Fluid and Electrolyte Balance

Interrelationship of Fluid and Electrolyte Balance

• Chemical bonds dissociate into separate particles
• Electrolytes' dissociated particles are called ions with electrical charge
• Organic substances like glucose have bonds preventing dissociation, and are known as non-electrolytes
• Fluid and electrolyte balance implies homeostasis
• Both fluid balance and electrolyte balance are interdependent
• Cations = positive charge, while Anions = negative charge

Total Body Water

• The fluid content in the human body ranges from 45% to 75% of total body weight
• Fluid content differs depending on age, gender, weight, and body fat
• As one ages, the kidneys produce less concentrated urine and sodium-conserving responses become less effective
• Adipose (fat) tissue has the least amount of water compared to other tissues
• In newborn infants, roughly 75% of body weight is water
• Males have higher water content compared to females

Body Fluid Compartments

• The important fluid compartments are extracellular and intracellular
• Extracellular fluid (ECF) makes up the internal bodily environment and allows for a constant environment for cells, and transports substances to and from cells
• ECF mainly constitutes plasma and interstitial fluid (IF)
• Lymph, blood, cerebrospinal fluid (CSF), and joint fluids are regarded as extracellular
• Intracellular fluid (ICF) holds water inside cells
• ICF is important for intracellular chemical reactions that maintain life
• By volume, more fluid is intracellular than extracellular

Extracellular Versus Intracellular Fluids

• Plasma and IF in ECF have identical chemical makeup
• Intracellular fluid is different substantially
• Blood has a slightly greater total of ions than Interstitial Fluid does
• Blood has protein anions, whereas IF has few, if any

Measuring Electrolyte Reactivity

• Electrolyte concentration or weight equals milligrams per 100 ml of solution (mg%)
• Milliequivalent (mEq) measures number of ionic charges/electrocovalent bonds in solution; used for electrolytes

Electrolytes

• Sodium is abundant in plasma and interstitial fluid
• Potassium is abundant in intracellular fluid
• Knowing homeostatic levels helps determining an electrolytic imbalance
• A blood test returns a value

Avenues by Which Water Enters and Leaves the

• The body gains water through the digestive tract
• Water leaves the body via urine, expired air, sweat, and feces

General Principles of Fluid Balance

• Cardinal rule of fluid balance requires intake to equal output
• Mechanisms exist to adjust output/intake to maintain fluid balance, such as the renin-angiotensin-aldosterone system (RAAS) which can decrease urine output during dehydration
• Rapid fluid balance mechanisms control water movement between fluid compartments

Mechanisms that Maintain Homeostasis of Total Fluid Volume

• Homeostasis of total water volume gets maintained by adjusting urine volume and fluid intake
• Reduced fluid intake elevates antidiuretic hormone (ADH) secretion by osmoreceptors in the thirst center, wall of the third ventricle (subfornical organ [SFO]), and the supraoptic and paraventricular nuclei of the hypothalamus
• Osmoreceptors are specialized cells that can notice when there is an increase of solute concentration (osmolality) in the ECF from water loss

Regulation of Urine Volume

• Urine volume depends on glomerular filtration rate (GFR), generally constant except when abnormal, and the rate of tubular reabsorption of water which fluctuates
• Tubular reabsorption is adjusted by the amount of ADH and aldosterone secreted

Factors that Alter Fluid Loss Under Normal Conditions

• Rate of respiration and volume of sweat secreted may alter fluid output
• Vomiting, diarrhea, or intestinal drainage may cause electrolyte imbalance
  • Simple thirst to muscle weakness and kidney failure can result
• Dehydration severity gets measured by weight loss' percentage relative to normal body weight
• Clinically, dehydration gets normally detected by the loss of turgor (skin elasticity)
  • Tenting, in which there is a slow return of pinched skin

Regulation of Water and Electrolyte Levels in Plasma and Interstitial Fluid

• Law of capillaries is a theory about water movement between blood plasma and interstitial fluid
• The mechanism consists of blood hydrostatic pressure (BHP), blood colloid osmotic pressure (BCOP), interstitial fluid hydrostatic pressure (IFHP) and interstitial fluid colloid osmotic pressure (IFCOP)
• Two pressures create a vector in one direction, while the other two create a vector in the opposite one

Starling’s Law

• Blood hydrostatic pressure promotes filtration
  • Fluid exits the capillary and enters the interstitial fluid
  • Process is similar to the Bowman's capsule
• Interstitial hydrostatic pressure resists filtration, by drawing fluid back into the capillary (~1mmHg)
• Blood colloid osmotic pressure utilizes large plasma proteins (Albumin) which do not exit the blood and resist filtration
• Interstitial osmotic pressure has little protein, favoring filtration

Flow Direction

• Arterial end of the capillary has blood pressure's outward driving force being greater than the inward osmotic pressure force, leading to outward fluid movement
• Venous end of the capillary has osmotic pressure greater than hydrostatic pressure, promoting inward fluid movement
• Fluid leaving the capillary at the arterial end reenters, before exiting, at the venous end
• Lymph drains excess fluid and proteins from interstitial space into the venous system

Starling's Law, Data

• Capillary end values
  • Blood hydrostatic pressure: 35 mmHg
  • Interstitial fluid hydrostatic pressure: 2 mmHg
  • Blood colloid osmotic pressure: 24 mmHg
  • Interstitial fluid colloid osmotic pressure: 0 mmHg
  • The 8 mmHg overall pressure forces fluid out of the blood and into the interstitial fluid
• Venous end values
  • Blood hydrostatic pressure: 15 mmHg
  • Interstitial fluid hydrostatic pressure: 1 mmHg
  • Blood colloid osmotic pressure is 25 mmHg
  • Interstitial fluid colloid osmotic pressure: 3 mmHg
  • Overall negative pressure causes fluid to flow back from the IF to the blood

Albumin

• Albumin is is the greatest plasma protein in blood
• The liver synthesizes most
• It prevents fluid loss in interstitial tensions
• It also acts as a transport protein
• At the arterial end, the blood hydrostatic pressure is highest, so it pushes fluid from the IF
• If a patient is edematous or has ascites, common test is albumin

Edema

• Edema results from any disruptions of in factors maintaining the interchange between blood plasma and IF
• A classic instance of fluid imbalance
• Defined as too much fluid in intercellular tissue spaces
• Electrolyte retention in the ECF can cause elevated capillary blood pressure or reduced concentrations of normally retained plasma proteins
• Pitting edema: Indentations from an examiner remains in its place on the anterior leg after pressure

Regulation of Water and Electrolytes in Intracellular Fluid

• Plasma membrane affects intracellular fluid composition
• Forces of IF and ICF control water transfer between the ECF and ICF
  • Osmotic pressure influenced by protein molecules in ICF that cannot diffuse through cell membrane pores
  • Electrolyte transport
  • Diffusion, charge difference across cell membrane
• Osmosis causes water movement

Regulation of Sodium and Potassium Levels in Body Fluids

• Normal sodium levels in the IF and potassium in ICF depending on factors (ADH and aldosterone)
  • By regulating amount of water reabsorbed by the renal tubules, ADH controls electrolyte concentrations and colloid osmotic pressure in ECF -Sodium retained by renal tubule is regulated by aldosterone that effect the ECF
• The kidney regulates sodium levels
• Chlorides are usually excreted in the urine with potassium
• Hypokalemia occurs in starvasion, burns, dehydration

Sodium and the Body

• The kidney is a chief regulator of sodium, as its capable of essentially sodium-free urine
• Sweat loss can become important for sodium
• Water dilutes sodium with its intake as opposed to normal replacement, ex: drinking gatorade after marathon run
• Excreting essentially sodium-free urine occurs when water is conserved
• Chlorides are always linked to sodium as they are its main negative charged partners

Fluid and Electrolyte Disorders

• Excessive water loss is also know as hypovolemia, a cause of inadequate fluids in the ECF leading to hypovolemia
• Kidneys effect fluids volume excess a condition known as hypervolemia, this also occurs alongside many conditions like failure
• Electrolyte disturbances occur in fluid related conditions
• Low plasma sodium known as hyponatremia, or an excess of fluids at 136 mEq/L
• Hypokalemia imbalance is a loss of potassium from the body with levels at under 3.5 mEq/L

Acid-Base Balance

Introduction

• Acid-base balance is a key homeostatic mechanism
• Acid-base balance refers to regulation of the body fluids' hydrogen ion concentrations
• Processes depend on hydrogen ion concentration
• Small deviation in normal pH is fatal
• CO2 + H20 ↔ H2C03 ↔ HCO3 + H+
• Study of acid-base physiology studies hydrogen ions

Review of pH Concept

• pH ranges from 0-14
• When H+ concentratrions increase, pH goes down and turns to acidic
• When H+ concentrations decrease, pH and alkalinity increase
• Negative logarithm refers to the number of hydrogen ions in a solution
• pH shows the acidity or alkalinity of a solution
  • pH of 7 marks neutrality
  • pH value lower that 7.35 refers to acidosis
  • pH value higher than 7.45 refers to alkalosis
• Gastric juice, pH of 1, is the most acidic bodily substance

pH

• pH indicates acidity or a solution's alkalinity
• With increasing amounts of acidity [H+], the pH goes down. In opposition, alkilinity is also present and increases the pH with reduced acidity
• Neutrality = equal amounts of both and has a pH value of 7
  • lower number indicates acidity over alkalinity
  • higher number greater than 7 indicates alkalinity over acidity

Sources of pH-Influencing Chemicals

• Carbonic acid gets produced via aerobic glucose metabolism
  • CO2 + H20 ↔ H2C03 ↔ HCO3 + H+
• Lactic acid gets produced during anaerobic glucose metabolism
• Sulfuric acid: oxidation of sulfur amino acids produces
• Phosphoric acid comes from phosphotein/ribonucleotide breakdown
• Acidic ketone bodies occur during incomplete fat breakdown (keto diet)
• Acids/bases enter blood through absorption from foods

Types of pH Mechanisms

• Chemical mechanism buffers pH
• Physiological mechanism is a secondary defense
• Homeostatic balances buffers, respiration, and kidney acids

Types of pH Mechanisms

• Chemical type is fast and changes or neutralizes hydrogen and pH imbalances
• Physiological type occurs as a secondary defense
• Homeostatic type buffers, respiration and excretions

pH

• pH values range from 7.36-7.41
• Maintaining the pH range is vital for chemical processes

Buffers

• Buffers prevent pH changes when acids/bases are presented
• The buffer system is either a weak acid (or acid salt) with a basic salt
• Ex: bicarbonate pairs, plasma and protein pairs, hemoglobin/phosphate pairs
• Important when adjustments in concentration are small
  • Increased H+ pulls H+ from buffer pairs
• Decreased H+ allows the blood to donate/donate to blood

Buffers

• Adding acid lowers H+ (lesser acidity) where pH will still diminish whether if buffers (help minimize them) is present
• A buffer example occurs when lowering pH from 6.5 to 6.2
• If buffers are present, corrections to normal will occur so as not to become too acidic
• If a base is vice versa, then blood/h+ values increase because pH has lowe acidity so the pair will remove H+ from blood

Buffers

• Addition of hydrochloric acid will decrease numbers to pH 7.27
• Not adding buffer would increase numbers to pH 3.4
• In both instances though, pH will likely be present for lower numbered acidity though can be helped minimized by buffers

Explanation of Respiratory Mechanisms

• Increased carbon directly influences hydrogen concentration and acid
• Increased respiration means less dioxide, ions and hydrogen
• Decreased will increase the concentrations
• The body's responses will be adjusted if carbon dioxide raises or lowers to make for easier breathing

Respiratory mechanisms of pH

• When blood pH lowers, hydrogen concentration increases and needs to increase respirations to eliminate H2O
• Arterial blood sensitive to carbon dioxide content, stimulate carotid chemoreflexes , hydrogen and increases pH levels back to setpoints
• Rises in levels lead hyperventilation
• CO2 often reaches a state, or setpoint while an increased state of alkalinity triggers hypo to compensate for by decreasing points
• An increase in blood the normal (or ) triggers that serves as a by decreasing set point

Arterial Blood gas (ABG) Analysis

• ABG assesses artery samples
  • PH
  • PC02
  • HC03 Results can display how good breathing or balance is Oxygen levels test well or saturating the blood and how well balances Analyzing carbonic dioxide is good assessing venting quality or if bicarbonate

ABGs

• pH below 7.35 signifies acidosis
  • If it is above 7.45 is signifies alkalosis
• Low pH and increased PCO2 refer to respiratory acidosis
• High pH and low PCO2 refer to respiratory alkalosis
• Low pH and low [HCO3-] refers to metabolic acidosis
• High pH and high [HCO3-] refers to metabolic acidosis

Acid-Base Imbalances

• High presence of acids increases bicarbonate amounts relative to carbonic acid
• Not addressing issues can develop into acidosis
• Abnormal intake results in vomiting/improper antiacid intake
• High pressure can alter balances due to bodily infections or increased intakes
• In cases of overdose may induce breathing to be supressed
• Infections may cause hyperventilation as well with carbonic acid reduction

Urinary Mechanisms that Control pH

• Acid-based can be regulated because waste and hydrogen gets excreted and then reabsorbed when turning acid
• High acid amounts will result in high absorption and with no sodium when high alkaline
• Kidneys are in change of matching amounts

Regulating pH of Urine and Blood

• Reduced pH accelerates renal mechanisms to remove acid from conserving blood
• Reduced acid in the kidney leads for increased extraction ions in exchange for sodium, as well to increasing blood
• If it acidic, then kidneys increase extract + and add a base
• Similarly, Dioxide diffused/water mixes with acid form carbon acids to combine and mix with carbonate and potassium will be excreted