Human Development Terms 3

Germinal Period

The period that begins at conception and lasts until the developing organism becomes attached to the wall of the uterus about 8 to 10 days later

Embryonic Period

The period that extends from the time the organism becomes attached to the uterus until the end of the 8th week of pregnancy, when all of the major organs have taken primitive shape

Fetal Period

The period that begins in the 9th week after conception, with the first signs of the hardening of the bones, and continues until birth

Amnion

A thin, tough, transparent membrane that holds the amniotic fluid, and surrounds the embryo

Chorion

A membrane that surrounds the amnion and becomes the fetal component of the placenta

Placenta

An organ made up of tissue from both the mother and the fetus that serves as a barrier and filter between their bloodstreams

Umbilical Cord

A flexible helical structure containing blood vessels that connects the developing organism to the placenta

Ectoderm

Cells of the inner cell mass that develop into the outer surface of the skin, the nails, part of the teeth, the lens of the eye, the inner ear, and the central nervous system

Endoderm

Cells of the inner cell mass that develop into the digestive system and the lungs

Mesoderm

The cells of the inner cell mass that give rise to the muscles, the bones, the circulatory system, and the inner layers of the skin

Neural Tube

An embryonic structure that later develops into the brain and spinal cord

Large for Gestational Age

Babies whose weight at birth is above the 90th percentile of babies of the same sex who are the same gestational age

Gestational Age

The amount of time between conception and birth. The normal is between 37 and 43 weeks

Teratogens

Environmental agents that can cause deviations from normal development and can lead to abnormalities or death

Fetal Alcohol Syndrome

A syndrome found in babies whose mothers were heavy consumers of alcohol while pregnant. Symptoms include and abnormally small head and underdeveloped brain, eye abnormalities, congenital heart disease, joint abnormalities, and malformations of the face

Apgar Scale

A quick, simple test used to diagnose the physical state of newborn infants

Brazelton Neonatal Assessment Scale

A scale used to assess a newborn’s neurological condition

Preterm

The term for babies born before the 37th week of pregnancy

Low Birth Weight

The term used to describe babies weighing 5 pounds, 8 ounces (2500 grams) or less as birth, whether or not they are premature

Small for Gestational Age

Newborns whose birth weight falls in the lowest 10% for their gestational age because they have not grown at the normal weight