intro to renal grassl Flashcards
osmolarity and osmolality
- osmolarity is volume of solvent (water) containning solutes so milliosmoles per liter
- osmolality is units of weight of solvent (water) and solutes in the solvent (milliosmoles per kg)
regulatory functions of kidney
-maintains extracellular fluid volume
-maintains extracellular fluid osmolarity which takes into consideration the combines solute concentrations inside and outside the cell
-maintains extracellular flui composotion-Na, K, H, HCO3
clears metabolic end products, toxins, and drugs in plasma
-has endocrine functions- erythropoitin for regulating number of rbc and O2 carrying blood capacity, active vitamin D bc kidney has 1 alpha hydroxylase, and renin
-supports finctions of cardiovascular system bc it maintains blood volume and osmolarity for BP and blood flow
body fluid compartments
in a 70 kg patient:
- total body water is 60% aka 42 L
- intracellular fluid is 40% of weight, extracellular fluid is 20% of weight. so 28 L intracellularly and 14 L extracellulrly. This is 40% and 20% of the total weight, corresponding to 66 and 33 percent of the water weight
- of the 14 L and 20% ECF, 25% is intravascular and 75% is extravascular in lymph and interstitial fluid
- of the 5L 25% ECF in the intravascular compartment, 3L is plasma, 2L is RBC, WBC, and platelets
- body fluid dereases as we agem we dry out. neonates are 75% water and aged adults are 50% water. normal person is 60% water.
- ECF also contracts as we age from being 50% TBW in babies (33% in adults).
- TBW is inversely related to fat. so if you have alot of fat, you have less total body water. at puberty women accumulate fat and their TBW goes down.
- solute composition bw ICF and ECF is different, but the osmolarity is the same at 300mosm.
kidneys maintain whole body fluid balance just from the monitioring of plasma
- kidneys maintain plasma volume and osmolarity which then ends up mainitaing total body water and osmolarity due to water and solute exchange between the ECF and ICF compartments.
- so ECF plasma goes to kidneys, and gets acted on. some goes to urine and rest goes back into circulation and ICF acts to compensate for the change.
kidneys are ONLY effector organ which REGULATE salt and water excretion
- TBW is unregulated and lost by sweat, feces, and skin and lung loss.
- skin and lung onlyloses H2O, not salt. Sweat and feces lose water and dalt
- kidneys compensate for whats lost by skin, sweat, and feces
- also compensate for the differences in comsumption of solutes and water on the ECF volume and osmolarity by either increaing or decresing excretion in urine
fluid and volume distribution bw plasma and interstitial fluid
-fluid distribution bw plasma and ISF is driven by hydrostaic and osmotic pressure differences across the capillary wall. depends on starling forces:
-Pc (35) capillary hydrostatic pressure, Pi (1) interstitial hydrostatic pressure
-πc (25) capillary osmotic pressure, πi (2) interstitial osmotic pressure
-at arteriolar end, hydrostatic osmpitc ressure Pc is very high so there is net filreation through the capillary wall. protein from the capillary osmotic pressure cant get through the all, so on the venous end, there is a build up of protein and less hydrostatic pressure, so on venous end there is net reabsorption of fluid across the capillary wall.
-oncotic pressure acts to resisit hydrostaic, is for resabsorption.
-the hydrostayic pressure gradient is greater than osmotic.
-Lp= hydraulic conductivity coefficient. relates magnitude of fluid volume transfer across capillary wall pur unit hdrstatic pressure difference or oncitic pressure difference
Lp= [(Pc-Pi)-(πc-πi)]
-hydrostatic pressure pushes fluid out but osmotic pressure pulls fluid in
-proteins are negatively charged so there is a slightly higer cation conc in plasma and a slightly higher anion conc in ISF. this cation anion conc is in a state of electro chemical equilibrium called gibbs donnan equilibrium
EDEMA
- excess accumulation of fluid in interstitial space bc of renal, hepatic, or endcrine dysfunction
- a localized or generalized imbablance of hydrostatic and osmotic pressure across a capillary wall which causes a fluid shift from intra to extrvascular space
before was capillary vs outsde capillary, now intracellular vs extracellular fluid
fluid and solute distribution
- movememnt of water bw ICF and ECF is driven ONLY by osmotic pressure differences across the membrane. so there is no hydrostatic driving force for fluid. water moves passively to follow the solute.
- water moves down its conc gradient, from side of lower tonicity to side of higher tonicity. moves through lipid biliayer through aquaporin channels.
examples of pertubrations to body fluid distribution:
isoosmotic fluid expansion. IV isosmotic fluid gain to ECF
- you add isosmotic fluid to ECF, so you only increase the volume of the ECF. the osmolarity stays the same since it was isosmotic. the volume of the ICF stays the same too since water has no conc gradient to follow. so ECF volume increases and osmolarty of everything stays the same.
- you get dilution of plasma proteins and decreased hematocrit
isosmotic fluid contraction. dairrhea
- you decrease ECF volume. osmolarity stays the same though so no change in ICF volume or osmolarity. ECF volume goes down though.
- concentration of plasma proteins and hematocrit increase
hyperosmotic volume contraction- loss of water in excess of solute from the ECF
sweating alot or water deprivation.
- youre taking away ECF salt and water so ICF volume decreases.
- decrease ECF volume and increasing ECF osmolarity. water will go from ICF to ECF. you end up decreasing ICF volume and increasing its osmolarity.
hyperosmotic volume expansion-high NaCl intake w/o fluid
retaining salt
-ECF osmolarity inicreases so ICF volume moves to ECF so that you can increase ICF osmolarity and decrease ECF osmolarity. the volume of ECF increases bc you didn’t lose any water from ECF.
- ICF Na conc stays the same bc of the Na-K pump Na extrusion equalling the Na entry
-if you got this problem bc of an initial increase in Na of plasma, you initially “buffer” the increased plasma Na by increasing the cellular uptake of Na. This diesnt increase the ICF Na bc the Na/K ATPase pump balances this. Na K pump obeys michaelis menton so that an increase substate (Na) causes an increas rxn
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hypoosmotic volume expansion-
syndrome of inappropriate antidiuretic hormone (SIADH) gain of water in excess of solute
- excess water reabsorption from collectiing ducts into ECF
- caused by inappropriate excess of circulating ADH that causes increase water reabsorption(without reabsorbing solute) from renal tubule into ECF
- increase ECF volume, decrease ECF osmolarity. Fluid moves into the ICF and decreases its osmolarity too.
hypoosmotic volume contraction-
aka salt wasting
adrenal (aldosterone) insufficiency and decreased renal NaCl reabsorption (loss of solute in excess of water)
- decreased ECF osmolarity. Fluid moves from ECF into ICF. You increase ICF volume and decrease ICF osmolarity. you also decrease ECF volume.
solute distribution
-despite differences in intracellullar and extracellular fluid compostitons,
the sum of the solute concentrations is the same,,,, 290 mosm
