4 Lab: Normal Histology of the Lung Parenchyma, Airways, & Blood Vessels Flashcards Preview

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Flashcards in 4 Lab: Normal Histology of the Lung Parenchyma, Airways, & Blood Vessels Deck (24)
1

  • Trachea
  • Longitudinal section of trachea
  • Note the four layers
    • Mucosa (epithelium and lamina propria)
    • Submucosa (with glands and large blood vessels)
    • Cartilage rings
    • Skeletal muscle
  • The structure of the trachea is maintained by C-shaped rings of hyaline cartilage seen as ovals in longitudinal sections
  • The submucosal glands are particularly obvious

2

  • Trachea 
  • Longitudinal section
  • The structure of the trachea is maintained by C-shaped rings of hyaline cartilage seen as ovals in longitudinal sections
  • The submucosal glands are particularly obvious

3

  • Trachea
  • Cross-section
  • Identify mucosa, submucosa, cartilage & adventitia
  • Note trachealis muscule at posterior aspect
  • The structure of the trachea is maintained as a plate in true cross sections
  • Illustrates the trachealis muscle joining the ends of the cartilage "C"

4

  • Trachea
  • Cross-section
  • Note cartilage ring and trachealis muscle
  • The structure of the trachea is maintained as a plate in true cross sections
  • Illustrates the trachealis muscle joining the ends of the cartilage "C"

5

  • Trachea
  • The "respiratory epithelium" is a pseudostratified columnar epithelium with goblet cells and cilia
  • In this slide, the trachea has
    • A fairly thick basement membrane, which thickens during chronic asthma
      • Normally, the basement membrane is only visible in electron microscopy
    • A thin, dense lamina propria
  • The submucosa has glands and a lymphocyte cluster
  • The cartilage rings are hyaline cartilage with a perichondrium
  • Identify...
    • The pseudostratified columnar epithelium
      • The goblet cells and cilia are not clearly seen in this thick section
    • A narrow lamina propria
    • Submucosal glands, blood vessels and lymphocytes
    • The hyaline cartilage

6

  • Trachea
  • In this tracheal section, the denser lamina propria is easily distinguished from the submucosa with seromucous glands
  • Easier to distinguish the lamina propria from submucosal structures

7

  • Trachea
  • Seromucous glands of the submucosa release their secretions via ducts (through the denser lamina propria), and eventually onto the respiratory epithelium
  • Mucus and cilia combine to create the mucociliary escalator to trap and remove particulates from air in the conducting airways
  • Follows the path of a mucus secreting submucosal gland, to its duct passing through the lamina propria, on its way to the epithelium and tracheal lumen

8

  • Trachea, respiratory epithelium
  • The "respiratory epithelium" of the trachea is really a misnomer as no respiration or gas exchange occurs here
  • Histologically, it is classified as a pseudostratified columnar epithelium with cilia and goblet cells
  • While goblet cells are not obvious in this fairly thick section, the cilia are clearly identified because they are longer than the width of a nucleus, clumped and marked by a row of basal bodies in the apical cytoplasm
  • How you can tell this epithelium has cilia & not microvilli
    • Darkly stained row of basal bodies

9

  • Trachea & esophagus
  • The trachea lies anterior to the esophagus
  • The trachea (right) requires cartilage rings to prevent collapse during inspiration and is well vascularized to warm the passing air
  • The esophagus (left) is lined by a thicker stratified squamous epithelium designed to withstand friction of swallowed food, and a thick muscular tunic to propel the bolus

10

  • Bronchus
  • Irregular cartilage patches characterize the bronchi
  • Progressing to smaller bronchi, the amount of cartilage will diminish, the amount of smooth muscle will increase
  • The epithelium is a low pseudostratified columnar, still with cilia and goblet cells
  • Seromucous glands are present in the submucosa
  • At the top are two blood vessels: a thicker walled bronchial artery and a thin walled pulmonary artery
  • To the far left and far right are two bronchioles
  • A bronchus is characterized by patches of cartilage, gradually replaced by smooth muscle

11

  • Bronchus
  • Low pseudostratified "respiratory epithelium” with cilia & goblet cells
  • Submucosa with seromucous glands and a few small clusters of smooth muscle
  • Irregular cartilage patches
  • Adventitia with blood vessels: a thin walled pulmonary artery & thicker walled bronchial artery
    • Both these vessels travel with the arborizing conducting airways
  • Submucosal seromucous glands are seen that secrete onto the luminal surface
  • The respiratory epithelium is a lower pseudostratified columnar than the trachea
  • Accompanying the bronchus are a branch of both the pulmonary artery (thinner wall) and the bronchial artery (thicker wall of a systemic muscular artery)

12

  • Bronchus
  • Good close up of a bronchus
  • What would distinguish this slide from a close up of the trachea?
    • The smooth muscle lying at the interface of the lamina propria & the submucosa
  • Submucosal seromucous glands are seen that secrete onto the luminal surface
  • The respiratory epithelium is a lower pseudostratified columnar than the trachea
  • Goblet cells and cilia are present indicating an active mucociliary escalator in the bronchi
  • Scattered patches of smooth muscle are seen beneath a thin lamina propria
  • The smooth muscle will become a complete circle in the smaller branching of bronchi
  • Stimulation of the parasympathetic nervous system will contract the smooth muscle

13

  • (Preterminal ) Bronchiole
  • Bronchiole - Verhoeff's stain
  • Classic bronchiole with a continuous tunic of smooth muscle (and no cartilage)
  • Lingering submucosal glands indicate the probably persistence of a few ciliated cells for mucus transport
  • These will rapidly disappear from bronchioles
  • Note the presence of black staining elastin, which is an increasing component of the lamina propria from the bronchioles through the alveoli
  • Note, that often these largest bronchioles are simply called bronchioles (without the “preterminal” designation)
  • The epithelium is simple columnar with a few clear goblet cells and probable cilia
  • A complete ring of smooth muscle is the clear diagnostic feature here
  • There is no cartilage, but seromucous glands persist in the submucosal layer
  • Note that this slide is stained with Verhoeff’s to emphasize the elastin component

14

  • Terminal Bronchioles
  • Bronchioles at bifurcation point
  • Usually bronchioles are distinguished by their LACK of cartilage
    • Do be aware though, that small pieces may persist at bifurcation points
  • The most important positive diagnostic of a bronchiole is the folded appearance of the simple cuboidal epithelium due to a continuous tunic of smooth muscle
    • The complete ring of smooth muscle contracts as it is fixed resulting in a highly folded lumen, which makes a bronchiole easy to identify
  • The blood vessel in the upper right-hand corner is a thinner walled pulmonary vein (travels independently of the respiratory tree), while at "6 o'clock" is a thicker walled bronchial artery
  • At "10 o'clock" is a thinner walled pulmonary artery
  • The bronchial arteries only accompany conducting airways, until alveoli begin to bud from the respiratory bronchioles
  • Lingering support of cartilage and submucosal glands at the split, but none around the bronchioles themselves
  • Epithelium is simple cuboidal with no clearly discernable goblet cells

15

  • Terminal Bronchioles
  • Simple cuboidal epithelium, with few/no goblet cells or cilia
  • The tunic of smooth muscle contracts giving a folded appearance to the epithelium
  • Cells in the lumen are alveolar macrophages moving by amoeboid action to a bronchus where they can be carried up to the esophagus by the mucociliary escalator
  • The cartilage and cluster of submucosal glands are remnants of an earlier bronchial segment that linger into this branch point
  • Lingering support of cartilage and submucosal glands at the split, but none around the bronchioles themselves
  • Epithelium is simple cuboidal with no clearly discernable goblet cells

16

  • Terminal Bronchiole, Respiratory Bronchiole, Alveolar Duct & Sac, Alveoli
  • (Diagonal from lower right)
    • Terminal bronchiole
    • Respiratory bronchiole
    • Alveolar duct
    • Alveolar sacs
    • Branching into alveoli
  • Focus ont he numerous alveoli in this low power view of the lung parenchyma

17

  • Terminal Bronchiole (lower right) to Respiratory Bronchiole (upper left)
  • Terminal bronchiole
    • Last portion of the conducting airways
    • Simple cuboidal epithelium, with no goblet cells or ciliated cells (80% replaced by Clara cells)
      • Clara cells are distinguished only in EM
    • Patches of smooth muscle
      • A complete ring of smooth muscle produces a folded epithelium
      • No cartilage or submucosal glands
  • As soon as alveolar outpocketings interrupt, the airway is called a respiratory bronchiole
    • The first of the respiratory airways for actual gas exchange
    • There are three levels of bifurcations in the respiratory bronchioles, each with progressively less and less smooth muscle
    • The blood vessel is a pulmonary artery
    • The deepest level that the bronchial arteries penetrate is to the terminal bronchioles
    • Single alveolar outpockets interrupt a wall whose structure is otherwise similar to the terminal bronchiole
    • Note the minimal blue-staining collagenous connective tissue (Mallory stain) and the alveolar macrophages in the bronchiole lumen

18

  • Respiratory Bronchiole
  • Verhoeff stain
  • This elastin stain emphasizes the importance of the elastic component in the lamin propria/ interstitial area of the lung acinus
    • Elastin increases in the lower conducting airways and in the true respiratory portions of the lung
  • The acinar unit passively recoils after inspiration, decreasing the need for a forced muscular expiration
    • Diseases that compromise elastin, such as emphysema, have substantial effects on the ability of the lung to recoil after inhalation

19

  • Lung Alveoli
  • The attenuated lung epithelial cells, the type I pneumocytes, line 97% of the alveolar surfaces that face the air
  • Capillary endothelial cells are found in the center of the alveolar septal walls
  • Interstital cells occupy the thicker angular wedges of the alveoli
  • Alveoli branch out from the alveolar duct
  • Alveolar walls are built of ccapillaries coated by type I pneumocytes

20

  • Lung Alveoli
  • Alveoli (L19 & 20) branch out from the alveolar duct
  • Alveolar walls are built of ccapillaries coated by type I pneumocytes

21

  • Alveolar Macrophages
  • Macrophages migrate freely in the airspace of the lungs
  • These are from a smoker and have been given an undigestible "meal" of tar
    • These macrophages have ingested cigarette tar
  • Note the tar deposits in the wedges of interstitial tissue as well
    • The black patches are tar; this slide was not stained with Verhoeff's
  • Since there are no lysosomal enzymes for digestion of the tar, residual bodies accumulate
    • The amoeboid macrophages migrate up to the preterminal bronchioles and bronchi where they are cleared by the mucociliary escalator
    • Macrophages also exit the lung via the minimal lymphatic drainage
    • The life span of an alveolar macrophage is about 24 hours

22

  • Type I Pneumocyte
  • A transmission electron micrograph is necessary to visualize the gas diffusion barrier of the alveolus
  • The capillary lumen is identified by the presence of two RBCs, another cell (WBC) and precipitated plasma proteins
  • The air space is above & below
  • The walls of the lung alveoli are composed of two cell types, type I and
    type II pneumocytes
  • Type I pneumocytes are a thin attenuated cells that face the air space and are limited at their base by a basement membrane shared with the endothelial cells of alveolar capillaries
  • Type I pneumocytes form a portion of the gas diffusion barrier (from blood to air):
    • Red blood cell plasma membrane
    • Blood plasma
    • Endothelial cell (continuous)
    • Basement membrane
    • Type I pneumocyte
    • Surfactant
    • Air

23

  • Respiratory Barrier
  • The barrier for the diffusion of gases (from RBC to air sac)
    • RBC PM (red)
    • Plasma
    • Capillary endothelial cell (pink)
    • Basement membrane (green)
    • Type I pneumocyte (blue)
    • Surfactant (not visualized in this photo)
  • The walls of the lung alveoli are composed of two cell types, type I and
    type II pneumocytes
  • Type I pneumocytes are a thin attenuated cells that face the air space and are limited at their base by a basement membrane shared with the endothelial cells of alveolar capillaries
  • Type I pneumocytes form a portion of the gas diffusion barrier (from blood to air):
    • Red blood cell plasma membrane
    • Blood plasma
    • Endothelial cell (continuous)
    • Basement membrane
    • Type I pneumocyte
    • Surfactant
    • Air

24

  • Type II Pneumocyte
  • The epithelium of the alveolus is not only composed of type I pneumocytes, but type II pneumocytes as well
  • The type II pneumocyte seen here is easily identified by the lamellar granules of surfactant
  • As a TEM artifact, the lipid components of the surfactant aggregate into sheets upon processing
  • Lung surfactant lowers the surface tension to allow for easier expansion of the air sacs
  • Type II pneumocytes are rounded cells in the same sheet of epithelium as the type I cells
  • Lamellar granules in the cytoplasm contain surfactant proteins and lipids that are secreted into the alveolar space and form a coat on the outer aspects of both the type I and type II pneumocytes
  • Lung surfactant lowers the surface tension to allow for easier expansion of the air sacs
  • Surfactant is composed of 50% cholesterol, 40% phospholipid dipalmitoyl- phosphotidylcholine (DPPC) and 10% proteins
  • There are four surfactant proteins: SP- A, B, C and D
    • SP-A and SP-B have carbohydrate recognition receptors that bind bacteria and aid in the activation of alveolar macrophages
    • SP-B and SPC are hydrophobic proteins that stabilize the surfactant/air interface
    • Type II pneumocytes can also undergo mitosis and differentiate into both new type I or type II cells

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