Principles of embryology Flashcards
What are weeks 0-3 classified as
Conceptus
What are weeks 3-8 classified as
Embryonic period
What are weeks 9-40 classified as
Foetal period
How many stages of embryogenesis are there
6
What are the six stages of embryogenesis
- Gametogenesis
- Fertilisation
- Cleavage
- Gastrulation
- Formation of body plan
- Organogenesis
what happens in Gametogenesis
Formation of a gamete - 23 chromosomes = haploid
How do gametes arise
Mitosis and meiosis which causes genetic variation
What is formation of female gametes called
oogenesis
What is formation of male gametes called
spermatogenesis
When does oogenesis occur in females
Starts in development and ends at menopause
By week 28-30 Primary oocytes begin myosis but arrest in prophase until puberty
Reproductive lifespan determined in fetal life
When does spermatogenesis occur in males
Occurs at puberty and continues throughout life: outcome is 22+ X or 22+ Y
What is trisomy 21
Down syndrome- happens when there is an additional copy of chromosome 21 cause by nondisjunction
75% nondisjunction occurs in oocyte formation
What is non-disjunction
Failure of chromosomes to separate
What happens in Fertilisation
Union of gametes forming a zygote
-fusion of sperm and egg
What happens in Cleavage
Period of rapid mitotic cell division
Forms morula then blastocyst (days 1-4) (NO INCREASE IN SIZE)
What happens in Gastrulation
Formation of germ layers (week 3)
What are the germ layers that form in gastrulation
Ectoderm, mesoderm and endoderm (by mitosis in yolk sac)
What happens in formation of body plane
Embryonic folding (Tube within a tube)
Specifically gut tube in body wall
What happens in organogenesis
Formation of organs and organ systems
All in place by end of embryonic period
What is the foetal period
Growth and weight gain
-tissues mature and become functional
-Apparent sexual differentiation
-Bone laid down, connections made in CNS
What anatomical terminology is used for embryos
Superior= Cranial
Inferior= Caudal
Anterior= Ventral
Posterior= Dorsal
What are the primary processes turning a zygote into a human
Cell division
Differentiation
Cell attachment
Apoptosis
Induction (1 cell causes other to differentiate)
Cell migration
What are the secondary processes when turning a zygote into a human
Axis formation
(cells knowing position in relation to all other cells and embryo)
Folding/Rotation
(Gives 3D form to embryo and structures within e.g. heart)
What controls are there of development
Genetic- gene expression is tightly regulated in time and space
Epigenic- Preferential expression of either maternal or paternal gene copy
