Water and Electrolyte Balance Quiz

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Questions and Answers

What percentage of water content do adult males typically have in their bodies?

60% (correct)

70%

45%

50%

Which of the following statements about body fluid compartments is incorrect?

Adipose tissue is the most hydrated tissue in the body. (correct)

Plasma is a component of extracellular fluid.

Intracellular fluid constitutes about 25 L of body water.

Extracellular fluid comprises 20% of body weight.

How much of the total body water volume do infants have as a percentage?

60%

73% or more (correct)

50%

40%

At what age does body water content typically decline to around 45%?

Old age Signup and view all the answers

What is the total volume of body water in adults on average?

40 L Signup and view all the answers

What is the approximate daily water intake needed to maintain balance?

2500 ml Signup and view all the answers

What triggers the release of ADH when the osmolality rises?

Increase in plasma osmolality Signup and view all the answers

Which of the following accounts for the highest percentage of water output?

Urine Signup and view all the answers

What effect does a decrease in osmolality have on thirst and ADH levels?

Inhibits thirst and ADH release Signup and view all the answers

Where is the majority of water intake derived from?

Ingested foods and beverages Signup and view all the answers

What occurs when there is an increase in extracellular fluid potassium concentration (K+)?

Decreased resting membrane potential Signup and view all the answers

What is the primary site of potassium balance regulation in the kidneys?

Distal convoluted tubule Signup and view all the answers

How does acidosis affect extracellular fluid potassium levels?

K+ levels rise Signup and view all the answers

What can result from a disruption in potassium levels in the heart?

Irregular electrical conduction Signup and view all the answers

What role does aldosterone play in potassium balance?

Stimulates secretion of K+ into the filtrate Signup and view all the answers

What is the primary consequence of hypotonic hydration?

Cells swell due to an excess of water Signup and view all the answers

What is edema primarily characterized by?

Atypical accumulation of interstitial fluid Signup and view all the answers

Which ion is designated as the most abundant cation in the extracellular fluid (ECF)?

Sodium (Na+) Signup and view all the answers

What initiates the sensation of thirst in an individual?

Stimulation of osmoreceptors Signup and view all the answers

How does sodium influence water distribution in the body?

Water follows sodium, controlling ECF volume Signup and view all the answers

Which physiological response occurs when ECF osmolality increases?

Stimulated thirst mechanism Signup and view all the answers

What triggers the release of aldosterone?

Increased potassium levels in ECF Signup and view all the answers

How does water absorption from the gastrointestinal tract affect plasma volume?

It increases plasma volume Signup and view all the answers

What characteristic of angiotensin II is crucial for its role in regulating blood pressure?

It stimulates the secretion of aldosterone Signup and view all the answers

What role does renin play in sodium balance regulation?

It catalyzes the production of angiotensin II Signup and view all the answers

What physiological process describes the relationship between Na+ and water balance?

Water levels adjust primarily based on solute concentration in the blood Signup and view all the answers

What triggers the release of granular cells in the kidney?

Dry mouth Signup and view all the answers

What is NOT a possible effect of edema on tissue function?

Decreased interstitial pressure Signup and view all the answers

Which mechanism counteracts increased ECF osmolality?

Antidiuretic hormone secretion Signup and view all the answers

What is the primary result of osmoreceptor stimulation in the hypothalamus?

Increased thirst and fluid intake Signup and view all the answers

What is the consequence of water moistening the mouth and throat?

Stretching the stomach and intestine Signup and view all the answers

What physiological response is triggered when there is low blood calcium (hypocalcemia)?

Release of parathyroid hormone (PTH) Signup and view all the answers

Which of the following actions does PTH NOT promote?

Decreased calcium absorption in the small intestine Signup and view all the answers

How does chloride ion (Cl–) reabsorption typically occur in the kidneys?

It passively follows sodium (Na+) in the proximal convoluted tubule (PCT) Signup and view all the answers

What occurs during acidosis in relation to chloride ion reabsorption?

Fewer chloride ions are reabsorbed in favor of bicarbonate (HCO3–) Signup and view all the answers

Which of the following statements about PTH is true?

It stimulates osteoclast activity to release calcium into the blood Signup and view all the answers

What is the primary role of chloride ions in extracellular fluid (ECF)?

Maintenance of osmotic pressure Signup and view all the answers

Which mechanism is responsible for chloride reabsorption in the nephron?

Coupling to sodium active transport in kidney tubules Signup and view all the answers

What result does PTH have on the kidney tubules?

Stimulates calcium reabsorption Signup and view all the answers

Study Notes

Water, Electrolyte, & Acid-Base Balance

Body Water Content:
- Infants have 73% or more water (low body fat, low bone mass)
- Adult males have ~60% water
- Adult females have ~50% water (higher fat content, less skeletal muscle mass)
- Adipose tissue is the least hydrated tissue
- Total body water in adults averages ~40 liters
- Water content declines to ~45% in old age

Body Fluid Compartments

Total body water: 40 liters, 60% of body weight
Intracellular fluid (ICF): 25 liters, 40% of body weight
Interstitial fluid (IF): 12 liters, 80% of extracellular fluid (ECF)
Plasma: 3 liters, 20% of ECF
Extracellular fluid (ECF): 15 liters, 20% of body weight

Composition of Body Fluids

Electrolytes:
- Dissociate into ions in water
- Examples: inorganic salts, all acids and bases, some proteins
- Conduct electrical current
- Greater osmotic power than nonelectrolytes
- Greater ability to cause fluid shifts
- NaCl → Na+ + Cl− (electrolyte; 2 particles)
- MgCl2 → Mg2+ + 2Cl− (electrolyte; 3 particles)
- Glucose → glucose (nonelectrolyte; 1 particle)

Electrolyte Composition of Body Fluids

Sodium (Na+) is super abundant in ECF
Potassium (K+) abundance is super in ICF
Other electrolytes (calcium, magnesium, chloride, bicarbonate, phosphate, sulfate) present in both ECF and ICF, but with different concentrations.

Exchange of Gases, Nutrients, Water, and Wastes

Exchange occurs between lungs, gastrointestinal tract, and kidneys, as well as blood plasma, interstitial fluid, and intracellular fluid.

Water Balance and ECF Osmolality

Water intake must equal water output (~2500 ml/day)
Water intake comes from ingested foods and beverages, and a small amount from metabolism (metabolic water)
Water output includes urine (60%), insensible water loss (skin and lungs), perspiration, and feces

Water Balance and ECF Osmolality Regulation

Osmolality is maintained around 280-300 mOsm
Rise in osmolality:
- Stimulates thirst
- Causes ADH release
Decrease in osmolality:
- Causes thirst inhibition
- Causes ADH inhibition

Major Sources of Water Intake and Output

Average daily intake: 2500 ml
Average daily output: 2500 ml
Intake sources: beverages (60%), foods (30%), metabolism (10%)
Output sources: urine (60%), insensible loss (skin, lungs) (28%), sweat (8%), feces (4%)

Regulation of Water Intake

Thirst is the driving force for water intake
Governed by the hypothalamic thirst center
Hypothalamic osmoreceptors detect ECF osmolality and are activated by:
- Increased plasma osmolality of 1-2%
- Dry mouth
- Decreased blood volume or pressure
- Angiotensin II or baroreceptor input

Regulation of Water Intake: Mechanisms and Consequences of ADH Release

Osmoreceptors detect changes in ECF osmolality and trigger ADH release.
Increased ADH increases water reabsorption in the kidneys, resulting in concentrated urine and increased blood volume.
Decreased blood ADH release results in dilute urine, decreased blood volume

Water Balance Disorders

Dehydration: ECF water loss due to hemorrhage, burns, prolonged vomiting/diarrhea, sweating, water deprivation, or endocrine disturbances; symptoms include “cottony” oral mucosa, thirst, dry/flushed skin, and oliguria; can lead to noticeable weight loss, fever, mental confusion, hypovolemic shock, and loss of electrolytes
Hypotonic Hydration: Cellular overhydration (water intoxication); occurs with renal insufficiency or rapid water ingestion; symptoms include severe metabolic disturbances, nausea, vomiting, muscular cramping, cerebral edema, and possible death; treated with hypertonic saline
Edema: Atypical accumulation of interstitial fluid, not cell swelling; impairs tissue function; caused by increased fluid flow out of blood or decreased return of fluid to blood

Central Role of Sodium in Fluid and Electrolyte Balance

Sodium (Na+) is the most abundant cation in extracellular fluid (ECF)
Controls extracellular fluid (ECF) volume and water distribution due to water following salt
Changes in Na+ levels affect plasma volume, blood pressure, and intracellular and extracellular fluid volumes
There are no known receptors monitoring Na+ levels directly in body fluids, so Na+ and water balance is linked to pressure and volume control mechanisms.
Changes in blood pressure or volume trigger neural and hormonal controls to regulate Na+ content.

Regulation of Sodium Balance

Influence of aldosterone and angiotensin II:
- Renin (from kidneys) catalyzes angiotensin II production.
- Angiotensin II prompts aldosterone release from adrenal cortex.
- Increased aldosterone results in increased Na+ reabsorption and thus water retention by the kidneys.
- Aldosterone release is also triggered by elevated potassium (K+) levels.
Influence of atrial natriuretic peptide (ANP):
- Released by atrial cells in response to stretch caused by increased blood pressure.
- Decreases blood pressure and blood volume.
- Inhibits ADH, renin, and aldosterone production.
- Increases excretion of Na+ and water.
Influence of other hormones, such as female sex hormones (estrogen and progesterone) and glucocorticoids. Estrogen—increases Na+ reabsorption, leads to water retention; progesterone—decreases Na+ reabsorption, blocks aldosterone; glucocorticoids increase Na+ reabsorption.

Potassium Balance Regulation

Potassium (K+) in ECF affects resting membrane potential (RMP).
- Elevated ECF K+: decreased RMP, and depolarization—reduced excitability
- Decreased ECF K+: hyperpolarization and nonresponsiveness
Disruption of K+ (hyperkalemia or hypokalemia) in the heart can interfere with electrical conduction.
K+ balance is controlled by regulating the amount secreted into the filtrate in cortical collecting ducts.

Regulation of Anions

Chloride (Cl−) is the major anion accompanying Na+ in ECF.
Helps maintain osmotic pressure and blood pH.
99% of Cl− is reabsorbed passively in the PCT.
Follows Na+ transport; related to active transport of Na+.
When acidosis occurs, fewer chloride ions are reabsorbed.

Acid-Base Balance

pH affects all functional proteins & biochemical reactions.
Normal pH of body fluids:
- Arterial blood: 7.4
- Venous blood/interstitial fluid: 7.35
- Intracellular fluid: 7.0
Alkalosis: arterial pH >7.45
Acidosis: arterial pH <7.35

Acid-Base Balance: Regulation

Regulation involves three mechanisms:
- Chemical buffer systems (fast, first line)
  - Bicarbonate buffer system: HCl + NaHCO3 → H2CO3 + NaCl
  - Phosphate buffer system: HCl + Na2HPO4 → NaH2PO4 + NaCl
  - Protein buffer system: Intracellular proteins are major buffers; plasma proteins also important.
- Brain-stem respiratory centers (acts within 1-3 minutes)
- Renal mechanisms (hours to days to effect change)

Respiratory Regulation of H+

Alkalosis depresses the respiratory center, causing a decreased respiratory rate and depth, thus increasing H+ concentration.
Respiratory impairments cause acid-base imbalances (hypoventilation causes respiratory acidosis, and hyperventilation causes respiratory alkalosis).

Conserving Filtered Bicarbonate Ions: Bicarbonate Reabsorption

Kidneys replenish (reabsorb) bicarbonate to maintain the alkaline reserve.
Tubule cells are impermeable to bicarbonate, but permeable to CO2.
Bicarbonate gains entry in a roundabout way, converting to CO2 and back into bicarbonate.
The mechanism is coupled to H+ secretion.

Generating New Bicarbonate Ions

Metabolism generates H+, which is balanced by new bicarbonate.
Secreted H+ reclaims filtered HCO3-.
Body has the same amount of HCO3− and H+

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Description

This quiz focuses on the water content in the human body, including variations across different age groups and genders. It also covers fluid compartments and the composition of body fluids, particularly the role of electrolytes. Test your understanding of these essential concepts in physiology!