Development with Neurulation, Folding, and Body Cavities Flashcards
Organogenesis occurs when?
Week 3-8
What is Organogenesis?
When the primary germ layers give rise to tissues and organs
Define Neurulation
Process by which the neural plate forms the neural tube
Where does neurulation occur and via what process?
In the ectoderm via notochordal inducation
What are the 4 main events in neurulation?
- Formation of neural plate
- Shaping of neural plate
- Invagination of neural plate
- Closure of neural groove
What is the neural plate?
A thickening in overlying ectoderm along the midline of the embryo
What are the neural folds?
Laterally elevated edges of the neural plate
What is the neural groove?
Depressed midregion of neural plate
How is the neural tube formed?
Neural folds begin to move together and eventually fuse
How does the fusion of the neural folds progress?
Both cranially and caudally
Where is the neural tube located?
Under the surface ectoderm
The neural groove will eventually become what?
The neural canal
The final opening on the cranial end during neural tube closure is called what?
The cranial neuropore
When does the cranial neuropore close?
Day 25
The final opening on the caudal end during neural tube close is called what?
The caudal neuropore
When does the caudal neuropore close?
Day 27
What does the closing of the caudal neuropore signal?
The end of neurulation
What are neural crest cells?
Cells at the lateral border (crest) of the neuroectoderm when neural folds fuse
What kind of transition do neural crest cells undergo?
Epithelial-to-mesenchymal transition
After their epithelial-to-mesenchymal transition, where do the neural crest cells go?
The underlying mesoderm
What 3 parts does the mesoderm differentiate into?
Paraxial mesoderm, Lateral plate mesoderm, and Intermediate mesoderm
What is the paraxial mesoderm?
Mesoderm near midline that becomes thicker
What is the lateral plate mesoderm?
Thin mesoderm that is more lateral
What is the intermediate mesoderm?
The mesoderm between the paraxial and lateral plate mesoderm.
Lateral plate mesoderm is eventually split into?
Somatic (parietal) and Splanchnic (visceral)
What does the somatic mesoderm line?
The amnion
What does the splanchnic mesoderm line?
The yolk sac
The cavity between the somatic and splanchnic mesoderm is called what?
The intraembryonic cavity
The paraxial mesoderm eventually organizes into segments called what?
Somites
Somites form in which direction?
Cranially –> Caudally
How do somites appear?
In pairs
The somites eventually give rise to (3)
Axial skeleton, skeletal muscles, and the dermis of the back
What can you determine by counting the somites?
The age of the embryo
What do they mesoderm cells do when they originally differentiate?
They go through epithelialization and arrange in a donut shape around small lumen
Where do cells in the ventral and medial walls shift to?
They shift to surround the neural tube
What do ventral and medial cells create when they shift to surround the neural tube?
Sclerotome
Where do dorsomedial and ventrolateral cells form?
Dermatome
What do some of the dermatome cells eventually become when they migrate beneath the dermatome?
Myotome
What does the Sclerotome form?
Vertebrae and ribs
What does the Dermatome form?
Dermis
What does the Myotome form?
Muscles
What does the Intermediate Mesoderm differentiate into?
The urinary and reproductive system
What forms the lateral body wall folds?
Parietal mesoderm layer along with overlying ectoderm
What does the lateral body wall fold help to close?
The ventral body wall
What forms the mesothelial membranes (serous membranes)
Mesoderm cells of the parietal layer surrounding the intraembryonic cavity
What do serous membranes line?
The pritoneal, pleural, and pericardial cavities
What forms the walls of the gut tube?
Visceral mesoderm layer together with endoderm
What do the mesoderm cells of the visceral layer form?
Thin serous membranes around each organ
The endoderm will eventually differentiate into what?
The GI tract
Endoderm derivates line the ___ surface of the embryo and forms the roof of the ___ ___
Ventral, yolk sac
What happens simultaneously in both the sagittal plane (cranial/caudal) the the horizontal plane (lateral)?
Folding
What acts as a hinge in cranial folding?
The oropharyngeal membrane
In cranial folding, what does part of the yolk sac endoderm become?
The foregut (proximal part of GI)
When does the oropharyngeal membrane rupture and why?
It ruptures around day 26 to form the mouth
In caudal folding, what acts as a hinge?
The cloacal membrane
In caudal folding, what does part of the yolk sac endoderm become?
The hindgut (distal part of GI)
What happens to the connecting stalk during caudal folding?
It attaches to the ventral aspect of the embryo
In lateral folding, what is the dorsal part of the yolk sac endoderm incorporated as?
The embryonic midgut
By the end of week 4, all lateral folds are fused except for what region?
The region of the connecting stalk
The midgut connection to the yolk sac constricts, leaving a narrower connection called what?
The omphaloenteric duct (vitelline duct)
Where are the parietal and visceral layer of serous membranes continuous at?
The dorsal mesentery
What does the dorsal mesentery do?
Suspends the gut tube from the posterior body wall into the peritoneal cavity
What does the ventral mesentery result from?
Thinning of the septum transversum
What are the boundaries of the ventral mesentery?
Caudal foregut to upper part of the duodenum
What 3 things make up the embryonic body cavity?
Pericardial cavity, 2 pericardioperitoneal canals, and a peritoneal cavity
What is the septum transversum?
The mesoderm between the thoracic cavity and the yolk sac
Does the septum transversum separate the thoracic and abdominal cavities completely and why?
No: 2 pericardioperitoneal canals
As lung buds grow, what do they expand into?
Pericardioperitoneal canals
In what direction do pleuropericardial folds grow?
Laterally –> Medially
What do pleuropericardial folds divide the pericardial cavity into?
A definitive pericardial (1) and pleural cavities (2)
What are the 4 components of the diaphram?
Septum transversum, Pleuroperitoneal membranes, Mesentery of esophagus, and Body wall mesoderm
