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BDS 2 Semester 1 > Endocrinology: Endocrine Control of Growth > Flashcards

Endocrinology: Endocrine Control of Growth Flashcards

1
Q

Define growth

A

Growth = the organised addition of new tissue that occurs normally in development.
Except for longitudinal growth, many of the processes involved continue to operate throughout life (e.g., tissue remodelling)

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2
Q

Factors that influence growth

A
  • Genetics
  • Nutrition
  • Growth influencing hormones – growth hormone, thyroid hormone, somatomedins/IGFs, insulin, sex hormones
  • Chronic stress and disease
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3
Q

What is growth hormone also known as?

A

Growth hormone, aka somatotropin; somatotropic hormone

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4
Q

Where is growth hormone produced? What type of hormone is it?

A

Polypeptide hormone produced in somatotrophs of anterior pituitary

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5
Q

How is secretion of growth hormone regualted?

A

Secretion regulated by GHRH and GHIH (somatostatin)
growth hormone releasing hormone and growth hormone inhibiting hormone

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6
Q

Growth hormone mechanisms of action

A
  • Transported bound to growth hormone binding protein
  • Targets many tissues where it influences fuel metabolism
  • GH binding to enzyme-linked receptor produces activation of kinase cascade which ultimately alters gene transcription
  • Overall effect is to use up fat stores and promote protein synthesis
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7
Q

Growth hormone secretion pattern

A
  • Irregular pulses
  • Largest bursts during deep sleep
  • Pulse amplitude maximum at puberty, then declines
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8
Q

What is secretion of growth hormone stimulated by?

A
  • GH-releasing hormone (GHRH)
  • Oestrogens and androgens
  • Decreased blood glucose
  • Decreased blood fatty acids
  • Exercise
  • Excitement/ stress/ trauma
  • Sleep
  • Increase in amino acids
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9
Q

What is secretion of growth hormone inhibited by?

A
  • GH-inhibiting hormone (GHIH; somatostatin)
  • Somatomedins (-ve feedback)
  • Obesity
  • Increased blood glucose
  • Increased blood fatty acids
  • aging
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10
Q

Hypothalamus role in growth hormone secretion

A

Hypothalamus
- Growth hormone releasing hormone (GHRH) and somatostatin (GHIH) are produced
- GHRH stimulates release of growth hormone from the pituitary gland, somatostatin inhibits it

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11
Q

Pituitary gland and growth growth hormone

A

Synthesises and stores growth hormone

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12
Q

What happens once growth hormone is secreted?

A

Negative feedback
- Once growth hormone is secreted into the bloodstream, it exerts is effects on target tissues (liver, adipose tissue, skeletal muscle)
- It promotes growth, metabolism and other physiological processes
- Regulates its own secretion: high levels of GH in blood inhibits release of GHRH, stimulates release of somatostatin, and vice versa

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13
Q

What are somatomedins?

A

Somatomedins (insulin-like growth factors = IGF)
Peptide hormones that have strong mitogenic properties (encourage cell division)

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14
Q

Where are IGFs produced?

A

Insulin-like growth factors
IGFs are produced primarily in the liver, but also in most other tissues (where it has an autocrine/ paracrine effect)

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15
Q

Types of IGF

A

Insulin-like growth factors
There are two types (IGF-1, IGF-2)
IGF-1 effects most cells in the body where it stimulates cell growth, multiplication and inhibits apoptosis (programmed cell death)
IGF-2 is a growth promoting hormone during gestation

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16
Q

Most important IGF

A

Somatomedin C (IGF-1) is the most important IGF: pygmies and some dwarfs lack IGF-1

17
Q

What do pygmies and some dwarfs lack?

A

IGF-1

18
Q

Bone growth via IGF-1

A

Bone growth: growth hormone (via IGF-1)
- Stimulates proliferation of epiphyseal cartilage
- Increases conversion of cartilage to new bone (increasing length of long bones and skeleton until epiphyses of long bones fuse with shafts)
- Increased proliferation of periosteal osteoblasts (increasing bone thickness)
- Increase in bone remodelling

19
Q

Metabolic actions of growth hormone

A
  • Increase fat breakdown into fatty acids (lipolysis)
  • Decrease glucose uptake by muscles
  • Decrease sensitivity to insulin
  • Increased blood glucose
20
Q

Target cells of growth hormone

A

Unlike other anterior pituitary hormones, growth hormone doesn’t function through a target gland as such, it exerts its effects on almost all tissues of the body.

21
Q

Additional factors (besides growth hormone) that influence foetal growth

A
  • Promoted by placental hormones (GH-independent)
  • Birth size determined mainly by genetics and environment
  • Neurological growth maximum in late intrauterine and early postnatal life
22
Q

Factors that affect postnatal growth

A
  • Largely determined by GH (+ somatomedins, T3 and T4, insulin, androgens, and estrogens)
  • Increase in GH during puberty
  • Increase in androgens (from testes and adrenal gland) contribute to pubertal growth spurt by increasing protein synthesis and bone growth
23
Q

Hormones that influence growth (besides growth hormone)

A
  • Thyroid hormones: permissive for GH synthesis, release (via increase GHRH receptor) and actions (increase GH receptor, increase IGF-1, increase IGF-1 receptor). Children with hypothyroid conditions have their growth severely stunted, however, hypersecretion of thyroid hormone doesn’t stimulate excess growth
  • Insulin: required for optimal effects of growth hormone (IGF-1 is low in diabetes). Growth hormone fails to cause growth in an animal that lacks a pancreas or if carbohydrate is excluded from the diet-lack of energy source and attenuated transport of amino acids into cells
  • Gonadal hormone: during puberty estrogens increase GH pulse amplitude and frequency; also play a role in closure of epiphyseal plates – terminating growth in both sexes. Andogens involved in the pubertal growth spurt by stimulating protein synthesis (increase muscle mass)
  • Glucocorticoids: permissive for optimal growth; increase GHRH receptor and GH synthesis. High concentrations inhibit growth (e.g., pharmacological doses to treat asthma and inflammations)
24
Q

Effects of hypersecretion of growth hormone

A

If in childhood, then rapid, excessive growth; body remains in proportion (gigantism)

If after adolescence, then bones don’t lengthen but will thicken; increased soft tissue formation (acromegaly)

25
Q

Cause, affect and treatment of gigantism

A

o Cause: pituitary adenoma; pituitary hyperplasia
o Effect: rapid growth of all tissues, hyperglycaemia (leading to diabetes mellitus in 10%)
o Treatment: somatostatin analogs, surgery

26
Q

Cause effect and treatment of acromegaly

A

o Cause: pituitary tumour after adolescence
o Effect: bones grow in thickness not length (cranium, nose, supraorbital ridges, mandible, vertebrae). Enlargement of hands and feet, elongation of ribs (barrel-chested appearance). Enlarged tongue, liver, kidneys, heart. Diabetes
o Treatment: somatostatin analogs, surgery

27
Q

Cause, effects and treatment of growth hormone deficiency

A

Pituitary dwarfism

  • Cause: congenital defect, pituitary tumour or trauma causing panhypopituitarism (decrease secretion of all anterior pituitary hormones) or isolated GH (or IGF-1) deficiency
  • Effect: slow and reduced growth (to ~4ft). proportional appearance. Craniofacial dysmorphisms include frontal bossing, midfacial hypoplasia and micrognathia. If panhypopituitarism, will also have hypothyroidism, hypogonadism and low glucocorticoids
  • Treatment: human GH +/- thyroxine, cortisol
28
Q

Symptoms of acromegaly, related to the oral cavity

A

Acromegaly and oral health: dental professionals may be the first healthcare providers to note early symptoms and signs of acromegaly (and gigantism)
- Enlarged lips and tongue (macroglossia)
- Increased spaces between teeth
- Mandible growth after puberty: class 3 malocclusion; prognathism
- Accelerated tooth eruption in children
- Facial features become broader and thickened
- Maxillary sinuses are larger
- Hyperglycaemia/ diabetes mellitus: increased risk of gingivitis and periodontal disease

29
Q

Are all growth abnormalities directly related to aberrant growth hormone secretions? Give examples

A

No
- Laron dwarfism is characterised by abnormal GH receptors
- African pygmies have IGF-1 (or receptor) deficiency
- Primordial dwarfism doesn’t respond to GH treatments (due to mutation of pericentrin gene causing abnormal cell division)
- Cartilage-hair hypoplasia is due to mutations in the ribonuclease mitochondrial RNA-processing (RMRP) gene

BDS 2 Semester 1 (21 decks)

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