PHYS Respiratory Flashcards
- The anatomical structure of the airways provides a remarkable balance between two competing demands. What are they?
- To minimise the total resistance to airflow
- To minimise the total volume of air in the conducting tubes where exchange cannot occur (the “dead space”)
- Fill in the following:
The alveoli are ____-walled, inflatable sacs.
- ___ exchange is their function. They are encircled by _________ capillaries.
- The alveoli are close to the capillaries, offering tremendous s______ a___ for ___ exchange by diffusion.
- There is a single layer of flatted ____ _ alveolar cells.
- Type __ alveolar cells secretes pulmonary __________. This substance facilitates lung e________.
The alveoli are thin-walled, inflatable sacs.
- Gas exchange is their function. They are encircled by pulmonary capillaries.
- The alveoli are close to the capillaries, offering tremendous surface area for gas exchange by diffusion.
- There is a single layer of flatted Type I alveolar cells.
- Type II alveolar cells secrete pulmonary surfactant. This substance facilitates lung expansion.
- Which of the following are incorrect regarding mechanics of ventillation?
- The thoracic cavity is a closed compartment, bounded by muscles and connective tissue.
- Firmly attached to the entire interior of the thorax is a thin membrane called the visceral pleura, forming two completely separate sacs, one on each side of the midline.
- The lungs are also coated with a membrane, called the visceral pleura.
- The space between the two pleural membranes (pleural cavity) is occupied by a thin layer of intrapleural fluid.
- Normally, there is very little friction between the two pleural membranes, so they slide over each other easily as the lungs expand and contract.
- should be parietal pleura attached to thorax interior.
- should be visceral pleura attached lungs.
- Contrast inspiration with expiration in terms of
Inspiration begins with the contraction of respiratory muscles: the diaphragm (phrenic nerve innervation) and the external intercostal muscles (innervated by intercostal nerves).
- chest expansion decr’s intrapleural pressure; lungs drawn into area of lower pressure and expand
- volume incr lowers intra-alveolar pressure below atmospheric presssure; by difference, air enters lungs
- accessory inspiratory m’s (sternocleidomastoid, scalenus) can further enlarge thoracic cavity
- m’s of active expiration: internal intercostal, abdominal
The onset of expiration begins with the relaxation of the inspiratory muscles.
- m’s: diaphragm, chest wall - also, elastic recoil of alveoli - decr’ size of chest cavity
- intrapleural pressure incr’s, lungs are compressed
- intra-alveolar p incr’s; when above atmospheric p, air is driven out - an expiration
- forced exp - by contraction of expiratory m’s - abdominals, int intercostals. Their contraction further incr’s the p gradient bw alveoli (greater p) and the atmosphere
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- Describe how transmural pressure affects the lungs.
There are multiple pressures that act on the physiology of the lungs. Transmural pressure acts across the lung wall, and pushes the lungs outward. This is produced by an intra-alveolar pressure (760 mm Hg) that is greater than the intrapleural pressure (756).
See attached.
- Describe the following lung volumes & capacities:
- TV
- IRV
- IC
- ERV
- RV
- FRC
- VC
- TLC
- TV, Tidal Volume, 500 mL - volume air that moves in and out of lungs during quiet breathing.
- IRV, Inspiratory Reserve Volume, ~2000-3000 mL - extra air that you can inspire over and above tidal volume
- IC, Inspiratory Capacity, 2500-3500 mL - total volume you can inspire from rest (TV + IRV)
- ERV, Expiratory Reserve Volume, 1000 mL - extra air you can expire over and above tidal volume
- RV, Residual Volume, 1200 mL - the amount of air that remains in lungs after maximum expiration
- FRC, Functional Residual Capacity, 2200 mL - amount of air remaining in lungs at rest (ERV + RV)
- VC, Vital Capacity, 3500-4500 mL - maximum amount of air you can move in and out of lungs (TV + IRV + ERV)
- TLC, Total Lung Capacity, 4700-5700 mL
Also - Minimal Volume, ~100 mL - the amount of air that would remain if lungs were allowed to collapse.
See attached for inspiration/expiration graph over time
- During inspiration, force is required to overcome what factors of the lungs?
Elastic recoil of the lungs and thoracic wall tissue
Surface tension created by the fluid layer lining the inner surface of the alveoli
Resistance to airflow in the airways
Frictional resistance created by deformation of the lung and thoracic wall tissue as it’s deformed during inspiration
- What is compliance of the lungs?
Compliance is the effort required to stretch/distend the lungs. Eg a thin, toy balloon is more compliant than a thick, rubber balloon.
A highly compliant lung stretches further for a given incr in pressure than a lung with less compliance.
- Describe the relationship between pulmonary elastic behaviour and pulmonary surfactant.
-
Pulmonary elastic behaviour depends on pulmonary elastic properties and alveolar surface tension. This tension is determined by the thin liquid film that lines the inside wall of each alveolus.
- This film causes the alveolus to resist expansion. This film also squeezes the alveolus, assisting recoil.
- A coating of pulmonary surfactant helps prevent the alveoli from collapsing from this surface tension.
- An insufficient amount of pulmonary surfactant can produce newborn (infant) respiratory distress syndrome.
- How is the FEV1 affected by obstructive lung diseases?
FEV1 is defined as the volume of air expired in 1 second, during maximal forced expiration. Normally this is about 80% of VC.
In obstructive lung disease:
- The TLC is essentially normal, but the FRC and RV are incr’d bc additional air is trapped in lungs following expiration.
- Bc the RV is incr’d, VC is reduced compared to normal
- The FEV1 is also reduced, usually even more than the VC, so that the FEV1:VC ratio is usually less than 80% (normal value)
- TLC, IC, VC all reduced - lungs can’t expand as much as normal
- Bc there’s normal resistance to airflow, FEV1:VC ratio is normal or greater than normal
- Therefore the FEV1:VC ratio can be used to distinguish bw obstructive and restrictive lung disease.
(see attached)
- Describe the Control of Respiration
Inspiration initiated by increase in firing rate of neurons in the respiratory centre (brainstem)
These neurons make connections with motor neurons in the cervical and upper SC
- in turn innervate the inspiratory muscles, causing inspiration
- What are some factors that regulate the depth and rate of respiration?
- Inputs to the respiratory centre signalling PCO2, pH, PO2 of arterial blood
- Afferent (sensory) inputs from receptors in lungs
- Inputs arising from higher centres of the brain, e.g. the motor cortex
- Which of the following are correct regarding Respiratory Centres in the Brainstem?
- Dorsal Respiratory Group (DRG) neurons consist mainly of expiratory neurons
- Ventral Respiratory Group neurons consist of both inspiratory neurons and expiratory neurons
- Pneumotaxic Centre inhibits inspiratory neurons
- Apneustic Centre inhibits expiratory neurons
2 and 3 are correct.
Incorrect:
- 1) DRG neurons most inspiratory nuerons
- 4) Apneustic centre excites inspiratory neurons
