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 Physiology, Sheet 1, Dr.yanal 5\2\2012 "Corrected by Eman Al-shawawreh"

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Majed Sharayha



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PostSubject: Physiology, Sheet 1, Dr.yanal 522012 "Corrected by Eman Al-shawawreh"   Thu Feb 09, 2012 12:09 am

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Introduction to the Respiratory System (Hypoxia)
The Respiratory system is highly connected to the cardiovascular system (The Heart).
As known, the right heart (right atrium and right ventricle) pump the blood to the lung to oxygenate it.
Thus, the main purpose of the respiratory system is to make the oxygen available to the cells.
For any reason, if the cell does not utilize enough oxygen, this is called “Hypoxia”.
Hypoxia can be defined as: The Decrease of oxygen utilization by the cells.
The Respiratory system helps in the homeostasis of O2, CO2 and H2.
As we know, when CO2 binds to H2O it is converted to carbonic acid (H2CO3), which dissociates to H+ and HCO3- according to the equation:
H2O+CO2 ⇋ H2CO3 ⇋ H+ + HCO3-
CO2 is considered as masked Hydrogen.
The Respiratory system helps in maintaining the normal level of these 3 elements, mainly O2 and CO2, but hydrogen in addition .
The Respiratory system also has non-respiratory functions, for example:-
It can regulate blood pressure by converting of Angiotensin I to Angiotensin II.
Helps in regulating body temperature by the process of inspiration and expiration.
Helps in venous return by the process of inspiration which act as a pump that vacuum and takes the blood from the venous system to the right atrium.
What are the potential causes of Hypoxia?
No Oxygen is available in the outside air, so we expect that the cells are not receiving O2.
Ascending to High Altitudes (How?)
The Oxygen at sea level, where the atmospheric pressure is around 760 mmHg, there is 21% of this pressure is oxygen (0.21×760=159160 mmHg) so this is the partial pressure of oxygen at the atmospheric air.
When ascending to high altitudes (Top of the mountain) the atmospheric pressure decreases according to the altitude above the sea level.
When ascending to high altitudes the percentage of the oxygen (21%) remains the same, but the partial pressure decreases.
When ascending 5.5 km (5500 m) the atmospheric pressure decreases to the half.
For example, at the altitude of 5500 m above the sea level the atmospheric pressure instead of being 760 mmHg it is 380 mmHg. {0.5×760=380 mmHg}
Ascending another 5500 (at 11000m above sea level) the pressure is also the half of 380 mmHg, which is 190 mmHg, and we ascend until eventually reaching 0 mmHg.
From the information above we conclude that the other cause of Hypoxia is ascending to High altitudes so the oxygen is not enough to supply the cells.
Chronic Obstructive Pulmonary Diseases (How?)
Oxygen from outside will enter the respiratory system through the airways (trachea, major bronchi, medium and small bronchiole,….etc) until reaching the alveoli; so maybe the airways are partially closed, which means increase in the airway resistance .
Remember: R
{Where: R=Resistance r= radius}
So we might have many different diseases (related the airways obstruction) we collectively sort them in one family called “Chronic Obstructive Pulmonary Disease” (COPD).
Examples of Some of (COPDs)
Emphysema
Chronic bronchitis
Bronchial (asthma) ± {May be present or not}
These diseases are mainly related to the narrowness of the airways mainly in the small bronchioles (when they become stenosed, narrowed or obstructed).
Chronic Restrictive Pulmonary Diseases (How?)
Chronic Restrictive Pulmonary Diseases: (Inability to inflate the lungs).
When the alveoli are stiff and incompliance, and are unable to be inflated by air.
Examples:
Respiratory distress syndrome (Rds) when there is no enough surfactant => resitricting collaps occure (will be explained later on).
Pulmonary fibrosis, the presence of too many fibers that prevent the stretching of the lung.

The thickness of the respiratory membrane (How??)
Oxygen diffuse into the blood , the capillary bring the blood from right heart "right ventricle " take the blood to the left heart "left atrium"
Oxygen in order to diffuse into the circulation, it has to cross five layers {The Respiratory Membrane}.
These layers are :
Alveolar epithelium ( alveolar type I cells )
Basement membrane
Interstitium (area between the alveolar wall and the capillary wall)
Capillary basement membrane
Capillary endothelial layer
These 5 layers are very thin 0.2m.
{Important Note: Respiratory membrane is different than Respiratory epithelium}.
The respiratory membrane itself does not limit O2 availability, so O2 cross the 5 layers of the membrane, as this membrane does not exist {Not diffusion limited}
Diseases that lead to the thickness of the respiratory membrane: -
Pneumonia (inflammation of the lung)
Bronchitis (inflammation of the airways the upper part of the respiratory tract).
Bronchiolitis (inflammation of the bronchioles).
Pulmonary edema (Accumulation of fluids in the interstitial space).
When there is fluid accumulation on the interstitial space, the oxygen can pass but not very efficiently.
We have a limited period for gas exchange which is equal to one cardiac cycle.
At rest this period is 0.8 seconds and during exercise it is 0.5 or 0.4 seconds.
So during exercise some risks may be faced because the blood that has gone to the lung comes back not fully oxygenated.

Partial Pressure
Partial pressure: in a mixture of gases each gas behaves as it is
the only gas available in the mixture.
Oxygen flows according to the partial pressure gradient (from high partial pressure to low partial pressure).
Oxygen is not affected by any other gases, only by the partial pressure gradient. (This is unlike other known gradients such as: concentration gradient, electrochemical gradients …etc).
We have 300 to 600 million alveoli in both lungs ,each alveolus has a diameter around 300 m ,during inflation this diameter might increases and during deflation this diameter might decreases.
The alveolus is surrounded by a huge network of capillaries, each alveolus is approximately surrounded by 1000 capillaries.
The reason that each alveolus is surrounded by this number of capillaries is to prevent the oxygen from flowing to the interstitial fluid.
Sometimes the alveoli may be inflatable due to stiffness or the alveolus maybe surrounded by foreign materials such as “Asbestosis” or “silicosis” .

Which is easier to inflate a child balloon or the lung?
{Note that the lungs are similar to 2 balloons inserted inside each other, one balloon represents the lung and the other balloon represents the thorax, so when we inflate we are inflating the 2 balloons}.
It takes 100 times more effort to inflate the child’s balloon, and inflating the lung takes no effort.
So why do we inhale to provide oxygen.
Why do we need oxygen to burn it with glucose to produce ATP (36 molecules of ATP).
To inflate the lung we need the help of respiratory muscles and these muscles need ATP.
How much does the respiratory muscles utilize from the oxygen entering our body?
2-3% leaving more than 95% to the rest of the body and these muscles are considered as a very efficient machine, because this machine takes for itself less than 5% of the oxygen and give us more than 95% of the oxygen.
When having collapsing forces or restrictions to the inflation process, the respiratory muscles may consume 80% of the oxygen instead of 5%!! In order to have the ability to inflate the lung, and overcome the collapsing forces, nevertheless, we might die because of lack of oxygen or muscle fatigue.
In this case, the respiratory system is non-efficient machine, because it has consumed all the available oxygen that was supposed to be available to the circulation.
Thus, it is very important for the lung to be stretchable, inflatable, elastic, and compliant in order to work efficiently, otherwise, the lung will take too much effort and consume all the available oxygen ending by hypoxia.
CO2 cross from the blood to the alveoli according to the partial pressure gradient (PCO2 in the blood > PCO2 in the alveoli).
Which of these 2 gases can cross the respiratory membrane more easily CO2 or O2?
Co2, because it is more soluble so it crosses the respiratory membrane 20 times easier than O2.
When having a respiratory disease, which gas is affected first CO2 or O2??
Oxygen is affected first leading to hypoxia, even though the CO2 level is normal.
If we take a blood sample and we find that O2 levels are low and CO2 levels are high, this indicates that the lung tissue is destructed.
Now we enter the cardiovascular system, do we expect that the blood can cause hypoxia???
Yes, and this might be due to anemia or maybe there are RBCs but no hemoglobin or it might not be the normal hemoglobin (2 , 2) or abnormal hemoglobin (hemoglobinopathies).
In addition, hemorrhage, Iron deficiency anemia (microcytic anemia, hypochromic anemia), heart failure (Inability to pump the blood), narrowness of the artery supplying the tissues may all cause hypoxia.
In the cellular level, poisoning of the mitochondrial chain, although the oxygen is available , the mitochondria will not utilize the oxygen and the cells are not able to take the oxygen , this might be due to toxins such as cyanide poisoning (that block the mitochondria so the cells will die)
Septicemia " تسمم الدم "(sepsis) in the blood (blood poisoning) may also cause hypoxia.

{Sorry For any Mistakes}
Done by: Muneer Jarad
Special Thanks to: Khaldoon Al Qaddum
Think , Plan , Have the courage , be indecisive and stay with god then u will achieve your goals whatever the road is !

Corrected by : Eman Al-shawawreh
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Physiology, Sheet 1, Dr.yanal 5\2\2012 "Corrected by Eman Al-shawawreh"
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