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Growth and Ageing
Growth
•Growth occurs during gestation,
childhood and adolescence.
•Growth rate = change in size per unit
time.
•Growth curve = when growth rates are
plotted graphically.
•Humans have two growth spurts, one
between 0-2 years called the infant
growth spurt and one during puberty
known as the pubertal growth spurt.
Growth
Allometric Growth is the differential growth of
body parts. This causes our body proportions to
change between infancy and adulthood.
Growth
Infancy
Childhood
Adolescence
Growth is very rapid during the first two years of life. The
pituitary gland secretes a hormone called pituitary growth
hormone (PGH). Also it secretes a hormone called thyroid
stimulating hormone (TSH) which stimulates the thyroid
gland to secrete thyroxin. Thyroxin and PGH both stimulate
growth.
During childhood boys and girls grow at the same rate this
growth is controlled by hormones. The hormonal control is
the same as in the infant period.
During puberty the pituitary gland produces LH and FSH
which cause the ovaries to produce oestrogen and the
testes to produce testosterone. These hormones are the
sex hormones and cause the development of secondary
sexual characteristics. During puberty there are also
increased levels of PGH which are responsible for the
increased rate of growth.
The Pituitary Gland
Growth Hormone
Puberty
Puberty
Growth
Main Points about growth in humans
 Growth of brain and head very rapid in early years, which
enables scope for greater learning in childhood. This allows
development of complex types of behaviour because the extended
childhood allows longer period of learning
 There is no need for reproductive organs to develop until
adulthood. Reproductive organs develop slowly until puberty (12/13
years), when development is faster. Growth of reproductive organs
at puberty allows reproductively mature individuals to be
distinguishable. Reproductive organs are developing when the
body/ person is mature enough to rear children
Ageing
Senescence is the deterioration of bodily functions and the
appearance of features associated with old age. It is usually
investigated by one of the following techniques
• A cross sectional study. This involves studying large
samples of people at several ages. In the case of research
into ageing measurements of physical and physiological
features are taken and averages for the different age
groups established.
• A longitudinal studies. This involves studying a small
sample of people and following the individuals over time.
Ageing
Main Physiological effects of ageing
Effects on skin (collagenase produced, collagen* structure
altered). There is a loss of elasticity due to x-links in elastin +
collagen.
 Faulty copying of DNA and a lifetime of exposure to mutagens
leads to accumulated genetic changes/mutations. So faulty
proteins may be made.
 Degeneration of tissues – due to ‘wear & tear’. Organ function,
metabolic rate and lung capacities all decrease.
 Immune system, efficiency decreases + incidence of
autoimmune diseases increases.
Ageing
Remember collagen is a fibrous protein
Ageing
More Physiological effects of ageing
 Women: Osteoporosis /loss of calcium from bones/ rate of cell replacement
decreases/ less protein made as DNA becomes defective;
 Loss of brain cells causes slower responses, slower learning ability, loss of
memory;
 Lower rate of nervous conduction reduces reaction time;
 Cartilage on joints wears out/arthritis reduction in ease of movement;
 Arteriosclerosis/atherosclerosis reduce efficiency of circulatory system;
 Cross-linking of proteins such as collagen* in connective tissue, causes
connective tissue to stiffen e.g. in heart, this is what affecting resting cardiac output
and max heart rate;
 Other effect include wrinkling of skin/ reduced renal filtration rate/ slower
circulation of blood.