Chapter 8 Fluids, Electrolytes, Acids and Bases Flashcards
Learning Objectives
- Differentiate the intracellular from the extracellular fluid compartments
- Relate the concept of a concentration gradient to the processes of diffusion and osmosis.
- Describe the control of cell volume and the effect of tonicity on cell size.
- Relate the functions of sodium, chloride, potassium, magnesium, and phosphorus to the manifestations of hypo- and hyper-levels.
- Compare the roles of the kidneys and respiratory system in regulation of acid–base balance.
- Define metabolic acidosis, metabolic alkalosis, respiratory acidosis, and respiratory alkalosis.
Body fluid homeostasis
dynamic process
disease is caused by an imbalance of this homeostasis
body fluid distribution
- how much of our body is made up of water?
- how much of that is intracellular v extracellular
our bodies are made of about 60% water
40% is intracellular (about 28 L or 280mL)
20% is extracellular (interstitial fluid in between the cells > blood plasma > transcellular)
extracellular fluid electrolyte concentration
note: extracellular levels can be measured via blood draws
Na+ and Cl- are the most abundant in the EC fluid
Bicarbonate HCO3- is also at a significant level extracellularly
Phosphate and Ca+ are at higher concentrations extracellularly than intracellularly but not at high concentrations
intracellular fluid electrolyte concentration
reminder: we have more intracellular water than extracellular (body is 60% water. 40% (of that 60) is intracellular)
K+ is the electrolyte of highest concentration in our cells
(upon injury, K+ will be released into the extracellular fluid)
Mg+ is also at significant levels
Concentration Gradient
the difference in concentration over a distance
Diffusion
the movement of charged or uncharged (particles) along a concentration gradient from higher to a lower concentration
Osmosis
the movement of water across a semipermeable membrane from the side of the membrane with the lesser number of particles to the side with the greater number of particles
Which ion is in the highest concentration in the ICF?
K+
Tonicity
The effect of osmotic pressure of a solution on cell size
(because of water movement across the cell membrane)
What is a hypertonic solution?
a solution where the cell shrinks due to more particles in the fluid.
osmotic pull is higher
ex: dehydration
What is a hypotonic solution?
Cells swell because there is a lot of water in the extracellular fluid
“HypO H2O” excess water
(example: water to particle ratio outside the cell 5:1, inside the cell 1:2 –> water wants to balance the ratios… )
How do you balance a hypertonic solution
give a hypotonic solution such as a 0.45 NaCl solution (reintroduces water into the cells)
Capillary fluid forces:
Capillary filtration pressure (hydrostatic force)
capillaries are where arteries and veins meet
fluids can shift based on capillary pressures
capillary filtration pressure is based on the heart and is the output of blood into the tissue
more output leads to higher tissue hydrostatic pressure (higher BP)
Capillary fluid forces:
Capillary Colloidal Osmotic Pressure (osmotic force)
Created by the concentration gradient of albumin
Albumin: a protein that exists only inside the capillaries and cannot be filtered out (due to size)
fluid wants to be pulled back into the capillaries on the venous side in order to balance the solute concentration (set by albumin)
( solute concentration inside the cell»_space;> solute concentration outside the cell … therefore water wants to come in and fix out solute imbalance)
Why does edema occur in malnutrition
Edema is swelling caused by too much fluid trapped in the body’s tissues.
In malnutrition, there are insufficient albumin levels so water does not want to enter back into the capillaries
excess of extracellular fluids and insufficient water reabsorption leads to edema and poor circulation
what role does the lymph play in circulation
lymph channels can transport and leftover fluids back into the capillaries
4 causes of Edema Formation
edema: the moving out /excess of fluid into the interstitial space
mechanisms that contribute to edema formation:
- ^^^ capillary filtration pressure (hydrostatic forces)
- ex: pregnant women have swelling in their ankle due to the increased pressure from the distended uterus - decreased colloidal osmotic pressure
- increased capillary permeability
- obstruction to lymph flow
- impairs recirculation of residual fluids
3 Location Types of Edema
- Localized
- General
- everywhere - Dependent
- wherever gravity takes the fluid
- ie: sacral area (back & butt) in bedridden patients, legs in pregnant
Edema can also be organ specific
- ie: fluid filled lungs, cerebral edema
Pitting v Nonpitting edema
pitting: indents
- when you push on it with your finger, the dent stays there
nonpitting: no indents
Methods for assessing edema
daily weight- assesses general edema
visual assessment
measurement of affected part
application of finger pressure to assess pitting edema
Loss of bodily fluids
insensible v sensible
we can lose bodily fluids via:
kidneys
skin (sweat)
lungs
GI tract (feces)
insensible=unmeasurable
ex: breath
4 pillars of fluid balance (IADE)
- Intake (thirst, habit, age)
- we are thirsty when we are low on volume
- Absorption (GI tract and kidneys absorb water –funnels–> blood)
- the different types of fluids you drink impact osmolarity (ie: soda will cause you to retain more water due to the body’s attempt to balance out the sugar. coffee will make you lose water since it’s a diuretic) - Distribution
- 2/3 of our fluids are intracellular, 1/3 is extracellular
- Excretion
- urine
- GI tract
- lungs
- skin
Hypovolemia vs Hypervolemia
hypovolemia= dehydration (low volume of water)
hypervolemia= too much fluid
What is the mechanism of thirst?
mention ADH
Thirst is triggered from the hypothalamus in response to osmolarity changes
Antidiuretic Hormone (ADH): hormone formed in the posterior pituitary gland
- reabsorbs more water in kidneys
- retains more water in overall extracellular water volume
- stops our feelings of thirst
clinical signs of low/lost fluids
dehydration/hypovolemia
vital signs:
increased Heart rate
decreased Blood pressure
Venous volume/filling
- could even cause collapsed veins
decreased Capillary refill rate (delayed redness return on skin)
Psychogenic polydipsia
compulsive water drinking
- large amounts of water intake and urine excretion
how does cigarette smoking affect thirst?
smoking releases antidiuretic hormone (ADH)
this leads to fluid retention in kidneys and decreases sense of thirst
how do psychiatric medications affect thirst?
antipsychotic medications increase ADH levels
- increased ADH levels
- renal fluid retention
- decreased sense of thirst
how does drinking large amounts of water impact blood tonicity?
your blood becomes hypotonic
the increase of water leads to the excess of water wanting to enter RBCss
Diabetes Insipidus
deficiency of or decreased response to ADH
patients unable to concentrate urine during periods of water restriction and excrete large volumes of dilute urine
decreased concentrated blood volume
caused by damage / defect to posterior pituitary (central or neurogenic diabetes) or kidneys (nephrogenic diabetes)
SIADH (syndrome of inappropriate ADH)
failure of the negative feedback system that inhibits of ADH
- this increases ADH release
leads to very little outputs of concentrated urine
blood becomes very dilute because body is attempting to save water
Causes of Isotonic fluid volume excess (hypovolemia)
- inadequate sodium and water elimination
- kidney failure, heart failure, liver failure, medications - excessive sodium and water intake in relation to output
- dietary intake
- isotonic IV fluid replacement (saline 0.9mm)
Baroreceptors
receptors for sodium that sense changes in blood pressure (sensing fullness of circulation, how much blood volume there is)
located in the atria of the heart, the pulmonary blood vessels, and kidneys
sends signals to the kidneys via SNS stimulation to alter amount of urine production, aka GFR (globular filtration rate)
how do the kidneys regulate sodium?
- baroreceptors sense BP change
- SNS is stimulated which tells the kidneys to alter urine production (GFR) and Na reabsorption rate (pulling Na+ back into the blood volume)
(low BP= release aldosterone and retain Na+ and water)
(high BP eliminate Na+ and water) - if the BP is low, activation of the RAAS (renin-angiotensin-aldosterone system) leads to production of aldosterone which increases Na+ (sodium) and water reabsorption
- if the BP is high (heart stretching), ANP (atrial natriuretic peptide) hormone is released to increase sodium and water excretion
Na+ follows water*
Sodium (Na+) imbalance
(Range, Hypo, Hyper)
blood plasma value: 135-145 meQ/L -or- mmol/L
Hyponatremia (below 135):
- headache
- lethargy/confusion
- orthostatic tension
- tachycardia
- seizures
could be caused by: hypotonic IVs, diuretics
Hypernatremia (above 145)
- seizures
- thirst, dry mucous membranes
- fever
- restless, irritable
- high BP
- edema
- decreased urine output
Potassium K+
(Range, Hypo, Hyper)
Blood plasma value:
3.5-5.0 meQ/L -or- mmol/L
(remember there is a lot of Calcium inside the cell… only 2% outside the cell)
Hypokalemia (below 3.5):
-Weak irregular heart rhythm & pulse
-Muscle weakness
-Leg cramps*
-Lethargy
- greater risk for cardiac arrest
-Nausea/Vomiting (N/V)
Causes include Vomiting/Gastric sx. Diarrhea, Diuretics, High glucose
Treatment: supplements
Hyperkalemia (above 5.0):
-Weak, slow, irregular heart rhythm & pulse –> cardiac arrest
-Muscle weakness
-N/V/Diarrhea
Causes include renal failure, acid/base imbalance, cell injury (trauma), ^^ intake
Treatment:
- calcium antagonizes potassium’s effect on heart excitability
- sodium bicarbonate can cause K+ to move into the ICF (into the cell)
- insulin decreases ECF K+ concentration (K+ moves into the cell)
- increasing renal excretion (dialysis)
what are the major bodily divalent cations and what is their pathway in the body
?
Calcium, Phosphorus, and magnesium
ingested in the diet
absorbed from the intestine
filtered, reabsorbed, and eliminated by kidney
3 forms of extracellular (ECF) Calcium (Ca2+)
- protein bound (40% of ECF calcium is bound to albumin
- Complexed: 10% is chelated with citrate, phosphate, and sulfate
- Ionized: 50% of ECF calcium is present in the ionized form
*normal range is 4.6-5.3 mg/dL
how is calcium regulated (2)?
- Vitamin D: increases GI absorption to sustain normal plasma levels of calcium and phosphate
- calcitriol increases calcium absorption from the intestines
- Calcitonin: (from parathyroid gland of the neck) acts on the kidney (tells kidney to keep Ca) and bone (draws C out of the bones) to remove calcium from the extracellular circulation.
Calcium Imbalanca
(range, hypo, hyper)
normal blood plasma levels: 8.5-10 mg/dL
Hypocalcemia:
- Tachy or brady, Hypotension
- ^^ neuro-muscular excitability (seizures, tetany… due to too little Ca in the gap)
-Nerve cells less sensitive to stimuli (numbness in toes, fingers, face)***
- Bone fractures
Causes may include:
Dietary deficiency, ETOH, Impaired mobilization from bone, Kidney loss, decreased Vit D
Renal failure, decreased Mg++, ^^^Phos
Hypercalcemia:
-Bradycardia, HTN (^^ BP)
- decreased N-M response: decreased DTR (deep tendon reflex), weakness
-GI: anorexia, N/V, abd. pain, ileus
Causes may include:
Increase dietary intake
Hyperparathyroidism or Cancer are most common
Antacid overuse, decreased Phos^
increase in vitamin D (helps retain calcium)
Chvostek and Trousseau’s signs of hypocalcemia
Chvostek’s: brief contraction of upper lip, nose, or side of face when tapping facial nerve by the ear
Trousseau’s: carpopedal spasm after BP cuff has been inflated 20 mmHg above systolic for 1 to 4 minutes
which 3 electrolytes have the biggest impact on the heart
- potassium K+
- Calcium Ca2+
- Magnesium Mg2+
Phosphorus
role/function
Functions:
Bone formation
Cellular metabolism
N-M regulation
Hematologic function (WBCs, RBCs, platelets)
Acid/base buffer in kidneys
Regulated by PTH (parathyroid hormone)
is like the inverse to Ca2+
Phosphorus imbalance
normal range: 2.5-4.5 mg/dL (decilitre)
Hypophosphatemia-
Symptoms:
* Same as ^^Ca++ (weak, numbness, N/V/ileus)
Causes:
decreased intestinal absorption (pancreatitis, Vit D deficit)
Acid base imbalance resp alkalosis
Hyperglycemia –> insulin –> Phos into cells
Symptoms:
Same as decreased Ca++ (cramps, tetany, hypotension)
Causes:
Renal failure (^ Ca and lower phos – kidney reabsorption)
Acid base imbalance resp acidosis
Laxative overuse
Role of Magnesium
Essential to all reactions that require ATP: Cellular energy metabolism
Metabolism of carbohydrates and protein synthesis
Helps Na and K cross cell membranes (involved in Na/K pump)
Maintains Ca levels by stimulating PTH secretion (parathyroid hormone)
Regulates cardiac and skeletal muscle contractions, rhythm
Ingested in the diet, Absorbed from the intestine, Excreted by the kidneys
Magnesium Imbalance
Normal plasma levels: 1.8-3.0 meQ/L
What is the normal range for arterial blood pH
7.35-7.45
what 2 extracellular substances work together to regulate pH
carbonic acid ( H2CO3) and bicarbonate (HCO3-)
what is an acid?
a substance that releases H+ ions
(electron donors)
CO2
what is a base
a substance that accepts H+ ions (electron acceptor)
HCO3 bicarbonate
Arterial Blood Gas Normal Values
pH, pCO2, HCO3
pH: 7.35-7.45
pCO2 35-45 (partial pressure CO2… how much is dissolved into the blood)
- lowers pH if added
- regulated by the lungs (respiratory)
HCO3 Bicarbonate 22-26
- adds base and raises pH
- kidney regulated (metabolic)
Buffering
a normal body mechanism that occurs rapidly in response to acid-base disturbances in order to prevent changes in H+ concentration
What 2 systems work to regulate pH in acid-base balance? which system works fastest?
The respiratory and renal systems
Respiratory works fastest
ROME (Acid Base Balance disorders mnemonic)
Respiratory
Opposite
(alkalosis: ph ^ pCO2 decreases
acidosis: pH decrease pCO2 ^)
Metabolic
Equal
(alkalosis: ^^ both pH and HCO3
acidosis: both pH and HCO3 decrease)
Respiratory Acidosis
ph under 7.35
respiratory CO2»_space; 45
we are retaining CO2 (hypoventilation)
body would try to self regulate by raising bicarb (increasing the level of a base) in the blood to fix pH
Respiratory Alkalosis
pH above 7.45
CO2 is below 35
hyperventilation (blowing off lots of CO2)
body would try to self regulate by getting rid of HCO3 (bicarb)
Metabolic Acidosis
ph «_space;7.35
Metabolic bicarbonate (HCO3) «_space;22 (kidney is excreting. lower levels of base allow for more acidic pH)
body starts hyperventilating to get rid of the acid (CO2)
anion gap is a method of fixing metabolic acidosis
Metabolic Alkalosis
ph > 7.45
HCO3 > 26
body starts hypoventilation (retaining CO2) to bring more acid
Respiratory Control Mechanisms
Works within minutes to control pH; maximal in 12-24 hours
Only about 50-75% effective in returning pH to normal
Excess CO2 & H+ in the blood act directly on respiratory centers in the brain
CO2 readily crosses blood-brain barrier reacting w/ H2O to form H2CO3
Carbonic acid, H2CO3, splits into H+ & HCO3- & the H+ stimulates an increase or decrease in respirations
