Lecture 14: Respiratory System

Question 1

Clinical divisions of respiratory tract

Answer 1

1. Upper
2. Lower

Question 2

Functional divisions of respiratory tract

Answer 2

1. Conducting (respiratory epithelium)
2. Respiratory (alveolar epithelium)

Question 3

Nasal cavity

Answer 3

-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

Question 4

Nasal conditioning of air

Answer 4

Nasal cavity slows, warms, and humidifies incoming air through the meatuses.

Question 5

Olfactory epithelium

Answer 5

Part of upper concha, contains OSNs, sustentacular (support) cells, microvillar cells, Bowman’s small olfactory glands

Question 6

Olfactory sensory neurons

Answer 6

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.

Question 7

Respiratory epithelium cells

Answer 7

Psueodstratified, ciliated conducting airways.
-Ciliated cells
-Mucous cells
-Brush (tuft) cells
-Small granule (neuroendocrine) cells
-Basal cells
-In distal bronchioles: club cells, ionocytes

Question 8

Mucociliary escalator

Answer 8

Cilia in respiratory epithelium pushes mucus up towards the throat to clear microbes, debris.

Question 9

Brush cells

Answer 9

Rare; have microvillous border and may play some immune function

Question 10

Basal cells

Answer 10

Resident SCs of respiratory epithelium

Question 11

Ciliated cells

Answer 11

Most numerous cell of respiratory epithelium. Contains many ACE2 receptors (COVID-19 path.)

Question 12

Conducting portion of respiratory tract

Answer 12

Nose -> trachea -> bronchi -> bronchiole -> terminal bronchiole

Question 13

Respiratory portion of respiratory tract

Answer 13

Respiratory bronchiole -> alveolar duct -> alveolar sac -> alveolus

Question 14

Trachea

Answer 14

-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)

Question 15

Bronchus

Answer 15

Plate-shaped hyaline cartilage. Divided into extra and intrapulmonary regions; first branching of airway.

Question 16

Bronchioles

Answer 16

Smallest branches of conducting airways. Contains club cells and ionocytes

Question 17

Club cells

Answer 17

Form modified epithelium of bronchioles. Secretory protein + surfactant-LIKE substance for epithelial production/airway patency. Non-ciliated domed apical aspect.

Question 18

Ionocytes

Answer 18

Small subset of club cells; express Cl- transporter gene to thin airway mucus. LoF -> cystic fibrosis

Question 19

Terminal bronchioles

Answer 19

End of conducting airway; smooth transition into respiratory bronchioles, which have both conduct. and respiratory functions.

Question 20

Respiratory epithelium immune functions

Answer 20

-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.

Question 21

Alveolus/alveolar sac/alveolar duct

Answer 21

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

Question 22

Alveolar epithelium

Answer 22

Alveolar epithelium/alveolar septum lines entire respiratory portion of lung. Maintains blood-air barrier

Question 23

Interalveolar septum (alveolar wall) features

Answer 23

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

Question 24

Pleural space

Answer 24

Space surrounding lungs. Inspiration creates negative pressure to passively expand lungs.

Question 25

Atelectasis

Answer 25

Lack of expansion in lungs; complete/partial collapsed lung e.g. w/ pulmonary edema (fluid in alveoli)

Question 26

Alveolar cells

Answer 26

1. Alveolar Type 1 pneumocytes (AT1) 2. Alveolar Type 2 pneumocytes (AT2)

Question 27

AT1 cells

Answer 27

Thin squamous cells bounding capillaries; primary gas exchange site. Form occluding junctions.

Question 28

AT2 cells

Answer 28

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)

Question 29

Serous surfactant in alveoli

Answer 29

Lipid monolayer which reduces surface tension in alveoli to promote gas exchange. Mostly p-tidylcholine, produced from AT2 lamellar bodies

Question 30

Alveolar SCs

Answer 30

Resident SCs for AT1, AT2 cells

Question 31

2 main types of lung capillary endothelial cells

Answer 31

1. Aerocytes 2. General capillary (gCap)

Question 32

Aerocytes

Answer 32

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).

Question 33

gCap cells

Answer 33

Aerocyte progenitors (endothelial cells) which only border thick alveolar wall, contacting CT elements (pericytes, ECM, etc.). Produce compounds for vasomotor tone.

Question 34

5 types of lung macrophages

Answer 34

1. Alveolar 2. Interstitial 3. Systemic monocytes 4. Airway 5. Pleural Dust cell = generic term for old lung mΦ's

Question 35

Alveolar mΦ's

Answer 35

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

Question 36

Interstitial mΦ's

Answer 36

Coordinate local/systemic immunity w/ DCs. Found in large numbers in collagenous CT w/ supravital staining

Question 37

Systemic monocytes

Answer 37

Resident marginal pool found in lung vasculature stuck to endothelium; "on demand". Lung vessels also contain the largest neutrophil marginal pool

Question 38

Airway mΦ's

Answer 38

Found in bronchial/bronchiolar lumens

Question 39

Pleural mΦ's

Answer 39

Majority cell found in pleural fluid. Phagocytose debris.

Question 40

2 lung circulations

Answer 40

1. Pulmonary (oxygenation of blood from right heart; low P) 2. Bronchial (small systemic supply to lung)

Question 41

3 main functions of respiratory system

Answer 41

1. Air conduction 2. Air filtration/conditioning 3. Gas exchange (respiration)

Question 42

Pleural surface

Answer 42

Continuum forming closed pleural space. Visceral/parietal pleura lubricated and coupled via serous fluid for free, rapid lung movement relative to chest wall.

Question 43

Pulmonary circulation

Answer 43

Functional vessels that run ALONG airway tissue; arteries within the alveoli and travel alongside bronchi, veins in CT septum adjacent to lungs

Question 44

Bronchial circulation

Answer 44

Systemic vessels that run WITHIN airway walls; branch from aorta. Venous return w/ rest of systemic circulation OR anastamosis w/ pulmonary circulation

Question 45

Blood-air barrier components

Answer 45

Thinnest part of alveolar membrane. 1. Thin surfactant 2. Alveolar epithelium (AT1s) 2. Fused alveolar/endothelial basement membranes 4. Endothelial cell aerocytes

Question 46

Pores of Kohn

Answer 46

Alveolar pores, Equalize alveolar P and enable collateral ventilation, mΦ migration