Week 8: Fluids, Electrolytes, and Acid-Base Balance Flashcards
Balance
reflection of overall body function (homeostasis)
Acid Base Balance
- disruption of the balance pH (acid/base) has profound effect on overall health
- outside of the “normal” pH range can lead to death
Body Fluids
- transport gases (CO2 and O2) –> dissolved and transported throughout the body
- make up 60% of body weight
- water content affected by age, sex, and fat cells
- infants = high water content
- decreases with age
Water
-primary body fluid
-content varies with age, sex, adipose tissue (fat cells)
-contains dissolved gases (CO2, O2)
-contains solutes (solid substances)
>electrolytes (sodium, potassium)
>non-electrolytes (glucose, urea)
Electrolytes: Electricity?
- electrolytes develop an electrical charge when dissolved in water
- non-electrolytes do not conduct electricity
Important Function of Bodily Fluids
- maintain blood volume
- regulate body temperature
- transport material to and from cells
- serve as a medium for cellular metabolism
- assist with digesting food
- serve as medium for excreting waste
Body Fluid Compartments
- Intracellular
- Extracellular
Body Fluid Compartments: Intracellular
- within the cells
- essential for cell function and metabolism
Body Fluid Compartments: Extracellular
-Interstitial
-Intravascular
-Transcellular
>outside the cells
>carries water, electrolytes, nutrients, and oxygen to the cells and removes waste products of cellular metabolism
Extracellular: Interstitial Fluid
between body cells
Extracellular: Intravascular Fluid
plasma within the body – transports blood cells
Extracellular: Transcellular Fluid
special fluid such as peritoneal, synovial, pleural, CSF
Third Spacing
-occurs when fluid is “trapped” in a third space
-not within cells or intravascular spaces (blood vessels)
-occurs in illness, trauma, or disease
>pleural effusion (pleural space)
>ascites (peritoneal cavity)
>vesicles (blisters)
Major Electrolytes in Intracellular Fluid?
- potassium
- magnesium
- phosphate
Major Electrolytes in the Extracellular Fluid?
- sodium
- chloride
- bicarbonate
Transcellular fluid –> (gastric + intestinal secretions) – contain electrolytes
Non-electrolyte Present in ECF?
albumin (mostly intravascular)
Electrolyte Imbalances
-when electrolytes move into a compartment not normally occupied
-lost in excessive amounts from body:
>perspiration
>wounds
>injury
>illness
How Do Fluids and Electrolytes Move in the Body?
-passive or active mechanisms across the selectively permeable membranes that separate the ICF and ECF
Passive Transport
requires no energy
- Osmosis
- Diffusion
- Filtration
Active Transport
- requires energy (ATP) to move against a concentration gradient
- occur when molecules (particles such as electrolytes) move across cell membranes from area of low concentration to area of high concentration
- Adenosine triphosphate (ATP) helps in active transport movement
Osmosis
- passive transport
- water moves from less concentration to higher concentration to dilute the higher concentration of solutes
- think of it as if the solute particles are pulling the water over
Diffusion
- passive transport
- molecules from higher to lower concentration
- solute (particles) move through a cell membrane
- movement occurs until concentration is equal on both sides of the membrane
Filtration
- passive transport
- movement of both water and smaller particles from area of high pressure to one of low pressure
- hydro-static pressure takes place in blood stream (closed system), allows for normal circulation
Crystalloids
solutes that readily dissolve (electrolytes– intravenous solution)
Colloids
larger molecules that do not dissolve readily (proteins– blood products/ transfusions)
Osmolality
- number of particles of solute per kilogram of water (Osmols)
- concentration of solutes providing pressure in body fluid
- expressed is milliosmols per kilogram (mOsm/kg)
- serum osmolality = 275-295 mOsm/kg
Greatest Determinant of Serum Osmolality
sodium
Greatest Determinant of Intracellular Osmolality
potassium
What Contributes to both Intracellular and Extracellular Osmolality?
- glucose
- urea
Isotonic Fluid
-when a fluid has the same osmolality (number of particles) as blood
>0.9% NaCl, LR (sodium chloride + lactated ringers electrolyte solutions)
-isotonic intravenous fluids often given when blood volume is low
>fluid will remain in the vascular space because it has the same concentration as blood — NO OSMOSIS
Hypotonic Solution
- lower osmolality (solutes) than blood
- moves by osmosis (passive) from vascular system into cells
- cells swell
- 0.45% NaCl and 0.33 NcCl
Hypertonic Solution
- higher osmolality (solutes) than blood
- water moves by osmosis (passive) from cells into the extracellular fluid (vascular system)
- cells shrink
- D10W, D5W w/ 0.9% NaCl, D5W w/ 0.45 Nacl
Osmotic Pressure
- power of a solution to draw water (more molecules in solution)
- osmotic pressure from plasma proteins maintains fluid in vascular space
Fluid Intake
-primarily through drinking fluids
-IOM recommends: 2700 ml/day women, 3500/day men
-regulated by thirst
>change in plasma osmolality (solute to fluid ratio)
>less solutes in blood (fluid overload)
>more solutes in blood (fluid loss)
-hypothalamus (thirst center)
Fluid Output
-fluid loss is constant + needs to be replenished
-intake = output
-Sensible loss: measurable
>urine (min 30 mL/hour)
>diarrhea
>feces
-Insensible loss: non-measurable
>skin; perspiration, wound drainage, burns
>lungs: exhalation
Hormonal Regulation
- antidiuretic hormone (ADH)
- renin-angiotensin system
- aldosterone
- kidneys are principle regulator of fluid + electrolyte balance
- entire process occurs when fluid volume is low
Principle Regulator of Fluid + Electrolyte Balance?
kidneys
ADH is Released From?
pituitary gland
Hormonal Regulation: ADH
- pressure sensors in the vascular system stimulate or inhibit release
- (kidneys will retain or excrete more fluid)
Hormonal Regulation: Renin-angiotensin System
(only when needed)
- Renin (enzyme) is released in kidneys when fluid volume is decreased–> leads to release of angiotensin and angiotensin II (hormones)
- angiotensin II retains sodium and water in kidneys and directs release of aldosterone (hormone)
Hormonal Regulation: Aldosterone
- stimulates distal tubules of kidneys to reabsorb sodium + excrete potassium
- sodium reabsorption results in passive reabsorption of water
- increase plasma volume and kidney perfusion
How Does the Body Regulate Electrolytes?
- balance loss + intake
- loss must be replaced by dietary potassium or supplements
- normal serum electrolyte levels depend on dietary intake as well as body regulatory mechanisms
Major Electrolytes
- Sodium (Na+)
- Potassium (K+)
- Calcium
- Magnesium
- Chloride
- Phosphate
- Bicarbonate
Sodium (Na+)
(135-145 mEq/L)
- regulates fluid volume
- major electrolyte in ECF
- moves by active transport
- interacts with calcium to maintain muscle contraction
- stimulates conduction of nerve impulses
- kidney excretes + reabsorbs– maintain ECF volume
- excessive intake can affect BP (high)
- regulated by aldosterone + ADH levels
- low sodium–> excess water intake
Potassium (K+)
(3. 5- 5 mEq/L)
- key in cellular metabolism
- major electrolyte in ICF
- transmits electrical impulses in multiple body systems
- regulates conduction of cardiac rhythm
- deficiency associated with high BP; risk of stroke
- kidneys retain or excretes; assists with acid-base balance
- regulated by aldosterone
- lost though vomiting, diarrhea, many diuretics
Calcium
- most abundant electrolyte in the body
- catalyst for many cellular activities
- important in bone + teeth health, neuromuscular function, cardiac function
- regulates muscle contraction
- essential in blood clotting
- insufficiency–> osteoporosis
- formation of clots
- absorption needs vitamin D
- increased calcium = decreased phosphorus (vice versa)
Magnesium
- second most abundant electrolyte in ICF
- many cellular functions
- involved in protein + CHO metabolism
- needed for protein + DNA synthesis
- loss–> triggered by diuretics, poorly controlled diabetes mellitus, excess alcohol intake
- involved in electrical activity in nerve + muscle membranes Including the heart)
Chloride
- major electrolyte in ECF
- bound to other ions like Na+ to maintain fluid balance
- essential for production of HCl for gastric secretions
- functions as buffer in oxygen carbon dioxide exchange in RBGs
- assists with acid-base balance
Phosphate
(phosphorus)
- major electrolyte in ICF
- catalyst for many intracellular activities
- promotes muscle + nerve action
- bound with calcium in teeth + bone; inverse relationship
Bicarbonate
- major buffer in body
- maintains acid-base balance
- regulated by kidneys
- lost through diarrhea, diuretics, renal insufficiency
Acid
- compounds that contains hydrogen (H+) ions
- stronger the acid is, the lower the pH
Base
compound that accepts hydrogen ions
How is Acid-Base Balance Regulated?
>Buffer Systems >Respiratory Mechanisms > Renal Mechanisms -measured by arterial blood gases (ABGs) -serum pH between 6.9 and 7.8
Acid- Base Balance Regulated: Buffer Systems
prevent a wide swing in pH
Acid-Base Balance Regulated: Respiratory Mechanisms
remove carbon dioxide through rapid, deep breathing
Acid-Base Balance Regulated: Renal Mechanisms
kidneys regulate the concentration of plasma bicarbonate (buffer)
