5.1 Structure and Function of the Respiratory System Flashcards
What is the largest surface area in the body that is exposed to the outer environment?
The alveoli
Alveoli diameter in micrometers
75-300
Describe six types of cells present in the alveoli-capillary unit
- Type 1/Type 2 pneumocytes
- Pericytes
- Capillary endothelium
- Fibroblasts
- Immune cells (APCs, macrophages and T cells)
What percentage of the alveoli surface area is made of type 1 vs type 2 pneumocytes?
- Type 1: 95%
- Type 2: 5%
What type of cell occupies most of the alveolar surface (in terms of cell number)?
- Type 2 pneumocytes (60%)
- Since type 1 are so flat, they make up more area despite smaller numbers
How is it that type 2 pneumocytes are a “reservoir” of cells?
Type 1 pneumocytes can be generated out of type 2 pneumocytes, enabling them to be replenished
Which cells recycle surfactant from the alveolar surface? What proportion of recycling occurs in each?
Type 2 pneumocytes: 90%
Macrophages: 10%
List five functions of pulmonary surfactant
- Reduction in surface tension
- Increase in compliance
- Stabilisation of alveolar structure
- Prevents movement of fluid into alveoli
- Activates the immune system
Recall the Law of Laplace
P = 2T/r (P: Pressure, T: Tension, r: radius)
As an alveoli decreases in size, the surfactant ____ their surface tension
Decreases
Describe the three classes of substances that make up pulmonary surfactant, and the percentage made up by each
- Phospholipids (80%)
- Neutral lipids (10%)
- Surfactant proteins (10%)
At what day of embyronic development does the respiratory system begin to develop?
28 days
Which germ layer does the pulmonary epithelium arise from?
Endoderm
Which germ layer do the muscles and connective tissue of the respiratory system arise from?
Mesoderm
At what week of embryonic development are cilia present?
Wk 10
At what week of embryonic development are mucosal glands present?
Wk 12
At what week of embryonic development is there enough surfactant to support lung function?
~Wk 35
Other than gas exchange, cell production, and surfactant production, what is the other role of pneumocytes?
Controlling fluid exchange into and out of alveoli (want to prevent oedema)
How do the pneumocytes regulate fluid levels in the alveoli of an uninjured lung? (in terms of the bloodstream, not the lymphatics)
Actively transporting sodium, and chloride ions into bloodstream, creating an osmotic gradient that causes water to follow through aquaporins
Where do alveolar macrophages reside in the respiratory system?
In the mucous layer
Briefly describe the process of alveolar fibrosis following an insult to the epithelial lining
- Insult to epithelial lining
- Detected by T2 pneumocytes
- Signal to fibroblasts, which migrate and proliferate at the site of the insult
- Over time, more fibroblasts migrate, and fibrous clot increases in size, thus decreasing the efficiency of the alveolus
Cigarette smoke leads to overactivation of the immune system. Describe to mechanisms by which this causes harm
- Alveolar wall destruction (emphysema) from overactivated proteases
- Mucus hypersecretion leads to decreased efficiency of gas exchange (caused by inflammatory response)
Is the pulmonary circulation a low-pressure system or a high-pressure system? How does this influence the thickness of pulmonary artery walls?
- Low pressure.
- Therefore, pulmonary arteries have relatively thin walls
Do arteries and veins travel together in pulmonary circulation? If not, where?
- No
- Arteries travel with air ways
- Veins travel in septa between pulmonary lobuli
