14 lung Flashcards
How do you differentiate bronchi from bronchioles?
Bronchi have cartilage and submucosal glands within the walls
What is the acinus (lung anatomy)?
The part of the lung distal to the terminal bronchiole - composed of respiratory bronchioles that proceed into alveolar ducts and alveolar sacs
Describe the microscopic composition of the alveolar walls.
Capillary endothelium
Basement membrane and surrounding interstitial tissue
Alveolar epithelium
Alveolar macrophages
What cells compose the pulmonary interstitium?
Fine elastic fibers, small bundles of collagen, a few fibroblast-like cells, smooth muscle cells, mast cells, rare mononuclear cells
What are alveolar macrophages?
Mononuclear cells of phagocytic lineage, usually lying free within the alveolar space. Often contain phagocytosed carbon particles.
What cell types are found in alveolar epithelium?
Two principal cell types - type I pneumocytes, type II pneumocytes
What is the difference between Type I pneumocytes and Type II pneumocytes?
Type I pneumocytes are flattened, platelike cells covering 95% of the alveolar surface
Type II pneumocytes are rounded, and are the source of pulmonary surfactant. They are the main cell type involved in repair of alveolar epithelium when type I cells are damaged.
What are pores of Kohn?
Pores between the alveolar walls which permit passage of bacteria and exudates between adjacent alveoli
What are the three divisions into which lung diseases are organized?
Lung diseases that affect…
The airways
The interstitium
The pulmonary vascular system
What is atelectasis?
Also known as collapse - loss of lung volume caused by inadequate expansion of airspaces.
Either incomplete expansion or collapse of previously inflated lung producing areas of airless parenchyma
If complete collapse of one lung occurs, five sixths of blood is routed to the normal lung resulting in only mild desaturation to 90%
What processes occur following atelectasis?
Inadequate expansion of airspaces results in shunting of inadequately oxygenated blood from pulmonary arteries into veins - giving rise to a ventilation-perfusion imbalance and hypoxia.
What are the three forms of atelectasis?
Resorption atelectasis
Compression atelectasis
Contraction atelectasis
What is resorption atelectasis?
Occurs when an obstruction prevents air from reaching distal airways. The air already present becomes absorbed and alveolar collapse follows.
Asthma, chronic bronchitis, bronchiectasis, aspiration of FB
What is the most common cause of resorption atelectasis?
Obstruction of a bronchus by a mucous or mucopurulent plug - frequently occurs postoperatively but may also complicate bronchial asthma, bronchiectasis, chronic bronchitis, or aspiration of foreign bodies.
What is compression atelectasis?
Sometimes called passive or relaxation atelectasis - usually associated with accumulations of fluid, blood, or air within the pleural cavity - mechanically collapses the adjacent lung.
Cardiac failure, lung Ca, peritonitis, subdiaphragmatic abscesses
What may cause compression atelectasis?
Pleural effusions (CHF) Pneumothorax - air leaks into the pleural cavity Basal atelectasis from elevated position of the diaphragm in bedridden patients, patients with ascites, and pre/post-op
What is contraction atelectasis?
Also known as cicratization - occurs when either local or generalized fibrotic changes in the lung or pleura hamper expansion and increase elastic recoil during expiration.
Which forms of atelectasis are reversible? Irreversible?
Contraction atelectasis - irreversible
Compression atelectasis - reversible
Resorption atelectasis - reversible
How does acute lung injury manifest clinically?
Acute onset of dyspnea
Decreased arterial oxygen pressure (hypoxemia)
Development of bilateral pulmonary infiltrates on radiographs
Absence of clinical evidence of primary left-sided heart failure
What is ARDS?
Acute Respiratory Distress Syndrome
Acute capillary endothelial injury or alveolar epithelium.
Damage results in Increased capillary permeability Interstitial then intra-alveolar oedema
Fibrin exudation
Formation of hyaline membranes
Capillary injury is probably due to release of mediators. Mediators either originate from macrophages or neutrophils.
Damage mediated by: Cytokines Oxygen free radicals Complement Enzymes Eicosanoids.
Endotoxins are particularly important in initiating these cellular events. Endotoxins cause:
Release of cytokines from macrophages Leucocyte and endothelial activation Amplifies complement-mediated response of neutrophils
Exudate and diffuse tissue destruction result in scarring
What are the basic causes of ARDS?
Diffuse alveolar capillary and epithelial damage, resulting from an imbalance of pro-inflammatory and anti-inflammatory mediators.
Associated with either direct injury to the lung or indirect injury in the setting of a systemic process.
Describe the onset of ARDS
Rapid onset of life threatening respiratory insufficiency
Cyanosis
Severe arterial hypoxemia that is refractory to oxygen therapy
Progression to multisystem organ failure
What is the histological manifestation of ARDS?
Diffuse alveolar damage - DAD
What are the two barriers forming the alveolar capillary membrane?
Microvascular endothelium
Alveolar epithelium