28 - Structural Properties of the Lung

Question 1

1) Functions of the lung

Answer 1

• Defense mechanism
• Metabolism/handling of bioactive materials
• Phonation
• Acid/base balance
• Gas exchange

Question 2

2) Components of the upper airway

Answer 2

• Nose, sinuses, larynx (nose  vocal cords)

Question 3

Function of upper airway

Answer 3

o Condition inspired air so that by the time it reaches the trachea, it is at body temperature and fully humidified.
o Nose also filters, entraps, and clears particles larger than 10 micro meters in size.
o Also, resistance to airflow – nose does 50% during quiet breathing and increases during viral infections and increased airflow (Ex. Exercise).
o If nasal resistance becomes too high, mouth breathing begins.
o Epiglottis/arytenoids cover vocal cords during swallowing.
o Also, defense – interior of nose line by respiratory epithelium interspersed with surface secretory cells (that produce important immunoglobins, inflammatory mediators, and interferons).
o Sinuses lighten the skull, protection during trauma, and add resonance to voice.

Question 4

3) Differentiate airway conducting zone and respiratory zone

Answer 4

• Conducting zone:
o First 16 of 23 generations of airways including the bronchi, bronchioles, and terminal bronchioles.
• Respiratory zone:
o 17 thru 23 of generations including the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.

Question 5

4) Describe main structural properties and roles of different zones of airway

Answer 5

• Conducting zone
o Inner mucosal surface, smooth muscle layer, outer connective tissue (in large bronchi contains cartilage)
• Bronchial wall
o Contains ciliated psedostratified epithelium, smooth muscle cells, mucus glands, connective tissue, and cartilage
• Smaller bronchioles
o Psuedostratified epithelium, cartilage absent, thin wall. Contains tall cells and shorter basal cells (all attached to basement membrane)

Question 6

5) Describe structural properties and roles of mucous production/clearance systems

Answer 6

• Goblet cell
o Interspersed among epithelial cells
o Produce mucous in airways and increase in smokers
• Submucosal tracheobronchial glands
o Present wherever there is cartilage.
o They increase in chronic bronchitis.
o Mucous and serous cells
• Both above not found in bronchioles or lower
• Clearance system
o Respiratory tract is covered with pseudostratified, columnar epithelium up to bronchioles with cilia. Mucociliary escalator is important airway clearance mechanism and part of the defense.

Question 7

6) Describe main contributors to airflow resistance in upper/lower respiratory tracts

Answer 7

• Upper respiratory:
o Nose accounts for 50% during quiet breathing
o Also, epiglottis that is swollen
• Lower respiratory:
o Bronchioles/bronchi muscle cx and secretion of glands.

Question 8

7) Define respiratory unit and components of the respiratory membrane

Answer 8

• Respiratory unit
o Consists of respiratory bronchiole, alveolar ducts, atria and alveoli (site of gas exchange in the lung)
• Respiratory membrane
o Layer of fluid containing surfactant, Alveoli epithelium, epithelial basement membrane, interstitial fluid, endothelial basement membrane, endothelium

Question 9

8) Name main cell types of the alveolar wall and their functions

Answer 9

• Squamous lining cells (type I)
o Primary lining cells (large cytoplasmic extensions), fewer in number than type II but contribute larger surface area.
• Granular pneumocytes (type II)
o Contain lamellar inclusion bodies. Produce/secrete surfactant which lowers surface tension
• Also have pulmonary alveolar macrophages, lymphocytes, plasma cells, mast cells.
o Mast cells contain heparin, various lipids, histamine, proteases that participate in allergic reactions.

Question 10

9) Describe main components of lung interstitium and their roles

Answer 10

• Fibroblasts
o Synthesize and secrete collagen and elastin (play a large role in matrix formation and physiology of lung).
o Collagen – major structural component of lung that limits distensibility.
o Elastin – major contributor to elastic recoil of lung.
• Cartilage
o Resilient, CT supporting conducting airways of lung
• Smooth Muscle
o Can dilate or constrict in response to chemical, irritant, or mechanical stimulation.
• Kultschitzy cells
o Neuroendocrine cells that secrete biogenic amines like dopamine and serotonin
• Also contains lymphatics, capillaries, and variety of other cells

Question 11

10) Describe differences between parietal and visceral pleurae

Answer 11

• Stomata: located only in parietal pleura and is the lymphatic exit for pleural liquid, protein, and cells. Eventually drains into the mediastinal lymph nodes.
• Microvessels: are much closer to the pleural surface in parietal pleura than the ones in visceral
• Blood Supply:
o Parietal
 Supplied by branches of intercostal arteries. Venous system drains into bronchial veins.
o Visceral
 Supplied by bronchial circulation. Venous system drains largely into pulmonary veins.

Question 12

11) Describe formation of pleural fluid in physiological states

Answer 12

• Changes that affect balance of [water/proteins]: microvascular hydrostatic/oncotic pressure, pleural pressure, microvascular permeability, and impaired lymphatic drainage.
• Microvascular endothelium only important barrier to solute/water exchange in pleural space
• Visceral pleura microvasculature is father away from pleural space and bronchial veins drain into pulmonary veins meaning there is a lower pressure in the pulmonary veins  (Lower filtration pressure in visceral compared to parietal)
• Pleural liquid/protein leave by parietal pleura stomata.

Question 13

12) Describe main pathophysiological mechanisms of pleural effusion

Answer 13

• Increase rate of formation
o ↑ microvascular hydrostatic pressure: congestive heart failure or chronic venous hypertension leading to increased pulmonary venous pressure (leaks thru visceral meothelium)
o ↓ microvascular oncotic pressure: probably because of the functional reserve of parietal pleural lymphatic system
o ↓ in pressure of pleural space: Atelectasis and separation of lung from chest wall ↓ pleural space fluid movement during respiration (inhibiting optimal parietal pleural lymphatic drainage)
o ↑ in microvascular permeability: inflammation of microvessels, which also could occlude lymphatic drainage with debris
o Movement of fluid from peritoneal to pleural space: diaphragmatic defects or diaphragmatic lymphatics
• Decreased clearance rate
o Systemic Venous Hypertension
o Blockage of clearance: anywhere from stomata to mediastinal lymph nodes
• Fluid formation can occur slowly or rapidly depending on etiology