Renal Pharmacology & The Urinary System, Pt. 5 Flashcards
How much of the body weight is made up of water? What are the 2 major compartments?
TBW = 60%
- ECF (20%) - plasma (5%), IF (15%), TCF (1% - aqueous humor, pleural/abdominal fluid)
- ICF (40%)
What membranes separate body fluid compartments?
semipermeable capillary membranes (plasma/IF) and cell membranes (IF/ICF)
(increased osmotic pressure attracts water to move between compartments)
What is responsible for maintaining fluid compartments? How? What are the 2 major responses?
osmoreceptors in the hypothalamus detect significant changes in ECF composition or volume and trigger endocrine response of the pituitary to secrete ADH, aldosterone, ANGII, or ANP
- urinary excretion of water
- dietary absorption of water
What are the 5 major functions of electrolytes?
- maintain cell metabolism
- contribute to body structure
- facilitate the osmotic movement of water between body compartments (sodium)
- maintain hydrogen ion concentration (acid-base balance) required for normal cellular function (bicarbonate, chloride, phosphate)
- production and maintenance of membrane potentials and action potentials (hydrogen, potassium, sodium)
What are the major cations and anions found in the extracellular and intracellular fluids?
EXTRACELLULAR - Na+, Ca++, Cl-, HCO3
INTRACELLULAR - K+, Mg++, P, protein
(both compartments are electroneutral)
How is plasma osmolality calculated? What is the normal value?
plasma osmolality = 2[Na] + (glucose/18) + (BUN/2.8)
~290-300 mOsm/kg
(approximation, for accuracy an osmometer is used in the lab)
What are the 4 most common causes of hypernatremia?
- excessive loss of water with inadequate replacement, causing the ECF to become concentrated
- DISEASES: diabetes insipidus (PU), fever, diarrhea, vomiting
- IATROGENIC: administration of hypertonic saline or sodium bicarbonate solution
- ACCIDENTAL: heat stroke, salt poisoning (sea water ingestion)
What is hypervolemic hypernatremia? What are 4 causes? How is it treated?
impermeable solute gains with fluid overload and hypertonic urine
- excessive salt intake (sea water, salt lick)
- hypertonic fluid administration
- hyperaldosteronism
- hyperadrenocorticism
diuretics and 5% dextrose solution
What is isovolemic hypernatremia? What are 4 causes? How is it treated?
pure water loss with absent to minimal dehydration and normal to hypotonic urine
- diabetes insipidus
- fever
- stroke
- inadequate water intake
5% dextrose solution, correct water deficit, desmopressin for diabetes insipidus centralis
What is hypovolemic hypernatremia? What are the extrarenal and renal causes? How is it treated?
hypotonic fluid loss with moderate to severe dehydration
- EXTRARENAL = concentrated urine; GI disease (vomiting, diarrhea), third-space loss
- RENAL = dilute urine; osmotic diuresis (DM, mannitol), diuretics, post-obstructive diuresis, renal insufficiency
balanced electrolyte solution or normal saline, with hypotonic saline as required to reduce serum sodium
What are the 3 common causes of hyponatremia?
excess water in the ECF caused by…
- hypovolemia: GI loss, hypoadrenocorticism
- hypervolemia: CHF, nephrotic syndrome, heaptic disease
- iatrogenic: administration of hypotonic fluids or mannitol infusions
What is hyperosmolar hyponatremia? What are 2 causes? How is it treated?
initial normovolemia with a plasma osmolality > 310 mOsm/kg
- hyperglycemia
- mannitol infusion
manage underlying disease causing elevates glucose (DM), discontinue infusion
What is normosmolar hyponatremia? What are 2 causes? How is it treated?
normovolemia or pseudohyponatremia with a plasma osmolality = 290-310 mOsm/kg
- hyperlipidemia
- severe hyperproteinemia
(artefactual displacement of ions)
manage underlying case of elevated lipids or proteins
What is hypoosmolar hyponatremia? What are the hypervolemic, normovolemic, and hypovolemic causes?
varied volume status with a plasma osmolality < 290 mOsm/kg
- HYPERVOLEMIC: hepatic disease, CHF, nephrotic syndrome, renal disease
- NORMOVOLEMIC: inappropriate ADH secretion, antidiuretic drugs, hypothyroidism, hypotonic fluids, psychogenic PD
- HYPOVOLEMIC: GI loss, third space loss, hypoadrenocorticism, diuretics
How are asymptomatic and symptomatic hypoosmolar hyponatremia treated?
ASYMPTOMATIC: water restriction and serum sodium monitoring
SYMPTOMATIC: conventional crystalloids (LRS, saline) for slow correction
(manage underlying disease)
What organs are responsible for adjusting pH?
LUNGS - respirate CO2
KIDNEYS - secrete H+ and HCO3-