Lecture 28

Partial Pressure of Gasses – calculate the partial pressure:

 
 

• The Partial Pressure of the Gas is equal to the percent of gas in the atmosphere times the total air pressure.
  
• Gases diffuse from areas of higher partial pressure to areas of lower partial pressure (the greater the difference between the two the faster the flow will occur)
  
• HANDOUT has the partial pressures – DON'T MEMORIZE but only know what he says
  
  • 0.21 (is the percent of O2 in atmosphere) x 760mmHg (atmospheric pressure at sea level) = 160mmHg. This is the Partial Pressure of oxygen. This Partial Pressure is based on dried air.
    
  • PO2 is 158 mmHG because water is included (it is wet air).
    
• For the Alveoli, we have the PO2 here of 100mmHg, the CO2 is 40mmHg, H2O is 47mmHg (b/c it is saturated air now), and the N2 changed b/c the partial pressures of the other gasses changed
  
• Functional Residual Volume (is 2.2L for the male and 1.8L for female see chart – it is an average of 2L) for a typical person, who is 150 lbs.  TV is .5 but that is not what the ventilation is (it is 500ml). You subtract the 150ml of dead space and you get 500-150=350ml of ventilation (you are changing very little air)
  
  • A normal person has 350 ml inhalation.  This means that only 17.5% of the air is changing with each breath, this is why we can state the alveolar volumes as fairly stable. This is at rest.
    
• The alveolar air was up to 40mmHg for CO2 and then it dropped to 32mmHg when it is exhaled – this is because it mixed with dead space air when it was being exhaled.
  
• The nitrogen changes when it gets into the alveoli and for exhaled air – it only changes because the other partial pressures of the other gasses change – it is not doing anything, not reacting with anything in our bodies.
  
• Look at the oxygen in the alveoli will reach 100mmHg, that means that your blood of the capillary of the lung it is 100mmHg. When we look at the artery it is only 95mmHg – this dropped b/c of the Physiological Shunt
  
• Physiological Shunt has 2 parts:
  
  • 1.) We have some bronchiole arteries in the thorax, and the bronchiole arteries are sending blood to the bronchioles.  Some blood is going to the lungs to supply the bronchi and some blood of the bronchi is very close to the alveoli. Some of the capillaries exiting the bronchi will anastomose with the capillaries of the alveoli, and the alveolar blood was exposed to air, but the bronchi blood was not, so it is higher in CO2 and this is why artery blood is lower in oxygen.
    
  • 2.) In the heart itself we have some heart blood returns by the Theabesian veins (they are veins in the heart where blood from them going directly into on of the chambers of the heart from heart muscle). The blood from these returned mostly of this occurs in the RA, then second most occurs in the RV, and some is going to LV because the blood is low in O2 (high in CO2).  By the time the blood mixes with the capillaries from bronchioles, pulmonary capillaries, and Theabesian veins coming back to the heart this explains why the O2 drops down to 95 in arteries
    
  • Oxygen and Carbon dioxide in the tissues. Pull the CO2 to 46mmHg and drop the oxygen to 40mmHg – and we just have the tissues at less than 40mmHg on the CO2 and greater than 46mmHg otherwise it would not be able to flow into it.
    
  • 47mmHg was maintained in the water – bringing water that is low in moisture and exhaling water that is high in moisture.
    
• Air Flow – In the Lung itself, we have some monitoring of the amount of PCO2 in the alveoli, and that will change the Air Flow. The alveoli have an Auto-regulatory System. The alveoli can regulate Air Flow, and air flow is regulated by the partial pressure of carbon dioxide.
  
  • In an alveoli, if we have a high partial pressure of CO2, then the bronchioles that lead to that alveolus will dilate (trying to get rid of the CO2). The alveoli will constrict if we have a low PCO2.
    
  • Air flow to a bronchiole is based on the partial pressure of carbon dioxide to that bronchiole.  
    
• Blood Flow – it is regulated by the partial pressure of oxygen in the alveoli. If we have high PO2 then blood vessels to the alveoli will dilate. If we have low PO2, blood vessels will constrict. We are trying to send the blood to where the oxygen is. This is still part of the Auto-regulatory System of the alveoli.
  
  • There is about 1L of blood in the Pulmonary Circulation at any one time. Of that 1L there is about 100mL of that blood in the Pulmonary Capillaries at any one time (exchanging O2 and CO2)
    

     
     

• See handout
  

   
   

• We are talking about a Pulmonary capillary flow with a RBC entering. It takes the RBC at rest ¾ of a second to get out of the capillary – to get across the capillary in .75 seconds. It will be short of oxygen when it gets there, but the oxygen takes .3 seconds to diffuse across the alveoli (oxygen has a pretty stable diffusion rate).  The RBC is in the capillary long enough to get saturated with oxygen (it is about 1/3 of the way down into the capillary when it finally get saturated). 
  
• If we want to increase the amount of oxygen going to the tissues (doing exercise), all we have to do is increase the number of RBC's and the speed at which the RBC's go through the capillary. This allows more oxygen to get into the system because more RBC's are being moved through.
  
  • Perfusion Rate Limited – the more we profuse blood through, the more O2 we take up, b/c there is more RBC going through the system.
    
• Now you are doing even harder work until the RBC goes through in 0.25 seconds, now many of the RBC's are going through and not getting filled with oxygen.
  
• So when we get to 0.3 seconds (the amount of time the blood is taking to cross through the capillary to get replenish itself with oxygen) it changes to Diffusion Rate Limited b/c diffusion is the limiting factor now.
  
  • Diffusion Rate Limited – even if you increase the number of RBC's you are not going to get more oxygen to the tissues. You have reached the limit, however there is no limit for the diffusion of CO2 out.  The blood cannot go fast enough to get all the CO₂ out of it. Keep increasing to get rid of the CO₂. CO₂ is 20 times more soluble in the plasma and the alveolar fluids, so it diffuses much faster.  CO₂ retention is rare – except if you have emphysema or there is something wrong with lungs. The tissues are burning oxygen, and we are actually building an Oxygen Debt.
    

 
 

Oxygen Debt – talking about RQ's and R's.

• RQ = CO2 Produced/ O2 Consumed = R
  
• These are exchange ratios and respiratory quotients.
  
• RQ – Respiratory quotient = CO2 produced / O2 consumed.
  
• R – Respiratory Exchange Ratios – they are listed as R values = CO2 produced / O2 consumed.
  

CO2 Produced/ O2 Consumed

• RQ is independent of any respiratory activity of the body. It depends upon what you are metabolizing.
  
  • If you are just metabolizing Carbohydrates that we are burning RQ = 1
    
  • If you are just burning Fats then RQ = 0.7
    
  • It is measured over a period of time (ex. perhaps a whole day or 5 hours)
    
  • Note: This is a why for the doctor to check if you are actually on a diet.  If someone is burning carbohydrates, then they are not sticking to their diet
    
• R depends upon activity and it will fluctuate with heavy exercise
  
  • During anaerobic exercise, R may go as high as two.
    
  • During anaerobic exercise, your R value may go up as high as 2.  After you exercise you have to pay an oxygen debt, and it might drop as low as 0.5 to pay the debt. 
    
  • The R value will stabilize and when it does, it will stabilize to RQ.
    
  • The R value is over is measured over seconds.  It is determined with 1, 2, or 3 breaths. When you are resting R and RQ are the same.
    

Getting Oxygen to Tissues from the Blood

• The oxygen is going to be transported on Hemoglobin from the blood to the tissues
  
• The Hemoglobin will have 4 iron atoms and each iron atom can hold one molecule of oxygen.
  
• When all 4 ions of the hemoglobin are empty, it is in the T-state (Tense State).
  
• If we add one molecule of oxygen to the Hemoglobin, it goes into the R-state (Relaxed State).
  
  • The Hemoglobin can hold 4 oxygen.
    
  • Hemoglobin works via Cooperative binding. Each additional oxygen increases the affinity for the next oxygen to bind.
    
  • Once it has 4 molecules of oxygen bound, we say it is Saturated.
    
  • At rest your Venous blood is 75% saturated.
    
    • Your blood returning to the lungs is generally missing just 1 molecule of oxygen
      
  • 1.5% of the oxygen will be transported by the plasma, but oxygen is not very soluble in the plasma.  Most of the oxygen is on the Hemoglobin.
    

 
 

Getting the O2 to leave the Hemoglobin and get into the tissues:

• Temperature – the more active the tissue the warmer it will be compared to the inactive tissues. When the blood gets to an increase in temperature in the tissue, this change will decrease hemoglobin's affinity for O2.  The Hemoglobin will start to give up O2 when traveling through warmer tissues (more oxygen will be released to the warmer tissues)
  
• Blood pH – active tissues have a lower blood pH b/c there is more CO2 generated there.
  
  • CO2 + H2O ß à HCO3- + H+
    
  • pH is the concentration of Hydrogen ions in the body à –log [H]
    
  • The more CO2 we get, the more H+ ions we will have in the area, and the lower the blood pH will be.  This tissue will cause a loss in the affinity for O2 on the Hemoglobin.  The lower the pH the more O2 will come off.
    
  • It also affects 2,3DPG.  2,3DPG is plentiful b/c it is a product of Glycolysis.  It causes O2 to be released.  2,3DPG can lower the affinity of Hemoglobin for oxygen, and it does this by binding the beta chains of the hemoglobin. If you have a high amount of 2,3DPG present it is going to release more oxygen in response to the temperate increase of the pH decreasing.
    
  • The hormones that increase 2,3DPG are:
    
    • Thyroxin
      
    • Testosterone
      
    • Growth Hormone
      
    • Circulating Catecholamines
      
  • Increasing Exercise will increase 2,3DPG
    
  • Increasing Altitude will also increase 2,3DPG – oxygen is a little bit more scarce for you to breathe at higher altitudes (ex. Denver).
    

 
 

3 Transport Systems to get rid of the CO2: (blood CO2 transports)

• 1.) Chloride Shift –
  
  • RBC contain Carbonic Anhydrase
    
  • CO2 + OH- + H+ à HCO3- + H+ (we have to remove these immediately) this gets buffered by the heme protein and this is exchanged
    
  • In exchange for the bicarbonate being kicked out of the RBC cell, the Cl is brought in.  That is called the Chloride shift. 
    
  • 60-70% of all CO2 transported in blood to the lungs is transported in the chloride shift.
    
  • The hemoglobin is going to be buffered by the globular portion of the hydrogen ion.
    
• 2.) CarbAmino Hemoglobin
  
  • CarbAmino Hemoglobin carries CO2 into the hemoglobin. It can carry CO2 on amino acids.
    
  • The CO2 can attach to an amine group and it creates an acid group out of it
    
    • This reaction is driven to the left and right by CO2 (depends on the amount of CO2 around). 
      
  • 20-30% of CO2 is transported as  CarbAmino Hemoglobin
    
  • If we put Hemoglobin in a high environment of CO2, the more the change of the shape that the hemoglobin will have, and it will lose it's affinity for O2 and will bind CO2 well. If we put Hemoglobin into an environment with high O2, the change of shape of the hemoglobin will lose affinity for CO2 and will bind O2 well.
    
• 7 to 10% of CO2 will be just dissolved/transported in the plasma. CO2 is much more soluble in fluids. 
  

   
   

The Brain Centers that Control Breathing:

Controlling the Muscles of Breathing:

• The Medulla has 2 Medulla Respiratory Centers in the Medulla Oblongata (we have 2 brain centers controlling respiration)
  
  • Dorsal Respiratory Group – this is an inspiration center only. This is controlling how you are breathing at rest. The Ramp Signal is coming from here.  All we are doing to exhale is we are relaxing. 
    
    • The brain has you inspire and then just stops – it does a Ramp Signal.
      
  • 2.) Ventral Respiratory Group – it is both an inspiratory and expiratory center. It is stimulating the heavier breathing that is going beyond normal breathing. It is forced inhalation and forced exhalation.
    
• The Pons also has 2 Pons Respiratory Center that affect the Ramp Signal – but both of these centers talk to the Dorsal Respiratory Center (only deal with inspiration):
  
  • Pneumotaxic Center – is sending continuous inhibitory impulses to this Dorsal respiratory group – this shortens the ramp signal, fires constantly, and it creates a short inspiration.
    
  • Apneustic Center – is sending continuous excitatory/stimulatory impulses to the dorsal respiratory group – this lengthens the ramp signal, this high firing rate will end up creating a prolonged inspiration.
    

 
 

We have higher areas of the Brain that control breathing

• Medullary Chemoreceptors – they regulate breathing under normal circumstances
  
• Under strange circumstances Medullary Chemoreceptors respond to the pH of the CSF (Cerebral spinal fluid))
  
• H+ ions cannot cross the blood brain barrier (so acidosis isn't a factor here), but CO2 can cross, and once the CO2 is in there it can drop the pH
  
• Hypercapnia – when we increase the CO2; that is when the pH receptors detect a drop in the pH in the CSF and they will increase both the depth and the rate of the respiration
  
• Hyperventillation – when you increase both the depth and the rate of respiration
  
• Hyperpnea – when you only increase the depth of respiration – it is the brain correcting/adjusting for any oxygen you are not getting (you are always doing this, you never think about it)
  
• Hypoventilation – when the pH rises in the CSF, we are going to shallow the breathing and slow the rate of breathing.  
  
• Apena – when breathing might stop for a while (it is stopping the breathing when you are exhaling)
  
• Apenusis – is the a prolonging the Ramp Signal for the inspiration (it is stopping the breathing when you are inhaling)
  

 
 

Aortic and Carotid Bodies – are chemical receptors that affect the breathing (recall these can affect the blood pressure)

• They measure the oxygen level of the blood.
  
• When the partial pressure of oxygen in the blood goes below about 60mmHg, the pH receptors are starved for oxygen and they do not work. Then the Carotid and Aortic bodies take over and continue you breathing (no matter what the pH of the CSF is)
  
• Suppose you go into a cave, and you go into a pocket of the cave that is very low in oxygen.  You are still getting rid of the CO2 fine b/c you are burning O2 you have stored, but you are not taking in the O2 that you need.  You don't know that, but your Carotid Bodies do and they take over your breathing.
  
• The Carotid Bodies can detect Atrial pH and during metabolic acidosis they can increase your respirations, even through your PO2 and PCO2 are normal.
  
• These Carotid and Aortic Bodies helps you blow off some of the CO2 – they help lower the pH of your body.
  

Proprioceptors – when you start to move your arms and your legs, or if you are standing at the start line of a 5K you are automatically going to increase the ventilation. The brain knows that we are going to need more oxygen so it increases our breathing. Psychology – starts to breath at a quicker pace if you know what you are about to do.  

Lung Receptors:

Irritant Receptors for Coughing and Bronchial Contriction

Stretch Receptor called a Hering-Breurk Reflex Receptor, which protects the Lungs from over inflation