Respiratory Anatomy - Bronchi to Alveoli PDF

Respiratory Anatomy – Bronchi to Alveoli Lecture Outline I. Tracheobronchial Tree II. Bronchioles III. Tissues of the Airways 1 Respiratory Anatomy – Bronchi to Alveoli Objectives 1.Describe the generations of the tracheobronchial tree and differences in diameter, glands, and cartilage 2.Identif...

Respiratory Anatomy – Bronchi to Alveoli Lecture Outline I. Tracheobronchial Tree II. Bronchioles III. Tissues of the Airways 1 Respiratory Anatomy – Bronchi to Alveoli Objectives 1.Describe the generations of the tracheobronchial tree and differences in diameter, glands, and cartilage 2.Identify differences between left and right main bronchi 3.Describe the structure and significance of bronchopulmonary segments 4.Explain the circulation of bronchi 5.Describe the organization of conducting and respiratory bronchioles and their characteristics 6.Explain how the venous drainage of bronchioles decreases pO2 of arterial blood 7.Explain how the pulmonary plexuses provide the motor and sensory innervation of the lungs 8.Compare the smooth muscle of bronchi and bronchioles 9.Identify characteristics of respiratory epithelium 10.Describe cells and mediators that affect respiratory airways including club and mast cells and chemical mediators 11.Describe the structure of an acinus 12.Identify the cells found in an adult alveolus and explain their function 2 References Assigned reading from your text: Moore Chapters 4 Images from: Ash, JF, Morton, DA, Scott, SA The Big Picture: Histology. China: McGraw-Hill Education/Medical, 2013. Ganong’s Review of Medical Physiology Netter Atlas of Human Anatomy 6th edition 3 I. Tracheobronchial Tree- Bronchi 4 Tracheobronchial Tree ❑ Tracheobronchial tree includes: the trachea, 3 generations of bronchi, and bronchioles ❑ Three generations of bronchi include: • 1º - Main bronchi to each lung (2) • 2º - Lobar bronchi to each lobe (5 total; 3 right and 2 left) • 3º- Segmental bronchi to each segment (~10 per lung) ▪ Note changes in characteristics of airways with each bifurcation/ generation of smaller airways • Epithelium height and complexity decreases • Cartilage rings are replaced by irregular plates • Number of glands, goblet cells, smooth muscle, and elastic fibers decreases 5 Primary (Main) Bronchi ❑ Main bronchi are located after the trachea bifurcates at the carina • Trachealis muscle replaced by smooth muscle wrapped around airway • Incomplete cartilage bands ❑ Differences in bronchi: • The right main bronchus is wider, shorter, and runs more vertically than the left making it the likely affected side of: • Aspiration • Main stem intubation • How deep is your tube? • The left main bronchus is longer- passes inferiorly to the arch of the aorta • Subcarinal angles more equal in children than adults • • Adult Infant 25o R: R: 55o 45o L: L: 55o Adult Infant 6 Secondary (Lobar) Bronchi ❑ Lobar bronchi supply lung lobes • Intrapulmonary • 5 lobar bronchi • 2 on left and 3 on right • Scattered cartilage plates 7 Tertiary/ Segmental Bronchi ❑ There are about ~10 segmental bronchi per lung • Supply corresponding bronchopulmonary segments • Contain plates of cartilage instead of rings • The last portion of conducting airways with mucous glands or consistent cartilage 8 Bronchopulmonary Segments ❑ Bronchopulmonary segments are the largest subdivisions of a lobe – Pyramidal-shaped segments of the lung, with their apices facing the lung root and their bases at the pleural surface – Separated from adjacent segments by connective tissue septa – Supplied independently by a segmental bronchus and a tertiary branch of the pulmonary artery – Surgically resectable- named according to bronchi supplying them – Gravity-assisted (postural) drainage positions relate to bronchopulmonary segments Postural Drainage Positions 9 Components of a Bronchopulmonary Segment ❑ Each bronchopulmonary segment includes : • A tertiary bronchus • A tertiary branch of the pulmonary artery • Venous drainage by intersegmental parts of the pulmonary veins that lie in the connective tissue between segments and drain adjacent segments 10 Arterial Supply of the Lung Stroma ❑ Bronchial arteries branch with bronchi • Bronchial arteries supply blood to: • Tracheobronchial tree from the main bronchi to the terminal bronchioles • Structures of root of lung and visceral pleura • • 2 left bronchial arteries usually arise from thoracic aorta 1 single right bronchial artery from aorta • Common variation: Right bronchial arises indirectly from an upper posterior intercostal artery or left bronchial 11 Venous Drainage of the Lung Stroma ❑ Venous Drainage : • Bronchial veins drain the proximal part of the root of the lung • Right bronchial vein drains → Azygos vein → SVC • Left bronchial vein drains → Accessory hemi-azygos vein → Azygos vein → SVC • Bronchial veins exit lungs at the hilum • Blood flow in bronchial circulation = 2% CO of LV 12 II. Tracheobronchial Tree-Bronchioles 13 Bronchioles ❑ Each terminal bronchiole gives rise to several generations of respiratory bronchioles • Bronchioles are the narrowest airways • Diameters often < ~1 mm • Occur after tertiary bronchi- successive generations have smaller diameters • Bronchioles lack cartilage and glands 14 Conducting and Respiratory Bronchioles ❑ Bronchioles are located in the conducting and respiratory zones • First 16 generations of passages are the conducting zones • Terminal bronchioles are the smallest and last the generation of the conducting zone • Respiratory bronchioles/zones have alveoli present for gas exchange 15 Bronchiole Blood Supply ❑ Bronchioles and pulmonary arteries course and branch together ❑ Bronchial arterial supply • Bronchial arteries: – – – Arise from the aorta and intercostal arteries Deliver oxygenated blood at systemic pressures Supply intrapulmonary structures proximal to the terminal bronchioles, connective tissue septa, and visceral pleura ❑ Bronchial venous drainage is Atypical • Bronchial veins drain structures proximal to the root of the lungs to the right atrium via bronchial veins • Pulmonary veins drain the remaining blood from distal structures to the left atrium via pulmonary veins- creating venous admixture • The most distal (smallest) branches of bronchial arteries anastomose with branches of the pulmonary arteries in the walls of the bronchioles and visceral pleura. This is likely more prominent in neonates and pathologic conditions 16 Bronchopulmonary Anastomoses ❑ Bronchopulmonary anastomoses occur between bronchial and pulmonary circulation at the arterioles and capillaries • Between bronchial capillaries and pulmonary capillaries • Between bronchial arteries and branches of the pulmonary artery ❑ A substantial portion of bronchial venous blood (deoxygenated) enters pulmonary veins (oxygenated) • Bronchial venous blood entering pulmonary venous blood becomes part of the normal anatomic right-to-left shunt • Venous admixture decreases the pO2 of “arterial” blood • Bronchial veins • Visceral pleura 17 III. Tissues of the Airways 18 Innervation of the Lungs ❑ Right and left plexuses follows the trachea and bronchial tree ▪ Pulmonary plexuses provide sensory and motor innervation to the smooth muscle and glands • Parasympathetic (cholinergic) • Sympathetic (adrenergic) fibers provide weak motor effect on airway diameter- do produce vasoconstriction and inhibition of gland secretion • Visceral afferents travel with CNX fibers ▪ Non-adrenergic/non-cholinergic (NANC) system provides inhibition- including bronchodilation ▪ Predominant balance to the excitatory cholinergic system 19 Neural Control of Airways ❑ Pulmonary plexus includes autonomic and visceral afferent fibers from CNX and thoracic nerves ❑ Vagal parasympathetic fibers are: • Secretomotor- glands • Bronchoconstrictive – smooth muscle – Postganglionic parasympathetic innervation is a major source of unitary smooth muscle contraction ❑ • • • Sympathetic innervation from fibers of T1 to T4: Inhibit secretion from bronchial glands Vasoconstrict of pulmonary vessels Inhibit bronchoconstriction of smooth muscle • Sympathetic fibers may weakly bronchodilate • • • Visceral afferent fibers transmit sensory information: Sparse compared to somatic structures Nociceptive and reflexive 20 Hormone Signaling of Airways ❑ Humoral release of epi/NE during “flight or fight” circumstances result in relaxation of airway smooth muscle • 2 adrenergic receptors are widely distributed in smooth muscle • Epi/NE combine with GPCRs in the plasma membrane of myocytes • β2 adrenergic receptor stimulation by NE/Epi causes smooth muscle relaxation followed by bronchiole dilation ❑ Paracrine secretions from cells present in respiratory epithelium affect smooth muscle • eg Histamine and bradykinin • Physical stimulation of stretch receptors located in smooth muscle can cause contraction • Laryngoscopy • Foreign objects trapped in the trachea or bronchi 21 Mast Cells Reside in the Connective Tissues of Airways ❑Below the epithelium of the airways- Heavily granulated mast cells reside in connective tissue • Abundant in tissues (eg lungs) that contact the external environment contain secretory granules that consist of many inflammatory • Stored inflammatory mediators include histamine, proteoglycans, lysosomal enzymes, and metabolites of arachidonic acid • When degranulation (exploding) occurs, these mediators can: • induce bronchoconstriction, • stimulate mucus secretion, and • induce mucosal edema by increasing permeability of bronchial vessels • Treatments aimed at symptoms and stabilizing mast cells from further degranulation (epi) 22 Smooth Muscle of Airways ❑ Walls of bronchi and bronchioles contains smooth muscle with significant amounts of collagen and elastic connective tissue fibers • Airway diameter is larger in bronchi • In bronchioles- the layer of smooth muscle is thick relative to the diameter of the bronchiole lumen ❑ Smooth muscle function in airways • • Contraction produces airway constriction Relaxation produces dilation Comparison of bronchi to bronchiole 23 Respiratory Epithelium ❑Descending the tracheobronchial tree: height and complexity of epithelium decreases • • • • Trachea/bronchusConducting BronchiolesTerminal bronchiolesAlveoli- Ciliated pseudostratified columnar epithelium Ciliated simple columnar epithelium Ciliated simple cuboidal epithelium Type I and Type II epithelial cells 24 Club Cells ❑ Goblet cells end at the terminal bronchiole and Are replaced by Club cells • Club cells (previously Clara cells/ aka nonciliated bronchiolar exocrine cells) appear first in terminal bronchioles and are present in respiratory bronchioles • Club cells: • Secrete Proteins- including surfactant apoproteins A,B, and D • Secrete lipids, glycoproteins, and modulators of inflammation • Act as progenitors for Club cells and ciliated epithelial cells to replace damaged cells • Destroy airborne toxins that reach bronchioles 25 IV. Alveoli 26 Respiratory Zone- Site of Gas Exchange ❑ Respiratory zone- the segment of airways completely lined with alveoli- alveolar ducts and sacs • • • • Each respiratory bronchiole gives rise to 2-11 alveolar ducts Alveolar ducts are elongated airways with walls completely lined with alveoli There is a very small amounts of smooth muscle and elastic tissue at junction of duct and sac Each alveolar ducts gives rise to 5-6 alveolar sacs- clusters of alveoli open into sacs 27 Acinus ❑ An acinus is part of the lung supplied by a single 1st order respiratory bronchiole and all structures to and including the alveolar sac • All parts of an acinus are involved in gas exchange: respiratory bronchioles, ducts, sacs An acinus 28 Cells of Alveoli ❑Alveoli are composed mainly of a thin layer of squamous Type I epithelial cells •Type I Alveolar cells are squamous epithelium specialized for gas exchange • Agranular pneumocytes represent • Form 90% of the wall surface of the alveolus • Large, thin, flattened cells- simple squamous epithelial cells • Basal lamina fused to pulmonary capillaries • Tight junctions prevent leakage into alveolar space •Type II Alveolar cells are cuboidal epithelium • Granular pneumocytes that produce surfactant • Surfactant reduces surface tension- produced in lamellar bodies derived from Golgi • Cover 10% alveolar surface - although there are as many or more Type II Simple cuboidal epithelial cells Function as stem cells→ if Type I cells lost, Type II can differentiate into Type I cells ~1% alveolar epithelium replaced daily •Free-ranging phagocytic alveolar macrophages monitor and remove debris/microorganisms • Macrophages migrate through Pores of Kohn to the mucociliary escalator 29 Prominent Cells in the Adult Human Alveolus FIGURE 34–3 Ganong Prominent cells in the adult human alveolus A) A cross-section of the respiratory zone shows the relationship between capillaries and the airway epithelium. Only 4 of the 18 alveoli are labeled. B) Enlargement of the boxed area from (A) displaying intimate relationship between capillaries, the interstitium, and the alveolar epithelium. C) Electron micrograph displaying a typical area depicted in (B). The pulmonary capillary (cap) in the septum contains plasma with red blood cells. Note the closely apposed endothelial and pulmonary epithelial cell membranes separated at places by additional connective tissue fibers (cf); en, nucleus of endothelial cell; epl, nucleus of type I alveolar epithelial cell; a, alveolar space; ma, alveolar macrophage. D) Type II cell formation and metabolism of surfactant. Lamellar bodies (LB) are formed in type II alveolar epithelial cells and secreted by exocytosis into the fluid lining the alveoli. The released lamellar body material is converted to tubular myelin (TM), and the TM is the source of the phospholipid surface film (SF). Surfactant is taken up by endocytosis into alveolar macrophages and type II epithelial cells. N, nucleus; RER, rough endoplasmic reticulum; CB, composite body. 30 1. What is an average distance from the teeth to the vocal cords? a. 26 cm b. 10 cm c. 10 inches d. 13 cm e. 2 cm 2. Which of the following is the largest subdivision of a lung lobe? a. Acinus b. Duct c. Lobar d. Bronchopulmonary segment 3. Which of the following is most likely to produce bronchodilation? a. Histamine and paracrine secretions b. Humoral release of epinephrine/norepinephrine c. Parasympathetic innervation d. Sympathetic innervation 4. What is a possible response to attempting laryngoscopy in a fully awake patient? a. Bronchodilation b. Inhibition of secretions c. Laryngospasm d. Decreased permeability of mucosal vessels 5. What is the angle of the right main bronchus (away from the midline of the trachea) in an infant? a. 25 b. 45 c. 55 d. 90 31