Disorders of Fluid, Electrolyte, and Acid-Base Balance Flashcards
Define electrolytes
Substances that dissolve in a solution to form a charged particle (an ion)
What is the #1 rule regarding the exchange of anions and cations?
Cations (+) and anions (-) are attracted to each other. A cation can be exchanged for a different cation (H+ for K+) and an anion can be exchanged for a different anion (Cl- for HCO3-)
what is mEqL?
milliequivalents per liter (one of the measurements for electrolytes)
Why is the total concentration gradient between the intracellular and extracellular fluid equal?
Osmosis
Define osmolarity
osmolar concentration in 1 L of solution
Define tonicity
Tension on cell due to water movement across the membrane
Isotonic, hypotonic, hypertonic
What happens to cells placed in a hypotonic solution?
They swell (solution has a lower osmolarity than the ICF of the cell and water moves towards the area with more particles)
What happens to cells placed in a hypertonic solution?
They shrivel (the hypertonic solution has a higher osmolality than the ICF, causing water to move out of the cell to dilute the particles outside the cell)
What are the compartments of the ECF?
- Plasma compartment
- Interstitial compartment
- Transcellular compartment (CSF and fluids in body cavities)
What is third space?
Large amounts of fluid enter the transcellular compartment (this fluid is not available for exchange with the other ECF compartments readily)
Capillary filtration pressure
Pushes water out of the capillary and into interstitial space
Capillary colloidal osmotic pressure
Pulls water back into the capillary
Interstitial hydrostatic pressure
Opposes water movement out of the capillary
Interstitial colloidal osmotic pressure
Pulls water out of the capillary and into the interstitial space
Physiologic mechanisms that lead to edema
(1) increase the capillary filtration pressure
(2) decrease the capillary colloidal osmotic pressure
(3) increase capillary permeability
(4) produce obstruction to lymph flow
examples of edema caused by Increased Capillary pressure
Increased vascular volume (e.g., heart failure, kidney disease)
Venous obstruction (e.g., thrombophlebitis)
Liver disease with portal vein obstruction
Acute pulmonary edema
Examples of edema due to Decreased Colloidal Osmotic pressure
Increased loss of plasma proteins (e.g., protein- losing kidney diseases, extensive burns)
Decreased production of plasma proteins (liver disease, malnutrition)
Causes of edema due to Increased Capillary permeability
Inflammation Allergic reactions (e.g., hives, angioneurotic edema)
Malignancy (e.g., ascites, pleural effusion)
Tissue injury and burns
Causes of edema due to Obstruction of Lymphatic Flow
Malignant obstruction of lymphatic structures
Surgical removal of lymph nodes
Pitting edema
- accumulation of interstitial fluid exceeds the absorptive capacity of tissue gel.
- tissue water becomes mobile and can be moved with pressure by a finger.
Nonpitting edema
- swollen area becomes firm and discolored
- occurs when plasma proteins accumulate in tissue spaces and coagulate.
- most commonly seen in areas of localized infection or trauma.
Assessment of edema
- daily weight (1 L of water weighs 2.2 pounds)
- visual assessment
- measurement of the affected part
- application of finger pressure to assess for pitting edema evaluated on a scale of +1 (minimal) to +4 (severe)
Treatment for edema
- if swelling involves vital structure: correcting or controlling the cause and preventing tissue injury.
- lower extremities: elevating the feet.
- Diuretic therapy to treat edema associated with an increase in ECF volume.
- Serum albumin levels can be measured, and albumin administered intravenously to raise the plasma colloidal osmotic pressure when edema is caused by hypoalbuminemia.
- Elastic support stockings increase resistance to outward movement of fluid from the capillary into the tissue spaces. prescribed for patients with venous or lymphatic obstruction
- Moderate to severe lymphedema: light-pressure massage designed to increase lymph flow by encouraging opening and closing of lymph vessel valves; compression garments or pneumatic compression pumps; range-of-motion exercises; and skin care to prevent infection
Ascites
accumulation of fluid in peritoneal cavity
Effusion
Movement of fluid into serous cavities
Hydrothorax
fluid in pleural cavity
Where is edema life threatening?
brain
larynx
lungs
What is the main determinant of water and sodium balance in the body?
effective circulating blood volume
monitored by stretch recepotors in vascular system: causes thirst and stimulates posterior pituitary to release ADH
Sodium concentration in ECF
135-145 mEq/L (mmol/L)
Ideal sodium intake per day
500 mg
Where do most sodium losses occur?
Kidneys
How does the sympathetic NS and renin-angiotensin-aldosterone system contribute sodium balance?
- sympathetic nervous system: adjusts glomerular filtration rate in response to changes in blood volume. Also regulates renal reabsorption of sodium and renin release.
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renin-angiotensin-aldosterone system:
- Angiotensin II acts on renal tubules to increase sodium reabsorption
- constricts renal blood vessels= decreases glomerular filtration rate and slows renal blood flow so less sodium is filtered and more is reabsorbed.
- Angiotensin II regulates aldosterone from adrenal cortex. Aldosterone increases sodium reabsorption by the kidneys and increases potassium elimination (gotta trade one for the other due to positive charges)
- Angiotensin II acts on renal tubules to increase sodium reabsorption
How is thirst controlled?
hypothalamus: osmoreceptors in thirst center in hypothalamus respond to changes in ECF osmolality
Stimuli:
- cellular dehydration caused by increase in ECF osmolality
- decrease in effective circulating volume
- production of angiotensin II by renin-angiotensin mechanism in the kidney increases in response to low blood pressure (backup thirst mechanism)
Hypodipsia
Inability to detect thirst due to head trauma/disease affecting the hypothalamus
Polydipsia
Excessive thirst
mechanism of action of ADH
- exerts effects through vasopressin receptors in collecting tubules of kidney.
- aquaporins are inserted into the tubular membrane.
- increased water permeability allows water from the urine filtrate to be reabsorbed into the blood, making the urine more concentrated
Does nicotine increase or decrease ADH?
Alcohol?
Nicotine increases ADH
alcohol decreases ADH
diabetes insipidus
- caused by deficiency of adh or decreased renal response to adh
- inability to concentrate urine, so large amounts of water leave through the kidneys = a lot of pee
- strong sensation of thirst, polyuria, bedwetting, drink 2-20 L of water per day
- central (neurogenic: autoimmune or vascular disease affects hypothalamus) or nephrogenic (defects in vasopressin receptor synthesis)
Syndrome of Inappopriate Antidiuretic Hormone
failure of negative feedback system that regulates release and inhibition of ADH
ADH secretion continues even when serum osmolality is decreased, causing water retention and dilutional hyponatremia.
caused by medications and many diseases including tumors, HIV, TB, head injury, and other infections
