Chapter 26: Fluid, Electrolyte and Acid-Base Homeostasis

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Dr. T, APSU

body fluid

(1) Any natural liquid (water and dissolved solutes) found within the body or any liquid secretion of the body, e.g., blood, lymph, CSF, urine, semen, or saliva. (2) Total body water, contained principally in blood plasma and in the intracellular and interstitial compartments.

intracellular fluid

[aka cytoplasm] (1) The water and dissolved solutes located within individual cells. (2) The fluid compartment consisting of the cytoplasm (internal contents) of all the cells of the body.

extracellular fluid

(1) The water and dissolved solutes located between individual cells in the body, including both tissue fluid and blood plasma. (2) The fluid compartment consisting of the various fluids found external to all the cells of the body. The extracellular fluid is often subdivided into the interstitial fluid and the plasma.

interstitial fluid = intercellular fluid = tissue fluid

(1) The clear, yellowish protein-poor fluid located between cells in all tissues except blood; it may also be referred to as lymph; this fluid is the medium of exchange for respiratory gases, nutrients, wastes, and regulatory substances between the plasma and the tissue cells. (2) The fluid compartment consisting of the tissue fluid but not the blood plasma. [Note: in terms of composition and physiological functions, lymph is equivalent to the interstitial fluid.]

lymph

The specific name give to the clear, yellowish protein-poor fluid located between cells in all tissues except blood after it has been collected into the vessels of the lymphatic drainage system; it may also be referred to as lymph before it is collected into those vessels; its functions include transport of absorbed lipids from the meals, the return of excess extracellular/interstitial fluid to the cardiovascular system, and a variety of immune defense functions.

blood plasma

The clear, yellowish fluid portion of blood in which red and white blood cells and platelets are suspended; it differs from serum in that it contains fibrin and other soluble clotting elements; this fluid is the medium of transport and solvent for respiratory gases, nutrients, wastes, and regulatory and immune defense molecules between the organs and tissues in different parts of the body.

intracellular compartment = cytoplasmic compartment

The hypothetical space, used in physiological models, which would contain all the fluid found within the cytoplasm of all the cells of the body.

two fluid compartment model

A simplifying mathematical description of water distribution within the body which may be used to understand certain physiological processes, such as exchange of dissolved solutes between cells and their environments, which assumes body water is separated into two locations: (1) water inside cells, the intracellular = cytoplasmic compartment, and (2) the water outside cells, the extracellular compartment.

three fluid compartment model

A simplifying mathematical description of water distribution within the body which may be used to understand certain physiological processes, such as exchange of dissolved solutes between cells and their surroundings and the blood, which assumes body water is separated into three locations: (1) water inside cells, the intracellular = cytoplasmic or intracellular compartment, (2) the water outside cells but not in the blood plasma, the intercellular or interstitial compartment, and (3) the water outside cells in the blood plasma, the plasma compartment.

semipermeable

The property of biological membranes which allows passage of some substances through the membrane while restricting the passage of other substances.

fluid balance

The homeostatic equilibrium maintained by the body for water (hydration status); water gain or deficit = water intake - water loss; it is regulated by the hypothalamus and ANS and influenced by a large number of hormones including antidiuretic hormone (ADH) = vasopressin, atrial natriuretic peptide (ANP), aldosterone, renin - angiotensin system, parathyroid hormone (PTH) = parathormone and calcitonin.

preformed water

Water obtained from the external environment by drinking fluids (~one third of the total water intake) and ingesting foods with a high moisuture content (~two thirds of the total water intake); typically more than 15% of the water obtained by the body.

metabolic water

Water obtained from the internal environment as a byproduct of the catabolic, oxidative breakdown of nutrients; typically less than 15% of the water obtained by the body.

vesicular transport

The processes of movement of water and dissolved solutes within or across cells while packaged in membrane-bound containers, vesicles; inward movement is termed endocytosis, outward movement is termed exocytosis, movement through the cell is termed transcytosis; the Golgi apparatus is often involved in the formation or processing of these vesicles; it is a form of bulk flow at the cellular level.

transcytosis

The process of transport of material across an epithelium, i.e., through the cytoplasm of an epithelial cell, by uptake (endocytosis) on one face (cell membrane) into a coated vesicle, which may then be sorted through the trans Golgi network and transported to the opposite face (cell membrane) in another set of vesicles (exocytosis); e.g., the movement if IgA molecules to the surface of a mucous membrane and the transport of lipoproteins through capillary endothelial cells.

diffusion

The spontaneous movement of molecules or other particles in solution, owing to their random thermal motion, to reach a uniform concentration throughout the solvent, a process requiring no addition of energy to the system.

bulk flow

The movement of water and dissolved solutes, in mass as opposed to a molecule at a time, within the body due the application of some form of pressure; e.g., the movement of vesicles inside cells or across cell membranes (endocytosis, exocytosis), the circulation of blood, lymph, and CSF, the secretions of various glands; the pressure may be applied by the continued synthesis of material or by the application of contractile forces.

edema

Any excessive accumulation of serous fluid or interstitial fluid (lymph) in tissue spaces or a body cavity; significant edema will produce obvious swelling of the involved tissues; it may be localized, due to venous or lymphatic obstruction or to increased vascular permeability (e.g., in inflammation), or it may be systemic due to heart failure or renal disease.

dehydration

Excessive loss of water from the body or from an organ or body part, as a result of illness or fluid deprivation or fluid loss from severe vomiting, diarrhea, or excessive sweating.

electrolyte

A substance which carries an electrochemical charge because its structure has unequal numbers of electrons and protons; all types of charged ions dissolved in body fluids.

monovalent

Describing an atom or molecule with one binding site available for bond formation or a charged ion carrying a charge of +1 or -1.

divalent

Describing an atom or molecule with two binding sites available for bond formation or a charged ion carrying a charge of +2 or -2.

cation

An ion or group of ions having a positive charge and, characteristically, attracting and having the potential to make ionic bonds with negatively charged anions; such positively charged ions move toward the negative electrode in electrolysis and electrophoresis.

anion

An ion or group of ions having a negative charge and, characteristically, attracting and having the potential to make ionic bonds with positively charged cations; such negatively charged ions move toward the positive electrode in electrolysis and electrophoresis.

nonelectrolyte

A substance which does not carry an electrochemical charge because its structure has equal numbers of electrons and protons; all types of uncharged solutes dissolved in body fluids.

percent concentration

A unit of measure of substances commonly used in clinical laboratory medicine; it measures mass per unit volume with the specific unit of milligrams/100 mL = mg/dL (deciliter).

milliequivalents

A unit of measure of electrolytes = charged ions commonly used in clinical laboratory medicine; it measures one-thousandth of an equivalent per unit volume; an equivalent represents the "hydrogen equivalence" when comparing the strength and bond forming relationships between acids and bases; this relationship is the mole (Avagadro's number of atoms or molecules) divided by the valence or Equivalent = Mole/Valence.

milliosmoles

A unit of measure of particles in solution commonly used in clinical laboratory medicine; it measures one-thousandth of an osmole per unit volume; an osmole represents the number of ions or particles into which a given substance dissociates when dissolved into solution; it is used when comparing the osmotic strength of different solutions, e.g., plasma and urine; this relationship is the molecular weight of the solute divided by the number of ions or particles into which a given substance dissociates or Osmole = Molecular Weight/Number of Ions or Particles. [Note: For example, one mole of glucose is also one osmole because glucose molecules do not dissociate into smaller particles in solution while one mole of sodium chloride is equal to two osmoles because salt dissociates into sodium and chloride ions: NaCL Û Na+ + Cl-.

osmotic pressure

The hydrostatic force which can be generated when water moves across a selectively permeable membrane, following its concentration gradient, to a fluid compartment which is hypertonic to the compartment on the other side of the membrane. This force contributes to the overall size and shape of many cells.

osmolarity

The concentration of osmotically active particles in a solution expressed in terms of the Osmoles of solute particles per liter of solution; this measure is commonly used to quantify the tonicity or osmotic strength of solutions (isotonic/isosmotic; hypertonic/hyperosmotic; hypotonic/hyposmotic).

isotonic

An adjective describing any two solutions which have the same or equal osmotic pressure = osmotic strength.

isotonic contraction

The type of skeletal muscular contractions in which the force applied by the muscle is sufficient to move the load, and as a result, the muscle shortens while its muscle tension remains relatively constant.

hypertonic

An adjective describing any solution which has the greater osmotic pressure = osmotic strength of two solutions being compared.

hypotonic

An adjective describing any solution which has the lesser osmotic pressure = osmotic strength of two solutions being compared.

sodium = natrium

A soft, light, extremely malleable silver-white metallic element which reacts explosively with water, is naturally abundant in combined forms, especially in common table salt; symbol Na, atomic number 11; atomic weight 22.99; valence +1; as an electrolyte, the most abundant extracellular cation (90%); important for maintaining the polarized state of cells and a major contributor to the osmolarity of the extracellular fluid; serum reference range: 136-142 mEq/liter; serum sodium levels are regulated by the hormones aldosterone, ADH, and atrial natriuretic peptide.

hyponatremia

An abnormal decrease of sodium ions in the blood; it may occur secondary to inadequate salt intake, water retention (overhydration), solute loss, e.g., excessive sweating or vomiting, or as a drug side-effect; symptoms include muscle weakness, neurologic dysfunction due to cranial edema, and possible coma; serum sodium levels are regulated by the hormones aldosterone, ADH, and atrial natriuretic peptide.

hypernatremia

An abnormal increase of sodium ions in the blood; it may occur secondary to renal disease, dehydration, burns, fever diarrhea; symptoms include altered mental states, muscle twitching, seizures, or coma; serum sodium levels are regulated by the hormones aldosterone, ADH, and atrial natriuretic peptide.

chloride

Any compound containing a chlorine atom or ion; the element chlorine is a greenish-yellow diatomic gas; it is naturally abundant in combined forms, especially in common table salt; symbol Cl, atomic number 17; atomic weight 70.906; valence -1; as an electrolyte, the most abundant extracellular anion; important for maintaining the polarized state of cells, forms HCL for gastric acidity, and a major contributor to the osmolarity of the extracellular fluid; serum reference range: 95-103 mEq/liter; serum chloride levels are regulated by the hormones aldosterone, ADH, and atrial natriuretic peptide. [Note: elevated sweat chloride is diagnostic of Cystic Fibrosis.]

hypochloremia

An abnormal decrease of chloride ions in the blood; it may occur secondary to prolonged vomiting or as a result of diuretic therapy; it usually occurs with hyponatremia; symptoms include alkalosis, muscle spasms and coma; serum chloride levels are regulated by the hormones aldosterone, ADH, and atrial natriuretic peptide.

hyperchloremia

An abnormal increase of chloride ions in the blood; it may occur secondary to metabolic acidosis, hypernatremia, or with the use of carbonic anhydrase inhibitor diuretics; symptoms include altered mental states, muscle twitching, seizures, or coma; serum chloride levels are regulated by the hormones aldosterone, ADH, and atrial natriuretic peptide.

potassium = kalium

A soft, silver-white, highly or explosively reactive metallic element which occurs in nature only in compounds; symbol K, atomic number 19; atomic weight 39.098; valence +1; as an electrolyte, the most abundant intracellular cation (90%); important for maintaining the polarized state of cells; serum reference range: 3.8-5.0 mEq/liter; serum potassium levels are regulated by the hormones aldosterone, ADH, and atrial natriuretic peptide.

hypokalemia

An abnormal decrease of potassium ions in the blood; it may occur secondary to renal disease, vomiting and diarrhea, or with the use of certain drugs including many diuretics; symptoms include neuromuscular and cardiac abnormalities, irritability, cardiac fibrillation, and death; serum potassium levels are regulated by the hormones aldosterone, ADH, and atrial natriuretic peptide.

hyperkalemia

An abnormal increase of potassium ions in the blood; it may occur secondary to renal disease, hemolytic anemia, chemotherapy, and various drug side effects; symptoms include cardiac arrhythmias and cardiac arrest; serum potassium levels are regulated by the hormones aldosterone, ADH, and atrial natriuretic peptide.

bicarbonate

The anion, HCO3-, formed from the dissociation of carbonic acid, H2CO3, which is an important body fluid buffer; the concentration of bicarbonate ions is regulated by both the respiratory system and the kidneys; the concentration of bicarbonate ions in the blood is the major indicator of the buffering capacity of the blood at any given moment; serum bicarbonate levels are regulated by the ventilation of the lungs and by the kidney under further complex regulation from the hypothalamus and endocrine system.

calcium

A silvery, moderately hard metallic element which occurs widely in nature; symbol Ca, atomic number 20; atomic weight 40.08; valence +2; as an electrolyte, the most abundant mineral ion in the body (98% stored in the matrix of bone); important for many processes including regulation of depolarization of neurons, muscle cells, and gland cells, and as a trigger for many biochemical pathways including blood clotting and the cortical reaction in a fertilized egg; serum reference range: 4.6-5.5 mEq/liter; serum calcium levels are regulated by the hormones thyrocalcitonin and parathyroid hormone.

hypocalcemia

An abnormal decrease of calcium ions in the blood; it may occur secondary to renal disease, hypoparathyroidism, vitamin D deficiency, pregnancy, and certain bone diseases; symptoms include muscle cramps and spasms, hyperactive reflexes, and convulsions; serum calcium levels are regulated by the hormones thyrocalcitonin and parathyroid hormone.

hypercalcemia

An abnormal increase of calcium ions in the blood; it may occur secondary to hyperparathyroidism, multiple myeloma, excessive vitamin D intake, with diuretic use, and certain cancers, especially if they metastasize to bone; symptoms include vomiting, cardiovascular problems, coma, abnormal calcium deposition in tissues, and stone formation; serum calcium levels are regulated by the hormones thyrocalcitonin and parathyroid hormone.

phosphate

The anions, H2PO4- and HPO4-2, and PO4-3, which are important intracellular anions as well as being a major constituent of the matrix of bone as calcium phosphate salts, also combined with lipids, proteins, carbohydrates, nucleic acids (DNA and RNA), and high energy phosphate transport compounds, e.g., ATP, and an important body fluid buffer; serum reference range: 1.7-2.6 mEq/liter; serum phosphate levels are regulated by the hormones thyrocalcitonin and parathyroid hormone.

hypophosphatemia

An abnormal decrease of phosphate ions in the blood; it may occur secondary to hyperparathyroidism, bone wasting diseases, vitamin D deficiency, and certain renal tubular diseases; symptoms include hemolysis, weakness, and convulsions; it usually occurs with hypercalcemia; serum phosphate levels are regulated by the hormones thyrocalcitonin and parathyroid hormone.

hyperphosphatemia

An abnormal increase of phosphate ions in the blood; it may occur secondary to hypoparathyroidism, vitamin D deficiency, and certain bone diseases; symptoms include muscle cramps and spasms, hyperactive reflexes, and convulsions; serum phosphate levels are regulated by the hormones thyrocalcitonin and parathyroid hormone.

magnesium

A light, silvery-white, moderately hard metallic element which occurs widely in nature; symbol Mg, atomic number 12; atomic weight 24.305; valence +2; as an electrolyte, the second most abundant intracellular ion (the majority stored in the matrix of bone); important as an enzyme cofactor and in regulating depolarization events; serum reference range: 1.3-2.1 mEq/liter.

hypomagnesemia

An abnormal decrease of magnesium ions in the blood; symptoms include vomiting and cardiac arrhythmias.

hypermagnesia

An abnormal increase of magnesium ions in the blood; symptoms include nausea and vomiting.

hypothalamic thirst center

The site in the hypothalamus, close to the site of production of ADH, to which osmoreceptors send visceral sensory information about hydration status in the blood and body fluids; the threshold for thirst is a plasma osmolarity > 290-295 mOsm/L and is rapid in onset; it is also the site to which baroreceptors send visceral sensory information about blood pressure which is influenced by blood volume (hydration status); it is also a site where angiotensin II interacts; all of these influences cooperate to generate a conscious desire to drink.

antidiurectic hormone (ADH) = vasopressin

the neurohypophyseal peptide hormone which stimulates contraction of smooth muscle in blood vessel walls and stimulates the kidney tubules to reabsorb water; both target responses tend to increase blood pressure.

atrial natriuretic peptide (ANP)

The peptide hormone released from special endocrine cells in the walls of the upper chambers/atria of the heart in response to the stretching of the chamber walls due to increased blood volume or increased blood pressure; ANP is the antagonist to aldosterone and thus triggers salt (NaCl) and water excretion and potassium ion reabsorption at the kidney tubules.

aldosterone

The main steroid hormone produced by the outermost layer of the adrenal cortex, whose release is stimulated by increased potassium levels in the plasma; this mineralocorticoid targets the kidney to actively transport sodium ions out of the urine and potassium ions into the urine (chloride ions and water passively follow the sodium ions back to the bloodstream); the net effects of this hormone are to increase blood pressure and blood volume and to adjust sodium and potassium levels in the blood.

renin - angiotensin system

A complex endocrine negative feedback control system which plays important role in regulating blood volume, arterial pressure, and cardiac and vascular function; in response to sympathetic stimulation, low blood pressure or low blood sodium levels, (1) the juxtaglomerular apparatus of the kidney will release the enzyme renin, (2) renin will catalyze the activation of an inactive precursor substance, angiotensinogen, which is made by the liver, into angiotensin I, (3) angiotensin I (which has some activity of its own) will be further activated by an enzyme found in the lungs, angiotensin-converting enzyme (ACE), into active angiotensin II, (4) angiotensin I & II stimulate these physiological responses: (a) enlargement of the heart and blood vessels, (b) systemic vasoconstriction, (c) aldosterone release from the adrenal cortex, (d) activation of the hypothalamic thirst center, (e) ADH release from the posterior pituitary/neurohypophysis; processes (c, d, and e) cause retention of salt and water by the kidneys and as a result, increased blood volume; thus this system has a powerful hypertensive effect.

parathyroid hormone (PTH) = parathormone

A protein hormone, produced by the principle or chief cells of the parathyroid gland which increases plasma calcium levels (mechanisms 1, 2, and 3) and decreases plasma phosphate levels (mechanism 3) by (1) targeting oseoclasts to increase dissolution of bone matrix, (2) targeting the intestinal lining to increase calcium ion absorption from the digested meal, and (3) targeting the kidney to reaabsorb calcium ions from and secrete phosphate ions into the urine; PTH is the antagonist to thyrocalcitonine.

calcitionin = thyrocalcitonin

A protein hormone, produced by the parafollicular cells/C cells of the thyroid gland which lowers plasma calcium and phosphate levels by targeting oseoblasts to increase formation of bone matrix; the antagonist to parathyroid hormone.

buffer

A chemical or mixture of chemicals, usually a weak acid or base and its corresponding salt, which minimizes change in the acidity of a solution, the pH, when an acid or base is added to the solution.

protein buffer system

The most abundant buffer system in cell cytoplasm and in blood plasma; because proteins are composed of amino acids joined in a linear string by peptide bonds, they always possess at least one free amino group (-NH2) and one free carboxylic acid group (COOH-) at opposite ends of the strand, and they often possess additional free amino groups and carboxylic acid groups because those groups are present on the R-group side chains of a variety of amino acids; these free amino groups and carboxylic acid groups act as weak acids and bases respectively, and, as a result, can combine with H+ ions, reducing the concentration of free H+ ions in the solution, a buffering function.

hemoglobin buffer

The property of hemoglobin which allows its various exposed or free amino groups and carboxylic acid groups to act as weak acids and bases respectively, and, as a result, hemoglobin can combine with H+ ions, reducing the concentration of free H+ ions in the erythrocyte cytoplasm, a buffering function; hemoglobin plays a significant secondary buffering role in the blood, supporting the more important carbonic acid-bicarbonate buffer system found in the plasma; the capacity of hemoglobin to form ionic bonds with H+ ions is also related to hemoglobin's ability to transport oxygen because when a hemoglobin molecule ionically bonds with H+ ions it tends to favor a consequent dissociation from oxygen; therefore, in the presence of increased hydrogen ions, hemoglobin has less affinity for oxygen and this means that hemoglobin will "unload" oxygen more readily in the capillaries of metabolically active tissues which are liberating H+ ions and CO2, both of which contribute to a more acidic pH environment; this property is known as the Bohr effect.

phosphate buffer system

A secondary buffer system in cell cytoplasm, body fluids and blood plasma; phosphate ions (HPO4-2) can form ionic bonds with one or two H+ ions, reducing the concentration of free H+ ions in the surrounding solution, a buffering function.

carbonic acid-bicarbonate buffer system

Bicarbonate ions can absorb H+ ions to form carbonic acid which can be transported to the lungs where the reaction is reversed, the H+ ions are converted to water molecules and CO2 is excreted. [See the chemical equation under carbonic anhydrase below.] It is an extracellular buffer. The main role of this system is to buffer against the acids produced by fat & protein metabolism or ones produced in oxygen deficiency or starvation; it cannot buffer against the acidity of excess CO2, which occurs with hypoventilation; this buffer system is dependent on a functioning respiratory system to excrete the carbon dioxide. [Note*: A buffer is a substance which minimizes change in the pH (acidity) of a solution when an acid or base is added to that solution.]

carbonic anhydrase

An enzyme found in erythrocytes and renal tubular epithelial cells which catalyzes the reversible reaction in which carbon dioxide and water combine to form carbonic acid; it is an enzyme with great catalytic efficiency so it can be present in very low concentration and still be effective. [Note: Carbonic acid spontaneously dissociates into hydrogen ion and bicarbonate ion at normal body fluid pH.]

volatile acid

An alternative name or nickname referring to carbonic acid or the bicarbonate ion which emphasizes the contribution of carbonic acid and the bicarbonate ion to the pH of body fluids and to physiological acid-base balance and emphasizing the fact that this one type of physiological or metabolic acid can be excreted by the lungs into the atmosphere. [Note: in chemisry, "volatile" means vaporating readily at normal temperatures and pressures.]

fixed acid

An alternative name or nickname referring to any acid other than carbonic acid or the bicarbonate ion, acids which are found in and contributes to the pH of body fluids and to physiological acid-base balance and emphasizing the fact that these physiological or metabolic acids, usually organic acids, cannot be excreted by the lungs into the atmosphere and are, instead, excreted into the urine; examples include lactate, phosphate, sulphate, acetoacetate and beta-hydroxybutyrate.

acidosis

Any abnormal increase in the acidity of the body's fluids (with a corresponding drop in the pH below 7.35), caused either by the accumulation of acids (increase in hydrogen ions) or by depletion of bicarbonate ions which serve as buffers; there are a variety of specific causes which fall into two main groups, respiratory and metabolic.

acidemia

(1) Any situation in which the hydrogen ion concentration in the blood is increased to the degree that the blood pH is < 7.0; it may or may not fall outside of the normal range for blood pH. (2) A group of relatively rare inherited metabolic disorders in which the absence of a critical enzyme causes the accumulation of a particular organic acid intermediary metabolite in the blood and body fluids; many specific examples are known.

respiratory acidosis

A metabolic derangement of acid-base balance in which the blood pH is abnormally low (<7.35) and the cause is improper ventilation, hypoventilation, which leads to the accumulation of carbon dioxide in the blood (pCO2 > 45 mm Hg), secondary to a variety of disorders including chronic obstructive pulmonary diseases (COPDs), e.g., asthma, emphysema, pulmonary fibrosis, pneumonia, tuberculosis, etc.

metabolic acidosis

A metabolic derangement of acid-base balance in which the blood pH is abnormally low (<7.35) and the cause is anything other than improper ventilation, hypoventilation, and which usually leads to the loss of significant amounts of bicarbonate buffer in the blood (HCO3- < 23 mEq/L), secondary to a variety of disorders including hemorrhagic shock, cardiogenic shock, severe dehydration, septicemia, ingestions of toxic chemicals, e.g. methanol, isopropyl alcohol, salicylates (aspirin poisoning), severe diarrhea, alcoholic ketoacidosis, diabetic ketoacidosis, lactic acid, renal failure, etc.

alkalosis

Any abnormal decrease in the acidity of the body's fluids (with a corresponding rise in the pH above 7.45), caused either by the loss of acids (decrease in hydrogen ions) or by the accumulation of bicarbonate ions which serve as buffers; there are a variety of specific causes which fall into two main groups, respiratory and metabolic.

alkalemia

Any situation in which the hydrogen ion concentration in the blood is decreased to the degree that the blood pH is > 7.0; it may or may not fall outside of the normal range for blood pH.

respiratory alkalosis

A metabolic derangement of acid-base balance in which the blood pH is abnormally high (>7.45) and the cause is improper ventilation, hyperventilation, which leads to the loss of carbon dioxide, and therefore of both H+ and HCO3-, from the blood (pCO2 < 35 mm Hg), secondary to a variety of disorders including asthma, fever, and emotional hysteria.

metabolic alkalosis

A metabolic derangement of acid-base balance in which the blood pH is abnormally high (>7.45) and the cause is anything other than improper ventilation, hyperventilation, and which usually leads to the accumulation of significant amounts of bicarbonate buffer in the blood (HCO3- > 26 mEq/L), secondary to a variety of disorders including prolonged vomiting, diuretic therapy, hyperadrenocortical disease, and the administration of exogenous bases (antiacids, bicarbonate IV, citrate toxicity after massive blood transfusions)

compensation

The increase in size or activity of one part of an organism or organ which makes up for the loss or dysfunction of another part; in terms of acid-base derangements, the first line of defense against disturbances in pH are the intra- and extracellular buffering systems which minimize the change in pH; in more serious situations, additional mechanisms to resist further changes in pH are respiratory adjustments of extracellular fluid (ECF) PCO2 and renal adjustments of ECF HCO3- concentration; such adjustments for acid base imbalance are only partially effective; perfect compensation, without correcting the underlying cause of the pH disturbance, is not possible because it would remove the stimulus for the compensatory mechanisms and the imbalance would be re-established; furthermore the compensatory mechanisms act not only to minimize changes in the pH but also operate, after correcting the cause of the pH disturbance, to restore the body's buffer reserves leaving it more able to cope with repeated episodes of acid-base disturbance.

respiratory compensation

Any change in the rate and depth of ventilation which the body makes in the attempt to resist a derangement of acid-base balance of metabolic origin; hypoventilation will resist a metabolic alkalosis while hyperventilation will resist a metabolic acidosis; perfect or permanent compensation, without correcting the underlying metabolic cause of the pH disturbance, is not possible.

hypoventilation

Abnormally slow or shallow respiration, which results in the retention of carbon dioxide in the blood, the retention of CO2 may lead to respiratory acidosis.

hyperventialation

Abnormally fast or deep respiration, which results in the loss of carbon dioxide from the blood, thereby causing a fall in blood pressure, tingling of the extremities, and light-headedness, dizziness, and sometimes fainting and chest pain if continued; the loss of CO2 may lead to respiratory alkalosis.

metabolic comepensation

Any change in the secretion of H+ or the production and retention (reabsorption) of HCO3- by the kidneys, which the body makes in the attempt to resist a derangement of acid-base balance of respiratory origin; reduced H+ secretion and reduced HCO3- reabsorption will resist a respiratory alkalosis while increased H+ secretion and increased HCO3- reabsorption will resist a respiratory acidosis; perfect or permanent compensation, without correcting the underlying metabolic cause of the pH disturbance, is not possible.

salicylate poisoning

The toxicity caused by the ingestion of excessive amounts of salicylates, usually aspirin (acetyl salicylic acid); symptoms include hyperventilation and consequent respiratory alkalosis, hypoglycemia, pulmonary and cerebral edema, and impaired platelet function and poor blood clotting, possible metabolic acidosis as well.

chronic obstructive pulmonary disease (COPD)

Any chronic, usually irreversible, lung disease, e.g., asthma, chronic bronchitis, emphysema, pneumonia, tuberculosis, etc., in which breathing becomes slowed or forced, and wheezing and chronic cough are often present; symptoms and progression are aggravated by smoking.

emphysema

A common pathological condition of the lungs marked by an abnormal increase in the size of the air spaces, resulting in labored breathing and an increased susceptibility to infection; it can be caused by irreversible expansion of the alveoli or by the destruction of alveolar walls; it is classified among the chronic obstructive pulmonary diseases (COPDs).

cystic fibrosis

A hereditary disease (autosomal recessive) of the exocrine glands, usually developing during early childhood and affecting mainly the pancreas, respiratory system, and sweat glands (elevated chloride levels); it is characterized by the production of abnormally viscous mucus by the affected glands, usually resulting in chronic respiratory infections and impaired pancreatic and intestinal function.

1. the inputs versus losses of water responsible for fluid balance in the body.

Water Inputs
(1) preformed water = ingested water in beverages and foods
(2) metabolic water = generated as a byproduct of metabolic reactions
Water Losses
(1) evaporation across the skin and exposed mucous membranes
(2) sweating = perspiration
(3) respiration
(4) excretion in the feces
(5) excretion in the urine

2. the ways the body can buffer blood and body fluid pH.

(1) Body fluids contain a wide variety of buffering substances including proteins, bicarbonate ions, and phosphate ions. Buffers form chemical bonds with H+ ions which neutralize them for as long as they are associated with the buffers.
(2) Exhalation of breath reduces CO2 content in the blood. This reduction in pCO2 indirectly reduces H+ ion concentration in the blood because some of the carbon dioxide is generated as a result of the synthesis of carbonic acid from H+ and bicarbonate ions . This reaction occurs spontaneously but can also be catalyzed by the enzyme carbonic anhydrase which is present in erythrocyte cytoplasm. [See the chemical reaction in the definition for carbonic anhydrase above.]
(3) The kidney is capable of actively transporting large quantities of H+ ions into the urine by means of several molecular mechanisms.

3. pathological causes of dehydration.

(1) prolonged hyperventilation
(2) vomiting and diarrhea
(3) fever with perspiration
(4) burns
(5) hemorrhage
(6) diabetes mellitus or diabetes insipidus
(7) dehydration from starvation (coma, digestive disorders, exposure to the elements, etc.)

4. the compartments in the two fluid compartment model.

(1) intracellular compartment = cytoplasmic compartment and
(2) extracellular compartment

5. the compartments in the three fluid compartment model.

(1) intracellular compartment = cytoplasmic compartment,
(2) interstitial = intercellular compartment (lymph) compartment and
(3) plasma compartment

6. the electrolytes which predominate in the intracellular fluid compartment.

potassium (K+), magnesium (Mg++), bicarbonate (HCO3-) [lesser], phosphate (HPO4-2), sulfate (SO4-2)

7. the electrolytes which predominate in the extracellular fluid compartment.

sodium (Na+), chloride (Cl-), bicarbonate (HCO3-)

8. the compartments in the three fluid compartment model which have large concentrations of proteins.

(1) intracellular compartment = cytoplasmic compartment, and
(2) plasma compartment

9. the three actions which can quench thirst.

(1) wetting the oral mucosa (temporary; (2) stretching/filling the stomach;
(3) increasing hydration status to dilute the blood and decrease blood/body fluid osmolarity

1. a simple diagram illustrating the two fluid compartment model of the body.

1. intracellular compartment = cytoplasmic compartment
2. extracellular compartment

2. a simple diagram illustrating the three fluid compartment model of the body.

1. intracellular compartment = cytoplasmic compartment
2. interstitial = intercellular compartment (lymph) compartment
3. plasma compartment

1. the mechanisms regulating thirst.

Osmoreceptors in the hypothalamus note changes in hydration status by checking blood volume and blood solute concentration. Dehydration stimulates the hypothalamic thirst center creating sensations of thirst and this may be reinforced by a sensation of a dry mouth from decreased saliva secretion as a result of the increased osmotic strength (decreased water) in the plasma. Once water has been ingested and absorbed, the improved hydration status will inhibit further activity from the hypothalamic thirst center.

2. the main differences in solute composition between the intracellular versus the extracellular fluid compartments of the body. What is the main difference in solute concentration between the plasma and the interstitial fluid compartments of the body?

Describe the main differences in solute composition between the intracellular versus the extracellular fluid compartments of the body.
1. Intracellular Fluid = Major solutes: potassium (K+), magnesium (Mg++), phosphate (HPO4-2), sulfate (SO4-2), proteins
2. Extracellular Fluid = Major solutes: sodium (Na+), chloride (Cl-), bicarbonate (HCO3-), fewer proteins
What is the main difference in solute concentration between the plasma and the interstitial fluid compartments of the body?
1. Plasma = Major solute difference: many plasma proteins
2. Interstitial Fluid = Major solute difference: few proteins

3. the hormonal regulation of Na+ and K+ in body fluids.

Antagonistic negative feedback control involving: (1) aldosterone which targets the kidney tubule to reabsorb Na+ ions from the filtrate and excrete K+ ions into the urine; and (2) atrial natriuretic peptide (ANP) which targets the kidney tubule to reabsorb K+ ions from the filtrate and excrete Na+ ions into the urine.

4. the hormonal regulation of Ca++ and HPO4-2 in body fluids.

Antagonistic negative feedback control involving: (1) parathyroid hormone (PTH) = parathormone which targets (a) the intestines to absorb more Ca++ and HPO4-2 ions from the chyme of digested meals, (b) the osteoclasts in bone to dissolve additional bony matrix liberating more Ca++ and HPO4- ions into the blood, and (c) the kidney tubule to reabsorb Ca++ ions from the filtrate and excrete HPO4-2 ions into the urine; and (2) thyrocalcitonin = calcitonin which targets the kidney tubule to reabsorb HPO4-2 ions from the filtrate and excrete Ca++ ions into the urine. [Note: the net effect of parathyroid hormone (PTH) = parathormone is to elevate blood calcium levels and decrease blood phosphate levels; the net effect of thyrocalcitonin = calcitonin is to elevate blood phosphate levels and decrease blood calcium levels.]

1. why anabolic metabolism is not a significant source of metabolic water in comparison to the metabolic water generated at the end of the electron transport chain in the catabolism of nutrient molecules?

While a small quantity of water can be generated by anabolic reactions such as the dehydration syntheses used in the formation of proteins from amino acids, triglycerides from glycerol and fatty acids, polysaccharrides from monosaccharrides, and nucleic acids from nucleotides; the quantity of water consumed by catabolic reactions elsewhere in cells such as the hydrolysis of polymers (proteins, lipids, polysaccharrides, and nucleic acids) to obtain the monomers used in the anabolic reactions must be credited against the water formed by anabolism. Therefore, very little, if any, net surplus water can be attributed to the metabolic water derived from anabolism. Some authorities dispute if even this minor quantity of water can be considered a net gain. On the other hand, a significant quantity of metabolic water is generated in the final step of nutrient molecule catabolism, where oxygen, the final electron acceptor, combines with two protons and two electrons, forming water at the end of the electron transport chain in the oxidative phosphorylation of ADP to ATP. This process generates far more water than could ever form from anabolism. In fact, some desert animals are able to live on the preformed water from the food they eat, and the metabolic water generated in their metabolism of these food molecules, without ever ingesting any liquid water.

2. the terms percent, equivalents, and osmolarity in referring to the concentrations of solutions.

Term - percent = percent concentration
Definition - A unit of measure of substances commonly used in clinical laboratory medicine; it measures mass per unit volume with the specific unit of milligrams/100 mL = mg/dL (deciliter).
Relevant Difference in Application - A clinical unit of measure frequently applied to nonelectrolytes in body fluids. [Note: It may also be applied to electrolytes, if desired.] It refers to the concentration (mass per unit volume) of a particular single substance with the specific unit of milligrams/100 mL = mg/dL (deciliter). It acquired the nickname of "percent" because the mass measurement is in reference to a volume of one hundred milliliters of solution.

2. cont.

Term - equivalent
Definition - A unit of measure of electrolytes = charged ions commonly used in clinical laboratory medicine; an equivalent represents the "hydrogen equivalence" when comparing the strength and bond forming relationships between acids and bases; this relationship is the mole (Avagadro's number of atoms or molecules) divided by the valence or Equivalent = Mole/Valence.
Relevant Difference in Application - A clinical unit of measure frequently applied to electrolytes = charged ions and refers not to a concentration (mass per unit volume) of a particular single substance, but, rather, to a substance's "hydrogen equivalence" when comparing the strength and bond forming relationships between acids and bases; this relationship is the mole divided by the valence, i.e., an Equivalent = Mole/Valence.

2. cont.

Term - osmolarity
Definition - The concentration of osmotically active particles in a solution expressed in terms of the Osmoles of solute particles per liter of solution; this measure is commonly used to quantify the tonicity or osmotic strength of solutions (isotonic/isosmotic; hypertonic/hyperosmotic; hypotonic/hyposmotic).
Relevant Difference in Application - A clinical unit of measure frequently applied to the tonicity or osmotic strength of solutions (isotonic/isosmotic; hypertonic/hyperosmotic; hypotonic/hyposmotic) which refers to the combined presence or influence of all dissolved solutes in a solution rather than a measure of any particular single substance. The unit of measurement refers only to the number of particles per unit volume and indicates nothing about either the mass or the "hydrogen equivalence" (acid-base reactivity) of any of the solutes in the solution.

3. the mechanisms used to regulate the Sodium (Na+) concentrations in the body. Why is regulation of Na+ almost the same as regulating the water concentration of the body?

Explain the mechanisms used to regulate the Sodium (Na+) concentrations in the body.
A. Primary mechanism: Antagonistic negative feedback control involving: (1) aldosterone which targets the kidney tubule to reabsorb Na+ ions from the filtrate and excrete K+ ions into the urine; and (2) atrial natriuretic peptide (ANP) which targets the kidney tubule to reabsorb K+ ions from the filtrate and excrete Na+ ions into the urine.
B. Secondary mechanism: Regulation of the water concentration of the urine by antidiuretic hormone (ADH) = vasopressin involves some tubular reabsorption of Na+ ions, and, therefore, has an indirect effect on regulate the sodium (Na+) concentration in the body.
Why is regulation of Na+ almost the same as regulating the water concentration of the body?
Water tends to follow passively any of the movements of solutes across body membranes, but it most strongly associates with and follows the movements of sodium (Na+) ions. Where sodium (Na+) ions move, water follows.

4. why homeostatic imbalances of Na+, K+, and Ca++ all have effects on nerve and muscle function; give specific examples at the molecular level of function.

Differences in the concentrations of Na+ ions and K+ ions between the cytoplasm and interstitial fluid of all cells influence their ability to maintain and regulate their resting potentials. Therefore, excitable cells such as neurons and muscle cells can be made to be more or less capable of depolarization if imbalances of Na+ ions and K+ ions develop between the cytoplasm and interstitial fluid. Cardiac muscle cells also involve slow calcium channels in their depolarization, so changes in the concentrations of Ca++ ions between the cytoplasm and interstitial fluid of cardiac muscle cells influence their ability to maintain and regulate their resting potentials.

In addition, the release of neurotransmitters from storage vesicles in motor neuron axon end bulbs requires the action of Ca++ ions, acting as second messengers, to initiate exocytosis of the neurotransmitter vesicles and the sliding filament mechanism of muscle contraction also requires the action of Ca++ ions, acting as second messengers, to initiate myosin-head binding to actin and to initiate ATP hydrolysis to power that binding and the subsequent power stroke (and ratchet effect). Therefore, neurons and muscle cells can be made to be more or less capable of performing their respective functions of impulse transmission and contraction, respectively, if imbalances of Ca++ ions develop between their cytoplasm and the surrounding interstitial fluid.

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