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Development Growth ( in mass of tissues) Differentiation ( in complexity)

Development does not stop at birth Development of teeth, breast

Brain triples in weigth between birth & 16 yrs Most development completed by the age of 25 Divided into:

Prenatal period (embryonic period: 3rd 8th week) Postnatal period Infancy (neotate 1st yr)

childhood (13 mo 12 yrs) puberty (12 15 , 13 16 yrs) adolescence (12 17 yrs) adulthood (18 21 yrs)

PURPOSE OF LEARNING EMBRYOLOGY.BASIC FACTS OF EARLY HUMAN DEVELOPMENT.

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Literally means study of embryos, 3rd 8th week Generally refers to prenatal development:

both embryos and fetuses. Developmental anatomy: prenatal and postnatal

periods. Teratology: study of abnormal development

(Birth defects, congenital malformations)

DIFFERENCES BETWEEN

CONCEPTUS, EMBRYO, FETUS

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Normal development vs. birth defects Illuminates gross anatomy: normal / abnormal Obstetrics: applied embryology: mother vs

embryo/fetus Pediatrics congenital anomalies: spina

bifida, congenital heart diseases Surgery cleft palate, cardiac defects

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1. Preformation: 18th

century. Development is merely the growth of an

already present diminutive being.2. Epigenesis: (Caspar Friedrich Wolff, 1759)

Development results from growth & differentiationof specialized cells.

3. Recapitulation (Carl Ernst von Baer, 1928):Biogenetic Law

Early stages in devpt are not like the adult stages.

4. Induction (Hans Spemann, 1869-1941): Nobel Prize 1935.Inducer, e.g. optic vesicle lens

(one tissue determines the fate of another)Organizer

Homeoboxes (DNA sequences, encoding AA)

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5. Germ layers Morphogenetic processes - cavitation

- invagination

- migration- proliferationPrimordium (anlage) earliest discernible indication

of an organ or a part of it.6. Epithelio - mesenchymal interactions

skin, hair, nails: Mesenchyme induces & specifies anepithelium.

7. Morphogenetic fields: organizing factorsdetermination: ectoderm neural tissue

8. Morphogenetic processesrearrangement of cells - Relative cell movement

- Cell adhesiveness- Invagination- Condensation- Fusion- Cell death

- Proliferation- Differential growth rates

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9. Cell death (necrosis): genetic control

Interdigital cell deathEstablishment of definite number of neurons cell volume chromatin condensation cell dies

apoptosis autophagy (with / without

lysosomal participation) swelling of a cell & cellular

membrane ruptures

10. Mechanical factors

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Figure 1 : The dwarf embryo as imagined by Leonardo da

Vinci from the 15th century (on the left)

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Figure 7 : Teratoma in the coccygeal region at the end of thespine

Turner's syndrome

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http://embryology.med.unsw.edu.au/Medicine/images/hcriticaldev.gif

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Trisomy 18: flecked, crossed-over fingers; deformed feet

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Trisomy 13: Cleft palate, lipand jaw

Trisomy 18: Dolichocephaly

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Turner's syndrome

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