Principles of Growth Flashcards
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
How does growth hormone affect growth plates specifically?
- Increases rate of mitosis of chondrocytes + osteoblasts
- Increases rate of protein synthesis (collagen, cartilage matrix, enzymes)
How does parathyroid hormone (PTH) affect growth plates?
- Increases resorption of calcium from bones -> blood
- Raises blood calcium levels
- Increases absorption of calcium by small intestine + kidneys
How does calcitonin affect growth plates?
- Decreases resorption of calcium from bones
- Lowers blood calcium levels
How do oestrogen and testosterone affect growth plates?
- Promotes closure of epiphyses of long bones
- Stopping growth
- Helps retain calcium in bones
- Maintains strong bone matrix
What is meant by crossing of growth centiles and what does this mean?
- Infants + children stay within 1 or 2 growth centiles
- Any crossing of height centiles warrants further evaluation
- Crossing of centiles = normal event in child development
- Though crossing centiles should be taken seriously
What is catch up growth?
- Catch-up growth characterised by height velocity above the limits of normal for age for at least 1 year after a transient period of growth inhibition; complete or incomplete
- Inc growth rate following IUGR = catch-up growth
- Complete - result in a mean final height close to mean target height
Describe catch down growth
- Seen in children who start off at high percentile in early infancy
- 6-18 months - show fall on their percentile growth chart
- Over time they match their genetic programming + then grow at lower percentile, but along genetic potential
- Have normal physical, psychological + behavioural development
- However, a fall of more than 2 major percentiles warrants investigations
What is puberty?
- Transition from childhood to achievement of adult stature through development of secondary sexual characteristics
- Influenced by genetic, nutritional, environmental + socioeconomic factors
What is the average age of onset of puberty?
- female - 11
- male - 12
What are the events of puberty in girls?
- First sign = breast development
- Pubic hair
- Growth spurt
- Menarche
What are the events of puberty in boys?
- First sign = testicular (4ml) (+ penile) enlargement
- Pubic hair
- Voice change
- Growth spurt
- Spermatogenesis
Why might some patients with pubertal development problems also have problems with smell?
GnRH neurones arise from the olfactory placode + migrate to the hypothalamus along the olfactory tract - under control of genes (KAL, FGF8)
