Week 1 Flashcards
How is development different than growth?
Growth: quantitative increase in size
Development: Progression from an immature to a mature state measured by functional capacity regardless of size
Define growth trajectory
The timing and speed of growth and maturation as they pertain to a “typical” growth of a human
After birth, body growth (increases/slows) compared to intrauterine growth
Slows
After birth, brain growth (slows/accelerates) compared to intrauterine growth
Accelerates
During infancy, most or all nutrition is provided via…
Lactation
Coinciding with weaning, this physical structure appears in infants
Deciduous dentition
Describe the digestive system of an infant
Immature – teeth and organs are not well developed, infants require liquid/soft nutrient-dense foods provided by adults
What parts of the body are growing significantly during childhood?
Brain - everything else is growing slowly
First permanent teeth erupt during this life stage
Childhood
Humans are vulnerable to predation and disease during this life stage
Childhood
On average, brain growth in weight ceases at this age
7 years
What are the “bookend” events of childhood?
Weaning until ~ age 7
What are the “bookend” events of the juvenile stage?
~7 years until the onset of puberty
Define the growth rate of the body, generally during the juvenile stage
Overall relatively slow growth rate
If not a lot of significant growth is happening during the juvenile stage, what is the importance of this stage?
Important time for LEARNING economic and social skills. At this point, juveniles can start learning to assist with food production and infant care
What important hormonal-brain axis is turned on at the onset of puberty?
The HPG axis
What are the 2 most important hormones involved in the onset of puberty?
Estradiol and Testosterone
Estradiol is produced in (1) from (2)
- Ovaries
- Aromatization of testosterone
In the hypothalamus, when the HPG axis is turned on, the hypothalamus secretes…
GnRH (Gonadotropin-releasing hormone)
Which anterior pituitary hormones are secreted in response to GnRH secretion by the hypothalamus?
FSH and LH
Both sexes require estradiol and testosterone, but undergo different sexual development due to a difference in…
The relative amounts of hormone present
Testosterone can be produced by these 3 organs/glands
Testes, ovaries, adrenal glands
Puberty is initiated by…
The return of GnRH pulsatility after a period of axis dormancy
True or false: once re-activated at the onset of puberty, GnRH secretion is constant
False: pulsatile release
How many neurons in the hypothalamus secrete GnRH?
approx. 2000
To initiate puberty, GnRH pulses need to occur once every…
90 minutes
During puberty, LH increases (1)-fold and FSH increases (2)-fold
- 25x
- 2.5x
What happens during puberty and how it happens (e.g. development of secondary sex characteristics) is determined by…
The frequency of GnRH pulses
Which sex hormone is important for the linear growth during puberty?
Testosterone
What are the “bookend” events of Adolescence?
Onset of puberty, ends 5-8 years after the onset of puberty
During adolesence, growth accelerates in this way
Increase in height and weight
Peak height velocity (PHV) is reached around this time after GnRH pulsatility resumes
~3 years
What are the average age ranges for adolescence in males and females?
F: 10-18
M: 12-21
How does estradiol act on the skeleton? How does this explain why the average female is shorter than the average male?
Estradiol contributes to closing of growth plates, this means female growth plates close sooner, therefore male growth can occur for longer
Adolescence continues until an individual stops…
Growing
Research on puberty uses a common marker, which is…
Age of max growth rate/peak height velocity
Cessation of growth in height and weight is usually accompanied by the appearance of (2)
- 3rd Molars
- Secondary sex characteristics
What are the “bookend” events of adulthood?
Completion of skeletal growth until the end of reproductive capability
Since growth is not occurring during adulthood, energy is funnelled towards
Body maintenance and reproduction
Which life stages are unique to humans compared to other primates?
Childhood, Adolescence, Post-reproduction
What is special about the growth rate achieved by humans during puberty?
It is incredibly fast, faster than the peak growth rate of any other mammal
Humans have a unique reproductive “schedule” in 3 ways: name these
- reach reproductive maturity very late
- once we reach reproductive maturity, there tends to be a significant lag between the first birth
- breastfeeding stops very early
What is special about the human inter-birth interval?
It is very short
What is special about human longevity?
Unprecedented longevity compared to other primates
How is the cessation of breastfeeding related to the inter-birth interval of humans?
Breastfeeding suppresses ovulation, it is energetically expensive to breastfeed and ovulate at the same time, by weaning earlier we can start ovulating sooner after birth
Why do humans most likely have childhood and adolescence?
Childhood: Weaning sooner = entry into childhood, shorten the interbirth interval, therefore increase mother’s fitness
Adolescence: Adolescents can help take care of young!
Why do humans have a long post-reproductive period?
Grandmother hypothesis: a post-reproductive parent can increase the fitness of their genes indirectly by helping the survival of her offspring which have her genes
Why do humans grow so slowly?
Because it takes us so long to grow our energetically expensive brains
Why do humans go through puberty?
It is essentially a catch-up time where our bodies have to catch up to our brains, which have grown significantly in size
The timing of the onset of puberty may be different due to…
Different body fat stores and nutritional status
Puberty likely evolved in a “flexibly timed” way so that…
The body may enter puberty when nutritional stores are optimal
