Unit 3 Day 1 (Tue 4/21) Flashcards
5 Phases of Lung Development
- embryonic stage
- pseudoglandular stage
- canalicular stage
- saccular stage (terminal sac stage)
- alveolar (postnatal stage)
Embryonic Stage
- 1st stage
- 4-7 weeks
- branching morphogenesis
- branching pattern determined by mesoderm
Pseudoglandular Stage
- 2nd stage
- 8-16 weeks
- differentiation of conducting airway epithelium
- glandular appearance
- formation of conducting airways completed at end of this stage
Canalicular Stage
- 3rd stage
- 17-26 weeks
- characterized by formation of repiratory bronchioles (deliniation of pulmonary acinus)
- possible to survive but respiratory distress trouble likely
Path of Air Into the Lungs
- trachea
- L and R primary bronchi
- secondary or lobar bronchi (3 in R lung, 2 in L lung)
- segmental bronchi
- terminal bronchioles (bronchioles do not have cartilage)
- respiratory bronchioles of exchange system
- alveolar ducts
- alveolar sacs
Blood Flow In the Pulmonary System
- pulmonary arteries
- terminate in interalveolar network of capillaries
- does not supply oxygen to the conduction system, but picks up oxygen in alveoli
- oxygenated blood returns to heart in pulmonary veins
Blood Flow in the Bronchial System
- bronchial arteries
- supply oxygen to the conduction system
- most blood in this system mixes with pulmonary supply through anastamoses with small pulmonary arterioles and capillaries
- bronchial veins drain only the connective tissues of hilar region of the lungs into the azygous vein
Path of Air Into the Lungs
- trachea
- L and R primary bronchi
- secondary or lobar bronchi (3 in R lung, 2 in L lung)
- segmental bronchi
- terminal bronchioles (epitherlium contains club cells)
- respiratory bronchioles of exchange system
- alveolar ducts
- alveolar sacs
Alveolar Septa
- indvidual alveoli are separated by interalveolar septa which are comprised of fibroelastic basal laminae and cells
- two main types of cells, type I and type II pneumocytes, are found on the side of the alveolar septa that faces air supply
Passage of Gas Through Air Blood Barrier
- surfactant layer
- plasma membranes and cytoplasm of thin type I pneumocytes
- common basal lamina between type I cell and capillary epithelium
- plasma membranes and cytoplasm of edothelial cell
- thus, oxygen must diffuse though plasma membranes 5 times before reaching hemoglobin in a RBC
Defense Mechanisms of the Alveoli
- alveolar tissues contains type I and II pneumocytes, monocytes, neutrophils, and fibroblasts
- monocytes differentiate into alveolar macrophages which enter the alveolar space and serve as third line of defense by phagocytosing small inhaled bacteria
Surfactant
- mixtures of lipids and proteins with polar and non-polar ends
- secreted by type II pneumoytes
- lowers surface tension in alveoli and prevents lung collapse and lung drying
- primary component of surfactant is phospholipids
- lack of surfactant is major problem in premature births
Cystic Fibrosis
- chronic congestive disease
- defect in chloride transport in epithelial cells
- autosomal recessive
- results in chronic infections and respiratory failure
Kartagener’s Syndrome
- severe genetic defect characterized by respiratory congestion and infections
- results from immotile cilia, due to defects in dynein arms
Particulate Overload Diseases (Black Lung, Silicosis)
- excessive smoking and/or air pollution leads to progressive loss of ciliated cells
- starts with loss of synchronized cilia wave
- cilia become gradually replaced with squamous cells as chronic coughing is used to clear congestion
Inspiratory Muscles
- diaphragm
- external intercostals
Expiratory Muscles
- none active during quiet breathing
- some active during forced expiration and exercise (muscles in abdominal wall)
Intrapleural Pressure
- Pip
- negative Pip (a vacuum) causes the lung to be attached to the chest wall
- allows inflation of chest cavity to cause inflation of lungs during inspiration
- loss of Pip can lead to pneumothorax
Elastic Recoil
- positive pressure = elastic recoil pressure during expiration
- drives expiration
Lung and Chest Wall Compliance
- reduced lung compliance happens during restrictive disease (moves down and right on compliance curve)
- inc. lung compliance happens during emphysema (elastin destruction) (moves up and left on compliance curve)
Lung and Chest Wall Compliance
- reduced lung compliance happens during restrictive disease (moves down and right on compliance curve)
- inc. lung compliance happens during emphysema (elastin destruction) (moves up and left on compliance curve)
- dec. chest wall compliance can be due to obesity, old age, scar tissue, etc
- dec. chest wall compliance can lead to premature saturation of the curve, reducing tidal volume
Club Cell
- same as Clara cell
- in epithelium of bronchioles
- protect the brochiolar epithelium by secreting products similar to surfactan
Lamina Propria
-layer of tissue exterior to epithelium in airway system
Surface Tension
- force that arises due to favorable water-water interactions and unfavorable air-water interactions
- causes dec. lung compliance, water accumulation in the lung, and collapse of small alveoli
Respiratory Distress Syndrome
- disorder with reduced surfactant
- dec. in lung compliance
- water accumulation in lung
- collapse of small alveoli
Chemical Factors That Affect Airway Resistance
• All act by affecting smooth muscle tone of bronchioles • Bronchoconstrictors (cause contraction of SM)
- Parasympathetic nervous system (acetylcholine)
- Histamine (asthma)
• Bronchodilators (cause relaxation of SM)
- Sympathetic nervous system (epinephrine/
norepinephrine via beta adrenergic receptors, ARs)
- Agonists for beta ARs (e.g., isoproteronol, albutenol) - CO2 in bronchioles
Air Flow
- laminar = deltaP/R
- turbulent
Mechanical Factors That Affect Airway Resistance
- mucous (bronchitis)
- lung volume
- dynamic airway collapse
Dynamic Airway Collapse
- resistance problem
- airway is closed when Paw
