Passage
The electric capacitance of biological tissues serves as the basis for numerous medical technologies. For example, dielectric spectroscopy glucose reading (DSGR) is a noninvasive diagnostic technique that uses the electric capacitance of blood to estimate blood glucose levels.A DSGR device records the electric current that results from applying a voltage source to the skin and underlying blood vessels. DSGR can be modeled by the circuit shown in Figure 1, in which V represents the applied potential, C_B represents the capacitance of the blood, and R_E, R_D, and R_B represent the electrical resistances of the epidermis, the dermis, and the blood, respectively.
Figure 1 DSGR circuit model including skin and superficial blood vesselThe capacitance of charged blood may be explained by red blood cell membranes acting as physical barriers that separate electrons introduced into the blood from positively charged ions in the red blood cell cytoplasm. The dielectric constant k of red blood cell membranes varies with glucose concentration (Figure 2) because glucose uptake by red blood cells alters the activity of membrane-bound proteins that regulate the flow of ions into and out of the cell.
Figure 2 Blood dielectric constant vs blood glucose concentrationDSGR readings vary with blood glucose concentration because the time needed to fully charge the blood is related to total blood capacitance. However, interpreting DSGR readings may be complicated by changes in biological variables other than blood capacitance. For example, the resistivity of blood varies in accordance with osmolarity such that changes in diet or hydration status influence the current measured by DSGR devices.
Livshits, L. et al. Dielectric response of biconcave erythrocyte membranes to D- and L-glucose. J. Phys. D: Appl. Phys. 40 (2007) , 15-19.
-Which of the following statements best describes the behavior of the circuit in Figure 1 when the fully charged capacitor (comprising red blood cells) is discharged?

Question

Passage
The electric capacitance of biological tissues serves as the basis for numerous medical technologies. For example, dielectric spectroscopy glucose reading (DSGR) is a noninvasive diagnostic technique that uses the electric capacitance of blood to estimate blood glucose levels.A DSGR device records the electric current that results from applying a voltage source to the skin and underlying blood vessels. DSGR can be modeled by the circuit shown in Figure 1, in which V represents the applied potential, C_B represents the capacitance of the blood, and R_E, R_D, and R_B represent the electrical resistances of the epidermis, the dermis, and the blood, respectively.

Figure 1 DSGR circuit model including skin and superficial blood vesselThe capacitance of charged blood may be explained by red blood cell membranes acting as physical barriers that separate electrons introduced into the blood from positively charged ions in the red blood cell cytoplasm. The dielectric constant k of red blood cell membranes varies with glucose concentration (Figure 2) because glucose uptake by red blood cells alters the activity of membrane-bound proteins that regulate the flow of ions into and out of the cell.

Figure 2 Blood dielectric constant vs blood glucose concentrationDSGR readings vary with blood glucose concentration because the time needed to fully charge the blood is related to total blood capacitance. However, interpreting DSGR readings may be complicated by changes in biological variables other than blood capacitance. For example, the resistivity of blood varies in accordance with osmolarity such that changes in diet or hydration status influence the current measured by DSGR devices.
Livshits, L. et al. Dielectric response of biconcave erythrocyte membranes to D- and L-glucose. J. Phys. D: Appl. Phys. 40 (2007) , 15-19.
-Which of the following statements best describes the behavior of the circuit in Figure 1 when the fully charged capacitor (comprising red blood cells) is discharged?

Quizplus · Accepted Answer

11ecba2d_12ca_fbe0_a3bf_0d4b39b5248d_MD0008_00 The arrangement of components in electric circuits affects the overall behavior of the circuit and the electric phenomena that occur at each circuit component. For example, series circuits position electrical components in succession and form a single channel through which a fixed quantity of current passes. In contrast, parallel circuits position circuit components side by side and have multiple channels through which current can flow. These differences alter the behavior of circuit components. For resistors in series, the current (I) passing through each resistor is constant because charge entering a resistor series cannot accumulate. As a result, the voltage drop associated with any given resistor results from its own intrinsic resistance R. However, the voltage drop that occurs over the course of a series of resistors is cumulative and equal to the source voltage (V): 11ecba2d_12ca_fbe1_a3bf_b3b9bcafa316_MD0008_00 Resistors in parallel act as multiple channels through which current can flow. Consequently, the current traveling through each resistor varies in accordance with its own unique resistance. However, the voltage drop that occurs as current crosses each resistor is identical because all resistors experience the same electric potential from the source voltage: 11ecba2d_12cb_22f2_a3bf_257cd8350fce_MD0008_00 During DSGR, the biological resistances formed by the blood (R_B) and epidermis (R_E) oppose the flow of current between terminals of the DSGR device. R_B and R_E are arranged in parallel, so the voltage drop across each will be identical to the voltage of the device (V_DSGR): 11ecba2d_12cb_22f3_a3bf_8d2456103bc3_MD0008_00 (Choices A and D) For the current traveling across R_B and R_E to be identical, both resistors would either have to be placed in series or the resistance of each resistor would have to be identical. R_B and R_E are arranged in parallel, and the individual resistance of both resistors is unknown. (Choice C) The current traveling through the blood is impacted by the value of R_B in relation to the other resistances within the circuit. No conclusions about the current can be reached without knowing the resistance values of all elements. Educational objective: Circuit components may be placed in series (positioned successively) or in parallel (positioned side by side). For resistors in parallel, the voltage drop across each resistor is identical. For resistors in series, the current passing through each resistor is identical.

Passage The Electric Capacitance of Biological Tissues Serves as the Basis