Fluid Balance and Osmolality in Physiology

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Questions and Answers

What is one potential cause of obstruction of lymphatic circulation?

Parasitic diseases (correct)

Low sodium diet

Diuretics use

Electrolyte imbalance

Which condition is associated with increased capillary permeability?

Heart failure

Cirrhosis

Chronic renal failure

Inflammation (correct)

How can edema be clinically manifested?

Pitting edema (correct)

Dehydration

Hypoglycemia

Bronchial spasms

What laboratory finding is indicative of edema?

Decreased hematocrit Signup and view all the answers

What management strategy is commonly used to treat edema?

Diuretics Signup and view all the answers

What is the primary defense for osmolarity?

Thirst Signup and view all the answers

Which hormone is responsible for stimulating water conservation at the kidneys?

Antidiuretic hormone (ADH) Signup and view all the answers

What triggers the secretion of aldosterone?

Rising potassium levels or falling sodium levels Signup and view all the answers

What effect do natriuretic peptides have on thirst?

Reduce thirst Signup and view all the answers

Which type of dehydration results in equal loss of both fluid and electrolytes?

Isotonic dehydration Signup and view all the answers

What happens when aldosterone is present at high plasma concentrations?

Kidneys conserve sodium and water Signup and view all the answers

Which hormone blocks the release of ADH and aldosterone?

Natriuretic peptides Signup and view all the answers

What is the primary result of osmotic concentration changes detected by osmoreceptors?

Secretion of ADH Signup and view all the answers

What is the primary component of the body that influences osmolality?

Sodium (Na+) Signup and view all the answers

What percentage of total body water (TBW) is made up by intracellular fluid (ICF)?

65% Signup and view all the answers

What would cause cells to swell?

Low osmolality outside the cell Signup and view all the answers

How is serum osmolality estimated in clinical practice?

2 x Na + urea + glucose Signup and view all the answers

What is the typical daily insensible loss of fluid through the skin and lungs?

1000 cc/day Signup and view all the answers

What fluid compartment contains the highest volume of water in a healthy 70-kg male?

Intracellular fluid Signup and view all the answers

What triggers thirst and ADH secretion in the body?

Hypothalamus Signup and view all the answers

Which of the following statements about body water composition is correct?

Adult males have a body water composition of about 60% Signup and view all the answers

Which of the following is NOT a cause of dehydration?

Increased capillary hydrostatic pressure Signup and view all the answers

What is a common clinical manifestation of severe dehydration?

Tachycardia Signup and view all the answers

What laboratory finding indicates dehydration?

Increased BUN > 25 mg/dL Signup and view all the answers

How does the body compensate for dehydration?

Constriction of vessels to skin Signup and view all the answers

Which of the following describes a treatment for mild dehydration?

Oral fluid replacement Signup and view all the answers

What is one effect of water gain (edema) on the extracellular fluid (ECF)?

ECF volume increases Signup and view all the answers

Which factor does NOT contribute to the development of edema?

Decreased capillary permeability Signup and view all the answers

What condition can cause hyperglycemia in severe dehydration?

Glucose levels > 120 mg/dL Signup and view all the answers

What is the main cation found in extracellular fluid (ECF)?

Sodium (Na+) Signup and view all the answers

What electrolyte imbalance occurs when serum sodium levels exceed 148 mEq/L?

Hypernatremia Signup and view all the answers

Which factor can correct changes in sodium concentration?

Antidiuretic hormone (ADH) Signup and view all the answers

What is the primary cause of hyponatremia?

Body water content rise (overhydration) Signup and view all the answers

What is the normal sodium plasma level range in mEq/L?

135-145 Signup and view all the answers

In which fluid compartment is potassium primarily found?

Intracellular fluid Signup and view all the answers

What is a common consequence of abnormalities in sodium levels?

Reduced blood pressure Signup and view all the answers

Which condition is related to impaired access to water leading to hypernatremia?

Poor Intake of Water Signup and view all the answers

Study Notes

Fluid Balance

Plays a vital role in daily IV maintenance
Intake (I) and Output (O) of fluids are crucial
Insensible loss (from skin and lungs) is about 1000 cc per day

Cell Fluid Movement

Water moves passively across the cell membrane based on the osmotic gradient
The intracellular fluid (ICF) has a high concentration of potassium (K+), around 140 meq/L, resulting in 280 milliosmoles/L
The extracellular fluid (ECF) has a high concentration of sodium (Na+), around 140 meq/L, also resulting in 280 milliosmoles/L

Osmolality

It is the measure of a solution's ability to create osmotic pressure, influencing water movement
Represents the number of osmotically active particles per kilogram of water
Plasma osmolality ranges from 280-300 mOsm/kg
ECF osmolality is mainly determined by sodium levels
The hypothalamus acts as an osmostat, regulating serum osmolality by triggering thirst and ADH secretion
The body's primary defenses for osmolality are thirst and renal water excretion
ADH (Antidiuretic Hormone) plays a crucial role in regulating water excretion

Primary Regulatory Hormones

ADH, aldosterone, and natriuretic peptides regulate fluid and electrolyte balance

Antidiuretic Hormone (ADH)

Promotes water conservation by kidneys, reducing urinary water loss and concentrating urine
Also stimulates the thirst center, encouraging fluid intake

Aldosterone

Secreted by the adrenal cortex
Responds to high potassium (K+) levels sensed by the adrenal cortex or low sodium (Na+) levels in the blood
Activated by the renin-angiotensin system, usually due to changes in blood volume
Controls Na+ absorption and K+ loss in the distal convoluted tubule (DCT) and collecting system
Enhances water retention by increasing Na+ reabsorption (“water follows salt”)

Natriuretic Peptides

Released by cardiac muscle cells in response to excessive stretching due to high blood pressure or volume
Examples include ANP (atrial natriuretic peptide) and BNP (brain natriuretic peptide)
They reduce thirst, block ADH and aldosterone release, promote diuresis, and lower blood pressure and plasma volume

Water Losses and Dehydration

Dehydration primarily affects the ECF
Categories of dehydration:
- Mild: less than 2% body weight loss
- Moderate: 2-5% body weight loss
- Severe: greater than 8% body weight loss
Dehydration often involves both water and electrolyte loss
Specific types include:
- Isotonic: equal loss of fluid and electrolytes
- Hypotonic: greater loss of electrolytes than water
- Hypertonic: greater loss of water than electrolytes

Causes of Water Loss

Vomiting and diarrhea, N-G suction
Excessive sweating
Diabetic ketoacidosis
Insufficient water intake
Fever
Burns
Diabetes insipidus (low ADH secretion)
Diuretic phase of acute renal failure
Use of diuretics

Effects of Dehydration

Dry mucous membranes
Decreased skin turgor
Decreased blood pressure
Increased hematocrit
Compensatory mechanisms: increased thirst, increased pulse, vasoconstriction leading to pale, cool skin
Decreased urine output
Severe dehydration: confusion, unconsciousness, coma

Clinical Manifestation of Dehydration

Dry tongue and thirst
Poor skin turgor
Concentrated urine (oligouria < 30 ml urine/hour)
Muscle weakness
Sunken eyes
Headache, confusion, and coma in severe cases
Increased temperature
Tachycardia
Weight loss

Laboratory Findings in Dehydration

Increased osmolality > 300 mOs/kg
Increased or normal sodium level
Increased BUN (blood urea nitrogen) > 25 mg/dL (normal range: 9-23 mg/dL)
Increased hematocrit > 55%
Increased urine specific gravity > 1.03 (normal range: 1.01 – 1.03)
Severe cases: hyperglycemia (glucose level > 120 mg/dL, normal fasting blood glucose 80 – 100 mg/dL)

Management of Water Losses

Mild dehydration: oral fluid replacement
Moderate-severe dehydration: IV fluids
If tolerated, oral fluid intake (1200-1500 ml)
If unable to tolerate solids, increase fluid intake to 2500 ml/24 hours

Water Gains and Edema

Excess water gain without electrolyte gain increases ECF volume and makes it hypotonic compared to ICF.
Fluid shifts from ECF to ICF, potentially leading to overhydration, cell damage, disrupted enzyme functions, and altered solute concentrations.
Overhydration causes:
- Cell destruction
- Changes in enzyme activity
- Disruption of normal cell functions

Edema

Excessive interstitial fluid accumulation
Seven main causes:

Increased capillary hydrostatic pressure:
- Etiology: hypertension, increased blood volume due to pregnancy, renal failure, CHF, cirrhosis
Loss of plasma proteins (especially albumin):
- Etiology: kidney disease, malnutrition, malabsorption
Obstruction of lymphatic circulation:
- Etiology: cancer, parasitic diseases, post-surgical
Increased capillary permeability:
- Etiology: inflammation, toxins, burns
Ingestion of large amounts of water
Injection of hypotonic solution into blood
Endocrine causes like increased ADH secretion
Inability to eliminate excess water in urine:
- Chronic renal failure
- Heart failure
- Cirrhosis

Clinical Manifestation of Edema

Constant irritating cough
Dyspnea and crackles in lungs
Cyanosis
Jugular vein distension
Increased blood pressure (HTN)
Pitting edema
Weight gain
Change in level of consciousness

Laboratory Findings of Edema

Serum osmolality < 275 mOm/kg
Low, normal, or high sodium level
Decreased hematocrit < 45%
Specific gravity of urine < 1.01 (normal range: 1.01 – 1.03)
Low level of BUN (blood urea nitrogen) < 8 mg/dL (normal range: 9-23 mg/dL)

Management of Edema

Diuretics (combination of potassium-sparing and potassium-depleting diuretics)
Low sodium diet
In cases of CHF, treatment with ACE inhibitors and β-blockers

Electrolyte Balance

Requires equal rates of gain and loss for each electrolyte in the body
Electrolyte concentration directly influences water balance
Individual electrolyte concentrations affect cell function

Solutes and Electrolytes

Solutes: dissolved particles
Electrolytes: charged particles
Cations: positively charged ions (Na+, K+, Ca++, H+)
Anions: negatively charged ions (Cl-, HCO3-, PO43-)
Non-electrolytes : proteins, urea, glucose, oxygen (O2), carbon dioxide (CO2)

Rules of Electrolyte Balance

Most common problems with electrolyte balance stem from imbalances between gains and losses of sodium ions
Potassium imbalances are less common but more dangerous than sodium imbalances
Changes in plasma sodium levels affect:
- Plasma volume and blood pressure
- ICF and interstitial fluid volumes

Sodium (Na+)

Main cation in the ECF
Contributes to normal ECF osmolality
Assists in maintaining acid-base balance
Activates nerve and muscle cells
Influences water distribution (along with chloride)
Normal plasma Na+ level: 135-145 mEq/L

Sodium (Na+) Regulation

Changes in sodium concentration are primarily corrected by ADH, not aldosterone

Abnormal Sodium (Na+) Concentrations in ECF

Hyponatremia: usually due to increased body water content (overhydration)
Hypernatremia: usually due to decreased body water content (dehydration)
Severe electrolyte imbalances often arise secondary to fluid balance problems

Hypernatremia

Serum Na+ level > 148 mEq/L
Serum osmolality > 295 mOsm/kg

Etiologies of Hypernatremia

Primary Sodium Excess:
- Excess intake of sodium
- Decreased urinary excretion of sodium:
  - Renal failure
  - Hyperaldosteronism
Primary Water Loss:
- Poor intake of water:
  - Impaired access to water (e.g., infants, elderly, bedbound)
  - Impaired thirst sensation or loss of thirst mechanism (hypothalamic lesions)
- Increased urinary loss of water:
  - ADH deficiency (Central Diabetes Insipidus)
  - ADH resistance (Nephrogenic Diabetes Insipidus)
- Increased GI loss of water (diarrhea and vomiting)

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Description

This quiz covers essential concepts related to fluid balance, cell fluid movement, and osmolality in human physiology. Key topics include the importance of IV maintenance, the mechanisms of water movement across cell membranes, and the regulation of plasma osmolality. Test your understanding of these fundamental principles vital for maintaining homeostasis.