Growth and Ageing

Growth•Growth occurs during gestation, Growth occurs during gestation, childhood and adolescence. childhood and adolescence. •Growth rate = change in size per unit Growth rate = change in size per unit time.time.•Growth curve = when growth rates are Growth curve = when growth rates are plotted graphically.plotted graphically.•Humans have two growth spurts, one Humans have two growth spurts, one between 0-2 years called the infant between 0-2 years called the infant growth spurt and one during puberty growth spurt and one during puberty known as the pubertal growth spurt.known as the pubertal growth spurt.

GrowthAllometric Growth is the differential growth of Allometric Growth is the differential growth of body parts. This causes our body proportions to body parts. This causes our body proportions to change between infancy and adulthood.change between infancy and adulthood.

Growth

Infancy

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.

Childhood

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.

Adolescence

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

AgeingSenescence is the deterioration of bodily functions and the Senescence is the deterioration of bodily functions and the appearance of features associated with old age. It is usually appearance of features associated with old age. It is usually investigated by one of the following techniquesinvestigated by one of the following techniques

• A cross sectional study. This involves studying large A cross sectional study. This involves studying large samples of people at several ages. In the case of research samples of people at several ages. In the case of research into ageing measurements of physical and physiological into ageing measurements of physical and physiological features are taken and averages for the different age features are taken and averages for the different age groups established.groups established.

• A longitudinal studies. This involves studying a small A longitudinal studies. This involves studying a small sample of people and following the individuals over time.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.

AgeingRemember 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.