Respiratory Anatomy

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Trachebronchial tree
Blood Supply
Innervation

TRACHEOBRONCHIAL TREE

Upper airway
-funtions to humidify and filter the inspired air
ex. nose, mouth, and pharynx

Tracheobronchial tree
-functions to conduct gas flow to and from the alveoli
-an estimated 23 divisions from the initial bifurcation of the trachea to the terminal alveolar sace
-each alveolar sace contains approximately 17 alveoli
-estimated 300 million alveoli within the adult lung

Epithelial changes: progressive changes down the tracheobronchial tree
-ciliated columnar epithelium:synchronized beating motion of cilia allows for upward motion of secretions created by secretory glands
-ciliated cuboidal epithelium:synchronized beating motion of cilia allows for upward motion of secretions created by secretory glands
-flat alveolar epithelium: allows for gas exchange and begins approximately at the 19th division down the tracheobronchial tree

Cartilagenous changes:
gradual loss of cartilagenous support down the tracheobronchial tree creates a greater dependency on radial traction in order to maintain patencey of smaller airways.

ALVEOLI
Alveolar size depends on:
-gravity/body position: ex. upright lung
-largest alveoli at the apex of the lung
-smallest alveoli at the base of the lung
-lung volumes : ex. inspiration
-the difference in alveolar size may diminish with an increase in lung volumes

Alveolar wall asymmetry
-thin wall:
-allows for gas exchange between the alveoli and capillaries
-alveolarcapillary membrane < 0.4 mm
-thick wall:
-allows for fluid and solute exchange
1-2 micrometer thich, therefore provides the structural support of the alveoli

Cell types in alveoli
-type I pneumocytes:
-flat cells which create tight junctions
-helps protect passage of large osmotically active molecules (ex.albumin) from the capillaries into the alveoli
-type II pneumocytes:
-round cells
-contains surfactant which allows for normal pulmonary mechanics
has the capacity of cell division (opposed to type I pneumocytes)

Other cell types in the alveoli
-pulmonary alveolar macrophages
-mast cells
-lymphocytes
-amino precursor uptake and decarboxylation cells (APUD)
-neutrophils

BLOOD SUPPLY

-bronchial circulation
-pulmonary circulation

Bronchial Circulation
-originates from the left heart
-supports the metabolic needs of the tracheobronchial tree above the respiratory bronchioles

Pulmonary Circulation
-pulmonary artery
-pulmonary vein
-pulmonary capillary
-lymphatics

Artery:
-mainly consists of cardiac output of the right side of the heart
-divides into right and left branches and each branch supplies its respective lung
-contains deoxygenated blood prior to reaching the lungs

Pulmonary vein:
-returns oxygenated blood from the lungs back to the left side of the heart
-consists of pulmonary veins ( two left pulmonay veins, two right pulmonary veins)

Pulmonary capillary:
-average diameter of the pulmonary capillary is appoximately 10 uM which allows for the passage of a single RBC
-the capillary network is integrated within the walls of the alveoli

Pulmonary capillary network flow determinants:
-gravity/ body position: ex. upright lung
apical alveolarcapillary network: decreased flow due to gravitational pull of blood to the base of the lung
basal alveolarcapillary network: increased flow due to gravitational pull of blood to the base of the lung

Alveolar size: ex. larger alveoli
larger alveoli have a decreased capillary blood flow because of an increased resistance
increased resistance is due to a smaller capillary cross sectional area

Pulmonary capillary epithelium
relatively large junctions allows passage of larger molecules ex. albumin
pulmonary interstitual fluid generally has higher concentrations of albumin and macrophages

Lymphatics:
-originates within the interspaces of large septae in the lung
-lymphatic drainage occure from both lungs
left lung; drains mainly into the thoracic duct
right lung: drains mainly into the right lymphatic duct

MOTOR INNERVATION OF TRACHEOBRONCHIAL TREE

Diaphragm:
-innervated by the phrenic nerve: C3-C5 nerve roots
-unilateral phrenic nerve block: may reduce pulmonary function approximately 25%
-bilateral phrenic nerve block: may produce profound respiratory depression
some patients may maintain adequate ventilation via accessory muscle use

Accessory muscles:
-ex. intercostals muscles innervated by respective thoracic nerve roots

Clinical correlate: spinal cord injury above the level of C5
-generally associated with impaired spontaneous ventilation
-impaired ventilation due to both phrenic and accessory muscle involvement

SENSORY INNERVATION OF TRACHEOBRONCHIAL TREE

Vagus nerve CNX

SLN

-internal branch
-external branch

RLN

AUTONOMIC INNERVATION OF TRACHEOBRONCHIAL TREE
main effects on bronchial smooth muscle tone and secretory glands

Sympathetic tone
relaxation of bronchial smooth muscle tone: bronchodilation
decreased secretions of secretory glands
mainly Beta 2 agonist receptors

Parasympathetic tone
constriction of bronchial smooth muscle tone: bronchoconstriction
increased secretions of secretory glands
mainly Muscarinic receptors

AUTONOMIC INNERVATION OF PULMONARY CIRCULATION

Sympathetic tone: minimal effects on the pulmonary vascular resistance

Parasympathetic tone: vasodilatory effects on the pulmonary vascular resistance
vasodilatory effects may be mediated by nitric oxide