What is Embryology?
Embryology is the branch of biology that studies the prenatal development of gametes, fertilisation and development of embryos and fetuses.
What is teratology?
The study of congenital disorders in embryology that occur before birth.
What are the three key periods in human development?
1. Germinal Period 2. Embryonic Period 3. Fetal Period The total gestation period is approx 40-weeks
What is the Germinal Period?
0-14 Days Rapid cell Division and Growth, Implantation and formation of embryonic (germinal) discs.
What is the Embryonic Period?
3rd Week - 8th Week Visible advances in differentiation
What is the Fetal Period?
9th-40th Weeks Differentiation and growth of tissues and organisation occur and the rate of body growth increases.
When is a critical period?
Where development and differentiation are primarily taking place.
What occurs during disruption?
A teratogen will occur (An Abnormality)
Before any processes begin with the development what happens in regard to a male counterpart?
Spermatogenesis. This is a Meiotic Process
Before any processes begin with the development what happens in regard to a female counterpart?
Oogenesis. has taken place (Meiotic Process) Ovulation has also occurred: There is a release of an egg (ovum) from the ovaries.
What occurs during fertilisation?
1. Fusion of Haploid gametes (sex cells) 2. Forms a Diploid zygote 3. Nuclear membrane breaks down, DNA replication commences (mitosis)
Where does fertilisation occur?
It occurs at the distal end of the fallopian tube (OVI Duct)
Once fertilisation occurs where does the newly formed zygote travel?
The newly formed zygote travels via motions generated by microscopic cilia and contractions towards the uterus.
What occurs on Day 0 of the Germinal Period?
Fertilisation. - Zygote Formation
What occurs on Day 0-3 of the Germinal Period?
Cleavage - Rapid Cell Division without cell growth - total cytoplasm remains constant - Cell size rapidly decreases as number of cells increased.
What occurs on Day 4 of the Germinal Period?
Morula - Now a ball of 16-20 cells flattened against the zona pellucida (The Morula is now located at the proximal end of the OVIduct)
What occurs on Day 5 of the Germinal Period?
Blastocyst - A cavity forms within the morula, and the ball of cells is now termed the blastocyst.
What occurs on Day 7 of the Germinal Period?
Implantation - Motility slows, Adhesion to uterine epithelium, as the cells of the blastocyst digest the uterine endometrium, permitting deeper penetration and attachment.
What occurs on Day 8-9 of the Germinal Period?
Formation of a Bilaminar Embryo - Epiblast: Gives rise to future germ cell layers Hypoblast: Transient - Gives rise to some umbilical tissues.
What are the four embryonic membranes that develop for the bilaminar embryo?
1. Amniotic Sac/Amnion 2. Yolk Sac (nourishment for disc) 3. Chorion (Eventually becomes the chorionic sac, which will, along with the uterine wall become the placenta) 4. Allantois (Connecting Stalk) - Contributes blood vessles from the embryo to the placenta; eventually becoming the umbilical cord.
What occurs at week 2-3?
Gastrulation: This is the emergence of the primitive streak (caudal) and node formation There is induction and migration of cells into three layers to become the trilaminar (3 Layered embryonic disc)
What is the Trilaminar Embryonic Disc?
It is made up of three layers. The Ectoderm, Mesoderm and Endoderm
The Ectoderm later gives rise to...
CNS, PNS, parts of sensory system, epithelium of skin, Oral mucosa, mucosa of nasal and sinus cavities, teeth enamel.
The Mesoderm later gives rise to..
Blood, bone, muscles, some organs, remainder of tooth structures.
The Endoderm later gives rise to...
Epithelial lining of pharynx, stomach, intestines, lungs, bladder and organs of the urogenital tract.
What is Neuralation?
The formation of primitive nervous system.
What is somitogenesis?
Mesoderm differentiates into specific sections that will later give rise to particular body tissues. (e.g. splanchnic mesoderm - Heart & GI tract tissues)
When does embryonic folding occur?
On the establishment of the trialaminar embryonic disc, the embryo then undergoes embryonic folding to establish the bodies axis.
What does embryonic folding allow?
The formation of body cavities as a series of tubes.