15
Q

Describe the pattern of GnRH release throughout puberty

A
  • Reactivation of HPG axis during early puberty first results in nocturnal rise in GnRH release
  • THis then gradually causes an increase in GnRH pulsatile release throughout the day until you get a consistant pulsatile release of GnRH throughout 24 hours during late puberty
  • Nocturnal rise stil present at late puberty
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16
Q

What are the main ideas for what it is exactly that stimulates the onset of puberty?

A
  • Kisspeptin
  • Body fat/nutrition
17
Q

How are reproductive function and nutrition linked?

A
  • It’s been shown that anorexic individuals and athletes have a reduced response to GnRH
  • This results in a decrease in Gonadotrophin hormone levels (LH and FSH)
  • Amenorrhea in females (absence of menstral cycle)
  • When the diets of the anorexic individuals returned to normal and when athletes stopped exercise their menstrul cycle returned and reproductive function went back to normal
18
Q

What does the body fat hypothesis state?

A
  • States that you need at least 17% body fat to induce menarche (first menstral cycle) and 22% in order to maintain female reproductive ability
19
Q

Explain how both Ghrelin and Leptin may play a role in the onset of puberty?

A
  • Ghrelin secreted from the gut and leptin secreted from adipose tissue are able to regulate secretion of kisspeptin from the hypothalamus
  • Secretion of kisspeptin leads to activation of rest of HPG axis which results in sexual maturation (production of mature gametes from gonads)
20
Q

How are reproductive function and kisspeptin linked?

A
  • Mutations that inactivate kisspeptin receptor or mutations that inactivate kisspeptin gene lead to:
    • Hypogonadism - Small gonadal structures
    • Failure to enter puberty
  • Mutations that activate the kisspeptin receptor without binding of kisspeptin lead to:
    • Precocious puberty (early puberty)
21
Q

Hypogonadism and failure to enter puberty are features of what disorder?

A

Hypogonadatrophic hypogonadism

22
Q

What is consonance?

A

A smooth ordered progression of pubertal chnages that occur during puberty

23
Q

What is the order of pubertal chnages that occur during male puberty?

A
  1. Genital development begins
  2. Growth of pubic hair begins
  3. Peak height spurt
  4. Genitalia fully developed
  5. Pubic hair fully developed
24
Q

What is the order of pubertal changes that occur in females?

A
  1. Breast bud develops
  2. Pubic hair develops
  3. Peak height spurt
  4. Menarche (first menstral cycle)
  5. Pubic hair fully developed
  6. Breasts fully developed
25
What are some of the physical changes that occur in girls during puberty?
* Breast enlargement * Growth of pubic/axillary hair * Uterus enlarges * Cytology changes in uterine tubes, cervix and vagina - cells in these area begin to produce secretions in response to Oestrogens * Re-activation of HPG axis * Menarche * Fertility
26
Why aren't females classed as fertile once menarche begins?
* Although menarche has occured HPG axis still has to be re-activated in order to induce follicle growth and recruitment * This means the first few menstral cycles won't release an egg cell
27
What are some of the physical changes that occur in males during puberty?
* External genitalia develop - increase in testicular volume * Lumen of vas deferens increases * Secretions from seminal vesicles and prostate * Enlargement of the larynx * Onset of fertility - boys are fertile once puberty starts
28
How do oestrogens result in the growth spurt seen during puberty?
* At first low levels of oestrogens result in linear growth and maturation of bones * Then high levels of Oestrogens result in bone fusion (marks end of bone growth)
29
What are the 2 types of pilosebaceous units (PSUs)?
* Sebaceous PSUs * Vellus PSUs
30
How do androgens affect the different types of pilosebaceous units?
* Androgens cause increased secretion sebum from sebaceous pilosebaceous units which leads to acne * Androgens cause the vellus pilosebaceous units to differentiate into terminal pilosebaceous units or the APO-pilosebaceous unit * Terminal PSUs cause beard hair growth * APO-PSUs lead to pubic/axillary hair growth
31
What psychological changes occur during puberty?
* Increasing need for independence * Increasing sexual awareness/interest * Development of sexual personality
32
What is precocious puberty?
* Development of any secondary sexual characteristic before the age of 8 in girls and before the age of 9-10 in boys
33
What are the two types precocious puberty?
* Gonadotrophin-dependent * Gonadotrophin-independent
34
What are some of the characterististics of gonadotrophin-dependent precocius puberty?
* Excess GnRH secretion * Excess gonadotrophin hormone secretion
35
What are some characteristics of gonadotrophin-independent precociuos puberty?
* Occurs when the gonads produce hormones at an usually high rate * This results in gonadal maturation occuring too early which results in mature gamete production occuring too early
36
McCune albright syndrome is a cause of gonadotrophin-independent precocius puberty. How does McCune albright syndrome lead to precocious puberty?
* Mutation in the GNAS1 gene causes hyperactivation of all G protein-couplled signalling pathways * This results in abnormal amounts of FSH, LH and GnRH to be produced leading to precocoius puberty
37
What is pubertal delay?
* Absence of sexual maturation by the age of 13 in girls and 14 in boys * Alos absence of menarche by age 18 in girls
38
What are the different types of pubertal delay?
* Constitutional delay * Pubertal delay due to Hypogonadotrophic gonadism * Pubertal delay due Hypergonadotrophic gonadism * ALL 3 RESULT IN DELAYED HPG-AXIS ACTIVATION
39
How does kallman's syndrome lead to hypogonadotrophic hypogonadism?
* Kallman's syndrome caused by mutation in X-linked KAL1 gene * Mutation in this gene results in impaired migration of GnRH neurons to the hypothalamus

Physiology 2 (29 decks)

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