What are the six stages of lung growth and approximately what weeks do they happen in?
Embryonal (1-7), Pseudoglandular (5-17), Canalicular (16-26), Saccular (24-38), the Alveolar stage (36 to 1-2 years), and then the microvascular stage which is birth to 3 years.
What is the embryonic stage of lung development?
It is the organogenesis and formation of the major airways. During this time there is the appearance of the lung bud from the primative foregut, the separation of the trachea and esophagus, and the first division of branching. The esophagus and the trache
What is the pseudoglandular stage?
It is a stage when the dichotomous branching is almost complete and there is early epithelial cell differentiation. In this the pulmonary vascularization also follows the airway branching and the closure of pleuroperitoneal canals.
What is the Canalicular stage?
It is the completion of the conducting airways, epithelial differentiation by the thinning of the mesenchyme, and the formation of early pulmonary acinus. The capillaries also invade, there is continued epithelial differentiation, and there is cellular pr
What is the saccular stage?
It is the early septal formation, fetal lung fluid production, respiratory saccules form, increasing number of Type II pneumocytes, and fetal breathing.
What is the alveolar stage?
It is the alveolarization by septation. This is a process that continues after birth and there is the reduction of the capillary bilary to a single layer.
What is the microvascular stage?
It is the remodeling of alveoli and the capillary bed.
What are the origins of the respiratory system?
It comes from the foregut endoderm and the epithelial cells of the lung and trachea. It also comes from the mesoderm as there is connective tissue, smooth muscle, tracheal cartilage, lymphatics, and mesothelial cells in the lung.
What is tracheoesophageal fistula?
It is when there is an abnormal connection of the trachea and esophagus and there are many types of ways that this could happen.
What happens in the development of the bronchi?
The lung bud divides into right and left bronchi and the bronchial bud gets signals fro mteh mesenchyme to direct branching. Additioanlly the primary buds give rise to the lobar bronchi.
What is pulmonary hypoplasia?
It is the incomplete development of the lungs leading to abnormally low number or size of bronchopulmonary segments or alveoli.
What is respiratory distress syndrome?
It is when there is not enough surfactant produced by infants and this is a development abnormality that the chances are reduced for as time passes.
What is the conducting portion of the lungs?
It is the nasal cavities, the sinuses, nasopharync, the oropharynx, larynx, trachea, bronchi, bronchioles and the terminal bronchioles.
What is the respiratory portion of the lungs?
It is the part that specializes in rapid gas exchange and is the respiratory bronchioles, alveolar duncts, alveolar sacs, and the alveoli.
What is the ventilating portion of the lung?
It is the thoracic cage, intercostal muscles along with other muscles, muscular diaphragm, and the elastic tissue of the lungs that causes the ventilation to occur due to pressure changes.
Where does the trachea run from and where does it bifurcate? Describe its structure.
It runs from the lower border of the larynx (the cricoid cartilage) to the upper border of T-5 where it divides into the two main stem bronchi. It is a hollow flexible tube whose patency is maintained by 16-20 C-shaped rings of hyaline cartilage. In the a
What is the innermost layer of the trachea?
There is the respiratory epithelium that is covered by mucus in places and overlies the lamina propria which has a superficial portion of loose conenctive tissue that is infiltrated with lymphocytes and a deeper portion of denser connective tissue with el
Describe the ciliated columnar cells and where they are located.
These have cilia at the apical surface (200-300 per cell) and they extend from the tracheobronchial tree into the respiratory bronchioles. This is the first line of defense against dirt and airborne infection and they have lymphocytes between the cells so
Describe the Goblet cells and where they are located.
These are filled with mucous secretory droplets and these are discharged into the lumen of the trachea where they form a mucous blanket on the epithelial surface. This mucous is needed for proper ciliary action.
What is the second layer in for the trachea?
There is the submucosa which is the middle stratum of the trachea. This is a layer of dense connective tissue in whch the tracheal glands are embedded. There are also blood vessels, nevers, and lymphatics here. The glands are mixed glands of tubuloalveola
What are the third and fourth layers in for the trachea?
This is the fibrosa layer which contains mainly C-shaped rings of hyaline cartilage. The open end of each ring is closed by a band of smooth muscle called the trachealis muscle. Each cartilagenous ring is covered by perichondrium on both sides. There is d
What is the extrapulmonary bronchi like?
The structure is like the trachea with the same C-shaped cartilage.
What are the layers of the intrapulmonary bronchi?
These have the mucosa, muscularis, submucosa, cartilage-fibrous layer, and the peribronchial layer.
What is different about the mucosa, submucosa, and cartilage-fibrous layers?
The mucosa now has a lamina propria with more elastic fibers for the recoil mechanism. The submucosa is loose connective tissue now and has bronchial glands and it extends between the cartilage where there are intervals. Lastly the cartilage-fibrous layer
What is the muscularis layer?
This is a layer outside the lamina propria that is made of two sets of smooth muscle fibers which extend down the bronchial tree in a right and left spiral.
What is the peribronchial layer?
It is a thin layer of connective tissue that is the outermost layer and separates the wall of the bronchus from the pulmonary parenchyma so that the bronchus can move independent of the pulmonary parenchyma. It has more elastic fibers.
What is the size of bronchioles and what is its significance?
It is about 1 mm in diameter and serves a unit of the lung called a lobule.
What are the layers of the bronchioles?
There are three layers the mucosa, muscularis, and the outer layer.
What is the difference between the mucosa from before?
Since there is no cartilage, the mucosa is more folded up as is the smooth muscle, and the goblet cells are rare. The pseudostratified ciliated epithelial cells are also not as tall anymore. The lamina propria is thin but rich in elastic fibers.
How is the muscularis layer different?
It is now the thickest layer that completely encircles the bronchiole.
What is the outer layer?
This is thin and is made of connective tissue that is continuous with the parenchyma of the lung and therefore this now moves with the lung and is not independent like in the bronchi.
What are the layers of the terminal bronchioles? What is the difference from bronchioles?
There is a mucosa, muscularis, and outer layer. These have epithelium that now varies in height from simple columnar to ciliated simple cuboidal. There are no more goblet cells and the mucosa is less folded and the lamina propria is thinner than that of t
What are the layers of the respiratory bronchioles and how is this different from before?
There come from the terminal bronchioles. There is the epithelium, the lamina propria, the muscularis, and the outer layer. The latter three cannot be seen separately but rahter are a network of elastic fibers and smooth muscle. The epithelium can be simp
What are the parts of the alveolar ducts?
These have epithelium, which is mainly simple squamous but some simple cuboidal. Then there is lamina propria that is made of fine elastic fibers, reticular fibers, and a few collagenous fibers. There is smooth muscle that is present only around the openi
Describe the alveolar wall and the different cells?
It is a thin wall which favors gas exchange. The type I (small alveolar) cells are squamous cells with darkly stained nuclei, flattened, and usually far apart. The cytoplasmic processes from these are thin that extend along the surface of the alveolar lum
What are dust cells?
They are macrophages of the lung. They are part of the reticuloendothelial system and look like macrophages elsewhere. There are some macrophages that will have carbon particles ingested and look black or brown and these are heart failure cells.
What are the pleuras and what are they made of? Do they have sensory receptors?
They are the linings around the thoracic wall and are called the parietal pleura, and the part around the lung is called the visceral pleura. There space between the two is the pleural cavity with a thin film of fluid. The free surfaces of both is lined w
Describe the pulmonary blood vessels of the lung and what is the difference?
There are the pulmonary arteries and their branhces that carry venous blood from the right ventricles to the lungs for oxygenation. They follow bronchi and their branches to the respiratory bronchioles nad then the capillary networks. The larger pulmonary
Describe the other lung blood vessels and what is their main significance?
There are bronchial arteries that are small vessels that come from the aorta with oxygenated blood to nourish the air tubes, the walls of the pulmonary vessels, and part of the visceral pleura. They go along the bronchi until they break up into capillarie