normal growth and clinical aspects Flashcards
growth is regulated by a number of factors
- growth hormone release from anterior pituitary (regulated by balance of GHRH and GHIH)
- thyroid hormones
- insulin
- sex steroids (esp puberty)
- availability of nutrients
- stress
- genetics
growth hormone
peptide hormone released from anterior pituitary
aka somatotropin
what controls GH release
GHIH (somatostatin)
GHRH
balance of GHRH and GHIH
determined by the myriad of factors that impinge on the hypothalamus
actions of growth hormones
growth and development (indirect action)
regulation of metabolism (direct action)
what does GH require to stimulate growth
permissive action of thyroid hormones and insulin
growth-prompting effect of GH
mediated through stimulation of both cell size (hypertrophy) and cell division (hyperplasia) in its many target tissues
how is the effect of GH on growth indirect
it is achieved through the action of an intermediate known as insulin-like growth factor-1 (IGF-1) aka somatomedin C as it mediates the action fo GH
IGF-1 structure
very similar to pro-insulin
IGF-1 receptor
IGF-1 binds to receptors very similar to the insulin receptor and has hypoglycaemic qualities
when is IGF-1 secreted
by the liver (and many other cell types) in response to GH release
how does IGF-1 control GH release
through a negative feedback loop
how are GH and IGF-1 transported in the blood
bound to carrier proteins
IGF-1 negative feedback loop on GH release
IGF exhibits negative feedback in GH release both via inhibiting GHRH and stimulating GHIH
GH/IGF-1 effects on bone growth
- GH stimulates chondrocyte precursor cells in epiphyseal plates to differentiate into chondrocytes
- during differentiation, the cells begin to secrete IGF-1 and become responsive to IGF-1
- the IGF-1 then acts as an autocrine/paracrine agent to stimulate the differentiating chondrocytes to undergo cell division and produce cartilage (the foundation for bone growth)
GH and regulation of metabolism (direct effects of GH)
- increase gluconeogenesis by liver
- reduce ability of insulin to stimulate glucose uptake by muscle and adipose tissue
- makes adipocytes more sensitive to lipolytic stimuli
- inc amino acid uptake and protein synthesis in almost all cells
how is GH diabetogenic
GH releases energy stores to support growth
it is having an anti-insulin effect and increases blood glucose
summart direct effects of GH
- mobilise Glc stores to inc blood glc
- inhibit action insulin
- promotes lipolysis - providing source of energy for most cells and so sparing Gcl
- promotes amino acid uptake into cells, supporting protien synthesis
stimuli that increase GHRH secretion
- actual or potential drop in energy supply to cells
- inc amounts of amino acids in plasma
- physical stress and illness
- delta sleep
- oestrogen and testosterone
stimuli that increase GHIH (somatosatin release)
- glucose
- FFA
- REM sleep
- cortisol
physiology of growth - complex phenomenon affected by 3 factors…
hormones
nutrition
genetics
physiology of growth - hormones
GH IGF-1 thyroid hormones sex steroids glucocorticoids insulin
thyroid hormones and growth
essential for growth, esp developent nervous system in utero and early childhood
effects are permissive to GH/IGF-1
physiology of growth - nutrition
adequate diet - protein content, essential vitamins + minerals very important
injury and disease stunt growth because increase protien catabolism
physiology of growth - genetic factors
helps determine maximum growth
interaction between genetic factors and nutrition
2 periods of rapid growth
infancy
puberty
puberty growth
due to androgens and oestrogens, produce spikes in GH secretion
promote bone elongation - inc height, weight and body mass
sex hormones at later stage of puberty act o close epiphses and so stop bone elongation
gigantism
excess GH due to pituitary tumour before epiphyseal plates close
excessive growth 1
acromegaly
excess GH due to pituitary tumour after ephyseal plates have sealed
no longutidinal growth but can grow in oher directins
characteristically enlarged hands and feet
