Chapter 30
APPENDIX B: Development and Aging of the Organ Systems
By Boundless
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The integumentary system develops from all embryonic layers (ectoderm, mesoderm and neural crest cells).
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Intrinsic and extrinsic aging describe cutaneous aging of the integumentary system primarily involving the dermis.
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Although bone initially forms during fetal development, it undergoes secondary ossification after birth and is remodeled throughout life.
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Bones adapt to the muscle force loads placed on them, becoming thicker and stronger under stress/use and weaker and thinner when unused.
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As individuals age, bone resorption can outpace bone replacement, which can lead to osteoporosis and fractures.
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Early in gestation, a fetus has a cartilaginous skeleton that becomes skeletal bones in the gradual process of endochondral ossification.
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In osteoporosis, bone mineral density (BMD) is reduced and the integrity of bone proteins is altered, increasing the risk of fracture.
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Movable joints are formed at the intersection of bones and are covered by cartilage, which allows the joint to move freely.
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Aging is a common cause of chronic joint pain, as wear and tear on the joints from use results in inflammation and osteoarthritis.
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Arthroplasty is an operative procedure in which the arthritic or dysfunctional joint surface is replaced or repaired.
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The CNS originally develops from a longitudinal groove on the neural plate that forms the rudimentary nervous system.
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The peripheral nervous system develops from two strips of tissue called the neural crest, running lengthwise above the neural tube.
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The peripheral nervous system is able to repair and regenerate itself, but the central nervous system is incapable of doing so.
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One of the effects of aging on the nervous system is the loss of neurons in cerebral cortex.
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The senses of taste and smell develop in the intrauterine environment and can deteriorate with age.
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The eye forms from the neural tube, epidermis, and the periocular mesenchyme, with sequential inductions of tissue during development.
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Critical periods have been identified for the development of the hearing and vestibular system.
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The endocrine system regulates growth, metabolism, and body homeostasis using hormones that effectively target organs via the bloodstream.
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Three hormone axes are affected by aging: growth hormone/insulin-like growth factor I, cortisol/dehydroepiandrosterone, and testoterone/estradiol.
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As a person ages, the walls of the heart thicken, the heart becomes heavier, valves stiffen and leak, and the aorta becomes larger.
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Vasculogenesis is the development of new blood vessels.
Heart failure is defined as the inability of the heart to supply blood to the organs of the body.
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New blood vessels are formed from endothelial stem cells, which give rise to the endothelial cells which line the vessels.
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The fetal circulation includes the blood vessels within the placenta and the umbilical cord that carry fetal blood.
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The health of the myocardium can be impaired with age as the arteries narrow or become clogged due to atherosclerosis.
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Lung development can be divided into distinct stages: the pseudoglandular period, the canalicular period, and the terminal saccular period.
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In mammals, breathing in is due to a flattening of the diaphragm and lung expansion. Lung elasticity declines with aging.
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The digestive system is an endoderm-derived structure that begins developing about the fourth week of embryogenesis.
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Aging can result in changes of the digestive system due to decreased nerve sensitivity, loss of muscle, and increased infection rate.