Histology of the respiratory system 1 Flashcards
What is the function of the respiratory system?
To provide O2 and to remove CO2 from the blood
Name the two divisions of the respiratory system.
- Conducting airways
- Respiratory airways
What is the function of the conducting airways? (4)
warming, humidifying, cleaning and delivering air
What is the function of the respiratory airways?
gas exchange
List the elements of the conducting airways (7)
Nasal cavity
Nasopharynx
Oropharynx
Larynx
Trachea
Bronchi
Bronchioles (regular and terminal)
List the elements of the respiratory airways (4)
Respiratory bronchioles
Alveolar ducts
Alveolar sacs
Alveoli
What are the 4 basic tissues that make up (almost) every organ?
Epithelial tissue
Connective tissue
Muscular tissue
Nervous tissue
The conducting airways possess structures that ensure…
uninterrupted supply of air (bone, cartilage, smooth muscle and connective tissue which provide rigidity, flexibility and extensibility)
What structures in the conducting airways help remove foreign particles?
Serous glands
Mucous glands
Ciliated cells
Which structures allow breathing (form a ventilation mechanism)?
Thoracic cavity
Intercostal muscles
Diaphragm
Elastic properties of the lungs
Is the pressure between the parietal and visceral pleura
a) positive
b) negative
b) negative
Trachea is composed of 16-20 rings of…
hyaline cartilage (attached by dense fibroelastic connective tissue)
Name the first layer of the tracheal wall adjacent to the lumen and its two subcomponents
Mucosa:
1. pseudostratified columnar ciliated epithelium (respiratory epithelium)
2. lamina propria
Describe in detail the two layers of the mucosa in the trachea.
Pseudostratified columnar ciliated epithelium
* Columnar ciliated cells
* Goblet cells
Lamina propria
* Loose connective tissue
* Rich in elastic fibers
* Rich network of blood vessels (help bring nutrients to the trachea and warm the air, esp. in the winter)
After the mucosa, the next layer of the wall of the trachea is…
Name its 4 components
Submucosa
- Denser irregular connective tissue
* rich in elastic fibres - Hyaline cartilage
* 16-20 C-rings of hyaline cartilage embedded in submucosa
* fibroelastic connective tissue between the C-rings - Smooth muscle cells
- Serous and mucous glands
* these glands open into the lumen of the trachea
Cartilage is mainly composed of…
collagen fibers and cells called chondrocytes (secrete ECM, including collagen)
Cartilage and smooth muscle of the conducting airways are considered a part of the…
submucosa
What is the 3rd and outermost layer of the wall of the trachea?
Adventitia: dense irregular layer of CT
Connects the trachea to adjacent organs in the mediastinum.
Specify the type of epithelium that makes up the mucosa of the trachea
Pseudostratified columnar ciliated epithelium with goblet cells
Do not confuse cilia with microvilli! Describe each of the cellular projections.
Cilia:
* Hair-like projections found on the surface of certain epithelial cells
* Move in a coordinated, wave-like manner to move fluid, mucus and particles
* Composed of microtubules
Microvilli:
* Tiny, finger like projections on the surface of certain cells
* Primarily designed to increased the surface area for absorption
* Composed of actin filaments
What is the name of the smooth muscle in the trachea?
Trachealis muscle
Name all the cell types found in pseudostratified columnar ciliated epithelium (respiratory epithelium) (6)
- Columnar ciliated epithelial cells
- Goblet cells
- Brush cells
- Basal cells
- Small granule cells
- Serous cells
The most abundant cell type in the respiratory epithelium (pseudostratified columnar ciliated epithelium) are..
ciliated columnar cells
How many cilia does each columnar ciliated cell have on its luminal aspect?
~300 cilia
What is the second most abundant cell type in the respiratory epithelium? Describe its characteristics
Goblet cells
Apical cytoplasm (near lumen) contains mucous vesicles filled with glycoproteins (these are mucous cells).
Function of the goblet cells
Production of sticky mucous (to which foreign particles bind). They do so by releasing the glycoproteins from the mucous vesicles found in their apical cytoplasm.
What is the difference in staining between ciliated columnar cells and goblet cells in the respiratory epithelium?
Columnar ciliated cells are well stained, whereas goblet cells are poorly stained (appear paler).
Brush cells have … on their surface. Explain how this suggests their function in the respiratory epithelium.
Unlike columnar ciliated cells, brush cells have MICROVILLI on their surface. Microvilli are absorptive projections. This leads us to believe that brush cells play a chemosensory role in the airways (absorb particles that bind chemoreceptors).
What is the only way brush cells in the respiratory epithelium can be identified?
Electron microscopy
Give the name and function of small granule-containing cells in the lower part of the respiratory epithelium. What system do they belong to? Describe these cells
Small granule cells
* Part of the diffuse neuroendocrine system (DNES)
* Part of the argentaffin cell family
* Granules can absorb silver
* Granules contain hormones and peptides that cells release towards the lamina propria
* Secrete serotonin
The DNES produces…(2)
serotonin and epinephrine
What is the name of the short cells in the respiratory epithelium? Describe them.
Basal cells
* Short cells that rest on the basement membrane
* They are the stem cells of the respiratory epithelium (produce ciliated cell, small granule cells, goblet cells, etc.)
Smoking cigarettes can cause…
squamous metaplasia of the respiratory epithelium.
The columnar ciliated cells are replaced by tougher, flat squamous cells that can better withstand the chronic irritation. These cells do not have cilia, so the ability to clear mucus and debris is lost.
What is an axoneme?
It is the central structure of cilia, surrounded by plasma membrane.
What is the average length and diameter of cilia?
Cilia are around 5-10 um long and 0.2 um in diameter.
The axoneme is composed of…
9 pairs of microtubules surrounding a tenth, central pair.
How many basal bodies are there for each cilia?
1
What are basal bodies?
A structure similar to a centriole, lying immediately beneath the epithelial cell membrane. It is the origin of microtubules that make up the axoneme of cilia.
Describe the microtubule doublets of the axoneme.
Each doublet is made up of 1 complete microtubule (13 protofilaments) and 1 incomplete microtubule (10 protofilaments). 3 protofilaments are shared between the doublet.
Is the central microtubule pair complete or incomplete?
The central microtubule pair are made up of two complete microtubules (two singlets).
The 9 microtubule doublets of the axoneme are connected to each other by…
dynein arms
What is the role of radial spokes in the axoneme of cilia?
Radial spokes connect the 9 microtubule doublets to the central microtubule pair. They interact with dynein arms to generate ciliary movement.
Unlike the axoneme, the basal body is composed of … instead of doublets
microtubule triplets
Name two diseases resulting from mutations in the ciliary axoneme.
- Primary ciliary dyskinesia (PCD)
- Radial spoke protein 2 (RSP) mutations
Describe primary ciliary dyskinesia (PCD)
Caused by a mutation resulting in a lack of dynein arms, which renders cilia and sperm immotile or dysmotile
What are consequences of primary ciliary dyskinesia?
Impaired mucus clearing (bronchiectasis)
Chronic sinusitis
Male infertility
Name and describe a subset of primary ciliary dyskinesia (PCD)
Kartagener’s Syndrome
* Cilia are abnormal in movement
* Condition causes difficulty in clearing of mucus from the respiratory tract
* The defining characteristic of this condition is situs inversus
What is situs inversus? What disease is it seen in?
Situs inversus is a reversal of abdominal and thoracic organs. It is a defining characteristic of Kartagener’s syndrome.
Describe radial spoke protein mutations
Like PCD, radial spoke mutations result in immotile cilia and sperm.
Goblet cells produce a mucous made up of…
glycoproteins
How is the mucous produced by goblet cells secreted into the lumen of the airways?
Vesicles fuse with the apical plasma membrane of goblet cells and release glycoproteins (mucus) into the lumen of the respiratory tract.
Cystic fibrosis is caused by…
mutations of the CFTR gene.
CFTR gene mutations affect…
CFTR gene mutations affect the translocation of the CFTR protein to the apical plasma membrane of goblet cells. This disrupts the transport of chloride and water ions across the plasma membrane of epithelial cells, resulting in thick, dehydrated, sticky mucus buildup.
What are the consequences of cystic fibrosis?
The thick, sticky mucus buildup in CF leads to airway obstruction and predisposes to bacterial infection.
What organs/systems are affected by mutations in the CFTR gene (cystic fibrosis)?
- Respiratory system
- Pancreas
- Reproductive system (bilateral absence of vas deference and infertility)
Conchae are 3 bony shelf-like projections in the nasal cavity. What type of epithelium lines the conchae?
Superior conchae: olfactory epithelium
Middle and inferior conchae: respiratory epithelium
What separates the two chambers of the nasal cavity?
The nasal septum (made of bone and cartilage)
Olfactory epithelium (3)
- Found in the superior conchae of the nasal cavity
- Pseudostratified columnar epithelium
- Composed of 3 cell types: olfactory cells, sustentacular cells, basal cells
What are the 3 cell types of the olfactory epithelium?
- Olfactory cells
- Sustentacular cells
- Basal cells
Describe the cilia of olfactory cells in the olfactory epithelium (superior part of the nasal cavity)
- 6-8 cilia are found on the surface of the olfactory bulbs of olfactory cells.
- These cilia are non-motile and 70 um long.
- Each cilium is attached to a basal body
Cilia of olfactory cells have different structures proximally and distally. Explain.
Proximally: Axoneme contains the typical 9+2 doublet microtubules
Distally: Cilium becomes more narrow and contains 11 single microtubules
Why are olfactory cells considered modified bipolar neurons?
Because they have an axon (0.5um in diameter) that pierces the basement membrane and enters the lamina propria
Why do the axons of olfactory cells pierce the basement membrane?
In the lamina propria, axons of multiple olfactory cells join together to form fascicles of unmyelinated axons enveloped by Schwann cells. They synapse with the olfactory lobe of the brain.
Olfactory cell axons are…
a) myelinated
b) unmyelinated
b) unmyelinated
(these axons are enveloped by Schwann cells)
Most of the projections on the surface of the olfactory epithelium are…
What purpose do these projections serve?
Most of the projections are microvilli (NOT cilia).
They play a SENSORY role (absorb chemicals that bind chemoreceptors, producing the sensation of smell).
What is the role of sustentacular cells in olfactory epithelium
Sustentacular cells are covered in sensory microvilli. They provide support and stability to olfactory cells.
What is particular about olfactory bulb cilia?
They are immotile.
What are olfactory nerves called?
Olfactory nerves = collections of olfactory axons enveloped by Schwann cells
Filia olfactoria
What is the role of basal cells in the olfactory epithelium?
They are stem cells
What are Bowman’s glands? What is the role of their secretions?
Serous glands located in the lamina propria of the olfactory epithelium. They produce watery, mucus-like secretions that clear chemicals from the olfactory surface, allowing new odors to be sensed.
The filia olfactoria are…
a) unmyelinated
b) myelinated
a) unmyelinated
Filia olfactoria establish a … connection to the brain
a) direct
b) indirect
a) direct (synapse on the olfactory lobe of the brain)
What type of epithelium is found in the lower part of the nasal cavity?
Respiratory epithelium
Type of gland UNIQUE to the olfactory epithelium
Bowman’s glands
(even though there are serous glands in the respiratory epithelium of the nasal cavity too, they are not called Bowmans glands!)
What is the name of the glands found in the trachea? What are the two types of these glands?
Acinar Glands
- Serous glands
- Mucous glands
Where in the trachea are acinar glands located?
In the submucosa of the trachea
What is the difference between the two types of acinar glands?
Serous glands: Secrete watery, enzyme-rich secretions
Mucous glands: Produce sticky mucous, a thicker secretion
What is the perichondrium?
Dense layer of connective tissue surrounding the hyaline cartilage C-rings of the trachea.
Serous acini are surrounded by …
myoepithelial cells
What are the two components of the pulmonary bronchus?
- Extrapulmonary bronchus (surrounded by adventitia)
- Intrapulmonary bronchus (surrounded by lung tissue)
Describe the layers of the pulmonary bronchi
- Mucosa
* Wavy pseudostratified columnar ciliated epithelial with Goblet cells (fewer than trachea) - Lamina propria
* Loose connective tissue rich in elastic fibers - Submucosa
* Connective tissue
* Smooth muscle
* Serous and mucous glands that open into the lumen
* Pieces of hyaline cartilage - Adventitia
* Surrounds the extrapulmonary component of the bronchi
Why are there fewer Goblet cells in the bronchus?
Because excessive mucus in the lower airways would obstruct airflow.
How does the cartilage in the bronchus differ from that found in the trachea
It is fragmented, not one uniform structure
Only one type of gland is present in the distal segments of the intrapulmonary bronchi. Which type?
Serous glands (watery secretions)
What characterizes regular bronchioles?
Absence of cartilage, goblet cells and glands
What are the layers of the wall of regular bronchioles
- Mucosa (wavy appearance)
- Lamina propria (very thin)
- Smooth muscle
- Thin adventitia
What type of epithelial cell lines the inside of regular bronchioles?
Proximally, columnar ciliated cells and distally cuboidal ciliated cells.
Compare the quantity of goblet cells in the trachea vs regular bronchioles
Trachea: numerous goblet cells
Respiratory bronchioles: NO goblet cells
What is a possible consequence of the absence of cartilage in the bronchioles?
There is no solid tissue to keep the lumen patent (open), so smooth muscle spasms due to inflammation can block the bronchiole (asthma).
Parasympathetic stimulation (via vagus nerve) leads to… of bronchioles.
Sympathetic stimulation (via vagus nerve) leads to… of bronchioles.
Parasympathetic stimulation: contraction
Sympathetic stimulation: relaxation
How are terminal bronchioles different from regular bronchioles? (3)
They are histologically identical, except…
* they are smaller in diameter
* epithelium is cuboidal
* contain fewer ciliated cells and more non-ciliated club cells
The terminal bronchiole is less “wavy” than the regular bronchiole. Why?
There is less smooth muscle in the terminal bronchioles and more smooth muscle in the regular bronchioles.
What are the two types of cells that make up the simple columnar epithelium of the terminal bronchioles?
- Ciliated cells
- Club cells (non-ciliated)
What are club cells?
They are non-ciliated cells, also known as exocrine bronchiolar cells. They secrete surfactant and antimicrobial peptides.
What is the role of club cells?
Surfactant production
What is surfactant, and what is its purpose?
Surfactant is a mixture of phospholipids and 4 surfactant associated proteins that help spread surfactant material at the air-water surface. It decreases the surface tension on the inner surface of alveoli, preventing alveolar collapse.
What is the “first” structure of the respiratory airways?
Respiratory bronchioles
What characterizes respiratory bronchioles?
The epithelial lining of respiratory bronchioles is interrupted by the opening of alveolar sacs.
Where are club cells located?
In the respiratory epithelium of terminal and respiratory bronchioles
What is a respiratory sac? Identify it in your notes!
A cluster of alveoli at the end of a respiratory bronchiole.
What type of cell composes the majority of the epithelium of respiratory bronchioles?
Club cells (non-ciliated)
What is an alveolar duct?
A small tubule leading from the respiratory bronchioles to the alveolar sacs
What does the wall of the aveolar ducts look like?
Highly interrupted, because the wall of these alveolar ducts open into alveolar sacs
Each interruption in the wall of the alveolar duct wall opens into…
an alveolar sac
Alveoli are 200 um in diameter and lined by two types of cells.. (2)
- simple squamous cells (type I pneumocytes)
- tall, bulging cells (type II pneumocytes)
Alveoli are surrounded by…
a rich capillary network
What separates an alveolus from other alveoli? Describe this structure.
Each alveolus is separated from other alveoli by the septum.
The septum contains
* connective tissue
* elastic fibers
* capillaries
* small pores leading from one alveolus to another
There are approximately … alveoli, for a total surface area of…
There are approximately 300 million alveoli, for a total surface area of 140 m2.
Describe alveolar type I cells
- Represent 95% of the surface area of the alveoli
- Smaller than type II cells
Describe alveolar type II cells
- Larger but less numerous than type I cells
- Bulge out onto the surface of the alveolar septum
- Secrete pulmonary surfactant
What type of cell can be found INSIDE the lumen of alveoli? What do they do?
Free alveolar macrophages: ingest and digest carbon and any foreign particles that were not cleared from the airways before reaching the alveoli (phagocytosis).
How do macrophages compare to other cells in the alveoli?
Macrophages are the largest cells found in the alveoli (2x bigger than type II cells)
After some time, the free alveolar macrophages are filled with phagosomes full of foreign particles. Where do they end up?
They migrate to the connective tissue of the alveolar septum where they become permanently fixed (fixed macrophages)
What are lamellar bodies?
They are secretory granules found in pneumocyte type II cells that contain surfactant.
They contain surfactant components, i.e. phospholipids and proteins A, B, C and D)
Through what layers does gas exchange occur? (name the layers separating the air in the alveoli from the blood in the capillaries) (3)
- Endothelial cells (lining the capillary)
- Shared basement membrane
- Pneumocyte type I cells (alveolar epithelium)
Identify these layers in your notes!
What do the following 3 layers form?
1. Endothelial cells
2. Shared basement membrane
3. Pneumocyte type I cells
Air-blood barrier (1.5-2 um thick)
Why is the basement membrane of the blood-air barrier “shared”?
At the site of gas exchange, the adjacent cells (endothelial and type I) are so tight and close that the two basement membranes fuse into a single basement membrane.
Gas exchange between the alveoli and capillaries occurs via … across the blood-air barrier.
DIFFUSION
What is the respiratory distress syndrome of the newborn?
A life-threatening disorder of the lung caused by a deficiency of surfactant.
What respiratory syndrome is associated with prematurity?
Respiratory distress syndrome of the newborn
What is the leading cause of mortality among premature infants?
Respiratory distress syndrome of the newborn
What is emphysema
It is a chronic lung disease characterized by the destruction of the inter-alveolar wall (septum).
What is the major cause of emphysema?
Cigarette smoking
(probably impairs synthesis of elastic fibers)
Some forms of emphysema can be caused by increased elastase production. Elaborate.
Increased elastase production by MACROPHAGES can cause emphysema!
* Elastase is an enzyme that breaks down elastin
* Elastin is a key component of elastic fibers in the lungs
Overproduction of elastase by macrophages leads to the destruction of elastic fibers in the alveolar walls. This results in loss of lung elasticity and reduced ability to expel air from the lungs (obstructive disease).
What is the difference between the cartilage found in the pharynx and the cartilage found in the trachea?
The pharynx is composed of both elastic and hyaline cartilage.
The trachea only comprises hyaline cartilage.
What are chondrocytes and where are they synthesized?
Chondrocytes are synthesized in the perichondrium surrounding the cartilage of the trachea and bronchi.
Chondrocytes secrete ECM components, collagen and proteoglycans, at the basis of the structure and integrity of cartilage.
