Body cavities and lund development Flashcards
(41 cards)
At the beginning of fourth week
Embryonic disc is flat trilaminar, bodyfolding commences, body folding is complete with tube-within-a-tube body plan enclosed in amniotic sac
Week 5
- Formation of Pleuropericardial Folds: These extend from the lateral body wall toward the midline, helping to partition the thoracic cavity.
- Separation of Pericardial and Pleural Cavities: The pleuropericardial folds grow medially, enclosing the developing heart in the pericardial cavity and isolating the pleural cavities.
- Connection to the Peritoneal Cavity: The pleural cavities remain temporarily continuous with the peritoneal cavity via the pericardioperitoneal canals.
- Formation of Pleuroperitoneal Folds: These develop to close off the pericardioperitoneal canals, contributing to diaphragm formation.
By week 6–7, the pleuroperitoneal folds fuse with the septum transversum and the esophageal mesentery
body folding
forms the endodermal foregut at the cranial end of the embryo, thereby delineating the inner tube of the tube-within- a-tube body plan .
respiratory diverticulum or lung bud
On day 22, the foregut produces a ventral evagination called the respiratory diverticulum or lung bud , which is the primordium of the lungs. As the lung bud grows, it remains ensheathed in a covering of splanchnopleuric mesoderm, which will give rise to the lung connective tissue and vasculature and to the connective tissue, cartilage, and muscle within the bronchi.
primary bronchial buds
On days 26 to 28, the lengthening lung bud bifurcates into left and right primary bronchial buds , which will give rise to the two lungs.
secondary bronchial buds
In the fifth week, a second generation of branching produces three secondary bronchial buds on the right side and two on the left. These are the primordia of the future lung lobes. The bronchial buds and their splanchnopleuric sheath continue to grow and bifurcate, gradually filling the pleural cavities
terminal bronchioles
By week 16, the 16th round of branching generates terminal bronchioles , which subsequently divide into two or more respiratory bronchioles
Respiratory diverticulum simple
first part of lungs to develop
on ventral side of foregut tube, * Will develop into:
* Trachea – windpipe
* Larynx – voicebox
* Will split into left and right bronchial buds
* Which will develop into left and right lung
Craniocaudal and lateral folding
happen
simultaneously
Lateral Folding
Lateral folding occurs during week 4 of embryonic development and is crucial for transforming the flat trilaminar embryonic disc into a cylindrical body. This process helps enclose the intraembryonic coelom and forms the primitive gut tube.
Initiation of folding: the lateral edges of the embryonic disc fold ventrally toward the midline due to rapid growth of the somites and expansion of the amniotic cavity. This folding is primarily driven by the growth of the ectoderm and mesoderm, while the endoderm follows passively
Closure of the ventral body wall:
the right and left sides of the embryo move toward each other and eventually fuse at the midline, closing the ventral body wall. The ectoderm becomes the outermost layer, forming the skin and other structures. The mesoderm contributes to muscles, bones and blood vessels
Formation of the gut tube:
As the endodermal layer folds inward, it forms the primitive gut tube. The gut remains connected to the yolk sac through the vitelline duct, which later regrasses.
Formation of the intraembryonic coelon:
the lateral plate mesoderm splits into two layers,
Somatic mesoderm and splanchinc mesoderm
The space between these layers forms the intraembryonic coelom which will later develop into the pericardial, pleural and peritoneal cavities
Fusion of midline:
The folding continues until the lateral body folds meet and fuse at the midline. The fusion is incomplete at the umbilical ring, which allows the umbilical cord to remain connected to the embryo
The vitelline duct
The vitelline duct acts as a communicating tract between the embryonic yolk sac and its primitive midgut during early human development
Key points of the lateral folding (4)
- Encloses the gut tube, which differentiates into foregut, midgut and hindgut
- Gorms the intraembryonic coelom, which allows development of major body cavities
- Establishes the cylindrical body shape of embryo
- Ensures proper positioning of the heart and diaphragm
somatic mesoderm
The somatic mesoderm refers to a specific layer of mesodermal tissue in the developing embryo. It plays a crucial role in the formation of various structures, including the musculoskeletal system, dermis, and connective tissues. The somatic mesoderm gives rise to somites, which are segmented blocks of tissue that eventually differentiate into skeletal muscle, cartilage, and other mesodermal derivatives. The development and differentiation of the somatic mesoderm are regulated by complex molecular signaling pathways and interactions with neighboring tissues, such as the neural tube and ectoderm
Craniocaudal folding
During week 4, essential for transforming the flat embryonic disc into a more cylindrical structure. This process is mainly driven by the rapid growth of the neural tube and somites, which causes the head and tail regions of the embryo to bend ventrally.
- Rapid growth of the neural tube and amniotic cavity
The ectodermal layer, the neural tube, grows faster than the underlying yolk sac. This forces the head and tail regions to fold ventrally, bringing the heart and developing structures into their proper positions
- Head fold (Cranial region)
The oropharyngeal membrane is repositioned from the cranial end to a more ventral position. The developing heart and pericardinal cavity, initially located in front of the brain move ventrally and caudally to their correct location in the thorax. Foregut forms as part of the gut tube - Tail fold (caudal)
The cloacal membrane is repositioned from posterior end to more ventral position. The connecting stalk shifts ventrally, incorporation part of the yolk sac into the embryo. The hindgut forms as part of the gut tube. - Formation of the midgut and umbilical connection
As the embryo folds, part of the yolk sac is enclosed inside the embryo formind the primitive gut tube. Midgut remains temporarily connected to the yolk sac via vitelline duct
Key points of craniocaudal folding
Corrects the position of key structures
Forms the foregut, midgut and hindgut
helps shape the umbilical cord
Combined Effect: Shaping the Embryo
✅ From a flat disc → to a C-shaped, three-dimensional body.
✅ Encloses the gut tube and creates the ventral body wall.
✅ Repositions organs, especially the heart and diaphragm.
✅ Defines major body cavities (pericardial, pleural, peritoneal).
✅ Establishes the umbilical cord connection for fetal-maternal exchange.
Where in the body are cavities in the adult
Thoracic cavity=the space within the chest that contains the organs of the thorax, including the heart, lungs, and major blood vessels
Pleural cavity=the space between the parietal and visceral pleurae that surrounds the lungs
Pericardial cavity=the space surrounding the heart, located within the thoracic cavity, between the parietal pericardium (outer layer) and visceral pericardium (inner layer, also called the epicardium)
The diaphragm=a dome-shaped muscle located at the base of the chest that separates the chest cavity from the abdominal cavity
The abdominal cavity=space within the body that extends from the diaphragm to the pelvic floor
Intraembryonic coelom
A primitive body cavity that forms within the lateral plate mesoderm and later divides into the pericardial, pleural, and peritoneal cavities.
1️⃣ Forms Major Body Cavities – Develops into the pericardial, pleural, and peritoneal cavities.
2️⃣ Allows Organ Growth & Movement – Provides space for the heart, lungs, and abdominal organs to expand and function properly.
3️⃣ Separates Organs from the Body Wall – Ensures mobility and reduces friction between organs.
4️⃣ Supports Circulatory & Respiratory Development – Facilitates the positioning of the heart and lungs within their respective cavities.
5️⃣ Prepares for Diaphragm Formation – Contributes to the partitioning of the thoracic and abdominal cavities.
The primitive pericardial cavity will be subdivided into
Definitive pericardial cavity
* Left and right pleural cavities
* By: pleuropericardial folds
Parietal (somatic) mesoderm lines inner walls of
- Pericardial cavity
- Pleural cavity
- Peritoneal cavity
Visceral (splanchnic) mesoderm covers
outside of organs
Septum transversum
A thick mass of mesoderm that forms between the thoracic and abdominal cavities in early development. It later contributes to the central tendon of the diaphragm, part of the liver’s mesenchyme, and the ventral mesentery. “folds inwards”
When does lung development start
day 22 with formation of a ventral outpouching of the endodermal foregut called the respiratory diverticulum
Stages of lung development
Embryonic, pseudo glandular, canalicular, saccular, alveolar
