Histopathology of the respiratory tract Flashcards
Pseudo stratified epithelium
Known as respiratory epithelium. Contain cilia that traps particles in mucus produced by goblet cells Not stratified, exists as a bi-layer.
In smokers there is goblet cell hyperplasia
Bronchial epithelium contains neuroendocrine cells taht release hormones e.g. 5HT and calcitonin.
Conduction part of the airway
Conducting part: From the nasal cavities to the terminal bonchioles. 150ml anatomical dead space
Respiratory part: Respiratory bronchioles and alveoli. Respiratory bronchioles have alveoli embeded in their walls. 3 litres
Functions of the nose
Provides a large surface area for warming and moistening inspired air.
Air is humidified by serous and mucus secretions and warmed by underlying blood vessels
Hairs, cilia and mucus help to trap particulate matter.
Cells of the nasal part of the respiratory tract
Psudostratified ciliated epithelium
Brush cells (olfactory epithelium)
Basal ceclls
Goblet cells
Lamina propria
Seromucus glands
Rich vascular plexus.
Four layers of the trachea
Mucosa:
Submucosa:
(loose connective tissue with mixed serous and mucus glands. Particles get trapped in the mucus which floats on serous secretions. Beating of cilia in epithelial cells sweeps secretions towards the oral cavity to be excreted.)
Fibrocartilage:
(C-shaped cartilage rings connected by connevtive tissue which prevent the trachea from collapsing. Joined at the back by muscle)
Adventitia
(psuedostratified, ciliated columnar epithelium. Lamina propra)
What is respiratory epithelium also known as?
Pseudostratified ciliated columnar epithelium.
Base of the cells rests on the basement membrane (simple). Epithelial cells are arranged at different heights and nuclei seen at different levels (stratified) - hence pseudo stratified.
Contains ciliated cells (most abundant)
goblet cels (mucus)
Basal cells (close to the BM, act as stem cells)
Brush cells (columnar cells with short microvilli, olfactory epithelium)
Structure of the bronchi
Pseudostratified columnar ciliated epithelium (with goblet cells)
Lamina propria ( glands)
Bundles of smooth muscle
Submucosa (contains serousmucus glands)
Cartilage plates
What are the histological changes that occur between the trachea and the bronchi?
pseudostratified epithelium becomes shorter
cartilage rings diminish to patches
thicker regular smooth muscle
Histological featrues of bronchioles
No nucus glands
Ciliated columnar epithelium
Increasing numbers of clara cells (ciliated cells that secrete GAGs)
Smooth muscle wall
Where are clara cells found?
In the bronchioles (most commonly in terminal bronchioles).
Act as stem cells, modulating inflammation (have an anti-oxidant and anti-protease activity)
Cell types in the alveolar epithelium
Type 1 pneumocytes: gas exchange
Type II pneumocytes: regeneration and surfactant production
Cells are very thin and flat, providing maximum surface area for gas exhange in the lung
Function of surfactant
Lipid-rish secreteion which acts to reduce surface tension in the lung.
Has two layers - osmophillic layer and an aqueaous layer.
Surfactant proteins act as opsonins.
Function of alveolar macrophages
Recruited from blood as monocytes
Main phagocytic cell of the lung
Remove the majority of foreign material entering alveoli
More numerous in smokers
Most removed by mucociliary escalator
Some migrate to hilar nodes (metastatic spread)
Structure of the olfactory mucosa
supporting cells – columnar cells with brush (microvilli) boarder.
basal cells
immature / differentiating olfactory neurones
mature olfactory neurone – bipolar neurones
Olfactory glands (Glands of Bowman) – secrete odorant binding protein (OBP)
Rich vascular plexus – of cavernous or erectile tissue. Hence the feeling of swelling in the nose is severe colds etc.
Cellular response to injury in the lungs
Type 1 pneumcytes die
Exudate and inflammatory cells fill the alveoli
Organisation of exudate occurs
Describe the pathology of acute respiratory distress syndrome
In ARDS the integrity of the alveolar capillar membrane is compromised by endothelial and epithelial injury.
This causes increased vascular permeability and alveolar flooding of fibrinous transudate causing diffuse alveolar damage and reducing the diffusion capacity of the alveoli.
Protein rich exudate traps debris of dead alveolar epithelial cells and forms a hyaline membrane. Lungs fill with granulation tissue. Cells becomes hypoxic and die. As a result lungs becoe stuff and do not respond to ventilation.
Resolution requires resorption of the exudate and dead cells by macrophages. Type II pneumocytes proliferate to restore the damaged epithelium and differentiate into type I pneumocytes. Loss of function dependent on extent of fibrosis.
