Water Balance Mechanisms and Abnormalities

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Questions and Answers

Which of the following is NOT a mechanism that regulates thirst?

Increased urine output (correct)

Hyperosmolarity

Hypovolemia

Hypotension

In which condition is hypotonic fluid primarily lost?

Diarrhea

Diabetes insipidus (correct)

Vomiting

Excessive sweating (correct)

What is the total daily water intake for an average individual as indicated?

1.3 L

2.0 L

3.0 L

2.5 L (correct)

Which physiological condition leads to decreased urine volume?

Fasting Signup and view all the answers

Which of the following correctly describes the relationship between water intake and water loss?

Water intake is equal to water loss Signup and view all the answers

What effect does hypervolemia have on the thirst center?

Inhibits thirst Signup and view all the answers

What is the daily water loss through sweating and insensible loss combined?

0.9 L Signup and view all the answers

Which condition primarily results in loss of isotonic fluid?

Heat exhaustion Signup and view all the answers

Which of the following would likely inhibit the thirst response?

Increased blood volume Signup and view all the answers

What daily water loss occurs through stool?

0.2 L Signup and view all the answers

What hormone inhibits the effect of angiotensin II on thirst?

Atrial natriuretic peptide (ANP) Signup and view all the answers

Which condition is characterized by excessive thirst due to a deficiency of ADH?

Diabetes insipidus (DI) Signup and view all the answers

What effect does hypertension have on thirst?

It inhibits thirst Signup and view all the answers

Which of the following accurately describes dehydration?

Water +/- salt depletion Signup and view all the answers

What is the primary function of anti-diuretic hormone (ADH)?

Control water loss and urine volume Signup and view all the answers

How does excessive secretion of ADH affect the body?

Causes edema and hypertension Signup and view all the answers

What type of dehydration is characterized by loss of both water and sodium?

Isotonic dehydration Signup and view all the answers

What is the primary action of aldosterone in the kidneys?

Reabsorb sodium (and water) Signup and view all the answers

Which mechanism results in the inhibition of thirst during baroreceptor stimulation?

Vagus nerve activation Signup and view all the answers

What condition can result from diuretic therapy affecting urine production?

Dehydration Signup and view all the answers

Study Notes

Water Balance

Water balance is maintained when water intake equals water loss.
Daily water intake comes from drinking, food and metabolism (1.3L, 0.9L, and 0.3L respectively).
Daily water loss comes from urine, stool, and sweating/insensible loss (1.4L, 0.2L, and 0.9L respectively).

Objectives

Explain the mechanism of water balance.
Relate water balance to common conditions like diarrhea, excessive sweating, burns, and diabetes insipidus.

Physiological Abnormalities of Water Balance

Exercise: Increased water loss (sweating, hyperventilation) balanced by decreased urine volume and increased intake.
Fasting: Decreased water intake balanced by decreased urine volume and increased intake.
High temperature: Increased water loss balanced by decreased urine volume and increased intake.

Pathological Abnormalities of Water Balance

Vomiting: Loss of isotonic fluid.
Diarrhea: Loss of isotonic fluid.
Diabetes insipidus: Loss of hypotonic fluid.
Burn: Loss of hypotonic fluid.
Heat exhaustion/excessive sweating: Loss of hypotonic fluid.
Hyperventilation: Loss of hypotonic fluid.
Excessive IV fluid: Excess isotonic fluid.
Excessive drinking (Psycogenic): Excess hypotonic fluid.

Control of Water Intake

Thirst center: Located in the hypothalamus.
Stimuli for thirst: Hyperosmolarity, hypovolemia, hypotension, angiotensin II.
Inhibitors of thirst: Opposite factors + ANP.
- Osmoreceptors: Located in the hypothalamus and respond to hyperosmolarity in the ECF (extracellular fluid), causing shrinking of the dendrites.

Control of Water Loss

Involves: Kidneys and hormones (e.g., ADH).
Kidneys: Reabsorb >99% of filtered water in glomeruli.
- About 7–13% reabsorption by ADH action.

Antidiuretic Hormone (ADH)

Deficiency of ADH: Increases urine volume (up to 23L/day), causing excessive thirst = diabetes insipidus (DI).
Excessive ADH secretion: Reduces urine volume, leads to hypertension and edema due to water retention = Syndrome of Inappropriate ADH Secretion (SIADH).

Dehydration

Water +/− salt depletion
Types: Isotonic, hypotonic, hypertonic
- Isotonic: caused by diarrhea or vomiting, no change in ECF and ICF osmolarity, no change in ICF and ECF volume.
- Hypotonic: caused by adrenal insufficiency/low aldosterone, decreased ECF osmolarity, increased ICF volume, decreased ICF osmolarity.
- Hypertonic: caused by Diabetes, sweating or diuretics, increased ECF osmolarity, decreased ICF volume, increased ICF osmolarity.

General Symptoms & Signs of Dehydration

Thirst
Dry mouth
Rapid heartbeat
Headache
Dry skin
Decreased urination

Treatment of Dehydration

Depends on the type.
Treatment of the cause.
Intravenous (IV) fluids.
Oral Rehydration Salts (ORS).

Effects of IV Solutions on Body Fluid Compartments

Isotonic: No change in ECF or ICF osmolarity or volume.
Hypotonic: Increased ECF volume, decreased ECF osmolarity, increased ICF volume and decreased ICF osmolarity.
Hypertonic: Increased ECF osmolarity, decreased ICF volume, decreased ICF osmolarity.

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Description

This quiz explores the concept of water balance in relation to daily intake and loss. It covers physiological and pathological abnormalities affecting water balance, including the effects of exercise, fasting, and conditions such as diarrhea and diabetes insipidus. Test your understanding of how the body regulates water homeostasis.