Fluid and Electrolytes Flashcards
What is body fluid?
Fluid in the body circulates in the blood and lymph vessels, surrounds the cells, and provides the environment inside cells in which they perform their cellular chemistry. The amount, concentration, and composition of the fluid in the body influence function at all levels from the cell to the whole person.
What is the concept and electrolytes of fluid?
The concept fluid and electrolytes refers to the process of regulating the extracellular fluid volume, body fluid osmolality, and plasma concentrations of electrolytes.
How do we maintain physiological balance of body fluid and electrolytes?
Dynamic interplay of 3 processes: intake and absorption, distribution, and output.
What is the scope of fluid and electrolytes?
One either has optimal balance or an imbalance. Fluid and electrolyte imbalances can be too little, too much, or misplaced. Conceptually, fluid balance has two aspects: extracellular volume and osmolality.
What are the categories?
Too dilute — Optimal —- Too concentrated
What are the three physiological processes whose interplay creates fluid and electrolyte balance
Intake and absorption, distribution, and output.
What are the two major extracellular compartments
Vascular and Interstitial.
How does distribution between the vascular and interstitial compartments occur?
Filtration, the net result of simultaneous opposing forces at the capillary level. Two forces tend to move fluid out of capillaries and two other forces tend to move fluid into capillaries.
Hydrostatic pressure pushes fluid out of its compartment. Capillary blood hydrostatic pressure (a relatively strong force) pushes fluid out of the capillaries;
interstitial fluid hydrostatic pressure (a relatively weak force) pushes fluid out of the interstitial compartment back into capillaries. Colloid osmotic pressure, caused by large protein particles in the fluid, pulls fluid into its compartment.
Water Distribution between ECF and Intracellular Fluid
The structure of cell membranes allows water to cross the membrane readily but Na+ enters with difficulty. This is the reason why cell membranes are called semipermeable.
The process of osmosis is movement of water across a semipermeable membrane that separates compartments with different concentrations of particles. As noted previously, the osmolality of a fluid is its degree of concentration.
What is Electrolyte Distribution
With the exception of Na+, which has a high ECF concentration that reflects osmolality, electrolytes have low concentrations in the ECF compared to their concentrations in electrolyte pools.
The K+ pool is inside cells, which contain almost 98% of total body potassium.
Bone is an important Ca2+ pool. Mg2+ pools include inside cells and bones.
Physiologically inactive forms of Ca2+ and Mg2+ bound to albumin or organic anions such as citrate also can be considered electrolyte pools.
What is Output?
The normal excretory routes of fluid and electrolytes are renal (urine), gastrointestinal (feces), through the skin (insensible perspiration and sweat), and the lungs (water vapor).
Some of these routes (urine, sweat, and, to some degree, feces) are regulated physiologically to maintain optimal balance, but the regulatory mechanisms can be overwhelmed.
Other excretory routes, including insensible water exiting through skin and lungs, are mandatory, regardless of fluid balance.
Abnormal routes of fluid and electrolyte output include emesis, hemorrhage, drainage through tubes or fistulas, and other routes of fluid and electrolyte loss often seen in clinical situations. These abnormal output routes do not have physiological regulatory mechanisms.
What is the largest route of output?
Renal excretion provides the largest output of fluid and electrolytes in normal circumstances. The hormone aldosterone (along with natriuretic peptides not discussed in this concept presentation) regulates renal excretion of Na+ and water (isotonic fluid), whereas antidiuretic hormone (ADH) regulates excretion of water.
Aldosterone increases renal excretion of K+ directly and probably Mg2+ indirectly.
What is Aldosterone?
The adrenal cortex secretes aldosterone in response to angiotensin II, one of the components of the renin–angiotensin system.
When the ECV is low, the resulting decreased blood flow through the renal arteries increases release of renin, formation of angiotensin I, and then formation of angiotensin II, thus increasing secretion of aldosterone.
Aldosterone acts on the kidneys to remove Na+ and water from the renal tubules and return them to the blood, which restores or even expands the ECV.
The liver cells normally metabolize aldosterone, which stops its action. Decreased renin release or damage to the adrenal cortex will decrease aldosterone secretion, thus increasing renal Na+ and water excretion. Aldosterone is the major hormonal regulator of ECV. Conditions involving excessive or insufficient secretion of aldosterone cause ECV imbalances.
What does aldosterone also facilitate in excreting?
Aldosterone also facilitates renal excretion of K+. Increased concentration of plasma K+ stimulates aldosterone secretion, which causes the kidneys to excrete more K+ and helps return plasma K+ concentration to normal. If plasma K+ concentration decreases, aldosterone secretion is suppressed and the kidneys excrete less potassium.
What is the Antidiuretic hormone?
ADH regulates renal excretion of water but not Na+. Its name describes its action on the kidneys; the antidiuretic effect removes water from the renal distal tubules and collecting ducts and returns it to the blood, which dilutes the ECV and other body fluids. The posterior pituitary normally releases ADH at a level that maintains osmolality (degree of concentration) within normal limits. When body fluids become too concentrated (osmolality too high), osmosensitive cells in the hypothalamus trigger more release of ADH from the posterior pituitary.
