2 Normal Histology of the Parenchyma, Airways, & Blood Vessels Flashcards
1
Q
Conducting vs. respiratory airways
- Conducting airways
- Include…
- Main functions
- Respiratory airways
- Include…
- Main function
- As air moves distally into the lung, the following is observed
A
- Conducting airways
- Include the nasal cavities, pharynx, larynx, trachea, bronchi, and bronchioles
-
Main functions
- Deliver atmospheric air to the site of gas exchange
- Clear the air of pollutants
- Normalize its temperature and humidity
- Respiratory airways
- Include the respiratory bronchioles, alveolar ducts, and alveolar sacs
- Main function: exchange oxygen and carbon dioxide between atmospheric air and blood
- As air moves distally into the lung, the following is observed
- Air flow velocity decreases
- Air turbulence increases (enhances circulation of air contacting the airways walls and later the alveolar walls)
- Humidity & warmth increase
2
Q
How trachea & bronchi are alike (components seen on cross-section)
A
- Mucosa
- Submucosa
- Muscularis & cartilage
- Adventitia
3
Q
Trachea & bronchi:
Mucosa
- Mucosa consists of…
- The trachea and bronchi are lined by…
A
- Mucosa consists of…
- The epithelium and the underlying connective tissue, the lamina propria
- The trachea and bronchi are lined by…
-
A classic “respiratory epithelium”
- Epithelium
- Basement membrane
- Lamina propria
- Pseudostratified columnar epithelium consisting of ciliated columnar cells and goblet cells
- Each of these cells is attached by a fine, deep cytoplasmic foot process to the underlying basement membrane
- Situated between the deep attachments of these cells, lie the basal or germinal cells, which are also attached to the basement membrane
- Ciliated cells are found throughout the lining epithelium of the bronchial tree as far distally as the terminal bronchioles
-
A classic “respiratory epithelium”
4
Q
Trachea & bronchi:
Pseudostratified columnar epithelium:
Ciliated cells
A
- Joined to each other by tight junctions near their luminal surfaces and contain numerous mitochondria
- The cilium is a cytoplasmic extension from the surface of the cell, being covered externally by the same cell membrane
- The ciliary rippling movement beats in one direction, returning to the original position by a slower sweeping movement
5
Q
Trachea & bronchi:
Pseudostratified columnar epithelium:
Goblet cells
A
- Normally interposed between ciliated cells
- Non-ciliated
-
Narrow at the base & bulge apically
- Looks like a wine glass
-
Produce mucus, which is an acid glycoprotein (sialomucin)
- Makes the walls sticky
- Ultramicroscopically
- Goblet cells contain distinctive round or oval cytoplasmic vesicles filled with mucin
- Their cytoplasm is rich in endoplasmic reticulum
6
Q
Trachea & bronchi:
Pseudostratified columnar epithelium:
Kulchitsky cells & basal layer of cells
A
- Kulchitsky cells
- Specialized secretory cells located at the base of the epithelium
- Endocrine cells in a class referred to as APUD cells (Amine Precursor Uptake & Decarboxylase)
- Concentrated granules at the basal aspect of the Kulchitsky cells contain a variety of pharmacologically active peptides
- Produce seratonin, ADH, calcitonin, somatostatin, and others
- When stimulated, the secretions are released 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
- Kulchitsky cells are small and pale staining and have long dendritic-like cytoplasmic processes situated between the bronchial epithelial cells
- Basal layer of cells
- Progenitors of the other varieties of bronchial epithelial cells
7
Q
Trachea & bronchi:
Basement membrane
- Respiratory epithelium
- Bronchial basement membrane
- Lamina propria
A
- Respiratory epithelium
- Mucociliary escalator for the trachea and bronchi
- Mucus secreted by the goblet cells and submucosal glands is carried by the action of cilia up to the junction with the esophagus, where it is swallowed
- Bronchial basement membrane
- Laminated structure about 5 μm thick
-
Neutrophils & other inflammatory cells can migrate to the surface
- Open-network structure through which nerve fibers and leucocytes and other inflammatory cells may migrate to the surface from the underlying connective tissues
-
Porous: allows fluids to pass freely to nourish the overlying epithelium
- Tissue fluid also passes freely through the basement membrane to nourish the overlying epithelium, passing into the intercellular canals between the epithelial cells
- Image: abnormal in asthma
- Lamina propria
- Beneath the basement membrane
- Normally contains a few lymphocytes, numerous mast cells, and an occasional polymorphonuclear leukocyte, together with a rich capillary network surrounded by non-myelinated nerve fibers
8
Q
Trachea & bronchi:
Metaplasia
- Metaplasia
- Squamous metaplasia
- Goblet cell metaplasia
- Smooth muscle cell metaplasia
A
- Metaplasia
- The change in the type of epithelial cells to a form which is not normal for the tissue/organ
- With persistent or chronic irritation or injury to the lung, the normal cellular constituents may change shape or proliferate such that the normal mucosa or mesenchyme of a site will be altered
- Usually serves a protective function
- Squamous metaplasia
- With chronic irritation of the airways, the pseudostratified epithelium of airways will change to a squamous epithelium
- Goblet cell metaplasia
- With lesser degrees of inflammation the respiratory epithelium will develop an abnormal number of goblet cells, which secrete more mucus to provide a more substantial protective surface gel
- Smooth muscle cell metaplasia
- Almost all scars of the lung will elicit hyperplasia and metaplasia of the smooth muscle of the airways and vessel walls and stromal fibroblasts
9
Q
Trachea & bronchi:
Submucosa
A
- Loose area of connective tissue outside of the lamina propria
-
Characterized by blood vessels and glands of mixed salivary type that secrete both mucous and serous components
- Glands occur in bronchi down to a diameter of about 1 mm and reach their greatest development in the second to the fifth generation of bronchi, where they are distributed about one gland per square millimeter of mucosal surface
- The gland acini are arranged in lobules surrounded by loose connective tissue containing scattered mast cells, and their draining ducts open on the surface of the bronchi
10
Q
Trachea & bronchi:
Muscularis/cartilage layer
A
- In the trachea
- Contains C-shaped rings of hyaline cartilage
- The posterior gap in the cartilage is spanned by smooth muscle, the trachealis muscle
- The trachealis muscle acts to keep the trachea open during the pressure swings of inspiration and expiration
- In the lobar bronchi the cartilage plates are continuous
- As bronchi become smaller, they are reinforced by progressively fewer islands of cartilage
- With decreasing cartilage, the smooth muscle slowly increases to form a complete ring in the smaller bronchi
11
Q
Trachea & bronchi:
Adventitia
A
- Layer of dense connective tissue containing large nerves, lymphatic vessels, fat, and occasional lymph nodules
- This layer blends into the general connective tissue of the central mediastinum
12
Q
Bronchioles
Within lung segments
Lined by simple columnar epithelium
Decreasing cilia and goblet cells
Clara cells
Full circle of smooth muscle
Decreasing submucosal seromucous glands
No cartilage
A
- Within lung segments
- Lined by simple columnar epithelium
- Decreasing number of goblet cells & cilia
- Clara cells
- Full circle of smooth muscle
- Decreasing submucosal seromucous glands
- No cartilage
13
Q
Terminal bronchioles
- Terminal bronchioles: main points
- Clara cells
- Bronchi divide to become bronchioles, which further divide to become…
- As the bronchioles become smaller, they…
- Each terminal bronchiole supplies a unit of the lung called…
- Each respiratory bronchiole and its surrounding structures is referred to as…
A
- Terminal bronchioles: main points
- Within lung lobule
- Lined by simple cuboidal epithelium
- No goblet cells or cilia
- Increasing number of Clara cells (80% of epithelial cells)
- Patches of smooth muscle
- No cartilage or submucosal glands
- Clara cells
- Non-ciliated peg-shaped cells
- Have numerous small microvilli
- Secrete surfactant proteins & lysozyme
- Serve as main progenitor cells after bronchiolar injury
- Bronchi divide to become bronchioles, which further divide to become terminal bronchioles
- These finally develop single alveolar pockets along their walls and are then referred to as respiratory bronchioles
- As the bronchioles become smaller, they progressively lose goblet cells, cilia, and seromucous glands
- The lining epithelium becomes less complex and changes from simple columnar to simple cuboidal and then low cuboidal
- Goblet cells are replaced by Clara cells that have a domed-shaped appearance
- Clara cells have numerous small microvilli projecting from their free surfaces, and the bases of the cells contain numerous mitochondria
- Their most characteristic feature is the osmiophilic lamellar bodies containing CC10, a Clara cell specific surfactant protein
- The surfactant decreases surface tension, allowing the bronchiolar lumen to remain patent
- Each terminal bronchiole supplies a unit of the lung called a lobule
- Each respiratory bronchiole and its surrounding structures is referred to as anacinus
14
Q
Respiratory bronchioles
A
- Within lung acini
- Low cuboidal epithelium
- Interrupted with outpockets of alveoli along wall
- First respiratory gas exchange
- Clara cells
- Patches of smooth muscle
- Lead into the alveolar duct
15
Q
Lung acinus
- Lung acinus
- Respiratory bronchioles
- Alveolar ducts
- Alveoli
A
- Lung acinus
- Functional unit of the lung
- Consists of a respiratory bronchiole, alveolar ducts, and alveolar sacs
- Respiratory bronchioles
- Only partly lined by a single layer of cuboidal epithelium, which covers the fixed portion of the wall adjacent to the accompanying branch of the pulmonary artery
- From the remainder of the wall arise numerous alveoli
- Alveolar ducts
- About 14 million in the adult lung
- Form the final alveolated canals before reaching the air sacs
- About thirty alveoli arise in a spiral manner down the length of the alveolar duct
- Alveoli
- The average number of alveoli at birth is 25 million and in an adult lung is 375 million
- The surface area formed by the alveoli of a single normal adult lung is estimated to be between 600 and 800 square feet
16
Q
Pulmonary parenchyma
A
- If you scan this slide & try to estimate what is the amt of air vs. tissue on this slide
- 99% air
- 1% tissue
- Lung interstitium
- Tissue in these thin lines in the alveolar walls
- So thin in normal lungs that it basically doesn’t exist
- This image: normal
- Little tissue
- Little to no inflammatory cells
- No increased interstitium
- Unfortunately, there are interstitial lung diseases
- This thickness becomes significantly greater
- Thick walls separate atmospheric air from blood
- Gas exchange is significantly impaired
17
Q
Lung acinus:
Alveolar wall
- The alveolar epithelium consists of two different types of cells
- Type I pneumocytes
- Type II pneumocytes
- Other characteristics of the alveolar wall
A
- The alveolar epithelium consists of two different types of cells
- Type I pneumocytes
- Cover 95% of the alveolar surface
- Flattened cells
- Ideally suited for gas exchange
- Type II pneumocytes
- Cover 5% of the alveolar surface
- Rounded cells that occupy the niches and corners of the alveolar walls
- Their most characteristic feature, the so-called “osmiophilic lamellar bodies,” represent surfactant material synthesized within the cells
- Surfactant has strong hydrophobic properties, decreases surface tension forces, and consists of surfactant proteins and lipids (dipalmityl lecithin, and dipalmityl phosphatidyl ethanolamine)
- Ability to proliferate, regenerate, & turn into type I pneumocytes (ex. if there’s damage to the alveolar structure)
- Type I pneumocytes
- Other characteristics of the alveolar wall
- Shared basement membrane
- Pulmonary capillary endothelium
18
Q
Lung acinus:
Alveolar macrophages
A
- Large phagocytic cells that are present within alveoli
- Often they appear to be free in the lumen but are actually loosely attached to the epithelium
- They are derived from peripheral blood monocytes
- Like other macrophages, these cells ingest material, in this case dust and debris that gain access to the alveoli
- The lungs of smokers appear black because of the ingested carbon contained within the cytoplasm of macrophages
- Image: not normal b/c too many macrophages
20
Q
Visceral pleura
A
-
Covers the surface of the lungs
- Also divides the underlying lung into lobules
- Consist of vascularized connective tissue, an elastic lamina, and an outer mesothelial layer
- Lined by mesothelial cells (simple squamous epithelium)
- Mesothelial cells are flattened and inconspicuous, but rapidly become rounded, cuboidal, and columnar in shape in response to damage
21
Q
Vasculature, lymphatics, lymphoid tissue, & pleura:
Pulmonary vasculature
- The pulmonary vasculature includes…
- The lungs receive..
- The low-pressure pulmonary arteries run…
- The pulmonary circuit…
- The high-pressure bronchial arteries…
A
- The pulmonary vasculature includes…
- Pulmonary arteries
- Bronchial arteries
- Pulmonary veins
- Bronchial veins
- Alveolar microvasculature
- 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 airways only to the terminal bronchioles
22
Q
Vasculature, lymphatics, & lymphoid tissue
- Pulmonary arteries vs. veins
- Endothelium-lined lymphatic channels
- Lymphoid tissue
A
- The distal branches of the pulmonary arteries pass through the center of the
pulmonary lobules, whereas the pulmonary veins are situated at the edge of the
lobules- The pulmonary arterial system is designed to function as a low-resistance
maximum-flow system of vessels
- The pulmonary arterial system is designed to function as a low-resistance
- Endothelium-lined lymphatic channels are present around terminal bronchioles and the muscular branches of the pulmonary arteries
- Lymphoid tissue is distributed throughout the entire lung
- It can be divided into the central lymph nodes, lymphoid nodules, and aggregates of lymphocytes in the periphery of the lung, including the pleura
- Lymph nodes and aggregates consist mainly of T-lymphocytes and B-lymphocytes and constitute the part of the immune system designated as bronchus-associated lymphoid tissue (BALT)
