Renal Flashcards
Fluid Compartments
2/3 ICF
- 1/3 ECF with 1/4 being plasm
- Manitol and inulin measure ECF
- D2O measures total body water
- Radioactive albumin measures Plasma
Volume determinants
ECF volume is a function of solute, if Na/Cl are lost the ECF will contract. The ICF will spill fluid there to maintain equal osmolarity
- 2*Na+glucose/18+BUN/2.8
- Osmolarity of compartments is always the same.
Expansions and Contractions
- Expansions and Contractions refer to the ECF volume
- Osmolarity effects the ICF volume
- Isoosmotic Expansion: ICF stays same volume and ECF expands by volume added (Isotonic saline infusion)
- Hyperosmotic expansion: ECF expands and ICF will shrink to maintain osmolarity. NaCl igestions
- Hypoosmotic expansion: ECF expands and ICF expands to maintain osmolarity. SIADH, free water resorbed without resporbtion in Na. ICF shrniks, throws off concentrations in nuerons leads to siexures
- Isoosmotic contraction: Diahhrea/burns/trauma
- Hyperosmotic contracction: Los of free H20 (DI, sweating (More dilute than plasma))
- Hypoosmotic Contraction: Loss of solute without water, aldosterone deficency (Addisons)
Clearance
- The ammount of plasma cleared of a given substance per unit time
- Ammount excreted in urine/plasma concentration
- (urine concentration time flow rate)/(Plasma concentration)
- Units are volume/time
- Inulin is GFR, PAH is RPF, glucose and albumin are zero
Renal Blood Flow
- Calculated using PAH clearance to get renal plasma flow
- Then can correct for hematocrit
Regulators of Renal Blood Flow
- SANS: Through alpha 1 receptors lead to a constriction of afferent and efferent. Decreases both RPF and GFR
- Ang II: Preferetial Constriction of efferent over afferent, leads to a decrease in RPF with a maintained GFR (graded response)
- ANP: Causes dilation of all arterioles and constriction of efferent only. Leads to increased renal flow and significantly increased GFR (Escape from aldosterone, lower Na content and lower ECF)
- Prostaglandins: Cause dilation of afferent and efferent. Allow escape from SANS/AngII contriction. If NSAIDs, decrease this effect leads to decreased GFR
- Myogenic: Stretch of smooth muscle cells leads to constriction and increased GFR
- Tubuloglomerular: Increased delivery of solutes to macula densa signals and increase in GFR, release vasoactive substance to constrict afferent and decrease GFR
- Dopamine: Causes contriction of skeletal muscle and dilation of renal, splanchinic, and cerebral vessels. Hemorrhage leads to preservation of vital organs in exchange for skeletal muscle
Filtration barrier
- Endothelial cells have pores that keep RBC but allow proteins to get through
- Basement membran, doesn’t allow proteins through
- Podocyte processes generate filtration slits to further reinforce boundary
- Negative chage from GAG’s and heparin decrease plasma protein filtration
Changes in GFR and Filtration
- Constriction of the ureter leads to decreased hydrostatic pressure and decreased GFR and filtration fraction at a given RPF
- Protein concentratoin in plasma will also effect GFR and FF without altering RPF
Filtration equilirium
At the end of the glomerular cappilary there is often quilibrim reached because loss of fluid leads to relative increase in plasma protein concentration and increase in osmotic pressure. Hydrostatic is little changed.
Pre-renal Azotemia
Decreased RPF will lead to a decreased GFR
- Creatinine is nor resorbed while urea is
- pre renal azotemia will lead to increased BUN/Cr ratio
Glucose Reabsorption
- Tm System, governed by sturation of carriers
- Carriers with 2 Na and one glucose on apical, basal is glut1, glut2
- Splay is the begining period of glucose in urine, haven’t completely saturated transporters, but have partially
- DM
- Physiologic glucosuria of pregnancy caused by an increase in GFR leading to an increase in filtered load
Urea
- Passively reabsorbed and secreted, flows down conentration gradient and highly dependednt on H20 Reabsorption
- In PCT H20 resprobtion leads to 50% of urea to be reabsorbed
- At the bottome of thin desceding limb, water has been resorbed and urea concentration in interstitial fluid is high, some is secreted. Total concentration is 110% o filtered load
- Impermiable in DCT, Ascending limb, and proximal collectin duct
- Distal collecting duct H20 will be resorbed leading to an increase in urea concentration and some will be reabsorbed.
- UT1 is a transported that increases permiablity
- Dependent on ADH mediated H2O resorption
- Eventuall approximatly 40% is excreted
PAH
- Organic anion transporter secretes into urine
- Freely filtered but Tm system
- At low plasma PAH concentrations, all PAH is secreted, at high plasma PAH secretion, saturation occurs and some is reabsorbed. no longer useful clincal measure of GFR
Weak acids and bases
- Ionization state effects lipid solublty and ability to diffuse back into paratubular capillaries
- Acids are ionized at high pH and trapped in urine
- Treat ASA and TCA overdose with NaHCO3
- Amphetamines and opiods are bases, charged at high pH, increase seccretion with NH4Cl leading to acidified urine
Tf/P
- Ratio of tubular fluid concentration to plasma concentration
- Dependednt almost exclusively on water reabsorption
- If equal 1 then resorbed with water (Na)
- If less than one, resorbed faster than water (glucose)
- If greater than one: Slowly resorbed or secreted (Inulin, urea, etc)
(Tf/P)/(Tf/Pinulin)
-Measureing the ratio when compared to inulin will give a measurment of the fraction of the filtered load that has beeen resorbed
Na Balance
- Na balance is primarily driven by Na/K ATPase gradient
- Coupled to the transport of many molecules
Early part of PCT
- Na is cotransported with Glucose, AA, HCO3, citrate, Lactate, etc
- Na is also antiporterd with H
- All metabolic necessary products are resorbed with Na but very little Cl is resporbed
Late PCT
- Na is resorbed antiport with H still
- Cl- is also resorbed in a Cl antiporter
- High Concentration leads to Cl- transcellular absorption
- Na follows charge difference
Isomotic absortion
-As solutes are absorbed actively water will follow
Tubuloglomerular feedback
- Assuming plasma concentrations remain the same, 67% of water and filtered load will be absorbed
- As GFR increases and filtered load increases there will be a higher oncotic pressure int he paratubular cappilay
- This higher oncotic pressure will lead to increased waater resorption keeping the total resorption constant
Thin Descending limb
-Permiable to water but impermiable to other solutes leads to concentration of solute
Thick ascending limb
- Na/K/2Cl, impermiable to water
- Some K leaks back into lumen generating a positive intraluminal electrical gradient
- Leads to a paracellular push of cations into the paratubular capillaries
- Transporter can be blocked with furosemide which binds to Cl site
- Normally resorbs 25% of filtered Na load, strong diuretic
- Absorption in thick ascending limb is load dependeny, if there is elevated Na, more will be resorbed and so on. Therefore proximal tubule diuretics are weaker
- Diluting segment
Early DCT
- Contains load dependent Na/Cl cotransporter
- Further dilutes urine
- Blocked by thiazides (Cl binding site)
- Macula Densa
Late DCT and Collecting Duct
- Alpha intercalated (acid)
- Principle (Na/K)
- Principle cell is responsive to aldosterone and synthesizes ENaC channels
- Can be blocked by Amilioride, Triameterene, and Spironolactone
- Dirutics are weaker due to only 3% of Na resorbed
- Normally Na and K reabsorption are opposed, increase Na leads to more K secretion. Blockers prevent this and spare K
- Load dependent, especially with K
Regulation
- Na is mainly funtional in maintaining ECF and effective blood volume.
- Decreases in blood volume lead to SANS activation and decreased GFR and RPF. Na is load dependent and so Na loss is reudced
- Elevated blood volumes leads to ANP secretion leads to afferent dilation and efferent constricion leading to increased GFR and increased secretion.
- Ang II will synthesize H/Na channels in PCT
- Aldosterone synthesizes ENaC in principle cells
K Balance
- More passive and depends on Na
- Depends primarilry on electrochemical gradient
PCT
-Isoosmotic reabsorption follows water
Thick ascending limb
- Na/K/2Cl transporter
- K leaks back into luminal side to allow positive charge and transcellular Ca and Mg absrption
Internal K regulation
-Put into cells: Insulin and beta agonists cuase increase in ATPase. Acidosis causes a transcellular shift to buffer acid, H in exchange for K. If ECF is hyposomolar then fluid wil leave cells and K will follow to keep osmolarities the same
Internal regulaion K excretion from cells (Hyperkalemia)
- Skeletal muscle exsercise or cellular death leads to increae K
- Lack of insulin or beta blockers
- Alkalosis will shift H out of cells in exchange for K
- Hyperosmolar ECF will caues water to rush out of cells and K will follow
Intercalated cell
Intercalated cell is crucial in acid base base balances and uses a pimary active transport H/K antiporter
- Acidotic states will lead to increased H secreted and increased K resorbed hyperkalemia
- Alkolotic state will lead to decreased H secreted and decreased K resorbed leading to hypokalemia
Principle Cell
- Main cell in K regulation. K secretion dependent on the ammount of Na absorbed. More Na absorbed, more K excreted
- Na resorption dependent on delivery and presence of ENaC channels
Aldosterone
-Increased ENaC channels and increased intracellular Na leading to increaed K secretion and hypokalemia
Diruteics
- Loops inhibit absorption and also increase Na delivery lead to major K loss
- Thiazides: increase Na deilvey and increase K excretion
- K sparing: Block ENaC and prevent increased intracellular Na leading to decreased secretion
Phosphate metabolism
- All is absorbed in the PCT
- Coupled to Na/P secondary active transport
- Function of transport is inhibited by PTH through Gs and cAMP leading to phosphate excretion
- Elevated PTH levels lead to elevated cAMP and P in urine
- Important role as a titratable acid
- PseudohypoPTH is from defective Gs leading to no response to PTH. Blood levels will be high in PTH but P will be up and Ca will be down. There will be no cAMP in urine
Ca metabolism
- 67% is absorbed in PCT with Na
- In TAL increased luminal charge from K leak drives Ca and Mg paracellular transport
- Loop diuretics abolish this action and lead to Ca wasting. Can precipitate a stone, or can treat hypercalcemia
- Regulation occurs in DCT
- Not coupled to Na and contains own transporter that is increased with PTH through cAMP
- Thiazides will increase Ca resporption, used to treat Ca stones and hypercalemiuria
Mg Metabolism
Minimally absorded in PCT
- Majority of absorptin occurs in the TAL through paracellular transport
- Loop diuretics cause hypomagnesiumemia
ADH actions
- Increase function of Na/K/2Cl transporter to increase the corticomedullary gradient
- Increased production of aquaporins in the collecting duct (medullary and cortical and inner)
- increase inner collecting duct urea transporters to increase urea contribution to gradient
Nephrogenic DI
Treatemtn with thiazides serves to increase the concentration of the urine and decrease fluid volume
- This will decrease GFR
- It will also decrease Na levels, whichs is a major risk factor for problems