Normal Growth and Clinical Aspects Flashcards

1
Q

What are the factors that regulate growth?

A
Growth hormone
Thyroid hormones
Insulin
Sex steroids (esp in puberty)
Availability of nutrients
Stress
Genetics
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2
Q

What kind of hormone is growth hormone?

A

A peptide hormone

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3
Q

Where is growth hormone released from?

A

The anterior pituitary

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4
Q

How is the release of growth hormone regulated?

A

By two hympothalamic neurohormones- growth hormone inhibiting hormone (GHIH) and growth hormone releasing hormone (GHRH).

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5
Q

What hormones are also known as somatotropin and somatostatin?

A

Somatotropin- growth hormone

Somatostatin- GHIH

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6
Q

What are the direct and indirect actions of growth hormone?

A

Direct effect- regulates metabolism

Indirect effect- growth and development

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7
Q

What is required by growth hormone before it will stimulate growth?

A

Permissive effects from insulin and thyroid hormones

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8
Q

Why is growth hormones effect on growth and development indirect?

A

It achieves this action through an intermediate called Insulin-like growth factor-1 (IGF-1)

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9
Q

Why is IGF-1 described as “insulin like”

A

It has a structure very similar to pro-insulin, binds to receptors very similar to the insulin receptors and has hypoglycaemic qualities

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10
Q

Where is IGF-1 released from and what triggers its release?

A

IGF-1 is secreted from the liver in response to growth hormone release

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11
Q

How does IGF-1 affect GH release?

A

Through a negative feedback loop that both inhibits GHRH and stimulates GHIH

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12
Q

What are the effects of GH and IGF-1 on bone growth?

A

GH stimulates chondrocyte precursor cells in the epiphsyeal plates to differentiate into chondrocytes. During the differentiation, the cells begin to secrete and become responsive to IGF-1. IGF-1 then acts as an autocrine or paracrine agent to stimulate the differentiating chondrocytes to undergo cell division and produce cartilage. This cartilage then becomes calcified and forms bone.

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13
Q

How does growth hormone regulate metabolism?

A

Increases gluconeogenesis in the liver
Reduces the ability of insulin to stimulate glucose uptake by muscle and adipose tissue
Makes apidocytes more sensitive to lipolytic stimuli
Increases amino acid uptake and protein synthesis into all cells

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14
Q

When do the highest rates of growth hormone secretion occur?

A

During teenage years

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15
Q

At what stage in sleep is the majority of growth hormone secreted?

A

During the first two hours of sleep

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16
Q

How are the spikes in growth hormone release buffered?

A

By keeping levels of IGF-1 constant

17
Q

What factors control growth hormone secretion?

A

Nutrition- mediated by modulating control of GHIH/GHRH release from the hypothalamus

18
Q

What stimuli increase the secretion of GHRH?

A

Actual or potential decrease in energy supply to cells
Increased amounts of amino acid in the plasma
Stressful stimuli
Delta sleep
Oestrogen and testosterone

19
Q

What stimuli increase the secretion of GHIH?

A

Glucose
Free fatty acids
REM sleep
Cortisol

20
Q

What are the three factors that affect growth?

A

Hormones
Nutrition
Genetics

21
Q

What hormones affect growth?

A
Growth hormone
IGF-1
Thyroid hormones
Sex steroids
Glucocorticoids
Insulin
22
Q

What hormones dominate growth in intrauterine growth and during puberty?

A

Intrauterine- insulin and IGF-1

Puberty- sex steroids

23
Q

What parts pf growth are thyroid hormones most important for?

A

Development of the nervous system in utero and in childhood

24
Q

What effects do thyroid hormones have on insulin and IGF-1?

A

They have permissive effects

25
Q

What is cretinism?

A

A condition in which children are hypothyroid from birth, resulting in retarded growth because of the loss of thyroid hormones permissive effect on growth hormone

26
Q

What factor of growth determines maximum growth?

A

Genetics

27
Q

What are the two periods of rapid growth in humans?

A

Infancy and puberty

28
Q

Describe the mechanism of increased growth during puberty

A

Androgens and oestrogens produce spikes in GH levels secretion that increase IGF-1 levels and thus increase growth.

29
Q

How does growth decrease towards the end of puberty?

A

The androgens and oestrogens cause the epiphyses of the long bones to fuse and thus terminate growth

30
Q

What is the most common cause of hypersecretion of growth hormone?

A

Endocrine tumours

31
Q

What are the two different effects of hypersecretion of growth hormone and what differentiates them?

A

Gigantism occurs when there is excess growth hormone before the epiphsyeal plates fuse
Acromegaly occurs when there is excess growth hormone after the epiphyseal plates fuse

32
Q

What are the cardinal features of gigantism and acromegaly?

A

Gigantism- excessive growth

Acromegaly- enlarged face, hands and feet

33
Q

How are gigantism and acromegaly treated?

A

Surgery to remove tumour or somatostatin analogues

34
Q

What are the possible causes of dwarfism?

A
Deficiency of GHRH
Abnormal GH secreting cells
End organ unresponsive to GH
Genetic mutations
Precocious puberty
Hypothyroidism