Embryology Flashcards
When does implantation of blastocyst occur?
Days 5-6
What two cell types does the trophoblast layer of blastocysts differentiate into?
Syncytiotrophoblasts and Cytotrophoblasts
Describe 3 functions of syncytiotrophoblasts
- Invade uterine wall
- Invade maternal blood vessels in the endometrium by forming lacunae
- Produce hCG
What are cytotrophoblasts?
The cellular layer
Which cells form the embryo?
Epiblast cells from the inner cell mass
What are hypoblast cells
Extraembryonic cells that form tissues that are important for development of the embryo but don’t contribute to it itself
Give 2 functions of the desidual reaction?
- The endometrium becomes Decidua for nutritional a
support and restricts invasion - Prevents the maternal immune response against the fetus
After how many days has implantation occurred (with embryo completely below the lining)
11-12 days
What do the epiblast and hypoblast form?
The bilaminar disc
Which layer of cells form the amniotic sac?
Amniotic ectoderm
Which cell layer forms the fetus?
Epiblast
What structure forms the umbilical cord and when does it start to develop?
The connecting stalk (day 13-14 so post-implantation)
Why does a secondary yolk sac form associated with the hypoblast?
Because the first, primitive yolk sac has regressed.
What is the single layer of extra embryonic ectoderm lined with extra embryonic mesoderm called?
Amnion (amniotic ectoderm)
What is the placenta in early development called
The chorion
Which cells make up the chorion?
Trophoblasts and extra embryonic mesoderm
Which 2 tests screen for Down’s syndrome, Edward’s syndrome or Patau’s syndrome? When can these tests be carried out?
Chorionic villus sampling (11-14 weeks of pregnancy) and Amniocentesis (15-20 weeks of pregnancy)
List the 6 derivatives of trophoblast, amnion and bilaminar disc at 5 weeks
Embryo - derived from epiblast
Amnion - derived from amniotic ectoderm
Amniotic sac is between amnion and embryo
Chorionic plate (extraembryonic mesoderm contribute to chorionic plate)
Chorionic cavity (between extra-embryonic mesoderm and fetus)
Syncytiotrophoblasts (cytotrophoblasts) contribute to chorionic villi
Describe the process of gastrulation
Process of bilaminar disc (of epiblast and hypoblast) becoming trilaminaer disc
What 3 germ layers does the epiblast form
Ectoderm
Mesoderm
Endoderm
Is gastrulation a common point of spontaneous termination?
Yes
Where are the embryonic axis established?
Gastrulation (polarity, dorsal/ventral, left/right)
When does gastrulation occur?
Day 13-14 (trilaminar disc formed by day 17)
What structure does the endoderm for?
The gut tube (it is associated and continuous with the yolk sac)
How does the disc elongate?
By convergent extension cell movements (this enables some polarity and the primitive streak forms to provide bilateral symmetry
Which end of the disc does the primitive streak form?
Tail/Posterior/caudal
What is the function of the primitive groove within the primitive streak
Epiblast layer moves through it to form Mesoderm and endoderm. Mesoderm is either extraembryonic (forms yolk sac and amnion) or embryonic (forms notochord and node mesoderm) Cells that don’t move through stay on dorsal side and become the embryonic ectoderm
What does bilateral symmetry define?
Left and right
What does polarity define
Caudal and cranial
What does embryonic ectoderm form?
Nervous system
State a function of notochord and node mesoderm
Important signalling centres that organise the development of embryo
What do the first wave of cells through the primitive groove become
Endoderm
What do the second wave of cells through the primitive groove become
Mesoderm
What does hypoblast differentiate into
Extraembryonic endoderm
Which cell layer is induced to form the neural plate by the notochord?
Embryonic ectoderm to Neural ectoderm to neural plate
What does surface ectoderm differentiate into?
Epidermis of the skin
What are neural crest cells derived from?
Neural ectoderm
Why would a patient with craniofacial defects be more likely to have cardiac defects
Both arise from the same neural crest cell population that may have abnormalities
Which 12 adult structures does embryonic mesoderm give rise to?
- Endothelium
- Bone.
- Skeletal muscle
- Smooth muscle
- Cartilage
- Blood
- Lymph
- Heart - lateral plate mesoderm
- Kidneys - intermediate mesoderm
- Spleen
- Reproductive system
- Limbs
Which adult 6 adult structures does embryonic endoderm give rise to?
- Gut tube.
- Liver
- Pancreas
- Trachea and lungs
- Auditory system
- Urinary system
What does extra embryonic ectoderm become?
Amniotic ectoderm
What do the two population of extra-embryonic endoderm become?
Those derived from hypoblasts contribute to yolk sac
Those derived from primitive streak contribute to the allantois
What is the role of the allantois?
Exchange of some nutrients (i.e. O2) it is an out pocket of the yolk sac
What do the two populations of extra-embryonic mesoderm form?
Amnion and chorion (Derived from blastocyst)
Contributes to Yolk sac (derived from primitive streak)
What is the developmental potential of the morula?
Pluripotent - any tissue except placenta
Inncer cells become inner cell mass and outer cells become trophoblasts
