Resp 5 - airways structure and function

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
When smooth muscle cell contracts it squeezes the gland - they work in tandem

Question 4

Describe the secretion of mucus by goblet cells.

Answer 4

Mucin granules accumulate at the cell surface, fuse with it.
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 like lysozyme 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 so a lot of NO gets produced in epithelial cells
Could be used to control beating of cilia

Question 10

What inflammatory mediators can be produced by smooth muscle cells?

Answer 10

NO, Prostaglandins, cytokines, chemokines

In response to cytokines (ie. inflammation) NOS can be upregulated
Chemokines lead to the recruitment of inflammatory cells

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

Massive input and output

Question 14

Explain the process of plasma exudation in the airways.

Answer 14

Plasma exudation usually takes place at the POST-CAPILLARY VENULES (tissues bathed in plasma)
Post-capillary venules have endothelial cells that will contract - when they do so, they pull away a bit from each other - plasma can leak out
Histamines, PAF and other mediators can activate the sensory nerves supplying these cells 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 organisation of airways

Answer 17

first layer is ciliated cells + goblet cells
then smooth muscle surrounding this with submucosal glands embedded
then cartilage

Question 18

In what disease is plasma exudation exaggerated?

Answer 18

Asthma

Question 19

Describe the cholinergic reflex.

Answer 19

It is used to make bronchoconstriction. Sensory nerves detects signal to constrict, this goes to brainstem then parasympathetic (cholinergic) motor pathway activated (both vagus nerves), gets to parasympathetic ganglion and this will cause constriction. –> contracts smooth muscle cells (in response to acetylcholine)

Question 20

What causes bronchodilation in humans?

Answer 20

Unlike other animals, humans do not have sympathetic pathway which will dilate the airways. Humans rely on adrenaline from the adrenal gland. It relaxes the airway.
We also have a neuronal pathway but it is not sympathetic, it releases NO.
Adrenaline and NO work together.

Question 21

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

Answer 21

Asthma
COPD
Cystic Fibrosis
-> abnormalities in airway obstruction and inflammation

Question 22

What are the characteristics of asthma?

Answer 22

Increased airway responsiveness to a variety of stimuli
Airway obstruction varies and is REVERSIBLE
Dyspnea, wheezing, cough
Airway inflammation leads to remodelling

Question 23

Describe the histological features of asthma.

Answer 23

Thickening of basement membrane
Mucus plug
Epithelial fragility
Prominent blood vessels
Infiltration of eosinophils

Question 24

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

Answer 24

Eosinophils

Question 25

How does asthma set up a central cholinergic reflex?

Answer 25

Epithelial fragility –> exposes sensory nerves –> can respond mediators produced by inflammatory cells –> sets up cholinergic reflex –> causes smooth muscle contraction and shutting down of airways + mucus secretion
This repeats itself
—-> hypertrophy of smooth muscle and the glands + increase in number of goblet cells
Chemical mediators are released by these cells

Question 26

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

Answer 26

epithelial fragility, goblet cell hyperplasia, enlarged submucosal mucus glands, angiogenesis, increased matrix deposition in the airway wall, increased airway smooth muscle mass, wall thickening