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Lecture

HLTB01 17th Jan.docx

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Department
Health Studies
Course
HLTC22H3
Professor
R Song
Semester
Winter

Description
th 17 Jan, 2013 HLTB01 The Human life course and Aging 1. Life history (from birth to death) 2. Stress and adaptive responses 3. Fetal programming 4. Menopause as a Biocultural event Crews 2003a: “Humans are unique in that they possess an array of interrelated adaptations that improve their adaptability; these include bipedality, large brains, dependence on vision, verbal communication, culture, manual dexterity, altricial-dependent infants and long lives.” Life history refers to the changes through which an organism passes in its development from its primary stage of life to its natural death (fertilization,embryogenesis, fetal development, birth, infancy, juvenile, childhood, adolescence, reproductive adulthood, menopause, old age and senescence) Human life history: prenatal, neonatal, infancy, childhood, juvenile, adolescence, reproductive adulthood, old age and senescence All humans are primates; all primates have an infant stage but in non-human primates, this tends to develop directly into juvenile period. (in primates, the juvenile period is the period where they sexually mature) After reproductive adulthood, other apes succumb to senescent and disease processes while humans enjoy a period of late-life adult survival followed by senescent degeneration (childhood and adulthood are unique human life stages) Note: the stage of childhood started with the H. habilis which lengthened over time (pan/ A. afarensis & A. Africans didn’t have the stage of childhood), the stage of Adolescent started with the H. erectus (change in life history due to selective pressure) st Growth can be marked by teeth as well; as time went by, the age of the eruption of the 1 molar teeth has increased over time as we have developed into a more reliant childhood. Graphs indicated that the rate of growth is greatest during prenatal- infancy and starts to decrease over time as we hit childhood, this rate steadies as we go through juvenile (there is a small peak as we go through the mid growth spurt) and peaks during adolescence again then falls greatly as we hit maturity. Prenatal growth and development Cellular growth: Hyperplasia: new cell growth (division) by mitosis Hypertrophy: enlargement (growth) of already existing cells 1 trimester: period of greatest cell production (multiplication of millions of cells and differentiation of cells into hundreds of different body parts) 2 trimester: completion of cell differentiation into tissues and organs; embryo now a fetus; see increase in rate of growth of length 3 trimester: growth rate in weight increases; see development and maturation of circularly, respiratory and digestive systems. Prenatal life is significance because it is a time of high susceptibility to growth pathology caused by either: a) Inheritance of genetic mutations (congenital) b) Exposure to harmful environmental agents that disrupt normal course of development Post-natal life is very stressful (different temperatures, no more reliance on mom’s oxygen and st nutrients), almost 50% of all neonatal deaths occur during the 1 24hrs. (most neonatal mortality due to low birth weight resulting from growth retardation during fetal life) Do note that SES plays a vital role after birth as well as before birth. Note: at birth, our brains are 50% adult size while chimps already have 75% size of an adult brain…. Thus we have more time to develop and mature our brains. INFANCY  Period (up to age 3) of most rapid postnatal growth, though decelerated compared to prenatal period.  Principle reliance on mother’s breast milk and deciduous dental eruption  Rapid development of motor and cognitive skills (skeletal/ muscular/ nervous systems)  Brain growth, the brain grows more rapidly in infancy than almost any other tissue/ organ (By age 2, the brain reaches 80% of adult size) - A newborn uses 87% of its resting metabolic rate (RMR, body energy expenditure during rest) for brain growth and function - By 5 years: 44% of RMR for brain growth/ function - Adult human: 16-25% of RMR for brain function Transition to solid food marks the end of infancy usually 24-36 months in pre-industrialized societies Weaning  Notably early compared to other mammals (generally when 3.2-4.9 times birth weight; humans before 3x birth weight)  Coincides with emergence of last primary tooth (usually m2) thus have all primary teeth to process solid foods …. Thus this is also the period of notable morbidity & mortality (to age 5); synergy of malnutrition-infection Note: childhood is the period following infancy when the youngster is weaned from nursing but still depends on older people for feeding and protection Childhood  3-7 years defined by its own pattern of growth, feeding behaviour motor development (including adult walking git by 7) and cognitive maturation  Growth rate now levels off at 5cm per year  Replacement of primary teeth with permanent dentition (M1=5-6 years and completion of brain growth) Dependence to others due to : small body size, need for diet dense in energy, lipids, motor and cognitive immaturity, social inexperience and vulnerability to disease and accidents requiring protection The mid-growth spurt is unique to humans and there is a small increase in growth velocity at end of childhood. Juvenile period  Prepubertal individuals who are no longer dependent on adults/ older siblings for survival (have physical and cognitive abilities to survive independently)  7-10 in girls, 7-12 in boys (later onset of adolescence)  This is the periods of slowest rate of growth since birth  Period of social learning and in industrialized nations, coincides with start of formal schooling Adolescence  Start of increased growth rate after juvenile decrease (from deceleration to acceleration now); begins with puberty or gonadarche: reinitiation of activity of hypothalamic-pituitary gonadal system of hormone production  Period of social and sexual maturation (sex organs, menarche)  Sexual dimorphism in body size and composition (muscle ma
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