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Phys II Unit II > 8 Regulation Of Growth > Flashcards

8 Regulation Of Growth Flashcards

1
Q

Who the fuck was the Turkana Boy

A

H. erectus who had the body of a 13 y.o. But was only 8 when he died.

Illustrates the prolonged development, with extended adolescence and teenage years, of modern humans

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2
Q

Modern humans are weaned at 2.5, have first molar at 6 and first breeding at 19.3. What about chimps?

A

Weaned at 4, first molar at 4, first breeding at 11.5 😳

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3
Q

What are some examples of hormones that regulate patterns of human growth and maturation

A

GH/IGF-1
Thyroid hormone
Steroids

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4
Q

Inadequate thyroid hormone affects both ______ and ______.

A

Growth and maturation —> cretinism

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5
Q

Deficiency of two or more anterior pituitary hormones is called…

A

Congenital pan-hypopituitarism

Effects include the targets of all pituitary hormones
Adrenal cortex atrophied
Secretion of adrenal glucocorticoids and sex hormones decreases
Individuals are more sensitive to stress, illness, trauma
Gonads atrophy (b/c low FSH/LH)*
Thyroid gland atrophied and function decreases*

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6
Q

_______ is the primary determinant of growth

A

GH

Signals rapid linear growth at puberty but not early childhood

Maintains lean body mass in adults

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7
Q

_______ factors play a large role in GH secretion

A

Environmental (Diet, sleep, stress, exercise)

GH directly recruits nutrient stores to make fuel reserves ready for new tissue synthesis

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8
Q

GH stimulates __________ to increase linear growth

A

Somatomedins (IGF-1), produced in liver

They increase protein synthesis, cell division, and bone growth

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9
Q

_______ from hypothalamus stimulates release of GH from ________.

A

GHRH —> GH from pituitary somatotrophs

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10
Q

_________ from hypothalamus inhibits release of GH from _________

A

GHIH (aka somatostatin) —X—> GH from pituitary somatotrophs

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11
Q

What causes the hypothalamus to stop releasing GHRH and start releasing GHIH?

A

Negative feedback from GH and IGF-1

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12
Q

GH directs growth primarily via…

A

Somatomedins (IGF-1)

IGF-1 is GH dependent

Occurs 12-18 hr after GH release

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13
Q

Which has a longer half life, GH or IGF-1?

A

IGF-1

Occurs 12-18 hours after GH release

Bound to at least 6 plasma binding proteins

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14
Q

GH/IGF-1 promotes long bone growth only as long as…

A

The epiphyseal plate remains cartilaginous (open)

PUBERTAL growth correlates well with IGF-1 plasma levels

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15
Q

At the end of adolescence, _________ induce ossification of the epiphyseal plate, thus ending growth.

A

Sex steroids, esp. testosterone

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16
Q

Increased linear growth due to excessive stimulation of epiphyseal plates

A

Gigantism

Ex. Robert Wadlow, who was 8’1” at age 13 and died at 8’11.1” at age 22

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17
Q

GH excess absent of linear bone growth (after puberty)

A

Acromegaly

Bone and soft tissue deformities
Viscera size increases
Thick skin
Increased protein and decreased body fat content
Propensity for diabetes
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18
Q

What are some promoters of GHRH release?

A 
A2-adrenergic receptors
Galanin
GABA
Ghrelin
Sex steroids
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19
Q

What are some promoters of GH release (other than GHRH)?

A

Ghrelin
Thyroid hormones
Glucocorticoids

20
Q

What are some promotors of Somatostatin release?

A

B2-adrenergic receptors
Free fatty acids
Glucose
Glucocorticoids

21
Q

What are some inhibitors of Somatostatin release?

A 
Arginine 
Dopamine
Serotonin
Acetylcholine
Ghrelin
22
Q

What sort of positive effects do glucocorticoids have on growth?

A

Induce GH gene expression
Induce GHRH receptor on somatotrophs
Increase Ghrelin receptors on GH-secreting cells

23
Q

What sort of negative effects does an excess of glucocorticoids have on growth?

A

Glucocorticoids increase hypothalamic somatostatin
Decrease GH receptor expression in peripheral tissues
Hypercortisolism (Cushing’s) associated with muted GH secretion
Exogenous glucocorticoids suppress growth in children

24
Q

What sort of negative effects does a deficit of glucocorticoids have on growth?

A

Adrenalectomy decreases expression of GHRH and Ghrelin receptors in the pituitary
ACTH deficiency/hypocortisolism associated with low GH levels

25
Q

What do we mean when we say that cortisol has a “biphasic” effect on the somatotrophic axis?

A

LOW levels of cortisol depress GH gene transcription and decrease response to GHRH stimulus (due to low GHRH receptors)

HIGH levels of cortisol increase somatostatin transcription and decrease GHRH actions

MODERATE levels of cortisol are just right and allow for GH activity

26
Q

What sort of effect do exogenous glucocorticoids have on GH?

A

Can stunt growth via disproportion of IGF-1 production

27
Q

What is the relationship between GH and Thyroid hormones?

A

T3/T4 is permissive for growth in children. GH alone is NOT SUFFICIENT for growth

28
Q

What is the relationship between Insulin and GH?

A

Insulin may directly promote growth through promotion of protein synthesis

Insulin resembles IGFs and excess may stimulate growth via the IGF receptor

29
Q

What is the relationship between Sex Steroids and GH?

A

Androgens promote protein synthesis

Androgens enhance long bone growth

Girls start puberty ~2 years before boys, resulting in more prepubertal growth in boys

Masculinization of the brain my enhance GH secretion

30
Q

________ is required for growth, but does not directly signal growth

A

Thyroid hormone

Key hormone for increasing metabolic needs prior to tissue accumulation

Facilitates linear growth of bone and increases activity of cartilage chondrocytes in the growth plate

31
Q

What are the maturation effects of T3?

A

T3 stimulates adult bone remodeling b/c of T3 receptors present in osteoblasts

Thyroid signaling required for tooth development and eruption

Growth and maturation of the epidermis, hair follicles, and nails

Alters subcutaneous tissue

32
Q

How does thyroid hormone act on bone growth specifically?

A

Accelerates linear growth of bone by:

Increasing activity of cartilage chondrocytes in the growth plate

Stimulating Osteoblasts for bone formation and osteoclasts for bone resorption

Activating transcription factors that alter the expression of genes related to growth and bone turnover

33
Q

T4/T3 is required for systemic effects of GH but…

A

Growth deficits are REVERSIBLE with return of thyroid hormone and GH

34
Q

How does thyroid hormone work in concert with other hormones for development (other than linear growth with GH)?

A

Thyroid hormone in concert with PRL regulates mammary gland development

T3/T4 necessary for PRL secretion in the pituitary

Development processes are not easily corrected by return of thyroid hormone

35
Q

In boys, _________ stimulates bone growth during puberty.

A

Testosterone

Accelerates the closure of the epiphyseal plates at the end of puberty

Achieved by aromatization of T to estrogen

T+GH in the liver ENHANCES IGF-1 secretion (positive synergistic effect)

T stimulates release of GH from pituitary

T has broad effects on masculinization

36
Q

__________ in women do not have the pronounced growth effects like ________ but do have important maturation effects

A

Estrogen and DHEA (not like Testosterone)

DHEA promotes early pubertal growth spurt in girls

Estrogen in the liver attenuated GH related IGF-1 secretion (NEGATIVE synergistic effect)

Estrogen promotes deposition of adipose tissue in breasts and buttocks

37
Q

Boys get _________ of prepubertal growth than girls

A

1-2 more years

Although puberty is delayed for boys, they start puberty being taller

38
Q

Exercise increases ______ entry into cells, absent of _______.

A

Glucose, insulin

Insulin is required for glucose to enter the muscle as rest, but not during exercise

39
Q

Muscle strength increases rapidly with …

A

Training

Occurs hours to days after resistance training

40
Q

________ can stimulate muscle protein synthesis without training required.

A

Infused amino acids

41
Q

What effect does insulin have on muscle growth?

A

Insulin facilitates muscle protein synthesis via mTORC signaling pathway

42
Q

_______ is a major intracellular hub for sensing nutrients

A

mTORC1

Insulin activates mTORC

Myostatin, stress, and cytokines inhibit mTORC

Amino acids activate mTORC

43
Q

During exercise, contracting muscle fibers release 100x more __________

A

Interleukin6 (IL6)

In muscles, IL-6 has an anti-inflammatory effect

Increases insulin-induced glucose uptake by increasing GLUT4

High levels of IL-6 exert pro-inflammatory effects in NON-skeletal muscles

IL-6 has the opposite effect when released from fat though

44
Q

What is the “fuel gauge” for muscle cells?

A

AMP-activated protein kinase (AMPK)

Influences genes in lipid and carb metabolic pathways and increases insulin sensitivity

45
Q

What is myostatin?

A

Developmental gene that blocks muscle cell growth and differentiation.

Also inhibits insulin action

46
Q

What is the phenotype for myostatin deficiency?

A

Huge muscles

Examples:
Myo-mouse
Belgian blue cattle
Familial human myostatin deficiency —> buff baby

Phys II Unit II (9 decks)

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