Histology Of The Respiratory System Flashcards
Upper vs lower respiratory tracts histologically divisions
Upper (dervived from the embryonic oral cavity)
- nasal cavities
- paranasal sinuses
- nasopharynx
- oropharynx
Lower (dervived from the ventral layrngotracheal diverticulum of the foregut)
- everything below the larynx and larynx
What part of the respiratory system is the laryngopharynx a part of?
It is not part of the respiratory system
Instead it is part of the alimentary canal
Conducting portion vs respiratory portion functional divisions
Conducting
- nasal cavity -> pharynx/larynx -> terminal bronchioles -> tracheobronchial tree
- functions to provide passage of air from external environment -> lungs as well as warm and humidify the air and filter it
Respiratory
- respiratory bronchioles, alveoli, ducts
- functions as the site of gas diffusion between air and blood
Secondary functions of the respiratory system
Aids in vocalization
Aids in smell
Aids in BP regulation
Aids in immune responses and endocrine signaling
Layers of the conducting portion in the respiratory system
deepest -> superficial
1) mucosa
- innermost layer of the conducting portion and provides the physical barrier between the external environment and the internal environment of the respiratory organs
- it is the ONLY layer found throughout all of the respiratory tract (both conducting and respiratory parts) and in the nasal cavity
- composed of epithelium w/ lamina propria (these two parts are cardinal to all mucosa layers)
2) muscularis
- consists of circumferential smooth muscles and is only found in the intrapulmonary bronchi/conducting bronchioles
- regulators diameter of passageways
3) submucosal
- found in the entire conducting portion of the respiratory system
- acts as a larger lamina propria
4) cartilaginous layer
- found ONLY in the trachea and bronchi
- contains hyaline cartilage and supports the airway so it doesnt close during exhalation
5) adventitia
- outermost layer of the respiratory tract
- consists of loose areolar CT which helps interconnect all the organs, as well as provide passageways for the large vessels of the respiratory tract
Lamina propria
Part of the mucosa layer that is highly vascularized
Contains the exocrine glands of the respiratory tract such as lymphoid tissues and BALT
Ciliated cells
Cells in the epithelium that function to move mucous and entrap particles up the passageway
found in both the conducting and respiratory parts
Mucous (goblet) cells
Cells in the epithelium that function to secrete and synthesis mucus
- only found in the conducting part*
Brush cells
Cells in the epithelium that function to detect noxious chemicals/stimuli in the respiratory system
are nociceptive cells w/ apical microvilli and innervated by afferent nerve endings
Small granule (kulchitsky) cells
Found within the epithelium only at the basal domain
Function as part of the neuroendocrine system and can receive/generate endocrine signals
Basal cells
Cells found in the epithelium that function to act as stem cells for the respiratory system
Club (Clara) cells
Cells in the bronchiole epithelium ONLY
- secrete surfactant lipoproteins
- secrete mucin
- detoxification of inhaled xenobiotic compounds
- secretes antimicrobial peptides and cytokines
- act similar to specialized goblet cells*
Squamous metaplasia
Damage to the respiratory epithelium (usually chronically) causes the ciliary epithelium (simple columnar) to be replaced by stratified squamous cells
- can lead to precancerous cell dysplasia
Primary ciliary dyskinesia (kartagener syndrome)
Genetic disorder of the Dynein proteins in the ciliated cells.
- this prevents the ciliated cells to move mucous through the respiratory system
Often causes respiratory infections and squamous metaplasia
Cystic fibrosis
Genetic disorder of the chloride ion channels which results in a thickening of mucus from the goblet cells
- can cause similar issues to kartanger syndrome
Parts of the nasal cavity
Nasal vestibules
- lined w/ stationed squamous epithelium and transitions between keritinzed and unkeritinized forms
- entrap large particles
Olfactory region
- superior nasal concha and cribiform plate area (sphenoethmoid recess)
- lined with specialized olfactory mucosa w/ olfactory neurons embedded within the mucosa
Respiratory region
- inferior/middle nasal concha region
- lined with respiratory mucosa (which is ciliated pseudostratifeid columnar epithelium w/ goblet cells)
- lamina propria in this region is extra vascularized
- brush cells are found here and directly communicate with maxillary and ophthalmic divisions of the trigeminal nerve
- entrap smaller particles, warm air, acknowledges noxious stimuli and facilitates blood flow
Chemethesis
NOT the same as olfaction or taste
Response and acknowledgement of noxious Stimuli and requires somatic and visceral afferent fibers to measure
Chemothesis, taste and olfaction often occur at the same time, but their signals are transmitted and received differently
Olfactory neruons pathways in the olfactory region
Cell bodies reside in the epithelium w/ dendrites extending into the nasal cavity (apical dendrites) and the cribiform plate (basal dendrites)
Neurons from the cell bodies synapse onto the olfactory bulb and transmit signals through the olfactory tract
Larynx histologically facts
Outlined primarily by respiratory epithelium, with patches of stratified squamous (usually around epiglottis and vocal folds)
Each focal fold of the larynx is composed of dense, elastic vocal ligaments, a deep vocalis muscle and overlying stratified squamous epithelium
Innervation
- sensory = nasopharynx/oropharynx is glossalpharyngeal, mucosa is the vagus nerve
- motor = vagus nerve (except stylopharyngeus muscle which is glossopharyngeal
Laryngitis
Inflammation of the larynx, usually due to viral infection sand edema of the lamina propria
Benign reactive polyps (singers nodules)
Hyperplasia of the stratified squamous epithelium of the vocal folds due to overuse
Trachea histologically facts
Similar mucosal layers of the respiratory epithelium except there are no club cells here
- numerous goblet and brush cells thou
Lamina propria layers possess a distinct basement membrane, lymphoid nodules, seromucous glands and BALT
Possess a unique cartilaginous, C-shaped hyaline ring
Bronchi histologically facts
Decreased number of goblet and brush cells
As bronchi get smaller, the lamina propria get smaller and fewer seromucous glands.
Muscularis layer is always present in bronchi and becomes more prominent as bronchi get smaller.
Cartilaginous plates are present
Basement membrane is present but somewhat small
- gets smaller as you move from primary -> secondary -> tertiary
Adventitia layer is continues with lung tissue and isn’t very distinguishable
Bronchioles
No cartilaginous plates are present
Simple, ciliated columnar/cuboidal epithelium w/ very few goblet cells being present
Club cell numbers are present and increase as bronchiole size decreases
- produces CC-16 material (which is used as a marker for lung damage)
Lamina propria and submucosal layers decrease in thickness and lack seromucous glands
Basement membrane is almost nonexistent
Muscularis layer is present that may or may not be more thick
Dry vs wet coughs
Coughing is a reflex action caused by infection or irritations
Bronchitis vs bronchiolitis
Bronchitis = inflammation of the bronchi
Bronchiolitis = inflammation of the bronchioles
Bronchospasms
Sudden constriction of smooth muscles that obstructs the airway initiated by rapid degranulation of mast cells
- often seen in asthma or allergic attacks
Atelectasis
Collapse of the pulmonary lobules due to airway obstruction
Terminal vs respiratory bronchioles
Are both bronchioles but terminal is the last part of the conducting portion, whereas the respiratory is the first part of the respiratory portion
Also, the respiratory bronchioles possess individual alveoli in outpocketings of the wall (but not continuous/numerous)
respiratory bronchioles are the first site of gas exchange
Alveoli cell types
Four main types
Type 1
- thin squamous cells form the barrier between air space and lung tissues
- make up 95% of the alveolar surface
- cannot mitosis
Type 2
- cuboidal cells that replenish type 1 alveolar cells when damaged and also produce surfactant
- make up 60% of the total number of cells residing in alveoli
- can mitosis
Brush cells
- scarce but are present and serve as noiceptors
Dust cells
- macrophages in the lamina propria in the alveolus
- phagocytize foreign objects in the alveolar spaces
When is the functional respiratory system official in neonates?
End of 2nd trimester (25th week)
- at this time, the type 2 alveolar cells can effectively produce mature surfactant
Pulmonary vessels
Arteries = Carry O2 poor blood to the lungs for gas exchange
- are closer to the bronchial tree
- possess a larger tunica media
Veins =Carry O2 rich blood to the heart To be used by the systemic circuit
- largest vessels in the pulmonary system
- are often isolated within alveolar tissues
- possess a larger tunica adventitia
Nervous tissues in the pulmonary system
Innervation consists of visceral afferents which provides pain and homeostatic feedback
Sympathetic fibers produce bronchodilation
Parasympathetic fibers produce bronchoconstriction
Major regulator of the microvasculature vasomotor activity is the local oxygen levels themselves
Major regulator of the macro vasculature vasomotor activity is the ANS
Diffuse alveolar damage (adult respiratory distress syndrome)
Injury to the alveolar walls and capillary beds often caused by one or more of the following
- infections
- inhalation of toxic fumes
- over excess of oxygen
Emphysema
Chronic lung diseases or damage causes permanent dilation of bronchioles and loss of walls/cells of the respiratory portion of the system
Lung cancers brief overview
most commonly occurs within the epithelium of the bronchi
Squamous cell carcinomas
- cancer derived from prolonged squamous metaplasia and dysplasia
Adenocarcinomas
- originates from epithelial lining of the exocrine glands
Small cell carcinomas
- originates from the small granule (kulchitsky) cells
Mesothelioma
- originates within the pleura membrane
