Growth

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

Name of Hormone	Site of Release	Actions
Somatotropin	Anterior pituitary gland	Stimulates mitosis, protein synthesis
Thyroxine	Thyroid gland	Stimulates rate of metabolism
Gonadotrophins	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
Oestrogen	Ovaries	- Growth of 2° sexual characteristics - Thickening of uterus lining
Progesterone	Corpus luteum	- Growth of breasts - Increases blood supply to uterus lining
Testosterone	Testes	- 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
Testes	Ovaries, Oviduct, Uterus, Vagina	ICSH (boys) FSH (girls)	Growth hormones	Testosterone	Oestrogen
Body growth	Breasts		Growth hormones	Testosterone	Oestrogen + Progesterone
Facial Hair, Larynx	Pelvic girdle			Testosterone	Oestrogen
Pubic and axillary (underarm) hair
	First menstrual flow (menarche)				Oestrogen + Progesterone