09: Secondary Functions

Secondary functions of the RT

• Filtration

• Immune function

• Conditioning: humidification and warming

• Thermoregulation

If the RT filters the air, why do we need immune function

It’s not a perfect filtration system

Why does the air need to be humidified

Non-humidified air can damage the RT

How much do we want the air humidified by the time it gets to the lower RT

100% humidified at body temperature

What mechanisms does the body use to condition air

Entirely passive mechanisms

The part of the RT with the largest heat gradient and the fastest movement of heat

The rostral part of the RT

At what point is the heat gradient basically equilibrated in a normal animal

By the time it gets to the trachea

What limits how fast the air can be humidified

How fast the air is warmed

Conditions that may result in only partially conditioned air making it to the lungs

Exercise

What cold weather condition may sound like lower RT disease

Ski asthma

Ski asthma pathology

Chronic, repetitive cold air injury to the lower RT due to exercising in the cold

How does cold air cause lower RT damage

It damages the mucosa, causing inflammation that can become chronic with repetition

What determines how much an animal relies on the RT for thermoregulation

Whether other thermoreg mechanisms are sufficient

What patient demographic relies more on the RT for thermoreg despite the efficacy of other mechanisms

Young animals

What part of the airway is involved in thermoregulation

Conducting airways

How does an animal increase RT thermoreg

Increases RR

What the animal is actually trying to modulate when it increases RR for thermoreg

Minute dead space ventilation

Problems that can happen if an animal increases RR simply for the sake of thermoreg

The unnecessary increase in minute alveolar ventilation will end up messing with the acid-base balance in the body, which is bad

How then does the animal properly increase thermoreg

Decreases V_T while increasing RR → panting

• V_D doesn’t change, so the minute dead space ventilation increases

• V_A is significantly reduced, so the minute alveolar ventilation can basically be normal

Reasons an animal may be increasing RR

• Voluntary increase if V_T: thermoreg

• Abnormal limitation of V_T: mechanical abnormality

• Derangement in gas exchange

What makes a particle easier to filter out of the air

• Moving fast

• Larger mass

T/F: anything other than O₂ and other air components in the lower RT means there is infection

False, you can have things there that should be there, but may not cause an infection

Where is most of the filtering done

Upper RT

What happens after a particle gets caught in the RT mucosa

Cilia on the epithelium of the conducting airways (nares → bronchioles) shuttle the mucus and particles towards the esophagus (mucociliary transport system)

Stimulation of what RT receptor will increase ciliary movement by a lot

β adrenergic receptor (βAR)

What types of drugs can increase mucus viscosity

Anti-cholinergic drugs (atropine)

Effect of RT disease on the mucociliary escalator

Cilia are only present on mature epithelial cells, and it is the last thing to recover after disease, so respiratory disease wreaks havoc on the mucociliary transport system

What do we call the secretions in the lower RT

Mucus

What do we call the secretions in the upper RT

Snot

…what do we call secretions that are on a sidewalk

Loogie (may be a bonus questions)

Under what circumstances can mucus production in the RT become a problem

During infection the RT often increases mucus secretion, and it can end up occluding parts of the lumen → increasing resistance → increasing the work of breathing

Mechanism for bulk movement of mucus through the RT

Coughing

At a base level, what is coughing

Forced exhalation

How does coughing work

Forced exhalation collapses or partially collapses the airway while moving air very rapidly through that point → causes things to dislodge from the airway walls

What determines where the RT collapses during forced exhalation

As lung volume decreases, the equal pressure point (where the thoracic pressure overcomes the pressure inside the RT) moves towards the central airways

What benefit does coughing repeatedly provide

Each forced exhale occurs with less and less lung volume, and so the point of collapse marches from the periphery to the central airways, moving the mucus with it

What upper RT structure plays a big role in coughing

Larynx

How does the larynx contribute to coughing

The larynx closes at the beginning of the cough to build up pressure, quickly opens to allow a quick jet of air (clearing the collapsed point), then closes and repeats, building and releasing pressure at lower and lower lung volumes

Stimulation for coughing

Irritation

Why is coughing a useful diagnostic tool

Can help screen for problems with inhalation and exhalation

What non-RT issue can cause problems with exhalation

Abdominal muscle problems

Where are most of the afferent nerves that stimulate coughing

In the larger airways (bronchi and up)

What does the location of those afferent nerves mean for disease detection

You can have resp disease start in the bronchioles, but not get any obvious clinical signs or coughing until it progresses up to the bronchi