4. Airways Function Flashcards
What is the division of the trachea into two called?
Dichotomous branching
Describe the arrangement of the lung structures
Trachea, Primary bronchus, Secondary bronchus (lobar), tertiary bronchus (segmental)
What are the lobes of the right lung?
Superior, middle and inferior lobe
What are the lobes of the left lung?
Superior and inferior lobe
What is the shape of the cartilage of the trachea?
C shape - the opening of the C is on the posterior side of the trachea so the oesophagus can run behind. The C shaped cartilage is off set from each other to increase tensile strength
What is the basic function of the airways?
Gas exchange
How is gas exchange facilitated?
Mechanical stability (cartilage)
Control of the airways (smooth muscle)
Protection and cleansing of the airways
Describe the layers of the airway structures going from the outside inwards
Cartilage, Submucosa, airway smooth muscle, Submucosal glands (part of it lies in the smooth muscle so when the muscle contracts it squeezes the gland squeezing out mucous), Systemic blood vessels, Epithelium (ciliated cells and goblet cells)
What do the vesicles in goblet cells contain?
Mucin (mucin granules)
What happens when mucin granules are released onto the epithelial surface?
They expand because they take in water x600 fold. This means a vast amount of mucus can be produced
What are the cells in the airway submucosal gland?
Mucous glands - secrete mucus
Serous glands - secrete antibacterials (lysozyme)
Glands also secrete water and salts (Na+ and Cl-)
Describe the location of the serous acini in association with the mucus acini
The serous acini are more distal from the mucous acini - The more water serous secretions can wash out the thick mucous secretions.
Describe the structure of the cilia?
9+2 arrangement a and b tubule dimers connected by nexin links and radial spokes. On the tubules there are dynein arms. Apical hooks attach to mucus
What is rhythm of cilia beating?
Metachronal rhythm - patches of cilia moving in motion of forward stroke and a recovery stroke
What are the functions of airway epithelium?
1) Secretions of mucins, water and electrolytes
2) Movement of mucous by cilia
3) Physical barrier
4) Production of regulatory and inflammatory mediators
What is the movement of mucous by cilia called?
Mucociliary clearance
What regulatory and inflammatory mediators are produced by the airway epithelium?
NO (by NOS), CO, Arachidonic acid (used to produce Protaglandins with COX), Chemokines (IL-8), Cytokines, proteases
What is function of NO?
Controls ciliary beat - lots of NOS in epithelium
What are the 3 functions of smooth muscle in the airways?
Structure, Tone and Secretion
What does the airway smooth muscle secrete?
Mediators, cytokines and chemokines
During inflammation how the smooth muscle change?
Structure - Hypertrophy + proliferatin
Secretion - increase in Mediators, cytokines and chemokines.
What do elevated levels of secretions do in the airways?
Recruits inflammatory cells into the airways
How much of the cardiac output is responsible for the tracheo-bronchial circulation?
1-5%
What is the blood flow to the airway mucosa?
100-150ml/min/100g of tissue (very high)
Where do bronchial arteries arise from?
Many sites on the aorta, intercostal arteries and others
Where does blood return from the tracheal circulation from?
via the systemic veins
Where does blood return from the bronchial circulation form?
via the bronchial and pulmonary veins to both sides of the heart
What are the functions of the tracheo-bronchial circulation?
1) Good gas exchange
2) Contributes to warming of inspired air
3) Contributes to humidification of inspired air
4) Clears inflammatory mediators
5) Clears inhaled drugs (good/bad, depending on drug)
6) Supplies airway tissue and lumen with inflammatory cells
7) Supplies airway tissue and lumen with proteinaceous plasma (plasma exudation)
What is the mechanism of plasma exudation?
1) Sensory nerves (with motor function) stimulate post capillary venules to leak plasma
2) Inflammatory mediators such as histamine and PAF also stimulate plasma leakage
What blood vessels leaks plasma?
Post capillary venules (pericytic)
What does PAF stand for?
Platlet activating factor
What controls airway function?
Nerves (parasympathetic and sympathetic)
Regulatory and inflammatory mediators
Proteinases (neutrophil elastase)
Reactive gas species (e.g O2-, NO)
What happens when something gets in the airways?
Sensory nerves send a signal to the brainstem causing a parasympathetic cholinergic reflex causing bronchocontriction. Vagus
How does the nervous system relax the airways?
Humans have nerves which contain nitric oxide synthase which produces and releases NO at the airway to cause relaxation
What is a blood borne relaxant of the airways?
Adrenaline is released from the adrenal glands and causes releaxation
What effects does ACh have on the airways?
It causes constriction of the airways and also secretion of mucous in the submucosal gland
Summarise the function of regulatory-inflammatory cells in airways
Cells produce more than one mediator and mediators do more than one thing.
What are 3 respiratory diseases with loss of airway control?
Asthma, COPD and cystic fibrosis
What does asthma, COPD and CF all present with?
Airway inflammation, obstruction (difficulty breathing), airway remodelling
Define Asthma
A clinical syndrome characterised by increased airway responsiveness to a variety of stimuli, always leading to obstruction.
How does airway obstruction called by asthma vary?
Airflow obstruction varies over short periods of time and is reversible (spontaneously or with drugs)
What are the symptoms of asthma?
Dyspnoea, Wheezing and cough (varying degrees - mild to severe)
Describe the pathology of asthma
Mucus plug in lumen, Epithelial fragility, basement membrane thickens, thickening of smooth muscle, glands get larger, vasodilation of blood vessels since they are congested with blood and cellular infiltration (eosinophils)
Describe how asthma can cause bronchoconstriction?
1) Due to epithelial fragility the epithelium falls away exposing the sensory nerves. These become activated setting up a central cholinergic reflex which causes bronchoconstriction, mucus secretion and possibly vasodilation
2) Inflammatory cellular infiltrate will also cause the same effects by secreting inflammatory mediators
