Intro To Development And Aging Flashcards
When is fertilisation age assume to be?
+1 day from last ovulation
When is gestational age calculated from?
Beginning of last menstrual period (LMP)
What are Carnegie stages based on?
Embryo features, not time
How many Carnegie stages are there?
23
What to Carnegie stages allow comparison of?
Developmental rates between different species
What window of time do Carnegie stages cover in humans?
0-60 days fertilisation age
When is the embryogenic stage?
14-16 days post fertilisation
What does the embryogenic stage involve?
Establishment of early embryo from fertilised oocyte
Determining two populations of cells:
1. Pluripotent embryonic cells (contribute to foetus)
2. Extraembryonic cells (contribute to the support structures eg placenta)
When is the embryonic stage?
16-50 days
What does the embryonic stage involve?
Establishment of the germ layers and differentiation of tissue types
Establishment of the body plan
When is the foetal stage?
50 to 270 days
What happens in the foetal stage?
Major organ systems now present
Migration of some organ systems to final location
Extensive growth and acquisition of fetal viability (survival outside the womb)
What are the stages of life in the first few days and how many cells?
Ovulated oocyte- 1
Zygote- 1
Cleavage stage embryos- 2-8
Morula- 16+
Blastocyst- 200-300
Until what cell stage are the genes of the embryo not transcribed?
4-8 cell stage
What is the embryo dependent on to get through the first few divisions?
Maternal mRNAs and proteins
What happens to outer cells at the 8 cell stage or later?
Outer cells become pressed against zona
Change from spherical to wedge-shaped.
Outer cells connect to each other through tight gap junctions and desmosomes
Forms barrier to diffusion between inner and outer embryo
Outer cells become polarised
What is the cavity in a blastocyst called?
the blastocoel
Name 4 structural features of a blastocyst
Blastocoel, Zona Pellucida, Inner cell mass, trophoectoderm
What is the blastocoel and how is it formed?
Fluid-filled cavity formed
osmotically by
trophoblast pumping
Na+ ions into cavity
What is the Zona Pellucida?
Hard protein shell inhibiting polyspermy and protects early embryo
What is the inner cell mass?
Pluripotent embryonic cells that will contribute to the final organism
What is the trophoectoderm?
Extra-embryonic cells that contribute to the extraembryonic structures that support development
What is hatching?
Where the blastocyst escapes the zona pellucida to implant
When does hatching occur?
Day 5-6
How does the blastocyst escape the zona pellucida?
Enzymatic digestion
Cellular contractions
From the morula, what are the 2 separations of cell lineage?
Inner cell mass (embryonic)
Trophectoderm (extra-embryonic)
