Lecture 12: Childhood Growth and Development

Question 1

what are the two important stages of development in childhood? what happens in these stages?

Answer 1

1) growth of bones
- drives increase in height

2) development of the neurons
- changes in properties of neurons
- changes in connections between neurons

Question 2

explain this diagram in terms of rates of growth

Answer 2

• During infancy, there is a very rapid growth
• During childhood, (4-12y), there is a stable growth of 5-6cm/year
• During adolescence there is another rapid growth spurt. this usually occurs earlier for girls than boys.

Question 3

what are the physical changes we notice during childhood growth?

Answer 3

• growth in height
• increase in weight
• improved motor skills
• loss of baby teeth, gain permanent teeth

Question 4

What does this show? How is it used? what does it mean?

Answer 4

• This is the New Zealand growth chart for 0-5-year-old girls. It shows the height and weight percentiles for monitoring childhood growth
• Percentiles indicate the percentage of measurements that fall below a particular value and how this value is relative to a population measurement
• every child will be in their percentile and it is important that they maintain growth along that ‘curve’.
• no curve is better than another

Question 5

what happens to bone during childhood growth?

Answer 5

bone elongation!
- long bones grow in length during childhood due to cell proliferation at the growth plates

Question 6

what are some important things to know about bones during childhood growth? in terms of what its made of, its function and activity

Answer 6

• bone is made of highly specialised connective tissue
• main function is to provide mechanical support for muscular activity
• it is in a constant state of turnover (being broken down and built-up) in a balance of bone formation and bone resorption

Question 7

what are bones like during infancy and then childhood?

Answer 7

during infancy (at birth) bones are still at least partly cartilage

• bones need to convert from cartilage to bone tissue
• this is achieved through the bone growth process

during childhood, bone growth takes place at the growth plates

Question 8

explain the process of bone growth during childhood

Answer 8

• done via the process of endochondral ossification
• this is when cartilage becomes bone tissue
• chondrocytes (cells that produce cartilaginous matrix), proliferate, grow bigger, and then due to the lack of blood supply, die.
• the matrix around the chondrocytes then become calcified, which strengthens the matrix
• the osteoblasts then invade into the outer space where there are blood vessels (vascularity) and will go on to produce more bone tissue
• a process of secondary ossification also occurs at either ends of the long bones

Question 9

what drives the proliferation of chondrocytes?

Answer 9

growth hormone! (GH)

Question 10

what are the features of growth hormones?

Answer 10

• it is a protein hormone
• secreted from the anterior pituitary gland
• has a pulsatile release, 2-4 times per 24hrs
• has direct and indirect effects which include the stimulation of IGF1 production

Question 11

what are the direct effects of growth hormone?

Answer 11

• fat mobilization from adipose tissue to provide energy to the sites that are growing
• protein anabolism to stimulate the turnover of cells
• carbohydrate metabolism
• bone growth

Question 12

what is IGF1? what is made from? what else in important about it?

Answer 12

• Insulin-like growth factor
• growth hormone acts on the liver to produce it
• it is carried in the blood circulation by binding proteins
• influenced by nutrition
• involved in protein anabolism, muscle growth and bone growth

Question 13

what happens when GH and IGF1 come together?

Answer 13

• together they are termed the GH/IGF1 axis
• this is essential for growth, metabolism and organ function

Question 14

explain the GH/IGF1 axis

Answer 14

it is a feedback loop.

1) GH is secreted from the pituitary gland
2) GH increases IGF1 secretion by the liver
3) IGF1 is bound by binding proteins in the circulation
4) IGF1 and GH acts via receptors found on most cells, to increase muscle mass, bone growth
5) IGF1 negatively regulates production of GH (self regulates to ensure it’s not growing to much)

*watch this section of the lecture for more detail*

Question 15

what is important about the importance of GH/IGF1 axis for growth and height?

Answer 15

• if there is not enough GH it leads to short stature.
• e.g. a gene mutation resulted in lon GH levels, hypoplasia of the pituitary gland
• if there is too much it leads to being extremely tall
• e.g. gigantism.
• this is a rare condition where children grow much taller than average due to a non-cancerous tumour on the pituitary gland (IGF1 no longer inhibits cell proliferation)
• don’t live very long as organs don’t grow that big and heart struggles to have sufficient blood supply

Question 16

what are some factors that influence growth/height

Answer 16

• genetics
• endocrine - GH and IGF1
• diet (adequate calories and protein)
• health
• genes and environment play an important part in growth (how do genes allow your body to respond to your environment?)

Question 17

how much variation in height is due to genetics?

Answer 17

• 75-80%, remaining due to environmental effects
• however, this number comes from studies involving white ppl so it may not be very accurate.
• there are 100’s of genome variants that have been linked to height through human genetic studies. so height isn’t the result of a single gene DNA squence
• the genetic variants are associated with genes linked to cellular processes required for growth. so more efficent processes lead to increased potential height

Question 18

• what is brain development shown by?

Answer 18

• behaviour changes
• a sign of brain development during childhood

Question 19

when is a brain expected to be developed? what functions are improved?

Answer 19

• around 25y
• impulse control
• reasoning
• focus
• planning
• memory

Question 20

how much bigger does the brain get overtime?

Answer 20

• postnatally from infancy to adulthood our brains increase by ~ a factor of 5

Question 21

how does the brain develop and what causes the size to increase?

Answer 21

1) by about mid-gestation all the neurons have been produced
- neurons are produced at the rostral end of the neural tube and neurons might migrate to the outer brain region

2) increase in size is due to
- increase/branching in projections (dendrites/axons)
- increase in synapses
- increase in support cells

Question 22

how does neural connectivity lead to improved efficiency of brain function?

Answer 22

through synaptogenesis!

• synapses are neuron to neuron communications where neurons are close together
• so through synaptogenesis, more connections between neurons are created
• experiences during life lead to synapse formation
• so early years are characterised by high level of synaptogenesis

Question 23

what is synaptic pruning and now is it relevant to neurological development?

Answer 23

-neurons are making new connections but are also pruning.

• pruning is the regression of unused or unnecessary connections
  (“use it or lose it vibe”)

Question 24

what are the rates of synaptic pruning in different brain regions?

Answer 24

• in sensory circuits, it is quite rapid at birth
• then happens in motor circuits
• then executive functioning occurs when we get a bit older (with deep thought and sense of self)

Question 25

what is myelination? how does it improve the efficiency of brain function?

Answer 25

• myelin is made of lipids and proteins
• it is an insulating layer that covers axons
• it speeds up electrical signals down the axons
• it is produced by oligodendrocytes (support cells in the brain)
• oligodendrocytes increase rapidly from 0-3 years of age and the levels stabilise from about 5 years of age

Question 26

what are some important things to consider in terms of neurological development

Answer 26

• early in life the brain is most plastic with an enhanced ability to learn new things
• as connections are reinforced and there is the development of specialised skills, there is also a reduction of plasticity in the brain
• genes form a blueprint from the brain and experience/reinforcement of connections provide the building blocks/foundation for the brain
• early years are very important for the trajectory of brain development and executive function for life

Question 27

how does the childhood environment influence neuronal development

Answer 27

prolonged stress means the body has a prolonged stress response which can negatively affect the processes of brain development.

• the neurons are essentially ‘bathing’ in cortisol, which results in neurons being in a toxic stress environment which leads to less projections and branching from happening, less circuitry and less synapses in the stressed region