Structure and Function of the Airways

Question 1

How do the airways divide into smaller airways?

Answer 1

Dichotomous Branching

Question 2

Describe the arrangement of cartilage rings in the airways.

Answer 2

They are slightly offset - gives them greater tensile strength to hold the airways open

Question 3

Where are submucosal glands found and what are their functions?

Answer 3

The lower part of the submucosal glands are embedded in the smooth muscle
They secrete mucus

Question 4

Describe the secretion of mucus by goblet cells.

Answer 4

Mucin granules accumulate at the cell surface
A little pore forms allowing water to move in
This causes rapid expansion of the (initially) very concentrated mucin - the pore opens more and the mucus pops out

Question 5

Describe the structure of submucosal gland.

Answer 5

Submucosal glands have functional units (acini)
The acini are either SEROUS or MUCOUS
The serous acini are found peripheral to the mucous acini
Serous acini produce WATERY secretions (containing antibacterials and ions)
Mucous acini produce MUCOUS
The serous secretions wash over the mucous secretions into the collecting duct

Question 6

Describe the structure of a cilium.

Answer 6

They have specifically arranged microtubules with 9 pairs of microtubules around the outside and 2 individual microtubules on the inside (9+2 formation)
There are apical hooks that interact with the mucus
There are roughly 200 cilia per cell

Question 7

What is the pattern of beating of cilia?

Answer 7

Metachronal Rhythm

Question 8

State some of the regulatory and inflammatory mediators produced by airway epithelial cells.

Answer 8

NO, CO, Prostaglandins, cytokines, chemokines

Question 9

In which cells of the airway do you find a high concentration of Nitric Oxide Synthase?

Answer 9

Epithelial cells

Question 10

What inflammatory mediators can be produced by smooth muscle cells?

Answer 10

NO, Prostaglandins, Cytokines, Chemokines

Question 11

How does blood return to the heart from the tracheal circulation?

Answer 11

Systemic veins

Question 12

How does blood return to the heart from the bronchial circulation?

Answer 12

Pulmonary veins AND Systemic veins

Question 13

What is the function of the tracheo-bronchial circulation?

Answer 13

Provides perfusion to the lung tissue

Also involved in WARMING and HUMIDIFYING inspired air

Question 14

Explain the process of plasma exudation in the airways.

Answer 14

Plasma exudation usually takes place at the POST-CAPILLARY VENULES
Post-capillary venules have endothelial cells have sensory innervation (have some motor function as well).
Histamines, PAF and other mediators can activate these sensory nerves and cause plasma exudation.

Question 15

What effect does platelet activating factor (PAF) have on exudation?

Answer 15

Causes contraction of the endothelial cells leading to exudation

Question 16

What are the most important motor pathways in the airways?

Answer 16

CHOLINERGIC

Question 17

Describe the cholinergic reflex.

Answer 17

Something can go into the airways and trigger a signal via an afferent pathway to the brain.
This will cause a CHOLINERGIC reflex —> BRONCHOCONSTRICTION

Question 18

What causes bronchodilation in humans?

Answer 18

Bronchodilation is caused by:
Release of ADRENALINE from the adrenal medulla (part of sympathetic response)
Release of NITRIC OXIDE from the neuronal pathway (NOTE: in this case NO is a neurotransmitter)

Question 19

What does the cholinergic reflex cause?

Answer 19

Constriction of smooth muscle

Secretion of mucus

Question 20

State three respiratory diseases that involve a loss of respiratory control.

Answer 20

Asthma
COPD
Cystic Fibrosis

Question 21

What are the characteristics of asthma?

Answer 21

Increased airway responsiveness to a variety of stimuli —> leads to reversible airway obstruction

Question 22

Describe the histological features of asthma.

Answer 22

Mucus plug formation (with a lot of eosinophils within it)
Epithelial fragility
Thickening of the basement membrane 
Congested/vasodilated blood vessels
Infiltration by eosinophils

Question 23

What cells are abundant in a mucus plug formed by asthma?

Answer 23

Eosinophils

Question 24

How does asthma set up a central cholinergic reflex?

Answer 24

Epithelial fragility means that there are exposed sensory fibres.
Sensory fibres are stimulated by inflammatory mediators resulting in messages being sent to the brain and setting up a cholinergic reflex.
The cholinergic reflex results in BRONCHOCONSTRICTION and SECRETION OF MUCUS

Question 25

What are the consequences of asthma to the structure of the airways?

Answer 25

Smooth Muscle Hypertrophy

Increase in number of goblet cells