CTB6: Cell biology of the respiratory tract

Question 1

How many L of air do we inhale a day under normal circumstances?

Answer 1

12000L

Question 2

Why is it important that the respiratory tract has adaptations to maximise airflow whilst minimising damage?

Answer 2

The air contains microbial and non-microbial particles as well as noxious gases

Question 3

What are goblet cells are responsible for secreting?

Answer 3

mucin, onto the airway surface. The goblet cells can secrete mucus globules almost as large as the size of the cell itself

Question 4

What is mucin?

Answer 4

high molecular weight glycoproteins

Question 5

How does secretion of mucin occur?

Answer 5

occurs by exocytosis and is a highly regulated, rapid process

Question 6

What induces the secretion of mucin?

Answer 6

ATP

Question 7

Where are submucosal glands normally found?

Answer 7

predominantly found in the larger airways and reduce greatly in number by the time the smaller airways are reached, the distal airways contain no submucosal glands

Question 8

What do submucosal glands contain?

Answer 8

Secretory acini 
- Mucous acini
- Serous acini
Collecting duct
Ciliated duct

Question 9

What do serous acini secrete?

Answer 9

Watery, serous secretions (lysozyme and lactoferrin) which have been hypothesised to wash the mucous acini’s thicker, mucous secretions (mucins) into the collecting duct

Question 10

What is secreted in order to make an aqueous electrolyte solution of mucins and other high molecular weight proteins?

Answer 10

Na+ and Cl-, along with water, secreted by the glands

Question 11

What give the mucus viscoelastic, gel-like properties which allows it to entrap particles and be swept away by cilia?

Answer 11

Other high molecular weight proteins

Question 12

What two characteristics of ciliated cells allow them to maintain the ciliary beat?

Answer 12

Numerous cilia on their apical surface and mitochondria to provide sufficient ATP to maintain the ciliary beat

Question 13

How frequently do cilia beat?

Answer 13

~7-9/s

Question 14

How are cilia arranged?

Answer 14

axoneme

Question 15

What is the axoneme made up of?

Answer 15

• 9+2 arrangement of microtubules
• Linking dynein arms
• Nexin links to prevent microtubules moving with respect to one another

Question 16

What allows the ciliary to beat?

Answer 16

microtubules slide over one another

Question 17

What can the ciliary beat be described as?

Answer 17

Metachronicity

Question 18

What does metachronicity mean?

Answer 18

This describes a sequential movement of fields of cilia, not a synchronised movement

Question 19

Describe how cilia move

Answer 19

A field of cilia first undergo a power stroke which moves the viscoelastic gel forward, then disengages with the mucus using a recovery stroke which is at 90˚ to the power stroke. The second field of cilia performs a power stroke whilst the first field undergoes recovery.

Question 20

What does airway smooth muscle control?

Answer 20

The patency of the airways

Question 21

Where is there greatest and least mass of airway smooth muscle?

Answer 21

It is found in greater mass in the larger airways and in smaller mass in the distal airways.

Question 22

What is tone (passive partial contraction) thought to be important for?

Answer 22

to prevent large accidentally inhaled objects from penetrating too far into the airways

Question 23

What happens to the airways smooth muscle to increase airflow?

Answer 23

It relaxes

Question 24

What is tracheobronchial circulation made up of?

Answer 24

Vast network of blood vessels found under the airway epithelium

Question 25

How much does blood flow to the airway mucosa make up of cardiac output?

Answer 25

Just 1-5%, but there is approx. 100-150ml of blood per minute per 100g of tissue which is higher than almost any other tissue

Question 26

How is high output of blood to airway mucosa facilitated?

Answer 26

• Bronchial arteries arising from many sites on aorta, intercostal arteries and other
• Blood returns from tracheal circulation via systemic veins
• Blood returns from bronchial circulation to both sides of the heart via bronchial and pulmonary veins

Question 27

What facilitates airway homeostasis?

Answer 27

This vascular plexus highly perfuses the airways includes:

• aiding gas exchange
• warms and humidifies the inhaled air
• clears inflammatory mediators and inhaled drugs
• supplies the airway tissue with inflammatory cells and proteinaceous plasma

Question 28

What influences influences smooth muscle contraction, mucus secretion, and vascular tone?

Answer 28

nervous control

Question 29

Under normal circumstances, what maintains minimal smooth muscle tone and airway patency?

Answer 29

parasympathetic (cholinergic) outflow

Question 30

What does accidental inhalation of a large object activate and lead to?

Answer 30

sensory nerves which sets up a cholinergic reflex to constrict the airways and induce mucus secretion to aid in expulsion of the foreign object.

Question 31

What induces relaxation of the airways?

Answer 31

Non-neuronal adrenaline from the adrenal medulla induces relaxation

Question 32

In humans and other animals, what causes neuronally-induced relaxation?

Answer 32

Humans: Nitric Oxide released from Nitric Oxide Synthase containing nerves (NOS nerves)
Other animals: sympathetic outflow has been shown to induce relaxation.

Question 33

How do immune cells protect the airways?

Answer 33

pulmonary macrophages ingest inhaled pathogens, neutrophils combat infections and eosinophils and lymphocytes fight nematode infections.
Mast cells produce histamines, prostaglandins and leukotrienes.

Question 34

What do histamines do to

a) airway smooth muscle
b) vascular smooth muscle
c) mucus secretion
d) plasma exudation
e) nervous system control

Answer 34

Histamines contract airway smooth muscle, relax vascular smooth muscle, induce mucus secretion and plasma exudation, and alter nervous control.

Question 35

What can cytokines and growth factors do to the respiratory tract?

Answer 35

Cytokines and growth factors can also remodel the respiratory tract in respiratory diseases