Lecture 14: Respiratory System Flashcards
Clinical divisions of respiratory tract
- Upper
- Lower
Functional divisions of respiratory tract
- Conducting (respiratory epithelium)
- Respiratory (alveolar epithelium)
Nasal cavity
-Divided into 3 regions (meatuses) by inf., middle, superior conchae (turbinates)
-Conduct + condition air and contains olfactory sensory neurons (OSNs)
-Mid. meatus = larynx, upper meatus backwater region
Nasal conditioning of air
Nasal cavity slows, warms, and humidifies incoming air through the meatuses.
Olfactory epithelium
Part of upper concha, contains OSNs, sustentacular (support) cells, microvillar cells, Bowman’s small olfactory glands
Olfactory sensory neurons
OSNs are part of CNS and regenerate via basal progenitor cells. Blood-olfactory barrier is extension of BBB. Loss of regeneration leads to olfactory metaplasia, presbyosmia. Olfactory receptors embed in mucus layer w/ ciliated surface.
Respiratory epithelium cells
Psueodstratified, ciliated conducting airways.
-Ciliated cells
-Mucous cells
-Brush (tuft) cells
-Small granule (neuroendocrine) cells
-Basal cells
-In distal bronchioles: club cells, ionocytes
Mucociliary escalator
Cilia in respiratory epithelium pushes mucus up towards the throat to clear microbes, debris.
Brush cells
Rare; have microvillous border and may play some immune function
Basal cells
Resident SCs of respiratory epithelium
Ciliated cells
Most numerous cell of respiratory epithelium. Contains many ACE2 receptors (COVID-19 path.)
Conducting portion of respiratory tract
Nose -> trachea -> bronchi -> bronchiole -> terminal bronchiole
Respiratory portion of respiratory tract
Respiratory bronchiole -> alveolar duct -> alveolar sac -> alveolus
Trachea
-Contains submucosal glands and Bronchial Assoc. Lymphoid Tissue (BALTs)
-No muscularis mucosae
-C-shaped hyaline cartilage rings; incomplete ring allows contraction/dilation
-Trachealis muscle (contract/dilate)
Bronchus
Plate-shaped hyaline cartilage. Divided into extra and intrapulmonary regions; first branching of airway.
Bronchioles
Smallest branches of conducting airways. Contains club cells and ionocytes
Club cells
Form modified epithelium of bronchioles. Secretory protein + surfactant-LIKE substance for epithelial production/airway patency. Non-ciliated domed apical aspect.
Ionocytes
Small subset of club cells; express Cl- transporter gene to thin airway mucus. LoF -> cystic fibrosis
Terminal bronchioles
End of conducting airway; smooth transition into respiratory bronchioles, which have both conduct. and respiratory functions.
Respiratory epithelium immune functions
-Thick basement membrane (lucida + densa); thickens more w/ chronic particulate exposure
-Local metaplasia to SSNK response to chronic insult; islands (“hillocks”) more resistant to chem. degradation; also causes impaired mucous removal + increase in mucus gland size -> coughing (e.g. smoker’s cough). Reversible w/ irritant removal.
Alveolus/alveolar sac/alveolar duct
Alveoli = basic respiratory units of lung, several share walls in alveolar sac. Alveolar duct connects shared airway w/ distal bronchioles. Outer rim of alveoli lined w/ elastic fibers for resting contractility
Alveolar epithelium
Alveolar epithelium/alveolar septum lines entire respiratory portion of lung. Maintains blood-air barrier
Interalveolar septum (alveolar wall) features
Mostly as thin as possible, but thickens to include ECM, CT cells, (elastic) fibers. Thin = air-blood barrier, capillaries
Thick = pulmonary interstitum: collagen, elastin, capillaries/lymphatics; fibroblasts, immune cells
Pleural space
Space surrounding lungs. Inspiration creates negative pressure to passively expand lungs.
Atelectasis
Lack of expansion in lungs; complete/partial collapsed lung e.g. w/ pulmonary edema (fluid in alveoli)
Alveolar cells
- Alveolar Type 1 pneumocytes (AT1)
- Alveolar Type 2 pneumocytes (AT2)
AT1 cells
Thin squamous cells bounding capillaries; primary gas exchange site. Form occluding junctions.
AT2 cells
Thicker cuboidal/spherical minority cells in alveoli, usually at corners of alveolar walls. Contain lamellar bodies to secrete surfactant, GM-CSF cytokines. High ACE2, TMPRSS2 receptor amount (Covid-19)
Serous surfactant in alveoli
Lipid monolayer which reduces surface tension in alveoli to promote gas exchange. Mostly p-tidylcholine, produced from AT2 lamellar bodies
Alveolar SCs
Resident SCs for AT1, AT2 cells
2 main types of lung capillary endothelial cells
- Aerocytes
- General capillary (gCap)
Aerocytes
Underlie all thin regions of alveolar wall and some of the thick regions too. Mediate gas exchange and leukocyte diapedesis (capillary diapedesis unique to lungs).
gCap cells
Aerocyte progenitors (endothelial cells) which only border thick alveolar wall, contacting CT elements (pericytes, ECM, etc.). Produce compounds for vasomotor tone.
5 types of lung macrophages
- Alveolar
- Interstitial
- Systemic monocytes
- Airway
- Pleural
Dust cell = generic term for old lung mΦ’s
Alveolar mΦ’s
Reside on luminal epithelial surface, w/in alveoli. Fetally seeded and less immunogenic than other mΦ’s. Either retain particles for life in CT (dust cells) or exit by mucociliary elevator
Interstitial mΦ’s
Coordinate local/systemic immunity w/ DCs. Found in large numbers in collagenous CT w/ supravital staining
Systemic monocytes
Resident marginal pool found in lung vasculature stuck to endothelium; “on demand”. Lung vessels also contain the largest neutrophil marginal pool
Airway mΦ’s
Found in bronchial/bronchiolar lumens
Pleural mΦ’s
Majority cell found in pleural fluid. Phagocytose debris.
2 lung circulations
- Pulmonary (oxygenation of blood from right heart; low P)
- Bronchial (small systemic supply to lung)
3 main functions of respiratory system
- Air conduction
- Air filtration/conditioning
- Gas exchange (respiration)
Pleural surface
Continuum forming closed pleural space. Visceral/parietal pleura lubricated and coupled via serous fluid for free, rapid lung movement relative to chest wall.
Pulmonary circulation
Functional vessels that run ALONG airway tissue; arteries within the alveoli and travel alongside bronchi, veins in CT septum adjacent to lungs
Bronchial circulation
Systemic vessels that run WITHIN airway walls; branch from aorta. Venous return w/ rest of systemic circulation OR anastamosis w/ pulmonary circulation
Blood-air barrier components
Thinnest part of alveolar membrane.
1. Thin surfactant
2. Alveolar epithelium (AT1s)
2. Fused alveolar/endothelial basement membranes
4. Endothelial cell aerocytes
Pores of Kohn
Alveolar pores, Equalize alveolar P and enable collateral ventilation, mΦ migration
