Download 12 Homeostasis

Laboratory
12
Homeostasis
(LM pages 157–171)
Time Estimate for Entire Lab: 1.5 hours
Seventh Edition Changes
This was lab 11 in the previous edition. Section 12.3 Kidneys was reorganized; Nephron Structure and
Circulation is new. The Experimental Procedure: Urinalysis was clarified.
New or updated figure: 12.8 Capillary exchange
MATERIALS AND PREPARATIONS1
12.1 Lungs (LM pages 158-160)
_____
slide, prepared: lung tissue (Carolina 31-5670, -5684)
_____
microscopes, compound light
_____
lens paper
12.2 Liver (LM pages 161-163)
_____
wax pencils
_____
rulers, plastic millimeter
_____
test tubes and racks
_____
model, liver (Carolina 56-6902)
_____
simulated serum samples
_____
Benedict’s reagent solution—50 ml per student group (Carolina 84-7111, -7113)
_____
boiling water bath
_____ hot plate
_____ boiling chips, pumice
_____ thermometer, Celsius
_____ beaker
_____ beaker clamps
_____ test-tube clamp
Test tubes. The exercises in this laboratory require students to add solutions to test tubes. As an expedient,
the students are asked to mark off the tubes at various centimeter levels with a ruler and then to fill to these
marks. You may prefer to have students use a standard method of measuring volume, such as with a graduated cylinder or a pipette. Most experiments use the standard size test tube. A few experiments require the
large size test tube. Mini test tubes can be substituted for most laboratory exercises as long as the total volume in a given tube does not exceed 9 cm. This will reduce the volume of reagents used by approximately
one-third.
Test tube sizes/volumes are as follows:
Mini
13 100 mm (Carolina 73-0008)
Standard
16 150 mm (Carolina 73-0014)
Medium large
20 150 mm (Carolina 73-0019)
Large
25 150 mm (Carolina 73-0025)
1
1 cm = 1.0 ml
1 cm = 1.5 ml
1 cm = 2.4 ml
1 cm = 4.0 ml
Note: “Materials and Preparations” instructions are grouped by exercise. Some materials may be used in more than one exercise.
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Simulated serum samples (glucose solutions). Prepare a stock glucose solution by adding (while stirring)
40 g of dextrose (D-glucose) to 40 to 50 ml of heated distilled water. Increase volume to 100 ml. Determine
the amount of each solution that will be needed, and add this amount of water to six flasks or beakers. Mark
the containers as indicated, and add stock dextrose, so that they contain the correct relative amounts of
dextrose:
A2 same as A1
A1 low glucose
B1 high glucose
B2 least glucose
C1 middle glucose
C2 same as C1
or prepare 20 ml of each glucose solution per student group as follows:
A1
B1
C1
A2
B2
C2
0.25% glucose
3% glucose
0.5% glucose
0.25% glucose
0% glucose
0.5% glucose
(dissolve 0.25 g glucose per 100 ml distilled water)
(dissolve 3 g glucose per 100 ml distilled water)
(dissolve 0.5 g glucose per 100 ml distilled water)
12.3 Kidneys (LM pages 164-169)
_____
model, kidney (Carolina 56-6917A to -6925A)
_____
Chemstrip—6 test strips (Carolina 69-5967)
_____
simulated urine sample
_____
dropping bottle, or bottle with dropper
Kidney models. Carolina Biological Supply has a large number of kidney models and model sets that vary
widely in price. See the “Models” section of the Carolina catalog to select the most appropriate one for your
needs.
Simulated urine sample. The patient is to be diagnosed as having diabetes mellitus. It would be appropriate for the sample to have a low pH and to test positive for glucose and ketones. The presence of ketones
(acetone) is caused by excessive fat metabolism. Use the stock glucose solution prepared for the serum samples in the “Liver”section of this laboratory, or prepare fresh. It is easiest to prepare synthetic urine in 1,000
ml quantities. Using a low concentration hydrochloric acid solution (0.1 M suggested), adjust the pH of 1,000
ml distilled water to pH 5, using pH paper or a pH meter. Add enough of the stock glucose solution and
acetone to yield positive tests for glucose and ketones. Approximately 5 ml of stock glucose solution and
4 ml of acetone should be adequate. Test with a dipstick, and add more if necessary. Add phenol red solution to yield a slight “urine-yellow” color if desired.
EXERCISE QUESTIONS
12.1 Lungs (LM pages 158-160)
Questions About Lung Function (LM page 158)
1. During gas exchange in the lungs, carbon dioxide (CO2) leaves the blood and enters the alveoli,
and oxygen (O2) leaves the alveoli and enters the blood. Label Figure 12.2b to show gas exchange
in the lungs. The arrows pointing inward should be labeled CO2, and the arrows pointing outward should be
labeled O2.
2. State one way the lungs contribute to homeostasis. The lungs oxygenate the blood.
3. Is blood more acidic when it is carrying carbon dioxide? yes, slightly Explain. Carbon dioxide combines with water to form carbonic acid, which dissociates to bicarbonate ions and hydrogen ions. The increase
in hydrogen ions makes the blood more acidic.
4. Is blood less acidic when the carbon dioxide exits? yes Explain. Hydrogen ions combine with bicarbonate ions to form carbonic acid, which dissociates to water and carbon dioxide. A decrease in hydrogen ions
makes blood less acidic.
5. State another way the lungs contribute to homeostasis. The lungs remove carbon dioxide.
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12.2 Liver (LM pages 161-163)
Urea Formation (LM page 161)
1. In the chemical formula for urea that follows, circle the portions that would have come from
amino groups: Circle both NH2 groups.
2. State one way the liver contributes to homeostasis. The liver makes urea, a relatively nontoxic
nitrogenous end product.
Regulation of Blood Glucose Level (LM page 162)
after eating (insulin)
—————>
glucose
glycogen
<—————before eating (glucagon)
3. State another way in which the liver contributes to homeostasis. The liver maintains the blood glucose
level.
Experimental Procedure: Blood Glucose Level After Eating (LM page 162)
Table 12.1 Blood Glucose Level After Eating
Test Tubes (in Order of Color Change)
Source of Serum
B1
Hepatic portal vein
C1
Hepatic vein
A1
Mesenteric artery
Results (LM page 163)
• Which blood vessel—a mesenteric artery, the hepatic portal vein, or the hepatic vein—contains
the most glucose after eating? hepatic portal vein
• Why do you suppose that the hepatic vein does not contain as much glucose as the hepatic portal
vein after eating? The liver removes sugar from the blood and converts it to glycogen.
Experimental Procedure: Blood Glucose Level Before Eating (LM page 163)
Table 12.2 Blood Glucose Level Before Eating
Test Tubes (in Order of Color Change)
Source of Serum
C2
Hepatic vein
A2
Mesenteric artery
B2
Hepatic portal vein
Results (LM page 163)
• Which blood vessel—a mesenteric artery, the hepatic portal vein, or the hepatic vein—contains
the most glucose before eating? hepatic vein
• Why do you suppose that the hepatic vein now contains more glucose than the hepatic portal
vein? During fasting, glycogen is being broken down in the liver into glucose in order to increase the blood
glucose level. Since the hepatic vein removes venous blood from the liver, its glucose level will be higher than
that of the hepatic portal vein, which enters the liver.
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12.3 Kidneys (LM pages 164-169)
Nephron Structure and Circulation (LM page 165)
1. With the help of Figure 12.5, list the parts of a nephron and tell whether they are located in the
renal cortex or the renal medulla. glomerular capsule (renal cortex), proximal convoluted tubule (renal
cortex), distal convoluted tubule (renal cortex), collecting duct (renal cortex and renal medulla), loop of the
nephron (renal medulla)
2. With the help of Figure 12.5 and Table 12.3, trace the path of blood toward, around, and away
from an individual nephron. Blood goes from a renal artery to an afferent arteriole, to a glomerulus, to an
efferent arteriole, to a peritubular capillary network, to a venule, to a renal vein.
Kidney Function (LM page 166)
Figure 12.6
tubular reabsorption
tubular secretion
glomerular filtration
Glomerular Filtration (LM page 167)
1. In the list that follows, draw an arrow from left to right for all those molecules that leave the
glomerulus and enter the glomerular capsule:
Glomerulus
Glomerular Capsule (Filtrate)
Cells
Proteins
Glucose
→
Amino acids
→
Salts
→
Urea
→
Water
→
2. What substances are too large to leave the glomerulus and enter the glomerular capsule? cells and
proteins
Tubular Reabsorption (LM page 167)
1. What would happen to blood pressure if water were not reabsorbed? The blood pressure would get
lower.
2. What would happen to cells if the body lost all its nutrients by way of the kidneys? The cells would
die.
3. In the list that follows, draw an arrow from left to right for all those molecules that are passively
reabsorbed into the blood. Use darker arrows for those that are actively reabsorbed.
Proximal Convoluted Tubule
Peritubular Capillary
Water
→
Glucose
→ darker arrow
Amino acids
→ darker arrow
Urea
→
Salts
→ darker arrow
4. What molecule is reabsorbed the least? urea
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Questions About Urine Formation (LM page 168)
Table 12.4 Urine Constituents
Substance
In Blood of Glomerulus
In Filtrate
In Urine
Protein (albumin)
X
—
—
Glucose
X
X
—
Urea
X
X
X
Water
X
X
X
1. What molecule is reabsorbed from the collecting duct so that urine is hypertonic? water
2. Based on this table, state one way the kidneys contribute to homeostasis. Kidneys remove waste
products from the body.
3. Which organ—the lung, liver, or kidney—makes urea? liver
4. Which organ excretes urea? kidney
5. Which organ excretes urine? kidney
6. If the blood is more acidic than normal, what pH do you suppose the urine will be? acidic
7. If the blood is more basic than normal, what pH do you suppose the urine will be? basic
8. State another way the kidneys contribute to homeostasis. Kidneys help regulate the pH of the blood.
Urinalysis (LM page 168)
Experimental Procedure: Urinalysis (LM page 168)
Figure 12.7
Tests for:
leukocytes
pH
protein
glucose
ketones
blood
Results
negative
low ph
negative
positive
positive
negative
Conclusions (LM page 169)
• According to your results, what condition might the patient have? diabetes mellitus Explain. Diabetes
mellitus is primarily diagnosed by glucose in the urine. Glucose is in the urine because insulin is not being
produced by the pancreas and the liver is not storing glucose as glycogen. Ketones appear in the urine because
the body is metabolizing fat instead of glucose. The urine has a low pH because ketones are strong organic
acids.
• Given that the patient’s blood contains excess glucose, why is the patient suffering from excessive
thirst and urination? Extra water is needed to “wash” the excess glucose from the blood.
• Since neither the liver nor the body cells are taking up glucose, why is the patient tired? Glucose is
metabolized in cells to produce ATP molecules. The patient has no energy because of the lack of glucose in the
cells.
• Since cells begin to metabolize fat when glucose is not available, why is this patient losing
weight? Metabolism of fat results in weight loss.
• The metabolism of fat can explain the low pH of the urine. Why? Fat metabolism results in ketone
bodies.
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12.4 Capillary Exchange in the Tissues (LM page 170)
1. Figure 12.8
carbon dioxide
glucose
wastes
amino acids
<
>
2. What type of pressure causes water to exit from the arterial side of the capillary? blood pressure
3. What type of pressure causes water to enter the venous side of the capillary? osmotic pressure
Questions About Homeostasis (LM page 170)
1. What organ studied in this lab exchanges gases with the external environment? lungs What gases
are exchanged? carbon dioxide for oxygen What happens to the oxygen? Oxygen leaves the alveoli of the
lungs and enters the blood.
2. In Figure 12.1, what structure digests food and puts glucose and amino acids into the bloodstream? digestive tract
3. What organ studied in this lab regulates the glucose level of the blood? liver
4. What organ studied in this lab removes urea from the blood? kidneys
5. Name several ways the kidneys contribute to homeostasis. The kidneys contribute to homeostasis by
excreting waste products and by regulating pH.
LABORATORY REVIEW 12 (LM page 171)
What process accounts for gas exchange in the lungs? diffusion
What molecule is excreted by the lungs? CO2
What are the air spaces in the lung called? alveoli
What blood vessel lies between the intestines and the liver? hepatic portal vein
In what form is glucose stored in the liver? glycogen
The liver metabolizes the amino group from amino acids to what molecule? urea
The hepatic vein enters what blood vessel? inferior vena cava
When molecules leave the glomerulus, they enter what portion of the nephron? glomerular capsule
Name a substance that is in the filtrate but not in the urine. glucose
Glucose in the urine indicates that a person may have what condition? diabetes mellitus
Name the process by which molecules move from the proximal convoluted tubule into the blood.
tubular reabsorption
12. Where does urine collect before exiting the kidney. renal pelvis
13. Does venous blood in the tissues contain more or less carbon dioxide than arterial blood? more
14. What type of pressure causes water to exit from the arterial side of the capillary? blood pressure
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Thought Questions
15. Which systemic blood vessel would you expect to have a high glucose content immediately after
eating? the hepatic portal vein Explain. The process of digestion releases glucose, which enters the blood at
the intestinal capillaries, which eventually drain into the hepatic portal vein.
16. In what ways do the kidneys aid homeostasis. The kidneys rid the body of urea and maintain the blood
volume and pH within normal limits.