Presentation on theme: "Chapter 8 Disorders of Fluid, Electrolyte, and Acid-Base Balance"— Presentation transcript:
1 Chapter 8 Disorders of Fluid, Electrolyte, and Acid-Base Balance Essentials of PathophysiologyChapter 8 Disorders of Fluid, Electrolyte, and Acid-Base Balance
2 PRE LECTURE QUIZ (TRUE/FALSE) The extracellular compartment contains approximately two thirds of the body water in healthy adults, and is the larger of the two compartments.Potassium is the most abundant cation in the body.Edema of the brain, larynx, or lungs is not an acute, life-threatening condition.Polydipsia is a term that means “excessive thirst.”Decreased vascular volume would yield manifestations such as full and bounding pulses, venous distention, and signs and symptoms of pulmonary edema, such as shortness of breath, crackles, dyspnea, and cough.
3 PRE LECTURE QUIZADHCalciumCardiacMetabolicpHDiabetes insipidus is a condition that is caused by a deficiency or a decreased response to __________, also known as vasopressin.The most serious side effect of hyperkalemia is on ______________ function.Serum _______________ is directly or indirectly regulated by parathyroid hormone (PTH) and vitamin D.Respiratory acidosis is characterized by a decrease in __________, reflecting a decrease in ventilation and an increase in PCO2.Vomiting, removal of gastric secretions through the use of nasogastric suction, and low potassium levels resulting from diuretic therapy are the most common causes of _________________ alkalosis in hospitalized patients.
5 Distribution of Water Intracellular Extracellular Interstitial Plasma 3rd Space
6 Scenario An athlete ran a marathon even though he felt ill… After the race he collapsed. He was pale with a low blood pressure and sunken eyes. One knee and ankle were badly swollen, and his abdomen was distended with fluid. The doctor diagnosed appendicitis and dehydration.Question:What has happened to his:Blood osmolarity?Cell size? Transcellular fluid volume? Vascular compartment volume?
7 Osmosis: Which Way Will Water Move? Forces Moving Fluid In and Out of Capillaries and CellsOsmosis: Which Way Will Water Move?Blood: (ECF)Few solutesLots of waterCell: (ICF)Many solutesLess waterWater Follows Solutes
8 Forces Moving Fluid In and Out of Capillaries Hydrostatic pressurePressure created by the Hearti.e. Blood PresssureForces water out of capillaries
9 Forces Moving Fluid In and Out of Capillaries Greatly reduced Hydrostatic pressure due to capillary resistanceHydrostatic pressure generated by the heart
10 QuestionWhat forces work to keep blood in the capillary?Capillary colloid osmotic pressure (COP) & tissue COPCapillary hydrostatic pressure & tissue COPCapillary hydrostatic pressure & tissue hydrostatic pressureCapillary COP & tissue hydrostatic pressure
11 AnswerCapillary COP & tissue hydrostatic pressureHydrostatic pressure can be thought of as “pushing pressure,” and osmotic pressure can be thought of as “pulling” pressure. Pressure in the capillary that pulled/kept fluid in (capillary COP) and pressure pushing fluid out of the tissue (tissue hydrostatic pressure) would result in more fluid in the capillary.
12 Sodium Normal level is 135–145 mEq/L Regulates extracellular fluid volume and osmolarityQuestion:Why would “retaining sodium” cause high blood pressure?
13 ScenarioIt’s a very hot day and you fall down the stairs on the way to see the doctor about your hepatitis and renal diseaseExplain why you have edema in your sprained ankle and foot
14 Controlling Blood Osmolarity High osmolarity causes: (Hypothalamic detection)Thirst ADH release Low osmolarity causes:Lack of thirst Decreased ADH release increased water intakewater reabsorbed from urinedecreased water intakewater lost in the urineNegative_________________ Feedback
15 QuestionTrue or False: Increased levels of ADH decrease urine output.
16 AnswerTrue ADH prevents diuresis by causing more water to be absorbed in the kidney tubules. If more water is absorbed, there is less water left to eliminate as waste, decreasing urine output.
17 Dehydration Due to Hypodipsia A common problem in elderly peopleScenario:Dr. Bob thinks it could be treated with ADH given in a nasal sprayDr. Bill thinks renin injections would be betterQuestion:What is your evaluation of these two theories?
18 ADH Imbalances Diabetes insipidus (DI) Neurogenic Nephrogenic Syndrome of inappropriate ADH (SIADH)Which will cause hyponatremia?
20 A man with hypernatremia was severely confused. ScenarioA man with hypernatremia was severely confused.Question:The doctor said this was due to a change in the size of his brain cells. Why would this happen?A medical student suggested giving him a hypotonic IV. Why?The doctor said that might worsen the change in his brain cell size, and that his blood osmolarity should be corrected very slowly. Why?
21 Potassium Normal level is 3.5–5.0 mEq/L Maintains intracellular osmolarityControls cell resting potentialNeeded for Na+/K+ pumpExchanged for H+ to buffer changes in blood pH
22 What Will Happen to Blood K+ Levels When the Client Has: Hyperaldosteronism?Alkalosis?An injection of epinephrine?Convulsions?Loop diuretics?
23 The Basics of Cell Firing Cells begin with a negative charge— resting membrane potentialStimulus causes some Na+ channels to openNa+ diffuses in, making the cell less negative, i.e. more positiveThreshold potentialResting membrane potentialstimulus
24 The Basics of Cell Firing (cont.) Action potentialAt threshold potential, more Na+ channels openNa+ rushes in, making the cell positive: depolarizationAction potential: the cell responds (e.g., by contracting)Threshold potentialResting membrane potentialstimulus
25 The Basics of Cell Firing (cont.) Action potentialK+ channels openK+ diffuses out, making the cell negative again: repolarizationNa+/K+ ATPase removes the Na+ from the cell and pumps the K+ back inThreshold potentialResting membrane potentialstimulus
26 Blood K+ Levels Control Resting Potential Hyperkalemia raises resting potential toward thresholdCells fire more easilyIncreased K+ can move resting potential to threshold, Na+ gates open and won’t closeThreshold potentialHyperkalemiaNormal resting membrane potential
27 Blood K+ Levels Control Resting Potential (cont.) Hypokalemia lowers resting potential away from thresholdCells fire less easilyThreshold potentialNormal resting membrane potentialHypokalemia
28 QuestionWhat effect does a potassium level of 7.5 mEq/L have on resting membrane potential (RMP)?RMP becomes less negative, and it takes a greater stimulus in order for cells to fire.RMP becomes less negative, and it takes less of a stimulus in order for cells to fire.RMP becomes more negative, and it takes a greater stimulus in order for cells to fire.RMP becomes more negative, and it takes less of a stimulus in order for cells to fire.
29 AnswerRMP becomes less negative, and it takes less of a stimulus in order for cells to fire.A potassium level of 7.5 mEq/L is considered hyperkalemic. In hyperkalemia, RMP is moved closer to the threshold (it becomes less negative). Because RMP is nearer to the threshold, a weaker stimulus will cause the cell to fire (a lesser distance must be overcome).
30 Calcium Normal level is 8.5–10.5 mg/dL Extracellular: blocks Na+ gates in nerve and muscle cellsClottingLeaks into cardiac muscle, causing it to fireIntracellular: needed for all muscle contractionActs as second messenger in many hormone and neurotransmitter pathways
31 Blood Ca2+ can be increased by: Calcium RegulationBlood Ca2+ can be increased by:Increased intestinal absorptionRelease from bones
32 Blood Ca2+ can be increased by: Calcium regulationBlood Ca2+ can be increased by:Increased intestinal absorptionRelease from bones
33 Scenario: PTH? Calcium levels? Vitamin D levels? A man with metastatic cancer complains of bone pain and sudden weakness.Question:Why did the doctor measure:PTH?Calcium levels?Vitamin D levels?
34 Magnesium Normal level is 1.8–2.7 mg/dL Cofactor in enzymatic reactionsInvolving ATPDNA replicationmRNA productionBinds to Ca2+ receptorsCan block Ca2+ channels
35 Extracellular Calcium Controls Nerve Firing HypercalcemiaBlocks more Na+ gatesNerves are less able to fireHypocalcemiaBlocks fewer Na+ gatesNerves fire more easilyWhich would cause Trousseau’s & Chvostek’s sign?Hypocalcemia because they indicate easy nerve firing
36 CHVOSTEK’S SIGN &TROUSSEAU’S SIGN Elicitation: Tapping on the face at a point just anteriorto the ear and just below the zygomatic bonePostitive response: Twitching of the ipsilateral facialmuscles, suggestive of neuromuscular excitabilitycaused by hypocalcemiaTROUSSEAU’S SIGNElicitation: Inflating a sphygmomanometer cuff abovesystolic blood pressure for several minutesPostitive response: Muscular contraction including flexionof the wrist and metacarpophalangeal joints,hyperextension of the fingers, and flexion of the thumbon the palm, suggestive of neuromuscular excitability
37 QuestionTrue or False: Both hyperkalemia and hypercalcemia cause cells to fire more easily.
38 AnswerFalse Recall that hyperkalemia cause cells to fire more easily by moving RMP closer to the threshold. Hypercalcemia, on the other hand, blocks more sodium gates. If less sodium enters the cell, it cannot depolarize as quickly (it is less likely to fire). Hypocalcemia blocks fewer sodium gates–cells depolarize more quickly (they are more likely to fire).
39 Balance between blood pH, HCO3= and H2CO3 Insert fig. 6-16 H2CO3 = .03 * PaCO2Normal BalanceMetabolic AcidosisRespiratory AlkalosisImportant Relationships
40 Controls respiratory rate Individual acids have different functions: Acid (H+)Normal value: pH = 7.35–7.45Blocks Na+ gatesControls respiratory rateIndividual acids have different functions:Byproducts of energy metabolism (carbonic acid, lactic acid)Digestion (hydrochloric acid)“Food” for brain (ketoacids)
41 Respiratory or Volatile Acid CO2 + H2O H2CO3 (carbonic acid)H2CO3 H+ + HCO3- (bicarbonate ion)An increase in CO2 will causeIncreases in CO2 (increased PCO2)Increases in H+ (lower pH)Increases in bicarbonate ion
42 Respiratory Acidosis and Alkalosis CO2 + H2O H2CO3 H+ + HCO3-(carbonic acid) (bicarbonate ion)Respiratory distress may be an attempt to compensate for low serum pHRespiratory acidosisRespiratory alkalosisIncreased PCO2Increased carbonic acidIncreased H+ = low pH (<7.35)Increased bicarbonateDecreased PCO2Decreased carbonic acidDecreased H+ = high pH (>7.45)Decreased bicarbonate
43 QuestionTell whether the following statement is true or false: Serum levels of pH and CO2 levels are directly proportional.
44 AnswerFalse As blood levels of CO2 increase, pH becomes more acidic (decreases).
45 Respiration and Buffers Adjust Blood pH Scenario:A woman was given an acidic IV. Soon she began to breathe more heavily. Why?When her blood was tested, it had:Slightly lowered pHLow bicarbonateLow PCO2Slightly increased K+Her urine pH was slightly loweredWhy?