(Transcribed from Dr. Kalliecharan’s lecture, 21 Mar 2000 by Brian Buschman)
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The respiratory system is made up of two main portions, the conducting and the respiratory parts. The conduction portion is responsible for providing a route of the air to get from outside the body into the lungs and in the process warming, adding moisture and removing large particles from it. The respiratory part includes all of the exchange area and is responsible for allowing exchange of O2 and CO2 between the blood and external environment.
Most of the conducting system is lined by a respiratory epithelium which is primarily pseudostratified columnar epithelia with cilia and goblet cells. This epithelia has five different cell types:
1) Ciliated columnar cells that function in lining the surface and helping move mucus towards the pharynx.
2) Columnar goblet cells function in secreting mucus to moisten the respiratory tract.
3) Columnar brush cells have microvilli on the apical surface and afferent nerve endings near the basal surface. They are through to play a role in sensory reception.
4) Basal cells only touch the basal surface and are believed to give rise to the other cell types as needed.
5) Small granule cells are similar to basal cells but are neuroendocrine cells that contain many granules.
If the cilia lack dynein arms then they do not have ATPase activity. This is known as immotile cilia syndrome. It leads to sterility in males and difficulty removing mucus from respiratory tract in both genders.
The nasal cavity is made of three areas:
I) The vestibule is where the air first enters the nose and there are many nose hairs (vibrissae) to remove large particles from the air. It is initially keratinized stratified squamous epithelia.
II) The respiratory segment is the place where the epithelia changes from keratinized to respiratory epithelia. It also has a mechanism to warm the air. One involves a countercurrent between blood flow and air flow. Another feature is the presence of swell bodies that are extensions of the venous plexus into the lamina propria that swell up to partially divert air flow through the other nostril to allow the one a break.
III) The olfactory segment is where the smell is sensed by the olfactory epithelia (pseudostratified columnar) on the conchi. Olfactory epithelia is composed of four cells types:
a) Olfactory bipolar neurons hat have cilia that act as sensory receptors.
i. Supporting cells that have lipofuscin granules.
b) Basal cells.
c) Brush cells (just a few) that help carry out sensory functions
The olfactory segment also has olfactory glands that secrete serious material to wash sensory receptors.
There are also paranasal sinuses that are well discussed in anatomy.
As discussed in anatomy there are two pharynx parts. The nasopharynx is lined with respiratory epithelia. The oropharynx is lined with stratified squamous epithelia.
Everything here are things you should know from Dr. Tabor. Remember that the vocal folds contain an elastic ligament.
The trachea is lined with respiratory epithelia with a thick basement membrane and lamina propria. It has lots of loose connective tissue and like large arteries has a fenestrated elastic membrane to separate the mucosa from the submucosa. The submucosa is a LCT with seromucous glands to keep it moist. It has a layer of cartilage rings and an adventitia.
The bronchus is the same as the trachea but the cartilage plates are irregular. The smooth muscle also forms a muscularis mucosae. The bronchus will branch into smaller tubes until getting to the bronchioles.
Bronchioles are of two types, terminal and respiratory. Neither have cartilage, glands or goblet cells. Both still have cilia to help the mucus up.
1) Terminal bronchioles have simple columnar epithelia with cilia. They also have Clara cells which secrete a mixture of glycosaminoglycans that act like surfactant to decrease luminal adhesion.
2) Respiratory bronchioles are made of simple cuboidal epithelia with intermixed Clara cells. They also have some alveoli with type I alveolar cells which makes this the first site of gas exchange.
Bronchiole smooth muscle receives innervation from two sources:
1) Sympathetic innervation causes the relaxation of smooth and therefore bronchiodilation.
2) Parasympathetic stimulation causes contraction of smooth muscle and therefore bronchioconstriction.
The alveoli are where the gas exchange actually takes place. The respiratory bronchioles branch into alveolar ducts that have a ring of smooth muscle and they go to alveolar sacs which are surrounded by alveoli.
The wall between two alveoli contains a rich vascular supply and an extensive network of pores to allow equilibration of pressure between the alveoli.
Alveoli are lined by type I and II alveolar cells. 95% are type I which are simple squamous for exchange. Type II are cuboidal and secrete surfactant which is essential to break the surface tension of the alveoli that would otherwise make respiration impossible.
The barrier between blood and the air is made up of:
1) Alveolar epithelial cells.
2) Basal lamina of alveolar cells.
3) Basal lamina of capillary endothelium.
4) Capillary endothelium.
The barrier boils down to the two layers of epithelium and their related structures.
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