Gas Exchange And Transport Flashcards
Hypoxia
Low levels of oxygen in the body
Hypercapnia
High levels of carbon dioxide in the body. Symptoms include decline in CNS function, confusion, coma, or death
Acidosis
When CO2 levels increase pH drops leading to acidosis
Gases require a
Pressure gradient in order to diffuse from one area to another. When the gradient reaches equilibrium diffusion stops.
When talking about gases we mean they’re partial pressure
Not the concentration.
*Example partial pressure of alveolar air is 100 mg of mercury, partial pressure of venous blood is 40 mg of mercury period is so oxygen diffuses from air into blood until the P02 of blood reaches 100 MMHG equilibrium
Some potential problems with this system (gas exchange) involve 
-  Low partial pressure of oxygen in the alveoli: mostly associated with high altitudes
- Inadequate ventilation: relates to lung compliance, increased resistance, or just cessation of breathing
- Other considerations are the rate of diffusion and solubility of the gases
As atmospheric pressure decreases
 partial pressure of oxygen decreases, so change in pressure decreases, meaning less oxygen is available to be moved into blood.
Diffusion rate will affect
How much gas is able to move into blood
*example if partial pressure of oxygen is normal, if it has trouble diffusing into plasma then it’s a problem
Ficks law of diffusion rate
Diffusion rate =
(surface area x pressure gradient x permeability) / distance2

Normally all of these are constant except pressure gradient
However in some pathologies diffusion rate may be influenced by
- Surface area may decrease
example emphysema destroys alveolar cells decreasing surface area - Permeability may decrease example fibrotic diseases thicken the membrane decreasing Permeability
- Diffusion distance may increase example: excess alveolar fluid such as pulmonary Edema caused by a decrease in left ventricular function or mitral valve disorders affect normal capillary pulmonary filtration/absorption rates that increase interstitial fluid and increase diffusion distance
Solubility of gases will influence (ability to dissolve into a fluid namely plasma here)
How much moves from air into plasma. The amount varies with pressure gradient, the gases solubility which is constant and temperature which in mammals is also relatively constant
Oxygen is not very soluble into
Fluids
🤔example at equilibrium partial pressure of oxygen is 100 mg of mercury, air contains 5.2 mm of oxygen per liter, but water contains only 0.15 mmol of oxygen per liter.
Because oxygen is hard to dissolve it necessitates
A helper to get into the blood in order to be transported a.k.a. hemoglobin
CO2 is 20 times more soluble then
Oxygen, for comparison equalliberated partial pressure of CO2 100 mg of mercury call my air contains 5.2 million moles of carbon dioxide per liter but water contains 3.0 mill the moles per liter of CO2. So CO2 dissolves much easier into plasma therefore no need for a transport molecule.
Mass delivery of oxygen depends on
Concentration of oxygen in blood and the flow rate (Q) of blood
So if blood contains 200 mL of oxygen per liter and flow rate is 5 L per minute
1000 mL of oxygen is available for use by tissues every minute
Using the concept of mass balance one in, one out we can calculate the amount of oxygen that is used by the tissue simply by
Subtracting the venous oxygen concentration from the arterial oxygen concentration
(O2 consumption = [O2]arterial - [O2]venous)
Ficks equation
If arterial and venous oxygen concentration is known, can be used to estimate cardiac output or oxygen consumption rate QO2 that is used all the time and physiological experience and medical diagnosis: QO2 = CO x ([O2]arterial - [O2]Venus)
Because if it low solubility only
2% of oxygen is transported as being dissolved in the plasma. 98% of it is transported by being loosely and reversed of bully bound to hemoglobin. The binding is strong enough to coax oxygen into the blood but loose enough to let it go at the tissues (compared to carbon monoxide which is very tightly founded to hemoglobin and does not let go which is why it’s so deadly)
Oxyhemoglobin
Hb+O2 HbO2
Each hemoglobin molecule contains
Four Heme groups that can bind up to four oxygen molecules
The binding and disassociation follows the law of mass action
increase oxygen causes increase oxyhemoglobin
And vice versa
This is convenient because when oxygen is high in the lungs it forms a lot of oxyhemoglobin for transport and where oxygen is low in the tissues where we need oxygen to be delivered it disassociate and lets the oxygen unbind
The total amount of oxygen in the body as oxyhemoglobin
Is actually higher than what is needed at the tissues allowing for a reserve for increased activity
Partial pressure of oxygen determines the
Percentage of hemoglobin that is bound to oxygen. termed the percent saturation of hemoglobin.
Percent saturation of hemoglobin mathematically
(Amount of bound oxygen/amount of potential binding sites) x100
So if all of the binding sites have oxygen down to them
The hemoglobin saturation is 100%
OXY hemoglobin saturation curve a.k.a. disassociation curves
Plot the percent saturation against partial pressure of oxygen to show the characteristics of how oxygen binds and unbinds at varying levels of oxygen, physiology relevant because partial pressure of oxygen changes and thus oxygen is picked up/delivered between the lungs and tissue
Saturation curves are created in a lab
By exposing a blood sample to a particular partial pressure of oxygen of air in a close test tube allowing it to equilibrium than measuring how much of the oxygen binds to the hemoglobin. The curve typically follows an S shape sigmoidal curve and reveals some interesting stuff
What are three things that the oxyhemoglobin saturation curve reveal
- Alveolar partial pressure oxygen usually around 100 mg of mercury so the hemoglobin saturation is nearly 100%
- High partial pressure of oxygen, though the saturation does not change much so not much oxygen can be delivered at this range so most stay bound to hemoglobin
- The largest change in saturation a.k.a. delivery of oxygen occurs at the partial pressure between 20 and 40 mg of mercury conveniently this is the range that cells in the tissue are usually at so a lot of oxygen is picked up in the alveoli and then is able to be released at the tissue
The saturation curves change with
Temperature, pH, and CO2 levels (the binding properties of hemoglobin change and lowers the ability of it to carry oxygen)
The curve shifts to the right as
Temperature and carbon dioxide increase, or pH decreases
The largest affect is on the saturation curve is
 steep part of the curve, so as these physiologically important factors change the amount of oxygen being delivered also changes to help undo any adverse effects (example of low pH or high CO2)
As the Cell runs out of oxygen they switch to
Glycolysis anaerobic metabolism, which increases hydrogen and decreases pH. This causes a shift to the right in the saturation curve more oxygen is released at the tissues the cells are able to switch back to aerobic metabolism. This particular shift is due to pH termed the Bohr effect
Saturation curves change Increasing temperature and carbon dioxide both which are influenced by activity/exercise
Increase exercise > increase in carbon dioxide > a decrease in Oxyhemoglobin saturation > an increase in oxygen delivery
Another influence on saturation (curve) is
With the release of 2,3 - BPG (bisphosphoglycerate) which is a byproduct of glycolysis, but also is released in response to anemia or high altitude. 2,3 -BPG shifts the saturation curve to the right lowering the infinity hemoglobin to oxygen
Fetal hemoglobin shows a higher affinity for
Oxygen which shifts the curve to the left. Which is adaptive considering placental blood has a lower oxygen concentration. This is due to the hemoglobin beta subunits being replaced by gamma subunits which does not interact well with 2,3-BPG. At birth the newborn begins making blood with the beta subunits 
What are the three ways that the transport of carbon dioxide occurs
- Conversion of HC03 bicarbonate 75%
- Bound to hemoglobin ~23%
- Dissolve in plasma ~2%
Note that the first to take place in the red blood cells
Conversion of carbon dioxide to bicarbonate is a reaction that occurs through
Mass action increasing levels of the reaction or products were driving reaction in the opposite direction. Their reaction takes place in the erythrocytes and uses the enzyme carbonic anhydrase.
CO2+H2O HCO3- + H+
As carbon dioxide dissolves into blood enters the
Erythrocyte driving the formation of bicarbonate but in order for the reactions to keep going bicarbonate must leave the cell. This occurs the action of an anti-porter which transports chloride in and simultaneously transfers bicarbonate out into the plasma termed the chloride shift
In the plasma bicarbonate acts as a 
Very important buffer preventing changes in blood pH (recall blood pH must be maintained within a very narrow limit 7.35 to 7.45 in order to function properly) 
Meanwhile the hydrogen formed in the reaction
Binds to the hemoglobin to form HbH, preventing lowering pH in the cell, if CO2 levels exceed the ability to bind all the hydrogen it can lead to respiratory acidosis
Some CO2 diffuses into the erythrocytes and binds to Amino groups on hemoglobin for me
Carbaminohemoglobin a reversible process since this binding takes place away from the heme groups it does not affect the ability of hemoglobin to bind it with oxygen at the same time
Even though carbon dioxide has a higher affinity then oxygen the amount that is able to dissolve into the plasma
Isn’t high enough to transport enough away requiring other mechanisms. Once blood reaches the alveoli the processes simply reverse as pressure of CO2 is lower and mass action drives its removal: bicarbonate is transported back into the cell through chloride shift and converted back to CO2 by carbonic anhydrase, carbaminohemoglobin disassociate; CO2 diffuses in to alveolar air down its pressure gradient
Regulation of ventilation is complex that relies on stimulation of respiratory skeleton muscles which is considered normally voluntary so it is believed that breathing patterns are controlled by
The CNS through a central pattern generator model. In this model, pacemaker neurons in a medulla oblongata and ponds set the basic rhythm with input from chemo receptors and higher brain centers. This info comes from patience with brain damage love animals and beheadings
Historically regions of the medulla/pons were considered different respiratory groups but
It appears that they control is more of a network than a distinct group with unique functions
The current Respiratory model
- Respiratory neurons in the medulla control muscles involved with inspiration and expiration
- pontine neurons integrate sensory information to modulate medullary controls.
- Rhythmic patterns originate from a network of spontaneously firing neurons in the brain stem
- Breathing is modulated by input from chemo receptors and Mechanoreceptor reflexes and higher brain centers
Important regions in the brain
- Respiratory Neurons formally known as centers in the medulla located in the dorsal respiratory group DRG control inspiration through glossopharyngeal(cnix), Vagus (cnx), and phrenic nerves.
- Pontine respiratory groups coordinate smooth initiation and termination of breathing
- Ventral respiratory groups VRG in the mid to that has different functions including pacemaker patterns of breathing, active expiration and inspiration example controlling larger breaths during exercise. Control the pharynx, larynx, and the tongue the latter being partly responsible for sleep apnea. 
The chemical composition of plasma and CSF
CO2, O2, ph influence respiratory rates in order to maintain homeostasis. Of these CO2 has the largest influenced
Chemo receptors are located peripherally and centrally
- Peripheral chemo receptors: are located in the carotid bones near the barrow receptors that help monitor blood pressure. Their glomus cells monitor plasma for low O2 and pH and high CO2 levels.
Peripheral chemo receptors have to have oxygen levels that are really low
Before the cells are stimulated less than 60 mmHg (which is the equivalent of being at 3000 m above sea level, Lake Tahoe is 1900 m, mount Everest is about 9000 m.)
*High CO2 levels and low pH in the plasma are the main triggers that will increase ventilation rate. The mechanism isn’t well understood it may involve the polarizing cells that alter sensitivity and increase the release of neurotransmitters to stimulate ventilation
Central chemo receptors
Are located in the medulla, adjacent to respiratory Control and Neurons centers. They mainly Cue on increased CO2 in CSF, but in an indirect way: increased CO2 causes increased formation of bicarbonate and hydrogen which causes increase in hydrogen that stimulates ventilation. however, hydrogen does not cross the blood brain barrier where CO2 can, so it’s the hydrogen formed by the CO2 that seems to initiate the response
Central chemoreceptor response
The response is strong at first but will adapt to increase CO2 by producing more bicarbonate buffer to handle the increase hydrogen.
Because of this oxygen which normally plays a small role in signaling an increase in breathing can start to play a larger role in the signal process.
*People with COPD may adapt to increase CO2 relying on decrease in oxygen is the primary signal to start breathing faster. If they are administered too much oxygen the signal is satisfied and they just stopped breathing
Because CO2 is the primary signal that initiates the urge to breathe
You can trick your body by hyper ventilating to blow off CO2 which allows holding your breath longer. Skin divers often do this and stay underwater longer however it’s dangerous his oxygen levels can drop to very low level before the urge to breathe kicks in online you just pass out and start breathing again underwater a pass out and die
