Respiratory Anatomy Listen to Audio 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