What 4 processes are repeated in order to achieve embryonic development
Proliferation
Movement (chemotaxis)
Differentiation
Loss (apoptosis)
What is the key difference in the repeated processes that occur in embryonic development compared to the adult
Mature somatic cells show characteristics one at a time, whereas in an embryo, cells may show the first 3 characteristics simultaneously (Proliferation, movement and differentiation)
What basic processes is embryonic development regulated by
Autocrine and paracrine effects
Changes in receptor expressoin
Why are there no endocrine effects in embryo development
Absence of a vascular system
What does regulation in factors and response in embryo development involve
Gradient
Combination
Spatial
Temporal
What are the basic steps in the general timeline of embryonic development
- Fertilisation
- Preimplantation development (day 0-6)
- Implantation
- Gastrulation
- Neurulation
Describe what occurs in pre-implantation development
Day 0-3 = cleavage, 1 cell to 2,4,8
Day 4 - morula formation as the 8-cell compacts and differentiates
Day 5-6 - blastocyst formation
Describe the blastocyst at day 6
Inner cell mass (embryo), fluid-filled blastocyst cavity and trophectoderm (placenta)
What occurs in implantation
- Hatching of the blastocyst to remove the zona pellucida
- Blastocyst begins to implant into the uterine lining (primed endometrium/decidua)
- The inner cell mass becomes a bilayer disc containing the epiblast and hypoblast
What areas that implantation can occur in may cause harm/fatality to the mother
Fallopian tube
Intraperitoneal space
Ovary
What is the overall change that occurs in gastrulation
Formation of the trilaminar disc (ectoderm, mesoderm, endoderm) from the bilayer
Explain the process of gastrulation
- Proliferation of the epiblast
- Differentiation of the epiblast into mesoderm
- Cells move into the space between epiblast and the hypoblast
- Mesoderm cells replace the hypoblast as they undergo apoptosis
- Mesoderm differentiates into the endoderm
- Epiblast differentiates into the ectoderm
What does the endoderm differentiate into
Gut
Liver
Lungs
What does the mesoderm differentiate into
Skeleton Muscle Kidney Heart Blood
What does the ectoderm differentiate into
Skin
Nervous system
What occurs in neurulation, when does it occur and what is it controlled by
The differentiation of the ectoderm to form the CNS
Occurs before gastrulation is complete (up to 4 weeks) and under the control of the notochord in the mesoderm
Explain the process of neurulation
- Formation of the neural plate from the ectoderm
- Development of the neural folds (day 20)
- Increase in size
- Meet over the neural groove and fuse to form the neural tube
- 4 weeks - more complex structure at the cranial end and brain development starts
When does the anterior pore neuroclose
25 days
When does the posterior neuropore close
28 days
What occurs in the yolk sac in week 3
Outside the embryo proper the primordial germ cells are in the yolk sac endoderm at the caudal end of the embryo
Cardiac and vascular progenitors in the primary heart field are at the cranial end of the embryo
Describe the folding of the embryo
Anterio-posterior direction
Folds the PGCs into the hind gut, and the developing heart progenitors under the head of the embryo
Folding laterally - fuses the ventral midline (chest and abdomen) of the embryo
