Lung mechanics and Gas exchange with question answers (2)

Pulmonary Physiology

Topics Covered

• Overview of lung mechanics

  • Breathing muscles

  • Lung compliance and disease implications

  • Air pressure, flow, and resistance relationship

  • Breathing cycle with pressure changes illustration

Muscles of Inspiration

Key Muscles

• Diaphragm

  • Most important muscle during inspiration

  • Moves downward upon contraction, increasing the thoracic volume and decreasing internal pressure (following PV = PV principle)

• External Intercostal Muscles

  • More active during physical exertion

  • Pulls ribs outward to increase tidal volume

Muscles of Expiration

Characteristics

• Expiration is primarily a passive process, with air exiting lungs following the pressure gradient

• Assisting Muscles:

  • Internal Intercostals: Pull chest inward, expelling air quickly during forced expiration

  • Abdominal Muscles: Assist by pushing the diaphragm upwards, compressing the abdominal contents

• Influences on expiration:

  • Exercise, asthma, COPD

Compliance

Definitions

• Compliance: Measure of lung and chest wall distensibility

  • Formula: C = ∆Volume / ∆Pressure

  • High compliance indicates greater distensibility (e.g., emphysema)

  • Low compliance indicates stiff conditions (e.g., fibrosis)

• Compliance vs. Elastance: Compliance is inversely related to elastance

Types of Pressure in Compliance

• Transmural Pressure: Pressure difference across a structure, e.g., transpulmonary pressure (intra-alveolar vs. intrapleural)

  • Inside the alveoli 760 mmHg

  • Outside air 760 mmHg

  • Intrapleural 756 mmHg

Surfactant

Functionality

• Surfactant is a mixture of phospholipids that:

  • Reduces surface tension within the alveoli

  • Keeps alveoli open at low pressure

  • Increases compliance by enhancing gas exchange efficiency

Importance in Health

• Neonatal Respiratory Distress Syndrome characterized by surfactant deficiency

  • Risk of collapsed alveoli (atelectasis) and decreased compliance

Airflow, Pressure, and Resistance Relationships

Airflow Mechanics

• Airflow depends on pressure gradients and airway resistance

  • Inspiration: Pressure gradient from 0 (atmospheric) to negative (intrapleural)

  • Expiration: Positive pressure from the alveoli to the atmosphere

Factors Influencing Airway Resistance

• Length, viscosity, and radius of airways play crucial roles

  • Greater length increases resistance

  • Reduced radius significantly increases resistance (radius halving raises resistance by 16 times)

  • Bronchial Resistance:

    • Medium sized bronchi show highest resistance

Gas Exchange Mechanisms

Gas Laws Overview

• Ideal Gas Law: Relates pressure, volume, and temperature in gases

• Dalton’s Law of Partial Pressures: Total pressure equals the sum of partial pressures of individual gases

  • Example calculations for PO2 in humidified tracheal air

• Fick’s Law: Governs gas diffusion rates:

  • Rate of diffusion is proportional to surface area, driving pressure, and diffusion coefficient; inversely related to membrane thickness

Lung Diffusion Capacity (DL)

• Measurement techniques involve assessing carbon monoxide absorption to estimate the diffusing capacity of the lungs, indicating conditions like pulmonary fibrosis or emphysema.

Clinical Considerations and Pathologies

Conditions Affecting Compliance

• Emphysema: Increased lung compliance

• Pulmonary Fibrosis: Decreased lung compliance

• Importance in assessing functional residual capacity and equilibrium pressures in the lungs.

Conclusion

• Understanding lung mechanics, compliance, and resistance is critical for diagnosing and managing pulmonary conditions effectively.

• Key attention to the function of surfactant and mechanical properties of inspiration and expiration.

25. Understand Dalton’s Law of Partial Pressures.

26. Be able to apply Dalton’s Law of Par=al Pressures to calculate a par=al pressure, including adjustment for water vapor.

Dalton's Law of Partial Pressures states that in a mixture of gases, the total pressure exerted by the gas mixture is equal to the sum of the partial pressures of the individual gases. Each gas in a mixture behaves as if it occupies the entire volume alone and its pressure is proportional to its concentration in the mixture. To apply Dalton's Law to calculate a partial pressure, you can use the formula: \[ P_{total} = P_1 + P_2 + P_3 + ... + P_n \] where \( P_{total} \) is the total pressure and \( P_1, P_2, P_3, ... P_n \) are the partial pressures of each gas. When considering water vapor, you must adjust the total pressure accordingly by subtracting the vapor pressure of water at the given temperature from the total pressure. This provides a more accurate measure of the partial pressures of the other gases present in the mixture.

27. Understand the relationship between the concentration of dissolved gases, solubility, and pressure. The relationship between the concentration of dissolved gases, solubility, and pressure is explained by Henry's law, which states that the amount of gas that will dissolve in a liquid at a given temperature is directly proportional to the partial pressure of that gas in contact with the liquid. This means that: - As the partial pressure of a gas increases, the concentration of that gas dissolved in the liquid also increases, assuming the solubility remains constant. - Solubility is a measure of how much gas can be dissolved in a specific volume of liquid at a given temperature. For example, if the pressure of oxygen is increased in a closed environment, more oxygen will dissolve in blood (or any liquid) until a new equilibrium is reached. Conversely, if the pressure decreases, the concentration of the dissolved gas will also decrease, which can lead to problems such as decompression sickness in divers.

28. Understand how Fick’s Law dictates rela=onship between volume of gas transferred per unit =me(VX) to diffusion coefficient (D), surface area (A), partial pressure difference (∆𝑃), and thickness of the membrane (∆𝑋). Fick’s Law of diffusion describes how gases transfer across a membrane based on several factors. The equation defines the relationship between the volume of gas transferred per unit time (VX) to the key variables: - **Diffusion Coefficient (D)**: A measure of how easily a gas diffuses through a medium. It depends on the properties of the gas and the medium it’s diffusing through. - **Surface Area (A)**: The larger the area available for diffusion, the greater the amount of gas that can be transferred. - **Partial Pressure Difference (∆P)**: This is the difference in partial pressures of the gas on either side of the membrane. A greater difference drives more gas to diffuse across. - **Thickness of the Membrane (∆X)**: The thicker the membrane, the harder it is for the gas to pass through; thus, increased thickness reduces the volume of gas that can be transferred. In summary, according to Fick’s law: \[ VX = D \times A \times \frac{\Delta P}{\

29. Be able to apply Fick’s law to determine how a change in one of the above variables: D, A, ∆𝑃, or ∆𝑋, might affect gas transferred per unit =me (VX).

30. Be able to name conditions that can increase or decrease Diffusion Capacity of Carbon Monoxide (DLCO). The Diffusion Capacity of Carbon Monoxide (DLCO) can be influenced by several conditions. Some of the conditions that can increase DLCO include conditions that lead to increased lung surface area, such as emphysema, where there is increased alveolar surface area due to the destruction of alveolar walls. On the other hand, DLCO can decrease in scenarios such as pulmonary fibrosis, where the thickening and scarring of lung tissue reduces the surface area available for gas exchange and increases the thickness of the membrane through which diffusion must occur. Other factors that might affect DLCO include conditions that impair blood flow in the lungs (such as pulmonary hypertension) or alter hemoglobin levels in the blood.

31. Be able to define shunting. Shunting refers to the diversion of blood flow in the circulatory system, particularly where blood bypasses the lungs or areas of the lung that are not receiving adequate ventilation. There are two main types of shunts: 1. **Anatomical Shunt**: This occurs when blood flows from the right side of the heart to the left side without passing through the lungs. This can happen with congenital heart defects or certain vascular malformations. 2. **Physiological Shunt**: This is when blood flows through non-ventilated parts of the lung, leading to a mismatch between ventilation and perfusion. This can occur in conditions such as pneumonia or pulmonary edema, where parts of the lung are filled with fluid and cannot take part in gas exchange. Shunting can negatively impact oxygen levels in the blood, leading to hypoxemia, as blood that is not oxygenated adequately is introduced into the systemic circulation.

32. Be able to describe the effect shunting may have on the gradient between alveolar oxygen content and arterial blood oxygen content. Shunting affects the gradient between alveolar oxygen content and arterial blood oxygen content by allowing blood to bypass areas of the lung that are not adequately ventilated, leading to decreased oxygenation of blood. This occurs in two main ways: 1. **Anatomical Shunt**: Blood flows directly from the right side of the heart to the left side without passing through the lungs, as seen in some congenital heart defects. This results in deoxygenated blood entering the systemic circulation, reducing overall arterial oxygen content. 2. **Physiological Shunt**: Blood flows through regions of the lung that are ventilated poorly or not at all. For example, in conditions like pneumonia or pulmonary edema, parts of the lung are filled with fluid and cannot participate effectively in gas exchange. As a result, the difference (or gradient) between the oxygen content in the alveoli and that in the arterial blood decreases, leading to hypoxemia, or low oxygen levels in the blood. This impaired gas exchange can have significant consequences for overall oxygen delivery to tissues throughout the body.

33. Be able to define perfusion and diffusion limited gas exchange. Perfusion-limited gas exchange refers to a situation where the rate of gas exchange is limited by the blood flow (perfusion) in the pulmonary capillaries. In this case, adequate time for gas exchange occurs during the blood's passage through the lungs, meaning that the characteristics of the gas and its ability to diffuse are not the limiting factors. An example of this is oxygen exchange under normal conditions where sufficient blood flow allows for efficient gas uptake. On the other hand, diffusion-limited gas exchange occurs when the gas transfer is limited by its rate of diffusion across the alveolar-capillary membrane. This means that even if blood flow is adequate, the ability of the gas to diffuse (due to membrane thickness, surface area, or pressure gradients) is insufficient. Conditions such as pulmonary fibrosis, where the lung tissue becomes thickened, can lead to diffusion limitation for gases like oxygen and carbon monoxide, reducing the efficiency of gas exchange.

34. Name conditions that might cause diffusion limited gas exchange.

Conditions that can cause diffusion limited gas exchange include: 1. **Pulmonary Fibrosis**: Thickening of the alveolar membrane reduces gas diffusion efficiency. 2. **Emphysema**: Although it increases lung compliance, the destruction of alveolar walls may impair the surface area available for gas exchange. 3. **Chronic Obstructive Pulmonary Disease (COPD)**: Alveolar damage can hinder effective gas diffusion. 4. **Pulmonary Edema**: Fluid accumulation in the alveoli increases the thickness of the membrane through which gases must diffuse. 5. **Acute Respiratory Distress Syndrome (ARDS)**: Inflamed alveoli also make gas exchange less efficient due to increased membrane thickness. 6. **Anemia**: Reduced hemoglobin levels limit the blood's capacity to carry oxygen, which can affect overall gas exchange despite normal diffusion rates. These conditions typically lead to a reduction in gas exchange efficiency despite normal or sufficient blood flow.

41. Describe the external structure of the kidney, including its loca=on, support structures, and
covering. ### External Structure of the Kidney - **Location**: The kidneys are located retroperitoneally in the abdominal cavity, one on each side of the vertebral column, just above the waist. - **Support Structures**: - The kidneys are supported by the following structures: - **Renal Fascia**: A layer of connective tissue that anchors the kidneys to surrounding structures and helps protect them. - **Adipose Capsule**: A layer of fat that surrounds and cushions the kidneys, providing insulation and protection against trauma. - **Renal Capsule**: The outermost layer, a thin layer of fibrous connective tissue that provides a protective barrier against infection and trauma. - **Covering**: The renal capsule serves as the covering of the kidneys, providing a smooth surface and contributing to the overall protection of the organ from physical damage and infections.

42. Describe the major func=ons of the kidney. The major functions of the kidneys include: 1. **Filtration of Blood**: The kidneys filter waste products and excess substances from the blood, producing urine that contains these waste materials. 2. **Regulation of Blood Volume and Pressure**: By controlling the amount of fluid excreted as urine, the kidneys help regulate blood volume, which in turn affects blood pressure. 3. **Electrolyte Balance**: The kidneys maintain the balance of electrolytes such as sodium, potassium, and calcium, which are crucial for various bodily functions. 4. **Acid-Base Balance**: They help maintain the body's pH level by regulating the concentration of acids and bases in the blood. 5. **Erythropoiesis Regulation**: The kidneys produce and release erythropoietin, a hormone that stimulates the production of red blood cells in the bone marrow in response to low oxygen levels in the blood. 6. **Reabsorption of Nutrients**: The kidneys reabsorb essential nutrients and minerals from the filtrate back into the bloodstream, ensuring they're available for the body's use. 7. **Detoxification**: The kidneys play a role in detoxifying the blood by removing drugs and other harmful substances that may accumulate in the body.

43. Name structures found in the cortex and medulla.

44. Be familiar with the components of the nephron including glomerulus, proximal convoluted
tubule, descending loop of Henle, ascending loop of Henle, distal convoluted tubule, and collec=ng duct. In the kidneys, the cortex and medulla contain several key structures: ### Cortex Structures: - **Glomeruli**: The part of the nephron where blood filtration occurs. - **Proximal Convoluted Tubule (PCT)**: The segment of the nephron where reabsorption of water, ions, and nutrients takes place. - **Distal Convoluted Tubule (DCT)**: A portion of the nephron involved in the reabsorption of sodium and water but is more fine-tuned compared to the PCT. ### Medulla Structures: - **Loops of Henle**: Divided into descending and ascending limbs, responsible for concentrating urine and maintaining osmotic balance. - **Collecting Ducts**: The final part of the nephron where urine is concentrated by reabsorption of water and is important in regulating water balance. These structures play vital roles in the kidney's ability to filter blood, regulate electrolytes, and maintain fluid balance.

45. Describe the general function of each part of the nephron ### General Function of Each Part of the Nephron 1. **Glomerulus**: - This is the part of the nephron where blood filtration occurs. It filters out waste products and excess substances from the blood into the Bowman's capsule. 2. **Proximal Convoluted Tubule (PCT)**: - The PCT is responsible for the reabsorption of water, ions, and nutrients like glucose and amino acids back into the bloodstream. It plays a crucial role in reclaiming substances that are valuable to the body. 3. **Loop of Henle**: - Composed of two limbs: descending and ascending. The descending limb is permeable to water but not to salts, allowing for water reabsorption and concentration of the filtrate. The ascending limb is impermeable to water and actively transports salts out, which helps maintain osmotic balance and contributes to the concentration gradient in the medulla. 4. **Distal Convoluted Tubule (DCT)**: - The DCT is involved in selectively reabsorbing sodium and calcium while also assisting in the secretion of potassium and hydrogen ions into the filtrate. It fine-tunes the composition of the filtrate before it moves to the collecting duct. 5. **Collecting Duct**: - This part of the nephron is responsible for further concentrating urine by reabsorbing water under the influence of hormones such as antidiuretic hormone (ADH). It plays a significant role in regulating water balance in the body and determining the final composition of the urine before it exits the kidney.

46. Describe the basic kidney func=ons of glomerular filtra=on, tubular reabsorption, tubular
secretion, and micturition.
47. Iden=fy the major blood vessels associated with the kidney and trace the path of blood through
the kidney.
48. Be familiar with the renal vasculature including afferent arteriole, efferent arteriole, glomerulus,
peritubular capillaries and vasa recta.
49. Understand the different factors that control the glomerular filtra=on rate.
50. Know the different factors controlling renal blood flow and GFR.

APP Exam 3 Study Guide
51. Iden=fy mechanisms responsible for autoregula=on of renal blood flow.
52. Describe the effects of vasoconstrictors and vasodilators on RBF and GFR.
53. Be familiar with myogenic and tubuloglomerulus feedback mechanism