Ch 26) Fluid, Electrolyte, and Acid/Base Balance

Question 1

Fluid Compartments

Answer 1

• Two Main Fluid Compartments
• Intercellular Fluid (ICF) compartment
  
  • 25 L (about 40% of the body weight)
• Extracellular Fluid (EFC) compartment
  
  • Outside the cells
  • 15 L (about 20% of Body weight)
  • Plasma) 3L
  • Intersitital Fluid) 12 L found in spaces between cells
    
    • Lymph, CSF, Eye Humors, synovial Fluid, Serous Fluid, Gastrointestinal secretions.

Question 2

Compasion of Extracellular and Intracellular Fluids

Answer 2

• ECF
  
  • All similar to Plasma (Plasma has a higher protein content/ lower Cl- Content compared to ECF)
  • Major cation) Na+
  • Major anion) Cl-
• ICF)
  
  • Low Na+ and Cl-
  • Major Cation: K+
  • Major anion: HPO₄^2-
  • Cells have more soluable protiens than plasma (ICF greatest protein content)

Question 3

Fluid Movment Among Compartments

Answer 3

• Osmotic and Hydrostatic Pressures regulate continuious exchange and mixing of fluide
  
  • Water moves freely along somotic gradients
• Changes in Solute concentration leads to net flow
  
  • ECF Osmolity High > Water Leaves the cell
  • Low ECF Osmoliity > Water enters the cell
• Rise In Osmality
  
  • Stimulates thirst, ADH release
• Decrease in Osmoality
  
  • Thirst inhibition, ADH inhibition

Question 4

Regulation of Water Intake

Answer 4

• Thirst Mechanism driving force for water intake
• Hypothalmic Thirst Center) primary stimilus
  
  • Osmoreceptors detect EFC osmality increase, Dry mouth,
  • Baroreceptors) Detect decreased blood volume or pressure (activate thirst centernter and angiotensin II)
• Drinking water = Inhibition of thirst center
  
  • Relif of Dry mouth
  • Activaion of Stomach and intestinal stretch receptors
    *

Question 5

Regulation of Water Output (ADH)

Answer 5

• Water Reabsorption in collecting ducts proportional to ADH release
  
  • Low ADH> Dilute urine and low volume of body fluids
  • High ADH > Concentrated Urine and high volume of body fluids because of reabsoprtion of water
• Hypothalamic osmoreceptors sense ECF solute concentration and regulate ADH accordingly
• Other facotrs that trigger ADH
  
  • Large changes in blood volume or pressure
  • Vomiting, Diarrhea, Servere blood loss

Question 6

Dehydration

Answer 6

• Dehydration) Negative fluid balance
  
  • ECF water loss (hemmorage, severe burns, prolonged vomiting/diarrhea, profuse sweating, water deprivation, ednocrine disurbances)
  • Sticky oral mucosa, thrist, dru flushed skin, oliuria
  • may lead to weight loss, fever, metal confusion hypovoemic shock

Question 7

Hypoteonic Hydration

Answer 7

• Cellular Overhydration or water intoxication
• Occurs with renal insufficency or rapid excess water ingestion
  
  • ECF osomality low > Hyponatremia (low ECF Na+ concentration) > net osmosis into tissue cells > swelling of cells > metabolic distrubances > possible death
• Treated with hypertonic saline to reverse osmotic gradients

Question 8

Edema

Answer 8

• Atypical accumulation of IF in tissues but not the cell
  
  • causes swelling
  • Increase of fluid out of blood caused by increaded Capillary Hydrostatic Pressure (HP_c) and permiablity
• Hypoproteinemia) down plasma protein levels resulting from protien malnutrition, liver diesease
  *

Question 9

Electrolyte Balance

Answer 9

• Salts, acids, bases and some proteins
• Electrolyte Balnce) ususaly refers only to salt
  
  • control fluid movments
  • provide minerals essential for excitibality, secretory activity, and memrane permiablity
    *

Question 10

Role of Sodium

Answer 10

• Most abundant cation in the ECF
  
  • only cation exerting signifigant osmotic pressure
• Concentration of Na+ in ECF) determines osmolaity of ECF
  
  • influences excitability of nuerons and mucles
• Content of Na+ in body) Determines ECF volume and blood pressure.
• Regulation of Sodium Blance
  
  • No Known receptors that moniter Na+ levels in body fluifs
  • Changes in blood pressure or volume trigger neural and hormonal controls to regulate Na+ content
• Aldosterone
  
  • Decreases urinary output; Increases blood volume
  • Increases active reabsorption of Na+
  • Increases K+ secretion

Question 11

Regulation of Patassium Blanace

Answer 11

• Impotance of Potassium
  
  • Affects Resting membrane potential (RMP) in nuerons and muscle cells.
  • High ECF K+ > Low RMP > leads to depolarization and decresed exitability
  • Low ECF K+ > Hyperpolarization and nonresponsiviness
• Hyperkalemi) too much K+
• Hypokalemia) too little K+
• Both disrupt electrical conduction to the heart
  
  • sudden death
• Aldesterone) K+ secretion and Na+ absorption

Question 12

Regulation of Calcium

Answer 12

• 99% of body’s calcium found in the bones
• Ca2+ in ECF important
  
  • blood clotting, cell membrane permiablity, secretoru activities
  • Nueromucular excitability (most important)
• Hypocalcemia) High excitability and muscle tetany
• Hypercalcemia) inhibits nuerons and mucle cells
  
  • may cause heart arrhythmias
• Calcium balance controlled by PTH from parathyroid gland
  
  • PTH promotes increase in calcium levels

Question 13

Acid-Base Balance

Answer 13

• pH affects all functional proteins and biochemcial reactions
  
  • closley regulated
  • Normal pH of body is 7.4
• Alkalosis (alkelemia) arterial pH > 7.4
• Acidosis Acidemia) arterial pH < 7.35
• Most H+ is produced by metabolism
  
  • Loading and transport of CO2 in the blood as HCO₃ - liberates h+
• Concantration Hydrogen ions regulated sequentially by
  
  • Chemical buffer system) rapid first line of defense
  • Brain stem Repritory centers) change in respritory rate to compensate for acidosis or alkalosis
    
    • 1-3 mins
  • Renal Mechanism) strongest but requires hours/ days to effect pH.

Question 14

Chemical Buffer Systems

Answer 14

• A system of one or more compounds that resists changes in pH when a strong acid or base is added.
  
  • Bind H+ ions when pH drops
  • Releases H+ when pH rises
• Water
  
  • strong acids completely dissociate
  • Weak acids partialy dissociate; efficent at preventing pH changes
  • Strong bases dissociate easialy; pick up H+
  • Weak bases less likley to pick up H+

Question 15

Bicarbonate Buffer System

Answer 15

• Mixture of cabronic acid (H2CO3 / weak acid) and sodium bicarbonate (NaHCO3 / weak base)
• Strong acid added
  
  • HCO3 ties up H+ and frome H2CO3
• Strong Acid + Weak Base > Weak acid + salt
  
  • HCL + NaHCO3 > H2CO3 + NaCl
  • increases pH only slightly
  • if enough acid is in blood avaible HCO3- will be used up (alkaline reserve) and bicarbionate becomes ineffective
• If Strong Base is added
  
  • H2CO3 dissociates to donate H+
  • H+ ties up the base (OH-
• Stong base + Weak acid > Weak Base and Water
  
  • NaOH + H2CO3 > NaHCO3 + H2O
  • pH rises only sightly
  • H2CO3 supply is almost limitless.

Question 16

Phosphate/ Protein Buffer Systems

Answer 16

• Phosphate Buffer System
  
  • Salts of H2PO4 (Weak acid) and HPO₄^2- (weak base)
  • Imporant in urine and ICF
• Protein Buffer System
  
  • Some amino acid side chains act as weak acids (COOH) or weak bases (-NH₂)
  • most important buffer in ICF and in Blood Plasma

Question 17

Physiological Buffering Systems

Answer 17

• Respritory an Renal Systems
  
  • Regulate amount of acid or base in the body
  • Acts slower than chemical systems
  • More capicicity than chemical systems

Question 18

Respritory Regulation of H+

Answer 18

• Eliminates CO2 (an acid)
• Reversiable equilibrium equation
  
  • CO2 + H2O <> H2CO3 <>H⁺ + HCO3^-
• Rising plasma H+
  
  • acitvates chemoreceptors
  • Increased respritory rate and depth
  • More CO2 removed/ H+ conentration is reduced
• Alkolosis Depresses respritory center
  
  • Rate and depth decrease
  • H+ concnetration increases
• Respritory impariment causes acid-base imbalance
  
  • Hypoventilation > Respritory acidosis and hyperventilation > respriatory alkalosis

Question 19

Renal Mechanisms of Acid-Base Balance

Answer 19

1. CO2 combines with water in tubular cell. Forms H2CO3
2. H2CO3 quickly split into H+ and HCO3-
3. H+ secreted into filtrate
4. For Each H+ secreted. one HCO3- enters the peritubular capillary
5. Secreted H+ recombines with HCO3- in filtrate forming carbonic acid
6. H2CO3 dissicoates to release CO2 and H2O
7. CO2 diffuses into the tubule cell, where it triggers further H+ secretion.

• To reabsorb bicarbionate kidneys secrete H+
  
  • rate of H+ secretion changes with ECF CO2 levels
  • CO2 up in peritubular capilary = Increased rate of H+ secretion

Question 20

Abnrormalitities of Acid-Base Balance

Answer 20

• All cases of acidoesis and alkalosis can be classed according to cause
  
  • either respritory or metabolic factors
• Respriotry Acidosis and Akalosis
  
  • causes by failure of respritory system to perform pH balancing role
  • Indicated by blood P_CO2
• Metabolic acidosis and alkalosis
  
  • All abnormalities other than those caused by P_CO2 levels in the blood
  • Indicated by abnormal HCO3- levels

Question 21

Respritory Acidosis and Alkalosis

Answer 21

• Most important indicator of adequacy of respritory function is a normal P_CO2 level
  
  • normally 35-45 mm Hg
• P_CO2 above 45 mm Hg > Respritory Acidosis
• P_CO2 below 35 mm Hg > Respritory alkalosis
  
  • result of hyperventilation (CO2 eliminated faster than produced)

Question 22

Metabolic Acidosis and Alkalosis

Answer 22

• Metabolic acisodis) Low blood pH and low HCO3- levels
• Causes
  
  • Ingestion of too much alchcol (metabolized to acetic acid)
  • Excessive loss of HCO3-
  • Accumulation of latic acic (excercise or shock), diabetic crisis, starvation and kidney failure
• Metaboic Alkalosis) much less common
  
  • rising blood pH and HCO3- levels
  • Causes incude vomiting of acid contents or excess bas intake.

Question 23

Effects of Acidosis and Alkalosis

Answer 23

• Blood pH below 6.8
  
  • Depression of CNS > Coma > deth
• Blood pH aboce 7.8
  
  • excitation of nervous system > Muscle tetany / Extrme nervousness > Convusions > and death from respritory arrest.

Question 24

Respritory and Renal Compensations

Answer 24

• If acid-base imbalnce is due to malfunction of physilogical buffer system another system will act to compensate
  
  • Respritoy system attempts to correct metabolic acid-base imbalances
  • Kidneys attempt to correct resrpiroty acid-base imbalance

Question 25

Respritory Compenstation

Answer 25

• Changes in respritory rate and depth are evident when the respritory system is attempting to compensate for acid-base imbalances
• Metabolic acidosis
  
  • high H+ levels stimulate respritory centers
  • Rate and Depth of breathing elevated
  • blood pH 7.35 and below / HCO3- levels low
  • as CO2 is elimintated P_CO2 is elimiated
• Metabolic alkalosis
  
  • shallow breathing allows CO2 accumulation in the blood
  • Evidence of metabolic alkalosis being compensated by resprirtory mechanism including a high pH / elevated HCO3- levels
  • P_CO2 levels above 45 mm Hg

Question 26

Renal Compensation

Answer 26

• Hypoventilation causes elevated P_CO2
  
  • ​respriotry acidosis
  • Renal compensation indicated by high P_CO2 and HCO3-
• Respritory alkalosis exhibits low P_CO2 and high pH
  
  • Renal compensation is indicated by descreasing HCO3- levels.