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.
-To simplify calculations, mathematical models of DSGR can be generated that replace R_E and R_D in Figure 1 with an equivalent resistor R_eq. The mathematical expression for R_eq is:

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.
-To simplify calculations, mathematical models of DSGR can be generated that replace R_E and R_D in Figure 1 with an equivalent resistor R_eq. The mathematical expression for R_eq is:

Quizplus · Accepted Answer

11ecba2d_12cc_a99a_a3bf_91598fd50169_MD0008_00 Resistors are electrical components that oppose the movement of charge (ie, current) and deplete electric potential energy (ie, voltage) according to Ohm's law. The ability of a resistor to oppose the movement of current is quantified by its resistance (R), which is an extensive property (measured in ohms Ω) that is related in part to the physical dimensions of the resistor itself. Like other circuit components, groupings of two or more resistors may be placed either in series or in parallel configurations. Arranging multiple resistors in series is the same as creating one equivalent resistor (R_eq) with a resistance equal to the sum of the resistances of each individual resistor: 11ecba2d_12cc_a99b_a3bf_61e0b305a6e3_MD0008_00 Conversely, placing two or more resistors in parallel yields an equivalent resistor (R_eq) with a resistance that is less than the resistance of any one resistor in the arrangement. Specifically, the value of the equivalent resistor is given by the following expression: 11ecba2d_12cc_a99c_a3bf_0b59025a9756_MD0008_00 In this scenario, two of the resistors within the DSGR circuit (R_E and R_D) are to be replaced with an equivalent resistor when modeling DSGR. R_E and R_D are parallel because they are located side by side and share the same voltage source. Therefore, the expression for R_eq is: 11ecba2d_12cc_a99d_a3bf_df2f0df7308a_MD0008_00 Multiplying each term on the right side of the expression by a ratio equivalent to 1 gives each the same denominator: 11ecba2d_12cc_a99e_a3bf_a713cbb670e7_MD0008_00 11ecba2d_12cc_d0af_a3bf_338f140e29b2_MD0008_00 11ecba2d_12cc_d0b0_a3bf_051496d2d49d_MD0008_00 Inverting both sides of the expression above yields: 11ecba2d_12cc_d0b1_a3bf_bda037a79809_MD0008_00 Therefore, a resistor equivalent to R_E and R_D would have a resistance calculated as the product of R_E and R_D divided by the sum of R_E and R_D (Choice D). Educational objective: Resistors are circuit components that deplete electric potential energy by opposing electric current. Placing multiple resistors in series increases the total resistance whereas placing multiple resistors in parallel decreases the total resistance.

Passage The Electric Capacitance of Biological Tissues Serves as the Basis