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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


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

Name of Hormone

Site of Release



Anterior pituitary gland

Stimulates mitosis, protein synthesis


Thyroid gland

Stimulates rate of metabolism


Anterior pituitary gland
(situated under brain)


  - FSH


- Development of follicle/egg cells and oestrogen secretion by follicle cells in ovaries

  - ICSH


- Spermatogenesis in testes

  - LH (females)


- Triggers ovulation, forms corpus luteum, thickens uterus lining, produces milk in breasts

  - LH (males)


- Secretion of testosterone by testes



- Growth of 2° sexual characteristics
- Thickening of uterus lining


Corpus luteum

- Growth of breasts
- Increases blood supply to uterus lining



- Growth of 2° sexual characteristics
- Sperm production

Table 16-3-2: Changes associated with puberty

In Boys

In Girls

Hormonal Stimulation

In Boys

In Girls


Ovaries, Oviduct,
Uterus, Vagina

ICSH (boys)
FSH (girls)

Growth hormones



Body growth



Growth hormones


Oestrogen + Progesterone

Facial Hair, Larynx

Pelvic girdle





Pubic and axillary (underarm) hair


First menstrual flow (menarche)




Oestrogen + Progesterone