Respiratory System Histology Flashcards
What are the functions of the respiratory system?
* Supplies oxygen to the blood for delivery to cells throughout the body
* Removes carbon dioxide that has been accumulated in the blood from body tissues
* Phonation (speech)
* Olfaction (smell)
* Lungs function in blood pressure control via renin-angiotensin system
What is the function of the renin-angiotensin system in the lungs?
Control of blood pressure
Explain the process of the renin-angiotensin system in the lungs
Angiotensin I is converted to angiotensin II via angiotensin-converting enzyme (ACE) in the lung capillaries
Explain the flow of air through the lungs
* Air enters the nose or mouth
* Travels via the pharynx and larynx into the trachea
* Trachea branches into the principal bronchi to convey the air to the lungs
* In the lung, each bronchus divides into smaller bronchi which divide into smaller bronchioles
* These bronchioles terminate in the alveolar sacs where gas exchange occurs
What are the functions of the nasal cavity?
* Warming inspired air
* Moistening inspired air
* Filtering inspired air
What cell types are present on the roof of the nasal cavity?
Olfactory epithelium
What is the initial part of the nasal cavity called?
The vestibule
What cell type is the vestibule lined with?
Keratinised stratified squamous epithelium
What is the rest of the nasal cavity (excluding vestibule) lined with?
Respiratory epithelium - pseudostratified, ciliated, columnar epithelium with goblet cells
What cells line the conducting part of the respiratory system?
Respiratory epithelium - pseudostratified, ciliated, columnar epithelium with goblet cells
Name the structures labelled 1-5
1) Pseudostratified, ciliated, columnar epithelium with goblet cells 2) Goblet cell 3) Basal cell (stem cell) 4) Cilia 5) Lamina propria/submucosa
What is the purpose of cilia?
Clearance of mucous
What is the purpose of goblet cells?
Production of mucous
Which areas of the respiratory tract have respiratory epithelium?
* Nasal cavity
* Nasopharynx
* Conducting airways
Which areas of the respiratory tract have stratified squamous epithelium?
* Vestibule
* Oropharynx
* Laryngopharynx
Where are olfactory epithelium located?
Olfactory mucosa
What lies beneath the respiratory epithelium?
Lamina propria
What is the lamina propria?
A band of connective tissue containing seromucous glands and a rich venous plexus
What happens to the venous plexus in the lamina proper in an allergic reaction?
Release of histamine causes the blood vessels to become engorged which āblocksā the nose
What cell type lines the oropharynx?
Non-keratinsed, stratified, squamous epithelium
What cell type lines the posterior surface of the epiglottis?
Non-keratinsed, stratified, squamous epithelium
Why is the oropharynx lined with non-keratinsed, stratified, squamous epithelium?
The oropharynx transmits both air and swallowed food - it must resist abrasion
What cell type lines the larynx?
Respiratory epithelium
What cell type is the anterior surface of the epiglottis lined with?
Respiratory epithelium
Which areas of the larynx are not covered with respiratory epithelium?
Vocal folds and adjacent structures
What are vocal folds and adjacent structures lined with?
Stratified squamous epithelium
Why are vocal folds lined with stratified squamous epithelium rather than respiratory epithelium?
Respiratory epithelium would be damaged by vocal folds rubbing together
What does trachea terminate into?
Right and left main bronchi
How many tracheal rings are there?
Trachea contains 15-20 āCā shaped cartilages
What lines the open side of the āCā of the cartilage?
* Fibroelastic tissue * Smooth muscle
What are tracheal rings composed of?
Hyaline cartilage
What happens if you cut the hyaline cartilage of the trachea?
It will collapse on itself
Explain the composition of the walls of the trachea
The wall of the trachea includes:-
* A lining of respiratory epithelium backed by a basal lamina
* A lamina propria of connective tissue with abundant elastic fibres
* A submucosa of connective tissue that includes numerous seromucous glands
What effect does smoking have on the airway epithelium?
Can paralyse the cilia, meaning mucous cannot be cleared from the airways
What happens to the āringsā of cartilage once the trachea bifurcates into the 2 main bronchi?
The āringsā of hyaline cartilage are replaced by irregularly shaped cartilage plates
What are the walls of the bronchi composed of?
* Respiratory epithelium (RE) * A lamina propria (LP) * A muscularis consisting of a ring of smooth muscle * A submucosa (SM) with adipose tissue and some seromucous glands
What happens to the cartilage as bronchi branch and become smaller?
Cartilage becomes more discontinuous and is finally lost when the airway is about 1mm in diameter
When is cartilage lost?
When the airway is about 1mm in diameter (i.e. bronchioles)
What are bronchioles?
Smaller airways lacking cartilage
What are features of bronchioles?
* Less than 1mm in diameter * Lack cartilage and glands * May contain a few goblet cells
What happens to the airway epithelium as you progress down the respiratory tree?
The epithelium decreases in height from columnar to cuboidal as you progress down the respiratory tree to the smallest bronchioles
What is the lamina propria composed of in bronchioles?
* Smooth muscle * Elastic and collagenous fibres
What are terminal bronchioles?
The smallest bronchioles that lack respiratory (gas exchange) function
What are respiratory bronchioles?
First part of the respiratory tree that has respiratory function (gas exchange)
What are 2 types of bronchiole?
* Terminal * Respiratory
How is the diameter of the bronchiole narrowed and widened?
The smooth muscle (SM) of the bronchioles respond to parasympathetic innervation, histamine and other factors by contracting and constricting
Why is the smooth muscle response to histamine and other factors significant?
Plays a significant role in asthma attacks and allergic reactions
Why can smooth muscle contraction in bronchioles cause collapse of the lumen?
They have no cartilage to give support
What are terminal bronchioles lined with?
Cuboidal ciliated epithelium that contain non-ciliated club cells
What specialised cell type do terminal bronchioles contain?
Club cells (also known as Clara cells)
What are the functions of club cells?
* Stem cells * Detoxification * Immune modulation * Surfactant production
How are club cells able to avoid sticking together and collapsing when breathing out?
Produce an anti-adhesion factor
What are alveoli lined with?
Discontinuous squamous type 1 alveolar cells
What is the beginning of the respiratory portion of the airways?
The respiratory bronchioles
Where is the conducting portion of the airways?
Extends from trachea to the terminal bronchioles
Does the conducting portion have respiratory function?
No exchange of oxygen/CO2 with blood occurs in these airways
What structures are alveoli associated with?
* Respiratory bronchioles * Alveolar ducts * Alveolar sacs
Why does gas exchange not occur in the conducting portion of the airways?
The walls are too thick
What are alveoli?
The terminal portions of the bronchial tree
What are responsible for the spongy nature of the lungs?
Alveoli
How many alveoli are contained within each lung?
Around 300 million
What 2 cell types line alveoli?
* Type I alveolar cells * Type II alveolar cells
What are alveolar cells called?
Pneumocytes
What are type I alveolar cells?
Simple squamous epithelium that lines the alveolar surfaces covering over 90% of the alveolar surface
What percentage of alveolar surface is covered by type I alveolar cells?
Over 90%
What is the function of type I alveolar cells?
Provide a barrier of minimal thickness that is permeable to gases
What are features of type II alveolar cells?
* Polygonal in shape * The free surface is covered by microvilli * The cytoplasm displays dense membrane bound lamellar bodies which contain surfactant
What is the function of type II alveolar cells?
* Release surfactant by exocytosis which spreads over the pulmonary surface to reduce surface tension * Prevents alveolar collapse
What are alveolar macrophages (dust cells)?
Free cells either in the septa or migrating over the luminal surfaces of the alveoli
What is the function of alveolar macrophages (dust cells)?
Phagocytose inhaled particles that may have escaped entrapment by the mucous lining of the airway
What happens to alveolar macrophages once they have phagocytosed particles?
* Will migrate up the bronchial tree, transported by ciliary action, to the pharynx where they are swallowed * Or will move into the septal connective tissue where they will remain
What is alveolar septa?
Separate adjacent alveoli in the lung tissue
What structures move between (permeate) the alveolar septa?
Capillary networks - allows gas exchange between blood and air
What does the air-blood barrier consist of?
* Type I alveolar cell (pneumocyte) and associated basal lamina * Endothelial cell of capillary and associated basal lamina
How thin is the air-blood barrier?
200-600nm (0.2-0.6um)
What is the lung surrounded by?
Visceral pleura that is multi-layered
What are the layers of the visceral pleura?
* Outer layer of simple squamous epithelium called mesothelium * Backed by layers of fibrous and elastic connective tissue
What exists between the parietal and visceral pleura?
Pleural cavity containing a small amount of pleural fluid
Which layer of the visceral pleura faces the parietal pleura?
Mesothelium
