Physiology, Sheet 5, Dr.yanal 12\2\2012

Download Link ------------------> Click here


------------------------------------------------------------------------
PHYSIOLOGY # 5
** In the previous lecture we talked about AIRWAY RESISTANCE, and we knew that it's accompanied with wheezing and coughing which may be productive (producing mucus).
**it's self corrected, but sometimes the patient needs to be given bronchodilators to help reducing the constriction of airways.
**a patient with productive coughing must not be given cough suppressants in any case. Moreover we consider any type of coughing in children as productive coughing so they must not be given cough suppressants at all.
BREATHING CYCLE ####
Keep in mind :-
1- FRC is the resting volume of the lung-thorax system
2- if we are moving the system away from the resting state (FRC) even increasing (inspiration) or decreasing (expiration) we need force (active) …. And to get back to the FRC we don't need any force (passive).
3-the lung is always tending to collapse to its resting volume that is the volume when the lung is not tending to collapse nor to expand.
4- the thorax tends to get to 75% of TLC
I. FRC (functional residual capacity)(resting state)
the lung tends to collapse to its resting volume ….. The thorax tends to expand to 75% of TLC
collapsing force = expanding force and opposite in direction the lung-thorax system is at rest.
II. VT (tidal volume)
Tidal volume means that we are adding 0.5 L of air to the FRC .. so volume of the lung increases.
The lung's tendency to collapse increases ….. the thoracic tendency to expand decreases
collapsing tendency > expanding tendency if we remove the muscles forces the system tends to collapse to FRV expiration is passive while inspiration is active.
III. TLC (total lung capacity)
The lung's tendency to collapse increases to the highest value ….. the thoracic tendency to COLLAPSE to its normal state is high
collapsing tendency of both the lung and the thorax tendency of the system is an extremely high collapsing tendency.
IV. RV (residual volume)
The lung's tendency to collapse is small ….. the thoracic tendency to expand increases
expanding tendency>collapsing tendency tendency of the system is to expand back to FRC the inspiration becomes passive while the expiration becomes active.
## WHY IS THE LUNG ALWAYS TENDING TO COLLAPSE ?? ##
Because of the collapsing forces that are in total of 2 types :-
1- elastic forces 70% surface tension 2/3 …. Elastic fibers 1/3
2- non elastic forces 30% airway resistance 80% …. Tissue viscosity 20%
Elastic forces are manifested during static conditions (no airflow) and during airflow.
Nonelastic forces are manifested just during airflow (inspiration or expiration)
total forces during air flow are elastic and nonelastic .. during static condition just elastic forces.
**And to face these forces we need work (work of breathing)
Work of breathing = dV * dP
Where dV = VT ………. dP = pressure difference
70% of this work is to overcome the elastic forces while 30% is to overcome the nonelastic forces .. in order not to allow the lung to collapse.
** TISSUE VISCOSITY **
Tissue viscosity opposes motion, whether it's inspiration or expiration. However, it's minimal (20%) !!
** SURFACE TENSION **
- Alveoli are spherical with a diameter of 200-400 microM , becoming larger during inspiration and smaller during expiration.
- They're lined from the inside with water vapor, polarity of the water makes the molecules try to aggregate (get closer to each others).
- as the water vapor lines the inner side of the alveolar membrane,, and the water molecules are trying to get closer to the middle portion,, then they are collapsing the alveolus.
- then .. surface tension : is the intermolecular attraction between water molecules trying to bring the organ to the center.
- to prevent the activity of the water vapor we need to apply an expanding force (-ve pressure) that exactly equals the collapsing force, therefore water molecules remain stable.
- how much –ve force do we need ??
Regarding Laplace's law P=2T/r
Where P = inflating pressure (force to oppose surface tension)
T = surface tension r = radius
If r decreases P increases
If T increases P increases
P increases work of breathing increases using ATPs increases this's bad !!
## SURFACTANT ##
- If we assume that the alveolus is sphere with a diameter of 300 microM (radius of 150 microM) and the wall is made of water vapor .. then the inflation pressure needed to keep the alveolus inflated at this radius = 23 mmHg (which is high as the normal is 4 mmHg) !!
- let's remove the water and replace it by plasma (92% water) .. here the pressure needed drops to 13 mmHg .. this indicates that the water is not favorable !!
- sooo we need a detergent to be added to water composed mainly of nonpolar lipid to lessen the intermolecular contraction of the molecules in order to lessen the pressure needed to keep the alveolus inflated .. and it's called "SURFACTANT" = surface active agent .. that is made of 90% lipid, 8% protein, 2% carbohydrate.
- in our bodies we have 2 types of alveolar cells :-
Alveolar type I :- the site of diffusion between alveoli and blood.
Alveolar type II :- produces the surfactant.


Done by :- Sally Abu-Jeries