1 embryology

DHS 2General EmbryologyLecture 1

Original Lecture: Prof. Grant Townsend, University of Adelaide

Dr. Sausan Al Kawas University of Sharjah

Copyright © 2006/07 The University of Sharjah slide 2

Objectives

To provide a general description of human embryological processes as follows:

• Germ cell formation & fertilization• Prenatal development• Induction, competence, and differentiation• Formation of three-layerd embryo• Formation of neural crest• Formation of human tissues• Folding of the embryo


Embryology

• Embryology is literally “the study of the embryo”

• More generally it refers to “the study of prenatal development”– Embryo = 2-8

weeks– Foetus = 9 weeks

to birth

UNSW Embryology 2007


Embryology

• Ontogeny : stages of development of an individual

• Teratology : study of abnormal development (congenital malformations)


http://embryology.med.unsw.edu.au/Notes/images/head/CleftPrimaryPalate1619.jpg


Mitosis and Meiosis


Gametogenesis

• Gametogenesis is a process of formation and development of male(sperm) and female (ovum)gametes.

• During this process a reduction of the the number of chromosomes takes place from diploid number (46) of primary germ cells to the haploid number (23) in the mature germ cell.


Gametogenesis

• It also involves the chromosomal and the cytoplasmic changes.

• These alteration of the shape of the primary germ cells allow them to become ready for fertilization.


Gametogenesis

• The large rounded primary male germ cells, lose most of their cytoplasm and develop head, tail and neck to assist in the movement of the sperms.

• The rounded female germ cells become larger as a result of increase in the a mount of their cytoplasm and called ovum.

Mature sperm

Mature oocyte


Fertilization

• The fertilization occur when sperm contacts an ovum to form a zygote in the uterine tube.

• The zygote, which contains 46 chromosomes, rapidly divide by mitosis to form mass of cells as 2,4, 8, 16, 32….

• This mass of cells continue dividing in order to give the different tissues then organs of the human body.

Ref: Dental Embryology, Histology, and Anatomy

Copyright © 2006/07 The University of Sharjah slide 10These images reproduced from Dr. Di Marzo

General Embryology

Mature Human Egg

Fertilized Human Zygote 4 Cell Human Embryo



General Embryology

• Fertilization– Zygote– Genotype, environment, phenotype

• Induction, competence, differentiation• Formation of the three layered embryo

– Morula, blastocyst, bilaminar then trilaminar germ disc

– Ectoderm, endoderm, mesoderm• Formation of neural crest cells• Folding of the embryo



Uterine tube

Uterus

.

Ovary

General Embryology



Division of the zygote Zygote.

Formation of the morula

Morula

Blastula

General Embryology



Structure of the blastocyt (blastula):


Implantation of the blastocyte:

Uterine wall

Endometrium

Digested endometrium

Blastocyte


Formation of embryonic layers:

Bilaminar embryonic disc

Secondary Yolk sacEndometrium

Hypoblast

amniotic cavity

second week

Epiblast



Formation of the tri-laminar disc:

Primitive streak

Bilaminar disc

Epiblast layer

Hypoblast layer

Third week

Formation of primitive streak at the midline causing the disc to have right and left half, each half will be as mirror to the other


Formation of primitive streak

Formation of the tri-laminar disc:



Ectoderm layer

Endoderm layer

Mesoderm layer

Formation of the mesodermal layer:

Movement of some cells of epiblast toward hypoblast at the primitive streak forms a third embryonic layer called mesoderm.


Formation of Neural Crest

The nervous system develops as a thickening within ectoderm giving the neural plate.



• Neural plate: will fold to form neural groove

• Neural groove: fuses to form neural tube

• Neural tube: Gives rise to brain and spinal cord




Copyright © 2006/07 The University of Sharjah slide 24Ref: Human Anatomy & Physiology/ Marieb



• Neural crest cells migrate throughout the body and give rise to:– Cranial and sensory ganglia

and nerves– Sympathetic neurones– Schwann cells– Pigment cells– Meninges– Cartilage of branchial arches– Most of the connective tissue

of the face “ectomesenchyme”

Ref: Avery (2003) Chapter 1992



• Neural crest is essential in development of the face, neck and oral tissues.

• All tissues of a tooth and its supporting structures, except enamel, are derived from neural crest cells

Ref: Avery (2003) Chapter 1992


The embryonic layers are distinct from each other and

give rise to specific tissues such as:

EctodermNervous system.

Sensory epi.of eye , ear & nose.Epidermis, hair and nails.

Mammary & cutaneous glands.

Epi.of sinuses,oral & nasal cavities.

Intra-oral glands.Tooth enamel.

Formation of the tissues:



Mesoderm

Muscle tissue

C.T

Bone .

Cartilage.

Pulp.Dentin .

Cementum.

PL.

Ecto-mesoderm

Alveolar Bone .



Endoderm GI tract epithelium & associated glands.

ECTODERM

ENDODERMMESODERM



Folding of the embryo

• Folding in two planes:

- Along longitudinal axis to form the stomatodeum (primitive oral cavity)

Ref: Ten Cate (2003) Chapter 2

Copyright © 2006/07 The University of Sharjah slide 31Ref: Ten Cate (2003) Chapter 2

-Along lateral axis to form the foregut.

Completion of the embryonic period (2-8 week)

Folding of the embryo


Ten Cate (2003) Chapter 2


Technology

1 embryology