15 Questions
What is the approximate percentage of alveolar surface composed of simple squamous epithelium?
95%
What type of fibers circumscribe the orifices of alveoli?
Elastic and reticular fibers
What is the function of type I pneumocytes in preventing the seepage of extracellular fluid into the alveolar lumen?
They form occluding junctions with each other
Which type of pneumocytes have membrane-bound lamellar bodies that contain pulmonary surfactant?
Type II pneumocytes
What is the role of alveolar macrophages in the alveolus?
To phagocytose particulate matter in the lumen of the alveolus as well as in the interalveolar spaces
In patients with emphysema, what is decreased in the lung tissue?
Elasticity
What is the narrowest barrier region in the lung?
Fused basal laminae of type I pneumocytes and endothelial cells
What is the primary mechanism of O2 and CO2 exchange in the lungs?
Passive diffusion
What is the function of the visceral pleura?
Covers and adheres to the lung
What is the main difference between the left and right thoracic cavities?
The number of lobes
What type of blood does the pulmonary artery supply to the lungs?
Deoxygenated blood
What is the primary function of the bronchial arteries?
To supply oxygenated blood to the lungs
What happens to the smooth muscle coats in individuals with asthma?
They undergo prolonged contraction during expiration
What is the effect of steroids and β2-agonists on bronchiolar smooth muscle?
They relax the smooth muscle
What is the characteristic of the pulmonary circulation?
Low-pressure system
Study Notes
Alveoli Structure
- Alveoli have a prominent basal lamina
- Alveoli openings are associated with alveolar sacs
- Devoid of smooth muscle cells, instead circumscribed by elastic and reticular fibers
Type I Pneumocytes
- Compose ~95% of the alveolar surface
- Simple squamous epithelium
- Form occluding junctions with each other to prevent fluid seepage
- Adluminal aspect covered by a well-developed basal lamina
- Luminal aspect lined by surfactant
Type II Pneumocytes
- Compose ~5% of the alveolar surface
- Dome-shaped apical surface juts into the alveolar lumen
- Contain membrane-bound lamellar bodies with pulmonary surfactant
- Synthesized on the RER and modified in the Golgi apparatus
Alveolar Macrophages
- Derived from monocytes that gain access to the pulmonary interstitium
- Migrate between type I pneumocytes and enter the alveolar lumen
- Phagocytose particulate matter in the alveolar lumen and interalveolar spaces
- Assist type II pneumocytes in the uptake of surfactant
Gas Exchange
- O2 is exchanged for CO2 carried by blood in the lungs
- CO2 is exchanged for O2 carried by blood in the tissues
- Passage of O2 and CO2 across the blood-gas barrier is due to passive diffusion
- Narrowest barrier regions consist of surfactant, type I pneumocytes, fused basal laminae, and endothelial cells
Thoracic Cage
- Divided into three regions: left thoracic cavity, right thoracic cavity, and mediastinum
- Each thoracic cavity is lined by a serous membrane (pleura) consisting of simple squamous epithelium and subserous CT
Pulmonary and Bronchial Arteries and Veins
- Pulmonary arteries arise from the right ventricle and drain into the left atrium
- Supply deoxygenated blood to the lungs from the right side of the heart
- Involved in gas exchange and are a low-pressure system
- Bronchial arteries arise from the systemic circulation and carry oxygenated blood
- Travel in the septa between lobules of the lung and are a high-pressure system
Innervation of the Lungs
- Parasympathetic, preganglionic fibers descend into the vagus and terminate in the ganglia
- Ganglia contain excitatory, cholinergic neurons and inhibitory, nonadrenergic neurons
- Postganglionic fibers to the smooth muscle are excitatory or inhibitory
Asthma
- Smooth muscle coats contract at the end of expiration and relax during inspiration
- In asthma, the smooth muscle coat undergoes prolonged contraction during expiration
- Steroids and β2-agonists relax bronchiolar smooth muscle and are frequently used to relieve asthmatic attacks
This quiz covers the structure and characteristics of alveoli in the respiratory system, including their composition and features.
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