Histology of Respiratory System Flashcards
What are the 2 portions of the respiratory system?
2 Portions:
Conducting Portion
Respiratory Portion
What are the components of the conducting portion?
Consists of all the components that condition air and bring it into the lungs: trachea, main bronchus, lobar bronchi, segmental bronchi, terminal bronchiole
What are the components of the respiratory portion?
Responsible for gas exchange: respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli
What are the histological features of the respiratory epithelium?
Pseudostratified ciliated columnar epithelium
- rests on very thick BM
- most abundant with long cilia on bulging apical ends
Identify the 3 types of cells of the respiratory epithelium.
3 Main Cell Types of Respiratory Epithelium:
- ciliated epithelial cells
- goblet cells
- basal cells
Role of Ciliated Epithelial Cells
Features: extend to the surface, possess cilia
Role: move the mucus toward lymphatics
Role of Goblet Cells
Features: mucinogen granules
Role: produce mucus
Where are stem cells in the respiratory epithelium located?
Located in the basement membrane
Most of the small rounded cells at the basement membrane are stem cells
Makeup ~30% of the epithelium
Identify the immune cells found in the respiratory epithelium.
Types of Immune Cells:
- mucus-secreting goblet cells
- intraepithelial lymphocytes
- dendritic cells: antigen-presenting cells; stimulate T cells
Give the functional significance of Cilia in respiratory epithelium
- film of mucus traps most airborne dust particles and microorganisms
- ciliary movements continuously propel the sheet of mucus toward the pharynx for elimination
What are brush cells and their characteristics?
Brush cells are another form of columnar cells
Characteristics:
- small apical surfaces
- short, blunt microvilli
What is the main role of olfactory epithelium?
-Olfactory epithelium contains olfactory chemoreceptors of the sense of smell
Where do olfactory receptor cells axons project?
-sends axons to the brain via small openings in the cribriform plate of the ethmoid bone
Give the histological features and cell types of the olfactory epithelium
Histology: pseudostratified epithelium
Cell types: basal stem cells, columnar support cells, bipolar olfactory neurons
-dendrites of these neurons have cilia specialized with many membrane receptors for odor molecules
How is the sense of odor detected and relayed to the brain?
Odor molecules bind to olfactory receptor cells - depolarization occurs, passing along basal axons to the olfactory bulb of the brain
Where is larynx located?
Between pharynx and trachea
What is the function of the Larynx?
Sound production: its wall contains skeletal muscles and pieces of cartilage for sound production (phonation)
Give the histological features of the larynx
- laryngeal vestibule is surrounded by seromucous glands
- lateral walls of this region bulge as a pair of vestibular folds
Identify the histological features of vestibular folds
- contain seromucous glands
- is areolar tissue with lymphoid nodules
- are largely covered by respiratory epithelium (regions near the epiglottis have stratified squamous epithelium)
- ventricles (narrow spaces) located below each large vestibular fold
- below each ventricle is another pair of lateral folds or cords
Identify the histological features of vocal cords
- covered by stratified squamous epithelium
- contains a large striated vocalis muscle and nearer the surface a small ligament
How is sound produced through vocal cords
Muscles cause variable tension of these ligaments that produces different sounds as air is expelled across the vocal cords
Give the major histological features of the trachea
- lines by typical respiratory epithelium
- connective tissue of the lamina propria lies below the RE
- seromucous glands are present in the lamina propria and submucosa
- submucosa also contains C-shaped rings of hyaline cartilage covered by perichondrium
Where do the primary bronchi enter the lungs?
- trachea bifurcates as right and left primary bronchi
- primary bronchi enter the hilum on the posterior side of each lung along with the pulmonary vessels, lymphatics, and nerves
- within each lung, bronchi subdivide further to form the bronchial tree
- bronchial tree is the last component of the air conducting system
Identify the branching features of a bronchial tree
bronchi –> bronchioles –> terminal bronchioles –> respiratory bronchioles –> alveolar ducts/sacs –> alveoli
Vestibules of nasal cavities
- epithelium: stratified squamous, keratinized to nonkeritinized
- musculoskeletal support: hyaline cartilage
- functions: filter and humidify air; has vibrissae (stiff hairs)
Most areas of the nasal cavities
- epithelium: respiratory
- musculoskeletal support: bone and hyaline cartilage
- functions: humidify and clean air; have glands and rich vasculature
Superior areas of nasal cavities
- epithelium: olfactory, with bipolar neurons
- musculoskeletal support: bone (ethmoid)
- functions: solubilize and detect odorant molecules in air
Nasopharynx and posterior oropharynx
- epithelium: respiratory and stratified squamous
- musculoskeletal support: bone and skeletal muscle
- functions: conduct air to larynx, pharyngeal, and palatine tonsils
Larynx
- epithelium: respiratory and stratified squamous
- musculoskeletal support: elastic and hyaline cartilage, ligaments, skeletal muscle
- functions: site for phonation, epiglottis closes while swallowing
Trachea
- epithelium: respiratory
- musculoskeletal support: C-shaped rings of hyaline cartilage with smooth (trachealis) muscle in posterior opening of each
- functions: conduct air to primary bronchi entering lungs; some MALT
Epithelium and Function of Bronchi
- epithelium: respiratory
- function: repeated branching;; conduct air deeper into lungs
Epithelium and Function of Bronchioles
- epithelium: simple ciliated cuboidal to columnar, with Clara cells
- function: conduct air; important in bronchoconstriction and vbronchodilation
Epithelium and Function of Alveolar Sacs
- epithelium: simple cuboidal between any alveoli
- function: conduct air; gas exchange
Give the major histological features of a tertiary bronchus
- the lining of respiratory epithelium and the mucosa are folded due to contraction of its smooth muscle; the wall is also surrounded by many pieces of hyaline cartilage
- contains many seromucous glands in the submucosa; these glands drain into the lumen
- arteries and veins are seen in the connective tissue surrounding the bronchi; these vessels branch as smaller vessels as they approach the respiratory bronchioles
- all bronchi are surrounded by distinctive lung tissue; lung tissue is characterized by many empty spaces of pulmonary alveoli
Give the histological features of the bronchial wall
- epithelial lining of bronchi; pseudostratified ciliated columnar cells with a few goblet cells
- lamina propria contains the distinct layer of smooth muscle surrounding the entire bronchus
- submucosa - site of supporting cartilage
- adventitia - blood vessels and nerves; surrounded by lung tissue
What are the prominent histological features of a large bronchiole?
- folded respiratory epithelium
- prominent smooth muscle
- supported only by fibrous connective tissue
What are the characteristics of the smooth muscle of bronchioles?
-smooth muscle has elastic fibers with high elastic content
Where are the elastic fibers present?
-elastic fibers present in the tunica media of large arteriola and to lesser extent in accompanying venule
What is the nature of epithelium in small bronchioles and terminal bronchiole?
Small Bronchioles: epithelium is columnar and ciliated
Terminal Bronchiole: epithelium is ciliated cuboidal cells and many low columnar nonciliated cells
Where are Clara cells present?
Terminal bronchioles*****, respiratory bronchioles, bronchioles
What are the histological characteristics of Clara cells?
nonciliated; have bulging domes of apical cytoplasm containing granules
What are the functions of Clara cells?
- secrete components of surfactant which reduces surface tension and helps prevent the collapse of the bronchioles
- also produce the secretory component for the transfer of: IgA into the bronchiolar lumen; lysozyme and other enzymes active against bacteria and viruses; several cytokines that regulate local inflammatory responses
Where are stem cells located in bronchiolar epithelium?
- give rise to all the cells within the bronchiolar epithelium
- also included among Clara cells
What are the components of the respiratory portion?
- respiratory bronchioles
- alveolar ducts
- alveolar sacs
- alveoli
What gives rise to respiratory bronchiole?
- similar to terminal bronchioles except for the presence of scattered alveoli along their length
- pulmonary blood vessels travel with the bronchioles
What structures surround each alveoli?
a dense layer of branching capillaries travel with the bronchioles
What are the histological features of respiratory bronchioles
- lung tissue has a spongy structure (due to alveoli)
- branching continuity with alveolar ducts and sacs
- have a layer of smooth muscle and some regions of cuboidal epithelium
- runs along a thin-walled branch of the pulmonary artery
- branches of the pulmonary vein course elsewhere in the parenchyma
- alveolar ducts and alveoli
What is the histology of alveoli?
Alveolar ducts consist of a linear series of alveoli
- each with smooth muscle fibers around the opening
- end in two or more clusters of alveoli called alveolar sacs
- individual alveoli all open to the sacs or ducts
What are the components of the air-blood barrier?
Air-blood barrier: gas exchange between air and blood occurs at a membranous barrier between each alveolus and the capillaries surrounding it
Components: alveolar type I cell, endothelial cell, their fused basement membranes
Where does gas exchange take place at the air-blood barrier?
Oxygen diffuses from alveolar air into capillary blood and carbon dioxide moves in the opposite direction
The inner lining of alveoli is covered by a layer of surfactant which lowers fluid surface tension and prevents the collapse of alveoli
Compare the features and functions of alveolar Type I and Type II cells
Type I alveolar cells: Squamous; line almost entire alveolus surface; gas exchange occurs across these cells
Type II alveolar cells: line a bit of each alveolus; are large rounded cells; often bulge into the alveolus; have many functions of Clara cells, including the production of surfactant
Where are alveolar macrophages present?
Present in alveoli or in interalveolar septa
What is the role of alveolar macrophages?
Clean debris to avoid hindrance of gas exchange
Outline the steps involved in surfactant production by type II cells
- protein-lipid complexes are synthesized initially in the ER and Golgi apparatus
- further processing and storage in large organelles: lamellar bodies
- smaller multivesicular bodies form initially
- the vesicles in multivesicular bodies are added to lamellar bodies
- surfactant is secreted continuously by exocytosis (forms an oily film containing phospholipids and surfactant protein)
What is asthma?
A chronic inflammatory disease of the airways characterized by episodes of acute bronchoconstriction
Symptoms: shortness of breath, cough, chest tightness, wheezing, rapid respiration
What are the histological changes occurring in asthma?
Airflow obstruction in asthma is due to bronchoconstriction that results from:
Contraction of bronchial smooth muscle
Inflammation of the bronchial wall
Increased secretion of mucus
What is COPD?
A chronic, irreversible obstruction of airflow that is usually progressive and characterized by persistent symptoms
Symptoms: cough, excess mucus production, chest tightness, breathlessness, difficulty sleeping, fatigue
What is the greatest risk factor for COPD?
smoking
What are the histological changes in COPD?
there is small airway fibrosis
Obstruction and/or destruction of alveoli and of elastin fibers in the lung parenchyma
What is pleura?
A serous membrane (serosa) associated with each lung and thoracic cavity
Parietal pleura
lines the inner surface of the thoracic cavity
Visceral pleura
Covers the outer surface of the lung
Pleural cavity
narrow space between the pleuras
What are the histological features of pleura?
Simple squamous mesothelium on a thin layer of connective tissue
