A&P chapter 21

What is the relationship between water and electrolytes in the body?

They are interdependent; a change in one causes a change in the other.

Which electrolytes are considered the most important?

Na+, K+, Ca2+, H+, OH−, Cl−, and Mg2+.

How does the body maintain water and electrolyte balance?

By replacing lost water and electrolytes and excreting any excess.

Why are body fluids not uniformly distributed?

Because they occupy different compartments with different volumes and compositions.

What percentage of body weight is water in the average adult male and female?

Male: 63%; Female: 52%.

What are the two major fluid compartments of the body?

Intracellular fluid (inside cells) and extracellular fluid (outside cells).

What types of fluids are found in the extracellular compartment?

Interstitial fluid, blood plasma, lymph, and transcellular fluids (cerebrospinal fluid, synovial fluid, etc.).

What is required for water balance to exist in the body?

Water intake (and metabolic production) must equal water output.

What are the primary sources of water intake?

60% from drinking fluids, 30% from moist foods, and 10% from metabolism (water of metabolism).

What are the main routes of water output?

60% urine, 6% feces, 6% sweat, 28% evaporation from skin and lungs.

How does temperature and activity affect water output?

Higher temperatures and activity levels increase water output.

How does the body regulate thirst?

Thirst centers in the hypothalamus detect changes in osmotic pressure or blood volume.

What role do osmoreceptors play in thirst regulation?

They detect increased osmotic pressure and stimulate the thirst mechanism.

What physiological changes occur when water is consumed?

Stomach distension inhibits the thirst center, and absorbed water returns osmotic pressure to normal.

How do kidneys control water excretion?

Through the action of ADH (antidiuretic hormone), which increases water reabsorption.

What effect does ADH have on the kidneys during dehydration and excess water intake?

During dehydration, ADH secretion increases water reabsorption; during excess intake, ADH secretion decreases, reducing water reabsorption.

What are the causes and symptoms of dehydration?

Output exceeds intake, leading to concentrated extracellular fluid, cellular water loss, nervous system dysfunction, and possible hyperthermia.

What is hypotonic hydration, and what causes it?

Water intoxication caused by excessive water intake leading to low blood sodium (hyponatremia).

What are the causes of edema?

Decreased plasma proteins, lymphatic obstruction, increased capillary permeability, or increased venous pressure.

What is electrolyte balance, and how is it maintained?

It exists when electrolyte gain equals loss, mainly regulated by the kidneys.

How does the body intake electrolytes?

Through foods, beverages, and metabolic by-products.

What mechanisms regulate electrolyte output?

Mainly urine production, with minor losses in sweat and feces.

How does aldosterone affect Na+ and K+ concentrations?

Aldosterone increases Na+ reabsorption and K+ secretion.

How does parathyroid hormone affect Ca2+ levels?

It increases blood calcium levels by promoting release from bones and increased reabsorption by kidneys.

What is hyponatremia ?

(low blood Na+ concentration):

• Caused by prolonged sweating, vomiting, drinking too much water

• Effects are hypotonic extracellular fluid, uptake of water by cells by osmos

What is Hypernatremia?

(high blood Na+ concentration):

• Caused by excess water loss, as in fever or diabetes insipidus

• Effects are central nervous system disturbances: confusion, stupor, coma

What is Hypokalemia?

(low blood K+ concentration):

• Caused by some diuretics, kidney disease, decrease in extracellular H+

• Effects are muscle weakness or paralysis, cardiac disturbances, breathing

problems

What is hyperkalemia?

(high blood K+ concentration):

• Caused by renal disease, aldosterone deficiency

• Effects are skeletal muscle paralysis, cardiac disturbances

What are acids and bases, and how are they defined?

Acids release H+ ions; bases release ions that combine with H+ ions.

Why is acid-base balance important for body functions?

Because slight pH changes affect enzyme activity, ion distribution, and hormone function.

What is the normal pH range of internal body fluids?

7.35 to 7.45.

What are the major sources of hydrogen ions in the body?

By-products of metabolism and some absorption from the digestive tract.

What differentiates a strong acid from a weak acid?

Strong acids ionize completely, releasing more H+ ions.

What differentiates a strong base from a weak base?

Strong bases ionize completely, releasing more OH− ions.

What are the three major mechanisms for regulating H+ concentration?

Chemical buffer systems, respiratory excretion of CO2, and renal excretion of H+ ions.

How does the bicarbonate buffer system maintain pH?

It converts strong acids to weak acids and strong bases to weak bases.

How does the phosphate buffer system work?

It buffers intracellular fluid and urine by binding or releasing H+ ions.

How do proteins buffer changes in pH?

Proteins (like hemoglobin) bind or release H+ ions depending on acidity.

How does respiratory rate affect carbon dioxide and pH levels?

Increased breathing rate removes CO2, raising pH.

How do kidneys contribute to hydrogen ion regulation?

By excreting H+ ions and reabsorbing bicarbonate ions.

What defines acidosis and alkalosis?

Acidosis: pH below 7.35; Alkalosis: pH above 7.45.

What are the causes and symptoms of respiratory acidosis?

Causes: Respiratory insufficiency, airway obstruction. Symptoms: Drowsiness, disorientation, cyanosis.

What are the causes and symptoms of metabolic acidosis?

Causes: Kidney failure, prolonged diarrhea, diabetes mellitus. Symptoms: Drowsiness, disorientation, cyanosis.

What are the causes and symptoms of respiratory alkalosis?

Causes: Hyperventilation from anxiety, fever, or altitude. Symptoms: Agitation, dizziness, light-headedness, tetany.

What are the causes and symptoms of metabolic alkalosis?

Causes: Vomiting stomach contents, excess antacids, diuretics. Symptoms: Agitation, dizziness, muscle contractions.

What mechanisms does the body use to compensate for acid-base imbalances?

Chemical buffers, altered breathing rate, and changes in renal H+ ion secretion.

How does the body compensate for metabolic alkalosis?

Buffers release H+, breathing slows to retain CO2, kidneys decrease H+ secretion.

How does the body compensate for respiratory acidosis?

Buffers bind H+, kidneys increase H+ secretion (since the respiratory system is impaired).