Embryology week 16 Flashcards
What is Gastrulation
- A formative process that establishes the three germ layers
Name the 3 germ layers
- Ectoderm
-Mesoderm
-Endoderm
What is the purpose of Gastrulation(2)
- It converts the bilaminar embryonic disc into a trilaminar embryonic disc
-And determines the axial orientation of the embryo
What cellular changes are invloved in gastrulation
- Cell changes shape
-Rearrangement, movement and changes in adhesion
What is the contributions of the Embryonic Mesoderm during gastrulation(2)
- Froms the skeletal muscle, blood cells and blood vessel linings
- Gives rise to smooth muscle of visceral organs
What is the Primitive Streak and where does it form
- The first sign of gastrulation, forming on the epiblast of the bilaminar embryonic disc
When does the primitive Streak appear
Third week
What is the function of the Primitive streak
- It establishes the craniocaudial axis, cranial and caudal ends, dorsal and ventral surfaces and the right and left sides of the embryo
What is the structures of the Primitive Streak and when do they form
- Primtive nodes forms at the cranial ends of ths streak
- Primitive goove and primitve pit form due to invagination of epiblastic cells
What does the primitive streak form
mesenchymal cells
What is the function of the mesenchymal cells in the primitive streak
- They form the three layers:
-Ectoderm
-Mesoderm
-Endoderm
Explain how each of the germ layers are formed`
- The cells displace the hypoblast to form the endoderm
- Remaining epiblast cells from the embrynoic ectoderm
- Mesoderm is formed by epiblastic cells that migrate through through the primitive pit and lie between the epiblast layer
When does the primitive streak disappear
- End of the fourth week
What do remenants of the primitive streak give rise to
- Sacrococcygeal Teratoma
- Which causes benign tumours in newborns
How is the notochordal process formed
- Some mesenchymal cells migrate through the primtive streak
- These cells move cranially from the primitive node and pit , forming the notochordal process
What does the notochordal process develops
- Lumen, called the notochordal canal
Explain the growth(extension) and interaction of the notochordal process with other structures.
- The notochordal process extends cranially between the ectoderm and endoderm until it reaches the prechordal plate.
What is the prechordal plate
- Small circular area of columnar endodermal cells, where the ectoderm and endoderm are fused
What is the function of the prechordal plate
- Gives rise to the endoderm
-Acts as a signaling center to regulate the development of cranial structures, including the forebrain and eyes
When does the Allantois appear
- Around day 16
Where does the Allantois extend into
-Connecting stalk
How does the Allantois Mesoderm from blood vessels
- The allantois mesoderm expands beneath the chorion and forms theblood vessels that supply the placenta
How does the Allantoic stalk form the umbilical arteries
- The blood vessels of the allantoic stalk develop into the umbilical arteries
What does the allantoic diverticulum persists as
- Urachus
What does Neurulation involve
- It involves the formation of the neural plate, enural folds and the closur of the neural tubes
When is neurulation completed
- By the end of the fourth week
How is the neural plate formed
( starting w the notochord)
- The notochord induces the embryonic ectoderm to thicken , forming the neural plate
What day is the neural groove formed
-Day 18
How is the neural groove formed
(neural plate)
- The neural plate invagnates to form the neural groove which has neural folds on each side
when and how is the neural tubes formed
+ what does it develop into
(neural folds)
- End of the third week
- The neural folds fuse , forming the neural tube
- It develops into the brain vesicle and spinal cord
What is the neural crest formed by
Formed by the neural crest cells between the neural tube and surface ectoderm
What do the neural crest cells migrate and give rise to
- Meninges
-Melanocytes
-Adrenal medulla
-Sensory ganglia
-Autonomic ganglia
Name a severe neural tube defect
- Meroenecephaly
What are somites
Are paired cuboidal blocks od mesoderm
When does the formation of somites begin
- End of the 3rd week
Explain the initial formation of the Somities:
- Formation of somits
-How they appear
- Where they develop near
- The paraxial mesoderm differentiates and condenses to form somits,(blocks of mesoderms)
-Somits appear from head to tail( craniocaudal sequence) - They develop near the head( occipital region)
What do Somites arise from
- Paraxial mesoderm
By the end of the 5 week how many somits are present
42-44 pairs
What is the function of somites
- Give rise to the axial skeleton( vertebrae, ribs skull)
- Form skeletal muscles
- Give rise to adjacent dermis of the skin
What does the intraembryonic coelom develop into and explain
- It develops into the lateral mesoderm and this divides into 2 layers:
- Somatic or parietal layer
-Splanchnic or visceral layer
In the intraembryonic coelom formation what does the lateral mesoderm divide into
- Somatic or parietal layer
-Splanchnic or visceral layer
What does the parietal layer from the lateral mesoderm in the intaembryonic coelom formation form
- Embryonic body wall-somatopleure
What does the visceral layer of the mesoderm from from the lateral mesoderm in the intraembryonic coelom formation
- Embryonic gut-Splanchopleure
What is Vasculogenesis
Formation of new vascular channels by angioblasts
What is Angiogenesis
- The formation of new vessels by budding and branching from preexisting vessles
When does blood formation-Hematogenesis start
5th week
Where does the heart and great vessles develop
-In the Cardiogenic area from the primordial heart tube
What days does the heart begin to beat
21-22nd day
How is the primordial cardiovascular system developed, starting from the tubular heart
- The tubular heat joins with the blood vessels in the embryo, connecting stalk, chorion and the umbilical vesicale to form a primordial cardiovascular system
What is the first organ system to reach the function state
- Cardiovascular system
when and how can the heart beat be detected
- By ultrasonography
- 5th week
