Regulation of Fluid and Electrolyte Balance, Exercises of Chemistry

Download Regulation of Fluid and Electrolyte Balance and more Exercises Chemistry in PDF only on Docsity!

REGULATION OF FLUID &

ELECTROLYTE BALANCE

REGULATION OF FLUID & ELECTROLYTE BALANCE

The kidney is the primary organ that maintains the total volume, pH, and osmolarity of the extracellular fluid within narrow limits. The kidney accomplishes this by altering urine volume and osmolarity. The kidney, in turn, is regulated by neural, hormonal, and local factors. In today’s lab we will study how the kidney responds to changes in the composition of the extracellular fluid.

OBJECTIVES: After completing this activity, students will be able to:

1. define fluid and electrolyte balance and to discuss the kidney’s role in its regulation.
2. understand the role of antidiuretic hormone (ADH), aldosterone, renin, and atrial natriuretic peptide (ANP) in regulating fluid and electrolyte balance and in maintaining homeostasis.
3. predict how changes in blood volume and osmolarity will alter urine composition (color, transparency, volume, specific gravity, and chloride concentration.)
4. analyze the results of case studies and explain the hormonal regulation occurring in each condition.
5. prepare and interpret graphs
6. use flow charts to model physiological changes that occur in response to disturbances in osmolarity or plasma volume.
7. use principles from chemistry (concentration and osmolarity), physics (specific gravity, density, transparency), mathematics (graphs, means), and physiology to explain the body’s responses to perturbations in fluid and electrolyte balance.
8. collaborate with team members to evaluate case studies.
9. communicate conclusions generated from the case studies during a class presentation
10. relate the changes in plasma osmolarity and volume that occur in these case studies to real world situations that may occur.

REGULATION OF FLUID AND ELECTROLYTE BALANCE

Have you ever noticed the need for a drink after eating that large bucket of popcorn at the movies? Or on television, patients entering the ER with substantial blood loss are immediately given intravenous fluids (an IV)? Both scenarios relate to fluid and electrolyte balance. What do these terms mean? Fluid refers to water. For water balance to occur, water intake through

these mechanisms, homeostasis is restored.

Atrial natriuretic peptide (ANP) is a hormone that promotes both fluid and sodium loss by the kidneys. The name natriuretic actually means “salt excreting.” ANP release from the atria is stimulated when blood volume and pressure are elevated. ANP has three major effects: 1) it decreases aldosterone release, resulting in a decrease in sodium reabsorption and increased sodium loss in the urine; 2) it decreases ADH release, which decreases water reabsorption and increases water loss to lower blood volume and pressure; and 3) it decreases thirst.

BLOOD VOLUME AND OSMOLARITY AFFECT THE VOLUME AND

COMPOSITION OF URINE

The volume and composition of urine reflect one's state of hydration. For example, if Phil Physiology has a low fluid intake and becomes dehydrated, he will excrete a small volume of concentrated urine. His body is trying to conserve water. Concentrated urine has a high specific gravity. Specific gravity is the ratio of the weight of a substance to the weight of an equal volume of water. Water has a specific gravity of 1.000, since equal volumes of water have equal weights at equal temperatures. The specific gravity of normal urine ranges from 1.001 to 1.035 and depends on the amount of solutes. The greater the concentration of solutes, the higher the specific gravity will be. At the other extreme, Anna Anatomy has a high fluid intake and is over-hydrated. She will excrete a large volume of dilute urine having a low specific gravity.

Let’s explore four specific cases in which blood volume and/or blood osmolarity has been perturbed. Use your understanding of the factors that regulate hormone release and the subsequent actions of the hormones to predict the effects of these perturbations on urine volume and osmolarity.

ACTIVITY: For each case, work with your team to predict how the parameters listed would be altered (increased, decreased, or not changed.) Put an , , or nc (no change) on each line. The information in the introduction to this lab will be helpful!

A practice table to help you summarize these hormones and their actions is located on page 15.

CASE I: BLOOD VOLUME EXPANSION / NO CHANGE IN BLOOD

OSMOLARITY

Can you think of a situation in which blood volume would be increased and blood osmolarity would be unchanged?

---

SITUATION: Blood volume: Ý Blood osmolarity: no change Ý^ Blood volume

___ Blood pressure

Y ___ Atrial naturetic peptide (ANP)

___ water reabsorption in DCT and CD ___ blood volume and pressure ___ water in urine

___ ADH ___ Thirst ___ Aldosterone

___ blood volume after drinking water

___ sodium reabsorption in DCT and CD ___ sodium excretion in the urine

CASE II: Blood Volume Expansion and Decrease in Osmolarity

Can you think of a situation in which blood volume would be increased and blood osmolarity would be decreased?

---

CASE IV: Blood Volume Depletion and No change in Blood Osmolarity

Can you think of a situation in which blood volume is decreased and blood osmolarity would be unchanged?

---

SITUATION: Blood volume: decrease Blood osmolarity: no change

ò Blood osmolarity

___ sodium reabsorption in DCT and CD

Angiotensionogen Angiotensin I Angiotensin II

___ blood vessel diameter

___ Blood pressure

___ renin release from juxtaglomerular apparatus

___ BP

___ aldosterone

Water follows sodium in urine

Renin

Angiotensin converting enzyme (ACE)

ACTIVITY: Group Reports.

1. Present your cases to the class. Justify your predictions and discuss them with your classmates and instructor.

Notes:

2. How will urine volume, specific gravity, and urine NaCl be affected in each case? Summarize your predictions in Table 9-1 below. After you have done this review this with your classmates. Table 9- Case

Urine Volume Increase, Decrease or No Change

Specific Gravity Increase, Decrease or No Change

Urine NaCl Increase, Decrease or No Change Blood Volume Expansion/ No change in Osmolariy Blood Volume Expansion/ Decrease in Osmolarity Blood Volume Unchanged/ Osmolarity increased Blood Volume Depletion/ No change in osmolarity

DRY LAB EXPERIMENT

In a lab experiment, a class of A & P students divided into one of the four groups below to drink the following solutions:

GROUP SOLUTION DRUNK

NORMAL FLUID INTAKE 25 ml of distilled water ISOTONIC SOLUTION 1 liter of 0.9% saline WATER LOADED 1 liter of distilled water SALT LOADED 150-250 ml of 2.0% saline

Please note: None of the groups were asked to significantly decrease blood volume as in one of the cases presented earlier. Why?

Before the experiment began each group voided their urine into a container labeled Time Zero. Each group then drank their assigned solution.

10

Group Color

Specific Gravity Volume NaCl Color

Specific Gravity Volume NaCl Color

Specific Gravity Volume NaCl Color

Specific Gravity Volume NaCl ml mg/ml ml mg/ml ml mg/ml ml mg/ml Unknown A yellow 1.025 35 8 pale yellow 1.01 60 4 no color 1.004 265 2 no color 1.001 285 1 Unknown B yellow 1.022 36 7 yellow 1.024 35 12 dark yellow 1.028 26 22 dark yellow 1.031 20 24 Unknown C yellow 1.023 29 8 yellow 1.022 56 9 pale yellow 1.017 85 12 pale yellow 1.022 125 15 Unknown D yellow 1.021 33 8 yellow 1.017 38 8 yellow 1.017 33 9 yellow 1.018 27 9

Time 0 Time 30 minutes Time 60 minutes Time 90 minutes

table below. However, the groups did not identify the solutions they drank! The data appears on the table as Unknowns A to D in no particular order.

EXPERIMENTAL DATA (Table 9-3): Mystery Results. Which of the four solutions did each of the “unknown groups” drink? Table 9-3.

ACTIVITY : DATA ANALYSIS.

1. GRAPHING: Prepare three graphs using the data from the table on the previous page: a. specific gravity vs. time b. volume (ml/min) vs. time c. NaCl (mg/ml) vs. time

On each graph, plot the data for each of the four unknown groups. You will need to choose axes that encompass the data for all of the unknowns. After plotting, be sure to label each line. Alternately, your instructor may direct you to prepare graphs using Excel.

Graph A. Changes in Urine Specific Gravity

1

1.

1.

1.

0 30 60 90

Time (Min)

Specific Gravity

11

0 30 60 90

Time (Min)

Volume (mls)

Graph B. Changes in Urine Volume

Graph C. Changes in Urine NaCl

0

5

10

15

20

0 30 60 90

Time (Min)

Chloride (mg/ml)

ACTIVITY: EXPLAINING THE MECHANISMS

1. Which group produced the greatest urine volume during the 90-minute period? Explain why.
2. Which group produced urine with the lowest specific gravity and chloride content? Explain why.
3. Explain the differences in color between the urine of the water loaded group and the urine of the salt-loaded group.
4. Which group produced a small volume of concentrated urine? Explain why.
5. Which group was trying to conserve water? Conserve salt?
6. How did the specific gravity of the urine produced by the salt-loaded group compare with that of the isotonic loaded group? Explain the differences.

7. How did the volume of urine output compare to the volume drank in each group? Explain the differences.
8. What hormone was inhibited in the salt loaded group? What hormone was stimulated?
9. Which hormone was inhibited in the water loaded group? What hormone was stimulated?
10. Which group was thirsty? What is the mechanism responsible?
11. Which group had elevated levels of Atrial Natriuretic Peptide? What are the benefits of high ANP levels under these conditions?

Check your understanding!

1. Define fluid and electrolyte.
2. What is osmolarity and what is the normal value for blood osmolarity?
3. What is the major ion that contributes to blood osmolarity?
4. Describe how the body regulates osmolarity and blood volume.
5. What is ADH? Where is it produced? What causes it to be secreted? What is its action? What affect does it have on blood osmolarity, blood volume, urine osmolarity, and urine volume?
6. What is aldosterone? Where is it produced? Name three factors that lead to aldosterone release. What is its action? What effect does aldosterone have on blood osmolarity and urine osmolarity?
7. What is renin? Where is it produced? What factors cause renin to be released? Describe in detail how renin leads to the production of angiotensin II? What are the 2 major actions of angiotensin II?
8. What is atrial natriuretic peptide? Where is it produced? What factors lead to its release? What is its action? What effect does it have on blood volume and urine volume?
9. In the dry lab, students divided into four groups that drank 4 different fluids: normal fluid intake (25 ml water), isotonic solution (1000 ml 0.9% sodium chloride), water loaded (1000 ml water) and salt loaded (150 ml 2% sodium chloride). For each of the four groups, how did the solution drunk affect blood osmolarity and blood volume? Predict how drinking these four solutions would affect urine color, urine volume, specific gravity, and chloride content. What hormones are stimulated and inhibited in each of these conditions? What events cause the observed changes? Which group was thirsty and why? Be able to examine experimental data in both numerical and graphical form and predict what group produced it and what mechanisms were working to produce this data.

0

5

10

15

20

25

0 30 60 90

[NaCl] (mg/ml)

time (min)

Specific gravity Volume [Cloride]

Sample Graphs