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Physiology 314- endocrinology > Lecture 4 - endocrine control of growth > Flashcards

Lecture 4 - endocrine control of growth Flashcards

1
Q

Growth depends on growth hormone but is influenced by other factors:

A

Genetic
Diet
Freedom from chronic disease and stressful environmental conditions
Normal levels of growth-influencing hormones

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2
Q

Prolonged stress-induced secretion of cortisol results in

A

Stunted growth: Anti-growth effects of cortisol
- Promoting protein breakdown
- Inhibiting growth of long bones
- Blocking secretion of growth hormone

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3
Q

Normal levels of growth-influencing hormones
- must be present for GH to perform function

A
  • Thyroid hormone
  • sex hormones
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4
Q

Gh is mostly secreted at

A

night

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5
Q

GH secretion is regulated by 2

A

hypophysiotropic hormones

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6
Q

GH secretion is regulated by which 2 hypophysiotropic hormones

A

GHRH and GHIH

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7
Q

Hormones that take part in the secretion of GH

A

GHRH
GHIH = somatostatin
GH = somatotropin
IGF = somatomedin

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8
Q

GH secretion is regulated by 2 hypophysiotropic hormones, GHRH and GHIH, how?

A

Both GHRH and GHIH act on the anterior pituitary somatotropes by binding with G-protein-coupled receptors linked to cAMP second messenger pathway: GHRH increasing cAMP and GHIH decreasing cAMP

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9
Q
A
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10
Q

Regulation of Growth Hormone Secretion

A

GH-somatotropin
GHIH- somatostatin
IGF-1- somatomedin

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11
Q

Growth Hormone exerts metabolic effects not related to growth. How and whats the result?

A

Binds directly to target tissue: adipose tissue, skeletal muscle and liver
- decrease blood amino acid levels
- increased fatty acid levels in blood
- increased blood glucose levels; increase glucose output by liver

THUS: mobilize fat stores as major energy source while conserving glucose for glucose dependent tissue such as the brain, eg. fasting or when body’s energy needs exceed glucose stores

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12
Q

GH primarily promotes growth indirectly by

A

stimulating liver’s production of somatomedins [Insulin-like growth factor (IGF-I)]

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13
Q

Insulin-like growth factor (IGF-I)

A

Secreted in bones and soft tissues
which results in protein synthesis, cell division, and lengthening and thickening of bones

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14
Q

IGF’s are produced in many tissues and result in certion actions

A

– endocrine, paracrine and autocrine actions

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15
Q

IGF’s bind to receptor-enzyme

A

tyrosine-kinase pathway

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16
Q

Major source of IGF-I IS THE _______. And the release is in response to ______

A

liver
GH

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17
Q

IGF-I also produced by most other tissue (not released into blood)

A

– act in paracrine manner

18
Q

IGF production is controlled by number of factors other than GH:

A

Nutrition status:
Inadequate food intake and fasting - IGF-I, BUT + GH secretion

Age-related factors:
Dramatic + in circulating IGF-I with modest increase in GH at puberty

Tissue specific increases:
Sex hormones stimulate IGF-I in male reproductive organs (testes) and female uterus and ovaries.

19
Q

IGF-II

A

Not influenced by GH
Primarily important during fetal development
Role in adults unclear

20
Q

Growth hormone (GH) /IGF-I promote growth of soft tissue by stimulating

A

hyperplasia and hypertrophy

21
Q

Hyperplasia

A

Increasing number of cells
Stimulating cell division
Preventing apoptosis

22
Q

Hypertrophy

A

Increasing size of cells
Favoring protein synthesis
Inhibit protein degradation
Promote uptake of amino acids by cells – decreasing blood amino acids levels in process
Increases DNA and RNA synthesis
Increases incorporation of amino acids into new proteins at ribosomal level

23
Q

Bone growth

A
  • Can be endochondral and linear
  • in compact and trabecular bone
24
Q

Growth in thickness of bone:

A

= Endochondral bone growth:
Osteoblasts in periosteum
Osteocalcin & osteonectin – proteins which aid in deposition of calcified matrix

25
Q

Linear bone growth

A

– epiphyseal plate

26
Q

Bone growth is under the influence of

A

GH and IGFs
without it = abnormal bone growth

27
Q

Long bone growth: Also influenced by steroid sex hormones

A

Puberty:
Boys: Growth spurt of puberty - + androgen production
Girls: Androgens from adrenal cortex: estrogens stimulate & inhibit linear growth

Adolescents: sex hormones inactivate epiphyseal plate

Adults: linear bone growth ceases; BUT bone are dynamic tissues – undergo continuous remodeling under control of hormones which regulated calcium metabolism in body

28
Q

36 year old professional body builder required emergency care for chest pain
Lost 40 kg in 12 months
Excessive urination, thirst & appetite
Admitted using anabolic steroids for 15 years and artificial GH for past 3 years
Took insulin a year after starting GH, but he stopped due to hypoglycaemia in gym
Tests: inflammed liver, enlarged kidneys, very high blood sugar, dehydration, diabetes
Treatment: intravenous fluids, gradually increasing insulin over few days
Use of GH increases among athletes and bodybuilders – easy to buy on line, difficult to detect in screening tests – unlike anabolic steroids
Question: What was the reason for taking insulin?

A

GH increases blood glucose levels, so took insulin to counteract effect

29
Q

Factors that influence GH secretion

A

Diurnal rhythm
Exercise
Stress
Low blood glucose
+ in amino acids after high-protein meal
Low blood fatty acids levels
Ghrelin (appetite stimulator) – coordinate nutrient acquisition with growth

30
Q
A
31
Q
A
32
Q

Why aren’t adult tissues still respond to GH growth-promoting effects?
Epiphyseal plates have closed, but why do soft tissue not continue to grow through hyperplasia and hypertrophy?

A

Speculation: GH secretion burst during deep sleep which is greatest in infancy and gradually decreases with age

33
Q

Growth hormone deficiency due to

A

pituitary defect or hypothalamic dysfunction

34
Q

Hyposecretion of GH in child is one cause of dwarfism

A

Retarded skeletal growth
Poorly developed muscles (- muscle protein synthesis)
Excess subcutaneous fat (- fat mobilization)

35
Q

Laron dwarfism

A

blood GH levels high
abnormal GH receptors, tissue fail to respond to GH

36
Q

African pygmies

A

GH levels and tissue response adequate, BUT IGF’s are lacking

37
Q

Deficiency of GH in adults:

A

produces relatively few symptoms – GH maintains cardiac muscle mass (increased risk of heart failure)

38
Q

Growth hormone excess

A

Most often caused by tumor of GH-producing cells of anterior pituitary
Symptoms depend on age of individual when abnormal secretion begins

39
Q

Gigantism

A

Caused by overproduction of GH in childhood before epiphyseal plates close

40
Q

Acromegaly

A

Occurs when GH hypersecretion occurs after adolescence

Physiology 314- endocrinology (16 decks)

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