Principles of Growth
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Growth can be divided into which 4 periods?
• Intrauterine • Infancy • Childhood • Adolescence
What are examples of non-pathological influences on growth?
• Genetic (family + racial) • Age • Sex • Environmental (altitude, urbanisation, smoking, psych stress) • Nutrition • Season • Diurnal • Socioeconomic • GH secretion
Which factor is most important from the beginning ie. from foetal growth all the way down to adulthood?
Genetics
What is the sequence of events from day 1 to day 12 in the first trimester, in regards to foetal growth?
At which point is the developing organism referred to as a foetus?
From the 10th week of gestation - all major structures are already formed in the foetus and continue to grow + develop.
When do the foetus’ eyelids close and reopen?
Eyelids close around 10-12 weeks + will not reopen until about the 28th week
What can be identified in a foetus at 10-12 weeks?
• Tooth buds appear • Limbs long + thin • Foetus makes a fist w/ fingers • Genitals appear well differentiated • RBCs produced in liver • Heartbeat detected by ultrasound
What happens at week 15?
At week 15, main development of external genitalia is completed
What can be identified in a foetus at 22 weeks?
• 28cm + 500g • Eyebrows + eyelashes well formed • All eye components are developed • Startle reflex • Footprints + fingerprints continue forming • Alveoli forming in lungs
What can be identified in a foetus at 24 weeks?
• 38cm, 1.2kg • Nervous system develops -> control some body functions • Eyelids open + close • Cochlea developed • Resp system develops -> gas exchange
What can be identified in a foetus at 30 weeks?
• 38-43cm, 1.5kg • Body fat rapidly increases • Rhythmic breathing movements occur • Lungs not fully mature • Thalamic brain connections form - mediate sensory input • Bones fully developed (soft + pliable)
What can be identified in a foetus at 34 weeks?
• 40-48cm, 2.5-3kg • Lanugo hair starts to disappear • Body fat increases
The foetus is considered full-term at the end of the 39th week of GA. What can be identified on the foetus from 35 weeks until term?
• 48-53cm • No lanugo except on upper arms + shoulders • Small breast buds on both sexes
List growth factors in foetal life
• Insulin like growth factors (IGF1, 2) • Foetal insulin • Foetal glucocorticoid • Thyroid hormone • Growth hormone
What is the role of foetal glucocorticoid?
• Tissue differentiation + prenatal development of organs • Eg. lungs - maturation of surfactant • Eg. liver - control of glycaemia
What is Karlberg’s ICP model?
• Infancy, childhood + puberty (ICP model) breaks down growth mathematically • Components of the human growth curve from birth to adulthood strongly reflect the different hormonal phases of the growth process • Model provides an improved instrument fro detecting + understanding growth failure
What factor(s) are important in early life for growth?
Nutrition
What factor(s) are important in infancy and childhood for growth?
• Nutrition • IGF 1 • GH
What factor(s) are important for growth during puberty?
• GH • Sex hormones
Describe the pathway of GHRH and GH
• GHRH release in a pulsatile pattern from hypothalamus • Stimulates pituitary to release GH • GH acts directly on GHr • OR GH combines to form GHBP • OR GH goes to liver -> IGF-1 Growth hormone acts in a multitude of ways
Why is it bad to measure a random growth hormone level in primary care?
• GHRH release in a pulsatile pattern • There is transient augmentation of the pulses during puberty • ie. GH levels differ throughout the day so can’t take samples every hour or measure at one point • Instead do growth hormone stimulation test
What is the structure of growth hormone?
• 4 alpha helices • 4 cysteine residue • 2 disulphide bridges • 2 GHR binding sites
What is the cellular action of growth hormone?
• Dimerized GHR • -> JAK • -> MAP kinase • -> STAT5 • -> translocation of GH responsive genes
Which 3 processes does growth hormone stimulate in skeletal growth?
• Subperiosteal apposition • Endosteal resorption • Remodelling