Structure and function of the airways Flashcards
Why does the trachea not have rings of cartilage?
There is the oesophagus running down the back of the trachea
So if rings went all the way around- they would impact swallowing food down the oesophagus
What is the shape of the cartilage in the trachea?
C shaped
What are the “basic” aspects of the airway?
airways, lungs, nasal passages
Go from the trachea down, what are the airways?
Trachea, primary bronchus, secondary bronchus (lobar), tertiary bronchus (segmental), bronchioles, alveolus
What provides mechanical stability to the airways?
cartilage (holds them open)
what type of branching does the airway have?
dichotomous branching
What happens at the alveolar region?
gas exchange
What are the components of the alveolar region?
Alveolar duct, alveoli, alveolar sac, respiratory bronchioles, terminal bronchiole (non-cartilaginous)
Where specifically in the alveolar region does gas exchange occur?
alveolar unit- capillary endothelium
What are the cells present in the pipework of the alveolar unit?
Type I cell, Type II cell, Macrophage, stromal cell (fibroblast)
What are type I cells?
very thin, delicate barrier (facilitate gas exchange)
What are Type II cells?
replicate to replace Type I, secrete surfactant and antiproteases
Part of xenobiotic metabolism
What is the role of surfactant in the lungs?
reduces surface tension
What is xenobiotic metabolism?
getting rid of bad stuff that has been inhaled in simple terms
The xenobiotic metabolism in the lung, an organ of first entry of xenobiotics into the organism, is crucial for inhaled compounds entering this organ intentionally (e.g. drugs) and unintentionally (e.g. workplace and environmental compounds).
How much do type I cells cover?
over 95% of alveolar surface
Are there more Type I or Type II cells?
more type II
What are 2 basic functions of the respiratory airways?
getting air efficiently to the gas exchange region, and keeping the pipework clear.
What are the conduits (pipes) for?
conduct O2 to alveoli, conduct CO2 out of the lungs
- for gas exchange
What are the conduits (pipes) facilitated by?
mechanical stability (cartilage)
control of calibre (smooth muscle)
protection and cleansing
What are the regions of the pharynx?
nasopharynx
Oropharynx
Laryngopharynx
What are the conchae in the nasal passage?
high vascularised- contribute to warming and humidification of intra-nasally-inhaled air
What do nasal hairs do?
they filter out large particles
What is the pharynx?
a common passage for food, liquids, and air
What is the organisation of airway structures (transverse section)?
What is the structure of the airway wall?
mucus layer–> cilia–> epithelial cells
What are the lining cells?
ciliated, intermediate, nursh, basal
What are the contractile cells?
smooth muscle (airway, vasculature)
What are the secretory cells?
goblet (epithelium), mucous, serous (glands)
What are the connective tissue cell types?
fibroblasts, interstitial cell (elastin, collagen, cartilage)
What are the neuroendocrine cell types?
Nerves, ganglia, neuroendocrine cells, neuroepithelial bodies
What are the vascular cells?
endothelial, pericyte, plasma cells (+smooth muscle)
What are the immune cells?
Mast cell, dendritic cell, lymphocyte, eosinophil, macrophage, neutrophil
How would you describe epithelial cells?
They have cilia
They have lots of mitochondria, because they are highly metabolically active, always wafting
What do goblet cells contain?
mucin granules
What do mucin granules contain?
mucin in a highly condensed form
What happens during mucin secretion?
expansion of intra-granular mucin upon secretion; to ATP
What do human bronchial glands have?
mucous and serous acini
What is the difference between mucous and serous acini?
mucous acini= more viscous mucus
serous acini= more watery mucus
What do mucous cells secrete?
mucus
What do serous cells secrete?
anti-bacterial enzymes (e.g., lysosomes)
What do airway submucosal glands secrete?
They also secrete water and salts e.g., Na+ and Cl-
How many cilia per ciliated cell?
roughly 200
What is the structure of a cilia?
What is the 9+2 referring to?
the microtubule arrangement
How do cilia beat?
in a metachronous beating/ metachronal rhythm
Why are there different fields of cilia?
They are out of time with each other
So overall mucus will move
Even though cilia go back and forth
What are the functions of the epithelium?
Secretion of mucins, water and electrolytes
Movement of mucus by cilia- mucociliary clearance
Physical barrier
Production of regulatory and inflammatory mediators
What is important about the secretion of mucins, water and electrolytes?
they are components of mucus (+plasma, mediators etc.)
What are the inflammatory mediators produced by the epithelium?
– Nitric oxide (NO - via nitric oxide synthase, NOS)
– Carbon monoxide (CO - via hemeoxygenase, HO)
– Arachidonic acid metabolites (e.g. prostaglandins – via COX)
– Chemokines (e.g. interleukin (IL)-8)
– Cytokines (e.g. GM-CSF)
– Proteases
What stains nitric oxide synthase?
anti-NOS antibody, brown staining
How can you “stain” for smooth muscle?
in culture- actin fluorescence
What happens to smooth muscle during inflammation?
structure: hypertrophy, proliferation
tone: (airway caliber) relaxation or contraction
secretion: mediators, cytokines, chemokines
What are the specific secretory functions of smooth muscle during inflammation?
bacterial products and cytokines lead to…
NOS and COX (cyclooxygenase)=> nitric oxide and prostaglandins
cytokines, chemokines, adhesion molecules=> inflammatory cell recruitment
What is the airway vasculature?
Tracheo-bronchial circulation (systemic)
What is the tracheo-bronchial circulation part of?
systemic- part of the systemic circulation that supplies nutrients and oxygen to the cells that constitute the lungs, as well as carrying waste products away from them
How much of the caridac output goes ot tracheo-bronchial circulation?
1-5%
What is the blood flow to airway mucosa?
100-150 mL/min/100g tissue (amongst the highest to any tissue)
Where do bronchial arteries arise from?
aorta, intercostal arteries and others
how does blood return from the tracheal circulation?
via systemic veins
How does blood return from the bronchial circulation?
Blood returns from bronchial circulation to both sides of heart via bronchial and pulmonary veins
What makes up the subepithelium microvasculature network of the trachea?
artery, capillary, vein
What is the function of the tracheo-bronchial circulation? (7)
- Good gas exchange (directly between airway tissues and blood)
- Contributes to warming of inspired air
- Contributes to humidification of inspired air
- Clears inflammatory mediators
- Clears inhaled drugs (good/ bad, depending on drug)
- Supplies airway tissue and lumen with inflammatory cells
- Supplies airway tissue and lumen with proteinaceous plasma (termed ‘plasma exudation’)
How is the airway function controlled?
Nerves
Regulatory and inflammatory mediators
Proteinases/ proteases e.g., neutrophil elastase
reactive gas species e.g., O2-, NO
How do nerves control the airways?
parasympathetic= cholinergic
sympathetic= adrenergic
sensory
How do regulatory and inflammatory mediators control the airways?
Histamines
Arachidonic acid metabolites (e.g., prostaglandins, leukotrienes)
Cytokines
Chemokines
What does the innervation of the airway look like?
What are the regulatory-inflammatory cells in the airway?
Eosinophils
Neutrophils
Macrophages
Mast cells
T lymphocyte
+ structural cells (e.g., airway smooth muscle)
What do structural cells, like the airway smooth muscle, do in terms of regulatory-inflammatory control?
(contraction, relaxation)
Secretion of mucins, water, etc.
Plasma exudation
Neural modulation
Chemotaxis
Remodelling
Can cells produce more than one mediator?
yes, and the mediators can do more than one thing
What are the mediators/ secretions/ whatever from the regulatory-inflammatory cells?
Histamine
Serotonin
Adenosine
Prostaglandins
Leukotrienes
Thromboxane
PAF
Endothelin
Cytokines
Chemokines
Growth factors
Proteinases
Reactive gas species
What are common respiratory diseases?
– Asthma – ~5% of population (industrialised countries)
– COPD – 4th cause of death in UK and USA
– CF – lethal autosomal recessive gene defect (~1:20 gene frequency; affects ~1:2,000 Caucasians)
What can cause chronic obstructive pulmonary disease?
smoking, cooking over open fire, very bad pollution
What are characteristics of respiratory diseases?
airway inflammation, airway obstruction, airway remodelling
What does dichotomous branching aid?
the efficient delivery of air into the alveoli
What is an example of homeostatic cleansing mechanism?
mucociliary clearance
What is the upper airway?
nasal passage,s they filter, warm and humidify nasally inhaled air
How many cell types are found in the airways?
at least 22
What can have a possible control over ciliary beating?
nitric oxide, cilia beat metachronally
Overall, what can the functions of the smooth muscle in the airway be split into?
contractile and secretory
How does airway relaxation occur?
via NOS containing nerves and adrenaline (adrenal glands)
What precipitates to lung disease?
Loss of homeostatic control
