CH 7: Fluid and Electrolyte Balance

ANP and BNP

-ANP: produced by the atria and is secreted in response to excess ECF volume that stretches the heart's atrial chambers. -BNP: is produced in the heart's ventricles and to a lesser extent, in the brain. It is excreted in response to fluid volume overload stretching the heart's ventricles. *Both ANP and BNP promote natriuresis at the glomerulus by increasing glomerular filtration rate

causes of hypernatremia and hyponatremia

-Causes of hypernatremia: adrenal insufficiency, burns, cirrhosis, congestive heart failure, diaphoresis with more salt lost than water, diarrhea, diuretic therapy, excess hypotonic fluid administration, hyperglycemia, hypoaldosteronism, laxatives, nasogastric suction, psychogenic polydipsia, renal disease, SIADH. -Causes of hyponatremia: certain meds such as osmotic diuretics, sodium bicarbonate, and sodium chloride, cushing's syndrome, diabetes insipidus (lack of ADH), diarrhea, excess sodium administration, excessive adrenocortical secretion, hypercalcemia, impaired thirst, increased aldosterone.

difference between stimulation of cardiac and skeletal muscle

-cardiac muscle: calcium influx through voltage-gated calcium channels on the plasma membrane causes muscle contraction. Changes in serum calcium levels can cause hypotension, cardiac dysrhythmias, heart failure, and diminished responsiveness to cardiac drugs. -skeletal muscle: stimulated by motor nerves, an influx of sodium quickly depolarizes the skeletal muscle cell.

electrolyte imbalances

-generation of adenosine triphosphate (ATP), transcription and translation of DNA/RNA, neural transmission, and muscular contraction are all dependent on electrolyte balances. Alterations in sodium, potassium, and calcium ion levels have a major effect on neurotransmission and muscular contraction.

causes of hypokalemia and hyperkalemia

-hypokalemia: alkalosis, diuretic therapy, elevated glucocorticosteroids, excessive GI renal or skin losses, hyperaldosteronism, inadequate intake, laxative abuse, nasogastric suction, redistribution of potassium. -hyperkalemia: addison's disease, burns, digitalis toxicity, excessive administration of K+ sparing diuretics, extreme exercise, hemolysis of red blood cells, hypoaldosteronism, medications, metabolic acidosis, sodium depletion, renal failure.

Different types of edema

-peritoneal cavity edema: known as ascites -pleural cavity edema: known as pleural effusion -lower extremity edema: ankle edema

What are the two main functions of the body's body fluid (solvent + constituent?

1. Deliver nutrients and electrolytes to cells 2. Carry away waste products from cellular metabolism

Water is found in which three fluid compartments?

1. Intracellular (ICF) 2. Extracellular (ECF) 3. Interstitial Fluid (ISF) *2/3 of the body's water content is contained within the intracellular fluid. *1/3 is contained in the extracellular fluid.

extracellular fluid compartment

20% total body weight. Most is found within the intravascular compartment or blood vessels. The ECF contains electrolytes, oxygen, glucose, and other nutrients to be delivered to cells, as well as cellular waste products designated for excretion.

intracellular fluid

40% of total body weight. If water diffuses from the ICF, it causes cellular dehydration, conversely if water enters the cell, it causes cellular edema.

What are the body's solutes?

Protein such as albumin, electrolytes, and others.

clinical assessment of fluid losses and gains

a basic method is to assess the patients weight daily. It is important to take the measurement with the same scale, at the same time of day, every day. A weight change of 2 lbs or less is likely caused by fluid gain or loss. a 24 intake and output record of a patient is also a way to record/monitor fluid status. The amount of fluid intake necessary for an adult with normal heart and renal function is 1,500 mL/m2 of body surface per day. On average, this is approximately 2 liters of fluid per day. -Intake includes: all fluids, oral, IV, and tube feedings. (all measurements taken in mL) *1 ounce of fluid is equivalent to 30 mL -Output includes: urine, vomitus, wound or ostomy drainage, and insensible water losses through the lungs, sweat, and feces. Wound or ostomy drainage and vomitus must be estimated. Insensible water loss is usually 1000 mL/day but may be more if fever is present. *Water needs increase based on certain conditions. Water requirements increase by 100 to 150 mL per day for each degree Celsius of body temperature elevation. I&O record can indicate fluid retention, which is positive fluid balance, or fluid deficit, which is a negative fluid balance. Another fluid status involves patient vital signs. The patient who is dehydrated may have tachycardia and hypotension, particularly postural hypotension. To assess for postural hypotension, test blood pressure in lying down and standing up positions. Symptoms of low fluid volume deficit: dehydration, thirst, dry mucous membranes, poor skin turgor, hypotension, low urine output, and dark colored urine. Poor skin tugor is demonstrated through non-elasticity of the skin.

hypovolemia

a diminished level of circulating blood volume that increases the osmolarity of the blood. For example, in uncontrolled diabetes, glucose rises to high levels and acts as a solute in the blood. The high amount of solute in the blood raises osmotic pressure, which creates an imbalance in the capillary forces. If osmotic pressure rises to exceed hydrostatic pressure inside the capillary, then water from the ICF and ISF moves into the capillary and cells lose water. This causes cells to shrink, a process known as cellular dehydration. The fluid shift into the circulation delivers more water to the kidneys, which is then excreted as excess urine. Because of these fluid shifts, in uncontrolled diabetes, polyuria and thirst are key symptoms. *Cellular hydration can also occur because of hypernatremia (high sodium content of blood) which raises solute content. Same process as described above happens.

dehydration

a state of diminished water volume in the body. A deficit of intracellular fluid causes body cells to shrink. There is also a decreased amount of water in the extracellular fluid. Has many causes including reduced fluid intake and excessive fluid loss caused by illness, lack of sufficient ADH production or lack of renal stimulation by ADH can also lead to excessive fluid loss and dehydration, as can certain gastro disorders such as prolonged diarrhea.

oncotic pressure

also called colloidal osmotic pressure, is the type of osmotic pressure exerted specifically by albumin in the bloodstream. Oncotic pressure and osmotic pressure exert the same type of pulling force from ICF and ECF. Albumin attracts water and helps keep it inside the blood vessel. Albumin is the main colloidal protein in the bloodstream and is essential for maintaining the oncotic pressure in the vascular system. Normal serum albumin level is 3.1 to 4.3 g/dL

fluid volume excess

ascites crackles in lungs dyspnea caused by pulmonary fluid accumulation edema, either ankle or sacral weight gain (2 lb = 1 liter of fluid)

starling's law of capillary forces

explains the movement of fluid that occurs at every capillary bed in the body. There are two major opposing forces at every capillary membrane: 1. hydrostatic pressure 2. osmotic pressure (includes oncotic pressure) *hydrostatic pressure pushes water out ( of extracellular space) *osmotic pressure pulls water in ( to extracellular space)

sequestered fluids (third-spacing & effusion)

during illness, fluids can become sequestered in body cavities that are normally free of fluids, such as the pericardial sac, peritoneal cavity, and pleural space. When this happens it is referred to as third-spacing. The fluid that accumulates in these cavities is commonly called effusion. An effusion can be transudate or exudate.

calcium imbalances

calcium and phosphorus are the major mineral contents of the bone. Small amounts of these electrolytes which are regulated by vitamin D and parathyroid hormone are found in the circulation. The major function of vitamin D is to facilitate the absorption of calcium from the gastrointestinal tract into the bloodstream; once in the bloodstream, PTH controls calcium levels. When plasma calcium level is low PTH is stimulated when ; when the calcium level is high, PTH is inhibited. PTH acts on bone to mobilize calcium and raise blood levels. Calcitonin, a hormone produced by the thyroid, acts at the bone and kidneys to remove calcium from the circulation. Calcium is stored in bone, bound to plasma proteins, and bound with organic ions such as citrate. A small amount of calcium also remains free. This free, ionized calcium interacts in normal physiologic functions. The ionized form participates in cellular activities such as enzymatic reactions, neuron excitability, muscle contraction, release of hormones, neurotransmitters, and other chemical messengers; blood vessel contractility and automaticity and blood clotting. Calcium is found in both ECF and ICF. Because calcium is highly protein bound, interpretation of calcium levels is based on serum albumin levels. About half of the calcium in the body is bound to albumin. Hypoalbuminemia can cause the appearance of low calcium levels called pseudohypocalcemia, there is a normal level of body calcium with more in the ionized state than in the bound state because there is a diminished amount of albumin able to carry calcium. It is important to recognize that calcium and phosphate PO4 have an inverse relationship in the bloodstream. Both are bone derived ions when Ca++ rises in the bloodstream, PO4 diminishes in the bloodstream. When PO4 rises in the bloodstream, Ca++ diminishes in the bloodstream.

High plasma osmolarity (osmoreceptors, ADH, and thirst)

changes in plasma osmolarity are responsible for both the sensation of thirst and the release of ADH, also called arginine vasopressin. High plasma osmolarity stimulates osmoreceptors in the hypothalamus. This stimulates the hypothalamic thirst center of the brain, as well as promoting the release of ADH from the posterior pituitary. *osmoreceptors respond to both changes in the blood osmolarity and blood fluid volume. *ADH stimulates water reabsorption from the nephron tubule fluid at the collecting duct into the bloodstream. This raises the blood's water content and decreases the water in the tubule fluid, which eventually becomes concentrated urine. When there is enough water in the bloodstream, plasma osmolarity decreases, and ADH secretion is inhibited.

hypocalcemia

consists of a blood calcium level of less than 8.7 mg/dL in adults. It is most commonly caused by lack of sufficient Ca++ in the diet, vitamin D deficiency, renal disease or hypoparathyroidism. Acute hypocalcemia is manifested by neuromuscular excitability, which is demonstrated in individuals as a subjective experience of paresthesias (numbness and tingling) around the mouth, hands and feet. Chvostek's sign and Trousseau's sign are examples of neuromuscular irritability caused by chronically low calcium levels. Other signs may include muscle spasms of the face, hands and feet; laryngeal spasm, seizures, and death. Cardiovascular effects of hypocalcemia include hypotension, arrhythmias (particularly heart block and ventricular fibrillation) and failure to respond to cardioactive drugs. Chronic hypocalcemia causes bone pain and fragility, dry skin and hair, cataracts, depression and dementia. Because of the inverse relationship between calcium and phosphate in the blood, hypocalcemia will cause hyperphosphatemia. Treatment: requires calcium replacement. oral calcium supplements with vitamin D is need for calcium absorption from the intestine.

hypophsphatemia

consists of a blood level of phosphate lower than 2.5 mg/dL. There are three main causes of hypophosphatemia: decreased intestinal absorption of phosphorus, increased excretion of phosphorus by the kidneys and an intracellular shift of phosphate. Low phosphate cause red blood cell, white blood cell, and platelet dysfunction and disturbed musculoskeletal function. Lack of sufficient phosphate can cause tremors, paresthesia, hyporeflexia, anorexia, dysphagia, muscle weakness, joint stiffness, bone pain and osteomalacia. Treatment of hypophosphatemia is replacement therapy.

hypertonic solution

contains more particles and less water than blood and body fluids. When a hypertonic solution is infused into the bloodstream, solutes are added to the bloodstream and cause fluids to shift from ICF to ECF, causing body cells to shrink. A commonly used hypertonic IV solution is mannitol. It can be used to diminish cell swelling, particularly cerebral edema. Another hypertonic solution that is used less often is 3.0% NaCl.

phosphorus imbalance

essential component of bone, red blood cells, and ATP formation, acid-base balance and cellular building blocks. Phosphorus is found in bone and circulates in the blood as phosphate. Phosphates are incorporated into nucleic acid of DNA and RNA an the phospholipids of the cell membrane. The kidneys excrete phosphate and the parathyroid glands regulate the phosphate level in the blood. Phosphate has a reciprocal relationship with calcium in the blood, meaning that when calcium is low in the bloodstream, phosphate is high and vice versa.

fluid volume deficit signs and symptoms

dark urine with high specific gravity depressed fontanelles (infant) dry mucous membranes low urine output orthostatic hypotension poor skin tugor thirst weight loss

interstitial fluid compartment

filtrate of the blood, is located between the cells and between the cells and capillaries. It contains water and electrolytes, mainly sodium. ISF lacks proteins because they are too large to diffuse out of the blood vessels into the interstitial spaces. However, during inflammation, the capillary membranes become extrapermeable; the pores enlarge, allowing proteins such as white blood cells out to the tissues.

hypotonic

has fewer particles and more water than blood and body fluids. When a hypotonic solution is infused, water is added to the bloodstream and causes a fluid shift from ECF to ICF to deliver water to the body, as in dehydration treatment. A standard hypotonic solution is .45% NaCl and is also referred to as half normal saline.

isotonic solution

has the same tonicity as blood; when infused as an IV solution, it does not cause fluid shifts or alter body cell size. It has a concentration of particles and fluid that is similar to the blood and body fluids. A standard isotonic IV solution is .9% NaCL, also called normal saline. Used as: a bloodstream volume expander, and to keep an open connection to the IV route for medication administration or blood transfusion.

Starling's law of capillary forces and left sided heart failure

high hydrostatic pressure develops in the pulmonary bloodstream. The high hydrostatic pressure forces fluid out of pulmonary blood vessels and into the alveolar spaces and the interstitial tissue.

dilutional hyponatremia

high water volume in the blood decreases the concentration of sodium.

hypoalbuminemia

low albumin levels in the blood; causing hydrostatic pressure to raise above oncotic pressure. High hydrostatic pressure pushes fluid out of the capillaries into the ISF and ICF. Edema occurs. Hypoalbuminemia occurs in severe protein starvation, often edema swelling is observed in the swollen abdomen of a patient. In persons who are starving this disorder is called kwashiorkor.

hyperphosphatemia

hyperphosphatemia is PO4 level of 4.5 mg/dL or greater in the blood. The most common cause is kidney failure, where the kidneys are unable to excrete excessive phosphorus. Hyperphosphatemia is usually accompanied by hypocalcemia, and many of its symptoms are related to low calcium levels. Treatment is directed at correcting the cause of the disorder. Calcium based phosphate binders, such as sevelamer and lanthanum carbonate inhibit GI absorption of phosphate. Dialysis can also reduce hyperphosphatemia.

RAAS

hypotension, hypovolemia, dehydration, and low cardiac output cause low circulation throughout the body. Reduced circulation causes low renal perfusion, which stimulates renin secretion by the kidney's juxtaglomerular apparatus. Renin --> converts angiotensinogen to angiotensin 1 -->angiotensin-converting enzyme (ACE) changes angiotensin I into angiotensin II--> Angiotensin II binds to receptors in the adrenal cortex, stimulating the synthesis and secretion of aldosterone.

hyperkalemia

is a blood K+ level greater than 5.2 mEq/dL. Renal failure is a major cause of hyperkalemia because the kidneys lose the ability to excrete K+. Any decrease in renal perfusion, such as decreased cardiac output will diminish the kidney's ability to excrete K+, thus increasing the amount of potassium in the body. Hyperkalemia can also occur in major muscle trauma such as a crushing injury because potassium is released rapidly from muscle cells. Clinical presentation: early symptoms include numbness or tingling of the extremities, muscle cramping, diarrhea, apathy and mental confusion. The ECG will show wide QRS complexes and tall, peaked T waves, as the potassium level rises, the ECG will show bradycardia, irregular pulse rate, and ultimately, cardiac arrest. Treatment: if hyperkalemia is severe (greater than 7.0 mEq/L) rapid treatment is needed to move K+ from ECF to ICF. Continuous ECG monitoring is necessary. An infusion of 50% dextrose, 10 units of regular insulin, and 75 mEq of sodium bicarbonate can be administered. If K+ levels continue to be elevated and the patient has a normal renal function, a diuretic such as furosemide can be administered. Calcium chloride or calcium gluconate can also administered. Albuterol and diuretics can be used to reduce high blood potassium. Another option for treatment is to give sodium polystyrene sulfonate which acts at the bowel to capture potassium and excrete it via feces.

hypernatremia

is a sodium level greater than 145 mEq/L. It can occur with an excess of sodium or decrease in body water. Most commonly, it is caused by water loss, although it can be caused by salt loading. With kidney dysfunction, other factors may be involved, such as the inability of the renal tubule to react to ADH, causing the kidneys to not reabsorb water. If the kidney's glomerular filtration rate is decreased, sodium and water reabsorption into the bloodstream is low, which stimulates the adrenal gland's secretion of aldosterone. Aldosterone causes reabsorption of sodium and water from the nephron tubule fluid into the circulation, raising the sodium level. In severe hypernatremia, water is lost from the brain cells. The brain cells compensate by moving water from the cerebrospinal fluid into the brain cells. Clinicians will use intravenous hypotonic solutions that are high in water content. During treatment, if the water is infused too rapidly, it will move into the brain cells which are hypertonic compared to the hypotonic intravenous fluid. This can cause cerebral edema, leading to seizures, coma, and death. In cases of severe hypernatremia, clinicians need to precisely calculate the free water deficit and replace water intravenously slowly over several hours to prevent cerebral edema from occurring.

hyponatremia

is a sodium serum level of less than 135 mEq/L. When dehydration has occurred, the body has lost sodium and fluid together, it is known as hypovolemic hyponatremia. This primarily happens due to losses from the kidney or GI tract. The causes of renal hypovolemic hyponatremia inlcude adrenal insufficiency, osmotic diuresis, diuretic use, and salt-losing nephritis. The causes of nonrenal hypovolemic hyponatremia include diarrhea, vomiting, excessive sweating, cystic fibrosis, gastric lavage, fistulas, burns and wounds. The symptoms of hypovolemia hyponatremia are thirst, dry mouth, orthostatic hypotension, tachycardia, azotemia (high blood urea nitrogen concentration), and oliguria. Hyponatremia can occur in the presence of hypervolemia, or excess of water. Symptoms include headache, lethargy, apathy, confusion, nausea, vomiting, diarrhea, muscle cramps, and muscle spasms. Hyponatremia most commonly occurs when water excretion is impaired and sodium is diluted within a large volume of water in the bloodstream. When there is an acute drop in the serum osmolality, neuronal cell swelling occurs because of the water shift from the extracellular space to the intracellular space. Swelling of the brain cell occurs in two consequences: 1. it inhibits ADH secretion from neurons in the hypothalamus, and hypothalamic thirst center, which leads to excess water elimination as dilute urine. 2. There is an immediate cellular adaption with loss of electrolytes and over the next few days there is a more gradual loss of organic intracellular solutes. In cases of hyponatremia resulting from inappropriate ADH, treatment includes restriction of water intake and investigating the source of ADH. If the etiology is fluid overload, diuretics will be used to remove excess water.

action potential

is an impulse generated along neuronal axons, and is created by changes in sodium and potassium ions in ICF and ECF. During an action potential, sodium channels open in the plasma membrane, allowing the entry of sodium ions into the cell. This is followed by the opening of potassium channels that allow the exit of potassium ions out of the cell. The influx of sodium ions in the cell initiates depolarization, where the potential in the cell is higher than the cell's resting potential. The sodium channels close at the peak of the action potential, whereas potassium continues to leave the cell. The efflux of potassium ions decreases the membrane potential in the repolarization phase. When there is an imbalance of sodium and potassium in the body, neural transmission in the body is widely disrupted. There is body-wide muscular weakness and changes in sensation such as paresthesia (numbness and tingling). The muscles of the GI tract dysfunction, causing nausea, constipation, and abdominal distention. Confusion and disorientation are common symptoms of central nervous system dysfunction. Cardiac dysfunction is particularly apparent with potassium level disruption. ECG changes, rhythm disturbances, and postural hypotension occur.

hypercalcemia

is calcium level greater than 10 mg/dL. Hypercalcemia occurs when he amount of calcium entering the ECF exceeds calcium exertion by the kidneys. The two most common causes are hyperparathyroidism and cancer. Risk factors/etiology: In hyperparathyroidism, PTH is overproduced, and the hormone pulls excessive amounts of calcium out of the bones and into the bloodstream. Cancer-related hypercalcemia is caused by malignant cells invading the bone, causing bone destruction. Cancer also releases a parathyroid-like hormone, causing an increase in serum calcium levels. Other causes of hypercalcemia are prolonged immobility that causes calcium to leech out of bone; excess calcium or vitamin D intake, toxic levels of drugs. Signs and symptoms: decreased neuromuscular excitability, muscle flaccidity, proximal muscle weakness of the lower extremities, bone tenderness, and decreased neuromuscular activity of the bowel causing constipation. High calcium concentrations in the urine increased susceptibility to renal calculi. The heart responds to hypercalcemia with increased contractility and ventricle arrhythmias. Other non-specific effects include: dulled consciousness, depression, anorexia, nausea, vomiting, and ulcers. Hyperreflexia and tongue fasciculations may also occur. Hypercalcemia causes hypophosphatemia. Treatment: enhancement of urinary excretion of calcium and inhibition of bone breakdown. Increased fluids and loop diuretics enhance calcium secretion. Bisphosphonates such as alendronate and calcitonin are used to inhibit bone breakdown. Dialysis can be used in patients with kidney or heart failure.

hypomagnesium

is magnesium blood level of 1.5 mEq/L. It occurs when magnesium ions are released from bone in exchange for increased uptake of calcium. It usually occurs in conjunction with hypocalcemia and hypokalemia. Causes of hypomagnesemia are prolonged diarrhea, laxative abuse, increased renal excretion of magnesium, sepsis, burns, and serious wounds requiring debridement. Signs and symptoms are similar to those of low potassium and calcium levels. Chvostek's sign and Trousseau's sign. Treatment involves replacement therapy, commonly with magnesium sulfate.

osmolarity

is the number of osmoles per liter of solution; it depends on the number of particles suspended in the solution. In the body the major solutes are: albumin, sodium, potassium, phosphate, magnesium, calcium, bicarbonate, and glucose. The major protein in the bloodstream is albumin, which is the solute in the ECF that exerts the most osmotic pressure. Sodium is the main determinant of osmolarity, it is a positive ion, also called a cation, it is found mostly in the extracellular fluid and assists in the maintenance of fluid balance and osmotic pressure. Potassium is the main intracellular cation, it assists in the maintenance of neuromuscular excitability and acid base balance. *Sodium is extracellular, potassium is intracellular ion. Phosphate is an intracellular negative ion (anion). Magnesium plays an important role in enzymatic systems within the body. Calcium plays an important role in neuromuscular irritability, blood clotting and bone structure. Bicarbonate is responsible for acid- base balance.

hypermagnesemia

magnesium blood level of greater than 2.5 mEq/L. Magnesium is often used to treat cardiac disorders and pregnancy related eclampsia and levels must be carefully monitored. The most common cause of hypermagnesemia is renal dysfunction. High magnesium inhibits acetylcholine release and can cause diminished neuromuscular function, demonstrated by hyporeflexia and muscle weakness. Magnesium also blocks calcium channels and can cause cardio effects such as hypotension and arrhythmias. Severely high magnesium (greater than 10 mEq/L) can cause cardiac arrest. Sedation, confusion, coma and respiratory paralysis can occur. To counteract hypermagnesemia, IV calcium or dialysis can be used.

fluid homeostasis

maintained by rennin-angiotensin-aldosterone-system (RAAS), osmoreceptors, thirst sensation, antidiuretic hormone (ADH), natriuretic peptides.

osmolality

measurement of the concentration of solutes per kg of solvent. It is based on 1 mole of a substance dissolved in 1 kg of water. Can be used in a clinical setting to evaluate the body's hydration status. Normal plasma osmolality is 282 to 295 milliosmoles per kg of water. Low osmolality indicates a lesser amount of solutes in a solution.

aldosterone

mineralocorticoid that increases sodium and water reabsorption into the bloodstream at the distal tubule of the nephrons.

natriuretic peptides

natriuresis is the excretion of a large amount of both sodium and water by the kidneys in response to excess ECF volume. It is a process of natural diuresis initiated by the body. Three major peptides are: 1. atrial natriuretic peptide (ANP) 2. B-type natriuretic peptide (BNP) 3. C-type natriuretic peptide (CNP)

dependent edema

observed in patients with poor venous return and allows blood to collect in the lower extremities.

active transport

occurs when a substance requires energy to pass through a membrane against a concentration gradient. Sodium and potassium require active transport using the sodium-potassium pump, which is within the plasma membrane to retain potassium as the major intracellular ion and sodium as the major extracellular ion. Sodium is a solute that draws water with it.

fluid volume overload

occurs when the bloodstream has an excessive amount of water. One of the most common causes is heart failure. In heart failure, RAAS is constantly cycling, which brings an excessive amount of water into the bloodstream. Blood volume increases, which increases the hydrostatic pressure. High hydrostatic pressure overwhelms osmotic pressure at every capillary bed, leading to edema in various places in the body. Fluid volume overload can also be seen in cancers that secrete ADH, causing the disorder known as "inappropriate ADH (SIADH". Other causes of ADH related fluid volume overload include cirrhosis of the liver, polycystic kidney disease and some forms of hypertension.

edema

occurs when there is excess fluid in the ISF and ICF compartments. It can occur because of elevated hydrostatic pressure created by excess water in the bloodstream or diminished osmotic force created by a low amount of solutes in the bloodstream. Can also occur because of inflammation, which causes increased capillary permeability'; the capillary pores enlarge to allow fluid and cells out of the bloodstream to reach the site of injury. Low amount of solute in the bloodstream such as albumin (hypoalbuinemia) causes an imbalance in capillary forces by creating a state of low oncotic pressure. Low oncotic pressure causes edema. *For homeostasis to occur oncotic pressure must equal hydrostatic pressure according to Starling's Law.

physiological response to dehydration

osmoreceptors respond to the blood's high osmotic content and stimulate the thirst center in the hypothalamus. Thirst occurs, which stimulates the person to drink to replace fluid lost from cells. The blood vessel baroreceptors sense a decreased blood pressure in dehydration. This stimulates the sympathetic nervous system, which vasoconstricts arterial vessels and increases the heart rate to compensate. Additionally, osmoreceptors stimulate ADH secretion from the posterior pituitary gland. Teh ADH works at the nephron to increase water reabsorption into the bloodstream. Simultaneously, because the blood volume is low, circulation to the kidneys is deceased. Decreased kidney perfusion provokes renin secretion, which activates the RAAS, resulting in increased sodium and water in the bloodstream, raising blood volume. Additionally, angiotensin II acts as a potent vasoconstrictor, which raises blood pressure. These compensatory mechanisms restore fluid balance and maintain blood pressure in states of dehydration.

facilitated transport

passing of certain molecules through the plasma membrane with assistance from carrier proteins. Glucose undergoes facilitated transport into the cell by the carrier protein insulin.

what is the main intracellular electrolyte?

potassium

potassium imbalances

potassium is the main electrolyte of the ICF. adults require 40 to 60 mEq/L/day. Muscle contains the bulk of the body's potassium and alterations in potassium levels have neuromuscular effects. A decrease in serum potassium causes decreased neuromuscular excitability, resulting in muscle weakness. Fluid shifts between the ICF and ECF can cause temporary changes in plasma potassium levels. Additionally, potassium levels should be assessed in relation to acid-base balance. Potassium will move from the ICF to the ECF based on changes in the hydrogen ion concentration in the bloodstream. When hydrogen levels are high in the bloodstream, excretion of hydrogen takes precedence over potassium. In acidosis, aldosterone stimulates excretion of H+ ions from the bloodstream instead of K+ ions, this makes it appear that there is excess K+ in the blood this is not true hyperkalemia. When acidosis is treated, K+ will move into the ICF compartment, which will demonstrate that K+ is actually low in the abdomen. In diabetic ketoacidosis, when treatment is instituted using insulin K+ moves into the intracellular compartment. This movement of K+ into the cells leaves an actual low K+ level in the blood, thereby requiring administration of supplemental potassium.

angiotensin II

powerful vasoconstrictor

osmotic pressure

pressure exerted by the solutes in a solution. In the bloodstream, osmotic pressure is exerted mainly by sodium ions and plasma proteins. Osmotic pressure is a force that pulls water into the bloodstream from the ICF and ISF and opposes hydrostatic pressure at all capillary membranes. Greater number of particles in a solution=greater osmotic pressure. High osmotic pressure=fluid movement from ICF/ISF into the bloodstream. Low osmotic pressure=fluid movement out of the bloodstream and into the interstitial/intracellular spaces.

diffusion

process by which molecules passively spread from areas of high concentration to areas of low concentration. Water and electrolytes diffuse from high concentration to lower concentration until an equilibrium is reached. *High concentration to low concentration*

hydrostatic pressure

pushing force exerted by water in the bloodstream. pushes water through the capillary membrane pores into the ISF and ICF compartments.

hypokalemia

refers to plasma concentration of potassium below 3.5 mEq/L. Diuretic therapy is the most common cause of hypokalemia, it is present in 20 to 50% of patients on non-potassium sparing diuretics. African Americans and females are more susceptible. Risk Factors: Inadequate intake, patients who are nothing by mouths status, alcoholics, patients who have undergone bariatric surgery, and those who suffer from eating disorders are at greatest risk. A daily potassium intake of at least 40-50 mEq is required of optimal function. Renal loses of potassium are increased by stress, trauma, metabolic alkalosis, and increased levels of aldosterone. Skin and GI losses of K+ can become excessive in burns, vomiting, nasogastric suctioning, and diarrhea. Signs and symptoms: associated with hypokalemia include anorexia, nausea, vomiting, sluggish bowel, cardiac arrhythmias, postural hypotension, muscle fatigue, and weakness. Leg cramps are particularly common. Also respiratory muscles can be weakened in severe hypokalemia. On ECG there is a prolonged PR interval, flattened T wave and prominent U wave. Clinical causes: large amounts of IV dextrose administered to patients may cause the pancreas to excrete excessive amounts of insulin which can cause hypokalemia. Administering adrenergic agents such as epinephrine and albuterol can also cause a drop in blood potassium levels. Diuretics can cause a loss of potassium from the bloodstream. Digitalis toxicity often occurs when the patient is in a state of hypokalemia. Digitalis is a drug used when a patient is in heart failure. Heart failure often causes hypokalemia because of the cycling of RAAS when the heart is weakened. Treatment: replacement of potassium with foods such as orange juice, bananas, dried fruits, meats and oral or parenteral K+. Potassium can also be prescribed intravenously, commonly 20 mEq of potassium chloride per liter of IV solution is administered to NPO patients not to exceed a total of 60 mEq/day.

Tonicity

refers to the concentration of solutes in solution compared with the bloodstream. The term is also used to describe the various intravenous solutions used in the clinical setting. There are three types of IV solutions: 1. Isotonic solution 2. Hypotonic solution 3. Hypertonic solution

osmosis

tendency of molecules of a solvent to pass through a semipermeable membrane from a less concentrated solution to a more concentrated one, equalizing the concentrations on each side of the membrane. Electrolytes and water move through the cell's semipermeable plasma membrane, but large proteins such as albumin cannot pass through the membrane. *Low concentrated to high concentration*

what is the main extracellular electrolyte?

sodium

sodium imbalances

sodium is the main electrolyte in the ECF and is the primary determinant of the ECF's osmolarity and volume. It must constantly be pumped out of the cell into the bloodstream. Sodium controls the distribution of water, helps maintain normal fluid balance, and contributes to osmotic pressure. Sodium is also important to maintain the electrical gradient of neural membranes. However, because it is an extracellular ion, alterations of fluid balance can adversely affect its levels, which is why serum sodium levels need to be interpreted based on hydration status.

Edema as a result of sodium

sodium retention from illness or poor diet can contribute to edema. Excess sodium in the ECF pulls fluid from the ICF into the ECF, causing cellular dehydration. Dehydration causes thirst. When a patient ingest more water and experiences the movement of fluid from the ICF to the ECF, an excess of water in the bloodstream occurs, which increases hydrostatic pressure. This is seen whenever there is an increased activation of RAAS. With increased cycling of the RAAS, enhanced sodium and water reabsorption into the bloodstream occurs, raising blood volume and blood pressure.

What is the body's solvent?

water.

exeduate

which contains materials such as blood, lymph, proteins, pathogens and inflammatory cells.

transudate

which is a serous filtrate of blood