Airways and Cough Flashcards
Why is a defense system needed for lung parenchyma
Airways are fine and fragile
What is the role of hair in the nostrils
They trap larger particles and stop them from entering the nose and sinus cavities
What is present in the sinus cavities
A mucus layer
What does mucus trap
Anything that hasn’t previously been caught and then travels to the oropharnyx and then is swallowed
Describe sinus mucosa
They are highly vascular
Why do people with asthma often find that they can’t breathe when they exercise
Unconditioned dry, cold air which is breathed in through the mouth can trigger bronchospasm
What do the sinus cavities do to air
Humidify and moisten it meaning that air is conditioned and won’t cause bronchospasm
What is the function of the oropharynx
It contains a large number of nerves and its function it to prevent food from entering the lungs
What is the trachea composed of
Cartilaginous rings which makes it a rigid pathway
How many generations are there between the trachea and alveoli
23
What is the respiratory system comprised of
The conducting zone and the respiratory zone
What is the conducting zone made up of
Nasal cavities, nasopharynx, larynx, trachea bronchii and bronchioles
What does the branching of the trachea
Two primary (main) bronchi, secondary bronchi, tertiary bronchi then branch successively to give rise to several orders of progressively smaller airways called bronchioles, the smallest of which are called terminal bronchioles
What are the last components of the conducting portion of the respiratory system
Terminal bronchioles
What do terminal bronchioles give rise to
Respiratory bronchioles which ultimately lead to alveoli
Describe the defense elements of the respiratory pathway
Defense elements are to warm and humidify air to trap particles. With each generation surface area increases which slows down air speed meaning that air is very slow by the time it reaches alveoli. Each generation traps smaller particles
How much fluid do the lungs normally produce
Around 1.5L per day which is swallowed and recycled
What does it mean if the sputum becomes green
It contains neutrophils
How many tracheal cartilages keep the lumen of the trachea open
20 tracheal cartilages
Describe the tracheal cartilages
C-shaped rings of hyaline cartilage
What are the gaps between the rings or cartilage filled by in the trachea
Trachealis muscle
Describe the trachealis muscle
A bundle of smooth and fibroelastic tissue
What do the hyaline cartilage and trachealis muscle do in the trachea
Hold the lumen of the trachea open but allow flexibility during inspiration and expiration
How are the respiratory mucosa and submucosa adapted
To warm and moisten air and to trap particles in the mucus
Describe the epithelium of the trachea
Pseudostratified epithelium. Also mosaic cells in the epithelium meaning that it contains secretory (goblet cells)
What do goblet cells produce
Mucus which is sticky
What do serous cells produce
Water
What are locates in the connective tissue below the pseudostratified epithelium of the trachea
Seromucus glands
What is the respiratory mucosa made up of
The epithelium and supporting lamina propria
Describe the epithelium of the trachea
Tall columnar pseudostratified with cilia and goblet cells
What does the lamina propria contain
Elastin which plays a role in the elastic recoil of the trachea during inspiration and expiration together with blood vessels that warm the air
Describe the sub-mucosa and associated secretions
Sub-mucosa contains gland which are mixed sero-mucus glands. The watery secretions from the serous glands humidify the inspired air. The mucous together with the mucus from the goblet cells trap particles from the air which are transported upwards towards the pharynx by cilia on the epithelium
Describe the tertiary bronchus
There is a smooth muscle ring (bronchial smooth muscle). Elastin in the submucosa. Tall columnar epithelium, less cartilage. Mucosa is folded
Describe the role of the bronchial smooth muscle in the tertiary bronchus
Used to control the diameter and length of the bronchii- contracts during expiration to help expel air
Describe the epithelium of the tertiary bronchus
Tall columnar not pseudostarified and contains very few goblet cells. Epithelium is quite corregated meaning that it can change shape easily
What is the diameter of bronchioles
1mm or less
Describe bronchioles
Epithelium is made up of ciliated columnar cells in larger bronchioles or non-ciliated columnar cells in smaller bronchioles. No goblet cells but are Clara cells. No cartilage. Corregated epithelium
Describe Clara cells
Found in bronchioles, they are secretory and secrete one component of surfactant
Describe the change of airway wall structure at the three principle levels (bronchus, bronchioles, alveolus)
The epithelial layer gradually becomes reduced from pseudostratified to cuboidal and then to squamous but retains its organisation as a mosaic of lining and secretory cells. The smooth muscle layer disappears in the alveoli. The fibrous coat contains cartilage only in bronchi and gradually becomes thinner as the alveolus is approaches. Basement membrane is continuous throughout
What are submucosal glands especially regulated by
Parasympathetic nerves which cause secretion
What does stimulation of sensory afferents in the airway lead to
Stimulation of the parasympathetic neurones and thus secretions from the glands
What are the afferents in the neural reflexes stimulated by
Irritating stimuli or inflammation
Describe the reflexes
They may pass through the CNS or take place purely in the walls of the airways
Describe sympathetic effects on the submucosal glands
Effects are rather weak with alpha1 adrenergic inhibiting secretion and beta2 stimulating secretion
How do inflammatory paracrines regulate submucosal glands
Stimulate secretion
Describe neural reflexes
Occur starting with stimulation of sensory afferents in the airways which can lead to stimulation of parasympathetic neurones and thus secretion from the glands. The afferents in these neural reflexes are stimulated by irritating stimuli or inflammation
What are the two components of the mucus layer
Mucus and water
What is the prime regulatory factor promoting secretion of fluid
Active transport of Cl- ions via phosphorylation of protein kinase causes release of water which lubricates. Net movement of Cl- from interstitial space into lumen= prime regulatory factor
What is the level of hydration of the mucus in the airways determined by
The amount of water secreted across the epithelium lining the airways. The amount of water secreted is determined by the net movement of ions across the epithelium. When there is a greater net movement of ions more water follows by osmosis
Describe the movement of chloride ions in the mucus layer
Chloride ions enter the epithelial cells from the interstitial fluid via a cotransporter which also carries sodium ions and potassium ions. Chloride ions enter the lumen via a regulated chloride channel. A second messenger, cyclic AMP, activates a kinase that phosphorylates the chloride channel which leads to its opening
What does the fact that the CT scan shows airways that are dilated and thickened walls mean
Results in bronchiectasis, as a result the patient would have excess sputum and their ciliary network would be compromised meaning that they would have to constantly cough
What neural pathways exist in the lungs
Parasympathetic system, sympathetic system, sensory fibres, nonadrenergic, noncholinergic (NANC) efferent system
What feels pain in relation to the lungs
Not the lungs themselves, only the pleural surface
What is the main effector system in the lungs
The parasympathetic system
Which systems are rudimentary in the lungs
The sympathetic system and sensory fibres
Which nerve does the parasympathetic system run through
The vagus nerve
What are the 3 main actions of the parasympathetic system on the lungs
Bronchoconstriction, vasodilation, mucus gland and goblet cell secretion
Describe acetylcholine actions
M1-Rs increase preganglionic transmission. M2Rs reduce further ACh release from nerve endings. M3-Rs stimulate airway smooth muscle contraction
What do the vagus nerves and second to fifth thoracic sympathetic ganglia contribute fibres to
The anterior and posterior plexuses in the peribronchovascular connective tissue at the lung roots
What are the two main plexuses fibres form on entering the lungs
The peribronchial plexus which follows the bronchi and contains both myelinated and unmyelinated nerves and the periarterial plexus containing only unmyelinated fibres
Describe preganglionic parasympathetic fibres
Arise primarily from cell bodies in medullary nuclei, and are carried in the vagus nerve to the lower airways. They synapse with postganglionic fibres in small ganglia along the vagus nerve and in local ganglia in the airway walls, predominantly in the larger central airways. The ganglia are mainly located external to the smooth muscle and cartilage, with only a few smaller ganglia within the submucosa
What neurotransmitters do parasympathetic ganglia and postganglionic fibres contain
Acetylcholine, vasointestinal peptide (VIP), peptide histidine isoleucine/methionine, helodermin, galanin and the enzyme nitric oxide synthase (NOS)
What do postganglionic cholinergic fibres supply
Bronchial smooth muscle and that stimulation causes bronchoconstriction, the effects of which can be inhibited by atropine. In addition, they also supply bronchial and pulmonary vascular smooth muscle causing relaxation and vasodilation
What do vagal efferent fibres also innervate
The mucous glands of the large airways and goblet cells causing an increase in secretion in both
What are the 3 effects sympathetic stimulation has
Vasoconstriction. bronchdilation (minor effect), modulate cholinergic transmission
What is the cough reflex mediated by
Sensory afferent nerves
What are the two main defense reflexes
Cough and expiration
What elicits the defense reflexes
Mechanical or chemical irritation of the airway mucosa
Describe the cough reflex
Forces explosive manoeuver usually against a closed glottis. Subject draws air into the lungs to reinforce a subsequent explosive effort
Describe the expiration reflex
Strong expiration without a preceding drawing in of air which aims to prevent aspiration of material into the lungs
Describe the C fibres in the lungs
Arise from jugular neurones, conduction velocity
Describe the A fibres in the lungs
Arise from nodose neurones, conduction velocity >3m/s, Aδ fibres are thin fibres, Aβ fibres and thick unmyelinated fibres.
Which fibres respond to mechanical stimuli and are responsible for expulsion
A fibres
Which fibres respond to chemical stimulation
C fibres e.g. capsaicin in chilli acts on TRPV1 receptors. When neuropeptides are released they have a potent effect on the epithelium itself and cause vasodilation and mucus secretion
What does the majority of afferent innervation of the lung occur via
The vagus nerve
What are the proposed mechanisms for the role of tachykinins in cough
Tachykinin containing c-fibres when stimualated antidromically release SP, CGRP and neurokinin A. These neuropeptides act on neurokinin 1,2 or 3 receptors which induce pronounced bronchoconstriction and localised inflammation
What is the primary characteristic of neurogenic inflammation
Increased vascualr permeability allowing leakage of serum inflammatory proteins into tissues and is associated with increased influx of inflammatory cells
What are NK-1 effects
Increased mucus hypersecretion, and airway smooth muscle contraction
What are the causes of chronic cough
Asthma, gastro-oesophageal disorders, post-viral cough, bronchiectasis, intersitial lung disease, idiopathic cough, rhinosinutis
What cells play a key role in asthma
Eosinophils result in smooth muscle contracting
How can reflux of gastro juices into the lungs cause chronic cough
C-fibres are highly sensitive to low pH
How can viruses cause a chronic cough
Some viruses cause the epithelial layer to shed resulting in the basemenet membrane being exposed. The epithelium takes a while to regrow meaning that the cough persists even after the virus has gone
What happens in bronchiectasis
Sputum builds up
What happens in interstitial lung disease
C-fibres are upregulated
What do you need to think of if a cough lasts for longer than 8-12 weeks
Other things that may be causing it e.g. COPD, ACE inhibitor therapy, lung neoplasm. pyschogenic cough, tic disorder
What are progressive conditions
Lung cancer and interstitial lung disease
