BN Ch.17 Fluid and Electrolytes Flashcards
Define homeostasis in fluid/electrolyte balance. Define negative and positive feedback.
Homeostasis is the dynamic process through which the body maintains balance; it constantly adjusts to internal and external stimuli.
Homeostasis is maintained by balancing fluids, electrolytes, acids, and bases.
Negative feedback occurs when the body reverses an original stimulus to regain physiologic balance (homeostasis). Body systems resist deviations, normally allowing for small variations only.
In positive feedback , the body enhances or intensifies an original stimulus. The body senses deviations, but positive feedback generally is not homeostatic.
Describe intracellular and extracellular fluid compartments, including their components, the total percentage of body weight, and the major cation and anion of each.
- 50- 60% of total body weight
- Intracellular fluid functions as a stabilizer for the parts of the cell and helps maintain cell shape.
- ICF also assists with transport of nutrients across the cell membrane, in and out of the cell.
- The adult body is about 60% water; therefore, ICF is 40% of total body weight (approximately 28 L).
- The major ions in ICF are potassium, magnesium, and phosphate (in addition to proteins).
- ECF appears mostly as interstitial (tissue) fluid and intravascular fluid ( IVF within blood and lymphatic vessels).
- Intravascular fluid is the watery fluid in blood ( plasma ).
- Interstitial fluid is found between cells and accounts for about 15% of body weight (approximately 3.5 L).
- Major ions in ECF are sodium, chlorine, and carbonate.
Describe how the thirst center, ANP, and the RAA system help regulate fluid balance.
- The thirst center in the hypothalamus stimulates or inhibits the desire for a person to drink.
- The RAA system controls fluid volume. When blood volume decreases, blood flow to the renal (kidneys’) juxtaglomerular apparatus is reduced, activating the RAA system.
- Renin is released by the kidneys, causing secretion of angiotensin I, which is converted to angiotensin II (by an enzyme) in the lungs.
- Angiotensin II causes both vasoconstriction (increasing blood pressure) and secretion of aldosterone by the adrenal cortex.
- Aldosterone causes increased reabsorption of sodium and water by the kidneys in an attempt to increase blood volume.
- (Water “follows” sodium [salt], explained later in this chapter.) Excretion of potassium is also increased in an attempt to restore homeostasis
- The heart also plays a role in correcting overload imbalances, by releasing ANP from the right atrium. ANP promotes renal diuresis (kidney excretion) of sodium and water
Explain “third-spacing”; describe four ways edema can occur. Describe client teaching to decrease/prevent edema.
- Third Spacing occurs when too much fluid moves from the intravascular space (blood vessels) into the interstitial or “third” space—the nonfunctional area between cells.
- Some causes of edema include:
- Obstruction of venous blood or lymphatic return
- Increased capillary permeability or increased capillary pressure
- External pressure (e.g., tight binders or casts)
- Inflammatory reactions
- Increased sodium intake, urine retention, endocrine disorders, and a loss of plasma proteins can also cause edema.
- Treatment of edema is directed at treating the underlying cause.
- Diuretics (medications that stimulate urination) are commonly given for systemic edema. (This causes increased loss of body fluids and salts via the kidneys.)
Identify four functions of water.
Water is vital for life and composes the greatest percentage of body weight; the human body consists of 45%–77% water
- Primary solvent within the body
- Primary compound in all body fluids
- Suspension agent
- Helps regulate body temperature, body pH, and fluid pressures inside and outside cells
- Assists or participates in chemical reactions
- May be end product of chemical reactions
Name three major electrolytes necessary for neuronal and muscular function; describe two nursing actions to help maintain electrolyte balance.
- Potassium (K+)
- Major ion in intracellular fluid (ICF)
- Calcium (Ca ++ )
- Magnesium (Mg ++ )
- Mainly in ICF
Encourage intake of foods and fluids; regulate temperature control
Be sure that the client on certain medications drinks enough water
Differentiate between freely permeable and selectively permeable membranes; state factors affecting permeability.
Freely permeable membranes allow almost any food or waste substance to pass through.
Freely permeable walls allow easy transfer of fluid and substances from intravascular fluid to interstitial fluid.
The cellular membrane is selectively permeable , meaning that each cell’s membrane allows only certain substances to pass through.
- Size of pores in the membrane (which can be altered in response to pressures or hormones)
- External and internal pressures exerted on the molecules ( osmotic pressure )
- Pressure of fluid against the membrane ( hydrostatic pressure )
- Electrical charges of the molecule, the plasma membrane, or the body fluid
- Solubility of the molecules
- Size of the molecules
Contrast transportation of fluids and other molecules by diffusion, osmosis, filtration, and active transport.
- Diffusion or the process of “being widely spread,” is the random movement of molecules from an area of higher concentration to an area of lower concentration.
- Molecules constantly move and bombard each other at random, with the goal of equalization the molecular equivalent of seeking homeostasis.
- The homeostatic mechanism of osmosis equalizes concentrations of nondiffusible solutes within the body.
- Thus, osmosis is the diffusion of a pure solvent, such as water, across a semipermeable membrane in response to a concentration gradient, in situations where molecules of the higher concentration are non diffusible.
- Filtration is the transport of water and dissolved materials through a membrane from an area of higher pressure to an area of lower pressure and is very common in the body.
- It operates somewhat like a sieve. Filtration requires mechanical pressure
- Active transport mechanisms require specific enzymes and energy expenditure, as adenosine triphosphate (ATP).
- Adenosine is a combination of adenine, containing nitrogen, and ribose, a 5-carbon sugar.
- Adenosine plus three phosphate groups makes up ATP.
- ATP must be converted to ADP in order to produce energy.
List normal sources of water gain and the mechanism of water loss. Identify normal daily intake and output for an average adult.
- Most water output occurs through the kidneys, in sweat, as water vapor from the lungs, and in feces.
- Sweat may be sensible (visible, able to be sensed) or insensible (not perceptible to the senses) water loss.
- Minute amounts are also lost through vaginal secretions.
- A fever can cause a person to require about four times the amount of fluids normally needed.
- Diaphoresis (profuse sweating) can cause considerable fluid loss.
- The average adult takes in approximately 2,000–3,000 mL (milliliters) per day (a little more than 2–3 quarts).
Describe major components and actions to maintain acid–base balance, including the significance of arterial blood gas values.
- The body needs many of these substances to regulate acid–base levels and coordinate water balance.
- Potassium acts within the cells in much the same way that sodium acts outside the cells.
- Chlorine plays a major role in acid–base balance because of its production of hydrochloric acid (HCl).
- Water contains equal components of both an acid (the hydrogen ion or H)
- A base (the hydroxyl ion or OH − ). Pure water is considered a neutral solution
- *Buffers**
- *-**Stabilizing system to prevent pH imbalance
- Chemical system set up to resist changes
- Many buffer systems found in body to help maintain homeostasis
- Arterial blood gas values: Arterial blood gasses (ABGs) are measured in a laboratory test to determine the extent of compensation by the buffer system.
- The pH level and amounts of specific gasses in the blood indicate if there is more acid or base and their associated values
Normal adult ranges:
- PH: 7.35-7.45
- PaCO2: 35-45 mm Hg
- PaO2: 80-100 mm Hg
- HCO3−: 22-26 mEq/L
Explain why infants, young children, and the elderly are at risk for fluid/electrolyte imbalance.
- Infants have a considerably higher percentage of body fluid than adults, most of which is ECF. They are at increased risk for fluid volume deficit because ECF is lost more easily than ICF.
- Also, immature kidney function places infants and young children at risk for alterations in fluid and electrolyte levels.
- Loss of thirst sensation in older adults often leads to decreased consumption of fluids; therefore, these clients are at increased risk for fluid volume deficit.
- Cardiovascular disorders, renal disorders, and poor nutritional habits may cause sodium and water retention, leading to fluid overload.
Describe two nursing actions to assist seniors to maintain homeostasis.
- Many medications cause fluid loss
- Medications may contribute to dehydration
- Be sure that the client on certain medications drinks enough water
- Muscle tissue turns to fat
- Older adults may gain weight
- Encourage exercise, activity, and a balanced diet
__________is the dynamic process through which the body maintains balance by constantly adjusting to internal and external stimuli.
Homeostasis
__________feedback occurs when the body reverses an original stimulus to regain physiological homeostasis.
Negative
Intravascular fluid is the watery fluid of the blood known as __________.
Plasma
