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

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Flashcards in 3 Lab: Normal Histology of the Lung Parenchyma, Airways, & Blood Vessels Deck (25)
1

Conducting vs. respiratory airways

  • Conducting airways
  • Respiratory airways

  • Conducting airways
    • Structures
      • Nasal cavities
      • Pharynx
      • Larynx
      • Trachea
      • Bronchi
      • Preterminal & terminal bronchioles
    • Functions
      • Clear the air of particulates (movement of air)
      • Deliver warm and humid air to the deeper sites of gas exchange
      • Muscle regulated control of air passage
      • Mucociliary escalator
  • Respiratory airways
    • Structures
      • Respiratory bronchioles
      • Alveolar ducts
      • Alveolar sacs
      • Alveoli
    • Functions
      • Actual respiration
      • Exchange of carbon dioxide in the blood for oxygen in the air (gas exchange)
      • Innate immunity
      • Surfactant

2

Conducting airway generation & respiratory tree

  • Conducting airway generation
  • Respiratory tree

  • Conducting airway generation
    • 16 generations of conducting airways (trachea to terminal bronchiole) develop by 16 weeks gestation
    • 16-23 generations of airway involve alveoli, respiratoyr bronchioles, & alveolar ducts
      • Many of these develop after birth up to age 5-8
  • Respiratory tree
    • Cross-sectional area increases
    • Air flow velocity decreases
    • Air turbulence increases
      • Enhances circulation of air contacting the mucociliary escalator
    • Humidity & warmth increase

3

Branching & cross-sectional area

  • In total, the airways branch...
  • Each parent gives rise to...
  • As air moves distally into the lung, the following trend is observed

  • In total, the airways branch...
    • 25-30 times
  • Each parent gives rise to...
    • 2 daughters, the cross-sectional area of which exceeds the area of the parent tube
  • As air moves distally into the lung, the following trend is observed
    • Cross-sectional area increases
    • Air flow velocity decreases
    • Air turbulence increases (enhances circulation of air contacting the mucociliary escalator and later the alveolar walls)
    • Humidity & warmth increase

4

Blood supply & respiratory tree

  • Blood supply
  • The hollow tube of the respiratory tree from the trachea through respiratory bronchioles is built of four layers

  • Blood supply
    • The lungs receive a dual arterial blood supply
    • The low pressure pulmonary arteries run alongside bronchi and bronchioles.
    • The pulmonary circuit continues to divide into the capillary networks of the alveolar walls
    • The high pressure bronchial arteries arise from the aorta, and accompany the bronchi to the terminal bronchioles only
  • The hollow tube of the respiratory tree from the trachea through respiratory bronchioles is built of four layers
    • Mucosa
    • Submucosa
    • Muscularis &/or cartilage
    • Adventitia

5

Trachea

  • The mucosa consists of
  • The trachea displays a classic “respiratory epithelium”
  • Mucus secreted by the goblet cells and submucosal glands
  • The columnar cells of the epithelium

  • The mucosa consists of
    • Respiratory epithelium
    • Underlying connective tissue, the lamina propria
  • The trachea displays a classic “respiratory epithelium
    • Pseudostratified columnar with cilia and goblet cells
    • Note that this epithelium is a misnomer, it is not the site of actual respiration or gas exchange
    • The respiratory epithelium produces the mucociliary escalator for the trachea and bronchi
  • Mucus secreted by the goblet cells and submucosal glands
    • Carried by the action of cilia up to the junction with the esophagus, where it is swallowed
  • The columnar cells of the epithelium
    • Contain receptors for IgA
    • Via transcytosis, secrete the immunoglobulin into the lumen of the respiratory tree

6

Trachea: mucosa

  • Migrating lymphocytes
  • Specialized secretory cells called Kulchitsky cells 
  • Concentrated granules at the basal aspect of the Kulchitsky cells

  • Migrating lymphocytes
    • Can occasionally be seen penetrating the basal layer of the epithelium
    • These lymphocytes are part of the mucosal immune system of the GI and respiratory tracts
  • Specialized secretory cells called Kulchitsky cells
    • Located in the base of the epithelium
    • Single endocrine cells, as a class referred to as APUD cells (Amine Precursor Uptake & Decarboxylase)
  • Concentrated granules at the basal aspect of the Kulchitsky cells
    • Store a variety of pharmacologically active peptides (bombesin, calcitonin & leu-enkephalin) and amines (serotonin, dopamine & norepinephrin)
    • When stimulated, the secretions are released into the basal lamina and carried away by the blood stream
    • These local agents act as paracrine and endocrine factors that respond to hypoxia and help to regulate the respiratory tract

7

Trachea

  • Lamina propria of the mucosa
  • Submucosa

  • Lamina propria of the mucosa
    • Thin wedge of dense connective tissue containing lymphocytes, plasma cells, mast cells and occasional polymorphonuclear leukocytes
    • Displays a rich capillary network with accompanying non-myelinated nerves
  • Submucosa
    • Looser area of connective tissue outside of the lamina propria
    • Characterized by blood vessels and glands that secrete both mucous and serous components

8

Trachea

  • Muscularis/cartilage layer
  • Trachealis muscle
  • Outer adventitia

  • Muscularis/cartilage layer
    • Contains C-shaped rings of hyaline cartilage
    • Posterior gap in the cartilage is spanned by smooth muscle,the trachealis muscle
  • Trachealis muscle
    • Keeps the trachea open during the pressure swings of inspiration and expiration
    • Lies in front of the esophagus, as the anterior-most structure of the neck
  • Outer adventitia
    • Contains large nerves, lymphatic vessels, fat, and occasional lymph nodules (like that of blood vessels)
    • Blends into the general connective tissue of the central mediastium of the chest cavity

9

Bronchi

  • The trachea bifurcates into two mainstem bronchi
  • In the bronchi, the respiratory epithelium
  • Lamina propria
  • Plasma cells
  • Submucosal glands

  • The trachea bifurcates into two mainstem bronchi
    • Right mainstem bronchus lies in direct line with the trachea and therefore increases the possibility of aspiration down this tube
  • In the bronchi, the respiratory epithelium
    • Is still pseudostratified columnar, but of a lower height than the
      tracheal epithelium
  • Lamina propria
    • Often contains lymphocytes
  • Plasma cells
    • Secrete IgA to be carried across the epithelium
  • Submucosal glands
    • Produce both mucous and serous secretions
    • Contain myoepithelial cells

10

Bronchi

  • Myoepithelial cells
  • Hyaline cartilage
  • In fixed sections of bronchi, the smooth muscle

  • Myoepithelial cells
    • Innervated by the autonomic nerves
    • Hhelp to squeeze secretions onto the luminal surface
  • Hyaline cartilage
    • Discontinuous, in irregular plates
    • The amount of cartilage decreases as the bronchi move distally into the lungs
    • As the cartilage decreases, smooth muscle slowly increases to form a complete ring in the smaller bronchi
    • The smooth muscle is sandwiched between the epithelium & cartilage
  • In fixed sections of bronchi, the smooth muscle
    • Contracts producing a convoluted lumen that distinguishes the bronchi
      from the trachea
    • The same contraction can constrict the airways in vivo
      (ex: asthma)

11

As the bronchi progress into the lung, they

  • Branch two-three more times
  • Decrease in diameter
  • Decrease the height of the respiratory epithelium
  • Decrease the number of goblet cells
  • Decrease the presence of submucosal glands
  • Decrease the amount of hyaline cartilage
  • Increase the amount of smooth muscle

12

Bronchioles: general features

  • Epithelium
    • Largest with low pseudostrat to simple columnar
    • Smaller with simple cuboidal
  • Smooth muscle complete ring
  • Loss of submucosal glands
  • No cartilage
  • No goblet cells (a few in largest)
  • Cilia decrease and disappear
  • Clara cells appear
     

13

Bronchioles

  • Bronchi divide to become
  • Structure of (preterminal) bronchioles

  • Bronchi divide to become
    • (Preterminal) bronchioles
    • Further divide to become terminal bronchioles (
    • Develop single alveolar pockets along their walls and are then named respiratory bronchioles
  • Structure of (preterminal) bronchioles
    • Within lung segments
    • Simple columnar epithelium
    • Decreasing cilia and goblet cells
    • Full circle of smooth muscle
    • Decreasing submucosal seromucous glands
    • Increasing clara cells
    • Travels w/ large pulmonary artery
    • No cartilage

14

Structure of terminal bronchiole

  • Root/stem of lung lobule
  • Simple cuboidal epithelium
  • No goblet cells or cilia
  • Increasing Clara cells (80% of epithelial cells)
  • Patches of smooth muscle (many)
  • No cartilage or submucosal glands

15

Structure of respiratory bronchioles

  • Root/stem of lung acinus
  • Low cuboidal epithelium
  • Interrupted with outpockets of alveoli along wall
  • First respiratory gas exchange
  • Clara cells
  • Patches of smooth muscle (fewer)
  • Pulmonary artery
  • No bronchial artery
  • Lead into the alveolar duct

16

Bronchioles

  • As bronchioles become smaller, they
  • Inflammation can cause 

  • As bronchioles become smaller, they
    • Progressively lose goblet cells, cilia, and seromucous glands
    • i.e. everything needed for the mucociliary escalator
  • Inflammation can cause
    • Bronchiolar goblet cell metaplasia
    • Increased mucus production
    • In some cases leading to airflow obstruction

17

Bronchioles

  • Goblet cells
  • Clara cells

  • Goblet cells
    • Are replaced by Clara cells that have a domed-shaped appearance in TEM
  • Clara cells
    • Secrete CC10, a Clara cell specific surfactant protein
      • The surfactant decreases surface tension, allowing the bronchiolar lumen to remain patent, even in the face of decreasing muscle and no cartilage
    • Secrete surfactant protein A (opsonize bacteria), lysozyme (digest bacterial cell walls), and transcytose immunoglobulins into the airspace

18

Pulmonary acinus

  • Components
  • Functions

  • Components
    • ​Respiratory bronchiole
    • Alveolar ducts
    • Alveolar scas
    • Alveoli
  • Functions
    • Gas exchange
    • Immune functions
    • Angiotensin converting enzyme
  • Image
    • Red = smooth muscle
    • Green = elastin

19

Acinus

  • Acinus
  • Consists of
  • The length of an alveolar duct contains
  • The final alveolar sacs
  • The walls of individual alveoli have three main layers through which gas diffusion occurs

  • Acinus
    • Functional unit of the lung
    • Structure distal to a terminal bronchiole, with the main stem being a respiratory bronchiole
  • Consists of
    • A respiratory bronchiole, alveolar ducts, alveolar sacs and alveoli.
  • The length of an alveolar duct contains
    • ~30 alveoli budding off its wall in a spiral fashion
  • The final alveolar sacs
    • Are blind ending cul-de-sacs lined by alveoli
  • The walls of individual alveoli have three main layers through which gas diffusion occurs
    • Pulmonary capillary endothelium
    • Shared basement membrane
    • Alveolar epithelium

20

Acinus

  • There are also wedges of
  • The alveolar epithelium consists mainly of 
  • Electron micrographs of the type II pneumocytes demonstrate
  • Type I pneumocytes

  • There are also wedges of
    • Intervening collagen, elastin, fibroblasts and a few inflammatory cells
  • The alveolar epithelium consists mainly of
    • Type I pneumocytes (an attenuated cell that covers 95% of the alveolar surface)
    • Type II pneumocytes (secretes lung surfactant)
  • Electron micrographs of the type II pneumocytes demonstrate
    • A rounded cell with limited surface area and unique granules filled with lamella of surfactant
  • Type I pneumocytes
    • Terminally differentiated cell incapable of proliferation when
      damaged. Alveolar wall repair occurs from primitive type II pneumocytes
      that later differentiate into new type I cells

21

Image

22

Image

  • Top: alveolar ducts w/ smooth muscle knobs
  • Bottom: white space = alveoli

23

Alveoli cell types

  • Type I pneumocytes
  • Type II pneumocytes
  • Interstitial cells
  • Alveolar macrophages

24

Type II pneumocytes

  • General
  • Main function
  • Other functions

  • Lamellar granules
  • Main function
    • Secrete pulmonary surfactant (tubular myelin)
  • Other functions
    • Turnover/ recycling of surfactant
    • Superoxide dismutase antioxidant
    • SP-A = activates macrophage phagocytosis
    • Proliferate & differentiate into Type I
       

25

Image

  • Alveolar macrophages

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