CAM201 Embryology Flashcards
Describe the development of the pleura
The pleura develop in the embryonic period, from lateral plate mesenchyme.
The lateral folding of the embryo creates a ventral body cavity (intraembryonic cavity) that is separate from the extraembryonic coelum.
This cavity becomes divided into 4 separate cavities by the pleuropericardial membrane, and by diaphragm-forming tissues: the two pleural cavities, the peritoneum, and the pericardium.
As the lung buds develop, they protrude into the ventral body cavity, resulting in evaginations in the splanchnic layer of the lateral plate mesoderm. This forms the visceral pleura. The parietal pleura is formed by the somatic layer of the lateral plate mesoderm.
Describe the development of the diaphragm
The cranial part of the septum transversum moves caudally, and becomes the central tendon portion of the diaphragm. Cervical somite myocytes migrate down from the neck region to form the basis of the muscular portion of the diaphragm (thus why the diaphragm is innervated by phrenic nerve C3-5). The pleuroperitoneal membrane and oesophageal dorsal mesentry also contribute.
Congenital Diaphragmatic Hernias
Usually arise from failure of the pleroperitoneal membrane to completely fuse, resulting in a hole in the diaphragm, through which abdominal viscera herniate into the thoracic cavity. The clinical significance of this depends on the amount of abdominal viscera which herniates into the thoracic cavity. This process results in some degree of lung hypoplasia and, in extreme cases, the development of lung may have been so inhibited that the situation is incompatible with life.
Describe the development of the nose (exterior)
The nasal placode - left and right ectodermal thickenings - invaginate to form the nasal pits (future nasal cavity).
The medial and lateral processes, on either side of each nasal pit, develop into the nose.
Describe the development of the oral cavity
Oral cavity = the stromodeum
The stromodeum (primitive oral cavity) is formed as a recess, from the folding of the head of the embryo.
At first, the stromodeum is separates from the pharynx/gut tube by the oropharyngeal membrane.
This eventually breaks down, resulting in continuity between the stromodeum and the gut tube.
Describe the development of the palate
The nasal pits (formed by invagination of the nasal placodes) enlarge, forming the nasal pits.
At this point, they are separated from the stromodeum by the primary palate (intermaxillary segment) anteriorly, and by the oronasal membrane more posteriorly.
The oronasal membrane breaks down, resulting in open communication between the nasal and oral cavities.
The Secondary Palate then forms (from the lateral aspects) from the maxillary process.
The Left and Right secondary Palate first fuses with the primary palate. Then, the left and right secondary palates fuse along the midline.
Abnormalities in URT and Face development
Can result in cleft palate and/or cleft lip.
Cleft lip occurs in 1/750: involves failure of the intermaxillary segment to fuse with the left and/or right maxillary process
Cleft palate occurs in 1/500: involves failure of the senondary and primary palates to fuse, and/or failure of the left and right secondary palates to fuse along the midline.
Any of these abnormalities can occur in isolation, or together.
Paranasal air sinuses: when do they develop? What bones are they in?
Frontal sinus in frontal bone, maxillary sinuses in maxilalry bones, ethmoid air cells in ethmoid bone, sphenoid sinus in sphenoid bone.
Develop as outgrowths of the nasal cavity into surrounding bones - purpose largely unknown, perhaps to reduce weight of face bones?
The paranasal air sinuses continue to develop until around 20 years of age.
