Download Embryology Ovum Chromosome Karotype Fertilization Cleavage

Embryology
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Timetable of Human Prenatal Development
Ovum
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Chromosome
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carries genetic material
picture of chromosome - karotype
23 pairs, 22 autosomes and 1 sex chromosome
sex pair determines sex
study of chromosomes =cytogenetics
Karotype
Fertilization
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single large cell, .14mm
zona pellucida -surrounding membrane
surrounded by corona radiata
full complement at birth
meiosis-cell preparation: reduction of genetic material
sperm enters ovum
“day one” of prenatal development
restores full complement of genetic material
determines sex of organism
initiate cleavage
perpetuates species variation
Cleavage
Week One
• fertilized ovum = zygote
• primarily cell duplication
• rapid succession of mitotic divisions
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Morula
• Day 4
• grape like cluster
• cell growth in number, not size
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Blastocyst/blastula
• Result of cell differentiation
• inner cell mass
• outer trophoblast
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Implantation - day 6
• blastocyst sinks into lining of uterus
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• nutritional connection established
• maternal and fetal circulatory systems
Formation of Germ Layers
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• from one cell comes a human
• process of cell differentiation
• “germ” layers are premordia for all tissues of organism
Day 8
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8-17th Day
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development of third germ layer
mesoderm
cells migrate/differentiate between endoderm and ectoderm
process called gastrulation
day 17, embryo is trilaminar
Gastrulation
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cells move along midline on craniocaudal plane = primitive streak
meet and fuse at cephalic end = prochordal plate
prochordal plate marks site of mouth
meet and fuse at caudal end = posterior opening (HAH)
Ectoderm
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day 8-two types of cells: endoderm and ectoderm
bilaminar disk = embryo
represents embryonic period of development
embryonic period extends to 7th week
7th week - beginning of all major structures present
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CNS, PNS
epidermis
hair
nails
subcutaneous glands
pituitary gland
tooth enamel
epithelial lining
lining of the oral and nasal cavities and pharynx
inner ear
lens
mammary glands
Endoderm
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Epithelial lining of most of respiratory tract and larynx
lining of esophagus, stomach and small intestine
epithelial parts of tympanic cavity
Epithelium of G.I. Tract
Liver, pancreas, bladder
Mesoderm
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Cardiovascular system
connective tissue
cartilage
bone-skeleton
joints
skeletal muscles
Blood and lymph systems
kidneys
gonads
spleen
Other 2nd-3rd week events
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• Flexion in embryo at cephalic end
• primitive forebrain -proencephalon
• neural fold along primitive streak = spinal cord
Somite Period
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characterized by paired blocks of mesoderm
craniocaudal sequence of growth
42-44 pairs
basic features for face and neck
Branchial Arches
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• Basic features for face and neck
• 4 arches separated by ectodermal grooves: 5th not visible
• within each arch, derivatives for:
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artery
nerve
cartilage
muscle
Arch 1 - Mandibular
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Cartilage - mandiular process, malleus and incus
nerve-mandibular branch trigeminal
muscle - mastication
Abnormalities:
micro/macrosomia
deformed ear ossicles
microagnathia
Syndromes: treacher Collins, Robin Sequence
Arch 2 - Hyoid
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• Cartilage - Reicherts - hyoid, styloid process, stapes
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nerve- 7th cranial
muscle - facial expression; stapedius
Abnormalities:
rare: defect of hyoid and styloid bones
Arch 3
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Cartilage - hyoid bone
nerve- 9th cranial
muscle - stylopharnygeus, middle constrictor of pharynx
Abnormalities:
extremely rare
Arch 4
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Cartilage - Thyroid
nerve- superior branch, 10th cranial
muscle - cricothyroid
Abnormalities:
extremely rare; clinically insignificant
Arch 5
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Cartilage - cricoid, arytenoids, cuniform, corniculate
nerve- recurrent branch, 10th cranial
muscle - laryngeal muscles
Abnormalities:
extremely rare; clinically insignificant
• Endodermal derivative: glottis
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Adult Landmarks
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palatoglossal fold -anterior fauces - 2nd arch
palatopharyngeal fold - posterior pillar - 3rd arch
pharyngo-epiglottic fold - 4th arch
aryepiglottic fold - 5th arch
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