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Gas Exchange

Gas Exchange

Since human cells are primarily reliant on aerobic metabolism, it is of vital importance to efficiently obtain oxygen from the environment and bring it to the tissues while excreting the byproduct of cellular respiration Respiration The act of breathing with the lungs, consisting of inhalation, or the taking into the lungs of the ambient air, and of exhalation, or the expelling of the modified air which contains more carbon dioxide than the air taken in. Nose and Nasal Cavity: Anatomy (CO2). Respiration Respiration The act of breathing with the lungs, consisting of inhalation, or the taking into the lungs of the ambient air, and of exhalation, or the expelling of the modified air which contains more carbon dioxide than the air taken in. Nose and Nasal Cavity: Anatomy involves both the respiratory and circulatory systems. There are 4 processes that supply the body with O2 and dispose of CO2. The respiratory system is involved in pulmonary ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing and external respiration Respiration The act of breathing with the lungs, consisting of inhalation, or the taking into the lungs of the ambient air, and of exhalation, or the expelling of the modified air which contains more carbon dioxide than the air taken in. Nose and Nasal Cavity: Anatomy, while the circulatory system is responsible for transport and internal respiration Respiration The act of breathing with the lungs, consisting of inhalation, or the taking into the lungs of the ambient air, and of exhalation, or the expelling of the modified air which contains more carbon dioxide than the air taken in. Nose and Nasal Cavity: Anatomy. Pulmonary ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing (breathing) represents movement of air into and out of the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy. External respiration Respiration The act of breathing with the lungs, consisting of inhalation, or the taking into the lungs of the ambient air, and of exhalation, or the expelling of the modified air which contains more carbon dioxide than the air taken in. Nose and Nasal Cavity: Anatomy, or gas exchange, is represented by the O2 and CO2 exchange between the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy and the blood.

Last updated: 2 Jun, 2021

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Contents

Anatomy of the Respiratory System Involved in Gas Exchange

Gas exchange occurs at the level of the alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) in the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy and capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries: Histology of the pulmonary circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment.

  • Respiratory unit:
    • Smallest functioning unit in the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy
    • Composed of a respiratory bronchiole, alveolar ducts, atria, and alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS)
  • Vascular beds: 
    • Capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries: Histology fill space between alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS).
    • Very little distance between blood in capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries: Histology and air in alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) 
  • Pulmonary membrane: 
    • Area of interface between capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries: Histology and alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS)
    • Averages 0.6 micrometers in thickness
    • Layers of pulmonary membrane (inside alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) → capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries: Histology):
      • Fluid layer coating inside of alveolus (contains surfactant Surfactant Substances and drugs that lower the surface tension of the mucoid layer lining the pulmonary alveoli. Acute Respiratory Distress Syndrome (ARDS) to break surface tension Surface tension The force acting on the surface of a liquid, tending to minimize the area of the surface. Acute Respiratory Distress Syndrome (ARDS))
      • Alveolar epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology
      • Epithelial basement membrane Basement membrane A darkly stained mat-like extracellular matrix (ecm) that separates cell layers, such as epithelium from endothelium or a layer of connective tissue. The ecm layer that supports an overlying epithelium or endothelium is called basal lamina. Basement membrane (bm) can be formed by the fusion of either two adjacent basal laminae or a basal lamina with an adjacent reticular lamina of connective tissue. Bm, composed mainly of type IV collagen; glycoprotein laminin; and proteoglycan, provides barriers as well as channels between interacting cell layers. Thin Basement Membrane Nephropathy (TBMN)
      • Interstitium
      • Capillary basement membrane Basement membrane A darkly stained mat-like extracellular matrix (ecm) that separates cell layers, such as epithelium from endothelium or a layer of connective tissue. The ecm layer that supports an overlying epithelium or endothelium is called basal lamina. Basement membrane (bm) can be formed by the fusion of either two adjacent basal laminae or a basal lamina with an adjacent reticular lamina of connective tissue. Bm, composed mainly of type IV collagen; glycoprotein laminin; and proteoglycan, provides barriers as well as channels between interacting cell layers. Thin Basement Membrane Nephropathy (TBMN) 
      • Capillary endothelial membrane

Physics of Gas Exchange

Physical properies of gases

During gas exchange, O₂ and CO₂ must cross the pulmonary membrane. This process is driven by multiple complex forces determined by the physical properties of these gases. 

  • Concentration: O₂ and CO₂ will flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure from areas of high concentration to those of low concentration.
  • Difference in partial pressure of gas in air in alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) and of gas dissolved in blood:
    • Partial pressure of gas in alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS): 
      • The air pressure in a fixed container is proportional to the concentration of molecules of air forced into that container.
      • Atmospheric air is composed of O₂, nitrogen Nitrogen An element with the atomic symbol n, atomic number 7, and atomic weight [14. 00643; 14. 00728]. Nitrogen exists as a diatomic gas and makes up about 78% of the earth’s atmosphere by volume. It is a constituent of proteins and nucleic acids and found in all living cells. Urea Cycle, and carbon dioxide. The rate of diffusion Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially facilitated diffusion, is a major mechanism of biological transport. Peritoneal Dialysis and Hemodialysis of each gas is proportional to the pressure exerted by that gas alone, called partial pressure.
      • Example: Atmospheric air is 760 mm MM Multiple myeloma (MM) is a malignant condition of plasma cells (activated B lymphocytes) primarily seen in the elderly. Monoclonal proliferation of plasma cells results in cytokine-driven osteoclastic activity and excessive secretion of IgG antibodies. Multiple Myeloma Hg and is 21% O₂. The partial pressure of O₂ (PO₂) in the alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) is 760 x 0.21 = 160 mm MM Multiple myeloma (MM) is a malignant condition of plasma cells (activated B lymphocytes) primarily seen in the elderly. Monoclonal proliferation of plasma cells results in cytokine-driven osteoclastic activity and excessive secretion of IgG antibodies. Multiple Myeloma Hg.
    • Partial pressure of gas dissolved in blood:
      • Gas dissolved in liquid exerts partial pressure determined both by its concentration and a constant known as solubility coefficient.
      • Example: partial pressure of O₂ dissolved in blood = concentration O₂/solubility coefficient of O₂ = 0.025 mm MM Multiple myeloma (MM) is a malignant condition of plasma cells (activated B lymphocytes) primarily seen in the elderly. Monoclonal proliferation of plasma cells results in cytokine-driven osteoclastic activity and excessive secretion of IgG antibodies. Multiple Myeloma Hg
    • Gas flows from areas of high partial pressure to those of low partial pressure.

Forces driving the rate of exchange of O₂ and CO₂

The rate of gas exchange is determined by the efficiency of the exchange across the pulmonary membrane and the speed at which it can be brought there from the air (for O₂) or from the body (for CO₂).

  • O₂:
    • The diffusion Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially facilitated diffusion, is a major mechanism of biological transport. Peritoneal Dialysis and Hemodialysis of O₂ into blood from alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) is extremely efficient.
    • Even ↑ speed at which O₂ brought to alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) ( ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing) cannot improve diffusion Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially facilitated diffusion, is a major mechanism of biological transport. Peritoneal Dialysis and Hemodialysis of O₂ across pulmonary membrane
    • The only factor that can affect Affect The feeling-tone accompaniment of an idea or mental representation. It is the most direct psychic derivative of instinct and the psychic representative of the various bodily changes by means of which instincts manifest themselves. Psychiatric Assessment diffusion Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially facilitated diffusion, is a major mechanism of biological transport. Peritoneal Dialysis and Hemodialysis is modification of the partial pressure of O₂ in breathed air (e.g., breathing pure O₂ or breathing at high elevations).
  • CO₂:
    • Diffusion Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially facilitated diffusion, is a major mechanism of biological transport. Peritoneal Dialysis and Hemodialysis is slower.
    • The speed of ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing is directly proportional to the speed of diffusion Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially facilitated diffusion, is a major mechanism of biological transport. Peritoneal Dialysis and Hemodialysis across the pulmonary membrane and of removal from the body.
  • Clinical correlation Correlation Determination of whether or not two variables are correlated. This means to study whether an increase or decrease in one variable corresponds to an increase or decrease in the other variable. Causality, Validity, and Reliability:
    • The O₂ saturation of blood is determined by the partial pressure of O₂ breathed by the patient.
    • The CO₂ saturation of blood is determined by the speed of ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing (breathing).

Gas Transport

O₂ and CO₂ must be transported through the bloodstream to reach sites of gas exchange.

O₂ transport

  • There are:
    • 0.295 mL of O₂ per dL of arterial blood
    • 0.124 mL of O₂ per dL of venous blood
  • 1.5% of O₂: dissolved in plasma Plasma The residual portion of blood that is left after removal of blood cells by centrifugation without prior blood coagulation. Transfusion Products.
  • 98.5% of O₂: loosely bound to each iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements atom of Hb in RBCs RBCs Erythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production. Erythrocytes: Histology.
  • Hb: 
    • Has 4 binding sites for O₂
    • Affinity of Hb for O₂ ↑ with amount of O₂ bound to it
  • O₂ saturation:
    • Percentage of Hb bound to O₂:
      • In arterial blood, Hb has O₂ saturation close to 99%.
      • In venous blood, Hb has O₂ saturation of around 75%.
      • Allows for reserve of O₂ to be preserved in blood
  • Hb loading and unloading:
    • Loading and unloading of O₂ are facilitated by changes in the shape of Hb.
      • As O₂ binds, Hb affinity for O₂ ↑
      • As O₂ is released, Hb affinity for O₂ ↓
    • Rate of loading and unloading of O₂ is regulated by:
      • PO₂ (↓ O₂ levels allow for O₂ to dissociate from Hb more easily)
      • ↑ Temperature will ↓ Hb affinity for O₂
      • ↓ Blood Ph pH The quantitative measurement of the acidity or basicity of a solution. Acid-Base Balance will ↓ Hb affinity for O₂
      • ↑ PCO₂  will ↓ affinity of Hb for O₂
      • ↑ Concentration of bisphosphoglycerate (BPG) will ↓ affinity of Hb for O₂
  • Saturation of hemoglobin gas exchange respiratory regulation

    Saturation of Hemoglobin:
    Percentage of bound hemoglobin increases with the concentration of O2. Notice the letter A, which signifies the saturation of hemoglobin in arterial blood (close to 99%). The letter V signifies the hemoglobin saturation of venous blood.

    Image by Lecturio. License: CC BY-NC-SA 4.0
  • Dissociation curve of hemoglobin gas exchange respiratory regulation

    Dissociation Dissociation Defense Mechanisms curve of Hemoglobin:
    Shows the right and left shifts that can occur when oxygen delivery to the tissues is increased or decreased, respectively.

    Image by Lecturio. License: CC BY-NC-SA 4.0
  • Percentages of co₂ gas exchange respiratory regulation

    Percentages of CO2 transported in the plasma Plasma The residual portion of blood that is left after removal of blood cells by centrifugation without prior blood coagulation. Transfusion Products:
    Notice how 90% is converted by the Carbonic anhydrase Carbonic anhydrase A family of zinc-containing enzymes that catalyze the reversible hydration of carbon dioxide. They play an important role in the transport of carbon dioxide from the tissues to the lung. Carbonic Anhydrase Inhibitors into HCO3– inside red blood cells Red blood cells Erythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production. Erythrocytes: Histology.

    Image by Lecturio. License: CC BY-NC-SA 4.0
  • Dissociation curve of hb and co₂ gas exchange respiratory regulation

    Dissociation Dissociation Defense Mechanisms curve of Hb and CO2:
    Notice how PCO2 increases from the arterial (a) to the venous side (v). The dissociation Dissociation Defense Mechanisms curve is elevated with the decrease in PO2, referencing the fact that a low O2 concentration allows for more CO2 to be bound to Hb.

    Image by Lecturio. License: CC BY-NC-SA 4.0

CO₂ transport

  • 7%–10% of CO₂: dissolved in plasma Plasma The residual portion of blood that is left after removal of blood cells by centrifugation without prior blood coagulation. Transfusion Products
  • 20% of CO₂: bound to Hb (carbaminohemoglobin)
  • The remaining 70% is bicarbonate Bicarbonate Inorganic salts that contain the -HCO3 radical. They are an important factor in determining the ph of the blood and the concentration of bicarbonate ions is regulated by the kidney. Levels in the blood are an index of the alkali reserve or buffering capacity. Electrolytes (HCO3); CO₂ is converted into HCO3 by carbonic anhydrase Carbonic anhydrase A family of zinc-containing enzymes that catalyze the reversible hydration of carbon dioxide. They play an important role in the transport of carbon dioxide from the tissues to the lung. Carbonic Anhydrase Inhibitors inside RBCs RBCs Erythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production. Erythrocytes: Histology.

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Ventilation/Perfusion (V/Q) Coupling

Ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing and perfusion are the mechanisms that transport O₂ and CO₂ between the pulmonary membrane and the body’s tissues.

Perfusion

Perfusion is the flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure of blood to pulmonary vasculature.

Ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing

  • Changes in PO₂ in alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) → changes in diameter of arterioles Arterioles The smallest divisions of the arteries located between the muscular arteries and the capillaries. Arteries: Histology affecting perfusion:
  • When PO₂ ↓ in all alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS), there is chemoreflex vasoconstriction Vasoconstriction The physiological narrowing of blood vessels by contraction of the vascular smooth muscle. Vascular Resistance, Flow, and Mean Arterial Pressure
  • Changes in PCO₂ → changes in diameters of bronchioles Bronchioles The small airways branching off the tertiary bronchi. Terminal bronchioles lead into several orders of respiratory bronchioles which in turn lead into alveolar ducts and then into pulmonary alveoli. Bronchial Tree: Anatomy:
    • If alveolar CO₂ is ↑, bronchioles Bronchioles The small airways branching off the tertiary bronchi. Terminal bronchioles lead into several orders of respiratory bronchioles which in turn lead into alveolar ducts and then into pulmonary alveoli. Bronchial Tree: Anatomy dilate
    • If alveolar CO₂ is ↓, bronchioles Bronchioles The small airways branching off the tertiary bronchi. Terminal bronchioles lead into several orders of respiratory bronchioles which in turn lead into alveolar ducts and then into pulmonary alveoli. Bronchial Tree: Anatomy constrict
  • Gravity and blood flow Blood flow Blood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute). Vascular Resistance, Flow, and Mean Arterial Pressure:
    • Gravity ↓ flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure of blood toward apex and ↑ toward base
  • Overview of pulmonary blood flow respiratory gas exchange

    Overview of pulmonary blood flow Blood flow Blood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute). Vascular Resistance, Flow, and Mean Arterial Pressure

    Image by Lecturio. License: CC BY-NC-SA 4.0
  • Effects of lung volume zone 1 respiratory gas exchange

    Zone 1 (Apex) of the lung and the effect of gravity on it:
    Arterial pressure (Pa) is lower than alveolar pressure (PA), making the flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure of blood difficult if not impossible. The relationship Relationship A connection, association, or involvement between 2 or more parties. Clinician–Patient Relationship between pressures can be seen in the green box.

    Image by Lecturio. License: CC BY-NC-SA 4.0
  • Effects of lung volume zone 2 respiratory gas exchange

    Zone 2 of the lung and the effect of gravity on it:
    There’s more blood flow Blood flow Blood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute). Vascular Resistance, Flow, and Mean Arterial Pressure allowed by the increase in arterial blood pressure. The relationship Relationship A connection, association, or involvement between 2 or more parties. Clinician–Patient Relationship between pressures can be seen in the green box.

    Image by Lecturio. License: CC BY-NC-SA 4.0
  • Effects of lung volume zone 3 respiratory gas exchange

    Zone 3 (Base) of the lung and the effect of gravity on it:
    It’s the zone with the greatest blood flow Blood flow Blood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute). Vascular Resistance, Flow, and Mean Arterial Pressure in the lung. The pull of gravity makes more blood available and the arterial blood pressure greater than the alveolar pressure. The relationship Relationship A connection, association, or involvement between 2 or more parties. Clinician–Patient Relationship between pressures can be seen in the green box.

    Image by Lecturio. License: CC BY-NC-SA 4.0

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Hypoxemia and Hypercapnia

There are 2 important PO₂ differences (gradients):

  • Alveolar–arterial (A-a): difference in PO₂ between the alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) and systemic arterial blood
  • Arteriovenous (AV): difference in PO₂ between venous and arterial blood
Pressures of o₂ and co₂ respiratory gas exchange

Arterial-venous (a-v) difference in PO2 between venous and arterial blood:
Pressures of O2 and CO2 in the alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) and systemic circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment before and after gas exchange.

Image by Lecturio. License: CC BY-NC-SA 4.0

Tissue hypoxia Hypoxia Sub-optimal oxygen levels in the ambient air of living organisms. Ischemic Cell Damage

  • Low O₂ availability to the tissues
  • Hypoxia Hypoxia Sub-optimal oxygen levels in the ambient air of living organisms. Ischemic Cell Damage is sensed by the kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy, stimulating RBC synthesis Synthesis Polymerase Chain Reaction (PCR) through the release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology of EPO EPO Glycoprotein hormone, secreted chiefly by the kidney in the adult and the liver in the fetus, that acts on erythroid stem cells of the bone marrow to stimulate proliferation and differentiation. Erythrocytes: Histology.

Hypoxemia Hypoxemia Neonatal Respiratory Distress Syndrome

  • Low PO₂ in the blood
  • Can be caused by:
    • Hypoventilation 
    • Reduced (< 21%) inspired fraction of O₂
    • Diffusional impairment: inadequate diffusion Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially facilitated diffusion, is a major mechanism of biological transport. Peritoneal Dialysis and Hemodialysis of gases into the capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries: Histology
    • Right-to-left shunt: communication Communication The exchange or transmission of ideas, attitudes, or beliefs between individuals or groups. Decision-making Capacity and Legal Competence between pulmonary arterial and venous circulations allowing deoxygenated blood to partially skip gas exchange
    • V/Q inequality
Diagram hypoxemia respiratory gas exchange

Diagram of a RIGHT-TO-LEFT shunt:
See the communication Communication The exchange or transmission of ideas, attitudes, or beliefs between individuals or groups. Decision-making Capacity and Legal Competence that allows blood to skip gas exchange and lower the arterial pressure of O2.

Image by Lecturio. License: CC BY-NC-SA 4.0

Hypercapnia Hypercapnia A clinical manifestation of abnormal increase in the amount of carbon dioxide in arterial blood. Neonatal Respiratory Distress Syndrome

  • Po₂ gradients in pulmonary and systemic circulations respiratory gas exchange

    PO2 gradients in pulmonary and systemic circulations:
    See the A-a gradient at the point of communication Communication The exchange or transmission of ideas, attitudes, or beliefs between individuals or groups. Decision-making Capacity and Legal Competence between the pulmonary capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries: Histology and the systemic arterial circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment. The a-v gradient would be the difference between the PO2 of the systemic arterial circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment before the capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries: Histology and the PO2 of the systemic venous circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment after the capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries: Histology.

    Image by Lecturio. License: CC BY-NC-SA 4.0
  • Diagrammatic examples of ventilation to perfusion mismatch respiratory gas exchange

    Diagrammatic examples of ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing (V) to perfusion (Q) mismatch:
    On the right, an example of low ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing to high perfusion can be seen. On the left, an example of high ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing to low perfusion can be seen. In the center is a normal situation of ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing to perfusion with a relation of 1 to 1.

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  • Ventilation perfusion relation gas exchange

    Ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing/Perfusion relation applied to the apex of the upright lung of a healthy individual:
    Reduced perfusion of the Apex (right), the inflating effect of the gravity due to the weight of the lung (center) and the resulting parameters during inspiration Inspiration Ventilation: Mechanics of Breathing (right). Notice the increase of the V/Q (V/P) ratio due to the increased ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing and the reduced perfusion.

    Image by Lecturio. License: CC BY-NC-SA 4.0
  • Ventilation perfusion relation gas exchange 2

    Ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing/Perfusion relation applied to the base of the upright lung of a healthy individual:
    See the increased perfusion of the Base (right), the compressing effect of the gravity due to the weight of the lung (center) and the resulting parameters during inspiration Inspiration Ventilation: Mechanics of Breathing (right). The V/Q (V/P) ratio is decreased due to the increased perfusion.

    Image by Lecturio. License: CC BY-NC-SA 4.0

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Clinical Correlation

  • Anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types: a decrease in RBCs RBCs Erythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production. Erythrocytes: Histology in circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment. Anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types causes a decrease in the amount of available O₂ as the overall amount of Hb is diminished. Etiologies can be grouped with those that feature a failure to produce sufficient RBCs RBCs Erythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production. Erythrocytes: Histology ( iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements deficiency, bone marrow Bone marrow The soft tissue filling the cavities of bones. Bone marrow exists in two types, yellow and red. Yellow marrow is found in the large cavities of large bones and consists mostly of fat cells and a few primitive blood cells. Red marrow is a hematopoietic tissue and is the site of production of erythrocytes and granular leukocytes. Bone marrow is made up of a framework of connective tissue containing branching fibers with the frame being filled with marrow cells. Bone Marrow: Composition and Hematopoiesis dysplasia Dysplasia Cellular Adaptation, and neoplasia) and those that feature increased destruction of RBCs RBCs Erythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production. Erythrocytes: Histology (autoimmune, infectious Infectious Febrile Infant, genetic). Common symptoms of anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types include pallor of the mucous membranes and easy fatigability. Pulse oximetry remains normal, as the percentage saturation of each hemoglobin molecule does not vary. The diagnosis of anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types is confirmed with blood tests that indicate a decrease in RBCs RBCs Erythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production. Erythrocytes: Histology. Treatment is directed at fixing the underlying pathology causing anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types.
  • Polycythemia Polycythemia An increase in the total red cell mass of the blood. Renal Cell Carcinoma: an increase in RBCs RBCs Erythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production. Erythrocytes: Histology in circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment. Polycythemia Polycythemia An increase in the total red cell mass of the blood. Renal Cell Carcinoma causes an increase in the amount of available O₂ as the overall amount of Hb is increased. Etiologies vary from nonpathological (high-altitude habituation, perinatal adjustment period) to serious disease processes (neoplasia, polycythemia Polycythemia An increase in the total red cell mass of the blood. Renal Cell Carcinoma vera). Polycythemia Polycythemia An increase in the total red cell mass of the blood. Renal Cell Carcinoma patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship typically have a ruddy complexion, and they can present with excessive clotting and its consequences. The diagnosis is confirmed by blood cell counts, and treatment varies by etiology.
  • Carbon monoxide Carbon monoxide Carbon monoxide (CO). A poisonous colorless, odorless, tasteless gas. It combines with hemoglobin to form carboxyhemoglobin, which has no oxygen carrying capacity. The resultant oxygen deprivation causes headache, dizziness, decreased pulse and respiratory rates, unconsciousness, and death. Carbon Monoxide Poisoning (CO) poisoning: breathing CO decreases the amount of available O₂ in a patient’s circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment by occupying binding sites of Hb meant for O₂ with greater affinity. Pulse oximetry often reports normal, even elevated saturations, as all binding sites of hemoglobin are occupied. Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship often report having a headache Headache The symptom of pain in the cranial region. It may be an isolated benign occurrence or manifestation of a wide variety of headache disorders. Brain Abscess and a decreased level of consciousness. Carbon monoxide Carbon monoxide Carbon monoxide (CO). A poisonous colorless, odorless, tasteless gas. It combines with hemoglobin to form carboxyhemoglobin, which has no oxygen carrying capacity. The resultant oxygen deprivation causes headache, dizziness, decreased pulse and respiratory rates, unconsciousness, and death. Carbon Monoxide Poisoning poisoning can be lethal if the patient is not removed from the source of CO.
  • Pulmonary edema Pulmonary edema Pulmonary edema is a condition caused by excess fluid within the lung parenchyma and alveoli as a consequence of a disease process. Based on etiology, pulmonary edema is classified as cardiogenic or noncardiogenic. Patients may present with progressive dyspnea, orthopnea, cough, or respiratory failure. Pulmonary Edema: presence of fluid instead of air in alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS). The presence of additional fluid impedes proper gas exchange, greatly decreasing available surface area. Pulmonary edema Pulmonary edema Pulmonary edema is a condition caused by excess fluid within the lung parenchyma and alveoli as a consequence of a disease process. Based on etiology, pulmonary edema is classified as cardiogenic or noncardiogenic. Patients may present with progressive dyspnea, orthopnea, cough, or respiratory failure. Pulmonary Edema has various etiologies, including cardiac failure Cardiac failure Congestive heart failure refers to the inability of the heart to supply the body with normal cardiac output to meet metabolic needs. Echocardiography can confirm the diagnosis and give information about the ejection fraction. Congestive Heart Failure and sepsis Sepsis Systemic inflammatory response syndrome with a proven or suspected infectious etiology. When sepsis is associated with organ dysfunction distant from the site of infection, it is called severe sepsis. When sepsis is accompanied by hypotension despite adequate fluid infusion, it is called septic shock. Sepsis and Septic Shock. Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship present with shortness of breath Shortness of breath Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea and often have audible rales Rales Respiratory Syncytial Virus on exam. Pulse oximetry is often low in these patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship. Treatment aims to remove the causes of excess fluid buildup.

References

  1. Hall, JE, & Hall, ME. (2021). Guyton and Hall textbook of medical physiology (14th ed.). Elsevier.
  2. Powers KA, Dhamoon AS. (2021). Physiology, pulmonary ventilation, and perfusion. StatPearls. Treasure Island (FL): StatPearls Publishing.
  3.  Biga, LM, Dawson, S, Harwell A, Hopkins, R, et al. Anatomy and physiology. Retrieved April 26, 2021, from https://openstax.org/details/books/anatomy-and-physiology
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