Respiratory System

Learning Objectives:

No Slide:

Draw a sketch or schematic (using arrows) of the respiratory tree, beginning at the site of inhalation (nose) and ending at an alveolus. Which parts are the conduction portion, and which are the respiratory portion?

Your sketch should include the nasal cavity, the pharynx, the larynx, the trachea, primary bronchi, secondary bronchi, bronchioles, terminal bronchioles, respiratory bronchioles, alveolar ducts, and finally alveoli. Respiratory bronchioles are the first region to be classified as the respiratory portion of the respiratory system.

This slide is a section taken from the lateral wall of the nasal vestibule and shows the internal and external surfaces. Which is which? How can you distinguish them?

The external surface has a stratified squamous keratinized epithelium, whereas the inside surface transitions to a stratified squamousnon-keratinized epithelium. The internal surface also has many thick hairs called vibrissae that distinguish it from the finer hairs present on the external surface.

Iowa Virtual Slidebox: Nasal Septum (211) or Nasal Septum (416)

These are great slides for exploring the various tissues of the face and nose. You should be able to spot two or three kinds of epithelium (not counting glands!), bone, cartilage, muscle, adipose tissue, lymphoid tissue, vessels, etc. Cruise around this slide and find as many as you can and try to draw correlations to what you know about the anatomy of the nose. Pay particular attention to the respiratory epithelium and the vascular and glandular supply of the lamina propria.

Iowa Virtual Slidebox: Nose: olfactory epithelium (397)

Olfactory epithelium consists of three different types of cells. Take a screenshot or draw and label those cells below. Explore the lamina propria to find venous sinuses, axons from the olfactory nerves, and olfactory glands. (Also be careful not to confuse the olfactory eptiehlium with the respiratory epithelium!)

Your schematic should include tall, columnar supporting cells with oval nuclei near the center of the cell;, short, pyramidal basal cells located on the basement membrane, and sensory cells. Sensory cells are bipolar neurons and are spindle-shaped with a central expanded region.

First, correlate the larynx with your schematic drawing for the first question. Which passageway have we passed through to arrive at the larynx?

We have passed through the nasal cavity and pharynx to enter the larynx.\

The larynx is an extremely complex organ. Identify in this slide:

o   Adipose tissue

o   Mucosa – what kind of epithelium?

o   Glands (serous or acinar?)

o   Lymphoid tissue

o   Cartilage

o   Muscle

See if you can identify which areas of the larynx are lined by stratified squamous epithelium, and which are lined by pseudostratified columnar epithelium.

The vestibular/ventricular folds and the vocal folds are lined by stratified squamous epithelium (nonkeratinized), whereas the rest of the larynx, including the vestibule itself, is lined by pseudostratified columnar epithelium.

The Iowa Virtual Slide shows one half of the larynx. The True vocal folds contain skeletal muscle while the false vocal folds contain glands and adipose tissue. Which side is which? (Don’t think you can forget about skeletal muscle!)

These slides demonstrate the epilogttis, which is part of the larynx. What does the epiglottis do, and why does it have elastic fibers in its cartilaginous matrix?

The epiglottis is a cartilaginous flap that closes the larynx off from the esophagus during swalloping. It has abundant elastic fibers because it is so mobile, while simultaneously requiring rigidity (to properly close the airway).

What kind of epithelium lines the epiglottis?

Stratified squamous nonkeratinized.

What other structures do you see in this section?

In addition to cartilage and elastic fibers, there are abundant seromucous glands in the lamina propria, especially closer to the base.

SLU Slide 35: Trachea

Iowa Virtual Slidebox: Trachea (212)

The SLU slide demonstrates a trachea sectioned both axially and longitudinally, While the Iowa slide is an axial section in situ with the surrounding organs. In these slides, note the ring of hyaline cartilage.  What type of epithelium exists in the trachea? What cells exist within this epithelium?

The trachea has a ciliated, pseudostratified columnar epithelium. In addition to ciliated cells and basal cells, the trachea has goblet cells. (Also present are brush cells and neuroendocrine cells, but these are hard to distinguish on H&E preparations).

What structures (observed in previous labs) do you see deep to the epithelium?

A prominent basal lamina, Lamina propria (loose connective tissue), Seromucous glands, Arteries and veins, Cartilage (hyaline), Adipose tissue, and nerves

The Iowa slide also includes the esophagus, so you will see skeletal muscle and a stratified squamous epithelium; and it includes the thyroid gland and some named nerves, arteries and veins that you already love or will come to love!!!

SLU Slide 79: Bronchus

Iowa Virtual Slidebox: Lung (82)

Does this slide have any bronchi? Identify an intrapulmonary bronchus by the irregularly shaped cartilage plates in its wall (i.e., adjacent to a large circular structure). Bronchioles, terminal bronchioles, respiratory bronchioles, and alveoli should also be apparent. How do you differentiate them from one another? Particularly, focus on bronchi and bronchioles.  Beginning with the larger structures, compare the epithelial innings of each of these portions of the respiratory tree. Identify and draw/screenshot:

o   Ciliated pseudostratified columnar epithelium

o   Ciliated simple columnar epithelium

o   Goblet cells

o   Bronchiolar secretory cells – these will bulge into the lumen of terminal bronchioles

o   Alveolar macrophages

You should be able to distinguish intrapulmonary bronchi with cartilaginous plates (secondary bronchi), from bronchioles, which are supported only by smooth muscle. As you continue down the respiratory tree, the epithelium with get shorter, eventually terminating in the respiratory bronchioles. Additionally, as cartilage plates disappear, Club cells will become more apparent and goblet cells will cease to appear.

In this slide you should be able to appreciate alveolar air spaces. You should also be able to observe Type I and Type II pneumocytes. Compare and contrast these two types of cells based on their shape/morphological specializations and their functions (and its relation to structure).

Type I pneumocytes form part of the blood-air barrier, which is apparent because of their broad, flat cytoplasm. 

Type II pneumocytes are more cuboidal with a "foamy" cytoplasm. These cells secrete a component of surfactant, which is apparent from the large spaces in their cytoplasm (occupied by lamellar bodies) 

To correlate your histological findings today with your embryology and physiology lectures, explore the slides below:

Iowa Virtual Slidebox: Lung-fetus (288) & Lung-baby (290)

What physiological changes happen at or around birth? How are they demonstrated with these slides?

Many of the morphological differences between these slides are due to the fact that fetuses don’t breathe air. For example, the Type I pneumocytes are “taller” in the fetus and flatter in the baby – you can see the capillaries (filled with erythrocytes) protruding into alveolar sacs in the baby. Alveolar sacs are still dividing, and may appear less organized and distinct. Before birth, the lungs are filled with a fluid rich in chloride ions and some mucus, and the fetus will respirate in amniotic fluid, which you can see in some of the lumens here. You can also examine the connective tissues and see that they are less differentiated than in either the baby or the adult.