Structure and Function of the Airways Flashcards
Describe the branching of the trachea.
Dichotomous branching
What provides mechanical stability to airways?
Cartilage
What are trachea held open by?
Trachea held open by C-shaped cartilage rings (C-shaped - transport of substrate down oesophagus, with minimum resistance).
Where does gas exchange occur?
Alveolar region - where the pipework leads.
Where does GE take place specifically?
Alveolar sac
What are type I alveolar cell?
Squamous epithelial cells, constitute majority of alveolar surface, permeable to gas. Squamous epithelium attached to thin, elastic membrane form a respiratory membrane, simple diffusion of gases (Oxygen transport and CO2 removal)
What are the function of type II alveolar cells?
- Replicates to form Type I cells.
- Secretes surfactant and antiproteases.
- Xenobiotic metabolism.
What does pulmonary surfactant contain?
Contains phospholipids and proteins that reduces surface tension of alveoli
Which cell cover most of the alveolar region?
~95% of alveolar surface - Type I alveolar surface.
Type II cells - greater in number than type I cells, but only cover ~5%.
What are the basic functions of the respiratory system?
Conduit to conduct O2 to the alveoli.
Conduct CO2 out of the lung.
Gas exchange
What are the basic functions of the respiratory system facilitated by?
Mechanical stability (Cartilage)
Control of calibre (Smooth muscle)
Protection and cleansing
What is the pharynx?
A common passageway for food, liquids and air.
What is the purpose of conchae?
Conchae increase SA of nasal cavity and disrupt flow of inspired air, contact with the epithelium results in filtration and humidification. Highly vascular enables warming through convection currents.
What is the purpose of paranasal sinuses?
Warm and humidify impaired air. Sinuses are lined with mucosa. Frontal, maxillary, sphenoidal and ethmoidal sinuses.
What is the epiglottis attached to?
Thyroid Cartilage
Organisation of airway structures.
Axial section of airway, smooth muscle ring → embedded within the smooth muscle is inferior portion of submucosal gland; contraction of smooth muscle stimulates secretion into epithelial lining (CONTRACTILE mechanism).
Ciliated and squamous epithelial, including goblet cells (Mucous secreting).
Deep to cartilage (superficial layer) is the smooth muscle. Bronchial systemic circulation, vessels supply the tracheal tissue with oxygen and respiratory substrates.
C-shaped cartilage are offset, angulated to maximise the mechanical stability of trachea.
Describe the structure of the airway wall.
Submucosal gland partially embedded within the contractile smooth muscle ring; goblet cells within the epithelium contribute to the production of mucous, lines superficially above the ciliated epithelial layer.
Mucociliary transport to release the pollutants.
What releases pollutants from airway wall?
Mucociliary transport to release the pollutants.
List the airway categories and examples of cell types for each.
Lining cells - Ciliated, intermediate, brush, basal
Contractile cells - Smooth muscle (airway, vasculature)
Secretory cells - Goblet (epithelium), mucous, serous (glands)
Connective tissue - Fibroblast, interstitial cell (elastin, collagen
Neuroendocrine - Nerves, ganglia, neuroendocrine cells, neuroepithelial bodies
Vascular cells - Endothelial, pericyte, plasma cell
Immune cells - Mast cell, DC, lymphocyte, eosinophil, macrophage, neutrophil
What do mucin granules contain?
Mucin in highly condensed form.
Function of epithelial layer?
Adjacent to ciliated cells are the goblet cells, the ciliated cells are stimulated, facilitating ATP-derived movements of cilia; consequent achieved through a higher proportion of MC.
What are the functional units of submucosal glands?
Acini
Function of submucosal glands?
Functional units (Acini) secrete mucous extracellularly into the collecting duct traversing to ciliated duct, the cilia waft the mucous out of gland.
Serous cells peripheral to the mucous cells; serous cells produce more dilute mucous (Contains antibacterial lysozymes).
What do mucous cells secrete?
Mucous
What are the 2 types of acini in airway submucosal glands?
Mucous acini
Serous acini - secrete antibacterial enzymes (lysozyme).
Glands also secrete water and salts.
Describe the relationship between mucous and serous acini.
Serous acini distal from mucous acini.
What is the function of ciliary structures?
Cilia beat to waft mucous. Apical hooks, engages with the mucous, assists with mucous removal. Sliding movement of rods facilitate bidirectional movement.
Describe the rhythm of beating cilia.
Metachronal rhythm (Time, mucous on superficial surface, mucous is transmitted by cilia), backwards cilia sequentially move through alternating forward and backward movements.
List airway epithelial functions.
- Secretion of mucin, water and electrolytes (Components of mucous + plasma, mediators)
- Movement of mucous by cilia - Mucociliary clearance.
- Physical barrier against inhaled insult.
- Production of regulatory and inflammatory mediators:
What regulatory and inflammatory mediators are produced by airway epithelium?
NO secreted by nitric oxide synthase (NOS); anti-NOS Ab results in brown staining to identify NOS. Significant presence of NO exhibits a regulatory function on ciliary beat - high presence within the epithelium.
CO by haem oxygenase (HO); enzyme catalyses the degradation of haem to produce biliverdin, Fe2+ (ferrous iron) and CO. Products activate vasodilatory pathways.
Arachidonic acid metabolites (COX, prostaglandins).
Chemokine (IL-8)
Cytokines (GM-CSF)
Proteases
What does brown-staining on a histological section in the human airway?
Anti-NOS Ab results in brown staining to identify NOS
Significant presence of NO exhibits a regulatory function on ciliary beat - high presence within the epithelium
Outline the functions of airway smooth muscles.
Secretion - Smooth muscle cells produce small amounts of secretions:
- In response to cytokines however, NOS is up-regulated; enhancing secretion of NO, accentuating its effect on cilia and inflammation
- COX enzymes produce more prostaglandins; chemokines lead to recruitment of inflammatory cells; smooth muscle subsequently gets involved in the inflammatory process
Tone (airway calibre - Level of relaxed or contracted the airway is
Structure - Inflammation and smooth muscle hypertrophy occurs through proliferation of smooth muscle cells, in addition to hyperplasia. This ^ in mass of smooth muscle simultaneously increases the contractile force of that muscle → Marked ^ in secretion of mediators.
What is the name of the airway vasculature?
Tracheo-bronchial systemic circulation
What % of cardiac output does this system represent and what volume of blood flow goes to airway mucosa?
1-5%
Blood flow to airway mucosa = 100-150 mL/min/100g tissue
The tracheo-bronchial systemic circulation blood flow is AMONG THE HIGHEST to any tissue
How does blood return from tracheal circulation?
Systemic veins
How does blood return from bronchial circulation to both sides of the heart?
Via bronchial and pulmonary veins.
List all the functions of tracheo-bronchial circulation
Direct GE between systemic circulation in the tissue of sub-epithelial micro-vasculature. Highly vascular system facilitates direct GE between tissues and blood
Contributes to warming and humidification of inspired air
Clearance of inhaled drugs (Benefit is dependent on the mechanism of delivery of drug)
Supplies airway tissue and lumen with inflammatory cells; in addition to proteinaceous plasma (mechanism of plasma exudation).
Outline the parasympathetic ‘motor’ pathway for airway control
Innervation via vagus nerve through corticospinal tract, motor pathway
Secretion of ACh NT via cholinergic synapse of postganglionic fibre and gland
This stimulates the bronchostriction and contraction of smooth muscles within trachea + stimulates submucosal glands to secrete mucous
Outline the sympathetic and nitric oxide (NO) pathway for airway control
Sympathetic - Adrenergic reflex causes bronchodilation, smooth muscle relaxes, dilating the airways
Adrenaline is secreted by adrenal gland, and directly relaxes the airways
NO - NO is a NT of neuronal pathway that dilates and opens airways
Adrenaline and the neuronal pathway producing nitric work to relax the airways
List the regulatory and inflammatory mediators for the control of airway function
Histamine, arachidonic metabolites (prostaglandins and leukotrienes), cytokines, chemokines, proteinases (e.g. neutrophil elastase).
Name 3 respiratory diseases associated with loss of airway control
Asthma, COPD and cystic fibrosis - all common conditions
These diseases are associated with abnormalities of airway inflammation and obstruction
