Biomedical Engineering Reference
In-Depth Information
12.5
Compartmental analysis is a technique that is used to describe the movement of various
solutes throughout different systems. Fick's law of diffusion is the governing equation for
this type of analysis. It states that
dc
dx
Solving this for a simple two-compartment system, the change in concentration of a single
species would be
dc
dt
52
DA
V
c
0
V
2
12.6
Dialysis is a method used to remove wastes from the blood, when the kidneys are no longer
functioning properly or efficiently. An extracorporeal device is designed with both a blood
compartment and a filtrate compartment. The direction of blood flow and filtrate flow is
typically opposing to maintain a concentration gradient along the entire device.
12.7
Renal calculi appear when the urine becomes supersaturated with salts. These salts can
crystallize, and therefore, they are no longer in solution. As these crystals pass through the
nephron (or kidney) they can become lodged within the tube, thus preventing flow through
that tube. The majority of renal calculi are formed from calcium salts.
dc
1
dt
1
DA
Δ
c
1
ð
V
1
1
V
2
Þ
V
1
V
2
DA
Δ
5
x
x
HOMEWORK PROBLEMS
12.1
The functional unit of the kidney is the nephron. Discuss some of the important functions
that the nephron performs and how the nephron performs those functions.
12.2
Urine formation involves all of the following process except which of the following and why?
(a)
reabsorption of water
(b)
reabsorption of particular solutes
(c)
hydrostatic pressure within the glomerular capillaries
(d)
secretion of excess nutrients
(e)
filtration of blood
12.3
What is the effect of having two capillary beds within the renal circulation? How is the
blood flow regulated within each of these capillary beds?
12.4
By increasing the diameter of the afferent arteriole and decreasing the diameter of the
efferent arteriole, what effect can one predict to occur for the glomerular filtration rate?
12.5
Discuss the juxtaglomerular complex functions and locations.
12.6
Calculate the expected filtered load for potassium ions, chlorine ions, and calcium ions.
What would you anticipate the percent reabsorption for each of these ions to be? Why?
12.7
There are some compounds that are filtered by the kidneys but not reabsorbed (such as
mannitol). Would a sudden increase in the mannitol concentration have an effect on the
glomerular filtration rate and the amount of urine produced? If it has an effect, why?
12.8
The daily elimination of magnesium is approximately 0.15 g/day at a concentration of
14 mg/dL. Calculate the amount filtered and amount reabsorbed if we assume that the
nephron does not secrete any magnesium.
12.9
Cellular matter enters the nephron at a rate of approximately 600 cells/mL of urine pro-
duced (combined red blood cells and white blood cells). What are some of the reasons
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