Fetal Development

Domain 1B.1

Fertilization, embryonic implantation, and separation into identical twins occurs in the _____ week of embryonic development.

• 3rd week

• fertilization: beginning of 3rd week

• implantation: end of 3rd week

Cleavage of the forebrain (holoprosencephaly) occurs in the _____ week, and the “All or None” period ends in that same week of embryonic development.

• 4th week

• Tip: cleavage of the forebrain occurs at four weeks

The heart starts beating in the _____ week of embryonic development.

• 5th week

• Tip: 5 letters in the word “h-e-a-r-t”

The neural tube closes in the _____ week of embryonic development.

• 6th week

• Tip: 6 letters in the word “n-e-u-r-a-l”

malformation

(congenital anomalies)

• structural anomaly due to a defect in tissue development (morphogenesis) of an organ or structure

• caused by an intrinsically abnormal developmental process

examples:

• hypoplasia (underdevelopment of an organ)

• incomplete closure (heart defect, ONTD)

deformation

(congenital anomalies)

• abnormal shape or position of a body part caused by extrinsic mechanical forces (oligohydramnios, uterine malformations, multiple pregnancies)

examples:

• clubfoot

• craniofacial asymmetry

disruption

(congenital anomalies)

• normal embryological development that is interrupted by external factors such as vascular insufficiency, trauma, or teratogens

examples:

• amniotic banding causing amputation of the fingers

dysplasia

(congenital anomalies)

• abnormal organization of cells within tissue resulting in structural changes

examples:

• protein structural changes in cartilage or bone can lead to dysplasias (i.e., achondroplasia)

sequence

(congenital anomalies)

• pattern of multiple defects resulting from a single primary malformation

examples:

• Pierre-Robin sequence: restriction of jaw growth (micrognathia) that causes the tongue to be placed further back in the mouth → interfere with the normal closure of the plate → airway obstruction and cleft palate

• Potter sequence: renal anomaly inhibits the production of urine → oligohydramnios → pulmonary hypoplasia, joint contractures, and craniofacial asymmetry