Introduction The slides for this lab are located in the “Respiratory System” folders on the Virtual Microscope. In this lab, you will learn about respiratory and olfactory mucosae as well as the organization of the bronchiole tree. Something to keep in mind as you go through this lab is that everything that you are looking at is on a continuum. If an area has several characteristics that seem to split it between two categories, then it is probably safe to assume that you are viewing a region of transition. Lucky you!

Learning objectives and activities

Using the Virtual Slidebox:

A Identify the characteristic features of respiratory mucosa.

B Identify the characteristic features of olfactory mucosa.

C Apply your knowledge of the basic tissues to identify the components of the bronchial tree.

D Distinguish between the cells of the inter-alveolar septum.

E Complete the self-quiz to test your understanding and master your learning. Identify the characteristic features of respiratory mucosa.

Examine Slide 1 (44) to identify the characteristics of respiratory mucosa.

This slide is a soft palate. The soft palate is a barrier that is involved in swallowing and breathing. The lower oropharyngeal surface is covered in oral lining epithelium (non-keratinized stratified squamous epithelium). The upper nasopharyngeal surface is covered in respiratory epithelium (pseudostratified ciliated columnar epithelium with goblet cells).

Respiratory mucosa is composed of:

i. Respiratory epithelium a. The epithelium is pseudostratified columnar epithelium.

b. The apical surface is covered with cilia that beat to produce a Examine the metachronal wave that propels mucus and any trapped particles respiratory mucosa in towards the oral/nasal cavities. Slide 1a (44) and locate the c. There are many goblet cells interspersed that secrete mucus that respiratory epithelium helps prevent the airway from dehydrating and traps small component. Find the airborne particles. major features of the respiratory epithelium. d. The basal cells close to the basement membrane give the epithelium its pseudostratified appearance and are stem cells that give rise to other cells of the epithelium.

ii. Lamina propria Examine the Lying immediately below the epithelium is the lamina propria. respiratory mucosa in Classify the connective tissue from which it is composed and note Slide 1b (44) the arteriole, venules and capillaries that denote its high level of and locate the lamina vascularity. propria.

A submucosa lies below the respiratory mucosa: Although not part of It is composed of dense irregular connective tissue and in the soft the respiratory palate is occupied by, skeletal muscle and large palatine salivary mucosa, locate the glands. You should be able to classify these glands based upon their submucosa and shape and secretory product. classify the glands in Slide 1c (44) Identify the characteristic features of olfactory mucosa.

This epithelium is a specialized area of the nasal mucosa covers the superior nasal concha. It is composed of an olfactory epithelium (pseudostratified columnar cells) and its underlying lamina propia. This is where we smell!

Examine Slide 2 (70) to identify the characteristic of olfactory mucosa

Olfactory mucosa is composed of:

i. Olfactory epithelium Find pseudo-stratified a. The epithelium is pseudostratified columnar epithelium. columnar epithelium in Slide 2a (70) b. Olfactory neurons Bipolar neurons that are inserted into the olfactory epithelium. Approximate the They have centrally located nuclei and non-motile cilia that location of bipolar extend from the apical surface. These contain the neurons based on chemoreceptors. The neuron axons come together in the lamina nucleus location in propria to form small nerve bundles as the pass through the Slide 2b (70) cribriform plate of the ethmoid bone and synapse at a ganglion in the olfactory bulb. Approximate the c. Sustentacular cells location of Sustentacular cells support the olfactory neurons and are bound sustentacular cells to them by junctional complexes. Their nuclei lie highest. based on nucleus location in Slide 2c d. Basal cells Basal cells are stem cells that line the basement membrane and Locate basal cells in give the epithelium its pseudostratified appearance. Slide 2d (70) ii. Lamina propria Lying immediately below the epithelium is the lamina propria which contains:

e. Bowman’s glands Identify Bowman’s The secretions of which wash away odors and permit the glands in Slide 2e (70) reception of new smells.

f. Olfactory nerve bundles and vessels Identify olfactory Neurovascular bundles located in the lamina propria. nerves in Slide 2f (70) Apply your knowledge of the basic tissues to identify the components of the bronchial tree.

i. Trachea

Examine the trachea in Slide 3 (72) to find its defining features.

a. Respiratory mucosa Identify the Confirm that the trachea has typical respiratory mucosa respiratory mucosa (respiratory epithelium and lamina propria) and its components in Slide 3a (72) b. C-shaped hyaline cartilage rings Examine the extent of the C-shaped cartilage ring that holds the Identify tracheal airway open during respiration. Remember that cartilage is cartilage in composed of Type II collagen and lots of ground substance. The Slide 3b (72) connective tissue cells in cartilage are called chondrocytes.

c. Submucosal glands Look at a submucosal You may be able to identify some sero-mucous glands in the gland in submucosa. Slide 3c (72)

d. Trachealis muscle A band of smooth muscle connecting the free ends of the Find the trachealis cartilage that contracts to narrow the lumen of the tube during muscle in coughing. Slide 3d (72)

Finally, for fun and to correlate with the gross anatomy you have been studying, examine the rest of the slide and identify the following organs and their basic tissue components: - thyroid gland (more on this in a future unit) - esophagus (more on this in a future unit) - vagus nerve (it's a nerve, whose structure you know from basic tissues) - internal carotid artery (it's a muscular artery, whose structure you know from this unit) - internal jugular vein (it's a vein whose structure you know from this unit) cartilage plate ii. Bronchus

Observe the section of lung in Slide 4 (75) to locate and examine the distinguishing features of a bronchus. respiratory mucosa

To locate a bronchus in the lung you just need to look for a tube with smooth irregular plates of cartilage in its wall. muscle a. Respiratory mucosa Confirm that the bronchus has a typical respiratory mucosa (respiratory epithelium and lamina propria). Identify these key b. Cartilage plates features of a bronchus Confirm that the rings of cartilage seen in the trachea now form in Slide 4a (75) disorganized plates in a bronchus. c. Smooth muscle Confirm that the bronchus is surrounded by a band of smooth muscle cells.

iii. Regular bronchiole

Observe the section of lung in Slide 4 (75) to locate and examine the distinguishing features of a number of regular bronchioles. respiratory mucosa To locate a regular bronchiole in the lung you just need to look for a tube surrounded by smooth muscle with respiratory epithelium. smooth muscle a. Respiratory mucosa Confirm that regular bronchioles has a respiratory mucosa. Note that the respiratory epithelium may be lower than a typical Identify these key respiratory epithelium as it prepares to make a change to simple features of a regular columnar/cuboidal. bronchiole in Slide 4b (75) b. Smooth muscle Confirm that regular bronchioles are surrounded by a thick band of smooth muscle cells. simple columnar-cuboidal epithelium iii. Terminal bronchiole

Observe the section of lung in Slide 4 (75) to locate and examine the distinguishing features of a number of regular bronchioles.

To locate a terminal bronchiole in the lung you just need to look for a tube surrounded by smooth muscle with a simple columnar – simple smooth cuboidal epithelium. muscle a. Simple columnar-cuboidal epithelium

Note that the respiratory epithelium has now transitioned into a simple columnar epithelium and along the length of these tubes Identify these key continues to change into a simple cuboidal epithelium. features of a terminal bronchiole in b. Smooth muscle Slide 4c (75) Confirm that terminal bronchioles are surrounded by a band of smooth muscle cells.

simple iv. Respiratory bronchiole cuboidal epithelium Observe the section of lung in Slide 5 (74) to locate and examine

the distinguishing features of a number of regular bronchioles. alveolus

To locate a respiratory bronchiole look for a tube similar in construction to a terminal bronchiole but has one or two alveoli budding from its wall. smooth muscle a. Simple cuboidal epithelium Note that the respiratory epithelium has now transitioned from into a simple columnar epithelium and along the length of these tubes continues to change into a simple cuboidal epithelium. Identify these key b. Smooth muscle features of a Confirm that respiratory bronchioles are surrounded by a band of respiratory bronchiole in smooth muscle cells. Slide 5a (74) c. Alveolus The presence of one/two alveoli in the wall is the only feature distinguishing this structure from a terminal bronchiole.

simple cuboidal epithelium cluster v. Alveolar duct

Observe the section of lung in Slide 5 (74) to locate and examine alveolus the distinguishing features of an alveolar duct.

To locate an alveolar duct look for passageway lined with alveoli. ‘knob’ of The entrance to these alveoli has a small ‘knob’ of muscle and smooth perhaps a cluster of low simple cuboidal epithelial cells associated muscle with it.

a. Alveoli Identify these key Identify the alveoli lining an alveolar duct. features of an alveolar

duct in b. Smooth muscle ‘knobs’ Slide 5b (74) Confirm that there are small lumps of smooth muscle that mark

the entrance to each alveolus in an alveolar duct.

v. Alveolar sac alveoli

Observe the section of lung in Slide 5c (74) to locate and examine the distinguishing features of an alveolar sac. atrium To locate an alveolar sac look for a space/atrium from which numerous alveoli bud. Note that now there are no smooth muscle ‘knobs’ associated with the entrance to the alveoli.

Distinguish between the cells of the inter-alveolar septum.

These cells are best identified at high magnification otherwise they are very difficult to differentiate. We have scanned slides at very high mag (so it may take a while to load on slow connections) to allow you to see these cells.

Examine the alveoli in Slide 6 to locate these cells of the inter-alveolar septa. a. Type I pneumocytes (squamous alveolar cells) These cells are responsible for the gas exchange between the Identify examples of lungs and the blood. Oxygen must diffuse through these cells into Type I pneumocytes in underlying capillaries. This ‘blood-air-barrier’ consists of a Type I Slide 6a cell, its basal lamina and a capillary endothelial cell. Type I cells have a long flat nuclei. They are the most numerous inter- alveolar cell. b. Type II pneumocytes (great alveolar cells) These cells have a dual purpose. They secrete a protein-lipid Identify examples of complex called surfactant which reduces surface tension in each Type II pneumocytes alveolus, thereby preventing alveolar collapse and decreasing the in required inspiratory force needed to inflate the alveoli. This Slide 6b secretion also acts as an antibacterial agent. Type II cells are more cuboidal/domed and less abundant than Type I cells. c. Alveolar macrophages (dust cells) Monocytes regularly leave the blood to enter the lung tissue, where they form alveolar macrophages that phagocytose inhaled Identify examples of particles and erythrocytes lost from damaged capillaries. They macrophages in keep the alveoli clean and as a result are often referred to as Slide 6c ‘dust cells’. They are difficult to observe within the inter-alveolar septum unless you can see debris in their cytoplasm. d. Endothelial cells The small vessels that run within the interalveolar septa are lined with endothelial cells. It is difficult to distinguish these from other Identify examples of cells, particularly the Type I cells. As a rule, endothelial cells have endothelial cells in a c-shaped nucleus that partially encircles the lumen of a capillary Slide 6d when viewed in cross section, or line larger blood filled lumens. In addition to all the basic tissues in slides you must be able to identify the following structures and their features:

Respiratory mucosa and submucosa Pseudostratified columnar epithelium Cilia Goblet cells Respiratory epithelium Basal cells Seromucous glands Olfactory mucosa and submucosa Olfactory epithelium Olfactory neuron, bipolar Lamina propria Sustentacular cells Basal cells Bowman’s glands Olfactory nerve, bundle Nasal cavity Nasal fossa Nasal conchae, turbinate bone Nasal septum, cartilage Olfactory mucosa (and its components) Respiratory mucosa (and its components) Trachea Hyaline cartilage Respiratory mucosa (and its components) Trachealis muscle Seromucous glands

Bronchus Bronchiole, regular Terminal bronchiole Respiratory bronchiole Alveolar duct Alveolar sac Alveolus

Interalveolar septum Type I pneumocyte, squamous alveolar cell Type II pneumocyte, great alveolar cell Alveolar macrophage, dust cell Endothelium, endothelial cell