Chapter 3

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Family Relations and Human Development
FRHD 2280
O' Brien

1FRHD 2280 Adolescent DevelopmentChapter 3 Puberty and Physical DevelopmentIntroductionChanges during puberty are many sudden and farreachingOne of the most noticeable changes are getting taller sometimes many inches in a yearThe age at which children enter puberty is influenced by their genetic makeup but also their response to their environment diet health care labour altitudeAs living conditions improve average age of puberty goes downPuberty is a social physical and psychological changeChanges their social roleThe Biology of PubertyPuberty is a biological eventan entire set of delicately synchronized biological eventsHormones Glands in various parts of the body make up the endocrine system they set the changes of puberty and keep them on trackEndocrine glands work by producing substances called hormones and releasing them into the bloodstreamHormones are chemical messengerswhen they reach cells that are sensitive to them those cells respond in a specific wayEndocrine is largely controlled by a part of the brain called the hypothalamusThe hypothalamus monitors and directs many bodily functions including hunger thirst and sex by checking and responding to levels of different hormones in the bloodEach hormone has a set point a particular level the system tries to maintain if the level dips below this hypothalamus sends out signal to produce more of that hormone and vice versaThe pituitary the master gland of endocrine system is right below the hypothalamus and is no bigger than a peaGonads ovaries in women and testes in men are controlled by the pituitary and they are the major source of sex hormones estrogens and androgensMost important estrogen is estradiol and the most important androgen is testosteroneDuring most of childhood levels of estrogen and androgen are the same in boys and girlsThe HPG AxisTogether the hypothalamus pituitary gland and gonads make up the HPG axis named for the initials of the three componentsThe HPG axis forms the feedback loop when the hypothalamus senses that the level of sex hormone in the system is too low it sends a substance called gonadotropinrelaxing hormone GnRH to the pituitaryIn response to this the pituitary produces more luteinizing hormone LH and folicstimulating hormone FSH and when LH and FSH reach the gonads they cause an increased production in sex hormonesThese two hormones also speed up production of egg cells and sperm cellsWhen the level reaches the set point the hypothalamus lowers production of GnRH which signals the pituitary to stop producing LH and FSHAt birth sex hormones are present at almost adult levels but they soon decline to very low levels and stay there until the start of pubertyHow Puberty BeginsThe earliest phase of puberty begins long before any outward physical changesThis phase is adrenarche which means the beginning of adrenal involvementBetween ages of 6 to 9 adrenal glands begin to mature Adrenal glands produce more of an androgen called DHEABy the age of 10 DHEA levels have reached the low end of the adult rangeThis increase in DHEA sets off the first appearance of pubic hair and is also linked to changes in the brain feelings of sexual attraction startThe increase levels of sex hormones together with higher production of growth hormones in the pituitary the thyroid and elsewhere set in motion a whole series of physical changesNo one knows why the hypothalamus starts producing more GnRHthis is the fundamental problem of developmental neurobiologyMost immediate cause is that the hypothalamus becomes less sensitive to sex hormonesThis causes a rise in the set point for these hormonesMenarchethe first menstrual period usually takes place once a girl reaches acritical body weight of about 105lbs and 23 body fat body weight theoryEven if the body weight theory is correct and there are a lot of exceptions it doesnt tell us what sets off pubertyAnother possibility is leptina protein secreted by fat cellsLeptin is known to increase sharply during weight gains of pubertyAnother element that may help to start pubertyis the central nervous system which can directly affect the level of GnRH production by the hypothalamusPhysical DevelopmentDramatic changes in pubertyGrowth SpurtStarting at around the age of two children get taller at about 5cm per yearWith puberty rate shoots upIts maximum defined as peak height velocity comes about 2 years after the start of thegrowth spurt for the few months that this lasts girls are adding about 8cm a year and boys are adding 9cm a yearThis is by far the fastest they were growing since they were toddlersFor girls growth spurt is at about 10 years of age for boys about 12Peak height velocity is around 12 years of age for girls and 14 for boysBetween 11 and 13 the average girl is some 4cm taller than the average boyBoys usually end up taller because of the two year delaywhen they start the
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