Download Stage 1

Stages of Human
Development
Ilse Pienaar
Lecture 4
Embryology
Stage 1
Developmental Periods

Prenatal Period

Developmental changes before birth
Sperm
Gr. sperma = seed
Spermatozoon
L. spermatos = seed; zōon = animal
Egg
Oocyte
Ovum (s), Ova (p)
Zygote
1×sperm * 1×ovum = 1 cell
An embryo
Stage 1
Developmental Periods

Gametogenesis

Meiosis
LL
LL
2*Diploid
46 X
2*Haploid
23 X
Developmental Periods- Meiosis I

Meiosis I

Interphase
Stage 1
Developmental Periods- Meiosis I

Meiosis I

Prophase
Stage 1
Developmental Periods- Meiosis I

Meiosis I

Metaphase
Stage 1
Developmental Periods- Meiosis I

Meiosis I

Anaphase
Stage 1
Developmental Periods- Meiosis I

Meiosis I

Telophase
Stage 1
Developmental Periods- Meiosis II

Meiosis II

Prophase II
Stage 1
Developmental Periods- Meiosis II

Meiosis II

Metaphase II
Stage 1
Developmental Periods- Meiosis II

Meiosis II

Anaphase II
Stage 1
Developmental Periods- Meiosis II

Meiosis II

Telophase II
Stage 1
Developmental Periods

End stage of Meiosis I & II
Diploid
46 X
Stage 1
23 X
23 X
23 X
23 X
Developmental Periods

Zygote

Mitotic cell divisions / cleavage
Stage 2
Zygote
Stage 3
Morula
Early blastocyst
Late blastocyst
Developmental Periods
Stage 4
Implantation
Gastrula
The Organogenic Period

Week 4 – 8


The major external and internal structures are
established
Minimal function
The Organogenic Period


Week 4 – 8
Phases of Embryonic Development
Stage 1
Growth
Stage 2
Stage 3
Morphogenesis
Differentiation
Germ Layer Derivatives


Formed during gastrulation
Pimordia of all tissues and organs
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
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
Germ Layer Derivatives

Mesoderm




Connective tissue
Cartilage
Bone
Muscle



Striated & smooth
Heart
Vessels

Blood & lymph
Ectoderm
Mesoderm
Endoderm
Germ Layer Derivatives

Mesoderm




Kidneys
Ovaries & testes
Genital ducts
Serous membranes



Line body cavities
Spleen
Cortex of suprarenal glands
Ectoderm
Mesoderm
Endoderm
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
The Organogenic Period
Embryonic Folding



From flat trilaminar embryonic disc
Cylindrical embryo
Median and Horizontal planes


Head Fold
Tail Fold
Cranial
Side
Side

Caudal
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 brain and heart – develops into the central
tendon of the diaphragm
Embryonic coelom – Primordium of body cavities
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 of
urinary bladder and rectum
The Organogenic Period

Horisontal Plane Folding

The Tail Fold




Right and left lateral folds
Produced by the rapidly growing spinal cord and
somites
Midgut: Primordium of small intestine – part of
the endoderm germ layer is incorporated into the
embryo
Initial wide connection between the midgut and
yolk sac
The Organogenic Period

Horisontal Plane Folding

The Tail Fold


After folding – connection reduced
Reduce communication between intra- and
extraembryonic coelomic cavities