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Physiology 3003 > Lecture 21--Hormonal regulation of growth > Flashcards

Lecture 21--Hormonal regulation of growth Flashcards

1
Q

What does growth depend upon?

A

Nutritional status and endocrine control by the brain

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2
Q

What hormone stimulates growth?

A

Growth Hormone

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3
Q

Where is growth hormone most abundant?

A

Adenohypophysis

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4
Q

What regulates the release of growth hormone?

A

Hypothalamus

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5
Q

What does the hypothalamus release that stimulates GH release?

A

Growth hormone releasing hormone

GHRH

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6
Q

Where does GHRH act?

A

Anterior pituitary

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7
Q

What does GHRH on the anterior pituitary do?

A

Stimulates release of GH

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8
Q

What inhibits GH release from the anterior pituitary?

A

Somatostatin

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9
Q

What are the direct effects of GH?

A

Acts on skeletal muscle, adipose and bone

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10
Q

What are the indirect effects of GH?

A

Acts on liver to release IGF-1 acting on GH

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11
Q

What effects the release of GH?

A

Stress, exercise and sleep

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12
Q

Can GH release affect weight gain?

A

YES

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13
Q

What are the effects of GH on the body?

A
  • Activates metabolic processes
  • ++ protein synthesis
  • ++ amino acid transport
  • ++ lipolysis
  • Reduces glucose transport and metabolism
  • ++ fibroblast differentiation
  • ++ in bone density
  • ++ IGF production in the liver and fibroblasts
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14
Q

What are IGFs?

A

Insulin-like growth factors, which are produced in the liver. They are multifunctional homrones that regulate cellular proliferation and cellular metabolism

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15
Q

Are IGFs similar to insulin?

A

Yes, they resemble insulin in structure and function

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16
Q

Does IGF have autocrine and paracrine effects?

A

Yes

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17
Q

How are IGF-I and IGF-II different in adults and babies?

A

IGF-I is prevalent in adults while IGF-II is the major form in the fetus

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18
Q

What growth does IGF have the most profound effect upon?

A
  • Cartilage
  • Bone
  • Soft tissues
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19
Q

What do IGFs stimulate in the body?

A

Amino acid uptake and activate protein and DNA synthesis

20
Q

What do IGFs act as?

A

Mitogens, to increase proliferation of target cells

21
Q

Where Is autocrine/paracrine IGF-I released?

A

Released from the muscles/organs in which it acts, for instance skeletal muscle and bone both release IGF-1 that act back on these organs

22
Q

When do serum IGF-1 levels peak?

A

In the young-adolescence age, around puberty. More IGF, the taller/larger the child is going to grow

23
Q

Does insulin stimulate IGF production?

A

YES

24
Q

Can GH increase IGF levels in the absence of insulin?

A

NO

25
Q

What nutrients stimulate IGF release? How?

A

High AAs ==> ++ GH release
++GH ==> ++ IGF

High blood glucose==> ++ insulin
++Insulin ==> ++ IGF

++IGF ==> growth

26
Q

Why don’t you grow during starvation?

A

Decreased blood sugar ==> decreases insulin.

Even though fasted/starved state increases GH, this does not result in growth because of the =lack of insulin.

27
Q

What does excess GH cause?

A

> > Gigantism (excess before puberty)

|&raquo_space;Acromegaly (excess after puberty)

28
Q

What causes an excess secretion of GH?

A

A benign tumour known as the ADENOMA

29
Q

What causes the problems associated with excess GH release after puberty?

A

Growing ends of bone fuse and completely stop growing in length, so over-secretion of GH after puberty causes increased thickness of bones but not length

30
Q

What is the main difference in the symptoms of pre-and post-puberty excess GH secretion?

A

Whether the growth is proportional or not. Gigantism (pre-puberty) is proportional growth

31
Q

What are the side effects of acromegaly?

A
  • Cartilage enlargements, ++ size of nose and eyes
  • Impinges on nerves (++ bone and cartilage)
  • Visual field losses (pressure on the optic nerves)
  • Bell’s palsy (pressure on facial nerve)
  • Spreading teeth or bite difficulties
  • Joint & bone aches and pains
  • Soft tissues enlarge => cardiac hypotrophy
  • Hypertension
  • Carpal tunnel (pressure on median nerve in wrist by excessive bone/tendon growth)
32
Q

What is carpal tunnel syndrome and what causes it?

A

It is tingly or pain in the hands/wrists and is caused by pressure on the median nerve in the wrist by excessive bone/tendon growth

33
Q

What are the symptoms of limited GH pre-puberty?

A

Dwarfism

34
Q

What are the symptoms of limited GH release post- puberty?

A

Few symptoms

35
Q

What can cause reductions in pituitary GH output?

A
  • Tumours of the hypothalamus which cause oversecretion of somatostatin
  • Infections which can affect hypothalamic GNRH or somatostatin secretion
  • GH secretion is very susceptible to irradiation (e.g. after radiotherapy)
36
Q

What is an example of people who have short stature due to low GH or IGF?

A

Laron dwards and African pygmies respectively

37
Q

What are some other factors that work with GH to stimulate growth?

A

• Steroid hormones (increase weight gain and muscle mass)
• Androgens act synergistically with GH to stimulate the hypothalamus to release more GH
• Testosterone and oestrogen enhance the growth hormone rhythms
Thyroid hormones – T3 and T4.

38
Q

Where are hormonal growth promoters used?

A
  • Food production androgens
  • Growth hormone treatment in children who are GH deficient
  • Sports
  • GRH peptides act on anterior pituitary to increase lean muscle mass and also reduce injury
39
Q

What are the side effects of IGF use

A
  • Carpal tunnel syndrome
  • Hypertension
  • Joint and bone aches
  • Cancers
  • Tumours
40
Q

GH cannot increase IGF in absence of _______

A

INSULIN

GH + Insulin => IGF1

41
Q

Stunted growth in thyroid deficient individuals –>

A

Due to deficiency in GH

42
Q

How do the thyroid hormones promote growth?

A

Act synergistically with GH to produce effects (stimulate GH synthesis, increase GH secretion, act on target cells to increase their sensitivity to GH)

43
Q

What happens to promote growth during puberty?

A

GH & IGF levels increase simultaneously

44
Q

What causes Laron dwarfism?

A

Genetic defect in expression of GH receptors (absent GH signalling before puberty)

45
Q

What causes african pygmism?

A

Impaired IGF production, normal GH levels

46
Q

Gigantism = _______ growth

A

PROPORTIONAL growth

Physiology 3003 (15 decks)

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