Adolescence

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Adolescence

• The Physiological Basis of Puberty

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• To specialists
• - Puberty refers to the activation of the
  hypothalamic- pituitary-gonadal axis that
  culminates in gonadal maturation.
• - Adolescence refers to the maturation of adult
  social and cognitive behaviours.

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Physiological Basis of Growth

• Growth is due to an increase in the size of
  organs and tissues.
• Is weight gain growth?
• No because weight gain may occur as a result of
  retention of excess H2O or fat without structural
  growth of tissues.
• Growth occurs by mitosis and by hypertrophy.
  There is a net synthesis of proteins and includes
  lengthening of bones as well as increase in size
  and number of cells of soft tissues
• Identify the factors that will influence growth.

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• Growth Hormone essential for growth but is not
  wholly responsible for determining rate and final
  magnitude of growth. Individuals maximum growth
  capacity genetically determined. Full growth
  potential depends upon
• Adequate diet proteins, essential amino acids,
  Ca2 Malnutrition and growth stunting effects
  70 of total growth of brain occurs in initial 2
  years of life.
• Freedom from chronic diseases and stress stress
  releases cortisol (anti-growth effects) from
  adrenal cortex. Promotes protein breakdown. Can
  be rectified in later teen years (growth spurt)
• Other growth-influencing hormones GH, Thyroid
  hormone, Insulin, sex hormones

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• Calcium and Bone Physiology
• Bone has two basic functions in the body
  structural support and a depot for calcium,
  phosphorus, magnesium, sodium, and carbonate.
• Bone acts as a reservoir for exchangeable
  calcium, which is always in equilibrium with
  calcium ions in the extracellular fluid. This may
  be a more important role than that of structural
  support.
• Exchangeable calcium is a continuously available
  buffering mechanism that keeps the calcium ion
  concentration in the extracellular fluid from
  rising to excessive levels or falling to very low
  levels.

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• Bone is a dynamic tissue that is continually
  being deposited by osteoblasts and resorbed by
  osteoclasts.
• Adequate calcium intake aids in keeping calcium
  levels high, thus preventing a negative calcium
  balance and excessive bone resorption.

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Normal Growth Curve
100
80
60
Percent of total growth
40
20
0
Birth
14
12
10
8
6
18
16
4
2
20
Age (yr)
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Puberty

• Puberty defines a period of sexual maturation
  resulting from activation of the
  hypothalamic-pituitary-gonadal axis
• Characterised by pulsatile secretion of
  gonadotropin-releasing hormone (GnRH)
• Most obvious features are
• - development of secondary sexual
  characteristics - and attainment of acceleration
  of growth

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• Both boys and girls experience pattern of growth
  deceleration before pubertal growth spurt
  (-0.46cm/year and -0.48cm/year respectively)
• When acceleration of growth occurs, boys greater
  than girls
• - average 9.0cm/year (boys)
• - average 7.1cm/year (girls)

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• Puberty is the age at which individuals become
  capable of sexual reproduction.
• Puberty usually begins at 11 13 years in
  females and 12 14 years in males.
• Fertility in males occurs before completion of
  puberty, not case in females
• Attainment of normal fertility (assessed by
  regular ovulatory cycles and ideal pelvic
  anatomy) may not occur for years after completion
  of puberty
• High incidence of intrauterine growth retardation
  and miscarriage in teenage pregnancies

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• Hypothalamus GnRH synthesised
• Pituitary GnRH relsed to Pituitary gland to
  signal synthesis and secretion of
  pituitary gonadotropins LH and FSH
• Blood-borne LH and FSH act on target cells in
  testes and ovaries to
• - direct production of sperm and eggs
• - secrete steroid hormones
• Gonadal steroids vital for gonadal function and
  reproductive behaviour
• In gonads steroid hormones participate in
  spermatogenesis and follicle maturation
• In brain steroids influence GnRH secretion and
  facilitate sexual behaviour

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• At the onset of puberty, there is an increase in
  the secretion of gonadotrophic releasing hormone
  (GnRH) from the hypothalamus.
• In turn, this hormone stimulates an increase in
  the secretion of Luteinising Hormone (LH) and
  Follicle Stimulating Hormone (FSH) from the
  anterior pituitary gland.
• FSH stimulates spermatogenesis in males and
  ovulation in females.
• LH stimulates Testosterone secretion in males and
  Oestrogen secretion in females.
• It is Testosterone and Oestrogen that underpin
  the physical changes that occur during puberty.

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The Physiological Basis of the Growth Spurt

• Secretion of Growth Hormone from the anterior
  pituitary gland increases general bone growth
  during childhood.
• At the onset of puberty, Oestrogen and
  Testosterone initially stimulate bone growth,
  hence the growth spurt.
• Oestrogen and Testosterone also stimulate
  ossification of the epiphysis plates (the growth
  zones) in bones. This is responsible for the
  cessation of bone growth.
• Explain how on average, females are shorter than
  males.

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Hormones Involved in Puberty
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The Role of the Adrenal Cortex

• This endocrine gland secretes androgens (male sex
  hormones) that target the reproductive organs,
  muscles and bone.
• These contribute to sex drive and the development
  of secondary sex characteristics.
• Tumours may occur in the adrenal glands to result
  in adrenogenital syndrome in which there is early
  pubertal development in males. What effect may
  this have on stature of affected males after
  adolescence?

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Development of Male Secondary Sex Characteristics

• Apart from increase in height, identify other
  physical changes that occur during puberty in
  males.
• These changes are due to the stimulatory effect
  of Testosterone.
• Testosterone stimulates hypertrophy of the
  larynx. In particular, mitosis occurs in the
  thyroid and cricoid cartilages. What effect does
  this have on voice?
• How does testosterone stimulate an increase in
  muscle mass?
• What effect will castration before puberty have
  on physical growth and development in males?

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Development of Female Secondary Sex
Characteristics

• Which two hormones stimulate the development of
  female secondary sex characteristics?
• Puberty in females is marked by the first period
  of menstruation. This is referred to as
  menarche.
• Oestrogen is an anabolic hormone. What effect
  will this have on growth of the genitalia?
• Oestrogen together with Progesterone stimulate
  development of the breasts.
• As well as stimulating long bone growth,
  oestrogen also stimulates growth of the pelvic
  girdle.
• Oestrogen inhibits the actions of parathyroid
  hormone. This hormone stimulates bone breakdown.
  What may happen when oestrogen levels decline
  after menopause?