The structure of the lower respiratory tract

Question 1

What are the main functions?

Answer 1

Gas exchange:
- 20m2 gas exchange area per lung
- Minute ventilation approx 5 litres
- Cardiac output approx 5 Litres/minute

Question 2

What are the main airways of the lower respiratory tract?

Answer 2

• Trachea
• Main Bronchi
• Lobar Bronchi
• Segmental branches
• Respiratory Bronchiole
• Terminal Bronchiole
• Alveolar Ducts and Alveoli
• Pleura

Question 3

Where is the trachea?

Answer 3

• Larynx to carina (5th thoracic vertebra)
• Heads into the superior mediastinum carina at the sternal angle level

Question 4

What are some features of the trachea

Answer 4

• Oval in cross section
• Pseudo stratified, ciliated, columnar epithelium
• Goblet cells (produce mucus in trachea)
• Semicircular cartilages
• Mobile (3 cm and 1cm, superior and inferior)

Question 5

What is the trachea arterial supply?

Answer 5

Inferior thyroid artery

Question 6

How is the trachea innervated?

Answer 6

Sensory innervation; recurrent laryngeal nerve

Question 7

How are the left and right bronchi arranged

Answer 7

• Sharp division between them
• The right main bronchus is more vertically disposed: 1-2.5cm long and it is related to the right pulmonary artery
• The left main bronchus is 5cm long and related to the aortic arch

Question 8

What are lobar bronchi?

Answer 8

Also called lobar bronchi, the secondary bronchi are located near the middle of the lungs. There is one secondary branch per lobe of the lung. The right lung has three secondary bronchi, and the left lung has two.

Question 9

What lobes do the lobar bronchi supply?

Answer 9

Right: Upper, middle, lower lobe
Left: Upper (+lingular) and lower lobe

Question 10

What are segmental bronchi?

Answer 10

Segmental bronchi undergo further branching and a decrease in diameter to the level of the bronchioles

Question 11

What is the right segmental bronchi divided into?

Answer 11

Upper lobe : Apical, Anterior, Posterior
Middle lobe: Medial and lateral
Lower lobe: Apical, Ant, Post, Med, Lat
Each segment supplied by small bronchi

Question 12

What is the left segmental bronchi divided into?

Answer 12

Upper lobe: Apico-posterior, Anterior
Lingular (part of upper lobe): Superior and Inferior
Lower lobe: Apical, Ant, Post, Lat

Question 13

What properties do the bronchioles, alveolar ducts and alveoli have?

Answer 13

• Multiple sub-divisions

Question 14

How are terminal and respiratory bronchioles distinguished?

Answer 14

• Respiratory bronchioles have discernible alveoli protruding from them
• Terminal bronchioles divide into respiratory bronchioles

Question 15

What is the acinus?

Answer 15

• Distal to the terminal bronchiole
• Alveoli more profuse with increasing generation of subdivision
• Ducts are short tubes with multiple alveoli
• Interconnection between alveoli exist (pores of Kohn)

Question 16

Where are type 1 pneumocytes found?

Answer 16

Type I pneumocytes cover 70% of the internal surface of each alveolus. These cells are thin and squamous, ideal for gas exchange.

Question 17

Where are Type 2 pneumocytes found?

Answer 17

Type II pneumocytes are identified as the synthesizing cells of the alveolar surfactant, which has important properties in maintaining alveolar and airway stability. Type 2 pneumocytes represent 60% of the alveolar cell population numerically, but occupy only 5–10% of the alveolar surface area.

Question 18

What do the alveoli contain?

Answer 18

• Alveolar macrophage (type of white blood cell)
• basement membrane
• interstitial tissue
• capillary endothelial cells

Question 19

What are the two main layers of pleura?

Answer 19

Visceral (applied to the lung surface)
Parietal (applied to the internal chest wall)

Question 20

What are some features of pleura?

Answer 20

• single cell layer
• small amount of fluid between them
• continuous with each other at lung root

Question 21

What sensation does parietal pleura have?

Answer 21

Pain sensation

Question 22

What inner action does visceral pleura have ?

Answer 22

Autonomic innervation