Fluid, Electrolyte, and pH Balance Practice Flashcards

A comprehensive set of practice flashcards covering fluid compartments, electrolyte balance, pH regulation, and compensatory mechanisms based on the lecture transcript.

What is the water content of an infant compared to an elderly person?

Infants are $73\%$ or more water, while in old age, water content declines to about $45\%$ of body weight.

Why do healthy females ($50\%$ water) typically have a lower body water percentage than healthy males ($60\%$ water)?

This difference reflects females' higher body fat and smaller amount of skeletal muscle.

What are the two main fluid compartments in the body?

Intracellular fluid (ICF), comprising about two-thirds by volume, and Extracellular fluid (ECF).

What are the volumes and body weight percentages for the main fluid compartments in a $40\,L$ total body water model?

Total body water is $40\,L$ ($60\%$); ICF is $25\,L$ ($40\%$); ECF is $15\,L$ ($20\%$).

Within the Extracellular Fluid (ECF), what are the volumes for Interstitial Fluid (IF) and Plasma?

Interstitial fluid is $12\,L$ ($80\%$ of ECF), and Plasma is $3\,L$ ($20\%$ of ECF).

How is electrolyte concentration expressed, and what is the formula?

It is expressed in milliequivalents per liter ($mEq/L$). The formula is: $mEq/L = (\text{concentration of ion in [mg/L]} / \text{atomic weight of ion}) \times \text{number of electrical charges on one ion}$.

What are the chief cation and major anion of Extracellular Fluids (ECF)?

The chief cation is Sodium ($Na^+$) and the major anion is Chloride ($Cl^-$).

What are the chief cation and chief anion of Intracellular Fluids (ICF)?

The chief cation is Potassium ($K^+$) and the chief anion is Phosphate ($HPO_4^{2-}$).

What percentage of the mass of solutes do proteins, phospholipids, cholesterol, and neutral fats account for in the ICF?

$97\%$.

Which fluid is the only one that circulates throughout the body and links external and internal environments?

Plasma.

What are the sources of water intake and their percentages?

Beverages ($60\%$), solid food ($30\%$), and metabolic water/water of oxidation ($10\%$).

What are the routes of water output and their percentages?

Urine ($60\%$), insensible losses via skin and lungs ($28\%$), sweat ($8\%$), and feces ($4\%$).

What stimuli activate the hypothalamic thirst center?

A decline in plasma volume of $10\text{--}15\%$, an increase in plasma osmolality of $1\text{--}2\%$, or input from baroreceptors and Angiotensin II.

What triggers the release of Antidiuretic Hormone (ADH)?

Increased plasma osmolality sensed by hypothalamic osmoreceptors or a significant decrease in blood pressure/volume.

What is the cellular consequence of dehydration?

The ECF osmotic pressure rises, causing cells to lose water to the ECF by osmosis and shrink.

What is Hypotonic Hydration (water intoxication)?

A condition where ECF is diluted (hyponatremia), leading to net osmosis into tissue cells, causing them to swell.

What is Edema and what are some factors that accelerate fluid loss from the bloodstream?

Edema is an atypical accumulation of fluid in the interstitial space. Accelerating factors include increased blood pressure, increased capillary permeability, or incompetent venous valves.

How does hypoproteinemia lead to edema?

Low levels of plasma proteins lower colloid osmotic pressure, forcing fluids out of capillary beds at arterial ends and preventing their return at venous ends.

What role does Sodium ($Na^+$) play in ECF solute concentration?

Sodium salts account for $90\text{--}95\%$ of all solutes in the ECF, contributing $280\,mOsm$ of the total $300\,mOsm$ ECF solute concentration.

How does Aldosterone affect sodium and water balance?

It triggers active reabsorption of the remaining $10\%$ of $Na^+$ in the distal tubules/collecting ducts; water follows sodium if ADH is present.

What is the function of Atrial Natriuretic Peptide (ANP)?

It reduces blood pressure and volume by promoting the excretion of sodium and water and inhibiting Angiotensin II production.

How do hyperkalemia and hypokalemia affect the heart?

They can disrupt electrical conduction in the heart and lead to sudden death.

How does Parathyroid Hormone (PTH) regulate calcium levels?

PTH increases calcium by activating osteoclasts in bone, enhancing intestinal absorption, and increasing renal reabsorption of calcium while decreasing phosphate reabsorption.

What are the normal pH levels for arterial blood, venous blood/IF, and ICF?

Arterial blood is $7.4$, venous blood/IF is $7.35$, and ICF is $7.0$.

What are the three major chemical buffer systems in the body?

The Bicarbonate, Phosphate, and Protein buffer systems.

Which chemical buffer system is the only important ECF buffer?

The Bicarbonate buffer system.

Define amphoteric molecules in the context of the protein buffer system.

Protein molecules that can function as both a weak acid (via free organic acid groups) and a weak base (via amino groups).

What is the physiological equation for the reversible equilibrium between carbon dioxide and bicarbonate ions?

$$\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3 \rightleftharpoons \text{H}^+ + \text{HCO}_3^-$$

Why are the kidneys considered the ultimate acid-base regulatory organs?

Only the kidneys can rid the body of metabolic acids (phosphoric, uric, and lactic acids and ketones) and prevent metabolic acidosis.

How do the kidneys generate new bicarbonate ions using ammonium?

PCT cells metabolize glutamine to produce two $NH_4^+$ ions (excreted in urine) and two new $HCO_3^-$ ions (moved to blood).

What are the partial pressure of carbon dioxide ($PCO_2$) limits for respiratory acidosis and alkalosis?

Values above $45\,mm\,Hg$ signal respiratory acidosis; values below $35\,mm\,Hg$ indicate respiratory alkalosis.

What defines metabolic acidosis and alkalosis?

Imbalances in bicarbonate ($HCO_3^-$) levels outside the normal range of $22\text{--}26\,mEq/L$ that are not caused by abnormal $\text{CO}_2$ levels.

What are some typical causes of metabolic acidosis?

Ingestion of too much alcohol, excessive loss of bicarbonate ions, accumulation of lactic acid, shock, diabetic ketosis, starvation, and kidney failure.

How does the respiratory system compensate for metabolic acidosis?

The rate and depth of breathing are elevated to eliminate $\text{CO}_2$, causing $PCO_2$ to fall below normal.

How do the kidneys compensate for respiratory acidosis (high $PCO_2$)?

The kidneys step up renal mechanisms to retain bicarbonate ($HCO_3^-$) to offset the low pH.

What factors make infants more susceptible to fluid and electrolyte imbalances?

Low residual lung volume, high rate of fluid intake/output, high metabolic rate, high rate of insensible water loss, and inefficient kidneys.