Growth and Disorders Flashcards
Describe the circulating GH molecules composition
Heterogenous composition of 22kDa and 20kDa. 75% of the pituitary GH secretion is of the 22kDa form. 20kDa has diabetogenic effects
Name some factors affecting GH secretion
The secretion can be increased during exercise, physical stress, trauma, hypovolaemic shock, infusion of single amino acids. Whereas decreased in emotional deprivation or hyperglycaemia. The gonadal steroids appear to be responsible for the rise in GH secretion in puberty.
What are the actions of GH?
This activation occurs by binding to 2 GH receptors causing signaling via JAK/STAT to stimulate epiphyseal growth. Stimulates osteoclast differentiation and activity, as well as osteoblast in the bone to increase bone mass formation (endochondral bone formation). GH acts on adipose to induce acute insulin-like effects, decreasing glucose transport, decreased lipogenesis.
It acts on the muscle to increase AA transport, increase N retention and increase energy expenditure.
What is the insulin like growth factor-1?
This mediates many of the anabolic and mitogenic actions of growth hormones. It can induce cellular change by binding to IGF-1 receptors or insulin receptors. The mitogenic and metabolic effects occur by binding to type I IGF receptors.
How can growth abnormalities be monitored and discovered?
The most basic tool useful to monitor the progression/severity of a growth abnormality is using the height vs weight chart to determine the growth velocity
What are primary growth syndromes? Onset?
Can be chromosomal abnormalities (down syndrome) or osteochondrodysplasia (genetic transmission). Can develop as early as gestational age due to intrauterine growth retardation.
The earlier it occurs the less likely complete recapture will occur. It can be caused by maternal and placental factors or intrinsic foetal factors.
State some primary growth disorders
Russel silver Noonans Cockaynes progeria Prader-willi
What are some causes of secondary growth disorders?
Emotional deprivation has shown to decrease GH secretion
- Chronic disease associated with malabsorption, poor intake, and increased metabolic rate
- e.g. DM, pulmonary disease, renal diseas, CKD, chronic inflammation
- Endocrine disorders have also been shown to induce secondary growth disorders
- e.g. IGF-1 def, GH def, hypothyroidism, rickets
What is constitutional delay in puberty and how is it examined?
Later pubertal growth spurt so short compared to peers - typically a family history associated with it.
Diagnosis: by comparing chronological age to bone age determined from X-ray of and wrist. Show chronological age greater than bone age
How is constitutional delay in puberty dealt with?
Accelarte the onset of puberty by administering testosterone - but can reduce height potenital
What are the characteristics of GH deficiency?
low GH and IGF-1
What causes GH def?
- congenital abnormalities of hypothalamus
- inflammation of brain
- trauma
- GHRH receptor defects
Symptoms of GH def
Short stature Decreased height velocity Delayed bone age Delayed dentition Prolonged jaundice
How is the diagnosis of GH done?
Random GH measurements are not very useful as its secretion occurs in a pulsatile manner. Instead physiological and pharmacological tests are used in diagnosis
What physiological tests are used to diagnose GH def?
Exercise test
- GH secretion should increase following exercise
- 15min of exercise with heart rate of >150.
Sleep studies
- Sample GH secretion in your sleep 15x2 min intervals
- most effective in children
