The Ventilation - Perfusion relationship & gas transport Flashcards

Question

How does the Bohr effect influence the oxyhemoglobin dissociation curve?

Answer 1

The Bohr effect describes how increased levels of carbon dioxide (CO₂) and lower pH (acidosis) reduce hemoglobin's affinity for oxygen, causing it to release oxygen more readily. This shifts the oxyhemoglobin dissociation curve to the right, enhancing oxygen unloading in tissues with higher metabolic activity (where CO₂ is produced, and pH drops).

Answer 2

Increased temperature (e.g., during exercise or fever) also shifts the oxyhemoglobin dissociation curve to the right, meaning that hemoglobin's affinity for oxygen is decreased. This facilitates oxygen unloading in metabolically active tissues, where the temperature is higher and oxygen demand is greater.

Answer 3

The sigmoidal shape of the oxyhemoglobin dissociation curve provides a balance between efficient oxygen loading in the lungs and efficient oxygen unloading in the tissues. The curve's steepness ensures that even small changes in PaO₂ in the tissues result in significant oxygen release, while the plateau in the lungs ensures nearly full oxygen saturation at high PaO₂ levels, even with small fluctuations in oxygen concentration.

Answer 4

If the curve were linear, the relationship between oxygen partial pressure and oxygen binding would not be as efficient. A linear curve would mean that oxygen would not be loaded as efficiently in the lungs or unloaded as effectively in the tissues. The sigmoidal curve allows for the optimal transfer of oxygen under varying conditions of oxygen demand and oxygen availability in the lungs and tissues.

Answer 5

The oxyhemoglobin dissociation curve is a graph that shows the relationship between the partial pressure of oxygen (PaO₂) and the percentage of hemoglobin saturated with oxygen (O₂ saturation). It demonstrates how hemoglobin binds with oxygen in the lungs and releases oxygen in the tissues, with a sigmoidal (S-shaped) curve.

Answer 6

The main factors that affect the oxyhemoglobin dissociation curve include: Partial pressure of carbon dioxide (PaCO₂) pH (blood acidity) Temperature 2,3-Bisphosphoglycerate (2,3-BPG) levels Hemoglobin variants

Answer 7

Increased CO₂ levels shift the oxyhemoglobin dissociation curve to the right, promoting oxygen unloading in tissues. This is due to the Bohr effect, where CO₂ and lower pH (acidosis) reduce hemoglobin's affinity for oxygen, encouraging oxygen release where it is needed most (in metabolically active tissues).

Answer 8

Lower pH (acidosis) also shifts the curve to the right, causing hemoglobin to release oxygen more easily. As CO₂ is produced in tissues, it combines with water to form carbonic acid, which dissociates into hydrogen ions (H⁺), decreasing the pH and promoting oxygen unloading in the tissues. This is a key mechanism in tissues with high metabolic activity.

Answer 9

Increased temperature shifts the curve to the right, meaning hemoglobin has a lower affinity for oxygen, which promotes oxygen unloading. This is particularly important during exercise, when muscle tissues generate more heat and have an increased demand for oxygen. Similarly, decreased temperature shifts the curve to the left, enhancing hemoglobin's affinity for oxygen.

Answer 10

2,3-BPG is a molecule produced in red blood cells that binds to hemoglobin and decreases its affinity for oxygen. Increased levels of 2,3-BPG shift the curve to the right, promoting oxygen unloading in tissues. Decreased levels of 2,3-BPG shift the curve to the left, making hemoglobin hold onto oxygen more tightly.

Answer 11

Different forms of hemoglobin can affect the affinity for oxygen. For example, hemoglobin F (fetal hemoglobin) has a higher affinity for oxygen than adult hemoglobin (HbA), which shifts the curve to the left and facilitates oxygen transfer from mother to fetus. Hemoglobin S (found in sickle cell disease) can alter the shape and function of hemoglobin, potentially affecting oxygen binding and release.

Answer 12

At higher altitudes, where oxygen partial pressure is lower, the body compensates by increasing the production of 2,3-BPG in red blood cells. This rightward shift in the oxyhemoglobin dissociation curve facilitates oxygen unloading in the tissues, helping the body adapt to lower oxygen availability at high altitudes

Answer 13

During exercise, increased CO₂ production, increased temperature, and lower pH all occur in muscle tissues. These factors cause a rightward shift in the curve, enhancing oxygen release to muscles that have a higher metabolic demand for oxygen.

Answer 14

Carbon monoxide (CO) binds to hemoglobin with a much higher affinity than oxygen, forming carboxyhemoglobin. This reduces hemoglobin's ability to bind and release oxygen, shifting the oxyhemoglobin dissociation curve to the left, and impairing oxygen delivery to tissues, even when PaO₂ is normal.

Answer 15

Oxyhemoglobin dissociation refers to the process by which oxygen (O₂) is released from hemoglobin in the tissues and bound to hemoglobin in the lungs. The relationship between the partial pressure of oxygen (PaO₂) and the oxygen saturation of hemoglobin is represented by the oxyhemoglobin dissociation curve.

Answer 16

Adult hemoglobin (HbA) is the primary hemoglobin found in adults. It consists of two alpha and two beta chains. It binds to oxygen in the lungs (where PaO₂ is high) and releases it in tissues (where PaO₂ is low). The oxyhemoglobin dissociation curve for adult hemoglobin is sigmoidal (S-shaped), which reflects cooperative binding—as one molecule of O₂ binds, the affinity for the next increases.

Answer 17

The sigmoidal (S-shaped) curve allows hemoglobin to efficiently load oxygen in the lungs at high PaO₂ and unload oxygen in the tissues where PaO₂ is low. The plateau portion at high PaO₂ ensures near-maximal saturation in the lungs, while the steep portion at low PaO₂ ensures significant oxygen unloading in metabolically active tissues.

Answer 18

Fetal hemoglobin (HbF) is the primary form of hemoglobin in fetuses. It consists of two alpha and two gamma chains. HbF has a higher affinity for oxygen than adult hemoglobin, which is essential for oxygen transfer from the mother's blood to the fetus across the placenta.

Answer 19

The oxyhemoglobin dissociation curve for fetal hemoglobin is shifted to the left compared to adult hemoglobin. This means that HbF binds oxygen more tightly, even at lower PaO₂, facilitating the transfer of oxygen from maternal blood (which has a lower oxygen affinity) to fetal blood in the placenta.

Answer 20

The leftward shift means that fetal hemoglobin can pick up oxygen from the mother's blood at lower oxygen levels in the placenta, ensuring efficient oxygen transfer despite the lower oxygen partial pressures in the fetal circulation. This is critical for fetal development, as the fetus needs oxygen for growth and development, even though its oxygen supply is limited by the placenta.

Answer 21

Myoglobin is a muscle protein found in skeletal and cardiac muscle. It is structurally similar to hemoglobin but consists of only one polypeptide chain and one heme group. Myoglobin's primary role is to store oxygen in muscle tissue and release it when needed during periods of high metabolic demand, such as during exercise.

Answer 22

The oxy-myoglobin dissociation curve is hyperbolic (not sigmoidal), meaning myoglobin has a higher affinity for oxygen at all oxygen partial pressures compared to hemoglobin. This curve is steep at low PaO₂, meaning that myoglobin binds oxygen very tightly and is only released under conditions of very low oxygen availability, such as during intense muscle activity

Answer 23

The hyperbolic curve reflects that myoglobin binds oxygen more tightly than hemoglobin and is not influenced by cooperative binding. This makes myoglobin an oxygen reservoir for muscles, ensuring that oxygen is readily available when muscles are working hard and oxygen demand increases.

Answer 24

Adult hemoglobin (HbA) is designed for oxygen transport in the blood, binding oxygen in the lungs and releasing it in tissues. Fetal hemoglobin (HbF) has a higher affinity for oxygen to facilitate oxygen transfer from mother to fetus across the placenta. Myoglobin is an oxygen storage protein in muscle cells, with a high affinity for oxygen to ensure oxygen supply during intense physical activity or low oxygen conditions.

Answer 25

Adult hemoglobin (HbA) is more suited for oxygen transport within the body, whereas fetal hemoglobin (HbF) is specialized for oxygen uptake from the mother’s blood in the placenta. The higher oxygen affinity of HbF ensures that oxygen can move from maternal blood (where HbA is present) to fetal blood, which is critical for fetal oxygenation during pregnancy.

Answer 26

Carbon dioxide (CO₂) is carried in the blood in three main forms: As bicarbonate ions (HCO₃⁻) – the majority of CO₂ is transported this way. Bound to hemoglobin as carbaminohemoglobin (CO₂Hb). Dissolved in plasma as dissolved CO₂.

Answer 27

Approximately 70% of carbon dioxide (CO₂) is carried in the blood as bicarbonate ions (HCO₃⁻). This occurs after CO₂ enters red blood cells and reacts with water to form carbonic acid (H₂CO₃), which dissociates into bicarbonate and hydrogen ions.

Answer 28

When CO₂ diffuses into red blood cells, it combines with water in the presence of carbonic anhydrase to form carbonic acid (H₂CO₃). Carbonic acid quickly dissociates into bicarbonate (HCO₃⁻) and hydrogen ions (H⁺). The bicarbonate ions (HCO₃⁻) are transported out of the red blood cell into the plasma, and chloride ions (Cl⁻) move into the red blood cell to maintain electrical neutrality (this is known as the chloride shift).

Answer 29

About 23% of CO₂ is carried in the blood as carbaminohemoglobin. This occurs when CO₂ binds to the amino groups of hemoglobin and other proteins in the blood, forming carbaminohemoglobin.

Answer 30

CO₂ binds to the amino groups of hemoglobin, specifically to the globin portion of the protein (not the heme group where oxygen binds). This forms carbaminohemoglobin, and this binding helps to facilitate the release of oxygen from hemoglobin, as CO₂ promotes oxygen unloading in tissues (the Bohr effect).

Answer 31

Approximately 7-10% of carbon dioxide (CO₂) is carried dissolved in the plasma of the blood. CO₂ is more soluble in plasma than oxygen, but only a small proportion of CO₂ is carried in this form due to its relatively low solubility.

Answer 32

Bicarbonate (HCO₃⁻) is the primary form of CO₂ transport because it is the most stable and efficient way to carry CO₂ in the blood. The conversion of CO₂ to bicarbonate helps maintain acid-base balance in the blood, as the formation of bicarbonate also involves the buffering of hydrogen ions.

Answer 33

The chloride shift is the movement of chloride ions (Cl⁻) into the red blood cell in exchange for bicarbonate ions (HCO₃⁻) moving out of the cell into the plasma. This occurs as part of the process by which CO₂ is converted into bicarbonate ions for transport in the blood, helping to maintain electrical neutrality within the red blood cell.

Answer 34

In the lungs, the bicarbonate ions (HCO₃⁻) re-enter the red blood cells, where they combine with hydrogen ions (H⁺) to form carbonic acid (H₂CO₃). Carbonic acid is then broken down by carbonic anhydrase into CO₂ and water. The CO₂ is then exhaled from the lungs, and the bicarbonate system is restored.

Answer 35

CO₂ is primarily removed from the body through exhalation. The majority of CO₂ is converted back from bicarbonate ions (HCO₃⁻) to CO₂ in the lungs, where it is exhaled. The carbaminohemoglobin form of CO₂ is also converted to CO₂ in the lungs, promoting the release of CO₂ from hemoglobin for exhalation.

Answer 36

Carbonic anhydrase is an enzyme found in red blood cells (RBCs), the kidneys, and the lungs. It catalyzes the reversible conversion of carbon dioxide (CO₂) and water (H₂O) to form carbonic acid (H₂CO₃), which quickly dissociates into bicarbonate (HCO₃⁻) and hydrogen ions (H⁺).

Answer 37

Carbonic anhydrase plays a crucial role in the transport of CO₂ in the blood by facilitating the rapid conversion of CO₂ to bicarbonate (HCO₃⁻). This reaction occurs primarily in red blood cells and enables the bulk of CO₂ to be carried in the form of bicarbonate, the predominant form of CO₂ transport.

Answer 38

In the red blood cells, CO₂ diffuses into the cell from tissues. Carbonic anhydrase then catalyzes the reaction: CO₂ + H₂O ⇌ H₂CO₃ (carbonic acid). Carbonic acid is unstable and quickly dissociates into bicarbonate (HCO₃⁻) and hydrogen ions (H⁺): H₂CO₃ ⇌ HCO₃⁻ + H⁺.

Answer 39

Once formed, bicarbonate ions (HCO₃⁻) move out of the red blood cells into the plasma. To maintain electrical neutrality, chloride ions (Cl⁻) move into the red blood cell (this is known as the chloride shift).

Answer 40

Bicarbonate (HCO₃⁻) is the major form in which CO₂ is transported in the blood (around 70% of CO₂ is carried this way). The conversion of CO₂ to bicarbonate allows CO₂ to be transported efficiently from tissues to the lungs, where it can be exhaled.

Answer 41

In the lungs, the process is reversed: Bicarbonate (HCO₃⁻) enters the red blood cell in exchange for chloride ions (via the chloride shift). Inside the red blood cell, carbonic anhydrase catalyzes the reaction: HCO₃⁻ + H⁺ ⇌ H₂CO₃ (carbonic acid). Carbonic acid then breaks down into CO₂ and water. The CO₂ is then exhaled from the lungs.

Answer 42

The conversion of CO₂ to carbonic acid (H₂CO₃), and its dissociation into bicarbonate (HCO₃⁻) and hydrogen ions (H⁺), plays a significant role in maintaining the pH balance of the blood. Bicarbonate acts as a buffer in the blood, helping to neutralize excess hydrogen ions (H⁺) and regulate blood pH. This process is essential for maintaining homeostasis.

Answer 43

Carbonic anhydrase activity can be influenced by changes in blood pH. In acidosis (low pH), the increased H⁺ concentration may stimulate the enzyme to accelerate the conversion of CO₂ to bicarbonate, helping to buffer excess acid. In alkalosis (high pH), the enzyme activity may slow down, allowing CO₂ to accumulate and lower the pH by forming more carbonic acid.

Answer 44

Carbonic anhydrase is crucial because it accelerates the reaction between CO₂ and water to form carbonic acid, which quickly dissociates into bicarbonate (HCO₃⁻). Without this enzyme, the conversion of CO₂ to bicarbonate would be much slower, hindering efficient CO₂ transport in the blood and impairing the body's ability to regulate acid-base balance.

Answer 45

- **Low CO₂ Levels in the Lungs:** The lower partial pressure of CO₂ in the alveoli creates a gradient that encourages CO₂ to move from the blood into the lungs. - **Lower Temperature:** Cooler temperatures in the lungs reduce hemoglobin's affinity for CO₂, aiding in CO₂ release. - **Higher pH (Alkaline Conditions):** Lower CO₂ levels in the lungs raise the pH, which helps convert bicarbonate back into CO₂ for unloading. - **Bohr Effect:** Low CO₂ in the lungs reduces hemoglobin's affinity for CO₂, encouraging CO₂ release. - **Carbonic Anhydrase Activity:** This enzyme helps convert bicarbonate back into CO₂, making it ready for exhalation. - **Reverse Chloride Shift:** Bicarbonate ions move back into RBCs in exchange for chloride, supporting CO₂ unloading.

Answer 46

Ventilation refers to the process of airflow into and out of the lungs. It is the movement of fresh air into the alveoli (where gas exchange occurs) and the expulsion of carbon dioxide (CO₂) from the lungs into the atmosphere.

Answer 47

Perfusion refers to the process of blood flow through the capillaries in the lungs, where gas exchange takes place. Oxygen (O₂) from the alveoli is transferred into the blood, and carbon dioxide (CO₂) is transferred from the blood into the alveoli to be exhaled.

Answer 48

The ventilation-perfusion (V/Q) ratio describes the relationship between ventilation (airflow) and perfusion (blood flow) in the lungs. It is the ratio of the amount of air reaching the alveoli to the amount of blood reaching the alveoli. V/Q ratio = Ventilation (V) / Perfusion (Q).

Answer 49

The ideal V/Q ratio is about 1:1, meaning that the amount of air reaching the alveoli is matched by the amount of blood flow to the alveoli. This allows for optimal gas exchange: oxygen enters the bloodstream, and carbon dioxide is removed efficiently.

Answer 50

The V/Q ratio is not uniform across the lungs: At the apex (top) of the lungs, ventilation is greater than perfusion (V/Q ratio > 1). At the base (bottom) of the lungs, perfusion exceeds ventilation (V/Q ratio < 1). This gradient exists because gravity affects both blood flow (perfusion) and airflow (ventilation) in different parts of the lungs.

Answer 51

A V/Q mismatch can lead to inefficient gas exchange: If there is more ventilation than perfusion (high V/Q ratio), some areas of the lungs may receive enough air but not enough blood, meaning oxygen is not effectively transferred to the bloodstream. If there is more perfusion than ventilation (low V/Q ratio), blood flows to areas of the lungs that do not receive enough air, leading to poor oxygenation of the blood.

Answer 52

Low ventilation occurs when areas of the lung receive inadequate airflow, such as in conditions like atelectasis or obstructive lung diseases (e.g., asthma, COPD). This leads to poor oxygenation of the blood and an increase in CO₂ levels because the carbon dioxide cannot be adequately exhaled.

Answer 53

Low perfusion occurs when blood flow to certain areas of the lung is reduced, as seen in pulmonary embolism (a blockage of blood vessels) or shock. This causes poor gas exchange because oxygen cannot effectively enter the blood, leading to hypoxemia (low blood oxygen levels) despite adequate ventilation.

Answer 54

A balanced V/Q ratio ensures efficient gas exchange, leading to optimal oxygenation of the blood and removal of carbon dioxide. Disruptions in the V/Q ratio (such as in diseases like pulmonary embolism, pneumonia, or COPD) can lead to hypoxemia and respiratory acidosis, significantly affecting overall health.

Answer 55

V/Q mismatch can be identified through imaging studies like a V/Q scan or by assessing blood gases: Low V/Q ratio may present with hypoxemia (low O₂) and normal or high CO₂ levels. High V/Q ratio may present with hypoxemia (low O₂) and normal CO₂ levels, as CO₂ is efficiently removed but oxygen is not effectively absorbed.

Answer 56

Treatment of V/Q mismatch depends on the underlying cause: For low ventilation (e.g., from airway obstruction), treatments like bronchodilators, oxygen therapy, and positive pressure ventilation may be used. For low perfusion (e.g., from a pulmonary embolism), treatments may include anticoagulants, thrombolytics, or surgical intervention.

Answer 57

An imbalance in the **ventilation-perfusion (V/Q) ratio** can affect oxygen (O₂) and carbon dioxide (CO₂) levels in the lungs and arterial blood. **Conditions Leading to V/Q Imbalance:** 1. **Low V/Q Ratio (Hypoventilation):** - Occurs when ventilation is less than perfusion (e.g., **pulmonary edema**, **asthma**, **COPD**). - **Effect on Alveolar Gas**: Low O₂, high CO₂. - **Effect on Arterial Blood**: **Hypoxemia** (low O₂) and **hypercapnia** (high CO₂). 2. **High V/Q Ratio (Ventilation > Perfusion):** - Occurs when ventilation exceeds perfusion (e.g., **pulmonary embolism**, **emphysema**). - **Effect on Alveolar Gas**: Normal or high O₂, low CO₂. - **Effect on Arterial Blood**: Normal O₂, **hypocapnia** (low CO₂).

Answer 58

1. Hypoxaemic Hypoxia: most common. Reduction in O2 diffusion at lungs either due to decreased PO2atmos or tissue pathology. 2. Anaemic Hypoxia: Reduction in O2 carrying capacity of blood due to anaemia (red blood cell loss/iron deficiency). 3. Stagnant Hypoxia: Heart disease results in inefficient pumping of blood to lungs/around the body 4. Histotoxic Hypoxia: poisoning prevents cells utilising oxygen delivered to them e.g. carbon monoxide/cyanide 5. Metabolic Hypoxia: oxygen delivery to the tissues does not meet increased oxygen demand by cells.

Answer 59

A shunt refers to a condition where blood flows through the lungs but does not participate in gas exchange. This occurs when blood passes through non-ventilated areas of the lung or areas with very low ventilation, such as in atelectasis, pneumonia, or pulmonary edema. Shunt results in hypoxemia because oxygen cannot be absorbed effectively by blood that bypasses the ventilated alveoli.

Answer 60

Alveolar dead space refers to the volume of the alveoli that are ventilated but not perfused with blood. These alveoli receive air but do not participate in gas exchange because there is insufficient blood flow to pick up oxygen or drop off carbon dioxide. Causes of alveolar dead space include pulmonary embolism and ventilation-perfusion mismatch.

Answer 61

Anatomical dead space refers to the parts of the respiratory system where no gas exchange occurs, such as the trachea, bronchi, and bronchioles. These structures are involved in air conduction but have no alveoli, and thus no gas exchange. Physiologic dead space includes both anatomical dead space and alveolar dead space. It is the total volume of the respiratory system that does not participate in gas exchange, which can increase in conditions like pulmonary embolism or ventilation-perfusion mismatch.

Answer 62

Anatomical dead space refers to the volume of the respiratory tract that does not take part in gas exchange, which includes the nose, pharynx, larynx, trachea, and bronchi. This space carries air to the lungs but does not allow for oxygen and carbon dioxide exchange, and it accounts for about 150 mL of the tidal volume in a typical adult.

Answer 63

Physiologic dead space increases in certain respiratory conditions, such as pulmonary embolism, emphysema, or ARDS, leading to inefficient ventilation. A high physiologic dead space means that a greater proportion of the ventilated air is not effectively participating in gas exchange, which can result in hypoxemia and respiratory distress.

Answer 64

Alveolar dead space increases when there is poor perfusion (blood flow) to ventilated alveoli, as in conditions such as: Pulmonary embolism (blockage of blood flow to the lung) Ventilation-perfusion mismatch (e.g., areas of the lung that are ventilated but not adequately perfused) Severe emphysema (damaged alveoli with reduced blood supply).

Answer 65

A shunt leads to hypoxemia because the blood passes through areas of the lungs that are not ventilated, meaning it does not pick up oxygen. The blood in the shunted areas is returned to the systemic circulation without being oxygenated, leading to low oxygen levels in the arterial blood (hypoxemia).

Answer 66

An increase in dead space, whether anatomical, alveolar, or physiologic, means that a larger proportion of the air being ventilated is not available for gas exchange. This results in reduced effective ventilation, where more air is wasted, leading to inefficient gas exchange and a potential decrease in oxygen levels in the blood

Answer 67

Dead space can be measured using various techniques, such as the Bohr equation, which calculates the ratio of dead space to tidal volume based on measurements of carbon dioxide in exhaled air. A high dead space-to-tidal volume ratio suggests inefficient ventilation and gas exchange, which may indicate respiratory pathology.