Structure & function of airways Flashcards
What term is used to describe the branching of the trachea?
Dichotomous branching
How is the trachea held open?
By C-shaped cartilage rings
What does the trachea divide into?
Two primary bronchi
Where does the trachea extend from?
Extends from the larynx towards the lungs
What type of cartilage forms the C-shaped rings?
Hyaline cartilage connected by tracheal muscle and elastic connective tissue, forming a fibroelastic membrane, encloses the posterior surface
Which membrane enables the stretching of the trachea and expansion during inhalation & exhalation?
Fibroelastic membrane
What type of epithelium lines the trachea and larynx ?
Pseudostratified columnar epithelium
Where does the trachea bifurcate?
At the tracheal carina (T4/5)
Which cells are integrated within pseudostratified columnar epithelium?
Goblet cells
Where does the bronchi enter the lungs?
At the hilum
What is the main function for the bronchi?
Conducting zone, passageway for inspired and expired air
What is the alveolar duct?
Tube composed of smooth, muscular and connective tissue, periphery opens into alveoli.
Alveolar sac comprises of multiple individual alveoli, responsible for gaseous exchange
What is the purpose of elastic walls in the alveoli?
Enables alveolus to stretch during inspiration, increases surface area available for gas exchange. Elastic recoil enables ventilation mechanism
What is the purpose of alveolar pores?
Connect adjacent alveoli maintaining equal air pressure
Which type of alveolar cells form the majority of the alveolar surface?
Type 1 alveolar cells
Which type of alveolar cells are permeable to gas exchange ?
Type 1 alveolar cells
Where are type 1 alveolar cells attached to?
Attached to thin, elastic membrane, borders capillaries
What forms the respiratory membrane?
Alveoli and capillary membranes
Which cells are interspersed amongst type 1 cells?
Type II alveolar cells
What is produced by type ii alveolar cells?
Pulmonary surfactant
What is contained within pulmonary surfactant?
Phospholipids and proteins that reduce surface tension of alveoli
What is the purpose of pulmonary surfactant?
Reduced surface tension of the alveoli, to enable elastic recoil
What are the 3 main functions of type II alveolar cells?
Replications to form Type I cells
Secretes pulmonary surfactant, and antiproteases
Xenobiotic metabolism
What is the purpose of alveolar macrophages?
Phagocytic cells removes pathogens and debris present in the alveoli
What are the 3 basic functions of the respiratory system?
Conduit to conduct oxygen to the alveoli
Conduct carbon dioxide out of the lung
Gas exchange
How are the basic functions of respiratory system maintained?
Mechanical stability (cartilage)
Control of calibre (smooth muscle)
Protection and cleansing
What does the lateral wall so the nasal cavity contain?
The superior middle and inferior nasal conchae
What are the three main types of conchae?
Superior
Middle
Inferior
What is the function performed by nasal conchae?
Conchae increases the surface area of the nasal cavity, and disrupt flow of inspired air, contact with the epithelium results in filtration and humidification
What enables the nasal conchae to humidify and warm air?
Highly vascular enables warming through convection currents
How is water conserved within the nasal cavity?
Conchae and meatuses conserve water & minimise dehydration of nasal epithelium during exhalation
What type of epithelium lines the conchae, meatuses and paranasal sinuses?
Columnar pseduostratified ciliated cells
What is the function of the columnar cells in the nasal cavity?
Produce mucous to trap debris
Goblet cells are present
What function is performed by cilia in the nasal cavity?
Assist in the removal of mucous and debris from nasal cavity
What cartilage is the epiglottis attached to?
Thyroid cartilage
What is the epiglottis?
Flexible piece of elastic cartilage that covers the opening of the trachea.
Act of the swallowing causes the pharynx and larynx to life upwards
Prevents aspiration of food
What is superficial to the submucosal glands?
Ring of smooth muscle
How do submucosal glands release mucous?
Contractile mechanism,
contraction of smooth muscle stimulates mucous secretion into epithelial lining and lumen of airways
What cells are found within the airway lumen?
Goblet cells
Ciliated and squamous epithelial
What is deep to cartilage of the airways?
Smooth muscle
What type of circulation supplies oxygen and respiratory substrates to the tracheal tissue?
Bronchial systemic circulation
How are the C-shaped cartilage arranged to maximise mechanical stability of the trachea?
Are offset and angulated
Where is the submucosal gland partially embedded?
Embedded within the contractile smooth muscle ring
What structures/cells form mucous within the airways?
Goblet cells and submucosal glands
How are pollutants released from the airways?
Mucociliary transport
What are ciliated cells?
The ciliated cells are stimulated, facilitating ATP-derived movement of cilia, consequently achieved through a higher proportion of mitochondria
Which granules are contained and secreted by goblet cells?
Mucin granules
What do mucin granules contain?
Mucin
What is mucin?
Highly condensed forms of mucous requires hydration
How is mucous formed from mucin?
Mucin secretion through mucin granules within goblet cells (fusion), hydration through water absorption within the trachea causes expansion of mucin generates expansive mucous
Which surface are mucin granules located in goblet cells?
Apical surface
What are the functional units of submucosal glands?
Acini
How do acini secrete mucous?
Secretes mucous extracellularly into collecting duct, traversing to the ciliated duct, the cilia waft the mucous out of the gland
What duct is mucous from submucosal glands secrete into?
Ciliated duct
What type of mucous is secreted by serous cells?
More dilute mucous, contains lysozyme
What antibacterial agent is secrete by serous cells?
Lysozyme
What is the purpose of more dilute mucous secretions from serous cells?
Flush over the vicous mucous secretions and washes it into the collecting duct
What is released from submucosal glands other than mucous?
Water, antibacterial enzymes, and salt
What characteristic microtubule arrangement is presented by ciliated cell?
9+2
What is the name of the cilia microtubule in ciliated cells?
Axoneme microtubule
What is the function of ciliated cells?
Cilia beat to waft the mucous. Apical hooks engages with the mucous, assist with mucous removal, sliding movement of rods facilitate bidirectional movement
What type of rhythm is exhibited by cilia beating?
Metachronal rhythm
What is metachronal cilia rhythm?
Time, mucous on superficial surface, mucous is transmitted by cilia.
Backwards cilia sequentially moves the mucous through alternating forward and backward movements.
Rafts of mucous are present in typical airways instead of a full layer.
What are the four main functions of airway epithelium?
Secretion of water, mucin and electrolytes
Movement of mucous by cilia, mucociliary clearance
Physical barrier against inhaled insult
Production of regulatory and inflammatory mediators
Which enzyme complex secreted nitric oxide?
Nitric oxide synthase
How does the addition of anti-NOS antibodies identify presence of nitric oxide synthase?
Brown staining
What effect does nitric oxide have on epithelium?
Influence ciliary beat
What is released by haemoxygenase?
Carbon monoxide
Biliverdin
Ferrous iron
What regulatory and inflammatory mediators are produced by airway epithelia?
Arachidonic acid metabolites (COX, prostaglandins)
Chemokines (IL-8)
Cytokines (GM-CSF)
Proteases
How is nitric oxide secretion controlled?
In response to cytokines, nitric oxide synthase is upregulated, enhancing secretions of NO, accentuating its effect on cilia and inflammation
What is the role of cycle-oxygenases in airway smooth. muscle?
Produces more prostaglandins, chemokine, leads to recruitment of inflammatory cells, smooth muscle subsequently gets involved in the inflammatory phase
What is tone (airway calibre)?
The level of relaxed or contracted the airway is
How can the contractile force of smooth muscle within airways increase?
Inflammation and smooth muscle hypertrophy occurs through proliferation of smooth muscle in addition to hyperplasia. The increase in the mass of smooth muscle simultaneously increases the contractile force of that muscle.
Marked increase in secretion of mediators
What % of cardiac output is represented by the trachea-bronchial systemic circulation?
1-5% cardiac ouput
What is the average blood flow to airway mucosa?
100-150 mL/min/100g tissue
What is special about the trachea-bronchial systemic circulation blood flow?
Among the highest to any tissues
Where do bronchial arteries arise from?
Arise from many junctions on the aorta and intercostal arteries
How does blood return from the tracheal circulation?
Systemic veins
How does blood return from bronchial circulation?
To both sides of the heart via bronchia and pulmonary veins
What is the main function of sub epithelial microvasculature within the trachea bronchia circulation?
Direct gas exchange between systemic circulation and respiratory surface
highly vascular system facilitates direct gas exchange between tissues and blood
What are the main four functions of the trachea-bronchial circulation?
Direct gaseous exchange
Contributes to warming and humidification of inspired air
Clearance of inhaled drugs *
Supplies airway tissue and lumen with inflammatory cells in addition to proteinaceous plasma
How is plasma exudation performed in respiratory tissues?
Bathed in plasma, plasma leaks out of the post-capillary venues.
Consists of endothelial cells
Contraction results in diapedesis mechanism, stimulates increased permeability to plasma - movement of plasma leakage
Plasma exudation can be exaggerated in respiratory diseases (asthma(
How are endothelial cells innervated?
sensor nerves the exhibit motor functions
What molecules are produced which stimulate activation of sensory nerves?
Histamines
Platelet activating factor
Which nerve supplies parasympathetic control to the airways?
Vagus nerve through the corticospinal tract
What does the parasympathetic nervous system stimulate in terms of airway control?
Stimulates bronchoconstriction and contraction of smooth muscles within the trachea; in addition to stimulating submucosal glands to secrete mucous
Secretion of acetylcholine neurotransmitter via cholingeric synapse of postganglionic fibre and gland
Which cerebral cortex does the sensory nerve transmit electrical impulses to?
Primary sensory cortex
Where are first order sensory neurones mainly located?
Dorsal root ganglion, synapse within dorsal horn
Where do second order neurones synapse with third order neurones?
Within the medulla
Where do third order neurones synapse with their respective cortex neurones?
Thalamus
How is sympathetic control exerted on the airways?
Adrenergic reflex causes bronchodilation, smooth muscle relaxes dilating the airways.
Adrenaline is secreted by the adrenal gland and directly relaxes the airways
Which two hormones dilate the airways?
Nitric oxide
Adrenaline
What are the main proteinases of airway control?
Neutrophil elastase
What is the inheritance pattern of cystic fibrosis?
Autosomal recessive gene defect (CFTR)
What is asthma?
A clinical syndrome characterised by increased airway responsiveness to a variety of stimuli (leads to airway obstruction).
Airway obstruction varies over short periods of time and is reversible (Adrenaline stimulates bronchodilation, airways reopen).
What is dyspnoea?
Shortness of breath affiliated with wheezing and coughing (Varying degrees mild severe).
What is airway remodelling?
Airway changes in structure over a long period of time.
Usually associated with inflammation
What forms through hyperplasia and hypertrophy of goblet cells to cause obstruction of airways?
Mucous plug
Which immune cells predominant in mucous plug?
Eosinophils
What is the main function performed by eosinophils?
Immunological mechanisms against parasites
Without submucosa, what immune cell predominates?
Eosinophils
What is the pathophysiology of asthma?
Epithelial fragility, thickening of the basement membrane. The blood vessels become prominent. Lumen folded attributed to smooth muscle contraction. Combination of bronchoconstriction and mucous plug causes airway obstruction and blockage.
Which factor stimulates plasma exudation?
AF (platelet activating factors)
Why does epithelial fragility cause increased mucous secretion?
Exposes sensory nerves, therefore responding to multiple mediators produced by inflammatory cells. This triggers a central cholinergic reflex, increases the level of sensory nerve activation
Repeated bronco constriction and mucous hyper secretion is associated with what of the smooth muscle and submucosal glands?
Hyperplasia and hypertrophy
Which immune cell produces mediators to stimulate mucous hypersecretion and smooth muscle contraction?
Mast cells
Which cells in response to chronic inflammation leads to basement membrane thickening?
Fibroblasts
Which factors causes hypertrophy of smooth muscle ,and submucosal cells?
Growth factors
