02 physical growth, maturation and aging

Prenatal development

• fusion of ovum and spermatozoon

• Extrinsic and genetic factors influence growth

Fetal development !!

organ and tissues grow in two ways

• Hyperplasia: increase in the absolute number of cells

• Hypertrophy: increase in the relative size of an individual cell

Fetal development directions

Growth tends to proceed in two directions

• Cephalocaudal: direction of growth beginning at the head and extending toward the lower body

• Proximodistal: direction of growth proceeding from the body toward the extremities

Plasticity

In regard to growth it is the ability of tissue to subsume functions otherwise carried out by other tissues

Fetal nourishment

Nourished by the

• diffusion of oxygen and nutrient between fetal blood and maternal blood in the placenta

Abnormal prenatal development 1

Congenital defects are anomalies present at birth, regardless of whether their causes are genetic or extrinsic

• Genetic causes: Dominant disorders result when one parent passes on a defective gene (…), new mutation, alteration or deletion of a gene during formation of the egg or sperm cell

• Results:

  • Single or multiple malformations of an organ, limb or body region

  • Deformation of a body part

  • Disruptions in development resulting from the breakdown of normal tissue

Abnormal prenatal development 2

Extrinsic causes: Fetal nourishment system deliver harmful substances to the fetus, if they are permeable to the placenta

• Teratogen: any drug or chemical agent that causes abnormal development in a fetus upon exposure

• Viruses (e.g. rubella, herpes virus)

• Exposure to x-rays

• External or internal pressure on the infant

Critical periods: e.g. rubella virus is harmful if the embryo is exposed to it during the first 4 week of pregnancy

Postnatal development

Postnatal growth proceeds in a precise and orderly pattern, but individual variability and not linear

Overall body growths shows an sigmoid curve, the slope of the curve can vary from average

Relative growth

Postnatal growth differ among body parts and body systems

Some body parts must growth faster than others (in childhood: the legs growth faster than the trunk and the head)

Physiological maturation

Physiological maturation is the developmental process leading to a state of full function.

Appearance of secondary sex characteristics during the adolescent growth spurt is a function of maturation

Extrinsic influences on postnatal growth

During periods of rapid growth, just after birth and in early childhood and in early adolescence, growth is particularly sensitive to alteration by environmental factors

Catch-up growth is a relatively rapid physical growth of the body to recover some or all of retarded growing during a period of negative extrinsic influence once the negative influence is removed

Adulthood and aging

Decreasing of body height because of the aging of the tissues (natural wear)

• Compression and flattening of the cartilage pads between the vertebrae

• Bones lose density