Respiratory Physiology II PDF

1 Rawan Asrawi + Ola Qutaiba Rawan Asrawi + Ola Qutaiba Yanal Shafagoj Respiratory system Respiratory system deals with the HOMEOSTASIS of its gases, which are O2, CO2, and H2, in order to maintain the Arterial Blood Gases (ABG’s). Note: you should memorize all numbers in the sheet!! In the system o...

1 Rawan Asrawi + Ola Qutaiba Rawan Asrawi + Ola Qutaiba Yanal Shafagoj Respiratory system Respiratory system deals with the HOMEOSTASIS of its gases, which are O2, CO2, and H2, in order to maintain the Arterial Blood Gases (ABG’s). Note: you should memorize all numbers in the sheet!! In the system of ABG’s we rename the gases as PaO2, PaCO2, PH, with their normal approximated values 100mmHg, 40mmHg, and 7.4 respectively. - If these potential gases are within the normal limits, we know that the lung is functioning properly, otherwise there’ll be some abnormalities. - We are focusing mainly on O2, because it’s the essential molecule for cells in order to live. Now moving into a normal living cell, in order to give energy in the form of ATP, we need to provide it with a GLUCOSE during the stages of Cellular Respiration: 1. Glycolysis, which occurs outside the mitochondria (1 glucose is converted to 2 pyruvates) and that gives 2 ATP. 2. The entry of the pyruvate to mitochondria (in the presence of O2), that will end with 34 ATP. So, in total 1 glucose gives 36 ATP (Max). ❖ Hypoxia: Is the decrease in O2 utilisation by the cells, and that can happen due to many reasons like decrease in O2 availability, or maybe the cell itself suffers from toxins like Cyanide poisoning, or negative bacteria. The main question here, what are the POTENTIAL causes of HYPOXIA? To answer the previous question, we have to clear some points, Firstly, the O2 in atmospheric pressure is actually taken from the SEA LEVEL, so the atmosphere makes a column of air that has weight (force), and force on area gives Pressure (Atmospheric pressure). - Column A is longer, which gives us an indication that the force is bigger and so the pressure. Patm= 760 mmHg Sea level - The atmospheric pressure is composed of 2 gases mainly, which are N2 (79%), and O2 (21%), we can find CO2, but in a very small amounts (0.3%) nothing to be compared with the previous two, so we consider it as 0%. The atmospheric pressure =760mmHg, and so the PO2=160mmHg, and the PN2=600mmHg, (we get these values by timing the atmospheric pressure with the gas percentage). ▪ Examples: 1- We have a mountain, which its height is 5.5 Km (5500m) away from the sea level, the atmospheric pressure here drops to ½ the original amount (760mmHg), because it is inversely proportional to altitude, so the Patm=380mmHg, and the PO2=80mmHg, also the PN2 will drop to 300mmHg. 2- We have a building that is 11Km away from the sea level, what will be the values of the pressure (Patm, PO2, PN2)? Notice that 11Km is actually double the height in the previous example, so you can solve it immediately either by dividing the original pressure by 4 or dividing the values of the previous example with 2. The answers will be Patm=190mmHg, PO2=40mmHg, and PN2=150mmHg. A question to ask!!! What will be the atmospheric pressure for a person standing on top of mountain EVEREST, which is 8888m above sea level? calculate the PO2 as well. Final answer: Patm=226mmHg, PO2~45mmHg (no one can breathe nor live there, due to high altitude.) In conclusion, High altitude is considered one of the main reasons in Hypoxia. Respiratory system is composed (in an Anatomical point of view) of 2 zones: A- The conductive zone, in that zone the main function is only conducting air in and out, so it must be opened, and there’s no gas exchange, due to the lack of capillaries, that zone is called (Anatomical Dead Space). B- The respiratory zone, there’s a gas exchange, where O2 diffuses to blood as if the biological membrane doesn’t exist, and the CO2 diffuses even more easily (in fact 20 times easier than O2, because it’s 20 times more soluble). ……………………………………………………………………………………. Previously, we mentioned that the airways (conducting zone) have to be opened, if any obstruction occur, that will increase the Resistance (R). - According to a law that (R) is directly proportional to the length (L) of the vessel and the viscosity (η) of the blood, and inversely proportional to the radius to the fourth power (r4), so any small change in the radius will give a HUGE change in Resistance. - Any obstruction in the conductive zone leads to an obstructive disease, and if it lasts for a period of time, we call it a Chronic Obstructive Pulmonary Disease (COPD), further more the resistance here will increase and the patient will suffer from a difficulty in breathing either in inhaling or exhaling, and so we prescribe a Branchiodilation drugs for them, in order to decrease the resistance. - Some vocabs you need to know: Inflatable=compliant, which means if we apply a little force, we can deform it by changing the shape and structure, and that is a MUST for the respiratory zone if not it’ll be rigid and spiffed. Obstruction always deals with the conducting zone. Restriction always deals with respiratory zone. ❖ Lung diseases are categorised into 3 families: 1- The conducting zone diseases (COPD) around 70%, the most common ones. 2- The respiratory zone diseases (Restriction pattern) around 20%, ex: pulmonary fibrosis. 3- The vascular zone diseases (vascular pattern) around 10%, the least common, ex: pulmonary hypertension. ……………………………………………………………………………………………………………………………. As we mentioned previously the conductive zone is called dead anatomical space, but is it dead? Obviously NO, it has many functions including filtration, moving mucus, brings the temperature of air to 37° & humidifying the dry air by adding water vapor (H2Og) → a function of goblet cells (if dry air reaches the alveoli, it causes physical injury). By adding water vapor a new gas contributes to the pressure in the dead anatomical space→ PH2O, PH2O at 37° Celsius equals 47 mmHg. So, in the conductive zone there are 3 gases contributing to the pressure: PO2, PN2, PH2O and the total pressure is 760 mmHg → 47 mmHg of it is PH2O, then → 760 – 47= 713mmHg → 21% of it is PO2 & 79% is PN2. Final value PO2=150mmHg, which represents the PO2 in an Anatomical space, notice it is kind of close to the atmospheric one (160mmHg). Then what are the values inside alveoli? PO2→ 100 mmHg PCO2→ 40 mmHg PH2O→ 47 mmHg PN2→760-(100+40+47)= 573 mmHg IMPORTANT NOTES: - We can’t take N2 from air and add to it H2 or O2 to get biological compounds - PN2 doesn’t have any importance; N2 is a spectator molecule and has no role in the RS. You’re not required to memorize it but it’s very easy to calculate (760-the rest of the partial pressure values of other gases). - We need just to know PO2 and PCO2 because they always affected ………………………………………………………………………………………………………………….. - Our physiological temperature is 37° Celsius thus PH2O in RS is always = 47mmHg. - Some abbreviations that will be used later on: PvO2 → venous O2 pressure, Pv-O2 (v bar) → mixed venous pressure, PAO2 → alveolar pressure, PaO2 → arterial pressure, PeO2 → expiratory pressure, PiO2 → interstitial pressure. A → Alveolar a → Arterial V → Venous → Mixed venous i → Interstitial →In vascular: Pv-O2= 40mmHg, Mixed venous blood is the combination of venous blood from both the superior and inferior vena cava systems. - Oxygen diffuses from high partial pressure to low partial pressure. - O2 attaches to hemoglobin in RBCs (we get HbO2) and the time that RBCs spend in capillaries equals one cardiac cycle duration which can be 0.8 second in case the heart rate is 75 (at rest), or 0.4 second in case of exercising (heart rate=150). - When the RBC reaches a point where the time=0.3sec the PO2 is at equilibrium with PAO2 (PO2=100mmHg) & till 0.8 sec the PO2 is 100 mmHg So only one third of the Respiratory Membrane is being used. - The Respiratory Membrane is composed of 6 layers (The doctor mentioned 3: Alveolar epithelium, interstitium, and capillary endothelium), O2 must cross these 6 layers. Imp: Oxygen can cross any biological membrane as if the membrane doesn’t exist so as we know O2 doesn't need any channels to transport it. Thus, hypoxia is unlikely due to diffusion problems. (Oxygen is not diffusion limited) - As we’ve mentioned before the diffusibility of CO2 is 20 times more than O2, then if O2 can cross any biological membrane as it doesn’t exist, CO2 will diffuse 20 times easier than O2. *In case there’s a problem in the lungs which gas is affected first? O2, because its diffusibility is less. In respiratory failure type 1 → O2 is affected, & in type 2 both O2 & CO2 are affected. ❖ Systemic Circulation: o In respiratory system: PO2 in pulmonary capillaries = 40mmHg and PAO2= 100mmHg - As we said O2 diffuses from high PO2 (alveolar) to low one (capillaries). o In circulation: PaO2= 100mmHg and PiO2= 40mmHg, O2 diffuses from arterioles to interstitial. Pcell O2 < 40mmHg, O2 diffuses from interstitial to the cell. *Why is the PO2 in venous = PO2 in interstitial? Because of the difference in volume. Remember Interstitium: is the space between cells and capillaries. - Quick revision: ▪ Blood = 7% of our weight = 5L = 5000ml 3000 ml in systemic veins (60%) 750 ml in sys arteries (15%) 350 ml in sys capillaries (7%) 450 in lungs (9%) 350 in the heart (7%) ▪ Water in our body: 60% of our weight, for ex: 70kg x 60% = 42L 2/3 inside cells = 28L 1/3 outside cells= 14L (divided into: 11L in interstitial and 3L in plasma) The End of sheet #1