Normal Growth and Clinical Aspects Flashcards
What are the factors that regulate growth?
Growth hormone Thyroid hormones Insulin Sex steroids (esp in puberty) Availability of nutrients Stress Genetics
What kind of hormone is growth hormone?
A peptide hormone
Where is growth hormone released from?
The anterior pituitary
How is the release of growth hormone regulated?
By two hympothalamic neurohormones- growth hormone inhibiting hormone (GHIH) and growth hormone releasing hormone (GHRH).
What hormones are also known as somatotropin and somatostatin?
Somatotropin- growth hormone
Somatostatin- GHIH
What are the direct and indirect actions of growth hormone?
Direct effect- regulates metabolism
Indirect effect- growth and development
What is required by growth hormone before it will stimulate growth?
Permissive effects from insulin and thyroid hormones
Why is growth hormones effect on growth and development indirect?
It achieves this action through an intermediate called Insulin-like growth factor-1 (IGF-1)
Why is IGF-1 described as “insulin like”
It has a structure very similar to pro-insulin, binds to receptors very similar to the insulin receptors and has hypoglycaemic qualities
Where is IGF-1 released from and what triggers its release?
IGF-1 is secreted from the liver in response to growth hormone release
How does IGF-1 affect GH release?
Through a negative feedback loop that both inhibits GHRH and stimulates GHIH
What are the effects of GH and IGF-1 on bone growth?
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.
How does growth hormone regulate metabolism?
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
When do the highest rates of growth hormone secretion occur?
During teenage years
At what stage in sleep is the majority of growth hormone secreted?
During the first two hours of sleep
How are the spikes in growth hormone release buffered?
By keeping levels of IGF-1 constant
What factors control growth hormone secretion?
Nutrition- mediated by modulating control of GHIH/GHRH release from the hypothalamus
What stimuli increase the secretion of GHRH?
Actual or potential decrease in energy supply to cells
Increased amounts of amino acid in the plasma
Stressful stimuli
Delta sleep
Oestrogen and testosterone
What stimuli increase the secretion of GHIH?
Glucose
Free fatty acids
REM sleep
Cortisol
What are the three factors that affect growth?
Hormones
Nutrition
Genetics
What hormones affect growth?
Growth hormone IGF-1 Thyroid hormones Sex steroids Glucocorticoids Insulin
What hormones dominate growth in intrauterine growth and during puberty?
Intrauterine- insulin and IGF-1
Puberty- sex steroids
What parts pf growth are thyroid hormones most important for?
Development of the nervous system in utero and in childhood
What effects do thyroid hormones have on insulin and IGF-1?
They have permissive effects
What is cretinism?
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
What factor of growth determines maximum growth?
Genetics
What are the two periods of rapid growth in humans?
Infancy and puberty
Describe the mechanism of increased growth during puberty
Androgens and oestrogens produce spikes in GH levels secretion that increase IGF-1 levels and thus increase growth.
How does growth decrease towards the end of puberty?
The androgens and oestrogens cause the epiphyses of the long bones to fuse and thus terminate growth
What is the most common cause of hypersecretion of growth hormone?
Endocrine tumours
What are the two different effects of hypersecretion of growth hormone and what differentiates them?
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
What are the cardinal features of gigantism and acromegaly?
Gigantism- excessive growth
Acromegaly- enlarged face, hands and feet
How are gigantism and acromegaly treated?
Surgery to remove tumour or somatostatin analogues
What are the possible causes of dwarfism?
Deficiency of GHRH Abnormal GH secreting cells End organ unresponsive to GH Genetic mutations Precocious puberty Hypothyroidism
