10.3 - Postnatal and child development 1/2 Flashcards
What factors can affect prenatal / postnatal growth? (4)
- genetics
- endocrine
- nutrition
- environment
How do genetics affect prenatal growth?
- minor effect overall
- maternal size important in determining birth size
- paternal genetic factors have little effect on birth
- maternal factors tend to override foetal genetic factors in determining prenatal growth
How do genetics affect postnatal growth?
- largely determines final adult height
- sex chromosomes have an affect:
- XY boys are taller than XX girls
How do endocrine factors affect prenatal growth?
- insulin and insulin-like growth factors (IGFs) are major prenatal hormones influencing growth:
- IGF-2 most important for embryonic growth
- IGF-1 most important for later foetal and infant growth
- (growth hormone has no effect on early growth)
How do endocrine factors affect postnatal growth?
Human growth hormone (hGH) is the major hormone controlling growth after birth
How does nutrition affect prenatal growth?
- placenta provides all nutrients to growing foetus, therefore essential for growth
- placental insufficiency most common cause of intrauterine growth restriction
- placenta also controls hormones necessary for foetal growth
- maternal diet influences nutritional availability
How does nutrition affect postnatal growth?
- adequate nutrition is essential for growth
- starvation due to lack of substrate availability can limit growth potential
- obesity mainly occurs as a result of excessive intake of food
- poor nutrition may delay the onset of puberty
- malabsorption of nutrients may cause reduced growth
How does the environment affect prenatal growth?
- uterine capacity and placental sufficiency important in providing optimal environment for foetus
- placental function is more influential in foetal growth than uterine capacity
How does the environment affect postnatal growth?
The following factors are known to influence growth:
- socioeconomic status
- chronic disease
- emotional status
- altitude (mediated by lower oxygen saturation levels)
What is the size of the head like at birth, and how does this change?
Head disproportionately large for the body at birth (1/3rd vs 1/7th in adulthood)
What is the overall growth (of the head?) like in the first two years of life vs after, and why?
- grows rapidly for the first 2 years, before slowing down
- cranial sutures open at birth and close by 18 months
What are the four recognised phases of growth (and what % of adult height do they contribute to)?
- fetal (30%)
- infantile (15%)
- childhood (40%)
- pubertal (15%)
What is important in the fetal phase of growth?
Uterine environment
What is important in the infantile phase of growth? (3)
- nutrition
- good health and happiness
- thyroid hormones
What is important in the childhood phase of growth? (4)
- growth hormone
- thyroid hormones
- genes
- good health and happiness
What is important in the pubertal phase of growth? (2)
- testosterone and oestrogen
- growth hormone
What is the fastest period of growth over the life-course?
Fetal growth phase
Describe the fetal growth phase.
- fastest period of growth over life-course
- accounts for approximately 30% of eventual height
- foetus repeatedly doubles in size over gestation
- growth mainly driven by hyperplasia during fetal life:
- ~42 cycles of cell division before birth
- ~only further 5 cycles of cell division from birth to adulthood
What is growth in the fetal growth phase mainly driven by?
Hyperplasia (cell division)
Describe the infantile growth phase.
- covers 0-18 months after birth
- accounts for approximately 15% of eventual height
- rapid, but decelerating growth (compared to fetal phase)
- length increases by 50%, head circumference by 30% and weight triples (vs birth)
- growth largely nutrition dependent
What is growth in the infantile growth phase largely dependent on?
Nutrition
Describe the childhood growth phase.
- covers 18 months to 12 years of age
- accounts for approximately 40% of eventual height
- steady, slow, prolonged growth
- 5-6cm annual increase in height, 3-3.5kg annual increase in weight
- good nutrition and health important, but endocrine growth regulation increasing
Describe the pubertal growth phase.
- AKA pubertal growth spurt
- accounts for 15% of eventual height
- rising levels of sex hormones boost human growth hormone (hGH) production
- ~25cm (XY boys), ~20cm (XX girls) increase in height over 3-4 years
- temporary growth spurt as sex hormones also cause fusion of growth plates
Why is the pubertal growth phase only a temporary growth spurt?
Temporary growth spurt as sex hormones also cause fusion of growth plates
Describe the activity of the HPG axis over the life-course.
- fetal - development of sexual organs and GnRH network, foetal HPG axis activity peaks around 20 weeks
- neonatal - priming of HPG axis, ‘mini-puberty’
- childhood - linear growth and developmental milestones, HPG shut down until puberty
- adolescence - sexual maturation, normal puberty, HPG activity rises
- adulthood - reproductive capacity, HPG activation stays high
Describe gonadotrophin secretion during pregnancy.
Gonadotrophin secretion commences towards the end of the first trimester, peaks mid-pregnancy, then declines
What is mini-puberty?
- HPG axis transiently activated after birth (mini-puberty), after release from restraint by placental hormones
- continues for around 6 months after birth before declining
Males: T elevated
Females: E2 fluctuates
What is the point of mini-puberty?
- elevated sex steroids in males during mini-puberty seems to be important for normal gonadal development (testicular tissue and penile development)
- role of mini-puberty less clear in female infants:
- oestradiol levels fluctuate through first few months after birth
- follicular development occurs in the ovary
- important for patterning and development of mammary tissue?
- elevated sex steroids in mini-puberty may also influence programming of body composition and linear growth
- high testosterone levels in boys during mini-puberty may partly explain the higher growth velocity observed in boys vs girls
What triggers puberty?
- control of puberty onset remains unclear, but influenced by metabolic status
- release of neurokinin KNDy neurons may regulate release of Kisspeptin peptides, which act on GnRH neurons to promote pulsatile GnRH release
- mutations in KISS1R affect puberty timing, implicating Kisspeptin-KISS1R signalling in regulation of this process
- adiposity also plays a role
What do the developmental events of puberty typically follow?
The developmental events of puberty typically follow a predictable pattern
What is compliance with the predictable pattern of developmental events of puberty known as?
Consonance
How has the age of menarche changed?
Decreased ~4y from 1850-1960, then by a further 3 months per decade from 1977-2013 (partly due to better nutrition and health status)
Describe the developmental milestones during puberty in a female.
- breast budding
- growth of pubic hair
- growth spurt (peak)
- first period (menarche)
- growth of underarm hair
- change in body shape
- adult breast size
Describe the developmental milestones during puberty in a male.
- growth of scrotum and testes
- change in voice
- lengthening of penis
- growth of pubic hair
- growth spurt (peak)
- change in body shape
- growth of facial and underarm hair
What are the four developmental domains?
- gross motor skills
- fine motor skills
- speech, language and hearing skills
- social behaviour and play skills
Describe the development of gross motor skills.
- newborn: flexed posture
- 7 months: sits without support
- 1 year: stands independently
- 15-18 months: walks independently
- 2.5 years: runs and jumps
Describe the development of fine motor skills and vision.
- newborn: fixes and follows face/object
- 7 months: palmar grasp (4-6 months), transfers objects from hand to hand
- 1 year: pincer grip (10 months), points
- 15-18 months: immature grip of pencil, random scribble
- 2.5 years: draws
Describe the development of speech, language and hearing skills.
- newborn: stills to noise, startles to loud noise
- 7 months: turns to voice, polysyllabic babble
- 1 year: 1-2 words, understands name
- 15-18 months: 6-10 words, points to four body parts
- 2.5 years: 3-4 word sentences, understands two joined commands
Describe the development of social behaviour and play, emotional and behavioural skills.
- newborn: smiles by 6 weeks
- 7 months: finger feeds, fears strangers
- 1 year: drinks from cup, waves
- 15-18 months: feeds self with spoon, beginning to help with dressing
- 2.5 years: parallel play, clean and dry
