Chapter 24 Fluid, Electrolyte, and Acid-Base Balance Flashcards

Chapter 24 explains how the body maintains homeostasis by regulating water balance, electrolytes (especially sodium, potassium, calcium, and chloride), and blood pH through the coordinated actions of buffers, the kidneys, hormones (ADH, aldosterone, ANP), and the respiratory system.

What is the total body water in an average 150-lb male?

Approximately $40\,\text{liters}$ of water.

What are the two major fluid compartments of the body and their respective percentages?

● Intracellular fluid (ICF) = fluid inside cells ($65\%$) \n● Extracellular fluid (ECF) = fluid outside cells ($35\%$)

What are the three subdivisions of extracellular fluid (ECF) and their percentages?

● Tissue (interstitial) fluid = $25\%$ \n● Blood plasma and lymph = $8\%$ \n● Transcellular fluid = $2\%$

What is transcellular fluid and where is it found?

Fluid found in specialized compartments such as Cerebrospinal fluid (CSF), Synovial fluid, and Eye fluids.

Which fluid compartment contains the greatest amount of water?

Intracellular fluid (ICF).

What determines water distribution between body compartments?

Electrolytes, especially $Na^+$ and $K^+$, determine water movement through osmosis.

What principle explains water movement across membranes?

Water moves toward the area with the higher solute concentration.

What are the two sources of water gain?

1. Preformed water from food and beverages\n2. Metabolic water produced during cellular respiration

What is metabolic water?

Water produced as a byproduct of aerobic metabolism.

What are the major routes of water loss?

Urine, Feces, Sweat, Expired air, and Cutaneous transpiration.

What is insensible water loss?

Water loss that is not consciously noticed, mainly through respiration and skin evaporation.

What is obligatory water loss?

The minimum unavoidable water loss required for survival.

What is the minimum daily urine output necessary for survival?

About $400\,\text{mL/day}$.

What is the body's primary mechanism for regulating water intake?

Thirst.

What physical changes occur in the body during dehydration?

● Blood volume decreases \n● Blood pressure decreases \n● Osmolarity increases

What are osmoreceptors and where are they located?

Specialized neurons in the hypothalamus that detect changes in blood osmolarity.

What hormone stimulates thirst when blood pressure falls?

Angiotensin II.

How does the hypothalamus respond to dehydration?

It stimulates thirst and releases ADH.

Why does dehydration cause a dry mouth?

Salivation decreases to encourage fluid intake.

What is the difference between short-term and long-term thirst inhibition?

Short-term: Moistening the mouth and stretching the stomach temporarily suppress thirst. \nLong-term: Water absorption lowers blood osmolarity and truly corrects dehydration.

What does ADH stand for?

Antidiuretic Hormone.

What three factors stimulate the release of ADH?

Increased blood osmolarity, decreased blood volume, and dehydration.

Where is ADH produced?

In the hypothalamus.

Where is ADH released from?

The posterior pituitary gland.

What is the primary function of ADH?

To conserve water.

What are aquaporins?

Water channel proteins inserted into collecting duct cells under ADH stimulation.

How does ADH affect urine output and concentration?

It decreases urine volume and increases urine concentration.

Why is ADH called an antidiuretic hormone?

Because it reduces urine production.

What is hypovolemia?

A decrease in body fluid volume without major changes in osmolarity.

What conditions can cause hypovolemia?

Hemorrhage, burns, vomiting, diarrhea, and aldosterone deficiency.

What is dehydration in terms of water loss and osmolarity?

Loss of body water resulting in increased osmolarity.

What conditions commonly cause dehydration?

Excessive sweating, diabetes, lack of water intake, diuretics, and ADH deficiency.

Why are infants more vulnerable to dehydration?

They have a higher metabolic rate, immature kidneys, and a larger surface area relative to body volume.

What are the most serious consequences of dehydration?

Circulatory shock, neurological dysfunction, and death.

What is volume excess?

Retention of both sodium and water.

What conditions commonly cause volume excess?

Aldosterone excess and kidney failure.

What is hypotonic hydration?

Excessive water retention relative to sodium.

What hormone is commonly responsible for hypotonic hydration?

Excess ADH.

What are the most dangerous consequences of fluid excess?

Pulmonary edema and cerebral edema.

What is the definition of edema?

Excess accumulation of fluid in the interstitial tissues.

What are the major functions of electrolytes?

Osmotic balance, nerve signaling, muscle contraction, and pH regulation.

What are the major cations ($^+$) of the body?

$Na^+$, $K^+$, $Ca^{2+}$, and $H^+$.

What are the major anions ($^-$) of the body?

$Cl^-$, $HCO_3^-$, and $PO_4^{3-}$.

Which ion contributes $90-95\%$ of ECF osmolarity?

Sodium ($Na^+$).

What are the major functions of sodium?

Controls ECF volume, generates membrane potentials, supports nutrient transport, and regulates water balance.

What hormone is known as the "salt-retaining hormone"?

Aldosterone.

How does aldosterone affect sodium in the kidneys?

It increases sodium reabsorption.

How does ANP affect sodium balance?

It increases sodium excretion.

What triggers the release of ANP?

Stretching of the atria due to increased blood volume.

What is hypernatremia?

Plasma sodium greater than $145\,\text{mEq/L}$.

What are the major consequences of hypernatremia?

Water retention, hypertension, and edema.

What is hyponatremia?

Plasma sodium below $130\,\text{mEq/L}$.

What is the most abundant intracellular cation?

Potassium ($K^+$).

What are the major functions of potassium?

Membrane potentials, protein synthesis, and cellular osmolarity.

What hormone increases potassium secretion by the kidneys?

Aldosterone.

Which electrolyte imbalance is considered the most dangerous?

Potassium imbalance.

What is hyperkalemia?

Excess potassium in the blood.

Why is hyperkalemia dangerous for the heart?

It can cause fatal cardiac arrhythmias.

What type of trauma can cause rapid-onset hyperkalemia?

Crush injuries.

What is hypokalemia?

Abnormally low blood potassium levels.

What common conditions cause hypokalemia?

Sweating, vomiting, and diarrhea.

What are typical symptoms of hypokalemia?

Muscle weakness, decreased reflexes, and arrhythmias.

What is the most abundant extracellular anion?

Chloride ($Cl^-$).

What role does chloride play in the digestive system?

It is required for hydrochloric acid ($HCl$) production.

What is the chloride shift?

Chloride movement that assists $CO_2$ transport in red blood cells.

What is the primary effect of chloride imbalances?

pH disturbances.

What are the five major functions of calcium?

1. Bone mineralization\n2. Muscle contraction\n3. Second messenger activity\n4. Exocytosis\n5. Blood clotting

Which hormone raises blood calcium levels?

Parathyroid hormone (PTH).

What vitamin promotes the absorption of calcium?

Calcitriol (Vitamin D).

Which hormone lowers blood calcium levels?

Calcitonin.

What is hypercalcemia?

Excess calcium in the blood.

What symptoms occur with hypercalcemia?

Muscle weakness, reduced reflexes, and cardiac arrhythmias.

What is hypocalcemia?

Low blood calcium levels.

Why is hypocalcemia dangerous for the nervous system?

It causes excessive nerve and muscle excitability.

What severe symptoms occur in hypocalcemia?

Tetany, laryngospasm, and death.

Name four important molecules that contain phosphate.

ATP, DNA, RNA, and Phospholipids (also cAMP).

Which endocrine hormone increases phosphate excretion?

PTH.

Why are phosphate imbalances usually less severe than sodium or potassium imbalances?

The body tolerates a wider range of phosphate concentrations.

What is the normal extracellular fluid pH range?

$7.35\text{--}7.45$.

Why is strict pH regulation essential for physiology?

Enzymes function properly only within a narrow pH range.

What is the definition of an acid?

A substance that releases $H^+$ ions.

What is the definition of a base?

A substance that accepts $H^+$ ions.

What is a buffer system?

A system that resists sudden changes in pH.

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

1. Bicarbonate\n2. Phosphate\n3. Protein

Which buffer system is most important in the extracellular fluid (ECF)?

The bicarbonate buffer system.

Which buffer system is most important in the intracellular fluid (ICF)?

The protein buffer system.

Which buffer system is especially important in kidney tubules?

The phosphate buffer system.

Which organ system provides the fastest pH regulation?

The respiratory system.

Which organ system provides the most powerful pH regulation?

The renal system.

How does hyperventilation affect blood pH?

It raises pH by removing $CO_2$.

How does hypoventilation affect blood pH?

It lowers pH by retaining $CO_2$.

How do the kidneys correct acidosis?

By increasing $H^+$ secretion.

How do the kidneys correct alkalosis?

By increasing bicarbonate secretion.

What causes respiratory acidosis?

Hypoventilation causing $CO_2$ retention.

What lung disease commonly causes respiratory acidosis?

Emphysema.

What causes respiratory alkalosis?

Hyperventilation causing excessive $CO_2$ loss.

What are common causes of metabolic acidosis?

Diabetic ketoacidosis, lactic acidosis, aspirin overdose, and severe diarrhea.

What are common causes of metabolic alkalosis?

Excess antacid use and chronic vomiting.

Why does acidosis often cause hyperkalemia?

$H^+$ enters cells and $K^+$ leaves cells.

Why does alkalosis often cause hypokalemia?

$H^+$ leaves cells and $K^+$ enters cells.