Normal Growth and Clinical Aspects Flashcards
How is growth regulated ?
Growth hormone release from ant. pituitary, Thyroid hormone, insulin, sex steroids, stress, genetics
Where is GH released from?
The anterior pituitary
Where is GHIH and GHRH released from?
They hypothalamus
What is the action of growth hormone?
Growth and Development (indirect), Regulation of Metabolism (direct)
When does GH take over the role of Growth in humans?
around 8-10 months of age
What conditions must be present for GH to stimulate growth?
GH requires permissive action of thyroid hormones and insulin
How is the growth effect of GH mediated?
Through stimulation of cell size and cell division in its many target tissue
What intermediate mediates the action of GH?
IGF-1
Where is IGF-1 secreted?
The liver
How does IGF-1 mediate GH?
Through a negative-feedback loop via inhibiting GHRH and stimulating GHIH
How does GH/IGF-I affect bone growth?
GH stimulates chondrocyte precursor cells in epiphyseal plates to differentiate into chondrocytes.
During differentiation, cells begin to secrete IGF-1 and respond to IGF-1
IGF-1 then acts as an autocrine or paracrine agent, stimulating the differentiation of chondrocytes to divide and produce cartilage
When do epiphyseal plates close?
During adolescence under the influence of sex hormones
What are the direct effects of GH?
Increases gluconeogenesis, reduces the ability of insulin to uptake glucose, makes adipocytes sensitive to lipolytic stimuli, increases muscle, liver and adipose tissue amino acid uptake and protein synthesis
What stimulates GHRH secretion?
Actual or potential decrease in energy supply to cells, increased amounts of amino acids in plasma, stressful stimuli, delta sleep, oestrogen and androgens
What stimulates GHIH?
Glucose, FFA, REM Sleep, Cortisol
What affects growth?
Hormones
Nutrition
Genetics
What hormones affect growth?
GH, IGF-I, Thyroid Hormones, Androgens, Oestrogens, Glucocorticoids and Insulin
What is cretinism?
A condition where children are hypothyroid from birth. Results in retardation of growth and retain infantile facial features
How does cretinism affect GH levels?
It doesn’t. GH levels are normal
Name the two periods of rapid growth in humans?
Infancy and Puberty
How many times do infants grow on average ?
Growth spurts of around 2.5 cm in a few days then nothing
What is growth like during puberty?
Androgens and oestrogens produce GH spikes that increase IGF-1 which increases growth
What is gigantism?
excess GH due to a pituitary tumour before epiphyseal plates of long bones close = excessive growth
Define acromegaly
Excess GH due to a pituitary tumour after epiphyseal plates have sealed. Long bones cannot increase so no increase in height but can have enlarged hands and feet
What may contribute to dwarfism?
A deficiency in GHRH, Abnormal GH secreting cells, End organ unresponsive to GH, Genetic mutation, Precocious Puberty, Hypothyroid Children
