Partial pressure of carbon dioxide decreases below normal value of 40 mmHg.
Partial pressure of oxygen increases above normal value of 100 mmHg.
Gas Exchange in Lungs (Pulmonary Circuit)
Deoxygenated blood comes from right side of heart through pulmonary arteries.
Partial pressure of oxygen = 40 mmHg.
Partial pressure of carbon dioxide = 46 mmHg.
Normal alveolar partial pressures:
Oxygen = 100 mmHg.
Carbon dioxide = 40 mmHg.
Oxygen diffuses from alveoli into blood.
Carbon dioxide diffuses from blood into alveoli.
Equilibrium in Pulmonary Capillaries
Diffusion across respiratory membrane reaches equilibrium quickly.
Blood leaving pulmonary capillaries has same partial pressures as alveolar air.
Oxygen = 100 mmHg.
Carbon dioxide = 40 mmHg.
Occurs due to thin respiratory membrane (about 0.25 seconds for equilibration).
Allows for faster blood flow (up to three times the blood flow rate) and still get full gas exchange.
Gas Exchange in Systemic Tissues
Gas exchange occurs between tissue cells and blood in systemic capillaries.
Direct movement is between capillary blood and interstitial fluid.
Oxygen moves from interstitial fluid into tissue cells.
Systemic arteries (oxygenated):
Partial pressure of oxygen = 100 mmHg.
Partial pressure of carbon dioxide = 40 mmHg.
Interstitial fluid surrounding capillaries:
Low oxygen (partial pressure = 40 mmHg).
Higher carbon dioxide due to metabolism.
Exact partial pressures depend on metabolic activity of tissue.
More active tissue:
Lower partial pressure of oxygen.
Higher partial pressure of carbon dioxide.
Faster rate of gas exchange.
Equilibrium in Systemic Capillaries
Gas exchange occurs until equilibrium is reached.
Oxygen moves into tissues, carbon dioxide moves into capillaries.
Blood leaving systemic capillaries (deoxygenated) has same partial pressures as tissues.
Partial pressure of oxygen = 40 mmHg.
Partial pressure of carbon dioxide = 46 mmHg.
Venous blood returns to right side of heart.
Blood in pulmonary arteries is mixed venous blood.
Going to lungs in the pulmonary circuit.
Transport of Oxygen and Carbon Dioxide in Blood
Because both gases have low solubility, need an efficient transport.
Oxygen: Only 1.5\% dissolved in plasma.
Rest is bound to hemoglobin(forms oxyhemoglobin).
Four oxygen molecules that can bind to hemoglobin.
Each hemoglobin protein consisting of four subunits.
Each of those globins has a heme group.
Each heme group can bind to one oxygen molecule.
Hemoglobin is 100\% saturated when all heme groups are binding to oxygen.
Binding is readily reversible (tight enough to pick up oxygen in lungs, loose enough to release it in tissues).
Reaction follows the law of mass action.
Hemoglobin and Oxygen
Binding and release of oxygen depends on partial pressure of oxygen in surrounding fluids.
In lungs (high partial pressure of oxygen), favors the formation of more oxyhemoglobin.
In tissues (low partial pressure of oxygen), favors the release of oxygen from hemoglobin.
In pulmonary capillaries, high partial pressure of oxygen leads to the formation of oxyhemoglobin in erythrocytes.
In systemic capillaries, the low partial pressure of oxygen in the tissues leads hemoglobin to dissociate from oxygen.
Hemoglobin Oxygen Dissociation Curve
At rest, arterial partial pressure of oxygen is about 100 mmHg.
Hemoglobin is about 98.5\% saturated.
At 40 mmHg (systemic veins), hemoglobin is around 75\% saturated.
At rest, only about 25\% of oxygen is diffusing and taken up by tissues.
Body has a very large reserve of oxygen.
Decrease in affinity:
Causes the curve to shift right.
Takes a higher partial pressure of oxygen to achieve a certain level of hemoglobin saturation.
Oxygen becomes unloaded from hemoglobin more easily.
Increase in affinity:
Causes the curve to shift left.
A lower partial pressure of oxygen is required to saturation.
Oxygen is loaded more easily onto hemoglobin.
Factors that Influence Hemoglobin's Affinity for Oxygen
Temperature, pH, and partial pressure of carbon dioxide work together to promote oxygen unloading in active tissues and loading in the lungs.
All these factors increase in active tissues.
Temperature drops as blood travels to lungs, increasing affinity of hemoglobin to oxygen.
In active tissue, temperature increases and that increased in temperature shifts the curve to the right.
The Bohr effect: The effect of pH on the hemoglobin oxygen dissociation curve. Amino acids release hydrogen ions from the hemoglobin protein.
HbO2 \leftrightharpoons Hb + O2 + H^+
Increased hydrogen ion concentration (lower pH) decreases affinity of hemoglobin for oxygen.
The carbamino effect: Carbon dioxide binds to amino acids in hemoglobin, forming carbamino hemoglobin.
Decreases hemoglobin's affinity for oxygen.
Increased carbon dioxide in active tissue promotes oxygen unloading.
Carbon monoxide prevents oxygen binding to hemoglobin.
Decreases oxygen carrying capacity of blood.
Pulse Oximeters
Use differences in red and infrared light absorption by oxyhemoglobin and deoxyhemoglobin to determine O_2 saturation.
Normal resting level is 95-100\%. Useful for assessing lung function in clinical settings.
Can be used to assess levels before or after surgery, or during anesthesia. Useful in monitoring patients that might reduce lung function, sleep disorders, asthma, etc.
Transport of Carbon Dioxide in Blood
Three ways:
Dissolved in plasma (higher solubility with carbon dioxide than oxygen).
Bound to hemoglobin (carbamino hemoglobin).
As bicarbonate ions (majority).
Bicarbonate ions are produced in erythrocytes, then move into plasma.
Erythrocytes have carbonic anhydrase.
CO2 + H2O \leftrightharpoons H2CO3 \leftrightharpoons H^+ + HCO_3^-
Law of mass action says an increase in the concentration of carbon dioxide will drive the reaction right, and a decrease will move left.
In biological systems, carbon dioxide is considered an acid because it produces hydrogen ions.
Bicarbonate acts as buffers to control blood pH.
Carbon Dioxide Exchange
Carbon dioxide moves down its pressure gradient, moving from the respiring tissues into the capillary blood.
Gas diffuses into the interstitial fluid and into the plasma, before going into the erythrocytes.
Some stays dissolved in plasma. Once in erythrocyte, some directly binds to hemoglobin, the rest combines with water from the carbonic acid via the carbonic anhydrase.
This equation has an effect on the partial pressure. Because carbonic anhydrase converts to carbonic acid, the reaction helps maintain pressure gradient.
The erythrocytes undergo a chloride shift. Bicarbonate is transported out of the erythrocyte with the transport of the chloride into the erythrocyte in order to equalize across the erythrocyte.
Majority will be transported in the blood as bicarbonate, and most of them move into the plasma.
Summary of Transport
Cells of our tissues diffuse carbon dioxide out into the blood.
Small portion stays dissolved in plasma, the rest moves into red blood cells.
In red blood cells, some binds to hemoglobin, becoming carbaminohemoglobin, and some converts into bicarbonate ions.
The bicarbonate causes hydrogen ions to also come off.
In order to reduce the concentration of hydrogen ions, they bind to hemoglobin.
Bi-arbonate ions are transported to the plasma (some will stay in the erythrocites).
The chloride shift maintains negative balance.
Alveoli Transport
In pulmonary capillaries, carbon dioxide diffuses into the alveoli, where it will be exhaled.
The loss of carbon dioxide will result in different processes.
The bicarbonate that was produced by the presence of carbonic anhydrase is produced from hydrogen ions and bicarbonate ions, and results in more carbon dioxide.
As the reaction proceeds, there will be less bicarbonate in the cell, which will form the process called, reverse chloride shift.
The overall is carbonic anhydrase allowing the process to proceed right in systemic vessels, in the alveoli, carbonic anhydrase allows the process to move left.
Control of Ventilation.
Body regulates minute alveolar ventilation to do so.
This is the volume of the volume of air in the Alveoli.
Doing so by regulating frequency and volume of breaths, as well as regulation of partial pressures of oxygen and carbon pressure.
The spinal cord creates the movement and control of the muscles with involuntary and voluntary regulation.
Inspiration = Active process, and Exhaling = Passive Process.
The respiratiory muscles are skeletal muscles with somatic motor neurons to signal these muscles.
Phrenic nerve innervates the diaphragm and the external intercostal nerve control the external intercostal muscles. With active breathing, the internal intercostal nerve stimulates the internal intercostal messages.
Respiratory control regions are in the brainstem, and has 2 major classes.
Inspiratory neurons, and expiratory neurons.
The ventral respiratory groups and the dorsal respiratory groups.
Central pattern Generator (CPG) is what creates a repeating pattern. A theory as to how this central pattern generator actually functions. Either exhibits pacemaker activity or involves interaction between neural networks. It is a network of neurons that's in the medulla that's generating a regular and repeating pattern of neural activity.
Pontine respiratory group in the pons. This area of the brain stem appears to receive information from higher brain centers and then issues output to the ventral and dorsal respiratory groups to address breathing to different situations like sleep or exercise or different vocalizations or emotional responses.
The central pattern generator stimulates the inspiratory neurons to make inspiration. Action potential increase with with breaths.
A large number of additional sources also affect, the process. Cerebellum Hypothalamus, chemoreceptors etc, are all involved.
There are pulmonary stretch receptors in muscles of airways, that are preventing over inflation. Irritant receptors line the respiratory tract, and are reactive to inhaled particles.
Cough and sneezing can also occur. Proprioceptors also have Input to CPG.
Proprioceptors can stimulate increase of ventilation, blood pressure affects, respiration as well.
Chemoreceptors
Detect changes in chemical concentrations in the blood.
Arteries monitor pH, pressure of oxygen, partial pressure of carbon dioxide.
Signals are sent to the rate and depth of breathing.
Increases ventilation and maintains arterial pressures.
The primary response comes from Arterial Blood Changes to Carbon Dioxide.
Peripheral chemoreceptors are located in the carotid bodies, and have direct blood contact.
Peripheral chemoreceptors mainly respond to arterial pH. (Indirect Carbon Dioxide).
Decreased Oxygen Levels. 60 mmHg and only become sensitive when oxygen is pretty low - Peripheral are not the primary trigger.
Central Chemoreceptors - Are on the medulla oblongata, and repond to the centralspinal fluid (CSF) and central nervous activity.
A slow response to activate ventilation.
Diagram Breakdowns.
Hydrogen ions can not pass thru - Carbon Dioxide has to pass and then hydrogen ions get formed. These hydrogens are what activate receptors
Increased Activation of of chemoreceptors lead to increased ventalation
Diagram of the Chemoreceptor Reflex
Peripheral chemoreceptors respond to severe decrease in the partial pressure, direct partial pressure, and increased H+ ions.
Central chemoreceptors respond to hydrogen concentrations.
Increasing ventilation and controlling CO2 levels control pH Balance levels (This will be really emphasized).
Hypoventilation
Hypoventilation when there is less than it needs to be.
There is decreased PCO2, and increased PP of carbon dioxide.
The chemoreceptors detect and trigger these rates.
Hyperventilation.
Aveolar Ventialtion is great than needed. Decreased Co2 is detected and the system adjust.
With the oxygen reserves, the rates won't change as quickly.
The ratio of 20 parts carb, and 1 is carbon dioxide level.
Ventilation Perfusion ratios
Ventilation = Rate of Air Flowing to the alveoli
Perfusion = Rate of Blood Flow of Alveoli
The cardiovasualr, and respectory goal is for this to = to 1
Notation = Ventilation, .V, and Q. for Perfusion rates of O2, and CO2 is at its normal values (100 vrs 40/40 vrs 40)
Matching Controls
Changing PP of o2/co2, can contract smmoth muscle actity in puymary arteroles/bronchioles. This adjusts ventilation by changing smooth muscle contraility to get the rato back to 1 to 1.
Oxygen acts Primarly. Its main effect is onarteriolar smooth muscle, where partial press causing vasoconstriciting and therefore reducing the rate of blood low.
Hi Partial pressures, do vasodilation
Carbon Dioxide acts primarily. Its main effect is the muscls cells of Bronchioles
Bronchodilation from high, ventilation increase.
Local Controls/Hypo and Hyper situations - Both Vasocnstrictting and brocholidation decrease perfusion, and causes brochoialdlation (High o2, Lo CO2)
Pulmonary system = Always matachung perfusion to ventilation (the goal)
Systemic= Ensuring that tissue that is the most active is going to get the most blood (diversfied)
Homeostasis Check for ventilation
With high ventilation, and Low perusion, that means ventiation is exceeing perfusion. As a reult ventilation must be decreaed and, blood flow must be increase towardds 1 to 1 balance. Vasodiation by O2 increase will cause perfusion. decrease CO2 increase will lower the rates. and the balance is achived.
Lungs
Lungs re able to accomodate 6 foold cardiac output, due to respiratory reserve mechanisms (two important)
The recruitment of reserve capillaries - at rest the CO onlty fills 30%.
The seonnd way is the the respiration Reserve Mechanism. It is able to accimodate for full gas exchange.
The Acid Basce Balance of the Lungs
The primary regulation is pH, the rest is oxygen and carbon dioxide.
Changing any pH willl affect nearly every cell. (Proteins)
Changing he functions of the proteins results in severe issues and potentialy death.
The Mainting Factors
The mainting is at 7.4 is Blood.
The range is - Between (7.35-7.45)
7.35 is acidosis - Central D Nervous system are depression. This can cuase coma and respiratory failure
Increasing above that , to Alkalosis is excitable is nervous. This can cuase muscle Seizures can cuase spasimc resp muscles.
Bicarbonate is a mjor body buffer. Increase h + 1 forms will combine carbondixode
Hemoglobin and Bicarbonate
Increase O2, in lung, the hydroggen is mostly cleared. Maintain blood pH. the maintain range is -20 /1 where, for every 20 the will be one carbon dioxide.