The integumentary system develops from all embryonic layers (ectoderm, mesoderm, and neural crest cells).
The integumentary system undergoes intrinsic and extrinsic cutaneous aging, primarily involving the dermis.
Although bone initially forms during fetal development, it undergoes secondary ossification after birth and is remodeled throughout life.
Bones adapt to the muscle force loads placed on them, becoming thicker and stronger under stress and use and weaker and thinner when unused.
As individuals age, bone resorption can outpace bone replacement, which can lead to osteoporosis and fractures.
Early in gestation, a fetus has a cartilaginous skeleton that becomes bone in the gradual process of endochondral ossification.
In osteoporosis, bone mineral density (BMD) is reduced and the integrity of bone proteins is altered, increasing the risk of fracture.
Movable joints are formed at the intersection of bones and are covered by cartilage, which allows them to move freely.
Aging is a common cause of chronic joint pain, as wear and tear from years of use results in inflammation and osteoarthritis.
Arthroplasty is a surgical procedure in which an arthritic or dysfunctional joint surface is replaced or repaired.
Myogenesis is the formation of muscle tissue during embryonic development from stem cells in the mesoderm.
The central nervous system (CNS) develops from a longitudinal groove on the neural plate that forms the rudimentary nervous system.
The peripheral nervous system develops from two strips of tissue called the neural crest, running lengthwise above the neural tube.
The peripheral nervous system (PNS) is able to repair and regenerate itself, but the central nervous system is incapable of doing so.
One of the effects of aging on the nervous system is the loss of neurons in the cerebral cortex.
The senses of taste and smell develop in the intrauterine environment and can deteriorate with age.
The eye forms from the neural tube, epidermis, and periocular mesenchyme, with sequential inductions of tissue during development.
Critical periods have been identified for the development of the hearing and vestibular system.
The endocrine system regulates growth, metabolism, and body homeostasis using hormones that target organs via the bloodstream.
Three hormone axes are affected by aging: growth hormone/insulin-like growth factor I, cortisol/dehydroepiandrosterone, and testoterone/estradiol.
Hematopoietic stem cells reside in the bone marrow and have the unique ability to differentiate into all mature blood cell types.
As a person ages, the walls of the heart thicken, the heart becomes heavier, valves stiffen and leak, and the aorta becomes larger.
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.
New blood vessels are formed from endothelial stem cells, which give rise to the endothelial cells that line the vessels.
Fetal circulation includes the blood vessels within the placenta and the umbilical cord that carry fetal blood.
The health of the myocardium can become impaired with age as the arteries narrow or become clogged due to atherosclerosis.
Lymphatic tissue development begins by the end of the fifth week of embryonic development.
Early in life, the immune system is not mature enough to fight off pathogens and must depend on antibodies from the mother.
As aging occurs, the immune system begins to lose its ability to ward off pathogens.
Lung development can be divided into distinct stages: the pseudoglandular period, the canalicular period, and the terminal saccular period.
In mammals, breathing is produced by a flattening of the diaphragm and lung expansion. Lung elasticity declines with aging.
The digestive system is an endoderm-derived structure that begins developing about the fourth week of embryogenesis.
Aging can result in changes in the digestive system due to decreased nerve sensitivity, muscle loss, and increased infection rate.
The gut or gastrointestinal tract is an endoderm-derived structure.
The urinary system develops from the intermediate mesoderm during prenatal development.
As kidneys age, the number of filtering units and nephrons decreases, slowing down function.
The balance of body fluids that are crucial for good health begins during fetal development.
Reproductive organs develop from the Wolffian ducts in males and the Mullerian ducts in females.
Puberty is the process through which a child matures and becomes capable of sexual reproduction.