Structure + Function of Airways Flashcards
What kind of branching do the airways have?
dichotomous branching
How is the trachea held open?
using cartilage
Why does the trachea have a gap in the back?
gap for the oesophagus
How are the lungs sectioned off?
superior lobes, middle lobes, inferior lobes
How is the trachea sectioned off?
trachea → primary bronchi → secondary (lobar) bronchi → tertiary (segmental) bronchi → bronchioles
What is the pathway of air from the bronchioles to the alveoli?
terminal bronchiole → respiratory bronchiole → alveoli duct → alveoli
What cells are found in the alveolar region?
→ type 1 cell
→ type 2 cell
→ macrophages
→ stromal cells (fibroblasts)
Why do alveoli have intimate contact with the capillary endothelium?
to allow for gas exchange across the two membranes
What is a Type 1 cell?
makes up the walls, very thin + delicate barrier for gas exchange
What is a Type 2 cell?
replicates to replace type 1 cells, secretes surfactant + antiproteases, has xenobiotic metabolism
Why do Type 2 cells secrete surfactant?
to reduce surface tension - prevents collapse of the alveolus + prevents sticking together of inner walls
Why are fibroblasts present in the alveoli?
produce the matrix that holds alveoli together
What percentage of alveolar surfaces are covered in Type 1 + 2 cells respectively?
Type 1 = 95%
Type 2 = 5%
Are there more Type 1 cells or Type 2 cells?
Type 2
What are the basic functions of the airways?
gas exchange (conduct O2 to alveoli, conduct CO2 out of lung)
What 3 factors facilitate the functions of the airways?
→ mechanical stability (cartilage)
→ control of calibre (smooth muscle)
→ protection + ‘cleansing’
What are the 2 main nasal passageways?
pharynx + conchae
What are the 3 regions of the pharynx?
nasopharynx, oropharynx, laryngopharynx
What is the purpose of the pharynx as a passageway?
foods, liquids + air
What is the purpose of the conchae as a passageway?
highly vascular - contributes to warming + humidification of intra-nasally-inhaled air - nasal hairs filter out large particles
What is the organisation of airway structures? (from out to in)
→ smooth muscle cells + mast cells
→ submucosal glands + blood vessels + fibroblasts
→ epithelial ciliated cells + goblet cells
→ airway lumen
What are the 7 airway call types?
→ lining → contractile → secretory → connective → neuroendocrine → vascular → immune
What are examples of lining cells?
ciliated, intermediate, brush basal
What are examples of contractile cells?
Smooth muscle (airway, vasculature)
What are examples of secretory cells?
Goblet (epithelium), mucous, serous (glands)
What are examples of connective cells?
Fibroblast, interstitial cell (elastin, collagen, cartilage)
What are examples of neuroendocrine cells?
Nerves, ganglia, neuroendocrine cells, neuroepithelial bodies
What are examples of vascular cells?
Endothelial, pericyte, plasma cell (+ smooth muscle)
What are examples of immune cells?
Mast cell, dendritic cell, lymphocyte, eosinophil, macrophage, neutrophil
What is the main purpose of goblet cells?
secrete mucus in order to protect the mucous membranes
How do goblet cells accomplish their main purpose?
secreting mucins continuously in order to repair + replace existing mucus layer
What is a mucin?
large glycoproteins formed mostly by carbohydrates
What’s responsible for the gel-like properties of mucin?
glycans (bound carbohydrates) - attracting relatively large quantities of water
How are mucins stored?
stored in in granules onside the goblet cells before being released to the lumen of the organ
How is mucin secretion stimulated?
stimulated by irritants e.g. dust + smoke
How is mucus in the airways swept away?
→ mucociliary clearance - cilia of the respiratory endothelium
→ propelled form lungs + out of pharynx
What are the benefits of mucociliary clearance?
results in removal of debris + pathogens
What are submucosal glands made up of?
mucous acini + serious acini
What is an acini?
any cluster of cells that resembles a many-lobed “berry”
What do the mucous acini + serious acini do?
m = secrete mucus s = secrete anti-bacterial
What function do the submucosal glands have?
→ secretion of mucus, water + salts (e.g. Na+ + Cl-)
→ physical barriers
→ production of regulatory + inflammatory mediators
What are the regulatory + inflammatory mediators released by submucosal glands?
→ Nitric oxide (NO) → Carbon monoxide (CO) → Arachidonic acid metabolites (e.g. prostaglandins via COX) → Chemokines (e.g. (IL)-8 ) → Cytokines (e.g. GM-CSF) → Proteases
How is nitric oxide produced in the airways?
via nitric oxide synthase
How is carbon monoxide produced in the airways?
via hemeoxygenase
What staining can be used to identify NOS?
brown staining
What happens to the structure of airway smooth muscle due to inflammation?
hypertrophy + proliferation
What happens to the tone of airway smooth muscle due to inflammation?
contraction + relaxation
What does airway smooth muscle secrete in response to inflammation?
mediators + cytokines + chemokines
What role does airway smooth muscle play in asthma?
airway narrowing
What percentage of tracheo-bronchial circulation makes up cardiac output ?
1-5%
What is the approx blood flow to airway mucosa?
100-150 mL/min/100g tissue
Where do bronchial arteries arise from?
many sites on the aorta, intercostal arteries, etc.
What vessels return blood from tracheal circulation?
systemic veins
What vessels return blood from bronchial circulation?
bronchial + pulmonary veins to both sides of the heart
What are some purposes of tracheo-bronchial circulation?
→ good gas exchange
→ contributes to warming + humidification of inspired air
→ clears inflammatory mediators
→ clears inhaled drugs (good/bad, depending on drug
→ supplies airway tissue + lumen w/ inflammatory cells
→ supplies airway tissue + lumen w/ proteinaceous plasma)
What nerves control airway function?
→ parasympathetic (cholinergic)
→ sympathetic (adrenergic?)
→ sensory
What regulatory + inflammatory mediators control airway function?
→ histamine
→ arachidonic acid metabolites (e.g. prostaglandins, leukotrienes)
→ cytokines
→ chemokines
What other aspects control airway function?
→ proteinases + proteases (neutrophil elastase)
→ reactive gas species (e.g. O2, NO)
What main nerve does a lot of innervation for the airways?
vagus (X)
What afferent pathways run through the vagus nerve?
sensory neurones from sub-cerebral nodose + jugular ganglion
What efferent pathways run through the vagus nerve?
parasympathetic ‘motor’ (cholinergic) neurones
Are there any sympathetic pathways for the control of the airways?
no <3
What is the main parasympathetic neurotransmitter in the airways?
Acetylcholine - regulated bronchoconstriction - mucus secretion
What nervous pathways cause airway constriction?
parasympathetic
What nervous pathways cause the airways to relax?
nerves that release nitric oxide
What 5 regulatory-inflammatory cells are usually present in the airways?
→ eosinophils → neutrophils → macrophages → mast cells → T-lymphocytes
What are the functions of the regulatory-inflammatory cells?
- Contraction and relaxation of smooth muscle
- Secretions (mucin, water etc)
- Plasma exudation
- Neural modulation
- Chemotaxis
- Remodelling
What respiratory diseases involve loss of airway control?
- asthma
- chronic obstructive pulmonary disease (COPD)
- cystic fibrosis
What is asthma?
clinical syndrome characterised by increased airway responsiveness to a variety of stimuli
What are symptoms of asthma?
- dyspnoea (shortness of breath)
- wheezing
- cough
What are the consequences of asthma?
leads to airway obstruction, mucus hypersecretion, mucus plugs etc.
