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Biological Growth and Decline

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Jacob Shane

on 9 September 2018

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Transcript of Biological Growth and Decline

Biological Growth and Decline
Germinal period (first 2 weeks after conception) (1st trimester)
Egg (ovum) and sperm cells fuse to create a zygote
23 chromosomes from each cell -> genetic variability
Attachment of zygote to uterine wall (implantation)
Cell division
blastocyst - embryo & trophoblast - support system
Embryonic period (2 to 8 weeks after conception) (1st trimester)
Rate of cell differentiation intensifies
Endoderm (innermost) - digestive & respiratory systems
Ectoderm (outermost) - nervous system, sensory & skin
Mesoderm (middle) - circulatory system, bones, muscles...
Support systems for cells form
Organs appear (organogenesis)
Fetal period (2 months to birth) (1st through 3rd trimester)
rapid growth, and continued development
viable as early as 6 months (beginning of 3rd trimester)
Genetic & Environmental Hazards to Prenatal Development
Harmful environmental influence
e.g., drugs, infectious disease, nutritional deficiency, maternal stress & age, pollutants, incompatible blood types
Severity depends on
Genetic susceptibility
Time of Exposure
Genetic & Chromosomal
Chromosomal abnormalities
Genetic abnormalities
Adolescent physical development
dramatic with onset of puberty
increase in hormone levels
hypothalamus, pituitary glands, thyroid glands, adrenal gland, gonads (sex glands)
testosterone: 18 fold increase in boys, 2-fold increase in girls
estrogen (estradiol): 8-fold increase in girls, 2-fold increase in boys
radical physical changes
rapid physical growth
changes in facial structure (baby face gone)
secondary sexual characteristics
growth of penis/breasts, pubic and armpit hair, facial hair
change in voice
Major Brain Remodeling
Increase efficiency of brain
Synaptic pruning "use it or lose it"
Increased myelination (speed)
Frontal cortex
early growth spurt
then pruning
Amygdala (emotions)
early growth spurt
Prefrontal cortex
later and sustained growth
until mid 20s
high dopamine activities
Asynchronous development of
capacities, emotions, and regulation
"motor works but breaks don't"
Larry Steinberg
risk behavior
susceptibility to peer pressure
increased emotionality
motivational changes
Adolescent brain development:
"The motor works, but the breaks don't"
Brain Development in
Infancy & Early Childhood
Rapid growth during first 2 years
Extensive myelination & neuronal connections
"Blooming & Pruning" - Strengthened if used; removed if not
Continued development through childhood, but at slower pace than in infancy
Brain & head grow faster than any other part of body
Myelination & Neuronal connections continue to develop
Adult physical development and hormonal changes
Peak functioning of joints occurs in the twenties
Peak of muscle tone and strength in late teens and twenties
Physical changes gradual, noticeable signs of aging by 40s - 50s
Climacteric - decline in fertility
between 39 and 59 years of age (mean 51) a lot more variable in timing than puberty
rapid decline of estrogen production in ovaries, menstrual period ceases
some, but not all experience mild to moderate symptoms (e.g., hot flashes, difficulty sleeping (insomnia), mood instability)
gradual decline in testosterone in midlife
gradual decline in sperm count
decline but not loss of fertility
increasing likelihood of erectile dysfunction after 40
wrinkles and pigment spots on skin
graying and/or loss of hair
Cardio-vasculatory system looses flexibility and strength
reduced lung capacity
reduced immune functioning
lessened hearing
diminished eyesight (short-sightedness starts in midlife)
joint diseases (osteroarthritis, osteoperosis)
Brain begins shrinking, especially in prefrontal cortex
Cognitive processing slows, coordination and reflexes become impaired
Synaptic communication less efficient, decreased brain lateralization
Old age
Biological Theories of Aging
Cellular Clock Theory
Cells can only divide 75-80 times
Telomeres get shorter with each cell-division
Free-Radical Theory
Unstable oxygen molecules (free-radicals)
Accumulate with age (By-product of metabolism)
Causes cell damage
Mitochondrial Theory
Free radicals & nutrient loss damage mitochondria
Over time, cell unable to produce enough energy to sustain itself
Hormonal Stress Theory
Accumulated stress exposure wears down & increases risk of disease
Allostasis = adaptation and adjustment
Short term adaptive; but long-term accumulation wears body down
Evolutionary Theory
Species-specific lifespan product of evolution
Time required for sexual maturation & caring for offspring
Post-reproductive contribution to welfare of grandchildren
Costs of survival into post-reproductive age
Coping with illness & disease in old age
Congruence principle
Match Engagement / Disengagement with control
Set "lines-of-defense"
Shift from goal engagement to organized retreat beind next line of defense if goal attainment becomes unfeasible
Heckhausen, Wrosch & Schulz, 2013
Body Growth & Change
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