Lecture/Lab: Respiratory System Flashcards
What makes up the respiratory system?
- Paired lungs
- A series of air passages that lead to and from the lungs
- Ventilation mechanism (diaphragm creates a low pressure environment)
What are the 3 principle functions of the respiratory system?
air conduction: bringing in air from external environment
air filtration: cleans the air
gas exchange (respiration): site of gas exchange. brining O2 into your blood stream
What is the function of serous fluid?
Serous fluid allows for the coupling of visceral and parietal pleurae
Result: free and rapid movement of the lung in relation to the chest wall. Able to pull the lungs open when you expand rib cage
Lubrication, not much friction as it moves
Conducting portion
Structure: varying levels of wall thickness
* Location: portions outside and inside the
lung
* Function: conduct and condition
* Conducting portion has regions outside and
inside of the lung
* Outside lung:
- Nasal cavity to primary bronchi
* Inside lung:
- Bronchi
- Bronchioles
- Terminal bronchioles
Respiratory portion
Structure: thin wall for efficient gas exchange
* Location: only in the lungs
* Function: gas exchange
* Includes respiratory bronchioles, alveolar
ducts and sacs
Two types of blood circulation in the lungs
Pulmonary circulation and bronchial circulation
Pulmonary circulation
Carrying O2-depleted blood to lungs for gas exchange - returns to heart as well oxygenated blood
What are the vessels within the pulmonary circulation and where are they located?
The pulmonary arteries and veins are the
functional vessels of the respiratory system:
Pulmonary arteries
* Carry deoxygenated blood
* Travel with the branches of the bronchi and bronchioles down to the capillary level
Pulmonary veins
* Carry oxygenated blood
* Located in connective tissue septum (do NOT run with the pulmonary artery)
Usually, arteries and veins are side by side. But in the pulmonary system, arteries are adjacent to the bronchioles as it reaches the alveoli, pulmonary veins are situated away with the CT septa of lungs
Bronchial circulation
Carrying oxygen rich blood to supply the tissues of the lung and airway
Bronchial circulation (nutrient arteries)
Nourish the tissues of the lung:
* Bronchial arteries are branches of the aorta
* Nourish connective tissues including the
walls of the bronchi and bronchioles, and pleura
* Found within the walls of the tissue
* Venous return of bronchial circulation can happen through the systemic system or anastomose with the pulmonary circulation
What type of capillaries are in the lungs?
continuous
because it needs to be the most selective so as to not get fluid or other things in the lungs
Lungs are the largest continuous capillary bed in the body.
What are the different materials in the RS and what so they do?
Cartilage
Hyaline cartilage
* C-shaped rings in trachea
* Plates become smaller at the level of the bronchi
(absent in the bronchioles)
Smooth muscle
* Regulates diameter of the airway
* Absent at the level of the alveolar sacs
Collagen fibers
* Primarily type I in upper regions
* Reticular fibers (type III) support capillary network
Elastic fibers
* Form a network that allow expansion (limited)
and recoil of the lung
* Increased in the distal aspect of the lungs
Too much collagen = not able to expand lungs
Too little elastic fibers = lungs can’t recoil = emphysema
Nasal cavity
Nasal Cavity
- Bony cavity that is divided into three regions
(meatus) by turbinates (concha)
- Majority is made up of respiratory epithelium:
ciliated pseudostratified epithelium
- Small portion in the upper concha is made up of
olfactory epithelium (specialized pseudostratified
columnar epithelium)
* Olfactory sensory neurons
* Sustentacular (support) cells
* Microvillar cells
* In the lamina propria: small olfactory
(Bowman’s) glands that produce specialized
mucous
Trachea
The wall of the trachea consists of the
following layers:
- Mucosa (pseudostratified epithelium, elastic rich lamina propria, no muscularis mucosae)
- Submucosa – glands present “Tracheal submucosa glands”
- Adventitia with C-shaped cartilage ring facing posteriorly
Tracheal epithelium
pseudo-stratified with 5 cell types
Ciliated cells
9+2 microtubules
- Maintain level of periciliary fluid in the periciliary layer (PCL) (layer of water and electrolytes)
- Forms a “mucociliary escalator” that clears mucous away from the airways (toward oral cavity; mucous can’t be too thick and inundate cilia, otherwise cilia can’t beat)
Mucous cells
- Mucinogen granules in cytoplasm
- The mucus floats on a serous fluid
- Cilia moves both serous and mucus toward the oral cavity
Brush cells
- Columnar cells with blunt microvilli
- Basal surface in synaptic contact with afferent nerve ending
- General sensory receptor cells
Brush cells are very difficult to observe in all but thin sections. They are recognized by their lack of cilia and mucus inclusions
Small granule cells
- Difficult to distinguish in light microscopy without special techniques
- Contain secretory granules
- May function in reflexes regulating the airway or vascular diameter
Basal and small granule cells are indistinguishable from each other without special stains
Basal cell
Stem cell for individual cell replacement in the epithelium
Basal and small granule cells are indistinguishable from each other without special stains
Where and how does metaplasia happen in the RS? What pathologies are associated with metaplasia?
Pseudostratified respiratory epithelium changes
to stratified squamous non-keratinized
epithelium
Removal of mucous impaired
Marked increase in the size of the mucus secreting glands of the submucosa in the trachea and large bronchi
Individuals must cough to clear secretions
Pathogenesis:
Inhaled irritants such as smoking
Reversible - if irritant eliminated
Bronchi
Starts at the bifurcation of trachea
The bronchus has the following layers:
- Mucosa - same epithelium, cells as trachea
- ***Muscularis - regulates diameter of airway, allows us to keep airways open
- Submucosa - glands present “BRONCHIAL SUBMUCOSA GLANDS”
- Adventitia/cartilage - plates smaller with decreasing diameter
What changes happen as you go from the trachea to the bronchi?
- Plates of cartilage that become smaller toward the bronchioles
- Layer of smooth muscle (muscularis) is found immediately below the mucosa layer
- Increase in elastic fibers
Bronchioles
No more cartilage
Airways that measure 1mm or less
Diameter increases/decrease with lung volume
Subdivided dependent on function:
- Terminal bronchioles - nonrespiratory (conducting airways)
- Respiratory bronchioles - function as sites of
gas exchange
Simple cuboidal epithelium
Gradual changes - no abrupt changes in this
system
From lab:
The last airway completely lined with a conducting (club cell) epithelium
What changes happen as you go from bronchi to bronchiole?
changes at the level of the bronchioles:
1. Bronchioles lack cartilage
2. Bronchioles lack submucosal glands
3. Note the thick layer of smooth muscle (organized in a spiral fashion)
4. Simple cuboidal epithelium: ciliated cells decrease in number and club cells increase distally
Club cells
Club cells manufacture “club cell secretory protein” that protects the epithelial lining as well as a surfactant-like substance that helps prevent collapse by reducing surface tension.
- Structure: Non-ciliated, dome-shaped apical aspect
projects into lumen
- Function: Detoxify harmful compounds in the air. Secrete a lipoprotein that prevents luminal adhesion. Mitotically active stem cell
- Location: Bronchioles
Outlined cell is a club cell. See the characteristic dome-shape apical surface and granules.
Terminal bronchiole
Most distal region of the conducting portion
Club cells with some ciliated cells
Respiratory bronchioles
- First region of gas exchange
- Wall is interrupted with alveoli
- Club cells (dominate) and some ciliated cells
From lab:
a passageway lined both with patches of club cell epithelium and patches of alveolar epithelium
Alveolar duct
Lined by type I and type II pneumocytes (AT1 & AT2 cells)
a passageway connecting adjacent alveolar sacs. Its outline is formed by the terminations of the alveolar walls
Alveolar sacs
Groups of alveoli clustered around a common air space
Epithelium: * type I pneumocyte (AT1 cells) * type II pneumocytes (AT2 cells)
the distal end of an alveolar duct, consisting of 8-12 alveoli
Type I pneumocytes (AT1 cells)
Structure:
- Thin, squamous cells with occluding junctions
Function:
- Provide a barrier optimal for gas exchange
Location:
- Cover 95% of the surface area of the alveolus
Type II pneumocytes (AT2 cell)
(also called septal cells)
Structure:
- Cuboidal secretory cells with apical cytoplasm that contains lamellar bodies
Location:
- Typically found at junctions and occupy 5% of the surface area
Function:
- Stem cell: type I and type II pneumocytes
- Continuously produce surfactant to prevent collapse of alveoli by reducing surface tension
Their location is most often at corners of the alveolar walls, where they can arrange themselves so as to take up the least amount of lumenal space possible.
Interalveolar septum
Thin region:
- Site of air-blood barrier, gas exchange areas
- Capillaries function in gas exchange
Thick region (pulmonary interstitium)
Composed of
- Collagen and elastic fibers
- Capillaries and lymphatic vessels
- Fibroblasts and immune cells
- Macrophages
Blood-Air Barrier (respiratory membrane)
Four components make up the blood air barrier:
- Thin layer of surfactant, 1st thing air comes iin contact with
- Alveolar epithelium (type I pneumocyte cytoplasm) –>thin squamous cell
- Fused basement membranes of the alveolar cell and the endothelial cell. Usually, under the basement membrane epithelium is CT. But here, you fuse the BM with the capillary underneath. Basal lamina of A1 cell is fused with the epithelial of the capillary
- Endothelial cell – specialized type for gas exchange and leukocyte diapedesis called aerocytes
Alveolar Pores
(pores of Kohn)
Functions include:
- Equalizing pressure in the alveoli
- Enable collateral ventilation, so that air doesn’t go only in one alveolus
- Allow macrophage migration
What are the two types of macrophages?
Alveolar macrophages and Interstitial macrophages
Alveolar Macrophages
- Function in luminal and airspaces of alveoli
- Some pass up the bronchial tree in mucus to
reach the pharynx - Some migrate to connective tissue where they
may stay with particles for the life of the
individual (dust cells) - Particles in the interstitium increase the
likelihood of lung damage - Less effective at stimulating an immune
response
From lab:
Alveolar macrophages crawl along the surfactant layer by extending pseudopodia, and thus are not permanently attached to the epithelium
Interstitial Macrophage
- Exist in the connective tissue
- Stimulates and coordinates with local and
systemic immune response
MALT/BALT
mucosa associated lymphoid tissue/bronchial associated lymphoid tissue.
lymphocytes in the trachea
Dense accumulations cells seen in the lamina propria and submucosa.
Though these cells are motile, they tend to congregate in areas where they are likely to encounter foreign antigen
Alveoli
the terminal cup-shaped passageways of the lung, lined with alveolar epithelium
Intrapulmonary bronchi vs extrapulmonary bronchi
Intrapulmonary bronchi retain some of the cartilage in their wall in the form of plates
can tell it’s intrapulmonary by looking at the alveolar tissue surrounding the bronchus
lamellar bodies
The intracellular surfactant, stored in lamellar bodies, gives the AT2 a bubbly appearance that may unfortunately be sometimes similar to macrophages
producing surfactant, a material that coats the apical surface of the alveolar epithelium and reduces the surface tension for gases, allowing them to better diffuse through to and from the circulation
Emphysema
Emphysema is any air-filled enlargement in the body’s tissues. Most commonly emphysema refers to the permanent enlargement of air spaces in the lungs, and is also known as pulmonary emphysema (From Google)
Too little elastic fibers = lungs can’t recoil = emphysema
(from lecture)
Key to recognizing this pathology is to note that alveoli in a normal lung are are always the same volume. A normal lung contains 100 millions of alveoli that, together with the other structures you have learned, should occupy the entire space.[2] To the extent that portions of the lung consist of larger spaces, capacity for gas exchange is lost.
