Chapter 21 Lecture: Water, Electrolyte, and Acid-Base Balance

Flashcards covering water and electrolyte balance, fluid distribution, and acid-base homeostasis based on Chapter 21 lecture notes.

What does the term 'balance' suggest regarding water and electrolytes?

A state of constancy where equal amounts enter and leave the body, helping to maintain homeostasis.

What is the approximate percentage of water by weight in average adult females and males?

Females are about $52\%$ water; males are about $63\%$ water.

How many liters of water are in the average adult body and into which two major compartments is it distributed?

There are about $40\,liters$ of water, distributed into Intracellular fluid ($63\%$) and Extracellular fluid ($37\%$).

What specific fluids compose the extracellular fluid (ECF) compartment?

Interstitial fluid, blood plasma, lymph, and transcellular fluid (such as cerebrospinal fluid, aqueous and vitreous humors, synovial fluid, and serous fluid).

Which ions are found in high concentrations in extracellular fluids?

$Na^{+}$, $Cl^{-}$, $Ca^{2+}$, and $HCO_3^{-}$ ions.

Which ions are found in high concentrations in intracellular fluids?

$K^{+}$, $Mg^{2+}$, $PO_4^{3-}$, and $SO_4^{2-}$ ions.

Of the two major factors regulating fluid movement, which is responsible for most fluid movement between compartments?

Osmotic pressure (hydrostatic pressure in cells and interstitial fluids remains relatively equal and stable).

What is the average daily water intake for an adult and what are its three sources?

Average intake is $2,500\,mL$ daily: $60\%$ from drinking fluids, $30\%$ from moist foods, and $10\%$ as water of metabolism from oxidative metabolism.

What is the primary regulator of water intake?

Thirst, controlled by the thirst centers in the hypothalamus.

What are the four methods of water output and their typical percentages?

$60\%$ in urine, $6\%$ in feces, $6\%$ in sweat (sensible perspiration), and $28\%$ through evaporation from skin and lungs (insensible perspiration).

How does the osmoreceptor-ADH mechanism respond to dehydration?

Osmoreceptors lose water and shrink, stimulating the secretion of ADH, which increases the permeability of renal distal convoluted tubules and collecting ducts to increase water reabsorption.

What is water intoxication and what clinical condition can it cause?

Excess fluid intake that results in hyponatremia, which is a low blood level of $Na^{+}$.

What is edema?

The abnormal accumulation of extracellular fluid in the interstitial spaces.

Which hormone regulates the concentrations of $Na^{+}$ and $K^{+}$?

Aldosterone; high $K^{+}$ concentration stimulates aldosterone secretion, leading to $Na^{+}$ reabsorption and $K^{+}$ secretion.

What triggers the secretion of PTH and what is its effect on electrolyte balance?

A decrease in plasma $Ca^{2+}$ levels stimulates PTH, which increases plasma $Ca^{2+}$ through bone resorption, intestinal absorption, and renal conservation.

Define hypernatremia and its potential effects on the body.

High blood $[Na^{+}]$ caused by excess water loss; it effects the central nervous system, potentially leading to confusion, stupor, or coma.

What characterizes the difference between respiratory acidosis and metabolic acidosis?

Respiratory acidosis is caused by an increase in $CO_2$ and $H_2CO_3$ levels, while metabolic acidosis is caused by the accumulation of other acids or the loss of bases.

Identify the three chemical buffer systems in the body fluids.

1. Bicarbonate buffer system, 2. Phosphate buffer system, and 3. Protein buffer system.

What is the chemical reaction for the bicarbonate buffer system?

$$H^{+} + HCO_3^{-} \rightleftharpoons H_2CO_3$$

How does the respiratory center help regulate pH when acidity increases?

It increases the rate and depth of breathing to expel more $CO_2$, thereby reducing the formation of carbonic acid and lowering $H^{+}$ concentration.

What is the normal pH range of the internal environment?

$7.35$ - $7.45$

Compare the time course for the different $H^{+}$ ion regulation mechanisms.

Chemical buffers function almost immediately; the respiratory mechanism functions within minutes; the renal mechanism takes $1$ – $3\,days$.