Anatomy of the Lungs Lecture Notes PDF

http://t3.gstatic.com/images?q=tbn:tfx74m7TG1-6kM:http://www.star.uclan.ac.uk/malta2009/uni_logo.jpg Anatomy of the Lungs...

http://t3.gstatic.com/images?q=tbn:tfx74m7TG1-6kM:http://www.star.uclan.ac.uk/malta2009/uni_logo.jpg Anatomy of the Lungs M.T.Camilleri The Lungs  The two lungs occupy the lateral parts of the thoracic cavity and each is surrounded by pleurae  Lobes:  Right lung – 3 lobes  Left lung – 2 lobes  Each lung receives a main bronchus, one pulmonary artery and two pulmonary veins.These subdivide in the lung.  Each lung also receives nerves and lymphatics.  Root of the lung:  Region of the mediastinum where the lung is connected to the trachea and the heart  Hilum of the lung:  Region of the lung where bronchi and pulmonary vessels enter  The lung conforms to the shape of the containing thoracic cavity. Its costal surface is convex and the diaphragmatic and mediastinal surfaces are concave.  The apex of the lung is blunt and projects into the neck for about 2.5cm above the clavicle The Principal Bronchi  The right main bronchus is shorter, wider and more vertical than the left.  Inhaled foreign bodies therefore more likely to enter the right lung  Before entering the hilum of the right lung, the right main bronchus gives off the superior lobar bronchus.  On entering the hilum it then divides into middle and inferior lobar bronchi  The left main bronchus is narrower, longer and more horizontal. It passes below the arch of aorta and divides into a superior and inferior lobar bronchus. The Bronchial Tree Lobes and Fissures  The right lung is slightly larger than the left.  It is divided into three lobes by the oblique and horizontal fissures  Upper  Middle lobes  Lower  The horizontal fissure runs horizontally across the costal surface of the fourth costal cartilage to meet the oblique fissure in the Midaxillary line.  The oblique fissure runs up and back from the inferior border to the posterior border of the lung Lobes and Fissures The Bronchopulmonary Segments  The anatomical, functional and surgical units of the lung.  The lobes of the lung are each supplied by a lobar [secondary] bronchus  This then divides into branches called segmental [tertiary] bronchi  The bronchopulmonary segments are each supplied by the segmental bronchi. The Bronchopulmonary Segments  Each bronchopulmonary segment has:  A surrounding layer of connective tissue  A branch of the pulmonary artery accompanying the segmental bronchus  The tributary veins that join to form the pulmonary veins run in the connective tissue adjacent to the bronchopulmonary segments  Lymphatic vessels and innervation to the bronchopulmonary segments  Each is pyramidal, with the apex towards the lung root The Bronchopulmonary Segments The Bronchioles  In the bronchopulmonary segments the segmental bronchi divide repeatedly and become gradually smaller.  They eventually lose their cartilage content and the smallest bronchi give rise to bronchioles.  The bronchioles are:  Less than 1mm diameter  Have no cartilage lining  Lined with a columnar ciliated epithelium  Possesses smooth muscle fibers  The bronchioles become terminal bronchioles and eventually respiratory bronchioles, where gas exchange commences. Trachea Bronchus Bronchiole The Bronchioles  As bronchioles become smaller  epithelium changes into a simple ciliated columnar epithelium  Goblet cells decrease  No cartilage plates  Thick smooth muscle  Small bronchioles have a simple cuboidal epithelium The Bronchopulmonary Segments  The respiratory bronchioles branch into alveolar ducts that lead into alveolar sacs.  The alveoli are chambers lined by simple squamous epithelium. This allows gas exchange between air in the alveolar lumen and the capillaries. Histology Alveolar Cells  Type I Pneumocytes  Type II Pneumocytes  Macrophages or Dust cells Type I Pneumocytes  Squamous Epithelial cells  Form the lining of 90% of the alveolar surface,  0.05 - 0.2 um thin, edges of the 2 cells overlap and are united by tight junctions- preventing leakage of blood from capillaries to the alveolar lumen  Form Blood Air barrier Type I Pneumocytes Type II Pneumocytes  Also known as Septal cells  Pulmonary Surfactant – is  Rounded or cuboidal the fluid secreted that secretory cells with spreads over the alveolar microvilli surface  Secretory granules are  These cells can multiply to made of several layers- replace damaged cells. lamellar bodies.  Surfactant also has  These lamellar bodies are bactericidal properties cytoplasmic inclusions made up of phospholipid which combines with other chemicals to form surfactant.  Type II Pneumocytes resemble Clara cells  Intersperesed amongst type I cells Form only 5% of the alveolar – air surface Pulmonary Surfactant  Surfactant contains  The reduced surface phospholipids, proteins tension in the alveoli and glycosaminoglycans, decreases the force that is reduces the surface needed to inflate alveoli tension and prevents during inspiration. collapse of the alveolus  Therefore surfactant during expiration. stabilizes the alveolar  Is constantly secreted. diameters, facilitates their  Removed from the expansion and prevents surface by Type I their collapse by pneumocytes and minimizing the collapsing macrophages forces Pulmonary Surfactant  Dipalmitoylphosphatidylcholine DPPC is the main surfactant phospholipid  Produced after 35th week of gestation  Premature births ➔RDS  Cortisol administration in threatened premature deliveries Blood Air Barrier  Thin layer of surfactant  Cytoplasm of Type I Pneumocytes  Basement membrane of Pneumocytes  Intervening Connective Tissue  Basement membrane of capillary endothelial cell  Cytoplasm of capillary Endothelial cells  The Bronchopulmonary Segments RIGHT LUNG LEFT LUNG Apical Apical Posterior Posterior Superior lobe Superior lobe Anterior Anterior Superior Lingular Inferior Lingular Lateral Middle lobe Medial Apical Medial basal Apical Inferior lobe Anterior basal Inferior lobe Medial basal Lateral basal Anterior basal Posterior basal Lateral basal Posterior basal The Lung Hila  The hila of the lungs are at the level of the 3rd and 4th costal cartilages and at the level of T5, T6 and T7.  At the hila, there is the entrance of:  1 (2) pulmonary artery(ies)  1 pulmonary bronchus  2 pulmonary veins  Lymphatics  Nerves The Lung Hila  Impressions on the hilar surface by the surrounding structures:  Right hilum – grooves for azygos vein and the superior vena cava  Left hilum – grooves for aorta and aortic arch and for the subclavian vessels Nerve supply to lungs  The autonomic nerve fibres (sympathetic and parasympathetic) form a pulmonary plexus at the hila and divide into the anterior and posterior plexuses.  Parasympathetic : Induce cough reflex (to clear bronchial tree of its secretions) Cause bronchoconstriction Cause vasodilation Are secretory to mucous glands  Sympathetic: Cause bronchodilation Cause vasoconstriction Lymphatic Drainage  By means of a superficial and deep plexus which drains onto the  bronchopulmonary lymph nodes,  into the tracheobronchial nodes,  up the bronchomediastinal lymph trunk. The Trachea  Around 10 cm long, [extends to 15cm on inspiration] and 2.5 cm in diameter, fibroelastic tube  Its wall contains U-Shaped bars of hyaline cartilage keeping the lumen patent  The posterior free ends of the incomplete cartilage rings are joined by the trachealis muscle  Begins in the neck, level of C6, at the level of the cricoid cartilage of the larynx  It ends in the thorax at the level of the sternal angle (T4/5) by dividing into the right and left main bronchi The Trachea  Lined by pseudostratified cilated columnar epithelium  Relations:  POSTERIOR Esophagus LRLN Sternum and Thymus  ANTERIOR Left Brachiocephalic vein Aortic arch and its 1st 2 branches  RIGHT SIDE Azygos Vein Right Vagus  LEFT SIDE Aortic arch Left common carotid and left subclavian arteries Left vagus and Left phrenic The Pleurae  2 Layers of pleurae containing the lungs  The parietal pleura : lines the  Thoracic wall – costal pleura  Thoracic surface of diaphragm – diaphragmatic pleura  Lateral aspect of the mediastinum- mediastinal pleura  Undersurface of the suprapleural membrane in root of neck – cervical pleura  The visceral layer lines the outer surfaces of the lungs and extends into the inter- lobar fissures  The two layers become continuous at the hilum – surround hilar structures in a cuff, which hangs down as a loose fold called the pulmonary ligament The Pleurae  Between the two layers is a potential space – the pleural cavity containing a small amount of pleural fluid.  The parietal pleura is named according to the region it covers. Hence:  Cervical pleura: extends above the clavicle  Diaphragmatic pleura  Mediastinal pleura  Costo-diaphragmatic recesses:  Costo-mediastinal recesses The Lung in Disease Pleural Effusions Lobar Pneumonia Pneumothorax Lung Malignancy Chronic Obstructive Pulmonary Disease