Growth and Development Flashcards by Katlyn Heneghan

____: activation of adrenal gland production of androgens

Adrenarche

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In adrenarche, the zona reticularis (adrenal gland) matures, becomes sensitive to ACTH, and leads to the production of what two molecules?

1) DHEA (becomes testosterone)
2) DHEA-S (becomes: DHT)

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At what age does the adrenal cortex become activates in boys and girls?

Age 8

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True or False: The presence of testosterone (DHEA) and DHT (DHEA-S) in the peripheral tissues allows for axillary and pubic hair growth

True

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What are the two causes of Hypothalamus-Pituitary decline during childhood?

1) Neural Inhibition of GnRH
2) Absence of adequate excitatory input

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Puberty starts at age ___ in girls and at age ___ in boys

11 (girls) and 13 (boys)

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True or False: Puberty involves the maturation of the HP-gonad Axis

True

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True or False: From early gestation to until mid puberty, GnRH, LH, and FSH are low, with FSH > LH

False - from late infancy to onset of puberty, GnRH, LH, and FSH are low; FSH > LH

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GnRH, LH, and FSH are slightly elevated after ___, then decline

birth

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What FOUR hormones are important for growth in utero?

What SIX hormones are important for growth ex-utero

Growth In Utero
1) Fetal IGF-II
2) Fetal Insulin
3) Thyroid Hormone
4) Peptide Hormones

Growth Ex Utero
1) Fetal IGF-I
2) Insulin
3) Sex Steroids
4) Thyroid Hormone
5) Growth Factor
6) Peptide Growth Factor

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Which ex-utero growth hormones are permissive for GH?

Insulin and Thyroid Hormone

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True or False: IGF-II depends on GH

False - IGF-I depends on growth hormone

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___ ___ are crucial for growth during puberty

Sex steroids

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Which hormone is important for CNS development?

Thyroid Hormone

Note: in 1st trimester, fetus uses the maternal supply of TH. however, in 2nd trimester, fetus makes own supply of TH.

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___ is the main growth mode of the fetus

Hyperplasia

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True or False: Insulin and Fetal Insulin can have anabolic effects

True

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At puberty, the sensitivity of pulse generator in the hypothalamus to negative feedback factors ____

diminishes

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True or False: Males must reach a certain weight to undergo puberty and have a growth spurt, while Females must reach a certain weight to have first occurrance of menstruation (have menarche)

True

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Which tissue is responsible for secreting the peptide hormone, leptin?

Adipose Tissue

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____ reduces inhibitory effects of NPY on Kisspeptin secretion nuclei and may be a PERMISSIVE agent in initiation of puberty

Leptin

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How can leptin affect GnRH release?

By blocking the inhibition by neuropeptide Y (NPY)

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What are the four steps of puberty in males?

1) Hypothalamic pulse generator becomes LESS sensitive to NEGATIVE feedback = ↑ GnRH

2) ↑LH/FSH due to:
a - sleep elevating GnRH
b - AP becomes more responsive to GnRH

3a) Spermatogenesis

3b) Testosterone syn/sec via: Leydig cells of testes → release of DHT and muscle/skeletal growth (anabolic effect)

4a) DHT →2 sex characteristics and GH

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What are the four major steps of puberty in females?

1) Sleep activates GnRH=↑LH/FSH
2) Pre-antral follicle (2) → antral follicle
3) estrogen released → growth of endometrium
4) menstruation occurs when estrogen levels DECLINE!

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True or False: Rise in Estrogen during the first few cycles after menarche DOES result in LH surge (and, therefore, ovulation)

False - rise in estrogen during the first few cycles after menarche does NOT result in LH surge

In females, when do positive feedback loops develop?

6-9 months

True or False: The first several menstrual cycles do not produce ovulations

True - anovulatory cycle

Menstrual bleeding occurs even in the absence of ovulation because the ___ of the follicular phase is sufficient to promote proliferation of endometrium. When dominant antral follicle becomes atretic without releasing the egg, the consequent drop in estrogen trigger sloughing off of the endometrium

Estrogen

If there is no E2 positive feedback → no ____ → follicle becomes ____→ decline in ____

No E2 positive feedback → no ovulation → follicle becomes atretic → estrogen decreases

What conditions can delay menarche? (hint: MI SIC)

- malnutrition - imbalance of thyroid - caloric insufficiency - stress - intense, consistent exercise

What two hormones leads to the following effects in both males and females? - release of growth hormone - bone deposition - pubertal growth spurt - closure of epiphyseal plates

Testosterone and Estrogen

____ leads to protein synthesis for muscle growth (anabolic effect) in males only

Testosterone

What are the two periods in one's life when growth is VERY pronounced?

1) First two years of life 2) Puberty (growth spurt)

Testosterone and estrogen DIRECTLY increases ____ and INDIRECTLY increase ____ via increase in ___

body growth; GH (growth hormone)

___ favors release of GnRH

IGF-1

Both __ and ___ can stimulate gonadal function

IGF-1 and GH

True or False: Testosterone is the only hormone that plays a critical role in pubertal growth spurt

False - testosterone and estrogen

True or False: Both GnRH and Growth Hormone are secreted in a pulsatile fashion

True

True or False: Pulsatile secretions of growth hormone produce a greater increase in body weight and longitudinal bone growth (when compared to continuous secretion of GH)

True

The sexually differentiated pattern of GH secretion only becomes manifest at ___

puberty

Describe frequency and magnitude of GH release in females vs. males?

Males: - regular, high magnitude secretory bursts Females - irregular, lower magnitude secretion pattern

True or False: During childhood there is a steady decline in plasma GH

False - there is a steady rise Especially in first two years of life + at puberty

Why is pubertal release of GH particularly elevated?

Stimulation by testosterone and estrogen

True or False: As one ages, there is a decline in sex hormones and GH secretion

True - May contribute to muscle wasting, decrease in skeletal muscle mass, and decrease metabolic rate

What time of the day do the strongest secretion of GH occur?

At night (during stage 3 and 4 of sleep)

What stimulates GH Secretion (hint: HELGAS EGS)

H - hypoglycemia E - elevated AA L - low free FA G - GHRH A - acute moderate stress S - sleep E - exercise G - ghrelin S - sex steroids

Inhibitors of GH release? (hint: SO EH -E^2 H^4)

S - somatostatin O - obesity E - elevated IGF-1 E - elevated GH H - hyperglycemia H - high free FA H - hypothyroid H - high chronic cortisol

Where structure is growth hormone released from?

Anterior pituitary

Which two hypothalmic hormones regulate release of GH from anterior pituitary?

1) Growth hormone releasing hormone (GHRH) 2) Somatostatin (growth hormone inhibitory hormone)

True or False: Somatostatin stimulates secretion of GH while GHRH inhibits GH secretion

False - Growth Hormone Releasing Hormone (GHRH) stimulates secretion of GH Somatostatin inhibits GH secretion

What are the two roles of Somatostatin (GHIH) in the anterior pituitary?

1) Inhibits release of GH 2) Inhibits TSH release

How are negative feedback loops utilized to inhibit GH secretion?

Elevation of plasma GH/IGF-1 inhibits GH secretion

___ operates with a short feedback loop to decrease release of GHRH ___ operates with a: short feedback loop that decreases ____ secretion AND long feedback loop that decreases ___ release and increases ___ release

A large drop in which two energy substrates will elevate plasma growth hormone?

Glucose or free fatty acids note: elevation of plasma glucose or free fatty acids can REDUCE plasma growth hormone

___ is a counter regulatory hormone to insulin

Growth hormone

How does an increase in plasma levels of free amino acids affect growth hormone secretion?

Increase in plasma levels of free amino acids leads to INCREASE in growth hormone secretion

Growth hormone requires normal levels of ___ and ____

Thyroid hormone and cortisol

Thyroid hormone enhances the sensitivity of the growth hormone-synthesizing cells in the pituitary to ___ and enhances sensitivity of target cells to growth hormone itself

GHRH

How does thyroid hormone deficiency affect GH release and its effects?

Hypothyroidisim leads to decreased GH release

While moderate levels of ____ stimulates GH release. However, with prolonged exposure to high levels, there is a direct inhibition of ___ release

cortisol; growth hormone

___ is a peptide hormone released by the stomach in response to fasting and hypoglycemia. It promotes appetite!

Ghrelin

What are the three DIRECT effects of GH?

1) Provides metabolic substrates for growth (spares glucose for brain during starvation) 2) Stimulates synthesis of IGF-1 (somatomedin) 3) Regulates gonadal function - participating in maturation of gametes + production of sex steroids + regulation of lactation/pregnancy

Indirect effect of GH?

Through action of IGF-1, growth hormone stimulates growth in different tissues (albeit: a limited amount)

What are two mechanisms by which GH spares glucose for the brain?

1) Enhances protein synthesis 2) Shifts metabolism of non-CNS tissues

Which molecule stimulates uptake of amino acids in skeletal muscle, as well as increases the number of ribosomes in those muscles?

Growth Hormone

What type of amino acids favor release of GH

Dietary amino acids

What are three mechanisms by which GH increases plasma fatty acids?

1) Stimulates lipolysis in adipose tissues 2) Increase plasma free fatty acids that become available to cells for energy production

How do high free fatty acids affect GH release?

High free fatty acids suppress release of GH

What is a reliable way to estimate growth hormone?

Measure IGF-1 (longer hald life)

What is the predominant IGF found in kids and adults, whose production strictly depends on GH stimulation?

IGF-1

Which IGF is the characteristics form seen in the fetus and does NOT depend on GH stimulation?

IGF-2

GH acts on the ___ to stimulate production of IGF-1, which then acts in classical endocrine fashion

liver

True or False: Growth hormone can stimulate production of IGF-1 at target tissue level in the bones. This locally IGF acts in endocrine fashion

False - while GH can stimulates IGF-1 production in target tissues in bones - this locally made IGF acts in AUTOCRINE/PARACRINE fashion

True or False: All activators and inhibitors of GH release indirectly affect secretion of IGF-2

False All activators and inhibitors of GH release indirectly affect secretion of IGF-1!

What type of receptor does IGF-1 bind to?

Tyrosine kinase

In bone, ____ increases production of epiphyseal cartilage and stimulation of linear growth.

IGF-1

True or False: Once long bones have matured and epiphyses have sealed, IGF-1 continues to stimulate linear growth

False - IGF-1 can NO LONGER stimulate linear growth (instead: it will increase width of bones)

In bones, there is ____ growth before puberty and ___ growth after puberty

linear growth before puberty radial growth after puberty

Malnutrition, hypothyroidism, and low insulin inhibits: A. IGF made by liver B. IGF made by bone

A. IGF made by liver

IGF-1 is transported in the plasma via ____

IGF binding protein

Why do abused and emotionally deprived kids fail to grow to their full potential stature?

High stress levels reduce GHRH release from hypothalamus and GH from pituitary

What causes Laron's dwarfism?

Mutation in GH receptor (insensitive to GH)

What are the following descriptions features of: - No IGF-1 release - Linear growth is compromised, as is metabolic activity of GH - commonly have low glucose, high cholesterol, and obesity

Laron's dwarfism

A pituitary tumor that develops before puberty can cause ____ because epiphyseal plates have not yet sealed, giving way to LONGITUDINAL growth

Gigantism

Individuals with ____ develop pituitary tumors AFTER puberty, which gives way to RADIAL GROWTH

Acromegaly

Which ex utero hormone will increase amino acid uptake and protein synthesis?

Insulin