THE RESPIRATORY SYSTEM III Dr. Mah Jabeen Muneera Assistant professor Department of Anatomy KEMU

RESPIRATORY BRONCHIOLE  Arise from terminal bronchiole  Diameter < 0.5mm  Transition between conducting & respiratory subdivisions  Structurally similar to terminal bronchioles EXCEPT  Walls interrupted by out pocketings (alveoli)– gas exchange  Epithelium  Ciliated cuboidal in larger  Simple cuboidal in smaller  Lamina propria  Smooth muscles  Fibroelastic tissue

ALVEOLAR DUCT  Arise from respiratory bronchioles  Completely lined by alveoli  Epithelium  Simple squamous  Smooth Muscles  Smooth muscles DISAPPEAR at end of alveolar duct  Only elastic & collagen fibers support the wall

ALVEOLAR SACS  Arise from alveolar duct  Epithelium  Simple squamous  Wall has:  Elastic fibers-for expansion  Reticular fibers- to prevent over distension  Capillaries embedded in this CT

ALVEOLI  Sac like evaginations open on one side  Size 200 µm  Between adjacent alveoli is interalveolar septum  Elastic & reticular fibers  Macrophages, fibroblast, mast cells  Continuous capillary bed (from pulmonary artery  vein)  Air in alveoli separated from capillary blood by respiratory membrane made of  Alveolar cells  Fused basal lamina of alveolar cell & capillary endothelium  Cytoplasm of endothelial cell

Jeanne Adiwinata Pawitan

 Alveoli surrounded by fine elastic fibers  Alveoli interconnect via alveolar pores of Kohn– equalize air pressure, collateral ventilation  Alveolar macrophages – free floating “dust cells”—Heart Failure Cells  Alveolar cells  Type I pneumocytes/alveolar cells - squamous alveolar cells) – tight junction – basal lamina – very thin region  permeable to gasses  Type II pneumocytes/alveolar cells - great alveolar cell – septal cells – surfactant – surface tension decreased  prevents collapse  Alveolar lining regeneration

 This “ Air-blood barrier ” (the respiratory membrane) is where gas exchange occurs  Oxygen diffuses from air in alveolus (singular of alveoli) to blood in capillary  Carbon dioxide diffuses from the blood in the capillary into the air in the alveolus

Alveolar cells

Surfactant  Type II alveolar cells scattered in alveolar walls  Microvilli over free surface  Lamellar bodies  Phospholipids, surfactant proteins (A, B, C & D)  Surfactant is a detergent-like substance which is secreted in fluid coating alveolar surfaces – it decreases surface tension  Without it the walls would stick together during expiration  Respiratory Distress Syndrome  Premature babies – problem breathing is largely because they lack surfactant  Role of Steroids

Pleura Pleural cavity – slit-like potential space filled with pleural fluid Around each lung is a flattened sac of serous membrane called pleura Parietal pleura Visceral pleura

Pleura  Mesothelial cells  Connective tissue  Pleural effusion - fluid  Haemothorax - blood  Pneumothorax - air  Pleuritis - infection

Clinical correlation  Asthma  prolonged contraction – expiration  Lumen << – wheezing, dyspnea  Hypersecretion goblet cell, mucus/serous gl  Steroids, Β2-agonist -relax  Emphysema  Longterm exposure- cigarette smoke ≈ inh – antitrypsin >< elastase – dust cells – elastic fiber destructed  Fibrosis  Increased activity of fibroblasts in response to diseases causing distress

normalemphysema

 Metaplasia  Tumors – squamous cell carcinoma Clinical correlations

you might want to think twice about smoking…. 16