what does surfactant do
- secreted by type ll alveolar cells and lines the inside surface of alveoli
- > decreases surface tension inside the alveoli
-> prevents alveoli from collapsing
-> makes the alveoli easier to expand
explain surfactant and surface tension
- at an air fluid interface, surface of the fluid is under tension due to attractive forces between fluid molecules
- results in inward directed pressure that is a function of the surface tension of the fluid
- surfactant decreases the tension thus decreasing the pressure and making alveoli easier to expand
- law of laplace = P=2T/r
explain what would happen without surfactant and the law of laplace
- without surfactant, inward pressure of alveoli would be high making them difficult to inflate and prone to collapse
-> this effect would be exaggerated in smaller alveoli, making them even harder to inflate
explain surfactant and the law of laplace
- surfactant reduces the surface tension and inward pressure, reduces work to inflate alveoli
- in the lungs smaller alveoli have more surfactant
- which equalizes the pressure between large and small alveoli
- air flow equalized to all alveoli
what is the law of laplace
P=2T/r
- if 2 bubbles have the same surface tension the smaller bubble with have a higher pressure (because it has a smaller radius)
explain alveolar pressures at rest
- at the end of normal expiration, volume of air left in the lungs = functional residual capacity (FRC)
- pressure inside alveoli = pressure of outside air = 0 mmHg
- elastic recoil of lungs inward equals elastic recoil of chest wall outwards
- result = negative intrapleural pressure (Pip) and lungs pulled towards chest wall due to resultant forces on pleural membrane
what is transpulmonary pressure
Palv - Pip = 4 mmHg
Pip = intrapleural pressure (756 mmHg) -> -4 mmHg relative to atmosphere
Palv = intra alveolar pressure (760 mmHg) -> 0 mmHg relative to atmosphere
- positive transpulmonary pressure = distending pressure -> is the force inflating the lungs
explain the elastic recoil, volume, pressure and force in lung, pleural sac, and chest wall
lung
- elastic recoil (<—-) of lung
- volume of air in lungs is at FRC
- Palv = 0 mmHg
Pleural sac
(—–> <——)
- force due to negative intrapleural pressure
- Pip = -4 mmHg
Chest wall
(——>)
- elastic recoil of chest wall
explain why intrapleural pressure must be subatmospheric to keep lungs inflated
- in the normal lung at rest pleural fluid keeps the lung adhered to the chest wall
- elastic recoil of the chest wall tries to pull the chest wall outward
- elastic recoil of the lung creates an inward pull
- pneumothorax = air enters the pleural sac
- intrapleural pressure is no longer negative
- the bond holding the lung to the chest wall is broken and lung collapses creating pneumothorax (air in the thorax)
what are the pressure changes during quiet breathing
- chest expansion causes decreased Pip
- increased transpulmonary pressure (Palv-Pip)
- increase in pressure forces pulling lungs towards chest wall
- lungs/alveoli expand and Palv decreases
- air flow into alveoli until Palv=Patm
what is lung compliance
- compliance = ability of the lung to stretch
- the change in volume for a given change in pressure exerted on the lung
- decreased in restrictive pulmonary diseases (fibrosis)
- high compliance of the lungs allows them to move outward with little force required
what is lung elastance
- ability of the lung to spring back after being stretched
- due to the presence of elastin fibers throughout the lung interstitial space
- decreased in emphysema (loss of elastin) (enzyme breaks it down)
what is Boyle’s law and explain in context of lung volume and pressure when inspiratory muscles contract and relax
P1V1=P2V2 (if volume increases, pressure decreases)
flow = P/R (air flows by convection down a pressure gradient (high->low)
inspiratory muscles contract
-> lung volume increases
-> pressure inside lungs decreases
-> air is sucked into lungs
inspiratory muscles relax
-> lung volume decreases
-> pressure inside lungs increases
-> air is blown out of the lungs
explain the mechanical changes of the thoracic cavity during quiet inspiration and how it creates a pressure gradient that drives ventilation
- diaphragm contracts and flattens
- muscles of inspiration contract and pull ribs up and out, sternum lifts up
-> thoracic and lung volumes increase, Pip and Palv decrease
-> Patm> Palv
-> air flows in
explain the mechanical changes of the thoracic cavity during passive expiration and how it creates a pressure gradient that drives ventilation
- diaphragm relaxes and moves upward
- muscles of inspiration relax, ribs and sternum fall back down
-> thoracic and lung volume decrease, Pip and Palv increase
->Palv>Patm
-> air flows out
how does spirometry measure pulmonary function
- traditional wet spirometer
- subject inserts a mouthpiece that is attached to an inverted bell filled with air or oxygen
- the volume of the bell and the volume of the subjects respiratory tract create a closed system because the bell is suspended in water
- spirometer can be used to measure changes in lung volumes during ventilation
what are the 4 lung volumes and 4 lung capacities
lung volumes
- tidal volume (Vt)
- inspiratory reserve volume (IRV)
- expiratory reserve volume (ERV)
- residual volume (RV)
lung capacities
- inspiratory capacities = Vt + IRV
- vital capacity = Vt +IRV+ERV
- total lung capacity = Vt +IRV+ERV+RV
- functional residual capacity = ERV+RV
what is total pulmonary ventilation
= ventilation rate x tidal volume
(12 breaths/min) x (500mL) = 6L/min
explain ventilation
total pulmonary ventilation = ventilation rate x tidal volume
- (= volume of air moved into/out of respiratory system per minute) = 6L/min
- because gas exchange does not occur in the conducting airways they are anatomical dead space (150mL)
what is alveolar ventilation
- better indication of ventilation is efficiency is alveolar ventilation -> the volume of air moved in/out of the alveoli per minute
- alveolar ventilation = ventilation rate x (Vt - dead space volume Vd)
- if dead space = 150mL
-> alveolar ventilation = 12 breaths/min x (500-150mL) = 4.2L/min
explain the pathway of alveolar ventilation and anatomical dead space
- at the end of inspiration dead space is filled with fresh air
- exhale 500 mL (Vt)
-> the first exhaled air comes out of the dead space (only 350ml leaves the alveoli) - at the end of expiration the dead space is filled with stale air from alveoli
- inhale 500ml of fresh air
-> the first 150ml of air into alveoli is stale from the dead space
-> only 350 ml of fresh air reaches alveoli
-> dead space is filled with fresh air
-
Lecture 118
-
Lecture 240
-
Lecture 320
-
Lecture 421
-
Lecture 539
-
Lecture 620
-
Lecture 727
-
Lecture 820
-
Lecture 921
-
Lecture 10/1132
-
Lecture 1221
-
Lecture 1339
-
Lecture 1424
-
Lecture 1522
-
Lecture 1615
-
Lecture 1718
-
Lecture 1811
-
Lecture 1920
-
Lecture 2018
-
Lecture 2120
-
Lecture 2221
-
Lecture 2325
-
Lecture 2422
-
Lecture 2521
-
Lecture 2616
-
Lecture 2714
-
Lecture 2820
-
Lecture 2916
-
Lecture 30+3123
-
Lecture 3221
-
Lecture 3325
-
Lecture 3414
