0.Stages of Human Development

8/7/2019 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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Prophase

Stage 1


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Metaphase

Stage 1


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Anaphase

Stage 1


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Telophase

Stage 1


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Developmental Periods- Meiosis II Meiosis II

Prophase II

Stage 1


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Metaphase II

Stage 1


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Anaphase II

Stage 1


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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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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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Mesoderm Connective tissue

Cartilage Bone

Muscle Striated & smooth

Heart Vessels

Blood & lymph

Ectoderm

Mesoderm

Endoderm


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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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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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Horisontal Plane Folding The Tail Fold

After folding connection reduced Reduce communication between intra- and

extraembryonic coelomic cavities


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