CTB6 - Cell Biology of the Respiratory Tract

Question 1

What are the two main functions of the airways?

Answer 1

Maximise airflow. Minimise airway damage.

Question 2

Give four key features of the airway epithelium. Describe each briefly.

Answer 2

Goblet cells - chalice shaped cells protruding from epithelium into lumen. Secrete mucus.
Granules within the goblet cells - contain dehydrated glycosylated mucin proteins which undergo hydration and are released into lumen.
Ciliates cells - contain cilia to participate in mucociliary clearance, clearing the lumen when needed. Protective feature.
High mitochondrial density - provides metabolic energy for beating of cilia to allow for mucociliary clearance.

Question 3

What is the main nutrient required from inspired air?

Answer 3

Oxygen

Question 4

What types of exogenous particles may cause damage to the airway if allow to penetrate deep into the airways?

Answer 4

Pollen. Pollutants. Microbes. Tobacco. Noxious gases.

Question 5

What is the main role of goblet cells, and which other airway epithelium structure do they work with, in order to perform this role?

Answer 5

Secretion of mucus - in the form of mucin glycoproteins. Work alongside submucosal glands.

Question 6

Discuss the process of how mucus is secreted onto the airway lumen.

Answer 6

Dehydrated mucin granules present within goblet cells. They translocated within the cell to the apical surface. Open pore is formed upon fusion of granule with membrane. Water is absorbed by the granules via the pore. Granule swells to great extent, hydrated mucin are then released via exocytosis into airway lumen.

Question 7

What is the role of ATP in mucin secretion?

Answer 7

ATP acts as a secretagogue - induces secretion of mucin.

Question 8

Does the secretion of mucin from goblet cells occur only in vivo or in vitro?

Answer 8

Can occur in vitro provided that water is present. But does not need other cells to allow for mucin release.

Question 9

Discuss the location of submucosal glands within the airways.

Answer 9

Found more abundantly in larger/proximal airways but not found in smaller distal airways,

Question 10

Discuss why submucosal glands are so called.

Answer 10

Referred to as submucosal glands as a large proportion of the gland exists within the submucosal layer of the airway wall.

Question 11

What are the two types of acini? How do they work together? Discuss how their location contributes to their function.

Answer 11

Serous acini - watery fluid secretion containing antibacterial lysozymes and lactoferrin.
Mucous acini - mucous secretion.

Serous acini are distal to mucous acini - allows watery fluid secretion from serous acini to wash the secretions of the mucous acini into the airway lumen,

Question 12

What components are present within mucus?

Answer 12

High molecular weight proteins - mucins.
Water,
Electrolytes - sodium ions, chloride ions.
Proteins - lactoferrin, lysozymes

Question 13

Describe the main purpose of the mucus and how it’s structure helps this.

Answer 13

Main role is to trap particles to avoid the, penetrating deep into the airways. Mucous is a viscoelastic gel like substance so is able to trap the particles

Question 14

Are cilia located on the apical or basal surface?

Answer 14

Apical surface. Apical means towards the lumen. This is where cilia need to be to remove any particles within; the lumen.

Question 15

How often do cilia beat?

Answer 15

Approx 9-17 beats per second.

Question 16

What are cilia? Describe their structure.

Answer 16

Cell membrane extensions that fold to fold protrusions. Axoneme present within each protrusion which forms the core of the cilia. Anchored to cell via intracellular anchoring proteins. Microtubule structures connected by nexin and dynein.

Question 17

What is dynein? What is its role in mucociliary clearance?

Answer 17

Dynein is a motor protein that is involved in the structure of the cilia. Ensure that cilia move in a synchronised manner, vital for mucociliary clearance.

Question 18

What is the type of rhythm that mucociliary clearance has?

Answer 18

Metachronal rhythm

Question 19

What are the two types of strokes performed by the cilia to allow for mucociliary clearance ? Briefly describe each.

Answer 19

Power/effective stroke - moves content within lumen forward and out of the lumen.
Recovery stroke - moves the cilia back to their original position to be loaded with the next region of mucus to be moved out of the lumen

Question 20

Discuss the movement of the ciliated cells during mucociliary clearance.

Answer 20

Do not move. It is only the cilia of the ciliated cells that move.

Question 21

Discuss the presence of airway smooth muscle at different stages of the airways.

Answer 21

All parts of the airway contain some smooth muscle. Greater amount of smooth muscle in the larger airways. Amount of smooth muscle decreases as you get into the smaller airways

Question 22

Why is it important that all regions of the airway have smooth muscle?

Answer 22

Ensures that tone can be regulated readily - if substance was to enter the airways and penetrate further into the airways, contraction of smooth muscle can close that airway and prevent the particle from penetrating even deeper down into the airways. Alternatively, if more air was required, airways can open up more on account of relaxation.

Question 23

What is the other name for the tracheobronchial circulation? How much of the cardiac output is reduced by this region of circulations?

Answer 23

Subeouthelial microvascular network. Approx 1-5%

Question 24

Despite receiving a low cardiac output, how is the tracheobronchial circulatory system well supplied with blood?

Answer 24

Contains extensive branched plus of arteries, capillaries and veins

Question 25

Where do bronchial arteries branch from?

Answer 25

Aorta, intercostal arteries, other arteries.

Question 26

How does blood return to the heart from the tracheobronchial circulatory system?

Answer 26

Returns via the systemic and pulmonary veins to both sides of the heart.

Question 27

Provide six reasons as to why the high perfusion of the tracheobronchial circulatory system is vital,

Answer 27

Efficient gas exchange.
Warming and humidifying of inspired air,
Clearing inflammatory mediators from tissue.
Clearing inhaled xenobiotics.
Supplying airway tissue and lumen with inflammatory cells.
Supplying airway tissue and lumen with proteinaceous plasma.

Question 28

What is the name of the process that allows the airway tissues and airway lumen to be supplied with proteinaceous plasma?

Answer 28

Plasma exudation

Question 29

Discuss the effects of the sympathetic and parasympathetic nervous system on the regulation of bronchial smooth muscle and mucus secretion,

Answer 29

Parasympathetic - increased mucus secretion and bronchoconstriction
Sympathetic - decreased mucus secretion and bronchodilation

Question 30

What neurotransmitter is used for the cholinergic pathway?

Answer 30

Acetylcholine

Question 31

Discuss the process of neuronal and non neuronal bronchodilation.

Answer 31

Neuronal - release of NO from NOS containing nerves.

Non-neuronal - release of adrenaline from adrenal medulla.

Question 32

What is the cholinergic reflex and why is it useful?

Answer 32

Refers to the activation of the cholinergic pathway uppon inhaling or ingesting a particle that could become trapped in the airway. Cholinergic activity allows for prompt bronchoconstriction