Structure And Function of the Airways Flashcards
What is meant by dichotomous branching?
Where each part of the bronchi splits into two
What does the cartilage around the bronchi provide?
Mechanical stability
What is the main unbranched part of the airway called?
Trachea
What is the first branch of the trachea called?
Primary bronchus
What is the carina?
A ridge at the base of the trachea (windpipe) that separates the openings of the right and left main bronchi (the large air passages that lead from the trachea to the lungs).
What is an alveolar duct?
Ducts that connect the alveolar sacs to the bronchioles
Do the respiratory bronchioles contain cartilage?
no - they are non-cartilaginous
What do Type II Pneumocytes secrete and why?
Surfactant - in order to reduce surface tension
What happens to Type II cells if Type I cells become damaged?
They form type 1 cells
What do the anti-proteases produced by Type 2 pneumocytes do?
They degrade foreign proteases which may have entered into the airways
Which type of alveolar cell is involved in xenobiotic metabolism?
Type 2
Describe the structure of Type 1 alveolar cells?
They are thin, and very flat that form a barrier between alveolus and capillaries
What percentage of the alveolar surface do type 1 cells cover?
95%
What percentage of the alveolar surface do type 2 cells cover?
5%
Are there more type 1 or type 2 alveolar cells?
Type 2
What are the two basic functions of the respiratory airway?
Conducting oxygen to the alveoli and conducting carbon dioxide out the lungs
What are the three things which facilitate the efficient gas exchange?
- Mechanical stability from cartilage
- Control of calibre from smooth muscle
- Protection and cleaning to remove foreign particles
What are the three regions of the pharynx?
Nasopharynx, oropharynx and laryngopharnx
What is the pharynx?
A common passageway for food, liquids and air
What do the conchae found in the nose do?
They contribute to the warming and humidification of intra-nasally-inhaled air
Why must the air be warmed before being breathed in?
Cool air damages the alveoli
What property of the conchae makes them able to humidify nasally inhaled air?
They are highly vascular
What filters out large particles from nasally inhaled air?
Nasal hairs
What is the main function of the goblet cells and submucosal glands?
To produce mucus
Label this diagram
What do the conchae, meatuses and paranasal sinuses produce?
Mucous to trap debris
What are the 7 types of airway cell types?
Lining cells Contractile Secretory Neuroendocrine Connective tissue Vascular Immune
Describe the structure of the airway wall
- Submucosal glands are partially embedded in the contractile smooth muscle ring
- Goblet cells in the epithelium produce mucous and lie superficially above the ciliated epithelial layer
- Mucociliary transport releases pollutants
What is contained within the granules found in the goblet cells?
Mucin
Why do the cillia contain many mitochondria?
They need ATP to move and waft mucous along the surface
What happens after the granules recieve a stimuli that they need to secrete their mucin?
Goblet cells take on water, causing the mucin granules to expand and release their mucous
What part of the granule attracts the large volume of water?
The glycans
What type of secretion do mucins show?
Constituitive
What can stimulate mucin secretion?
Dust and smoke
What is mucocilliary clearance?
The process by which mucus is swept by the cilia of the respiratory epithelium and propelled out the lungs and into the pharynx which results in the removal of debris and pathogens from the airways
What do mucous acini in the airways secrete?
Mucous
What do serous acini in the airways secrete?
- Anti-bacterial enzymes like lysozyme
- Water and salts
What is the 9+2 microtubule arrangement?
- Refers to how the microtubules are arranged in the cillia
- Helps the cilia to move rhythmically
How many cilia are there per ciliated cell?
Approx 200
What is the name given to the rhythm which cilia move by?
- Metachronal rhythm
- Different lines of ciliary hair move at different times to waft mucous to the back of the throat
What do the apical hooks do?
Engage with the mucous and assist with mucous removal
List 4 functions of airway epithelium
- Secretion of mucin, water and electrolytes
- Mucociliary clearance
- Physical barrier against inhaled insult
- Production of regulatory and inflammatory mediators
What does nitric oxide synthase do?
Produces nitric oxide (an inflammatory mediator)
What does nitric oxide do?
Interacts with the calcium ions to facilitate the beating of the cilia
What does haem oxygenase do?
- Produces carbon monoxide (inflammatory mediator)
- Haem oxygenase catalyses the degradation of haem
- This produces biliverdin, Fe2+ and CO to activate vasodilatory pathways
Apart from NO and CO, what other inflammatory mediators do the airway epithelium produce?
- Arachidonic acid metabolites (COX, prostaglandins)
- Chemokines (IL-8)
- Cytokins (GM-CSF)
- Proteases
What does brown-staining on a histological section in the human airway show?
Anti-NOS antibody results in brown staining to identify NOS
What exhibits a regulatory function on ciliary beat?
Nitric oxide speeds it up
What does contraction of airway smooth muscle lead to?
- Stimulates secretion into epithelial lining
- Closes airway to prevent accidentally inhaled particles from causing choking
Apart from secretion, what are 2 other functions of airway smooth muscle cells?
- Structure of airway
- Tone (airway caliber), contraction and relaxation
What does the smooth muscle in the airways secrete?
Mediators, cytokines and chemokines
How do the functions of airway smooth muscle cells change under inflammation?
- They contribute more to structure via hypertrophy and proliferation (e.g. in asthma)
- Secrete more mediators, cytokines and chemokines
- Produce prostaglandins, adhesion and NO molecules
What are some bronchoconstrictor mediators that are released from mast cells?
Histamine, cys-LTs and PGD2
What are mitogens?
Peptides that induce cell division
What is the blood flow levels to the airway mucosa?
100-150mL/min/100g
Where do bronchial arteries arise from?
Many sites on the aorta and intercostal arteries
How does the blood return from tracheal circulation?
Via systemic veins
How does blood return from bronchial circulation?
Via bronchial and pulmonary veins
What are the function of the tracheo-bronchial systemic circulation?
- Direct gas exchange between airway tissues and blood
- Warming and humidification of air
- Clears inflammatory mediators
- Clears inhaled drugs
- Supplies airways tissue with inflammatory cells and proteinaceous plasma for plasma exudation
What is plasma exudation?
The leak of plasma into the airway tissue and lumen
What are the four mechanisms of the control of airway function?
- Nerves
- Proteases
- Reactive gas species (e.g. NO)
- Regulatory and inflammatory mediators
What different types of nerves control airway function?
- Parasympathetic (cholinergic)
- Nitrous oxide sympathetic adrenergic pathway
- Sensory nerves
What effect does nitric oxide gas have on the smooth muscle in the airway?
It causes it to relax
What is the predominant parasympathetic neurotransmitter in the airway?
Acetylcholine
What does acetylcholine regulate?
Bronchoconstriction and mucus secretion
How many mediators do regulatory-inflammatory cells produce?
They can produce more than 1
What are the regulatory-inflammatory cells which are found in the airways?
Eosinophils, Neutrophils, Macrophages, Mast cells and T Cells
What are the functions of he regulatory-inflammatory cells found in the airways?
Contraction and relaxation of smooth muscle Secretions Plasma exudation Neural modulation Chemotaxis Remodelling
What percentage of the population suffers from ashtma?
5%
What event is common with asthma, COPD and cystic fibrosis?
An increase in airway inflammation
Why is it helpful for surfactant to be released by the alveolar cells?
Surfactant helps to create a moist surface for gas exchange to occur over as it is easier for oxygen to diffuse across the alveolar membranes when dissolved in a liquid
How does alveolar surfactant ensure that all the alveoli inflate at roughly the same time?
When the alveoli inflate with air, the surfactant becomes spread out. Smaller alveoli have more surfactant per area which reduces surface tension and allows faster inflation; eventually they all inflate at the same time
What is xenobiotic metabolism?
The metabolism of Nox-ous chemicals which might get into the airways
Describe what happens in the nerve pathways between the airway and brain/spinal cord when a peanut is inhaled
- The peanut goes down the airway and is detected by sensory nerves
- Sensory nerves send an AP up the vagus nerve, through the nodose ganglion and into the brainstem
- This sets up the cholinergic parasympathetic reflex, where ACh causes airway smooth muscle to contract to stop the peanut from going further down
- Once the peanut is coughed up, the adrenal gland secretes adrenaline, which relaxes smooth muscle to open the airway
What causes airway smooth muscle to relax due to the absence of sympathetic nerves that release noradrenaline?
Nitric oxide producing nerves cause brochondilation and airway smooth muscle relaxation
Outline the parasympathetic ‘motor’ pathway for airway control
- The vagus nerve innervates the corticospinal tract
- ACh is secreted in the cholinergic synapse of the postganglionic fibre and gland
- This stimulates bronchoconstriction, smooth muscle contraction and submucosal glands to secrete mucous
Outline airway control via the adrenergic reflex
Adrenal gland secretes adrenaline which directly causes bronchodilation and smooth muscle relaxation
