3.1 Control of Growth Flashcards
What is velocity of growth like during infancy?
Rate of growth drops immediately after conception (first cell division doubles the size of the embryo → no subsequent growth can match this rate)
What is velocity of growth like during childhood?
Plateaus after infancy (childhood growth occurs at a fairly steady rate)
What is velocity of growth like during puberty?
Adolescent growth spurt (increased velocity) → drops until zero after the spurt (adults do not grow at all)
What are factors affecting growth in the foetal phase?
Maternal nutrition: undernutrition or overnutrition of mother
• Undernutrition: deficiency of specific nutrients (e.g. folic acid) or deficiency of core nutritional components (e.g. protein, carbohydrate)
• Overnutrition: gestational diabetes mellitus leads to large for gestational age babies
Placental sufficiency: ability to transfer nutrients across to the foetus
Foetal growth factors: IGF-2, human placental lactogen (hPL), insulin
Length of gestation
Intrauterine growth restriction (IUGR)
what are factors affecting growth in the infancy phase?
Largely dependent on infant nutrition (achieving adequate nutrition is quite challenging due to high energy requirements and low density/calorie diet):
• Dependent on degree of parental care
Other factors: good health, normal thyroid hormones, insulin, GH
what are factors affecting growth in the childhood phase?
Largely determined by growth hormone
Other factors: adequate nutrition, good health, normal thyroid hormones, adequate vitamin D, psychosocial wellbeing
what are factors affecting growth in the puberty phase?
Largely determined by sex hormones + GH release increases ~2-fold with an increase in amplitude of pulses:
• Important factors: timing of puberty, length of spurt, health, nutrition, and general wellbeing
The endocrine axis for the control of growth involves the hormones GHRH, GH, and IGF-1:
• GHRH is released by the ________ and acts on the _____________ in the anterior pituitary
• Somatotrophs release GH (peptide hormone) in a pulsatile fashion (difficult to measure levels) → stimulates liver to produce _______ and also has direct effects on tissues
o IGF-1 causes bone and soft tissue growth
• Both ____________ exert negative feedback on the axis by stimulating somatostatin release
hypothalamus;
somatotrophs;
IGF-1
GH and IGF-1
What are the effects of GH on
- bone
- protein metabolism
- fat metabolism
- glucose metabolism
- increased mineralisation
- increased amino acid transport
- Increased fatty acid breakdown to release energy from fat stores
- Promotes hepatic gluconeogenesis by reducing insulin receptor expression
What are the effects of IGF-1 on
- bone
- protein metabolism
- glucose metabolism
- Stimulates bone growth
- Stimulates muscle cells to synthesise protein
- Increases glucose uptake by cells (especially muscles)
what factors increase release of growth hormones?
sleep (circadian rhythm-related), sex hormones
what factors decrease release of growth hormones?
stress, cortisol, negative feedback from GH and IGF-1
The height of an individual is mainly determined by bone growth (mostly of long bones) at the epiphyseal growth plates at both ends: • Bone age is a method of estimating the skeletal maturity (useful in the assessment of short stature to predict the final height) → more immature bones = more potential
• Plain X-ray of _______________ is compared to a standard reference guide
• Skeletal maturity is considered abnormal if the bone age is __________________ → normal bone age in a short child suggests _______________
non-dominant hand & wrist;
> 2 SD below the child’s age;
familial short stature or other non-endocrine causes
