Fluid and Electrolytes

3 purposes of fluids and electrolytes

-Fluids and electrolytes enter and leave the cells of the body to maintain a state of balance/equilibrium in order to maintain proper physiological functioning

.

-regulated by specific mechanisms to ensure that lost water and electrolytes are replaced and excesses are excreted

Body fluids distribution

-consist of water, electrolytes, blood plasma and component cells, proteins, and other soluble particles called solutes

.

-Not uniformly distributed, but occur in regions/ compartments of varying volumes and compositions

What are the two major fluid compartments in the body?

Intracellular fluid (ICF)-All water and electrolytes enclosed by cell membrane/ fluid within cells

and extracellular fluid (ECF)-All fluid outside cells

.

-The ECF and ICF are called fluid compartments because they commonly behave as separate sections, maintaining different ionic compositions.

What proportion of total body water is in the ICF and ECF in adults?

About 67% is ICF and 33% is ECF.

Difference in substances of the ECF AND ICF

ICF:

Fluid within the blood vessels, consisting of whole blood including plasma, red blood cells, white blood cells, and platelets.(cytsosl inside cells)

.

-The extracellular fluid, or ECF, is made up mostly of the interstitial fluid of peripheral tissues and the plasma of circulating blood;

Ions of ECF

sodium, chloride, and bicarbonate (HCO-3)

Ions of ICF

potassium, magnesium, and phosphate ions 3 (HPO ), 2 4 − plus large amounts of negatively charged proteins

Body Fluid Composition

What are the three major subdivisions of extracellular fluid (ECF)?

Intravascular fluid, interstitial fluid, and transcellular fluid.

What is intravascular fluid?

Fluid within the blood vessels, consisting of whole blood including plasma, red blood cells, white blood cells, and platelets.

What is transcellular fluid, and what are examples?

Fluid in specialized spaces; examples include cerebrospinal fluid, synovial fluid, serous fluids, aqueous/vitreous humor, and exocrine secretions.

Why does plasma contain more protein than interstitial fluid?

Plasma contains more protein, while most plasma proteins are normally retained within the blood vessels.

Why is intravascular fluid important for overall fluid balance and how can it be lost?

It maintains blood volume and circulation

.

excessive diuretic use, severe bleeding, vomiting, diarrhea, and inadequate oral fluid intake.

Implication sof interstitial fluid

Excess interstitial fluid referred to as edema

.

-Loss of intravascular fluid:

Deficient Fluid Volume (hypovolemia) resulting in hypovolemic shock as critical organs do not receive an oxygen-rich blood supply needed to perform cellular function

This is because the body cannot maintain adequate blood pressure and perfusion of vital organs.

What two forces regulate fluid movement between compartments and define

Hydrostatic pressure: Pressure exerted by fluid, including pressure associated with gravity, that can drive fluid movement

.

osmotic pressure: extra pressure applied on the solution to stop the flow of solvent through the semi-permeable membrane

What is hydrostatic pressure?

What is osmosis?

The movement of water from an area of higher water concentration to an area of lower water concentration across a semipermeable membrane.

What is osmotic pressure?

The pressure that must be applied to stop the flow of solvent caused by osmosis.

How does fluid normally move across capillaries?

Fluid leaves plasma at the arteriolar end because of outward hydrostatic pressure and returns at the venular end because of inward colloid osmotic pressure.

How does the lymphatic system help maintain fluid balance?

Interstitial fluid enters lymphatic vessels and is eventually returned to the plasma.

What causes osmotic pressure in body fluids?

Impermeant solutes that cannot freely cross the membrane.

How do Na+ and K+ help maintain different osmotic conditions in ECF and ICF?

The Na+/K+ pump moves Na+ out of cells and K+ into cells, helping maintain high extracellular Na+ and high intracellular K+.

What happens to cells when ECF Na+ concentration decreases?

Water moves into the cells, causing them to swell.

What happens to cells when ECF Na+ concentration increases?

Water moves out of the cells, causing them to shrink.

What principle describes the movement of water in response to changes in salt concentration?

Water follows salt until osmotic concentrations become equalized.

What is the approximate daily water input, and what are its three major sources?

About 2500 mL: approximately 1000 mL from food, 1200 mL from liquids, and 300 mL from metabolic water.

What is the approximate daily water output, and what are its major routes?

About 2500 mL: approximately 1200 mL through urination, 150 mL through defecation, 750 mL through sensible perspiration, and 400 mL through insensible perspiration.

What is dehydration?

A state in which more water is lost than is gained.

What happens to fluid compartments during dehydration caused by water loss without comparable electrolyte loss?

The ECF becomes hypertonic, causing water to move from the ICF into the ECF; both compartments become more concentrated and contain less water.

What is hypernatremia according to the lecture?

A blood sodium concentration above 145 mmol/L.

What are common causes and major signs of dehydration with hypernatremia?

It is usually caused by water loss, but may also result from salt gain without water or hypertonic sodium solutions; signs include severe thirst, dry/wrinkled skin, reduced plasma volume and blood pressure, confusion, rapid weak pulse, and reduced/absent urination.

What can severe dehydration and reduced tissue perfusion cause?

Hypotension, poor oxygen delivery, cellular anaerobic metabolism, lactic acid production, a fall in pH, and potentially hypovolemic shock.

What is the role of ADH in water balance?

ADH causes the kidneys to retain more water, reducing urine volume.

What is the role of renin in fluid and electrolyte regulation?

Renin is an enzyme released by the kidneys when blood pressure falls and helps regulate blood pressure and Na+/K+ balance.

What happens to ECF and ICF when excess water is gained without a corresponding increase in electrolytes?

The ECF becomes hypotonic, water moves into the ICF, and both compartments increase in volume while their osmotic concentrations decrease.

How does the body respond to excess water?

ADH secretion decreases and urine volume increases, allowing excess water to be eliminated.

What can cause overhydration or water intoxication?

Large amounts of freshwater intake, inability to eliminate excess water due to chronic renal or heart failure, or excessive ADH.

What can happen to cells during severe overhydration?

Cells become distorted because excess water enters them, altering the solute environment around enzymes and disrupting cell function.

What are major signs of severe hyponatremia caused by overhydration?

Drunken behavior, confusion, hallucinations, convulsions, coma, and potentially death.

How can severe overhydration be treated according to the lecture?

Diuretics may be used, and a concentrated salt solution can shift water from the ICF into the ECF.

What is electrolyte balance?

A state in which the rate of electrolyte gain equals the rate of electrolyte loss.

Why can sodium concentration remain relatively stable even when sodium intake changes?

Water shifts between compartments can occur along with sodium changes, helping maintain the sodium concentration.

What happens after eating a salty meal without drinking enough fluid?

Plasma Na+ concentration rises, causing water to move from the ICF into the ECF; ADH secretion and thirst increase, promoting water intake and retention.

How do renin and aldosterone respond to dehydration with sodium loss?

Renin is released, leading to increased aldosterone activity, which promotes sodium retention and helps maintain blood volume and blood pressure.

How does aldosterone regulate Na+ and K+ balance in the kidneys?

It promotes active Na+ reabsorption, with water following passively, while promoting K+ secretion.

How does the body respond to overhydration through natriuretic peptides?

Increased plasma volume stretches the atria and ventricles, promoting ANP and BNP release, which reduce thirst and inhibit ADH and aldosterone while increasing renal salt and water loss.

How is potassium balance primarily regulated by the kidneys?

K+ is regulated through secretion in the distal convoluted tubule and collecting system, influenced by ECF K+, pH, and aldosterone.

How does decreased ECF pH affect renal K+ secretion?

When ECF pH decreases, H+ is secreted in exchange for Na+ instead of K+, reducing K+ secretion.

What stimulates aldosterone release in relation to potassium?

An increase in ECF K+ stimulates aldosterone, which promotes K+ secretion by the kidneys.

What hormones regulate blood calcium levels?

Parathyroid hormone (PTH), calcitriol, and calcitonin.

What are the effects of PTH and calcitriol on blood Ca2+?

They increase blood Ca2+ by promoting bone Ca2+ release, increasing distal Ca2+/Mg2+ reabsorption, and increasing intestinal Ca2+ absorption.

What are the effects of calcitonin on calcium balance?

It decreases blood Ca2+ by inhibiting intestinal Ca2+ absorption, osteoclast activity, and renal Ca2+ and phosphate reabsorption.

What are major causes of hypercalcemia?

Hyperparathyroidism, cancers such as breast, lung, kidney, and bone marrow cancers, and excessive calcium or vitamin D supplementation.

What are major causes of hypocalcemia?

Hypoparathyroidism, vitamin D deficiency, and chronic renal failure.

What are the major roles of magnesium and phosphate in electrolyte balance?

Magnesium is found in higher concentrations in the ICF and is reabsorbed mainly in the proximal convoluted tubule; phosphate is reabsorbed in the proximal convoluted tubule, with reabsorption stimulated by calcitriol.

What is the major extracellular anion, and how is chloride handled?

Chloride is the most abundant ECF anion; it is absorbed from the GI tract with sodium and reabsorbed by the kidneys with sodium.

What is the normal ECF pH range, and what are acidosis and alkalosis?

Normal ECF pH is 7.35–7.45; acidosis is below 7.35 and alkalosis is above 7.45.

Why is acid-base balance important?

Acidosis and alkalosis strongly affect the cardiovascular and nervous systems, and survival is not possible below pH 6.8 or above pH 7.7.

What is acid-base balance?

The balance between H+ gains and H+ losses so that H+ produced by digestion and metabolism is matched by elimination through the urine and lungs.

What are the three categories of acids discussed in the lecture?

Organic acids, volatile acids, and fixed acids.

What are examples of organic acids and how are they produced?

Lactic acid is produced during anaerobic pyruvate metabolism, while ketone bodies are produced from acetyl-CoA.

What is a volatile acid, and why is carbonic acid important?

A volatile acid can leave body fluids through the lungs; carbonic acid forms from CO2 and water, and changes in CO2 strongly affect H+ concentration and pH.

What are fixed acids, and where do they come from?

Fixed acids remain in body fluids until eliminated by the kidneys; sulfuric and phosphoric acids are produced from the catabolism of amino acids, phospholipids, and nucleic acids.

What are the three major chemical buffer systems?

Protein buffers, the carbonic acid-bicarbonate buffer system, and the phosphate buffer system.

How do protein buffers help regulate pH?

Amino acids in proteins can accept or release H+; when pH changes, protein groups can bind or release H+ to help limit changes in ECF and ICF pH.

What is the role of hemoglobin as a buffer?

Hemoglobin is the only intracellular buffer system with an immediate effect on ECF pH and helps prevent drastic pH changes when plasma CO2 changes.

How does the carbonic acid-bicarbonate buffer system work?

CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3−; when pH falls, HCO3− binds H+ to form H2CO3, which can become CO2 and H2O for removal by the lungs.

What is the role of the phosphate buffer system?

It uses H2PO4− ↔ H+ + HPO4²− and supports the bicarbonate system, especially in the ICF and urine.

How does respiratory compensation regulate ECF pH?

Changes in respiratory rate alter CO2 levels; increased CO2 lowers pH, while decreased CO2 raises pH.

What stimulates an increase in respiratory rate during acid-base compensation?

A rise in CO2 stimulates the respiratory center, increasing respiratory rate to remove more CO2.

How does renal compensation regulate acid-base balance?

The kidneys alter H+ and HCO3− secretion and reabsorption in response to changes in plasma pH.

What are the main renal responses to acidosis?

Increased H+ secretion, increased buffer activity, increased CO2 removal, and increased NaHCO3 reabsorption.

What are the main renal responses to alkalosis?

H+ secretion decreases, bicarbonate reabsorption decreases, HCO3− is secreted, and HCl is reabsorbed.

What is respiratory acidosis, and what is its usual cause?

Respiratory acidosis is a decrease in pH caused by inability to eliminate enough CO2, resulting in hypercapnia; the usual cause is hypoventilation.

What is respiratory alkalosis, and what causes it?

Respiratory alkalosis is a decrease in plasma CO2 caused by hyperventilation, resulting in an increase in pH.

What symptoms can occur during hyperventilation-induced respiratory alkalosis?

Tingling of the hands, lips, and feet, light-headedness, and, if severe, unconsciousness.

What are the major causes and compensations for metabolic acidosis?

Causes include increased fixed/organic acid production, impaired renal H+ excretion, and severe HCO3− loss such as with diarrhea; compensation includes increased respiratory rate, buffering of H+, and renal H+ secretion with HCO3− reabsorption.

How can respiratory and metabolic acidosis occur together during drowning?

Struggling muscles produce lactic acid while stopped breathing causes CO2 accumulation; treatment involves artificial/mechanical respiratory assistance and appropriate IV buffering solutions.

What causes metabolic alkalosis, and how does the body compensate?

An increase in HCO3− causes metabolic alkalosis; compensation includes reduced breathing rate to retain CO2 and increased urinary HCO3− loss.

Why can repeated vomiting cause metabolic alkalosis?

Vomiting removes stomach HCl, increasing the relative amount of HCO3− in the ECF and causing alkalosis.