Human Biology > Growth

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Growth And Its Measurement

Methods Of Measuring Growth

• Human growth is diffuse (→spread throughout)
  • Adult is taller, larger from front to back, has larger organs than a child
• Growth: permanent increase in amount of organic matter
  • Produces new cells and increases size of existing cells
  • Somatotropin (→growth hormone) stimulates cell division, protein synthesis / released by anterior lobe of pituitary gland
  • Monitored by standing height and body mass
• Development: physical, emotional, mental, social changes throughout live

Supine Length (unable to stand → infant's length)

• Infant is placed, on it's back, on a table
• Ankles are gently pulled to straighten infant's leg
• Length is measured from top of its head to base of its heels

Standing Height

• Person standing with their heels flat on the ground
• Horizontal bar is moved to touch the top of the person's head

Body Mass → Amount of Organic Matter [Dry Mass → Plants]

• Wet body mass (weight) in humans is an INDICATION of organic matter
• Includes food + H2O → method can be misleading

Absolute Growth and Growth Rate

• ABSOLUTE GROWTH: total growth / cumulative height of a person
  • [GRAPH] Regular increase in size that levels out at ≈16 years
• GROWTH RATE: increase (in an appropriate feature) per unit time
  • GROWTH RATE = (SIZE AT T2 - SIZE AT T1) / (T2-T1)
  • Highest in the first year
  • Decreases rapidly during the first 2 years
  • Constant, low rate during childhood
  • Females and males have similar height until ≈14 → growth spurt occurs
    • later but greater in males than in females
    • Therefore, male becomes taller than the female at ≈14
  • Growth stops by the age of ≈18

Advantages and Disadvantages of Cross-Sectional Study

• Measures people of different ages
• Calculates mean of a population → Individual peaks tend to be smoothed out
• Generalised picture of growth (-) may not be related to one individual (-)
• Easy to perform during clinical investigation (+)
• Short-period of time measurement (+)

Longitudinal Study

• Measures same person at regular intervals over a long period of time
• Accurate picture of individual growth (+)
• Measurements taken at different times can be compared
• Not suitable for an investigation (-)
• People leaf study area/lose interest in being involved in investigation
• Migration/death
• Takes a long time to see a pattern/conclusion

Relatives rates of growth of tissues and organs from birth to adulthood

• [GRAPH] Different parts of the body grow at different rates
  • Head and brain develop first → being ≈90% of its adult size by the age of 5
    • Before growth of bones and muscles in limbs
    • Thus, results in a change in body proportion
  • Reproductive system develops latest → remains below ≈20% until puberty
  • Lymphoid tissues (appendix, spleen, thymus gland) reach max size before puberty → size is
  • reduced to its adult size after puberty → reduction in size caused by sex hormones
  • Curve of the whole body is similar to an ABSOLUTE GROWTH GRAPH as height is an
  • indicator of general body size
• Different growth rates result in changes in shape during embryological and post-natal growth

Puberty

Physical And Endocrine Changes Associated With Puberty

• Growth spurt occurs earlier in girls but is larger in boys
• Sex hormones (testosterone; oestrogen + progesterone) cause
  • Development of internal reproductive organs and 2° sexual characteristics
  • Increase activity of sweat and sebaceous glands
    • Blocked sebaceous glands cause acne
• Changes the relative amounts of protein and fat
  • Total body mass : body fat ratio is lower in boys than in girls
    • Testosterone causes greater growth of muscles
    • Oestrogen causes an accumulation of fat in the body
  • Menstrual cycle in females relates to the proportion of fat to muscle
• Testosterone stimulates growth of cartilage in thorax, pectoral girdle → shoulders expand
• Oestrogen stimulates growth of cartilage in pelvic → hips expand

The Role Of Hormones In Controlling Early Growth

• Puberty begins with release of gonadotrophin releasing factor (GnRF) form hypothalamus
• GnRF stimulates pituitary gland to release gonadotrophin hormone
  • Has a different name but is the same in (1) males and (2) females
    • (1) Interstitial Cell Stimulating Hormone ICSH → stimulates testosterone production by interstitial cells between seminiferous tubules
    • (2) FSH → stimulates egg-containing follicles in ovaries
  • Travels in blood stream to gonads (→ovaries or testes)
  • Causes gonads to release sex hormones
• Internal stimuli must be involved to trigger initial release of GnRF
  • Improved diets → faster grow of female, reach stage of maturity at younger age
    • Age of menarche (→first period) is earlier than it was in the 19th century
    • Relates to changes in female's muscle:fat ratio
  • Girls with low body fat tend to have a later menarche
    • Female athletes who have a high muscle:fat ratio
    • Women who starve during anorexia nervosa find that their periods stop as they lose body fat

Table 16-3-1: Summary of hormones controlling growth

Table 16-3-2: Changes associated with puberty