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Prenatal Growth, Embryonic & Fetal Periods, & Twinning. Dr. Akram M. Asbeutah, PhD Department of Radiologic Sciences Faculty of Allied Health Sciences Kuwait University. Embryology. Embryology – study of the origin and development of single individual Prenatal period
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Prenatal Growth, Embryonic & Fetal Periods, & Twinning
Dr. Akram M. Asbeutah, PhD
Department of Radiologic Sciences
Faculty of Allied Health Sciences
Kuwait University
Figure 3.7a, b
Figure 3.7c, d
Figure 3.10
Figure 3.9a–d
Neural tube is formed opposite the somites and it is widely opened at the rostral and caudal neuropores
By 24 days, the first two pharyngeal arches are visible. The first (mandibular arch) and the second (hyoid arch) are distinct
By 26 days, three pairs of pharyngeal arches are visible and the rostral neuropore is closed
Highlights of the 4th-8th weeks- Fourth WeekDay 22
Day 24
By day 27, the upper limb buds are recognizable as a small swelling on the ventrolateal body walls and the otic pits (primodia of the internal ears), are also visible
Ectodermal thickening (lens placodes) indicating the future lenses of the eyes are visible on the sides of the head
By the end of the 4th week, the fourth pair of the pharyngeal arches and the lower limb buds are visible and a long tail-like caudal eminence is a characteristic feature. The caudal neuropore is usually closed
Highlights of the 4th-8th weeks- Fourth WeekDay 26
Day 28
The rapidly growing 2nd pharyngeal arch overgrows the 3rd and 4th arches, forming a lateral ectodermal depression on each side (cervical sinus)
Mesonephric ridges indicate the site of the mesonephric kidneys, which are interim excretory organs in human
Highlights of the 4th-8th weeks- Fifth WeekEstimated time of fertilization
Ultrasound measurement of the chorionic sac and embryo
Examination of external characteristics of the embryo
Estimation of the embryonic ageTable 3.1 (1 of 3)
Table 3.1 (2 of 3)
Table 3.1 (3 of 3)
and swallowing
independent release of 2 oocytes fertilized by 2 separate sperm
as different as any 2 siblings
Identical twins (monozygotic)
2 individuals that develop from a single fertilized ovum
genetically identical & always the same sex
if ovum does not completely separate, conjoined twins (share some body structures)
Nature of Twins