Lecture 27

Buffering Systems, cont.

 

1. The Ammonia System: (NH3 = ammonia)(NH4+ = ammonium)
   

• We said that the bicarbonate is made in the liver, but since Amine groups have to be removed, and they form Ammonia which is toxic
  
• Amine groups must be removed.  The Amine groups get turned into Urea and Glutamate.  When we took that Glutamate it was broken down into 2 bicarbonates and 2 ammoniums (NH4+).
  
• NH4+ is a charged molecule and cannot cross the apical membrane b/c it has a positive charge
  
• However there is an Antiport of Na+ in and NH4+ out (we don't find many of these transports), but then we found them in the Proximal Tubule of the apical membrane
  
  • This is not the major way that the NH4+ gets out.
    
• If we have a low pH we have NH4+, and at a high pH we have NH3.
  
• The pK of this system is approximately 9.2 (so it is 50:50 there – the point of inflection). When we go up towards the ammonium it is closer to 7.0 but there is a small amount of ammonia being made, but most of it is ammonium (5% of ammonia still existing at this 7 pK)
  
  • So there is a small amount of this going to a H ion and an NH3.
    
• The Hydrogen ion can then be picked up by stuff in lumen.  But we now have to get rid of the NH3, and NH3 can cross the membrane. 
  
• NH3 has a concentration gradient to cross the apical membrane and leave the cell out into lumen which is at a much lower pH of 7 and instantly transforms to ammonium (NH4+), and it picks up a H ion and buffers that (the ammonium can't go back in b/c the pH is too low and the NH4+ would have to go against its concentration gradient to get back in)
  
• When we get to the Thin Descending Loop of Henle, we are losing all of the H2O quickly and we get a high concentration of H ions so the pH drops here so we get all NH4+ ammonium here
  
• In the Thin Ascending Loop of Henle in the apical membrane there is a 1 Na+, 1 K+ and 2 Cl- Cotransport going into the cell.
  
• The K+ can be replaced by the NH4+ and we will get Ammonium going into the medulla of the kidney.  We can have bicarbonate going out, but the bicarbonate goes to the interstitium.   The NH4+ is going to create more NH3, and this H+ ion is going to be neutralized by bicarbonate here.   This will go up to the Collecting Duct and as soon as it gets in there it changes to NH4+ and it neutralizes the urine (the urine is running between 5 and 6 in pH)
  
• This has buffered the urine because it is very acidic inside the collecting duct. A H+ ion is left behind but the bicarbonate picks it up – this allows us to get rid of more H+ ions.
  

   
   

   
   

  Lungs:
  

   
   

  Respiration: is the exchange of carbon dioxide for oxygen.
  

   
   

  • There is an External and Internal respiration.
    
    • External Respiration – is what we normally think of as respiration – it is the exchange of CO2 with O2 in the lungs.
      
    • Internal Respiration – is the exchange of O2 between the blood and tissues
      

       
       

Lung Volume	Abbrv.	Male	Female
Tidal Volume (TV) – amount normally breathing when strictly at rest.	TV	0.5L	0.5L
Inspiratory Reserve Volume (IRV) – take from what you inspire at end of tidal volume and move up and take maximum inhale.	IRV	3.3L	1.9L
Expiratory Reserve Volume (ERV) – push all the volume that you can out.	ERV	1L	0.7L
Vital Capacity (VC) = TV + IRV + ERV	VC	4.8L	3.1L
Residual Volume – remaining air after exhaling as much as you can.	RV	1.2L	1.1L
Total Lung Capacity (TLC) = VC + RV	TLC	6L	4.2L
Functional Residual Capacity (Useful) – Residual Volume + Exspiratory Reserve Volume	FRC	2.2L	1.8L
Inspiratory Capacity – IRV + TV	IC	3.8L	2.4L

 
 

 
 

 
 

Screen clipping taken: 3/30/2009, 12:19 PM

 
 

 
 

• Total Lung Capacity (TLC) – if we add the VC and the RV
  
• Functional Residual Capacity (FRC) – it is a combination of RV plus the Expiratory Reserve Volume (ERV); this is how much air that remains in your lungs at this time when you are inhaling and exhaling
  
• Inspiratory Capacity – it is the IRV plus the TV
  
  • Capacity  means multiple volumes (it is an indication that we are adding multiple volumes up)
    
• Lung volume switches from 2.0 to 2.5L and goes back and forth. This is pretty stable. Only replacing a small portion of the air with each breath. This allows the partial pressures of the gasses in the alvoli to be stated.
  
• Can measure the partial pressure of the alveoli when breathing TV.
  

   
   

  The lungs are held very firmly against the thoracic cavity and the diaphragm. Part of this has to do with Surface Tension (from the fluid) and part is due to Air Pressure.
  

• Surface Tension – lungs have movement so they will stick to the wall because the interthroacic space is filled with fluid.
  
• The visceral pleura lines the lungs, and the parietal pleura lines the thoracic cavity, and there is fluid here, and the surface tension is going to stick the lungs to the fluid
  
• Air Pressure holds the lungs in place b/c the pressure of the Intraplureal space is lower than atmospheric:
  
  • During exhalation its 2.5mm Hg less than atmospheric
    
  • During inhalation 6mmHg less than atmospheric - atmospheric air pushing lung against the wall
    
• There outward forces on the lungs are balanced by the Elasticity of the lungs
  
• The Lung is elastic – elasticity is not it's stretchiness rather it is how compliant it is/ the pull inward to return to its original shape after if its been stretched.  There are balanced forces.
  
• We have surface tension trying to collapse the lungs, but that is in the Alveolar Fluid. 
  
• If chest wall is breached lung will collapse
  
• If we lose elasticity of lung we will become Barrel Chested
  

   
   

  Breathing: Normal Quiet Breathing (at rest) – there are 12-15 respirations per minute at rest
  

• Quiet Inhalation is initiated firstly by the Diaphragm (which flattens and moves downward), and then by the Parasternal Intercostals (those intercostals, both external and internal, that are close to the sternum) and the Scalenes (which will elevate the rib cage and it will thrust the sternum forward). 
  
• Lungs stick to the thoracic wall and their volume increases.  This follows Boyle's law – the interpulmonary pressure (in the lung itself) drops to 2 mmHg below atmospheric pressure, and gas will flow in until equalization occurs. 
  
• Quiet Exhalation occurs when these contracted muscles are now relaxed, and normal elastic forces in the walls of the lungs return it to its original volume. Now the Interpulmonary pressure rises to 2mmHg above atmospheric – air exhales until it releases atmospheric again, and gas flows out of the lungs until it equalizes
  
• Electrical Impulses of Breathing – the impulse builds and then stops. It last for two seconds and then stops for three seconds and then repeats. Since it builds quickly and then repeats it is called the Ramp Signal.
  
• Electrical impulses that are sent to the muscles of Quiet Respiration will build quickly for about 2 seconds
  
• This is called a Ramp Signal – the increases in the electrical impulses are going to those muscles.  So over a period of 2 seconds the stimulation of those muscles increases quickly and then suddenly it stops completely for a period of approximately 3 seconds, which is called the Exhalation period (the muscles will relax b/c they are not be stimulated).
  
• Normal quiet breathing controlled by the steepness of this ramp and how high it goes before it gets cut off
  

   
   

• Forced Breathing (it is what you do when you are running in Track and Field) brings in many other muscles
  

  DON'T NEED TO KNOW THESE MUSCLES
  

  Forced inhalation: 3 muscle from before, sternocledomastoid, and the anterior serata
  

  Forced exhalation: oblique and transverse abdominals, internal intercostals, latisimus dorsi, the quadrates lumborum, and transverse thoracies)
  

• Know the muscles of Quiet Breathing (the 3 from above) KNOW THEM
  

  Inhaling – there is a certain amount of air that never reaches the alveoli during inhalation (it is not exchanging oxygen with anything) – this is Dead Air Space.
  

• If you increased your Dead Air Space – snorkeling is ok because you have not increased your dead air space to the point where you are not getting any air, if you have a pipe that is too long then you will keep exchanging the same air which will be carbon dioxide and you will die.
  
• The Dead Air Space in your body is the: Trachea, Nasal passages, Pharynx, Bronchi, and Bronchioles (the parts of the respiratory tract that don't have alveoli).  These all fill with air but there is no exchange until you get to Respiratory Bronchioles.
  
• If you want to see how much air is getting to the alveoli (Ventilation) you have to subtract the Dead Air Space. This is done by determining you ideal weight in pounds and then you change the pounds to milliliters, and then you subtract that volume from whatever volume you are trying to calculate.
  

  Ventilation will equal Tidal Volume (TV) – dead space – the amount of Ventilation will vary from lobe to lobe in the lungs. The variation of the ventilation in the alveoli is due to:
  

  For Inhalation: the greater movement of the diaphragm compared to the thoracic cavity. 
  

• The diaphragm will move a great distance upon inhalation
  
• The thoracic cavity with the ribs will not move that much upon inhalation.
  
• This causing a pulling down of the lower lungs, meaning that the lower lobes of the lungs are going to expand farther.
  
• Most of the air will stay in the lower lobe with the expansion.
  
  • The alveoli in the lower lobe will have a greater expansion with the inhalation.
    
• If we just breathe with our diaphragm we are breathing about 3L (this is 3L of a possible 4.8L) – most of the Vital Capacity is coming from ventilation. We know this because quadriplegics can only breathe with their diaphragm, because they cannot send electrical impulses to any of their other muscles responsible for normal breathing.
  
• The alveoli in the lower lobe will have a greater expansion with inhalation.
  

  For Exhalation: the intrapulmonary fluid in gravity pulls the fluid down when standing erect.
  

• Up higher=greater negative pressure = -7.4mmHg. Down lower = -1.8mmHg. When the lower lobes contract b/c everything is collapsing in for exhalation, the pressure that builds up in this is going to be much higher in the lower lobes than the upper lobes.  The lower lobes will contract more than the upper lobes b/c of the increased pressure that they are put under.  Therefore the lower lobes have great ventilation then the upper lobes (the lower lobes expand and contract more)