Water, Electrolyte, and Acid-Base Balance

Introduction to Water, Electrolyte, and Acid-Base Balance

• Electrolytes (ions) are dissolved in water within body fluids, intimately relating water and electrolytes.
• Water movement across cell membranes occurs due to solute concentrations inside and outside cells
• Crucial electrolytes include Na+, K+, Ca2+, H+, OH, Cl, and Mg+2
• Water and electrolyte balance is essential for maintaining homeostasis.
• Fluctuations in fluid and electrolyte levels must be balanced by replacement mechanisms and excess excretion
• The body must maintain balanced quantities of fluids and electrolytes entering and leaving

Distribution of Body Fluids

• The body fluids is not uniformly distributed
• Fluids reside in compartments, with water and electrolyte movement between them being regulated.

Fluid Compartments

• Adult females are 52% water by weight, while males are 63%, due to differences in adipose tissue and muscle content.
• Water averages 40 liters in the human body, divided between intracellular and extracellular compartments.
• Intracellular fluid (ICF) includes all water and electrolytes within cells, accounting for 63% of total body water.
• Extracellular fluid (ECF) contains all water and electrolytes outside of cells, making up 37% of total body water.
• ECF consists of interstitial fluid, blood plasma, and lymph.
• Transcellular fluid is a small portion of the ECF and includes fluids like cerebrospinal fluid, fluids within the eyeball, synovial fluid in joints, serous fluid, and exocrine gland secretions.

Body Fluid Composition

• Extracellular fluids (ECF) have high concentrations of sodium, chloride, and bicarbonate ions.
• ECF contains lesser amounts of potassium, calcium, magnesium, phosphate, and sulfate ions.
• Blood plasma, an extracellular fluid, has more protein compared to other ECF components.
• Intracellular fluid (ICF) has high concentrations of potassium, phosphate, and magnesium ions.
• ICF contains lesser amounts of sodium, chloride, and bicarbonate ions.
• ICF has more protein than blood plasma.

Movement of Fluid Between Compartments

• Hydrostatic and osmotic pressures regulate water and electrolyte movement between compartments.
• Fluid shifts from plasma to interstitial space at the arteriolar end of capillaries because blood hydrostatic pressure exceeds colloid osmotic pressure.
• Fluid moves from interstitial space back into plasma at the venular ends of capillaries, where colloid osmotic pressure (exerted by plasma proteins) exceeds hydrostatic pressure.
• Fluid migrates from interstitial fluid into lymphatic capillaries due to a higher hydrostatic pressure there.
• Body fluid compositions differ between compartments, but total solute concentrations and water amounts are generally equal.
• Water gain or loss causes shifts affecting intracellular and extracellular fluids via changes in osmotic pressure.

Water Balance

• Homeostasis is achieved by controlling water intake and output.
• Water balance exists when water intake equals water output

Water Intake

• The volume of water gained daily differs among individuals.
• 60% of daily water comes from drinking fluids
• 30% comes from moist foods
• 10% is produced during nutrient metabolism and is known as metabolic water

Regulation of Water Intake

• Thirst is the primary regulator of water intake.
• The thirst center is located in the hypothalamus.
• Thirst arises from increased osmotic pressure in extracellular fluids, involving neural and hormonal factors.
• Osmoreceptors detect these changes in the hypothalamus.
• A mere 1% decrease in total body water initiates the homeostatic thirst mechanism.
• The water intake inhibits the thirst mechanism due to the stomach distenstion

Water Output

• Water is lost through urine, feces, sweat (sensible perspiration), evaporation from skin (insensible perspiration), and during breathing.
• Water excretion breakdown: 60% in urine, 6% in feces, 6% in sweat and 28% by evaporation from the skin and breathing
• The exact percentages from each area depends on environmental variables like temperature, relative humidity, and exercise levels.

Regulation of Water Output

• Urine production is the main regulator of water output.
• Distal convoluted tubules (DCTs) and collecting ducts (CDs) in nephrons control water output and are usually impermeable to water.
• Antidiuretic hormone (ADH) from the posterior pituitary increases DCTs and CDs permeability, enhancing water reabsorption and reducing water loss in urine.
• Consuming enough or excess water inhibits the ADH mechanism, leading to more water excretion in urine

Clinical Application: Water Balance Disorders

• Dehydration occurs when water output exceeds water intake and can result from excessive sweating, water deprivation, prolonged vomiting, or diarrhea.
• During dehydration, extracellular fluid becomes concentrated, causing water to move out of cells by osmosis; results in hyperthermia due to reduced sweating and failure of the temperature-regulating system.
• Hypotonic hydration (water intoxication) happens when water intake exceeds output and extracellular fluid becomes hypotonic, causing water to enter cells by osmosis.
• Hyponatremia can occur, causing symptoms like confusion, exhaustion, headache, diarrhea, nausea, and vomiting.
• Edema an abnormal accumulation of extracellular fluid in interstitial spaces, caused by declining plasma proteins.
• Edema can also result from hypoproteinemia, lymphatic vessel obstruction, increased venous pressure, inflammation, or increased capillary permeability.

Electrolyte Balance

• Electrolyte balance is maintained when electrolyte quantities gained equal the amounts lost.
• Homeostatic mechanisms ensure proper ion concentrations in blood plasma and interstitial fluids.

Electrolyte Intake

• Crucial electrolytes: sodium, potassium, calcium, magnesium, chloride, sulfate, phosphate, bicarbonate, and hydrogen ions.
• Electrolytes come mainly from food, but also from fluids, and metabolism byproducts.
• Salt cravings may indicate a severe electrolyte deficiency.

Electrolyte Output

• Electrolyte loss occurs mainly through urine, as well as through sweat and feces.
• The Kidneys adjust electrolyte excretion in urine to maintain homeostatic ion concentrations.
• Sodium, potassium, and calcium concentrations impact nerve impulse conduction, muscle contraction and cell membrane potentials.
• Sodium ions make up ~90% of the positive ions in extracellular fluids and their reabsorption is controlled by kidney function and aldosterone.
• Aldosterone also regulates potassium ion concentration; potassium ions excretion increases when sodium ions retention increases.
• Elevated potassium levels increase, prompting aldosterone secretion

Electrolyte Output part 2

• Parathyroid hormone (PTH) is secreted when calcium concentrations in body fluids decline which increases the concentrations of calcium in extracellular fluids.
• Positively charged ion regulation impacts negatively charged ion concentrations.
• Chloride ions (Cl-) are passively reabsorbed alongside actively transported sodium (Na+) ions due to charge attraction.
• Some phosphate (PO₄³⁻) and sulfate (SO₄²⁻) ions are actively transported.

Acid-Base Balance

• Electrolytes releasing hydrogen (H+) ions in water are acids, while those combining with H+ ions are bases.
• Homeostasis depends the acid and base concentrations in body fluids balance
• Hydrogen lons originate as byproducts of metabolic processes which include aerobic/anaerobic respiration of glucose, incomplete oxidation on fatty acids, oxidation of amino acids containing sulfur, breakdown of nucleaic acids and phosphoproteins

Strengths of Acids and Bases

• Strong acids ionize fully, such as hydrochloric acid (HCl) in the stomach.
• Weak acids ionize less thoroughly, such as carbonic acid (H₂CO₃) in blood plasma.
• Bases that release negative ions can combine with (H+) ions to produce (H₂O) reducing acidity.
• Strong Bases ionize effectively like sodium hydroxide (NaOH) release OH¯ ions.
• Weak Bases ionize to a lesser extent. Sodium Bicarbonate (NaHCO3) that releases HCO3¯ ions

Regulation of Hydrogen Ion Concentration

• pH of body fluids is regulated by chemical buffer systems, the brainstem's respiratory center, and the kidneys.

Chemical Buffer Systems

• Chemical buffer systems are in all body fluids which minimize pH changes.
• Basic buffer components combine with strong acids, converting them to weaker forms
• Acid components buffer strong bases to weaker bases.
• Major chemical buffer systems in body fluids include bicarbonate, phosphate, and protein.

Bicarbonate Buffer System

• Bicarbonate buffer system is located in extracellular and intracellular fluids.
• The Bicarbonate (H₂CO₃) is the weak acid of the buffer and HCO₃¯ is the weak base
• Excess H+ ions combine with HCO₃¯ to make carbonic acid to help minimize the H+ increase
• In alkaline conditions, H+ and H₂CO₃ increase to neutralize excess body base

Phosphate Buffer System

• Phosphate buffer system are located in intracellular and extracellular fluids. it is important in kidneys.
• In acidic conditions, excess H⁺ +HPO₄²⁻→H₂PO₄⁻ is produced neutralizing excess acidity by binding H⁺ ions from body fluids.
• In alkaline conditions, H₂PO₄→H⁺ +HPO₄²⁻ is produced neutralizing excess base by releasing free H⁺

Protein Buffer System

• Protein buffer system consist of plasma proteins such as albumins, globulins, and hemoglobin.
• In acidic conditions, the amino groups bind to H⁺ ions and in basic/alkaline conditions, the carboxyl groups release H⁺ ions.

Respiratory CO₂ Excretion, Renal H+ Excretion

• The respiratory center in the brainstem regulates ion concentration by adjusting breathing depth and rate.
• Increase in exersice increases carobn levels in blood due to carbon dioxide and water combining to create H₂CO₃
• The H₂CO₃ then dissociates into H⁺ and HCO₃⁻ decreasing pH levels
• The respiratory center increases breathing rate and depth, to excrete more Carbon Dioxide to reach normal pH levels
• pH returns to normal reversed reactions, and the carbon dioxide is exhaled which follows the equation H⁺ +HCO₃ → H2CO₃ → CO₂ +H2O
• Excess hydrogen secreted through Nephrons regulate the concentration of H+ lons

Time Course of Hydrogen Ion Regulation

• Regulatory mechanisms of H+ concentration occur at varying rates.
• Chemical buffers are the first line of defense against shifts in pH due to immediate actions.
• Physiological buffer systems regulate the effects on the ph in the body (respiratory and renal) the function is slower
• Respiratory mechanisms work in minutes, and renal mechanisms take 1-3 days

Acid-Base Imbalances

• Chemical and physiological buffers usually keep body fluids within narrow pH ranges.
• Abnormal conditions may shift the acid-base balance out of this normal range.
• A normal blood pH is 7.35 to 7.45
• A pH below 7.35 is acidosis, and a pH above 7.45 is alkalosis
• Imbalances is life threatening, a pH less than 6.8 or more than 8.0 is fatal
• Acidosis is high acidity and alkalosis is high alkanity

Acidosis

• Acidosis symptoms: lowered CNS function drowseiness, disorientation, stupor and cyanosis with two types: respiratory and metabolic
• Respiratory Acidosis results in increased levels of H₂CO₃
• Respiratory Acidosis can be from injury and obstruciton Several factors attempt to resist pH change of respiratory acidosis through chemical buffers, increasing rate and depth of breathing and renal excretion of H + ions.

Metabolic Acidosis

• Metabolic Acidosis is from nonrespiratory acids and kidney and intestine diseases
• Diseases like kidney disease decreases glomerular acids, vomiting of stomach contents & diarrhea Increased respiratory rate, or increasing the amount of hydrogen ions compensate for the increased in acidity

Alkalosis

• Alkalosis: tight headedness, agitation, dizziness, tingling sensations, tetanic muscle contractions with respiration
• Respiratory results from hyperventilation Responses like the chemical buffers from low levels H + can decrease renal secretions for compensation

Metabolic Alkalosis

• Metabolic Alkalosis can be the result of gastric drainage and diuretics causing breathing compensation