HISTOLOGY LAB XII: RESPIRATORY SYSTEM

 

BE ABLE TO IDENTIFY:

alveolar pore (of Kohn)
Bowman's gland
bronchus , bronchiole, terminal bronchiole, respiratory bronchiole, alveolar duct, and alveolus
cells-- basal, Clara, macrophage (dust cell), mast cell, pneumocyte (I and II), sustentacular
concha
cricoid cartilage
epiglottis
true and false (ventricular or vestibular) vocal fold
interalveolar septum
laryngeal ventricle
olfactory epithelium
respiratory epithelium
trachea
vocalis m.

 

Slide #17 (Olfactory epithelium, mammal) In humans, olfactory epithelium is found in the roof of the nasal cavity and over the superior nasal conchae. Olfactory epithelium differs from respiratory epithelium in the following ways: it is thicker with prominent basal cells and there are fewer Goblet cells. Cilia and/or microvilli are often masked by a thick seromucous covering. The fluid coating the olfactory epithelium is secreted by Bowman's glands, which are not found elsewhere in the nasal epithelium, so the presence of these glands is a criterion for identification. Another criterion is prominent nerve bundles. This slide is a poor preparation and is thick so distinguishing olfactory from respiratory epithelium may be very difficult.

 

 

 

 

Slide #23 (Soft palate, mammal) Ventrally, it is covered by oral epithelium (stratified squamous epithelium) and dorsally by respiratory epithelium (pseudostratified columnar epithelium with Goblet cells). Your slide may not demonstrate the respiratory epithelium well or at all. Note skeletal muscle and mucous glands scattered throughout the connective tissue.

 

 

 

 

 

Slide #51 (Larynx, monkey) Note the types of epithelia lining the mucosa in various regions of the larynx. Fig.5 will orient you while viewing this slide. With the scanning lens, you should first identify the laryngeal ventricle. Superior to this is the false cord, inferior to this, the true vocal cord. The latter is easily identified by the presence of thin stratified squamous epithelium on the surface, as well as the vocalis muscle (striated) in the connective tissue close to the true cord. You should also see examples of hyaline cartilage and mucous glands.

Slide #49 (Trachea, monkey) Identify the following: ciliated pseudostratified columnar epithelium, goblet cells, basement membrane, diffuse lymphatic tissue (if present), seromucous glands, cartilage, perichondrium, and smooth muscle.

 

 

 

Slide #147 (intrapulmonary bronchus, human)

Slide #84 (Lung, horse)

Slide #183 (Lung, monkey)

Identify the following:

Bronchus: Similar to trachea, but C-shaped cartilage is replaced by discontinuous plates of cartilage. Complete layer of smooth muscle and occasional glandular tissue may be seen. Bronchi differ in size and amount of cartilage. If the tube has any cartilage at all, it is a bronchus. If it does not, it is a bronchiole!

Bronchiole: Smaller in diameter than bronchus and NO CARTILAGE or glands. Epithelium is simple ciliated or non-ciliated columnar. The smooth muscle in the wall of bronchioles constricts during fixation causing the wall to have a "ruffled" appearance in cross-section.

 

 

 

 

Terminal bronchiole: Some authors classify the very end of a bronchiole before it has openings into alveoli in its wall, as a terminal bronchiole.

 

 

 

 

 

Respiratory bronchiole: Similar to conducting, non-respiratory bronchiole, except walls (made up of low cuboidal epithelium) are interrupted by "budding" alveoli..

Alveolar duct: Discontinuous walls open into many alveoli and alveolar sacs. This structure may be hard to find, so rely on your atlas for the best illustration.

 

 

 

 

 

 

Alveoli: Chicken wire-like appearance whose walls are made up of four distinct layers (as seen by electron microscopy). Be able to identify alveolar space and the interalveolar septa in general. You won't be able to identify the 4 different layers described below using a light microscope.

1) simple squamous epithelium (facing air) (Type I and Type II pneumocytes)
2) basal lamina of #1 (above)
3) basal lamina of #4 (below)
4) endothelium (facing capillary)

Intralveolar Septa: Structures separating alveoli from one another. Appear very thin in light microscope but show more detail in the Scanning EM.

 

 

 

 

 

Dust cells: Just macrophages hanging out in alveolar space (usually on the surface of Type I Pneumocytes.)

Pore of Kohn: Otherwise known as alveolar pore, which is the opening between alveoli. They equalize the pressure between alveoli.

Type II Pneumocytes: What molecular constituent makes cytoplasm flocculant?

 

 

 

 

 

 

 

 

HISTOLOGY LAB XIII: GASTROINTESTINAL TRACT I

 

BE ABLE TO IDENTIFY:

Oral Cavity
acinus (mucous, serous, and seromucous)
glands: parotid
sublingual
submandibular (submaxillary)
Von Ebner's
papillae: circumvallate
filiform
foliate
fungiform
inter- and intralobular ducts
serous and mucous cells
serous demilune
taste bud

Esophagus to rectum-- be able to identify:
goblet cell
lamina propria
lymphatic aggregations
muscularis externa
muscularis mucosa
myenteric (Auerbach's) plexus
serosa
submucosa
submucosal (Meissner's) plexus

Esophagus-- be able to identify this organ and the following components:
upper, middle, and lower
cardiac gland
esophageal gland

Stomach-- be able to identify this organ and the following components:
cells-- chief, surface mucous, mucous neck, parietal
gastric pits (foveolae) and glands

 

I. Tongue

Normally, these are spike-like projections, but in slide #27, some of these projections have been knocked off during preparation of the tissue. Fungiform papillae are merely rounded projections, whereas circumvallate papillae are located only on the posterior part of the toongue, are much larger, and have a very characteristic mushroom shape (consult your atlas on this one). Look for examples of taste buds in the epithelium of fungiform, folliate, or circumvallate papillae. What kind of muscle is found in the tongue? Note the von Ebner's glands, which wash the taste buds.

 

 

Slides #27 & #173 The human tongue has four different types of papillae: foliate, filiform, fungiform and circumvallate. Foliate papillea are found in in infant humans but not in adults. Many other mammals have a lot of foliate papillae in adults as well as infants. This section was taken from the anterior dorsal part of the tongue which is rich in filiform papillae.

 

 

 

 

 

 

 

 

 

 

 

 

 

Foliate papillea are found in in infant humans, but not in adults. Many other mammals have a lot of foliate papillae in adults as well as infants. This micrograph was taken from the tongue of a rabbit.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

II. Salivary Glands

Compare and contrast the following three types of salivary glands. Find examples of intralobular ducts (within a lobule of glandular material) and interlobular ducts (between glandular lobules, in the connective tissue septa).

Slide #67 (Sublingual gland) The Sublingual gland is almost entirely made up of mucous acini. Mucous acini are occasionally capped with serous demilunes (a piece of serous acinar tissue).

Slide #68 (Parotid gland) The Parotid gland is made up entirely of serous acini.

Slide #118 (Submandibular (submaxillary) gland) Within the Submandibular gland, the majority of the secretory units are serous, although there should be some mucous components.

 

 

 

 

III. G.I. Tract

Each component of the gut tube is structurally specialized for its particular function, but there is a basic pattern of histological organization applicable throughout the digestive tract.

In general, each segment of the digestive tract has a characteristic epithelial lining supported by a thin layer of loose connective tissue, the lamina propria. Throughout most segments of the tract, a thin layer of smooth muscle, the muscularis mucosa, lies directly below the lamina propria. These three layers comprise the mucosal lining. Outside this, there is a thicker layer of connective tissue, the submucosa. The submucosa is surrounded by a double layer of smooth muscle: the muscularis externa. The cells in this muscularis externa are oriented circumferentially in the inner layer, longitudinally in the outer layer. The outer covering of most of the alimentary tract is a thin layer of connective tissue contained within an outer layer of mesothelial cells. This is the serosal layer.

You should be aware of two types of autonomic nerve plexuses found throughout the digestive tract.

a) Submucosal or Meissner's plexus

Meissner's plexuses are found in the submucosa.

 

 

 

 

 

 

 

 

 

b) Myenteric or Auerbach's plexus

Auerbach's plexuses are found between the inner circular and outer longitudinal layers of the muscularis externa. Look for large basophilic cells with large nucleus and prominent nucleolus.

Keep in mind that there are many variations in these basic layers, i.e. glands, goblet cells, throughout the entire digestive tract. Each section of the digestive tract is a modification of this basic plan. DID YOU BRING YOUR TEXT TO LAB? No? WhadidItellya?

Now that we have given you the GENERALIZED structure of the gut tube, we will start the lab with an ATYPICAL portion called the esophagus. Anatomists are like that, as you already learned in Gross.

 

 

 

 

 

 

Esophagus

Slide #28 (Section of Upper Esophagus) The epithelium is stratified squamous, which is not surprising since many ingested foods are coarse and abrasive. The muscularis mucosa is represented by isolated bundles of smooth muscle. The submucosa contains many blood vessels of all types. What type of muscle do you see in the muscularis externa?

 

 

 

 

 

 

 

 

 

 

Slide #29 (Section of Middle Esophagus) Compare this section to #28. This tissue appears more organized. The muscularis mucosa is a much thicker band of muscle separating lamina propria and submucosa. You should be aware that the lower esophagus is one of two segments in the entire GI tract (the other being the duodenum) that has glands in the submucosa. Are these mucous or serous? Do you see any Auerbach's plexuses? What kind of muscle is found in the external layer?

Slides #30 & #32 These slides illustrate the abrupt transition from esophagus to cardiac region of the stomach. The epithelium changes suddenly from stratified squamous to simple columnar. Also, the lamina propria of the cardia is loaded with cardiac (mucous) glands and usually many lymphocytes. What is muscle type in wall?

Stomach, Fundus Region

Slide #31 and/or #149 (#149 is usually better) The fundus (body) is the center of action in the stomach. Under low power, identify the four major layers of the wall. The stomach is decidedly difficult to preserve well due to the high acidity of the gastric secretion. Invaginations of the epithelial lining protrude deeply into the thick lamina propria. The upper one-third of the invaginations are known as gastric pits or foveolae. The remainder, still within the lamina propria (internal to the muscularis mucosa), is formed by fundic glands. Under higher power, examine the epithelium as it proceeds deep into the fundic gland.

 

 

 

Surface Epithelium - simple columnar epithelium.

Epithelium of Gastric Pit Surface mucous cells line the pit to its base. Mucous neck cells are difficult to distinguish from surface epithelium.

 

 

 

 

 

 

 

Epithelium of Fundic (Gastric) Gland Parietal cells are large eosinophilic cells with a prominent central nucleus. The cells look like "fried eggs." Parietal cells produce HCl and gastric intrinsic factor. Chief cells are pyramidal, basophilic cells, smaller than parietal cells, and produce pepsinogen.

 

 

 

 

 

Review the function of these different types of cells.

In addition, you should be aware of the existence of APUD cells and their important functional significance. Previously called enteroendocrine or argentaffin cells, they are not easy to see in stomach. Special stains may be needed to demonstrate their existence, histologically. Some APUD cells are visible on the thin sections of jejunum and ileum (Slides #179 & 180). The secretory granules are located in the basal part of the cell AWAY from the lumen. WHY?

 

 

 

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