TBL 10 - Tracheobronchial Tree and Pulmonary Alveoli

Question 1

Where is the epithelium of the trachea and its airways derived from and where does the lung bud (respiratory diverticulum) come from?

Answer 1

Endoderm

Caudal outgrowth from the anterior wall of the distal foregut

Question 2

Where does the connective tissue, cartilage, and smooth muscle of the airways come from?

Answer 2

Mesenchymal cells of visceral mesoderm

Question 3

What does the tracheoesophageal septum do?

Answer 3

Divides distal foregut into posterior and anterior portions occupied by the esophagus and trachea, respectively

Question 4

What is the most common type of tracheoesophageal fistula and why can it be associated with polyhydramnios and pneumonia?

Answer 4

The upper portion of the esophagus ending in a blind bound and the lower segment forming a fistula with the trachea.
TEF results in polyhydramnios where amniotic fluid enters the trachea instead of the stomach and intestines causing pneumonitis and pneumonia

Question 5

Describe the differentiation process that is associated with angiogenic proliferation of pulmonary capillaries from the segmental pulmonary arteries

Answer 5

lung buds branch, differentiation of lobar and segmental bronchi occurs leading to differentiation at the distal ends of the segmental bronchi

Question 6

Describe fetal breathing and aspiration of amniotic fluid

Answer 6

Breathing movements before birth are important for for lung developing and conditioning respiratory muscles. At birth, lung fluid is absorbed by blood and lymph and some is expelled through trachea. Some fluid is resorbed from alveolar sacs creating a surfactant on the membrane preventing an air-water interface with high surface tension preventing collapse of the alveoli

Question 7

What is the purpose of the conducting airways before the alveolar sacs and what allows this to happen?

Answer 7

Moisten, warm, and filter air before the sacs. The respiratory epithelium has an underlying connective tissue with a dense microcirculation and glandular acini to secrete mucus onto the epithelium

Question 8

What is the connective tissue under the epithelium that lines the lumen called and what is the mucosa?

Answer 8

Lamina propria and it plus the epithelium are called the mucosa

Question 9

What type of cells make up the respiratory epithelium?

Answer 9

Basal cells and tall columnar cells that are ciliated or filled with mucus forming goblet cells

Question 10

What nerves stimulate mucus production?

Answer 10

Parasympathetic nerves

Question 11

What nerves inhibit mucus production?

Answer 11

Sympathetic nerves

Question 12

What do the motile cilia do?

Answer 12

Move the mucus layer along the apical surface towards the oral cavity for elimination or swallowing

Question 13

What is the respiratory mucosa characterized by?

Answer 13

Longitudinal folds forms by densely packed longitudinally oriented elastic fibers in the lamina propria. These fibers extends into the walls of the pulmonary alveoli

Question 14

What do the 16-20 C shaped rings of hyaline cartilage in the trachea and main bronchi do? What muscle is associated with them and what does the muscle do?

Answer 14

Prevent collapse of airways during respiration. The muscle is the tracheal and it contracts during forced expiration like coughing to prevent the rings from flaring open posteriorly

Question 15

Where do the respiratory epithelium and mucous glands extend into?

Answer 15

Lobar and segmental bronchi

Question 16

How is hyaline cartilage organized in lobar bronchi? Where does it end?

Answer 16

Discontinuous plates that become smaller as they progress and eventually terminate in the distal ends of the segmental bronchi

Question 17

How are bronchioles characterized?

Answer 17

Lack cartilage and mucous glands. They have smooth muscle that resides external to the bronchiolar mucosa

Question 18

Where does the circumferential smooth muscle layer begin and what does it do?

Answer 18

Lobar bronchi and it is involved in bronchoconstriction and bronchodilation

Question 19

What is the functional relevance of the histological observation that bronchioles lack goblet cells and mucous glands?

Answer 19

The mucus will probably increase surface tension and cause the alveoli to collapse. It can also clog up the system at this point

Question 20

What is the pathogenesis of asthma?

Answer 20

Heightened response of the trachobronchial tree to numerous stimuli. Mucosal and submucosal edema in the bronchi and bronchioles occurs as does thickening of the basement membrane, hypertrophy of the smooth muscle, and infiltration of leukocytes (eosinophils)

Question 21

How do elastic fibers in lobar and segmental bronchi, bronchioles, and stroma of the interalveolar septa contribute to normal respiration?

Answer 21

They encircle the smooth muscle helping with recoiling after expansion or constriction

Question 22

What type of cells line the bronchioles?

Answer 22

Simple columnar epithelium that are often ciliated. There are also Clara cells

Question 23

What are Clara cells?

Answer 23

Nonciliated columnar cells in the bronchioles. There are secretory cells that discharge material into the airway lumen. They play an antiinflammatory and detoxification role. They also are progenitor cells for the other bronchiolar epithelial cells in response to injury

Question 24

What forms the lungs parenchyma? And what is the stroma?

Answer 24

The alveoli constitutes 90% of the lung parenchyma, the functional portion of the organ. The storm is everything else, the structures and supporting tissues

Question 25

What makes up the alveolar epithelium

Answer 25

Type I pneumocytes (simple squamous epithelial cells) make up 95% of surface area. Cuboidal shaped type II pneumocytes make up the rest

Question 26

What do type II pneumocytes secrete and what is the function of that secretion?

Answer 26

Pulmonary surfactant. It contains complexes of phospholipids, protein, and carbohydrates that are part of the fluid that coats the alveolar surfaces preventing collapse of the alveoli by reducing surface tension

Question 27

What is the pathological significance of interalveolar pores (of Kohn)?`

Answer 27

Allows air from one alveolus to move to another. Allows spread of infection

Question 28

Why is progressive surfactant accumulation in the fluid-filled lungs before birth critical for neonatal respiration? When is the mature number of pulmonary alveoli attained?

Answer 28

Prevents development of a high surface tension from an air-water interface which would cause collapse of the lungs during expiration. New alveoli are formed during the first 10 years of life

Question 29

Why are premature infants susceptible to respiratory distress syndrome (RDS) and how is it treated?

Answer 29

They don’t have enough surfactant leading to partial collapse of the alveoli. Treatment involves artificial surfactant or treating mothers with glucocorticoids that stimulate surfactant production

Question 30

What is the interalveolar septum

Answer 30

Wall that adjacent alveoli in the alveolar sacs share

Question 31

Where do pulmonary capillaries reside?

Answer 31

Elastic fiber-rich stroke of the inter alveolar septa

Question 32

What forms the blood-air barrier and what is the function?

Answer 32

A basement membrane between the epithelium of the capillary and the type I pneumocytes. It allows the pulmonary circulation to be exposed to the filtered air at a very short diffusion distance

Question 33

What engulfs pathogens in the alveolar lumens and what is their course after engulfing the pathogens?

Answer 33

Macrophages remove debris from alveoli, they move up the bronchial tree, where they are carried by cilia and are eventually swallowed or
expectorated with mucus

Question 34

What are heart failure cells?

Answer 34

Macrophages that phagocytosed erythrocytes from the bloodstream that escaped (due to heart failure) into the alveolar spaces