Structure and Function of the airways Flashcards
What does the trachea split into?
Bronchi
What is the name given to the type of branching that splits into two?
Dichotomous branching
Why is the cartilage ‘C’ shaped?
Mechanical Stability
What is the alveolar region made of?
Alveoli
Alevolar duct
Alveolar sac
Repiratory bronchioles
What is the function of the alveolar region?
Gas Exchange
What is the structure of an alveolar unit?
Alveolar macrophages = phagocytosis (ingest particles) = clean
Type I cell = v. thin, facillitates gas exchange between the alveoli and blood
Type II = replicate to produce more type I cells when the Type I cells get damaged, secrete surfactant (reduced surface tension), antiproteases and nullify toxins
Xenobiotic metabolism
Describe the image, spot where the Type I and Type II cells are?
(Two fried eggs)
Type I cells- incredibly thin like fried eggs
Cover 95% of alveolar surfaces
Type II cells: Greater number than type I but only cover 5% of surface
What are the basic functions of the respiratory airways?
Getting air efficently to the gas exchange region.
Keeping the pipework clear
Conduct O2 to the alveoli, allow for CO2 to exit
What are the basic functions of the airways faciliatated by?
Mechanical stability (cartilage)
Control of calibre (smooth muscle)
Protection and ‘cleansing’
What structure prevents air being taken into the stomach and food into the lungs?
Epiglottis
What are conchae? Where are they found?
Thin, scroll-shaped bony elements forming the upper chambers of the nasal cavities
Lots of vasculature = warming of air before it goes down
Nasal hairs = filter out the hair (first line of defence in protecting the lower airways
How are the airway structures organised?
Not a full circle of cartilage (C-shaped) = improve mechanical stability
When the smooth muscle contractes, it squeezes some of the mucus out
Many vasculature - fill tracheal tissue with oxygen
Goblet cells = produces mucus
Cilia
What are the different airway cell types?
Lining Cells
Contractile Cells
Secretory Cells
Connective tissue
Neuroendocrine
Vascular cells
Immune cells
What cells are Lining cells?
Ciliated
Intermediate
Brush
Basal
What are the three layers of the airway wall?
Mucus Layer
Cilia
Epithelial cells
Why are there many mitochondria in the ciliated cells?
Mitochondria = provide ATP to power sweeping motion of cilia
What is mucin secretion? Where is it from? How is it stimulated?
from goblet cells
Size expansion = intragranules release their contents
Enormous capacity
What is the role of the submucosal glands?
Washes mucus secretion to the collecting duct
Secrete mucus
What is the role of serous cells?
Secrete anti-bacterial enzymes
e.g. lysozyme
What do ciliated cells do?
What rhythm do the cilia follow for sweeping?
Waft molecules up and out of the airway
Some cilia go one way, and some go the other way - works like a mexican wave
Metachronal rhythm - movement controlled by calcium
What is the function of the epithelium?
Secretion of mucins, water and electrolytes
- components of ‘mucus’ (+ plasma, mediators etc)
Movement of mucus by cilia – mucociliary clearance
Physical barrier
Production of regulatory and inflammatory mediators
Give examples of regulatory and inflammatory mediators
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 is the function of the smooth muscles of the airway?
Structure = hypertrophy and proliferation
Function = contraction and relaxation to constrict and open up the airways
Constriction to stop something going too far down - gives better chance of coughing it up
What happens when there is inflammation in the smooth muscle of the airways?
Structure = hyper proliferated
Tone = more contracted
Secretion = excess
What is the airway vasculature?
Trachio-bronchial circulation system
What are the main features of tracheo-bronchial circulation?
1-5% of cardiac output
Blood flow to airway mucosa = 100-150 mL/min/100g tissue (amongst the highest to any tissue)
Bronchial arteries arise from many sites on
aorta, intercostal arteries and others
Blood returns from tracheal circulation via systemic veins
Blood returns from bronchial circulation to both sides of heart via bronchial and pulmonary veins
What vasculature is found under the epithelium?
Why is it structured this way?
Plexus of arteries, capillaries and veins found just under the epithelium
Direct exchange, contributes to warming, clear away inhaled drugs, supplies airway tissue with inflammatory cells and proteinaceous plasma
What are the functions of tracheo-bronchial circulation?
- 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’)
What are the nerves found in the airways that control airway function?
parasympathetic (cholinergic)
(sympathetic – adrenergic?)
sensory
What are the regulatory and inflammatory mediators involved in the control of airway function?
histamine
arachidonic acid metabolites (e.g. prostaglandins, leukotrienes)
cytokines
chemokines
Proteinases/proteases (e.g. neutrophil elastase)
Reactive gas species (e.g. O2-, NO)
What are some respiratory diseases that result in the loss of airway?
Asthma
COPD
Cystic Fibrosis
What is the risk factor for COPD?
Smoking
What is asthma? What are its characteristics?
A clinical syndrome characterised by increased airway ‘responsiveness’ to a variety of stimuli (® airways obstruction)
Airflow obstruction varies over short periods of time and is reversible (spontaneously or with drugs)
Dyspnoea, wheezing and cough (varying degrees - mild to severe)
Airway inflammation –> re-modelling
What are the pathological signs of asthma?
Eosinophils
bronchoconstriction
What is the current understanding of asthma?
‘simple’ schematic
excess mucus
Cholinergic reflex set off = bronchoconstriction + mucus secretion
