Fluids and Electrolytes in the Human Body (week 8)

Electrolyte

Ion, compound that dissociates in water to ions, conducts electricity.

common electrolytes (conduct electricity)

ionic compounds, inorganic acids, inorganic base, salts

Acids

Substances that release H+ ions in water.

Bases

Substances that release OH- ions in water.

Salts

Compounds that dissociate into cations and anions (not H, OH).

Non-electrolytes

Compounds that do not dissociate in water.

Ionic bonds

Chemical bonds formed by electron transfer of 2 opposing ion charges.

Covalent bonds

Chemical bonds formed by electron sharing, can't be broken except by chem.reactions/intense heat. (Organic compounds: lipids, carbohydrates, proteins, nucleic acids)

Compounds that don't form ions in water:

non-electrolytes, organic compounds (contain covalent bonds, don't dissociate, shared electron bond can't be broken by water molecules)

functions of electrolytes:

maintain fluid balance & acid-base balance, make electrical currents, be cofactors

Fluid balance

Control of water movement in body compartments.

Acid-base balance

Maintenance of pH levels in the body.

Electrical currents

Generated by electrolytes in muscles and neurons.

Cofactors

Substances that assist enzymes in biochemical reactions.

total body fluid of males, females, infants

60%, 55%, 75%

Intracellular fluid (ICF) (major fluid compartment)

Fluid (cytosol) within cells, comprising 2/3 of body fluids.

Extracellular fluid (ECF)(major fluid compartment)

Fluid outside cells, comprising 1/3 of body fluids.

Plasma

Liquid portion of blood, 20% of extracellular fluid.

Interstitial fluid (IF) (part of ECF)

Fluid between tissue cells (lymph, eye fluid, etc.), 80% of extracellular fluid.

Major cation in extracellular fluid

Sodium (Na+) is the primary cation, similar in plasma & interstitial fluid

Major anion in extracellular fluid

Chloride (Cl-) is the primary anion followed by bicarbonate ion (HCO3-).

protein anion concentration..

intracellular fluid>>plasma>interstitial fluid

Major cation in intracellular fluid

Potassium (K+) is the primary cation, Mg2+ also important.

Major anion in intracellular fluid

Phosphate is the primary anion.

Sodium-Potassium conc.

very low is ICF, reflect activity of cellular ATP dependant on Na+/K+ pumps

electrolyte composition of ICF

potassium, magnesium, phosphate, protein anions, sulphate

electrolyte composition of ECF

interstitial fluid: Sodium, calcium, chloride, bicarbonate.

blood plasma: sodium, calcium, chloride, bicarbonate, protein anions

Resting membrane potential

Negative charge inside plasma membrane relative to outside in all cells.

Resting membrane potential is due to three key factors:

1. Action of Sodium-Potassium Pump: 3 Na+ pumped out for every 2 K+ pumped in

2.Intracellular protein anions are trapped

3. Plasma membrane is more permeable to potassium than to sodium

Acid (special type of electrolyte)

Substance dissociate & releases hydrogen ions (protons) in water.

Strong acid

Completely dissociates, releasing many of H+ ions. ex. HCl

Weak acid

Partially dissociates, releasing few H+ ions. ex. carbon acid HCO3-

Example of strong acid

Hydrochloric acid (HCl) dissociates fully.

Example of weak acid

Carbonic acid (H2CO3) dissociates partially.

Base (special electrolyte)

Substance that accepts hydrogen ions from solution.

Strong base

Completely dissociates, removing H+ from solution. (ex. OH- + H+ = H2O)

Weak base

Partially accepts H+ ions in solution. (ex. H2CO3 = H+ + HCO3)

pH

Measure of H+ concentration per litre of solution.

pH scale

Ranges from 0 (acidic) to 14 (basic).

Neutral solution

pH of 7 indicates equal H+ and OH-.

Acidic solution

pH below 7 indicates higher H+ concentration less OH

Basic solution

pH above 7 indicates lower H+ concentration more OH.

pH change significance

Each 1 pH change equals 10-fold H+ change.

Salt

Electrolyte, ionic bonds, ions other than H+ & OH-, ex. NaCl

Salt formation

Acids and bases react to form salts and water (neutralization reaction).

Neutralization reaction

Reaction that prevents pH changes from acids/bases (not H+ donor or acceptor)

pH homeostasis importance

Big pH changes harm metabolic processes because they interfere with protein shape &

functions,

normal blood pH

7.35 - 7.45

Buffer

Solution resisting pH changes from added acids/bases.

How buffers work?

buffers has a weak acid & its salt (weak base), don't react with each other but with an added base/acid

Carbonic acid-bicarbonate buffer

Buffer system reacting to maintain pH balance. (H2CO3 HCO3- = + H+)

Acid component of buffer reacts when

base added by releasing H+ ions

Base component of buffer react when

acid is added by absorbing H+ ions

Chemical buffers (pH mechanism)

Immediate mechanism for short-term pH maintenance.

Respiratory system (lungs, pH mechanism)

Regulates carbon dioxide levels in body, works in 1-3 mins

Renal system (kidneys, pH mechanism)

Controls acid-base balance by excreting ions into urine, hours-days to affect pH

most abundant chemical buffer in ECF

regulator of blood pH bicarbonate to carbonic acid (HCO3- basic = H2CO3 acidic)

most effect buffer in urine & intracellular fluid:

phosphate buffer system, hydrogen phosphate to dihydrogen phosphate (HPO4 basic = H2PO4 acidic)

Add an acid to buffer (HCl)

Hydrogen ions released by the strong acid combine with the bicarbonate ions and form carbonic acid (a weak acid)

• The strong acid has been converted to a weak acid

• The pH of the solution decreases only slightly

add base to buffer (NaOH)

The released OH- group reacts with the H+ released from carbonic acid to form water and bicarbonate ion (a weak base)

• The strong base has been converted to a weak base

• The pH of the solution increases only slightly2. Respiratory system

• Negative feedback loop regulates

blood pH by altering respiration rate

respiratory pH regulation:

Negative feedback loop regulate blood pH by altering respiration rate (ventilation rate). CO2 + H2O = H2CO3 = H+ + HCO3

increase acidity of blood

increase acidity = increased H+, they'll combine with bicarbonate to make more carbonic acid which forms more CO2 & H2O. increased ventilation rate to remove excess CO2 to decrease H+

decrease acidic of blood

decrease acidity = decreased H+. Carbonic acid breaks down to make more hydrogen ions & bicarbonate, to do this lungs must retain more CO2 to make more carbonic acid (decreased ventilation), result in more H+ in blood

acidosis control in kidney

low blood pH:

1. H+ are secreted (from blood) into urine (proton pumps)

2. Bicarbonate ions are reabsorbed into the blood.

Urine pH Range

Normal urine pH varies from 4.5 to 8.

alkalosis control in kidney

high blood pH: The mechanisms to deal with

acidosis decrease

Acidosis

Condition with blood pH<7.35 (CNS depression → coma → death). blood may be alkaline, but still considered acidosis.

respiratory acidosis

Increased pCO2 in blood.

Impaired ventilation of the lungs (thus removal of CO2):

• Asthma

• Emphysema

• Barbiturate poisoning

• Damage of the brain stem

• Damage to respiratory muscles

metabolic acidosis

Increase in acids (increased H +/reduced bicarbonate ions in blood): Lactic acidosis, Ketoacidosis, Severe bicarbonate loss, Decreased renal excretion of H+

Lactic Acidosis

increased production of acids. Acidosis from strenuous exercise or hypoxia.

Ketoacidosis

Acidosis from uncontrolled diabetes mellitus or starvation.

severe bicarbonate loss

increases acids, caused from chronic diarrhea

decreased renal excretion of H+

increases acids, caused from kidney diseases

Alkalosis

Condition with blood pH greater than 7.45. Overexcitability of CNS → convulsions → death.

Respiratory Alkalosis

Decreased pCO2 due to hyperventilation: high altitudes, anxiety/stress, pain, aspirin OD.

hyperventilation decreases CO2:

cause reaction to shift and make more CO2 (HCO3- + H+ = H2CO3 = CO2 + H2O)

Metabolic Alkalosis

Increased bicarbonate ions in blood: loss of acids (excessive vomit, loose gastric HCl). too much alkaline drugs (antacid)

Proton Pumps

Transport proteins secreting H+ into urine.

CNS Depression

Reduced central nervous system activity, can lead to coma.

Overexcitability of CNS

Increased CNS activity, can lead to convulsions.

Bicarbonate Reabsorption

Kidneys reclaim bicarbonate ions into the blood.