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7. Endocrinology (Medical Knowledge)a > Endocrine Controls of Growth > Flashcards

Endocrine Controls of Growth Flashcards

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USMLE® Step 1 flashcards
1
Q

What are examples of some things that regulate growth?

A
  • growth hormone
  • thyroid hormones
  • insulin
  • sex steroids (especially at puberty)
  • availability of nutrients
  • stress
  • genetics
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2
Q

What is the classification of growth hormone?

A

Peptide hormone

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3
Q

What is growth hormone (GH) also called?

A

Somatotropin

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4
Q

What is growth hormone released from?

A

Anterior pituitary

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5
Q

Growth hormone release is controlled via the release of two hypothalamic neurohormones with opposing actions, what are these?

A

Growth hormone inhibiting hormone (GHIH)

Growth hormone releasing hormone (GHRH)

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6
Q

What is growth hormone inhibiting hormone also called?

A

Somatostatin

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7
Q

What are the 2 broad categories that the actions of GH can be defined into?

A

Growth and development (indirect action)

Regulation of metabolism (direct action)

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8
Q

What is the indirect action of GH?

A

Growth and development

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9
Q

What is the direct action of GH?

A

regulation of metabolism

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10
Q

When does the main driver of growth change from nutritional intake to GH?

A
  • foetal period and first 8-10 months: growth largely controlled by nutritional intake
  • after : GH becomes a dominant influence on rate at which children grow
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11
Q

GH requires the permissive action of what before it will stimulate growth?

A

Thyroid hormones and insulin

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12
Q

Why do children with untreated hypothyroidism of uncontrolled diabetes have stunted growth?

A

Because the permissive actions of thyroid hormones and insulin is required before GH will stimulate growth

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13
Q

Why do GH secretions continue throughout adult life even once a child has grown to their full height?

A

It is essential in the maintenance and repair of tissue

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14
Q

What do the growth promoting effects of GH stimulate on its target tissues?

A

Stimulate both cell size (hypertrophy) and cell division (hyperplasia)

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15
Q

How is the effect of GH on growth indirect?

A

Achieved through its action of an intermediate (insulin like growth factor-1, or IGF-1)

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16
Q

What does IGF-1 stand for?

A

Insulin like growth factor 1

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17
Q

What is insulin like growth factor-1 (IGF-1) also called?

A

Somatomedian C

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18
Q

Why is IGF-1 named as it is?

A

Similar structure to proinsulin, binds to receptors similar to insulin receptor and has hypoglycaemic qualities

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19
Q

Where are IGF-1 receptors found?

A

Muscle has many

Fat and liver have few

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20
Q

What is IGF-1 secreted by and in response to?

A

By the liver in response to GH release

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21
Q

How does IGF-1 control GH release?

A

Through a negative feedback loop

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22
Q

As well as IGF-1, IGF-2 exists. What is its functional importance?

A

Limited to the foetus and neonate

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23
Q

How are GH and IGF-1 transported around the blood?

A

Although they are peptide hormones, they are transported in the blood bound to carrier proteins (50% of GH is in this form)

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24
Q

What percentage of GH in the blood is bound to carrier proteins?

A

50%

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25
Q

What are advantages of GH and IGF-1 being transported in blood bound to proteins?

A
  • helps to provide a reservoir of GH in the blood to smooth out the effects of the erratic pattern of secretion
  • extends the half life by protecting from excretion
26
Q

How does IGF exhibit negative feedback on GH release?

A

By both inhibiting GHRH and stimulating GHIH

27
Q

As well as IGF, what else provides a negative feedback loop for GH release?

A

Somatotrophs in pituitary

28
Q

Explain the process of GH/IGF-1 having an effect on bone growth?

A
  1. GH stimulates chondrocyte precursor cells (prechondrocytes) in the epiphyseal plates to differentiate into chondrocytes
  2. during differentiation cells begin to secrete IGF-1 and to become responsive to IGF-1
  3. IGF-1 acts as an autocrine or paracrine agent to stimulate the differentiating chondrocytes to undergo cell division and produce cartilage, the foundation for bone growth
29
Q

What are the precursors of chondrocytes called?

A

Prechondrocytes

30
Q

When and why do epiphyseal plates close?

A
  • during adolescence
  • under influence of sex steroids
  • so no further longitudinal growth is possible
31
Q

What are some examples of the effects that GH has on metabolism?

A
  • liver: increases gluconeogenesis
  • muscle and adipose tissue: reduces ability of insulin to stimulate glucose uptake
  • adipocytes: more sensitive to lipolytic stimuli
  • increases amino acid uptake and protein synthesis in almost all cells (anabolic effect)
32
Q

Does GH have a pro or anti-insulin effect?

A

Anti-insulin effects, synergising with cortisol in this respect

So it is said to be diabetogenic (increases blood glucose)

33
Q

What effect does insulin and GH have on amino acid uptake?

A

Both increase amino acid uptake

34
Q

What effect does insulin and GH have on protein synthesis?

A

Both increase protein synthesis

35
Q

What effect does insulin and GH have on glucose uptake?

A

Insulin increases glucose uptake whereas GH does not

36
Q

How does GH impact glucose metabolism?

A

increases blood glucose by:

  • mobilising glucose stores
  • inhibiting action of insulin (reducing number of insulin receptors on muscle and adipose tissue)
  • promoting lipolysis (provides a source of energy for most cells of body sparing glucose)
  • promoting amino acid uptake into cells (to support protein synthesis)
37
Q

When does the highest rate of GH secretion occur?

A

During teenage years

38
Q

During sleep, when is the majority of GH released?

A

During the first 2 hours of sleep (deep delta sleep)

39
Q

Is GH release greater during waking or sleeping hours?

A

Sleeping hours, it is low during waking hours

40
Q

Despite GH spikes, plasma levels of IGF-1 remains relatively constant, what does this suggest?

A

IGF-1 buffers the pulsatile variance in GH levels

41
Q

What are examples of stimuli that increases GHRH secretion (causing increased GH)?

A
  • actual or potential decrease in energy supply to cells
  • increased amount of amino acids in plasma
  • stressful stimuli
  • delta sleep
  • oestrogen and testosterone
42
Q

Why does increased amounts of amino acid in the plasma increase the amount of GH secretion?

A

GH promotes amino acid transport and protein synthesis by muscle and liver

43
Q

What are examples of stressful stimulis that can increase GH secretion?

A

Infection or psychological stress

44
Q

How does oestrogen and testosterone affect the secretion of GH?

A
  • stimulate GH release from pituitary directly
  • decrease IGF mediated negative feedback
  • responsible for growth spurt in puberty
45
Q

What are examples of stimuli that increases GHIH (causing decreased GH)?

A
  • glucose
  • free fatty acids
  • ageing
  • cortisol
46
Q

Why does cortisol have an inhibitory effect on growth?

A

Increase GHIH secretion

Increased protein catabolism

47
Q

What are the 3 factors that affects the physiology of growth?

A

Hormones

Nutrition

Genetics

48
Q

What are some examples of hormones that impact growth?

A

GH

IGF-1

Thyroid hormones

Sex steroids

Glucocorticoids

Insulin

49
Q

What hormone dominates growth throughout your life?

A

None, different hormones dominate growth during different periods of growth

50
Q

When do the sex hormones start to dominate growth?

A

Minor influence until puberty when they dominate growth spurt

51
Q

When does GH not really impact growth?

A

Minor influence in foetal life (believed insulin and IGF-II dominate growth at that time)

52
Q

Thyroid hormons are essential for normal growth, particularly when?

A

During development of the nervous system in utero and early childhood

53
Q

Are thyroid hormones permissive or antagonistic to GH/IGF-I?

A

Permissive

54
Q

What effects do thyroid hormones have that means they contribute to growth in early childhood?

A
  • ossification of cartilage
  • teeth maturation
  • contours of the face
  • proportions of the body
55
Q

In terms of nutrition, what is important for growth?

A

Protein content and essential vitamins and minerals as well as enough calories

56
Q

Why does injury and disease stunt growth in childhood?

A

Injury and disease stunt growth because increase protein catabolism (glucocorticoid effects)

57
Q

In humans there are 2 periods of rapid growth, what are these?

A

Infancy

Puberty

58
Q

Why does the rapid growth period during puberty occur?

A
  • androgens and oestrogens produce spikes in GH secretion that increases IGF-1 which increases growth
  • same sex hormones terminate growth by causing the epiphyses of the long bones to fuse
59
Q

How do the effects of GH/IGF-1 contrast at the start of puberty and at the end?

A

Start - promote bone elongation and increased height, weight and body masss

End - close epithyses plates and stop bone elongation

60
Q

What do endocrine tumours usually cause?

A

Gigantism

Acromegaly

7. Endocrinology (Medical Knowledge)a (28 decks)

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