Pulmonary Anatomy 1b (Airways, Alveoli, and Defense Mechanisms)

What does the pulmonary artery deliver from the right ventricle to the lungs?

Deoxygenated blood

What does the pulmonary vein deliver from the lungs to the left atrium?

Oxygenated blood

What is the purpose of the bronchial arteries?

They do not participate in gas exchange but function to nourish the tissues by delivering oxygenated blood to the bronchi and connective tissues of the lung

What nerves innervate the lung?

Pulmonary plexus and the phrenic nerve

What is the function of the pulmonary plexus?

Surrounds bronchi and pulmonary vessels, has autonomic (parasympathetic and sympathetic) and sensory innervation

Parasympathetic innervation of pulmonary plexus

Bronchoconstriction and increases airway secretions and mucus production

Sympathetic innervation of the pulmonary plexus

Bronchodilation

Sensory innervation of the pulmonary plexus

Responds to stretch, irritation/noxious stimuli in lungs and airway

Bronchoconstriction

Narrowing of the airways due to contraction of airway smooth muscle

Bronchodilation

Widening/opening of the airways due to relaxation of airway smooth muscle

How many parts is the lower respiratory system divided into?

Two

What are the parts of the lower respiratory system?

Tracheobronchial tree (conducting airways) and acinar or terminal respiratory units

Where does gas exchange occur?

In the acinar or terminal respiratory units

Tracheobronchial Tree

The conducting airways, include all airways down to terminal bronchioles, does not participate directly in gas exchange

Key points pertaining to the tracheobronchial tree

There are 16 generations of conducting airways, this creates a large cross-sectional area for efficient air flow

What happens to airway diameter in the tracheobronchial tree?

With each branching generation, airway diameter decreases

Airway flow chart

Trachea → primary bronchi → secondary bronchi → tertiary bronchi → bronchioles → terminal bronchioles

In which bronchus is aspiration more likely to occur and why?

The right main bronchus because it is more vertical and wider, making food, liquid, and foreign objects more likely to enter the right lung (increases the risk of aspiration pneumonia)

What landmark can be used to find where the trachea divides into left and right main bronchi?

The sternal angle

Acinar or terminal respiratory units

Found distally to the terminal bronchioles and are composed of: respiratory bronchioles, alveolar ducts, and alveoli sacs

Respiratory bronchioles

The first airway branches that allow gas exchange

Alveolar ducts

Tiny airways that connect respiratory bronchioles to alveolar sacs

Alveoli sacs

Clusters of alveoli at the end of alveolar ducts

What structure is vital for gas exchange?

Alveoli sacs

Acinus

One terminal bronchiole and all gas-exchanging structures distal to it

Terminal respiratory units (TRU)

The gas-exchange portion of the lung, distal to a terminal bronchiole, consisting of respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli

Why do we care that as we move distally the airways become less rigid, less protected, and more specialized for gas exchange?

It makes them increasingly vulnerable to obstruction, collapse, and impaired ventilation

Alveoli

Primary site of gas exchange, has a huge surface area, extremely thing wall, has surfactant, alveolar macrophages, and very thin alveolar-capillary membrane

What is important about the huge surface area of alveoli?

It maximizes O2 and CO2 diffusion

What is important about the extremely thin wall of alveoli?

Minimizes diffusion for gas exchange

What is the extremely thin wall of the alveoli made of?

Type I cells

What is important about the surfactant of the alveoli?

Reduces surface tension and prevents collapse

What is the surfactant in the lung made of?

Type II cells

What is important about the alveolar macrophages of the alveoli?

Local immune defense (it is the last line of defense)

What is important about the very thin alveolar-capillary membrane of the alveoli?

It allows for efficient gas exchange

Optimal condition for our alveoli to be in

Thin, open (air-filled), dry, and intact

When is there reduced gas exchange in the alveoli?

When there is fluid, collapse, or thickening

Lung interstitium

Thin connective tissue layer between alveoli and capillaries that supports gas exchange, contains: extracellular matrix (ECM), fibroblasts, vessels, and lymphatics

Extracellular matrix (ECM)

Supports structure and facilitates stretch and recoil of the lungs

What are the key components of the extracellular matrix (ECM)?

Collagen (strength), elastin (stretch and recoil), fibroblasts (ECM production and repair), and proteoglycans (hydration and structural support)

As PT’s, why do wee care about the extracellular matrix (ECM)?

It keeps the alveoli open, helps maintain small airway patency (radial traction), and contributes to lung compliance and elastic recoil

Why is the ECM considered the lungs structural framework?

It keeps airways and alveoli open while allowing the lung to stretch and recpil during breathing

Radial traction

Elastic fibers in the ECM pull outward on bronchioles, this outward force helps keep small airways open, despite the absence of cartilage

Relationship between radial traction and inspiration

During inspiration: lung expansion → increased radial traction (which pulls open alveoli and airways) → bronchioles widen

Despite constant exposure to inhaled particles and pathogens, what is the role of airway clearance and pulmonary defense mechanisms?

To keep the lungs open (ventilation), dry (gas exchange), clean (air way clearance), and protected (immune defense)

What are the 3 major defense mechanisms that a healthy lung uses to clear pollution, dust, and foreign particles?

Mucociliary clearance (MCC), effective cough, and alveolar macrophages

Where is mucociliary clearance (MCC) found?

Trachea, bronchi, bronchioles (decreasing density distally) not present in alveoli

What is the role of mucociliary clearance (MCC)?

Removes inhaled particles, pathogens, and debris; helps keep airways clear and healthy

How does mucociliary clearance (MCC) work?

Mucus traps unwanted material, cilia then moves the mucus upward toward the mouth, so we can cough it out

How does smoking affect the MCC?

Causes ciliary damage

How does cystic fibrosis affect MCC?

Thicker mucus

How does bronchiectasis affect MCC?

Secretion retention

How does pneumonia affect MCC?

Impaired clearance

How does intubation/mechanical ventilation affect MCC?

It disrupts MCC, profound implications on normal mucociliary clearance (secretions accumulate, infection risk increases, and airway obstruction can occur)

Healthy Mucus

Thin, clear, and produced continuously, traps particles and is moved upward by MCC, and is usually swallowed without notice

When does mucus become a problem?

Too much is produced, it becomes thick or sticky, or MCC or cough cannot clear it

Mucus

A normal protective substance produced by the airways that traps inhaled particles and pathogens

Phlegm or Sputum

Mucus that has been coughed up (expectorated) from the lower respiratory tract

What is the relationship between mucus and sputum/phlegm?

All sputum is mucus, but not all mucus becomes sputum

Secretions

A broad clinical term for material within the airways, including mucus, sputum, pus, blood, or edema fluid

Features of gross sputum assessment

Colour, consistency, amount, odour, blood, purulence

What does gross sputum analysis help to determine?

The need for airway clearance treatment, treatment effectiveness, and need for further medical assessment or referral

Why is cough important?

Supports mucociliary clearance (MCC), removes secretions, irritations, and pathogens, and is essential when mucus accumulates

What part of the airway is most effective at clearing secretions from?

The larger more central airways

Why is an effective cough relevant to physiotherapists?

Many of our airway clearance techniques aim to move secretions into larger airways where an effective cough can clear them

What are the qualitative components of a phhysiotherapy cough assessment?

-spontaneous or directed?

-weak or strong?

-effective or ineffective?

-productive or dry?

-acute or chronic?

What are the phases of a cough?

Inspiratory phase (take a deep breath in), compressive phase (build up pressure), and expulsion phase (force the air out)

Inspiratory Phase

The glottis is open, the diaphragm and other inspiratory muscles contract, a larger breath increasing lung volume, providing the air needed for a strong cough

Compressive phase

The glottis closes briefly, the abdominal and other expiratory muscles contract, and pressure rises inside the chest and abdomen

Expulsion phase

The glottis suddenly opens, the built-up pressure produces rapid, forceful airflow, and this airflow moves secretions toward the larger airways and out of the lungs

Common reasons for an impaired cough

Pain, weak inspiratory or expiratory muscles, neurological impairments, cognition, or fatigue

What happens when cough is impaired?

Secretion retention, airway obstruction, and infection risk (including pneumonia risk)

Alveolar macrophages

Found on the alveolar surface; they engulf and remove particles, pathogens, and debris that reach the alveoli. They are the final defense mechanism protecting the gas exchange sites at the alveoli (no MCC here and cough cannot clear here either)