0.stages of human development
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Stages of Human
DevelopmentIlse Pienaar
Lecture 4
Embryology
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Developmental Periods Prenatal Period
Developmental changes before birth
SpermGr. sperma = seed
Spermatozoon
. spermatos = seed; zon = animal
Zygote
1sperm * 1ovum = 1 cell
An embryo
Egg
Oocyte
Ovum (s), Ova (p)
Stage 1
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Developmental Periods Gametogenesis
MeiosisLLLL
Stage 1
2*Diploid
46 X
2*Haploid23 X
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Developmental Periods- Meiosis I Meiosis I
Interphase
Stage 1
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Developmental Periods- Meiosis I Meiosis I
Prophase
Stage 1
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Developmental Periods- Meiosis I Meiosis I
Metaphase
Stage 1
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Developmental Periods- Meiosis I Meiosis I
Anaphase
Stage 1
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Developmental Periods- Meiosis I Meiosis I
Telophase
Stage 1
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Developmental Periods- Meiosis II Meiosis II
Prophase II
Stage 1
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Developmental Periods- Meiosis II Meiosis II
Metaphase II
Stage 1
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Developmental Periods- Meiosis II Meiosis II
Anaphase II
Stage 1
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Developmental Periods- Meiosis II Meiosis II
Telophase II
Stage 1
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Developmental Periods End stage of Meiosis I & II
23 X
Diploid46 X
23 X 23 X 23 X
Stage 1
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Developmental Periods Zygote
Mitotic cell divisions / cleavage
Stage 2
Zygote Morula Early blastocyst
Stage 3
Late blastocyst
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Developmental Periods
Stage 4
Implantation Gastrula
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The Organogenic Period Week 4 8
The major external and internal structures are
established Minimal function
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The Organogenic Period Week 4 8
Phases of Embryonic Development
Growth
Stage 2 Stage 3
Morphogenesis Differentiation
Stage 1
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Germ Layer Derivatives Formed during gastrulation
Pimordia of all tissues and organs
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Germ Layer Derivatives
Ectoderm Central Nervous System (CNS)
Sensory epithelial Eye, Ear, Nose, Epidermis, Hair, & Nails
Mammary glands
Pituitary gland Subcutaneous glands
Teeth enamel
Ectoderm
Mesoderm
Endoderm
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Germ Layer Derivatives
NeuroEctoderm Neural Crest Cells
Spinal Cranial V, VII, IX, X Autonomic ganglia
Ensheathing cells of PNS
Muscle Connective tissues
Meninges (brain & spinal cord)
Ectoderm
Mesoderm
Endoderm
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Germ Layer Derivatives
Mesoderm Connective tissue
Cartilage Bone
Muscle Striated & smooth
Heart Vessels
Blood & lymph
Ectoderm
Mesoderm
Endoderm
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Germ Layer Derivatives
Mesoderm Kidneys
Ovaries & testes Genital ducts
Serous membranes
Line body cavities Spleen
Cortex of suprarenal glands
Ectoderm
Mesoderm
Endoderm
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Germ Layer Derivatives Endoderm
Epithelial lining Gastrointestinal, respiratory tracts, tympanic cavity & bladder
Parenchyma of the tonsils Thyroid and parathyroud glands
Thymus
Liver
Pancreas
Ectoderm
Mesoderm
Endoderm
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The Organogenic Period
Embryonic Folding From flat trilaminar embryonic disc
Cylindrical embryo Median and Horizontal planes
Head Fold
Tail FoldCranial
Caudal
Sid
eSi
de
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The Organogenic Period Median Plane Folding
The Head Fold Brain: Primordium Developing forebrain grows beyond
oropharyngeal membrane
Heart: Ventral move septum transversum, primordial heart,pericardial coelom, oropharyngeal membrane
Foregut: Primordium of pharynx, esophagus - lie between the brainand heart develops into the central tendon of the diaphragm
Embryonic coelom Primordium of body cavities
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The Organogenic Period Medial Plane Folding
Tail fold Growth of the distal part of the neural tube primordium
of the spinal cord Caudal eminence projects over the claucal membrane Part of the endodermal germ layer is incorporated into
the embryo to become the hindgut primordium of
descending colon Terminal part of cloaca dilates primordium ofurinarybladder and rectum
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The Organogenic Period
Horisontal Plane Folding The Tail Fold
Right and left lateral folds
Produced by the rapidly growing spinal cord andsomites
Midgut: Primordium of small intestine part of theendoderm germ layer is incorporated into the
embryo Initial wide connection between the midgut and
yolk sac
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The Organogenic Period
Horisontal Plane Folding The Tail Fold
After folding connection reduced Reduce communication between intra- and
extraembryonic coelomic cavities
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