Lecture 3: Formation of the Body Cavity Flashcards
When does embryonic development occur?
Weeks 3-8.
During this period, most of our body organs will begin to grow.
What are the three phases of embryonic development?
- Growth- period of cell growth
- Morphogenesis- build tissue and organs and get size and shape. Controlled by gene expression
- Differentiation- cells turn on gene products and differentiated
Do the phases of embryonic development occur consequtively?
No. The phases are interconnected.
Ex. Growth must occur during morphogenesis and differentiation.
When does folding of the embryo occur?
Week 4
In what direction does folding of the embryo occur?
- Median (longitudinal) plane
- Horizontal plane
Embryo goes from a trilaminar flat disc–> 3-D embryo
Head and tail folding occur in what plane?
Median (longitudinal) plane
Describe the process of head folding and tail folding that occurs in the median plane.
Neural tube grows over the head and tail.
Head fold: The neural tube (brain) will grow over the heart and septum transversum, pushing both ventrally.
Tail fold: The neural tube (spinal cord) will grow over the cloachal membrane and the connecting stalk, pushing the structures to the ventral side of the embryo.
Intraembryonic coelum becomes the _______
Body cavity of the embryo
Septum transversum becomes _______
the diaphragm
Duriing longitudinal folding, how does the septum transversum change position and why?
Early in week 4, the septum transversum is located anterior to the oropharyngael membrane and developing heart.
Later in week 4, the septum transversum is located posterior to the oropharyngeal membrane and developing heart.
The septum transversum changed position due to head folding.
During head folding (longitudinal folding), the ________ will form the foregut endoderm, which will give rise to ________.
- umbilical vesicle
- GI structures
What is the cloachal membrane?
Outlet for the respiratory, GI and GU systems
In the tail region, the endoderm will become ________
hindgut endoderm
Horziontal folding of the embryo
At this point, the intraembryonic coelum is going to communicate with the extraembryonic coelom in the head region to form the intraembryonic coelum that will give rise our to our body cavities.
- We will have the formation of our somatopleura–> somatic layer of the lateral plate mesoderm+ ectoderms of the amnoitic cavity –> anterior nad posterior body walls.*
- &*
- our splanchopleura–> splanchnic layer of the lateral plate mesoderm + endoderm of the yolk sac (umbillical vessicle) –> gut tube (midgut)*
Lateral plate of the somatic mesoderm has 2 types: __________ and _______
Somatic layer and splanchnic layer
How does the intraembryonic coelum form?
Intraembronic coelum is formed during horizontal folding. IThe intraembryonic coelom is technically the cavity between the splanchnic and somatic portions of the lateral plate mesoderm.
Intraembryonic coelum will communicate with the extraembryonic coelum
Splanchnic layers will come down and form a horshoe called the intraembroynic coelum
What type of mesoderm forms the anterior and posterior wall?
Somatic layer
Where is the somatic and splanchic layers located?
The splanchnic portion of the lateral plate mesoderm is adjacent to the yolk sac. The somatic portion makes up the horizontal red portion next to the grey connective tissue and blue amniotic fluid.
What is the somatopleura?
Made up of somatic lateral plate mesoderm and ectoderm surrounding the amniotic cavity.
What is the splanchnopleura?
Splanchnic layer of the lateral plate and the endoderm that makes up the yolk sac adjancent
What can go wrong with folding?
Ecotopia cordis
- Occurs during week 4.
- Heart is trapped outside of the body
- Sternum is bifed (split)
- Heart will not have a pericardium
=DEATH.
______________ forms our body cavities
Intraembryonic coelom
The intraembryonic coelom is divided into
- Pericardial cavity- forms our heart
- Pericardiolperitoneal canals (2)- partitions form in each canal to seperate the cavities from one anoher
-
Pleural cavities- forms our lungs
- Canals are separated to form the cavities.
- Peritoneal cavity- forms abdomen.
What do the two pericardialperitoneal canals separate?
Pericardioperitoneal canals are going to be sepatated into our three cavities.
Partitions (pleuroperitoneal folds/membranes and the pleuropericardial membranes) will form to seperate the pericardial cavities, pleural cavities, and the peritonal cavities from one another.
The _____ layer of the lateral plate mesoderm is going to give rise to the parietal part of any organ
Somatic layer of the lateral plate mesoderm
Somatic layer= partietal pleura
Pleura around the mesenter yand gut tube is coming from the ________ layer of the lateral plate mesoderm.
This layer will give rise to the ______ pleura.
Splanchnic
This layer will give rise to the visceral pleura.
How do we form out pericardial cavity?
- Two endocarcardial primordia (2 heart tubes) will move down and around and combine into one, being followed by the septum transversum.
Our heart will be located in our pericardial coelom.
Where is our heart located?
? Pericardial coelom, located inside our pericardial cavity ?
Parietal pericardium is _______ layer of the lateral plate mesoderm.
somatic
Visceral pericardium is _______ layer of the lateral plate mesoderm.
Splanchnic
The ______ nerve inntervates the diaphragm, but comes from nerve roots C3, C4, C5. Why?
Phrenic
It moves down below the heart.
What seperates the pericardial cavity from the pleural canal?
Pleuropericardial folds (membranes).
Pleuropericardial folds come from _____ layer of the lateral plate mesoderm.
somatic
Where does the pleural cavity develop?
In the area between the pleuropericardial membrane and the pleuroperitoneal membrane.
Pleuropericardial membranes (folds) migrate to the midline, fuse and separate the area of the heart from the lungs.
How do we form the pleuropericardial folds?
Bronchial buds in the pericardioperitoneal canals enlarge and seperate the pericardial cavity from the pleural cavity.
Once the pleuralpericardial folds have separated, we have the formation of what?
1. Pleural cavity
2. Pericardial cavity
3. Primitive mediastinum
REMINDER: Around our heart, we have a visceral pericardium coming from the splanchnic layer of the somatic mesoderm. Pericardial sac surrounds the heart.
_____ layer of the parietal pericardial sac comes from somatic mesoderm.
Serous
____ layer of the parietal pericardial sac came from the somatic layer of the lungs.
Fibrous
Formation of the diaphragm
The septum transversum does not meet the posterior body wall by itself.
In order to do so, it needs pleuralperitoneal folds.
[Pleuralperitoneal fold + septum transversum] creates the diaphragm and closing off the peritoneal cavity.
Pleuroperitoneal membrane is derived from from the ______ layer of the mesoderm.
Somatic
Once the diaphragm is complete, what is formed?
- Septum transversum
- Pleuroperitoneal membranes
- Dorsal mesentery of the esophagus
- Body wall
Septum transversum gives us what?
Central tendon
Pleuroperitoneal membranes gives us?
Nothing.
They are overgrown by the muscle walls.
Dorsal mesentery of the esophagus gives us?
Crura
Body wall gives rise to what?
Peripheral muscles
