Histology of the Lower Respiratory Tract Flashcards
What are the section of upper respiratory tract?
Nasal cavity
Paranasal cavity
Sinuses
Nasopharynx and oropharynx
What are the parts of the lower respiratory tract?
Larynx
Trachea
Brochi
Bronchioles
Alveoli
What are the anatomical divisions of the respiratory tract?
Upper and lower respiratory tract
What are the functional divisions of the respiratory tract?
The conducting zone (movement of air from outside to the end of the bronchial tree
Respiratory zone (gas diffusion areas in respiratory bronchioles and alveoli)
Where does gas exchange occur in the respiratory tract?
In the lower bronchioles and the alveoli
What are the 3 main functions of the respiratory functions?
Air conduction
Air filtration and conditioning (fibrasae in the nasal cavity trap foreign bodies)
Gas exchange (respiration)
Where is the trachea located?
Trachea extends from larynx to the level of the sternal angle (T4/5) where it divides into 2 primary bronchi.
What is more anterior the oesophagus or the trachea?
The trachea
How many cartilage rings does the trachea have?
16 - 20 C-shaped rings
What bridges the ends of the cartilaginous rings of the trachea?
The trachealis muscle which are joined vertically by the annular ligamnets
What structure joins the trachealis muscles to each other vertically?
Annular ligament
What are the layers that surround the trachea?
Lumen -> Mucosa -> Submucosa -> Cartilage and muscularis -> Adventitia
What makes up the mucosa?
2 layers;
Respiratory epithelium containing pseudostratified ciliated columnar epithelium and numerous goblet cells which produce mucous. (they are closest to inner surface of the trachea)
Lamina propria containing loose connective tissue with lots of elastic fibers and diffuse nodular lymphatic extending from lamina propria to submucosa
Which tissues have respiratory epithelium?
nasal cavity, larynx, trachea, and bronchi
What kind of tissue is present in the submucosa?
Loose connective tissue which is similar to that of the lamina propria and different to the connective tissue in digestive tract.
What kind of tissue layer is present in respiratory tract and GI tract but absent in urinary tract?
Submucosa
What lines the lamina propria of the mucosa?
Loose connective tissue with lots of elastic fibers.
Diffuse and nodular lymphatic extending from lamina propria to the submucosa
What makes up the submucosa layer?
Relatively loose connective tissue and numerous submucosal glands
What makes up the cartilage and smooth muscle?
C-shaped hyaline cartilage rings keep tracheal lumen open
Posterior ends of the cartilage ring connected by trachealis
What kind of cartilage forms the cartilage rings?
Hyaline cartilage
What makes up the adventitia?
Dense irregular connective tissue which merges with adventitia of other organs such as the oesophagus
What part of the trachea meets the oesophagus?
The trachealis side
What are the functions of the trachealis muscle?
2 important functions:
During swallowing the trachealis relaxes to facilitate the passage of food and bulging of oesophagus into the lumen of the trachea.
Trachealis muscle is also important for coughing the trachea narrows the lumen to allow air to be expelled with more force.
What structures are contained within the submucosa of the trachea?
The ducts and the acini (mucous and serous)
Mucous glands + acini are more common than the serous glands + acini
What cells does the epithelium of the trachea contain?
Ciliated columnar cells (oval shaped nuclei and are tall cells with cilia)
Goblet cells (They produce mucous and are tall)
Basal cells (cuboidal cells sitting on basement membrane of epithelium)
What gives hyaline cartilage its glassy appearance?
Its matrix is homogenous with a special type 2 collagen fiber
Where is cartilage produced?
In the lacuna of the cartilage cells. In a rift between chrondrocytes.
What kind of cells are found in the respiratory mucosa?
Ciliated columnar cells (most abundant cells, columnar shaped with oval nucleus each has up to 300 cilia on its surface)
Goblet cells (They are numerous throughout respiratory tract but absent from the bronchioles and alveoli and secrete mucus that is expelled by cilia towards the pharynx)
Basal cells (progenitor cells)
Clara cells (exocrine bronchilar cells)
What do cilia do?
Expel debris opposite to air in a synchronous manner.
What occurs if cilia activity is ruined?
Dirt can accumulate inside lungs
What does mucus produced by goblet cells do in the respiratory tract?
It filters small dust particles that escape thick hairs in nasal cavity.
Conditioning and moistening of air in lungs
What do basal cells of the respiratory tract do?
They are stem cells that produce other epithelial cells
What do Clara cells do?
Non-ciliated cells with dome-shaped apical surface that produce surfactant-like substances secrete antimicrobial peptides
Where are clara cells located?
Bronchioles, they are absent from trachea and bronchi
What happens to people that smoke?
The cilia start to lose synchronous beating movement due to toxins in cigarette smoke and the mucous removal is reduced and accumulated in the lower respiratory tract
Squamous metaplasia (transformation of pseudostratified columnar epithelium to pseudostratified squamous epithelium)
What are the types of bronchi?
Primary bronchi (nearly same structure as trachea and same layers with C shaped cartilage ring)
Secondary/lobar bronchi have narrower lumen and same epithelial layer
How is cartilage different in the primary bronchi to the cartilage in the trachea?
They have smooth muscle between lamina propria and submucosa
They have discontinuous cartilage plates.
How are tertiary/segmental bronchi different to secondary and primary bronchi?
Epithelium becomes less stratified with less goblet cells.
Smooth muscles become prominent between lamina propria and submucosa.
Submucosa is reduced in amount with less mucous glands
Few isolated cartilage plates
What layers do bronchi have?
Lumen
mucosa
muscularis (continuous smooth muscle)
submucosa which has projections into the adventitia
Adventitia
How do serous acini stain on histology slides?
They are acidophilic so they stain purple
What is the difference between bronchi and bronchioles?
Bronchioles have a diameter of 1mm or less (branch of segmental bronchi)
Pseudostratified ciliated columnar epithelium in bronchi becomes simple ciliated columnar in the terminal bronchioles or simple cuboidal epithelium in the respiratory bronchioles.
No goblet cells in bronchioles except in smokers
Clara cells increase in numbers as ciliated cells decrease along the length of the bronchiole
No subepithelial mucous glands in the bronchioles
No hyaline cartilage in the wall of the bronchioles
Bronchiole and lung parenchyma it supplies is a ____?
Pulmonary Lobule
Important slide for revision of this lecture is the slide showing the changes from conducting to respiratory part of respiratory system with all the cellular changes that take place
If short on revision time check this slide out
What happens to the epithelial layer as we progress through the respiratory tract?
The large bronchioles initially have pseudostratified ciliated columnar epithelium that gradually transofrms into a simple ciliated columnar epitheliumand then into a simple cuboidal epithelium.
What layers do bronchioles have?
Lumen
Mucosa
Muscularis
Adventitia
Which cells are absent and which are present in epithelium of bronchioles?
No goblet cells but Clara cells are present in the mucosa of bronchioles.
How are layers of the bronchioles different to the
Walls are thinner and have less layers.
What does the muscularis layer of the bronchioles have?
Muscularis layer is a continuous thick layer of smooth muscle (in bronchioles these are super thick relative to their thickness)
Do bronchioles have any mucous glands?
No
Do bronchioles have cartilage plates?
No
How are terminal bronchioles different to the respiratory bronchiles?
They have thicker wall
What is the role of terminal bronchioles?
They are important for conduction of air without influencing respiration
What is the role of respiratory bronchioles?
They are the transitional zone between conduction and gas exchange.
Same structure as terminal bronchioles except that the lung epithelium becomes simple cuboidal epithelium instead of ciliated simple columnar epithelium.
The number of clara cells increases distally.
Does alveolar duct possess a wall?
No
What are the 3 parts of the respiratory zone of the lungs?
Respiratory bronchioles (give off alveoli) and alveolar ducts
Alveolar ducts (do not have a wall of their own and give off alveoli only)
Alveolar sacs are spaces surrounded by clusters of alveoli the surrounding alveoli open into these spaces
Where are alveoli located?
At terminal end of bronchial tree and forms lung parenchyma
What do alveoli look like under light microscopy?
Honeycomb like
How many alveoli does the normal lung have?
200mil
What type of epithelium lines alveoli?
Simple squamous epithelium (type I pneumocytes)
What does lamina propria of alveoli look like?
Extremely thin with a network of elastic and reticular fibers
What separates alveolii from each other?
Interalveolar septum. It is also the blood-air barrier.
What structures line the intralveolar septa?
Blood vessels
What pores are contained within the alveolus?
pores of Kohn?
What are type II pneumocytes?
Cuboidal cells that produce surfactant as well as being the site of gas exchange
What white blood cells are commonly found on alveolar surface and what is their cytoplasm like?
Macrophages (alveolar) They have darker cytoplasm
What is the blood air barrier?
The barrier between air and the alveolar blood vessels
What does the blood-air barrier consist of?
Thin layer of surfactant
Type I pneumocytes and its basal lamina
Intervening connective tissue
Capillary endothelial cells and its basal lamina
What kind of cells are type I pneumocytes and what percentage of alveoli do they line?
Squamous epithelium
lines 95% of the surface of the alveoli
What prevents leakeage of blood and fluid from the septum of the alveoli?
Edges of two alveolar cells overlap and are
uniting by tight junctions preventing the leakage of blood/fluid from the alveolar septum
to the alveolar space.
When does surfactant get produced during foetal development?
20 - 22 weeks of pregnancy
What is respiratory distress syndrome?
Foetuses born prematurely don’t produce enough surfactant causing this condition
What is done to prevent respiratory distress syndrome?
Pregnant at high risk of premature labour given betamethasone injection (at 28-32 weeks) to stimulate further production of surfactant.
What do alveolar macrophages look like under light microscope?
Present within alveolar spaces (alveolar macrophage) and alveolar septum (septal
macrophage).
Slightly darker than type II pneumocytes due to their content of dust and carbon.
What do alveolar macrophages do?
In alveolar space, they scavenging the alveolar
surface to remove inhaled dust particles.
In alveolar septum, they phagocytise RBCs that may enter the alveoli in heart failure.
What material is lung parenchyma rich in?
Elastic fibers (Abundance of elastic fibers present in lamina propria of bronchial tree and the alveolar septum)
Reticular fibers (Reticular fibers are present in the alveolar septum. Forms the framework of the lung parenchyma)
What is pleura?
Serous membrane that covers the thoracic structures.
What is the name of Inner layer attached to lung tissue?
Visceral pleura
What is the parietal pleura?
The outer membrane lining the thoracic
walls is the parietal pleura
What are visceral and pleural layers composed of?
Simple squamous cells (mesothelium) on a thin connective tissue layer containing collagen and elastic fibers
