Fluid, Electrolyte, and Acid-Base Balance Lecture Notes

200 vocabulary-style flashcards covering fluid, electrolyte, and acid-base balance based on the provided lecture notes.

Total body water percentage of a newborn baby

About $75\%$ of their body weight

Total body water content of adults

$60\%$ men, 50% women

Reason women average less body water than men

They average more adipose tissue, which displaces water

Total body water volume in a 70 kg (150 lb) adult

$$42\,L$$

Body water percentage in obese and elderly people

$45\%$ by weight

Fluid compartments

Areas separated by selectively permeable membranes and differing in chemical composition

65%

Percentage of body water in intracellular fluid

Percentage of body water in extracellular fluid (ECF)

$$35\%$$

Subdivision of ECF: Tissue (interstitial) fluid

$$25\%$$

Subdivision of ECF: Blood plasma and lymph

$$8\%$$

Subdivision of ECF: Transcellular fluid

$$2\%$$

Examples of transcellular fluid

CSF, synovial, peritoneal, pleural, and pericardial fluids; vitreous and aqueous humors; digestive, urinary, and reproductive tract fluids

ICF vs. ECF osmolarity relationship

They are equal because water moves easily through membranes

Osmotic gradients duration

They never last long because osmosis restores balance within seconds

Primary electrolytes in ECF

Sodium ($Na^+$) salts

Primary electrolytes in ICF

Potassium ($K^+$) salts

Principals governing body water distribution

Electrolytes

Fluid balance

Condition when daily water gains and losses are equal, approximately $2,500\,mL/day$

Metabolic water

Water formed by aerobic metabolism and dehydration synthesis

Preformed water

Water ingested in food and drink

Routes of water loss

Urine, feces, expired breath, sweat, and cutaneous transpiration

Cutaneous transpiration

Water that diffuses through the epidermis and evaporates

Insensible water loss

Output of which one is not usually aware, including expired breath and cutaneous transpiration

Sensible water loss

Noticeable output, including urine and moderate sweating

Obligatory water loss

Output that is unavoidable, such as in expired air and feces

Primary regulator of fluid intake

Sense of thirst

Conditions leading to thirst

Dehydration reducing blood volume and pressure, and increasing blood osmolarity

Osmoreceptors

Sensors that respond to angiotensin II and rising osmolarity of ECF

ADH (Antidiuretic Hormone) source and thirst role

Released by the hypothalamus to promote water conservation and stimulate the cortex for thirst

Long-term inhibition of thirst

Absorption of water from the small intestine reduces blood osmolarity

Short-term inhibition of thirst

Distension of the stomach and intestines by ingested water

Regulation of water output

Primarily achieved through variation in urine volume

Kidney limitation in fluid balance

Cannot replace water or electrolytes; can only slow the rate of loss

Mechanism of changes in urine volume

Linked to adjustments in sodium ($Na^+$) reabsorption, where water follows the movement of sodium

Role of ADH in urine volume

Allows control of water output independently of sodium by reabsorbing more water when blood osmolarity rises

Decline in blood volume and rise in osmolarity

Stimulates ADH release to produce less urine

Effect of low blood osmolarity on ADH

ADH secretion is less, kidneys reabsorb less water, and produce more urine

Fluid deficiency

Fluid imbalance occurring when output exceeds intake over a long period

Volume depletion (hypovolemia)

Loss of proportional amounts of sodium ($Na^+$) and water; osmolarity remains normal

Causes of hypovolemia

Hemorrhage, burns, chronic vomiting or diarrhea, and Addison disease

Addison disease

Aldosterone hyposecretion

Dehydration (negative water balance)

Loss of significantly more water than sodium ($Na^+$), leading to a rise in ECF osmolarity

Causes of dehydration

Lack of water intake, diabetes mellitus, diabetes insipidus, profuse sweating, and overuse of diuretics

Diabetes insipidus

ADH hyposecretion

Dehydration's effect on sweat

Sweat is produced by capillary filtration, leading to a drop in blood volume and pressure

Fluid shift during sweating

Blood volume is replaced by tissue fluid, which in turn pulls fluid from the ICF

Water loss breakdown for 1 L of sweat

$300\,mL$ from tissue fluid and $700\,mL$ from ICF

Volume excess

Retention of both sodium ($Na^+$) and water while ECF remains isotonic

Causes of volume excess

Aldosterone hypersecretion or renal failure

Hypotonic hydration (water intoxication)

Condition where more water than sodium ($Na^+$) is retained/ingested, making ECF hypotonic

Cellular effect of water intoxication

Water dilutes ECF, leading to cellular swelling and dysfunction

Fluid sequestration

Excess accumulation of fluid in a particular location while TBW may be normal

Edema

The accumulation of fluid in interstitial spaces; the most common form of sequestration

Pleural effusion

Fluid accumulation in the pleural cavity, often caused by lung infections

Metabolic importance of electrolytes

They are chemically reactive and participate in metabolism

Electrical function of electrolytes

They determine electrical potential (charge difference) across cell membranes

Osmolarity of blood plasma and ICF

Both are $300\,mOsm/L$

Resting membrane potential contribution of sodium

Sodium ($Na^+$) is essential to the depolarizations that underlie nerve and muscle function

Sodium and cartilage hydration

Sodium ($Na^+$) ions bound to proteoglycans of cartilage retain water

Percentage of ECF osmolarity from sodium salts

$90\%$ to $95\%$

Sodium-potassium pump thermogenesis

An important means of generating body heat

Role of NaHCO3 in ECF

Plays a major role in buffering pH

Adult daily sodium requirement

$$0.5\,g$$

Typical American sodium intake

$3$ to $7\,g/day$

Primary player in sodium excretion adjustment

Aldosterone

Stimuli for aldosterone secretion

Hyponatremia, hyperkalemia, and hypotension

Effect of aldosterone on kidneys

Stimulates reabsorption of sodium and secretion of potassium

Natriuretic peptides

Hormones that inhibit sodium reabsorption, causing the kidneys to eliminate more sodium and water to lower BP

Estrogen's effect on sodium

Mimics aldosterone, causing sodium ($Na^+$) and water retention

Progesterone's effect on sodium

Reduces sodium ($Na^+$) reabsorption, producing a diuretic effect

Glucocorticoids' effect on sodium

Promote sodium reabsorption and causes edema

Hypernatremia

Plasma sodium concentration greater than $145\,mEq/L$

Causes of hypernatremia

Administration of IV saline

Hyponatremia

Plasma sodium concentration less than $130\,mEq/L$

Most abundant cation of ICF

Potassium ($K^+$)

Potassium's role in action potentials

Involved in repolarization and hyperpolarization

Dominant determinant of cell volume

Potassium ($K^+$)

Glomerular filtrate potassium reabsorption

$90\%$ of $K^+$ is reabsorbed by the PCT

Potassium secretion site in kidneys

DCT and cortical portion of the collecting duct

Hyperkalemia

Plasma potassium concentration above $5.5\,mEq/L$

Effect of fast-onset hyperkalemia

Neurons and muscle cells become more excitable; can cause cardiac arrest

Cause of fast-onset hyperkalemia

Crush injury

Effect of slow-onset hyperkalemia

Inactivates voltage-gated $Na^+$ channels, making cells less excitable

Hypokalemia

Plasma potassium concentration less than $3.5\,mEq/L$

Symptoms of hypokalemia

Muscle weakness, loss of muscle tone, decreased reflexes, and arrhythmias

calcium functions

Strength of skeleton, muscle contraction, second messenger, exocytosis, and blood clotting

Calsequestrin

A protein that binds calcium ($Ca^{2+}$) in the smooth ER to keep it unreactive

Calcium regulation hormones

PTH, calcitriol (vitamin D), and calcitonin

Hypercalcemia

Plasma calcium greater than $5.8\,mEq/L$

Muscular effects of extreme hypercalcemia

Muscular weakness and depressed reflexes at levels over $12\,mEq/L$

Hypocalcemia

Plasma calcium less than $4.5\,mEq/L$

Electrical effect of hypocalcemia

Increases membrane sodium permeability, making systems abnormally excitable

Severe hypocalcemia symptoms

Tetany, laryngospasm, and death

Distribution of magnesium ($Mg^{2+}$)

$54\%$ in bone, $45\%$ in ICF

Magnesium and ATP

Most intracellular $Mg^{2+}$ is complexed with ATP

Magnesium cofactor function

Serves as a cofactor for enzymes, transporters, and nucleic acids

Normal blood levels of $Mg^{2+}$

$1.5$ to $2.0\,mEq/L$

Nephron segment determining magnesium retention

Ascending limb of the nephron loop

Hypermagnesemia effects

weakness, respiratory depression, and flaccid diastolic cardiac arrest