Embryology Flashcards
What are the 3 periods of development? What weeks are these
Pre-embryonic: Weeks 1,2
Embryonic: Weeks 3-8
Foetal: Weeks 9-38
Compare Embryonic and Gestational Age
Embryonic: Time since fertilisation
Gestational: Time since last menstruation
Where is the Oocyte fertilised by Sperm cell
Ampulla of Fallopian tubes
What 5 processes occur in Week 1
Cleavage Morula Formation Compaction Hatching Implantation
What is cleavage? What happens in this process
First mitotic division, produces 2 blastomeres, Zona Pellucida formed
What is the Zona Pellucida
A glycoprotein shell that keeps sperm from penetrating the blastomeres
What is a blastomere
Every embryonic cell formed after cleavage, until a blastocyst is produced
What is a Morula?
A ball of 16 blastomeres that are totipotent
What is Compaction
Describe the cell potency
Formation of the first cavity, and the Blastocyst
Pluripotent- Can become many types. (Not all types- totipotent)
What is a blastocyst
A hollow sphere of cells formed from the morula through compaction
Wha happens in the hatching stage
What is the blastocyst now able to do?
Blastocyst hatches from the Zona Pellucida
Blastocyst can now enlarge and implant on the uterine surface
What happens as implantation begins?
There’s now 100 cells
8 make the embryo
92 help development of fetal membranes
What 3 things happen on Day 8
- Embryoblast differentiates into Epiblast and Hypoblast
- Trophoblast differentiates into Synctio-/ Cytotrophoblsst
- Amniotic cavity formed
What 2 things happen on days 9-10
- Synctiotrophoblast develops rapidly
- Primitive yolk sac formed
What happens on Day 11
Primitive yolk sac membrane pushed away from Cytotrophoblast by extraembryonic reticulum
Extraembryonic mesoderm formed from extraembryonic reticulum
What 2 things happen on day 12
- Maternal sinusoids invaded by lacunae of Synctiotrophoblast
- Uterine stroma (layer of connective tissue) prepares to support embryo
What happens on Days 13-14
13: Secondary Yolk Sac Forms by pinching off Primitive Sac
14: Spaces in Extraembryonic Mesoderm join-> Chorionic Cavity
Embryo and it’s cavities are suspended by Connecting Stalk
Define;
- Gastrulation
- Germ layer
- Primitive Streak
- The differentiation of Bilaminar into Trilaminar Disc
- Group of embryonic cells that interact with each other and contribute to the formation of all organs and tissues
- Thickened region of Epiblast at Caudal end of bilaminar disk. Site from which Gastrulation begins
What are the 5 stages of Early Development
- Fertilisation and Implantation
- Gastrulation
- Neurulation
- Segmentation
- Folding
Describe the derivatives of the Ectoderm layer
Give 2 examples
Structures that maintain contact with outside world
Epidermis
Nervous system
Describe the derivatives of the Mesoderm layer
Give 4 examples
Supporting tissues
Muscle
Bones
Cartilage
Vascular System
Describe the derivatives of the Endoderm layer
Give 3 examples
Internal structures
Epithelial lining of GI tract and Respiratory Tract
Parenchyma of glands
What process is Migration and Invagination part of?
Describe the process
Gastrulation
Epiblast cells migrate to Primitive Streak and move through tight junctions, displacing the Hypoblast layer
What is responsible for establishing left-right asymmetry
How does this happen?
Primitive node
Actions of ciliated cells result in left-ward flow of signalling molecules, leading to a cascade of side-specific signals
What is situs invertus?
How does it occur
Is when internal organs are reversed/ mirror image
Occurs due to immotile cilia at Primitive Node
What is the notochord
What is it’s role
Solid rod of cells running in the midline, with an important signalling role
What does the Notochord convert
What do notochord signals cause?
- Ectoderm to Neuroectoderm
- Cause Ectoderm to thicken, forming NEURAL PLATE, whose edges curl up to form Neural Tube
What is Teratogenesis
What is the Intraembryonic Coelom
Major congenital malformation
A cavity( between Somatic and Splanchnic Mesoderm) into which organs can grow
What 5 things does the Mesoderm differentiate into?
- Parasail Mesoderm
- Intermediate Mesoderm
- Somatic Mesoderm
- Splanchnic Mesoderm
- Intraembryonic Coelom
What make up the Lateral Mesoderm (Differentiated from mesoderm)
Splanchnic and Somatic Mesoderm leaves
What happens to the Notochord in adult life?
Has no function
Forms Nucleus Pulposus of intervertebral disc
What do the Splanchnic and Somatic Mesoderm differentiate into?
Splanchnic- Viscera
Somatic- Connective Tissue of body
What structures are formed from the Paraxial Mesoderm, and how many?
Somites
44-44 made, but ONLY 31 remain
Describe how somites undergo ORGANISED DEGENERATION to form Sclerotome, Dermatome, Myotome.
What do these 3 end up as?
- Ventral walls of somites break down—> Sclerotome->Bones
- Further organisation of dorsal potion->Dermomyotome
- Myotome proliferates and migrates, Dermatome disperses
Myotome- Muscles
Dermatome- Dermis
What are the 2 folding types the trilaminar disc undergoes
- Cephalocaudal
- Lateral
What are the results of folding?
- Connecting stalk pulled ventrally
- Ventral body wall created
- Amniotic membrane pulled around disc
- Draws together the margins of the Trilaminar disc
What has happened by the end of week 4?
- Nervous system has started to form
- Segments have appeared, assigning specific cells to specific tasks
- Embryo has folded
Bleeding on Day ______ can be mistaken for menstrual bleeding
Day 14 (Chorionic cavity and connecting stalk form)
