6. Structure and function of the airways Flashcards
How are the cartilage rings specialised for their function in the airways?
C shape allows oesophagus to run down back of trachea
All rings are slightly offset which confers greater tensile strength to keep airways open
What is the basic function of the airways?
Gas exchange
Conduit pipes to:
Conduct O2 to the alveoli
Conduct CO2 out of the lung
What facilitates gas exchange?
Mechanical stability (cartilage)
Control of calibre (smooth muscle)
Protection and ‘cleansing’
Why are parts of submucosal glands embedded in the smooth muscle of the airway?
So when muscle contracts it helps squeeze mucous onto airway surface
Describe mucocillary transport
Mucous produced by submucosal glands and goblet cells
Secreted onto epithelium
Mucous wafted towards back of throat
What cell types found in the airway?
Lining cells Contractile cells Secretory cells Connective tissue Neuroendocrine Vascular cells Immune cells
What do cilia have many of?
Mitochondria
To produce ATP to keep cilia beating
What are goblet cells dense with?
Electrolucent mucin granules
What do mucin cells take on and what is the consequence of this?
Water
Expand enormously
Describe the structure of submucosal gland.
Submucosal glands have functional units (acini)
Acini are either SEROUS or MUCOUS
Serous acini are found peripheral to the mucous acini
Serous: produce WATERY secretions (containing antibacterials e.g. lysozyme)
Mucous acini produce MUCOUS
Serous secretions wash over the mucous secretions into the collecting duct
Glands also secrete water and salts (e.g. Na+ and Cl-)
Describe the structure of a cilium.
9 pairs of microtubules around the outside and 2 individual microtubules on the inside (9+2 formation)
Have apical hooks that interact with the mucus
Radial spokes and rods longitudinally
Have inner and outer (dynein) arms that slide over each other to move cilia back and forth
What is the pattern of beating of cilia?
Highly synchronised metachronal rhythm
How many cilia per cell?
~200
State 4 functions of airway epithelium
Secretion of mucins, water and electrolytes
Movement of mucus by cilia
Physical barrier
Production of regulatory and inflammatory mediators
State 6 of the regulatory and inflammatory mediators produced by airway epithelial cells.
NO CO Arachidonic acid metabolites e.g. Prostaglandins Cytokines Chemokines Proteases
In which cells of the airway do you find a high concentration of Nitric Oxide Synthase?
Epithelial cells
What are the main 3 functions of airway smooth muscle?
Provide structure to airways Produce tone (contracts and relaxes) Involved in secretion
What occurs to airway smooth muscle in airway inflammation?
Airway smooth muscle increases in mass
=Hypertrophy and hyperplasia
Massive increase in secretion
What inflammatory mediators can be produced by smooth muscle cells?
NO
Prostaglandins
Cytokines
Chemokines
Blood flow to airway mucosa
100-150 ml/min/100g tissue
(amongst the highest to any tissue)
=Massive perfusion
What is the function of the tracheo-bronchial circulation?
Provides perfusion to the lung tissue
Involved in WARMING and HUMIDIFYING inspired air
Clears inflammatory mediators and inhaled drugs
Supplies airway tissue with inflammatory cells and proteinaceous plasma
How does blood return to the heart from the tracheal circulation?
Systemic veins
How does blood return to the heart from the bronchial circulation?
To both sides of heart via
Pulmonary veins AND bronchial veins
What is plasma exudation in the airway? Where does it usually take place?
POST-CAPILLARY VENULES
Post-capillary venules have endothelial cells that leak plasma out to bathe tissue
What stimulates plasma exudation in the airway?
C fibres (Nerve) Inflammatory mediators e.g. histamine, platelet activating factor (PAF)
In which disease is plasma exudation a feature?
Asthma
What are the most important motor pathways in the airways?
Parasympathetic
CHOLINERGIC
‘Motor’ pathway
Describe the cholinergic reflex.
Something can go into the airways and trigger a signal via an afferent pathway to the brain.
Cause a CHOLINERGIC reflex= BRONCHOCONSTRICTION
What causes bronchodilation in humans?
Bronchodilation is caused by:
Release of NITRIC OXIDE from the neuronal pathway (NOTE: NO is a neurotransmitter)
Release of ADRENALINE from the adrenal medulla (part of sympathetic response)
What does the cholinergic reflex cause?
Constriction of smooth muscle
Secretion of mucus
Name 6 regulatory inflammatory cells in airways
Eosinophils Neutrophils Macrophages Mast cells T lymphocytes Structural cells e.g. smooth muscle
State 3 respiratory diseases that involve a loss of respiratory control.
Asthma
COPD
Cystic Fibrosis
What are the characteristics of asthma?
Increased airway responsiveness to a variety of stimuli Leads to reversible airway obstruction
Dyspnoea, wheezing and cough
Airway inflammation leads to re-modelling
Describe 8 histological features of asthma.
Mucus plug formation Epithelial fragility Goblet cell hyperplasia Thickening of the basement membrane Smooth muscle hypertrophy Vasodilation Infiltration by eosinophils Bronchoconstriction
What cells are abundant in a mucus plug formed by asthma?
Eosinophils
Describe the pathophysiology of Asthma
Epithelial fragility exposes sensory nerves, if stimulated initiates cholinergic reflex
Cholinergic reflex causes bronchoconstriction and mucous secretion
Also there is an influx of inflammatory cells which produce many inflammatory mediators resulting in remodelling of the airways e.g. submucosal gland and airway smooth muscle hypertrophy
What are the consequences of asthma to the structure of the airways?
Smooth Muscle Hypertrophy
Increase in number of goblet cells
