Lecture 28 Pulmonary Histology Flashcards Preview

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Flashcards in Lecture 28 Pulmonary Histology Deck (21):

Describe respiratory system components

* The respiratory system consists of a conducting portion and a gas exchange portion.
* Respiratory mucosa lines the respiratory passageway and consists of:
- Pseudostratified ciliated columnar epithelium:
-- = Respiratory epithelium
-- Lines most of conducting structures
- Lamina propria: Thin layer of loose connective tissue
- Submucosa: Dense irregular connective tissue


Use your text to acquaint yourself with the following anatomical components of the respiratory system

- Nose and olfactory mucosa
- Paranasal sinuses
- Pharynx
- Larynx
- Trachea
- Lung


Describe the epithelial regions of the nose

* Nares:
- Stratified squamous epithelium continuous with epidermis
- Contains sebaceous glands, sudoriferous glands, and hair follicles
* Mucosa begins at level of nasal septum; includes:
- Respiratory epithelium (pseudostratified ciliated columnar epithelium)
- Basement membrane
- Lamina propria (blends with underlying bone or cartilage)
- Depending on location, mucosa may be called mucoperiosteum, mucoperichondrium, or the Schneiderian membrane)

- See Slide 8


Describe the olfactory epithelium

* Located in nasal cavity roof:
* Pseudostratified columnar epithelium without goblet cells
* No distinct basement membrane


Describe the cell types of the olfactory epithelium

* Sustentacular cells (support cells) with pigment granules
* Basal cells with pigment granules:
- Stem cells –give rise to immature olfactory cells
* Olfactory cells:
- Bipolar neurons
- Apical end projects into nasal cavity as a knoblike ending with nonmotile cilia.
- Cilia possess G-protein-linked odor-specific receptors
- Basal end of the cell extends as an unmyelinated axon, bundled with other similar axons, through the ethmoid plate to mitral cells located in the olfactory bulb
- Olfactory cells senesce and are replaced from basal cells.
* Olfactory glands of Bowman:
- Located in the lamina propria
- Secrete odorant-binding protein
- Odorant-binding protein binds to odorant molecule in nasal cavity.


Describe the steps to generating an action potential in the nose

1. Odorant-binding protein + odorant molecule
2. Binds to odorant receptor protein (G protein) on olfactory cell cilium
3. G-protein activated adenyl cyclase
4. ATP
5. cAMP
6. Opening of Na+ channels

- See Slide 12-13


Describe the following components of the nasopharynx
1. Mucosa
2. Submucosa
3. Waldeyer's Ring

1. Mucosa:
* Respiratory epithelium
* Lamina propria with FECT, mucous glands, serous and mixed glands, and diffuse lymphatic tissue
2. Submucosa:
* Loose CT
* MALT (mucosa-associated lymphoid tissue)
3. Waldeyer’s ring:
* Ring of lymphoid tissue around nasopharynx
* Includes tonsils and adenoids


Describe the 4 histological regions of the larynx

1. Epiglottis:
* Lingual surface:
- Covered with stratified squamous epithelium
- Lamina propria with loose CT and elastic fibers
* Pharyngeal surface:
- Covered with pseudostratified ciliated epithelium
- Lamina propria with tubuloacinar seromucous glands
* Core of epiglottis consists of elastic cartilage.
2. False vocal cords (vestibular folds):
* Covered with pseudostratified ciliated epithelium
* Lamina with seromucous glands
3. True vocal cords:
* Covered with stratified squamous epithelium
* Lack seromucous glands in lamina propria
4. Remainder of larynx is covered with pseudostratified ciliated epithelium.

- See Slide 16


Summarize the three tissue types found in the larynx

1. Epithelium:
* Respiratory epithelium (pseudostratified ciliated columnar)
* Stratified squamous epithelium
2. Cartilage:
* Hyaline cartilages: Thyroid, cricoid, arytenoids
* Elastic cartilages: Corniculates, cuneiforms, tips of arytenoids, epiglottis
3. Muscle:
* Skeletal muscle


Describe the histology of the trachea

* Mucosa:
- Respiratory epithelium with thick basement membrane.
- Lamina propria with delicate FECT and lymphatic tissue
* Submucosa:
- Many sero-mucous glands
* Adventitia:
- 16-20 horseshoe-shaped cartilages interconnected by FECT
- Opening between arms of horseshoe-shaped cartilages closed by:
-- FECT, mucous membrane, and smooth muscles (trachealis muscles)
- Mixed glands and capillaries

- See Slide 19


Describe the Lung

* In the context of this lecture, the word “lung” refers to all the respiratory system components distal to the trachea. For our purposes, this includes the bronchial tree and the alveoli, which are actually terminations of the bronchial tree, as well as the connective tissue support system and vascular system.
* Anatomically, there are two lungs, each divided into lobes (three on the right and two –sometimes disputed –on the left). Each lobe is divided into a number of lobules (bronchopulmonary segments).
* Histologically, we are mostly interested in the hierarchical changes that occur in the bronchial tree from the primary bronchi to the smallest divisions of the bronchial tree –the respiratory bronchioles –as well as the terminations of the bronchial tree –the alveoli.


Describe the bronchi

* The trachea divides into two primary bronchi –one to each lung.
- These bronchi lie outside the lung and are referred to as extrapulmonary
- Except for a smaller diameter, these bronchi resemble the trachea.
- The cartilage rings that reinforce these bronchi are circular rather than horseshoe-shaped.
* Each primary bronchus divides into three (to the right lung) and two (to the left lung) secondary bronchi, also referred to as segmental bronchi.
- Segmental bronchi are mostly intrapulmonary
- These bronchi are reinforced by circular rings of hyaline cartilage that transition to irregular plates.
* We are not concerned with the individual names for the various subdivisions of the bronchi. We will focus on the changes in the histology of the bronchial tree from the larger intrapulmonary bronchi to the respiratory bronchioles.
* Generalization: As the bronchi become smaller there is a decrease in the height of the epithelium, a decrease in cartilage and glands, and an increase in the proportion of elastic fibers and smooth muscles.
* Examine Figures 13-6 and 13-7 for the general structure of the bronchial tree and the changes that occur from the segmental bronchi to the terminal bronchioles.

- See Slide 24


Describe the general histology of the intrapulmonary bronchi

* Refer to Figure 13-7.
* Mucosa:
- Similar to trachea and extrapulmonary bronchi
- Mucosal folds may be present due to smooth muscles
- Elastic fibers are prominent
* Submucosa:
- Characterized by loose CT and lymphatic tissue
- Contains mixed glands and mucous glands
* Adventitia:
- Contains hyaline cartilage plates surrounded by dense FECT

- See Slide 26


Describe the general characteristics of bronchioles

* Absence of cartilage
* Absence of glands
* Sparse goblet cells, especially in terminal bronchioles
* Large amount of smooth muscle tissue
* Diameter ranges from 1 mm to about 0.3 mm.
* Epithelium transitions from ciliated columnar with a few goblet cells to ciliated cuboidal with no goblet cells (terminal bronchioles).
* Smallest bronchioles are the terminal bronchioles.
* Each terminal bronchiole branches to form two or more respiratory bronchioles.
* Diameter < 0.5 mm
* Epithelium of low columnar to low cuboidal
* Cilia present only in larger respiratory bronchioles
* Goblet cells absent
* Wall consists of smooth muscle within FECT
* May have a few alveolar outpocketings:
- Because gas exchange may occur here for the first time in the respiratory tree, these bronchioles are referred to as respiratory bronchioles.

- See Slide 29


Describe the passage from the alveolar ducts to the alveoli

* Alveolar ducts:
- Continuations of respiratory bronchioles
- Cone-shaped
- Squamous epithelium
- Wall consists of smooth muscle with FECT
* Alveolar sacs:
- Each sac is composed of several alveoli
* Alveoli (Refer to Figures 13-16 and 13-18):
- Alveoli within alveolar sacs are separated by alveolar septa.
- Walls of alveoli and septa are thin and composed of: •
-- Type I alveolar cells (type I pneumocytes): Less numerous than type II pneumocytes, these Cover largest surface area
-- Type II alveolar cells (type II pneumocytes): Cuboidal or rounded, these Serve as stem cells for type I and type II pneumocytes
-- Macrophages (dust cells)
- Pores of Kohn:
-- Openings between adjacent alveoli

- See slides 32-34


What are the five cell types in the mucosa?

1. Ciliated columnar cells
2. Nonciliated columnar cells:
- Have microvilli but no cilia
3. Stem cells:
- Basal cells of pseudostratified epithelium
- Replace themselves
4. Goblet cells:
- Mucous secreting cells
- Also stem cells; can replace other cells of epithelium
5. Neuroendocrine cells (Small granule cells):
- May be associated with sensory reception and are more prevalent in infants.
- Release catecholamines


Describe surfactant

* Secreted by Clara cells and type II alveolar cells
* Type II alveolar cells contain numerous lamellar bodies:
- Distinctive under EM
- Contain dipalmitoyl phosphatidylcholine (lecithin)
-- Secreted from apical domain of cells
-- Combine with proteins from Clara cells
* Surfactant reduces surface tension on alveolar surface.
* Type II alveolar cells phagocytize old surfactant.


Describe pneumocystis

* Type I pneumocytes:
- Very thin cytoplasm
- Cover about 95% of the alveolar surface
- Tight junctions connect with other type I cells
- Basal lamina may be fused with basal lamina of nearby capillaries
* Type II pneumocytes:
- Rounded cells that bulge into the alveolar lumen
- Cover about 5% of the alveolar surface
- Can divide and replace type I pneumocytes
- Produce phospholipid-protein surfactant that coats alveolar walls

- See Slide 40


Describe Clara cells

* These cells are found only in bronchioles.
* Number of Clara cells increases as ciliated columnar cells decrease.
* Histologically, these cells can be identified by an apical surface that bulges into the lumen of the airway.
* Secrete surface-active lipoprotein that prevents collapse of terminal bronchioles during exhalation
* Contain abundant SER
* Refer to Figures 13-9 and 13-13.

- See Slide 42


Describe Dust Cells

* Dust cells are macrophages and are derived from monocytes.
* Dust cells phagocytize particles such as pollutants, bacteria, and surfactant that are not trapped in the mucous and expectorated.
* Relation to CHF (congestive heart failure):
- In CHF, fluid containing the breakdown products of hemoglobin (ironcontaining hemosiderin) leak into alveolar spaces and are phagocytized by the dust cells.
- The iron-containing dust cells are referred to as heart failure cells.


Describe the blood-air barrier

* Consists of:
- Thin capillary endothelium (continuous endothelium)
- Thin epithelium of pneumocyte
- Intervening basal lamina produced by both cell types
* Permits gas exchange but does not allow fluids or cells to enter alveoli (normally).

- See slide 46