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65 Cards in this Set

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What are the contents of alveolar fluid?
Water, surfactant
What is surfactant?
Complex mixture of phospholipids and lipoproteins that lowers the surface tension of alveolar fluid, reducing the tendency of alveoli to collapse
Besids type I and II alveolar cells, what other cells are present in alveoli?
Alveolar macrophages (dust cells)

Fibroblasts
How many alveoli are there estimated to be between the two lungs?
300 million
When put together, how large a surface area do the alveoli provide for gas exchange?
70 square meters, about the size of a racquetball court
What is different about the way pulmonary vessels respond to localized hypoxia compared to the way systemic vessels respond to localized hypoxia?
Pulmonary vessels constrict rather than dilate in response to local hypoxia so as to divert blood from poorly ventilated (hypoxic) areas to well ventilated regions
What is ventilation-perfusion coupling?
The constriction of pulmonary vessels in response to hypoxia so as to divert blood to better ventilate areas
What structures of the lung make up the respiratory zone (zone of gas exchange)?
Respiratory bronchioles, alveolar ducts, alveoli
What percentage of tidal volume actually makes it to the respiratory zone?
75% (350mL)
What is the anatomic dead space?
Those portions of the respiratory tract where gas exchange does not occur (conducting airways of nose, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles)
What is Dalton's Law?
Each gas in a mixture of gases exerts its own pressure as if no other gas was present.

The total pressure exerted by a gaseous mixture is the sum of the individual partial pressures exerted by each gas in the mixture.
What is Henry's Law?
Henry's Law states that the quantity of a gas that will dissolve in a liquid is proportional to the partial pressure of the gas above the liquid as well as the solubility of the gas in the liquid.

The higher the partial pressure of a gas over a liquid and the higher the solubility, the more gas will stay in solution.

Everyday example: gas bubbles emerging from a soft drink when the pressure above it is released.
Which has greater solubility: CO2 or O2?
Carbon dioxide has much greater solubility at the same pressure
Why does nitrogen not enter the bloodstream under normal conditions if 79% of the atmosphere is nitrogen?
Very low solubility in water
What is nitrogen narcosis and how is it explained by Henry's Law?
When divers breathe air under high pressure the high partial pressure of nitrogen is enough for some to dissolve into the bloodstream despite its low solubility in blood plasma

Excessive amounts of nitrogen may produce giddiness and other symptoms similar to alcohol intoxication

Nitrogen narcosis also called "rapture of the deep"
What is decompression sickness/the bends?
Symptoms of joint pain, dizziness, shortness of breath, extreme fatigue, paralysis and unconsciousness

Result of diver coming to surface too quickly

Nitrogen comes out of solution too quickly and forms gas bubbles in tissues, particularly nervous tissue
What is the respiratory membrane?
Tissue across which gas exchange occurs in the lungs

Alveolar wall (type I and type II cells)

Epithelial basement membrane

Capillary basement membrane

Capillary endothelium
What percentage of atmospheric air is nitrogen? Oxygen? Carbon dioxide?
Nitrogen: 78.6%

Oxygen: 21%

Carbon dioxide and other gases: less than 1%
Why does air reaching the alveoli have a lower percentage of oxygen than atmospheric air?
Air becomes humidified as it passes through the moist mucosal linings
What is the partial pressure of oxygen in deoxygenated blood?
40 mmHg
What is the partial pressure of oxygen in alveolar air?
105 mmHg
What is the partial pressure of oxygen in oxygenated blood as it leaves the alveolar capillaries?
105 mmHg
What is the partial pressure of oxygen in pulmonary veins and systemic arteries?
100 mmHg (blood that passed through alveolar capillaries had 105 mmHg but later mixed with blood that did not pass through areas of gas exchange, dropping it to 100)
What is the partial pressure of carbon dioxide in deoxygenated blood?
45 mmHg
What is the partial pressure of carbon dioxide in alveolar air?
40 mmHg
What is the partial pressure of carbon dioxide in oxygenated blood leaving the pulmonary capillaries?
40 mmHg
What is the partial pressure of oxygen in deoxygenated (venous) blood?
40 mmHg
What would be the partial pressures of oxygen and carbon dioxide in a normal arterial blood gas?
Oxygen: Around 100 mmHg

Carbon dioxide: Around 40 mmHg
What would be the partial pressures of oxygen and carbon dioxide in a normal venous blood gas?
Oxygen: Around 40 mmHg

Carbon dioxide: Around 45 mmHg
What are the partial pressures of oxygen and carbon dioxide at the tissue cells?
Oxygen: 40 mmHg

Carbon dioxide: 45 mmHg
Describe the structure of the hemoglobin molecule.
The hemoglobin molecule consists of 4 globin chains, each with a single heme group that can bind a single molecule of oxygen gas.

1) 4 globin polypeptide chains: 2 alpha chains and 2 non-alpha chains. The non-alpha chains determine which kind of hemoglobin it is (e.g. HbF has gamma non-alpha chains, HbA has beta non-alpha chains)

2) Each of the four polypeptide chains contains one heme group

3) Each heme group consists of an atom of iron surrounding by a porphyrin ring
What is a heme group?
A heme group is an atom of iron contained within a porphyrin ring.

Each of the 4 globin chains of hemoglobin contains a heme group.

Each heme group can bind 1 molecule of oxygen gas. Thus a single molecule of hemoglobin can bind 4 molecules of oxygen gas.
How many molecules of oxygen gas can bind to each hemoglobin molecule?
4
What is porphyrin?
Porphyrin is an organic molecule composed of 4 modified pyrrole subunits arranged into a larger ring.

In the body, porphyrin forms the backbone of heme, with an atom of iron in the middle of the ring.

In the catabolism of heme, iron is reused but the ring-like porphyrin is broken into a long chain becoming bilirubin.
What material reality accounts for the variable affinity of hemoglobin for oxygen?
The shape of hemoglobin changes between two opposite conformations.

In the taut (T) conformation, hemoglobin has low affinity for oxygen. This means that it binds oxygen LESS readily and releases oxygen MORE readily.

In the relaxed (R) conformation, hemoglobin has higher affinity for oxygen. This means that it binds oxygen MORE readily and releases oxygen LESS readily.

Factors such as the partial pressure of oxygen, partial pressure of carbon dioxide, pH, temperature, and presence of BPG can drive hemoglobin towards one conformation or the other, thus increasing or decreasing its affinity for oxygen.
What is the most important determinant of oxygen's affinity for hemoglobin and thus the % saturation of hemoglobin?
Numero uno, the most important, is the partial pressure of oxygen in the blood (oxygen tension), which essentially forces the binding of oxygen. The binding of oxygen promotes a conformational change towards the R conformation, increasing oxygen affinity.

This phenomenon of oxygen binding promoting further oxygen binding is known as cooperativity.
What is the Haldane effect?
The Haldane effect describes the reciprocal binding of carbon dioxide and oxygen to hemoglobin.

At the tissues, CO2 tension is high and CO2 binds to hemoglobin, driving the molecule towards its taut (T) configuration and thus facilitating oxygen release.

At the lungs, oxygen tension is high and oxygen binds to hemoglobin, driving the molecule towards its relaxed conformation and facilitating CO2 release.
What is the Bohr effect and how does it work on a molecular level?
The Bohr effect describes the reciprocal binding of oxygen and protons to hemoglobin, and thus the relationship between acidity and the oxygen affinity of hemoglobin.

At the tissues, an increase in acidity (drop in pH) enhances the unloading of oxygen from hemoglobin. Why? The binding of protons drives hemoglobin toward its taut (T) conformation, facilitating the release of oxygen. The release of oxygen, in turn, facilitates the binding of more protons, since deoxyhemoglobin is a stronger base than oxyhemoglobin.

At the lungs, the binding of oxygen to hemoglobin facilitates the release of protons. Oxygen affinity increases because of increased oxygen tension in the alveolar capillaries. Oxygenated hemoglobin is less basic than deoxyhemoglobin, so protons are released.
What effect does raising the body temperature have on oxygen affinity? Lowering the temperature?

Why does this occur?
Raising temperature reduces hemoglobin's affinity for oxygen and thus promotes the release of oxygen from hemoglobin.

Lowering temperature has the opposite effect, increasing oxygen affinity

These effects of temperature on hemoglobin's affinity for oxygen are phsyiologically useful. Metabolically active cells give off more heat. They also require more oxygen. Conversely, slow metabolic activity will have less heat, and less O2 will be released.
What metabolic pathway is BPG a product of?
Glycolysis
What is BPG?
2,3-bisphosphoglycerate, a side product of glycolysis
What effect does the binding of BPG have on hemoglobin's oxygen affinity?
Decreases oxygen affinity
On a graph representing an equation for the relationship between two variables, which axis is the independent variable and which axis is the dependent variable?
The x axis (horizontal) is the independent variable.

The y axis (vertical) is the dependant variable, "dependant" because it depends on the value of x.
Which two variables are displayed on the oxygen-hemoglobin dissociation curve?

Which variable is the independent variable?

Which variable is the dependent variable?
The oxygen-hemoglobin dissociation curve shows the relationship between the partial pressure of oxygen and the percent saturation of hemoglobin.

The partial pressure of oxygen is the independent variable and the percent saturation of hemoglobin is the dependent variable. This is because PO2 is the single most important factor determining how much O2 binds to hemoglobin.
On the oxygen-hemoglobin dissociation curve, which axis represents the P02 and which axis represents the % saturation of hemoglobin?
PO2 is the x axis (independent variable)

% saturation of hemoglobin is the y axis (dependent variable)
What is the normal PO2 in venous blood?


What is the % saturation of hemoglobin at this PO2?
40 mmHg

75%

This means that hemoglobin in venous blood is still about 75% saturated with oxygen.
Under stable conditions, what percentage of oxygen bound at the lungs is actually released at the tissues for use by cells?
About 25%

Think of it this way:

In arterial blood the PO2 is 100 mmHg and the % saturation of hemoglobin is 100%.

In venous blood the PO2 is 40mmHg and the % saturation of hemoglobin is 75%.

This means only 25% has been unloaded!
At what partial pressure of oxygen does the % saturation of hemoglobin approach 90%.
60 mmHg
At what partial pressure of oxygen does the % saturation of hemoglobin begin to nosedive?
40 mmHg

At this point curve becomes steep, and small drops in PO2 produce large drops in % saturation.
Sum up the shape of the oxygen-hemoglobin dissociation curve and the material reality that this shape represents.
The curve essentially has two portions, a steep portion between a PO2 of 0 mmHg and 40 mmHg, as well as a flat portion from a PO2 of 40 mmHg and up.

What this means is that changes in PO2 above 40 mmHg have relatively little effect on the % saturation of oxygen.

Changes in PO2 below 40 mmHg, on the other hand, result in large changes in % saturation of hemoglobin.
Under conditions in which hemoglobin has decreased affinity for oxygen, which direction would the oxygen-hemoglobin dissociation curve shift?
To the right (you need greater PO2 to achieve the same % saturation of hemoglobin)
Under conditions in which hemoglobin has increased affinity for oxygen, which direction would the oxygen-hemoglobin dissociation curve shift?
To the left (you need lower PO2 to achieve the same % saturation of hemoglobin)
What does a shift to the right in the oxygen-hemoglobin dissociation curve indicate?
This means that a greater PO2 is required to achieve the same % saturation of hemoglobin as under normal conditions.

It reflects a state of decreased hemoglobin affinity for oxygen (a shift towards the taut confirmation)
What does a shift to left in the oxygen-hemoglobin dissociation curve indicate?
This means that a lower PO2 is required to achieve the same % saturation of hemoglobin as under normal conditions.

It reflects a state of greater hemoglobin affinity for oxygen (a shift towards the relaxed confirmation)
What effect would a decrease in pH (increase in acidity) have on the oxygen-hemoglobin dissociation curve?

Why does this occur?
The curve would shift to the right, reflecting a decrease in hemoglobin's affinity for oxygen.

This occurs due to the reciprocal binding of H+ and oxygen to hemoglobin, a phenomenon known as the Bohr effect. As Hb picks up more H+, it releases O2 more readily.
What effect would an increase in PCO2 have on the oxygen-hemoglobin dissociation curve?

Why does this occur?
The curve would shift to the right reflecting hemoglobin's decreased affinity for oxygen.

This occurs due to the reciprocal binding of CO2 and O2 to hemoglobin, a phenomenon known as the Haldane effect.

The binding of CO2 facilitates the release of O2.
What effect does an increase in temperature have on the oxygen-hemoglobin dissociation curve?
Increased temperature shifts the curve to the right.

This is a dumb way of saying that increased temperature decreases hemoglobin's affinity for oxygen.

Thus more oxygen is released in warmer regions. This is physiologically useful because areas of higher metabolism are both warmer and have higher oxygen demand.
What effect does a decrease in temperature have on the oxygen-hemoglobin dissociation curve?
A decrease in temperature shifts the curve to the left, which is a fancy way of saying that decreasing temperatures cause oxygen's affinity for oxygen to increase.

Less oxygen is released in cooler areas. This is physiologically useful because cooler areas are less metabolically active and require less oxygen.
What is the proximate reason fetal hemoglobin has greater oxygen affinity than adult hemoglobin?

What is the ultimate reason fetal hemoglobin NEEDS greater oxygen affinity?
Fetal hemoglobin binds BPG less readily (BPG decreases oxygen affinity)

Maternal blood in the placenta has low oxygen saturation, so it's important for the fetal hemoglobin to rip off as much as possible
Describe what happens to carbon dioxide as it enters the bloodstream (i.e. what are the three pathways it follows in the blood):
In short: 1) 7% dissolved CO2, 2) 23% carbaminohemoglobin, 3) bicarbonate

1) Simply dissolves and travels through blood in dissolved form to the lungs where it diffuses into alveolar air. Only 7% of CO2 follows this pathway

2) Binds to proteins forming carbamino compounds. Mostly binds to hemoglobin forming carbaminohemoglobin. Through the Haldane effect, CO2 unloading is facilitated at the lungs and CO2 diffuses into the alveolar air. 23% of CO2 travels this way

3) Enters erythrocytes, forms carbonic acid (reaction catalyzed by carbonic anhydrase) which dissociates to form protons and bicarbonate. Bicarbonate diffuses down gradient out of erythrocyte into bloodstream where it travels to the lungs. At lungs converted back into CO2. About 70% of CO2 travels through the blood this way
Why does the reaction of water and carbon dioxide to yield carbonic acid proceed so readily within erythrocytes?
Due to the presence of relatively high amounts of the enzyme carbonic anhydrase.
What is the chloride shift and why does it occur?
At the tissues, some CO2 is converted to bicarbonate in the RBCs. Bicarbonate diffuses down its concentration gradient out of the RBC into the blood. To maintain electrical balance, negatively charged chloride ions enter the RBC to replace the negatively charged bicarb ions that diffuse out.
Describe the chemical conversion of CO2 to bicarbonate at the tissues:
CO2 + H2O (in presence of carbonic anhydrase) --> H2CO3 --> H+ + HCO3-
Describe the chemical conversion of bicarbonate back into CO2 at the lungs

Why does this reaction proceed?
HCO3- + H+ --> H2C03 --> H2O + CO2

Proceeds because hemoglobin releases its bound H+ at the tissues, giving the necessary fuel for the fire.
A patient has an arterial pO2 of 60 mmHg.

Assuming the oxyhemoglobin curve is not shifted, approximately what percentage of his hemoglobin will be saturated?
90%