BC1002: MODULE 1: LAB 4
EXCRETORY SYSTEM
week of February 14-18, 2005
Learning objectives:
1. To learn the anatomy and function of the excretory system.
2. To examine the components of urine.
Readings:
Asking about Life. 3rd edition, pp. 772-783.
Anatomy & Physiology for Dummies. pp. 237-253.
BC1002, Spring 2005, Module 1, Lab 4-1
Anatomy of the Excretory System
Excretory systems are involved in the disposal of metabolic wastes and the control of body fluid
composition. The kidneys maintain ion concentration and water volume by balancing the intake of
these substances with excretion (via the urine). Another important function of the kidneys is to
remove wastes from the body. Studying the structure of the excretory system helps us to understand
these functions. We will begin today’s lab by studying the anatomy of the excretory system.
Kidney
Ureters
Urinary Bladder
Internal
Sphincter
Urethra
External
Sphincter
Use the diagram on the following page as a guide to locate the underlined structures on the models
in the lab. The kidneys are dark brown, somewhat bean-shaped organs that are embedded in fat and
fibrous connective tissue on either side of the vertebral column. Blood enters the kidney through the
renal artery, which branches from the abdominal aorta. Blood leaves the kidney through the
renal vein, which empties into the inferior vena cava. Urine passes from the kidney to the urinary
bladder through the ureter. Leading from the urinary bladder to the exterior is a short tube, the
urethra. In females, the urethra is about 4 cm long, and in males, it is about 20 cm in length. The
exit of urine from the bladder is called micturition.
BC1002, Spring 2005, Module 1, Lab 4-2
The passage of urine from the bladder is controlled by two sphincter muscles: the internal
sphincter and the external sphincter. When approximately 300 ml of urine has accumulated in the
bladder, the walls of the bladder are stretched sufficiently to elicit a reflex that causes the bladder
walls to contract. These contractions force urine past the internal sphincter and into the upper
urethra. The presence of urine in this portion of the upper urethra creates the desire to micturate.
The external sphincter is under voluntary control; and thus, micturition does not occur until the
external sphincter is voluntarily relaxed.
Use the diagram to the right as a guide
to locate the underlined structures on
the model in the lab. The kidney itself
is divided into three regions. The
outermost region is called the renal
cortex, which has a somewhat granular
appearance. To the inside of the cortex
is the renal medulla. The medulla is
divided into the cone-shaped renal
pyramids, each of which terminates as
a renal papilla.
Extending down
between the pyramids are the renal
columns. The central cream-colored
region of the kidney is the renal pelvis.
The outer portions of the pelvis divide
into short tubes, the calyces (singular calyx). The papillae extend into the
calyces, and at this site the calyces
receive urine from the papillae.
The functional unit of the kidney is the nephron. There are approximately one million nephrons in
each kidney. Most nephrons are contained within the cortex, however, about 20% of them lie
partially in both the cortex and medulla. The formation of urine by the nephron is the result of three
distinct processes that occur in different regions of the nephron: (1) filtration, (2) reabsorption, and
(3) secretion.
At one end of the nephron is a bulbous structure, the renal corpuscle, which is composed of 2 parts,
an outer glomerular (or Bowman's) capsule, and an inner tuft of capillaries, the glomerulus. An
afferent arteriole leads into the glomerulus and the efferent arteriole leads out of the glomerulus.
The efferent arteriole then branches into many fine peritubular capillaries. The glomerular capsule
leads into the proximal convoluted tubule, followed by Henle's loop, which is divided, into a
descending loop and an ascending loop. Henle's loop leads into the distal convoluted tubule and
finally into the collecting duct, which eventually ends at the renal papilla.
BC1002, Spring 2005, Module 1, Lab 4-3
Blood enters the glomerulus through the afferent arteriole. High pressure within the glomerulus
causes a considerable amount of blood fluid to be forced into the glomerular capsule. Only blood
cells and large protein molecules cannot pass from the glomerulus into the glomerular capsule.
The fluid within the glomerulus contains glucose, amino acids, urea, salts, and a large amount of
water. While we want to eliminate urea from the body, we cannot afford to lose large quantities of
the other substances. The challenge for the nephron is to eliminate the urea while reclaiming the
other substances.
As the filtrate passes into the proximal convoluted tubule, essentially all the glucose and most of the
water, salts, and amino acids are reabsorbed. However, we are still losing too much water and
sodium. The descending loop of Henle is very permeable to water but not very permeable to
sodium. Consequently water moves out of the tubule, but sodium remains in the tubule. The fluid in
the tubule becomes more concentrated as it reaches the bottom of the loop. The ascending loop is
relatively impermeable to water, but sodium is actively pumped out of the tubule.
BC1002, Spring 2005, Module 1, Lab 4-4
As the fluid moves up the ascending loop, it becomes less concentrated, and by the time it reaches
the distal convoluted tubule, the composition of the fluid is little different from the fluid that entered
the descending loop. However, considerable amounts of water and sodium have been reclaimed as
the fluid passes through Henle’s loop.
After Henle's loop, the fluid enters the distal convoluted tubule. Water reabsorption here is
facilitated by antidiuretic hormone (ADH), which is released by the pituitary gland. The more
ADH released from the pituitary, the greater the water reabsorption in the distal tubule, and the more
concentrated the urine. The amount of ADH released is dependent on the hydration state of the
individual.
If you have been eating large amounts of watermelon, little ADH would be released, less water
would be reabsorbed in the distal tubule, and a dilute urine would be produced. If you are
dehydrated due to bouncing your buns off in aerobics class, more ADH would be released, more
water would be reabsorbed in the distal tubule, and a more concentrated urine would be produced.
Following the distal convoluted tubule, the fluid enters the collecting duct, and eventually leaves the
nephron at the renal papillae.
Observe the demonstration microscope slide of kidney tissue. Identify its parts.
Observe the kidney model and be sure you can identify its parts.
Kidney Function Kit: follow the instructions for the kidney function kit that will be provided
during lab.
URINE TESTING
Today in lab, you will work in pairs to test several urine samples. For each sample, you will test for
appearance, specific gravity, pH, protein, and glucose using the methods outlined below. For each
sample you test, please complete a column on the urine testing worksheet.
Appearance
The first thing to consider in a routine urine test is the visual appearance of the urine. Its color and
turbidity may suggest the presence of a pathologic condition. Normal urine varies from light straw
color to deep amber. The color of normal urine is due to a pigment called urochrome, a breakdown
product of hemoglobin. Normal urine does not have red blood cells. The appearance of red blood
cells in the urine is called hematuria. One cause of hematuria is acute inflammation of the urinary
organs as a result of disease or irritation from kidney stones. Other causes include tumors and
trauma in the excretory system. Although abnormal color may indicate pathology, some foods and
drugs can change the urine color without pathological significance.
BC1002, Spring 2005, Module 1, Lab 4-5
Specific gravity
Specific gravity is a measure of the density of a solution. Pure water has a specific gravity of 1.00.
When other substances are dissolved in water the specific gravity of the solution increases. Normal
urine has a specific gravity of 1.015 to 1.025. A low specific gravity will be present in chronic
nephritis, in which the rate of tubular reabsorption is low, and diabetes insipidus (a condition
different from diabetes mellitus). A high specific gravity may indicate diabetes mellitus, fever, or
acute nephritis.
To determine the specific gravity of urine:
1. Fill a urinometer cylinder 3/4 full of urine (there will be a mark on the side). Remove any
foam using a strip of paper toweling.
2. Insert the hydrometer into the urine and read the value on the stem where it intersects the
bottom of the meniscus. Make sure that the hydrometer is not touching the sides when
you take the reading.
3. Take the temperature of the urine and calculate the adjusted specific gravity.
Hydrometers are calibrated for a specific temperature; ours are calibrated for either 20º C
or 60º F (15.5º C). Look at the hydrometer scale to determine the calibration temperature.
If the temperature is greater than the calibrated temperature add 0.001 for each 3º C;
subtract 0.001 for each 3º C below the calibrated temperature.
Please see Appendix M1-L4 –1 for information on converting between Celsius degreesand
Fahrenheit degrees.
Protein
Protein is normally not present in the urine because the large size of protein molecules prevent them
from being filtered out of the blood in the glomerulus. When protein is present in the urine, the
condition is called albuminuria. Physiologic albuminuria can occur due to excessive muscular
exertion, prolonged cold baths, or excessive ingestion of protein. Pathologic albuminuria can occur
due to kidney congestion (higher filtration pressure), toxemia of pregnancy, febrile diseases, and
some anemias in which large amount erythrocyes break down. We will test for the presence of
protein with two methods. The first is the test strip; follow the instructions for their use. It is not
uncommon for women to test positive for protein in their urine at trace levels. This is usually of no
particular importance. Several other tests can be used to detect protein. All of these methods cause
protein to precipitate due to heat or chemical treatment. We will use Exton's method for detection of
protein in the urine.
Exton’s method:
1. Pipette 1 ml of urine and 1 ml of Exton's reagent into a test tube. Mix thoroughly.
2. Heat the mixture in a boiling water bath for a few minutes. If a precipitate forms in the
tube, protein is present in the urine.
BC1002, Spring 2005, Module 1, Lab 4-6
Hydrogen ion concentration
Freshly voided urine will normally have a pH ranging from 4.8 to 7.5, with an average pH of 6. The
pH will vary with the time of day the sample was collected and the diet. As a urine sample ages, it
becomes more alkaline. Urine test sticks will normally be used to determine the pH. To determine
the pH of your urine, dip a pH testing strip into the urine and match the color to the key on the side
of the strip tube.
Glucose
Glucose is normally present in the urine at very low concentrations (0.01 to 0.03 mg/100 ml). While
glucose freely passes from the blood into the glomerular filtrate, it is normally reabsorbed in the
proximal convoluted tubule. Glucosuria, the presence of glucose in the urine, occurs when an
individual suffers from diabetes mellitus. Persons with diabetes mellitus either release insufficient
amounts of the hormone insulin from their pancreas or their tissues are unresponsive to insulin. One
of the important functions of insulin is that it facilitates the transport of glucose from the blood into
cells. When insulin levels are insufficient, glucose is not transported into cells normally; thus, blood
glucose levels are elevated. The glucose levels in the glomerular filtrate directly reflect blood
glucose levels. The kidney has the ability to reabsorb up to 180 mg of glucose per 100 ml of
glomerular filtrate. If blood glucose levels exceed this amount, the kidneys cannot reabsorb all of
the glucose, and glucose will appear in the urine. We will look for the presence of glucose in urine
using both test sticks and Benedict's reagent. For the Benedict's test perform the following:
1. Label test tubes for the 4 samples of urine.
2. Pour 5 ml of Benedict's reagent into each tube.
3. Add 0.5 ml of urine to each tube.
4. Place the tubes in a boiling water bath for 5 min. Determine the amount of glucose
present using the following chart.
Color
Amount of Glucose
blue to cloudy green
yellowish green
greenish yellow
yellow
orange
red
negative
0.5 - 1 gm%
1 - 1.5 gm%
1.5 - 2.5 gm%
2.5 - 4 gm%
> 4 gm%
Test results confirmation
You may confirm your results using Four Factor Urinary Test Strips. These strips will test for pH,
glucose, proteins, and ketones. Please record these on your worksheet also. You will need to
carefully follow the instructions on the side of the canister, including the timing for each test.
BC1002, Spring 2005, Module 1, Lab 4-7
Assignment due at beginning of lab
next week
Lab data worksheet, to be completed during lab as a pair of students:
For each of the urine tests you perform today, report the results of the test on the data worksheet
(page 4-9).
The following parts should be typed and submitted INDIVIDUALLY at the beginning of
lab next week:
For each of the urine tests, state the normal range of values for the test and if the urine you tested
fell outside of that range.
For each test where you found an abnormal constituent in the abnormal urine, discuss
physiologic reasons why that substance should not normally be present in urine. Although in
your report you may refer to a disease that produces this abnormality, a reference to only the
disease with no mention of the underlying physiology is not an adequate answer. You MUST
reference and correctly cite the sources of your information. Please see Appendix M1-L4-2 for
more details on citation format.
Finally, what are ketones, why would one test for them in a medical setting? Why might ketones
be elevated, what symptoms might the patient have, and how could high ketones be prevented or
eliminated? (If you use online resources to answer these questions, please be careful and use
only legitamate websites (this leads to another question: how do you determine if a website
(particularly one that gives medical information) is legitamate and medically sound?).
BC1002, Spring 2005, Module 1, Lab 4-8
BC1002
Module 1: Lab 4 Urine Testing Worksheet
Spring 2005
Names_________________________ _________________________
Sample 1
Sample 2
Sample 3
Sample 4
appearance
Normal results
specific
gravity
pH
pH strip
4-factor
strip
protein
Exton’s
method
4-factor
strip
glucose
Benedict’s
test
4-factor
strip
BC1002, Spring 2005, Module 1, Lab 4-9
Appendix M1-L4-1 (http://www.ncdc.noaa.gov/ol/climate/conversion/tempconvert.html)
Celsius to Fahrenheit Conversion Chart
°C
50
49
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
°F
122.0
120.2
118.4
116.6
114.8
113.0
111.2
109.4
107.6
105.8
104.0
102.2
100.4
98.6
96.8
95.0
93.2
91.4
89.6
87.8
86.0
84.2
82.4
°C
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
°F
80.6
78.8
77.0
75.2
73.4
71.6
69.8
68.0
66.2
64.4
62.6
60.8
59.0
57.2
55.4
53.6
51.8
50.0
48.2
46.4
44.6
42.8
41.0
°C
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
-11
-12
-13
-14
-15
-16
-17
-18
°F
39.2
37.4
35.6
33.8
32.0
30.2
28.4
26.6
24.8
23.0
21.2
19.4
17.6
15.8
14.0
12.2
10.4
8.6
6.8
5.0
3.2
1.4
-0.4
°C
-19
-20
-21
-22
-23
-24
-25
-26
-27
-28
-29
-30
-31
-32
-33
-34
-35
-36
-37
-38
-39
-40
°F
-2.2
-4.0
-5.8
-7.6
-9.4
-11.2
-13.0
-14.8
-16.6
-18.4
-20.2
-22.0
-23.8
-25.6
-27.4
-29.2
-31.0
-32.8
-34.6
-36.4
-38.2
-40.0
For greater accuracy use formula below:
To convert from Celsius to Fahrenheit:
°F =(9/5)°C+32
To convert from Fahrenheit to Celsius:
°C=(5/9) x (°F-32)
°C = temperature in degrees Celsius
°F = temperature in degrees Fahrenheit
BC1002, Spring 2005, Module 1, Lab 4-10
Appendix M1-L4-2 (http://www.ncdc.noaa.gov/ol/climate/conversion/tempconvert.html)
Literature Cited
List any publications referred to in your report alphabetically by first author; do not number them. Every
item in your bibliography should be referred to in the body of your paper, or it shouldn't be listed at all. If
you use information from an intermediary source, you should list the original reference but should also
note the intermediary: "...cited in...".
We will use the following standard forms (some journals use variations of these), shown in order for (1)
an article with one author, (2) an article with more than one author, (3) a book, and (4) a chapter from an
edited volume:
Reynolds, P.D. 1992. Mantle-mediated shell decollation increases posterior aperture size in Dentalium
rectius Carpenter 1864 (Scaphopoda: Dentaliida). Veliger 35:26-35.
Gapp, D.A., R.N. Taranto, E F. Walsh, P.J. Favorito, and Y. Zhang. 1990. Insulin cells are found in the
main and accessory urinary bladders of the painted turtle, Chrysemys picta. J. Exp. Zool. 254:332-337.
Stokes, D., L. Stokes, and E. Williams. 1991. The Butterfly Book. Little, Brown and Co., Boston. 96 pp.
Pearcy, R.W., and W.A. Pfitsch. 1994. Consequences of sunflecks for photosynthesis and growth of
forest understory plants. Pages 343-359 in E.D. Schulze and M.M. Caldwell, editors. Ecophysiology of
Photosynthesis. Springer Verlag, New York.
For information you found online: (from: http://www.apastyle.org/elecsource.html)
•
If a document is contained within a large and complex Web site (such as that for a university or a
government agency), identify the host organization and the relevant program or department
before giving the URL for the document itself. Precede the URL with a colon.
•
Use the complete publication date given on the article.
•
Note that there are no page numbers.
•
In an Internet periodical, volume and issue numbers often are not relevant. If they are not used, the
name of the periodical is all that can be provided in the reference.
•
Whenever possible, the URL should link directly to the article.
•
Break a URL that goes to another line after a slash or before a period. Do not insert (or allow your
word-processing program to insert) a hyphen at the break.
Chou, L., McClintock, R., Moretti, F., Nix, D. H. (1993).
Technology and
education: New wine in new bottles: Choosing pasts and
imagining educational futures. Retrieved August 24, 2000, from
Columbia University, Institute for Learning Technologies Web
site:
http://www.ilt.columbia.edu/publications/papers/newwine1.html
BC1002, Spring 2005, Module 1, Lab 4-11