RSPT 1207 Cardiopulmonary Anatomy and Physiology

UNIT 2: THE LOWER AIRWAYS – Part I

I. THE TRACHEA – is the beginning of the lower airways. Its function is to transfer inhaled gas between the larynx (above) and the lungs (below).

 Location a. Located almost midline in the chest b. Immediately below the cricoid cartilage is the first cartilage ring of the trachea c. The great vessels of the heart are located immediately anterior and the esophagus is located immediately posterior to the trachea.

 Description a. 10-13 cm in length from the first ring to the bifurcation of the trachea b. The adult trachea is 1.5 – 2.5 cm in diameter c. Supported by 16-20 “C” shaped cartilage rings. The curve of the “C” faces the sternum.

II. THE CARINA – Bifurcation where the single structured trachea divides  Located at the angle of Louis (T3-4)  Site of the cough reflex. It contains a large network of tactile sensitive receptors that induce coughing.

III. RIGHT AND LEFT MAINSTEM BRONCHUS – as the trachea bifurcates it splits into two main bronchi  Continues to be protected by “C” rings  Diameter of both mainstems is approximately 1 cm  Right mainstem comes off the carina at a 20-30 degree angle, Left mainstem is at a more sharp angle of 45 to 55 degrees

IV. LOBAR BRONCHI – Each mainstem branches out to each lobe of each lung.  Each lobe has a lobar bronchus which is named for the love it ventilates  Diameter of most lobar bronchi is 0.5 cm  The “C” cartilage that protected the trachea and the right and left mainstem bronchus now have become cartilage plates  Lingula – a division of the LUL, that mirrors the RML

V. SEGMENTAL BRONCHI – Each lobe of the lung is separated into 2 or more segments.  Each segment has a segmental bronchi named after the segment that it ventilates  These bronchi are also supported by cartilage plates 2

RIGHT LEFT RUL LUL o Right apical o Apical-posterior o Posterior RUL o Anterior o Anterior RUL RML Lingula o Lateral o Superior o Medial o Inferior RLL LLL - o Superior o Superior o Medial basal o Anteriomedial o Anterior basal o Lateral basal o Lateral basal o Posterior basal o Posterior basal

VI. SUBSEGMENTAL BRONCHI  Bifurcate from each segmental bronchi  Supported by cartilage plates

VII. PERIPHERAL AIRWAYS AND RESPIRATORY ZONE  Peripheral airways – are non-cartilaginous airways o Bronchioles – begin 5-14 generations below segmental bronchi, are 1- 2 mm in diameter o Terminal Bronchioles – transfer of gases end here, diffusion of gas molecules through walls begin  Respiratory Zone – Where gas diffusion occurs and include three airways o Respiratory bronchioles o Alveolar ducts o Alveolar sac  The tracheobronchular tree: http://courses.washington.edu/envh515/slide17.gif

VIII. THE LINING OF THE AIRWAYS – The internal walls of the airways are lined with various tissues.  Epithelium – also called epithelial tissue  Mucous membrane – lies on top of epithelium

IX. EPITHELIAL TISSUE  Cover Internal and external surfaces of the body  Two types: protective cells, glandular cells 3

 The epithelium continually changes as we progress down the tracheobronchial tree.  In the respiratory tract you will find 4 basic types of these cells: o Stratified Squamous Epithelium o Pseudo-Stratified Columnar Ciliated Epithelium o Simple Cuboidal Epithelium o Simple Squamous Epithelium

X. STRATIFIED SQUAMOUS EPITHELIUM – Simple cells that are stacked.  Thick Layer, flexible, protective  Location a. Anterior 1/3 of the nasal cavity b. Oral cavity c. Oropharynx d. Laryngopharynx  Can sustain abrasive action  Regenerates easily

XI. PSEUDO-STRATIFIED COLUMNAR CILIATED EPITHELIUM – Cells are so close together that they appear to be stacked. Thus, the term pseudo- stratified. These cells contain microscopic cilia on their superior surface that extend into the lumen of the airway.  Location: a. Nasal cavity – level of the turbinates b. Nasopharynx c. Level of the vocal cords d. Cartilaginous central airways  At the level of the bronchiole, ciliated cells begin to disappear

XII. SIMPLE CUBOIDAL EPITHELIUM – Cubed- shaped cells. Single cells deep, but thicker that simple squamous cells  Location: a. Lumen of the Transitional bronchioles b. Terminal bronchioles – columnar cells are gradually replaced by this single layer of cubic cells

XIII. SIMPLE SQUAMOUS EPITHELIUM – These are simple cells, lie in a single layer, form the walls of the alveoli  Location: In the alveoli  This is where gas diffusion occurs  Provides as thin an interface as possible between the air in the alveoli and blood in the capillary.  The thickness of has a direct effect on the ability of gas to diffuse throughout the membrane into the blood. 4

XIV. THE MUCOUS MEMBRANE  Covers the pseudo-stratified columnar ciliated epithelium  Majority of the internal surface of the tracheobroncial tree covered by the mucous membrane  There are two glands involved in the production of mucous o Submucosal glands o Goblet cells

XV. SUB-MUCOSAL GLANDS – A collection of secreting glandular epithelium cells.  Vary in size can be up to 1 mm in length  Location: In the layer of the airway call the Lamina Propria, close to parasympathetic nerve endings  Connects to the bronchial surface with long, narrow ducts  Produce the majority of the mucous in the airways. Up to 100 mL of mucous a day  Any type stimulation of the gland by the parasympathetic nerves will increase mucous production  With chronic irritation, the number of submucosal glands will increase

XVI. GOBLET CELLS – Pseudo-stratified columnar ciliated epithelium that has lost its cilia, has gained the ability to secret mucous  Location: scattered throughout the ciliated cells at a ratio of 1:5, or one goblet cell for every 5 ciliated cells  Goblet cells will increase with prolonged irritation

XVII. MUCOUS  Produced by mucous glands and goblet cells, mucous from both cells are the same  Sticky, viscous fluid  Composition: 95% water, 5% glycoproteins, carbohydrates, DNA and cellular debris  When normal it is clear and low in viscosity  When abnormal it will become thick and the color may change  Mucous that is produced in the lower airway is called SPUTUM.

XVIII. THE MUCOCILIARY TRANSPORT SYSTEM  Mucosa and the ciliated cells propel particles that are <10 microns out of the tracheobronchial tree  90% of these microns will enter the central airways and land on the mucociliary bed  Particles <2 microns can reach the alveolar ducts and sac  The lack of cilia and mucous in these areas result in taking up to 24 hours to travel to a ciliated area. 5

XIX. HOW THE MUCOCILIARY TRANSPORT SYSTEM WORKS  Each Pseudo-stratified columnar ciliated epithelium cells has about 200 cilia on its surface. Each cilium is approximately 6 micron tall. Each cilium can beat 1000-1500 times a minute.

 Cilia propel particles 2-9 microns toward the larynx at a rate of 10-20 mm per minute. Cilia moves in a sequential motion called the meachronal wave which propels particles in certain directions  Once enough mucous reaches the carina a cough is stimulated  Click to see Cilia movement

XX. EFFECTS ON CILIA  The cilia propel in the watery SOL layer, and extend into the GEL layer of the mucous membrane.  The cilia must be able to extend through the sol layer to the gel layer to transport the mucous  Several factors can hinder the effectiveness of the cilia and the muco-ciliary transport system o Environmental factors o Certain medications o Smoking . When someone inhales tobacco smoke, the gel layer becomes thicker, mucous production increases and mucous dries faster . The nicotine and other toxic substances paralyze the cilia . Only when a person sleeps is when the cilia can function correctly. o Gravity – Because mucous must move upstream in the tracheobronchial tree laying flat will help facilitate the exit of sputum.