Posted by ESB on August 25, 2011 at 01:03:57:
In Reply to: Respiratory Development questions posted by Dr. Lazarus on August 21, 2011 at 12:04:54:
: 1. Anatomically food intake and air intake pathways are structurally shared. Describe the embryological events that lead to the development of the trachea and the relationship of these events, and pertinent tissues, to the gut tube.
The gut tube first develops when the folding of the embryo incorporates part of the yolk sac. During the 4th week of development, the endoderm on the ventral side of the gut tube begins to invaginate into the wall of the gut tube, forming a respiratory diverticulum. As this diverticulum lengthens and enlarges, the tracheoesophageal septum separates it from the lumen of the foregut. The remaining lumen becomes the esophagus, while the diverticulum continues to grow and divide forming lung buds that branch into bronchial buds that branch into the generations of bronchi. This branching occurs into the primitive pleural cavity laterally and inferiorly. The endoderm covering the outside of the bronchi from the gut tube becomes the visceral pleura of the lung and the somatic mesoderm around them becomes parietal pleura.
: 2. Anatomically, there are two pleura layers associated with the lungs within the thoracic cavity. Describe the relationship of the pleura layers to the lower respiratory systems. What key developmental events lead to this relationship? Include in your answer the origins of the following anatomical structures: visceral and parietal pleura, hilum and root of the lung, pulmonary ligaments, septum transversum and diaphragm and the importance of space (pericardioperitoneal canals).
The visceral pleura, or serous layer of parietal pleura is tightly bound to the surface of the lung tissue. It ordinarily secretes a thin film of fluid lubricating its interaction with the parietal pleura on the body wall while breathing or moving. The visceral pleura derives from endoderm while the parietal comes from splanchnic mesoderm. When the trachea was initially developing, the initial division of bronchi from the main bronchus formed the area of the root of each lung, while the great vessels and other structures of the hilum formed from splanchnic mesoderm. The septum transversum starts off life as a group of cranial mesenchyme cells that are folded into a position caudal to the heart. This mesenchyme continues to differentiate and develop into other structures of the mediastinum - like the central tendon of the diaphragm and pulmonary ligaments. As it continues to develop, it becomes innervatd by C3 - C5, the origin of the phrenic nerve. As divisions of the bronchi arise in the lungs into the surrounding mesenchyme, pericardiacoperitoneal space precedes the divisions and becomes the pleural cavity.