Renal physiology Flashcards
Understand the definition and the relative size of the various body water compartments.
Water is 60% of body weight, approximately 40 liters Transcellular (joints, eyes, gut) 2% of weight Intracellular Extra cellular, plasma and interstitial fluid
Know the composition and purpose of the intracellular, extracellular, and transcellular compartments
Be able to discuss the principles of measuring the different compartments of water within the body.
Volume = quantity of indicator / concentration Volume = (quantity given - quantity excreted) / concentration Antipyrine measures total body water Sucrose and inulin measure extra cellular water. Risa and evens blue dye can measure blood plasma by binding to albumin which stays in the plasma. The intracellular volume is not directly measured but calculated by subtracting the extracellular volume from total volume.
Define active transport and the various types of diffusion.
Delusion in the kidney - simple and facilitated Simple is spontaneous movement down a gradient. Facilitated is down a gradient but involves carrier molecules to provide specificity and rate control/inhibitions Transport - active and secondary The Na K pump is an active pump, often on the interstitial side of the tubule cell. The sodium “in” pump is critical to maintain the gradient That drives the other molecules back into the body. Glucose is an example of secondary transport, using the Na gradient establised by the pump to hitch a ride up its own gradient.
Describe the various ways to effect the movement of water between intracellular and extracellular compartments.
Water movement in the body is always through osmosis. Following the gradient established by sodium.
Name the condition causing the movement and be able to identify the associated clinical condition.
Hypotonic expansion - Water intake - high E h2o - diffuses into I compartment to balance pressures - both compartments loose osmolarity while gaining size Hypertonic expansion - taking in high osmotic fluid into the E space - water leaves I space to balance - overall size gains, osmoticly unchanged or increased. Isotonic expansion - taking in isotonic saline Hypertonic contraction - loosing water faster than electrolytes - water leaves I and goes into E Hypotonic contraction - loosing electrolytes too fast - E becomes low osmotic, puts water into I, both compartments reduced.
Diagram a coronal section of the urinary tract: kidney, ureter, bladder and urethra, and label its parts.
Glomerular capillaries Hydrostatic pressure is always greater than colloid pressure, allowing for “outgoing” filtration along the whole length of the capillary (Pc > Pcolloid) Peritubular capillaries The hydrostatic pressure is less than the colloid pressure along the whole length allowing for re-absorption
Key levels for Na k Mg Cl Hco3 Phosphates
Na 142 mEq/l external, K 141 mEa/l internal Mg 58 mEq/l internal, Cl 103 external, HCO3 24 external Phosphates 75 internal
Define The relative absorptive capabilities of the different renal tubular segments.
The glomerulus has an incoming pressure from high pressure fluid. Counter pressure is generated by bowmens capsule fluid and lack of proteins content… Proximal 65.. Loop 15…. Distal tube 10… Collecting tube 9.3 assumes ADH (without, that number goes to 0 and overall flow to the ureters goes up)… Ureter 0.7…
What is Tm for the kidney?
A transport maximum… When considering transport out of the tubes consider Tm = amount filtered - amount excreted. So long as you don’t see the stuff in the urine, you can’t directly measure the Tm. This makes sense because you haven’t reached your max yet…. When considering transporting things into the tubes TM=excreted - filtered. Measures how much extra material ends up in the tubes.
Describe the types of materials reabsorbed by the proximal SEGMENT (duct and tube) and their relative rates
Keep in mind that the different types of nephrons, cortical and juxta glomerular, have slightly different functions.. Proximal tubules take back Bold Sodium 65%.. Bold Chloride Bicarbonate Potassium Bold Glucose 100%… Urea <50% Creatinine 0% fully excreted… Bold Amino acids Ascorbate Bold phosphate
Describe the types of materials reabsorbed by the distal tubule and their relative rates
Calcium Magnesium Potassium Sodium and chloride Water
How much plasma protein gets filtered by the nephrons
None, trick question. In a functioned kidney the glomeruli do not filter plasma proteins, or cells.
How does ADH work
ADH facilitates the expression of aqua portion 2 channels on the basollateral membrane, which allows water movement. .. This is a cyclic AMP, adenelyl cyclese dependent function.
GFR
The glomerular filtration rate
Renal clearance
Calculated as follows… Cx=(mass excreted per time/plasma concentration)
Inulin
Inulin is a good measure for GFR. It is 1. Freely filtered. 2. It is not reabsorbed. 3. It is not secreted into the tubes. 4. It is not metabolized. 5. It is not toxic… Thus excreted inulin = filtered inulin Thus Pin x GFR = excreted inulin In order to get a good read, I.V. Infusion and bladder cannulation are required. Easier to use creatinine
Creatinine
The clearance of creatinine is a good approximation for GFR At usual rates of renal clearance, 180ml min. It’s concentration is solid and stable. It takes dropping kidney function to about half before plasma levels begin to drastically rise…. Secretion and direct measurement of creatinine over glucose complicate things, but usually in the same direction allowing the estimate to be used reasonably
PAH
pAH is almost entirely cleared by the nephrons, allowing measurement of this value to equal the approximate Renal Perfusion Flow
calculating renal blood flow
flow = RPF/(1-hematocrit)
functional boundaries for the kidney
between 75 and 160 mmHg the kidneys are able to adapt resistance to maintain nearly stable flow .
Macula densa
has the ability to monitor sodium and chloride levels… A low level prompts the MD to signal junta glomerular cells to release Renin, enhancing the renin angiotensin system… Angiotensin 2 receptors are preferentially located on the efferent arterioles. Thereby greatly in handing resistance and increasing filtration.
Where does hormonal control act on the nephron to preserve Na
The distal collecting ducts AFTER most has already been absorbed
Apical transport of Na varying from cell to cell
Proximal tube… NHE3 changes Na for H, bringing Na in… Thick ascending limb… NKCC2/BSC Brings in 2 Cl, 1 Na, 1 K, all at once,.. K is allowed to leak back out because lumin concentrations are so low Loop diuretics work here… Distal convoluted tube NCC Co transports Na and Cl inward.
Reflex control of Na+
Decreasing Venus pressure increases renal sympathetic nerves constriction of afferent arterioles … Arterial blood pressure Decreased glomerular capillary pressure … Both limit flow to the glomeruli.. This limits the amount of Na and H2O filtered out, and therefore less excreted. This is one response to diarrhea
Hormonal control
Aldosterone, secreted from the glomerular region of the supra renal gland… Secretion of renin is the rate limiting step of the renin, angiotensin, aldosterone system.
Renin secretion
Involves renal sympathetic nerves.. Baroreceptors in kidneys (the juxtaglomerular cells monitor pressure in the afferent arterioles) Macula densa
Atrial Natiuretic Factor
Produced bynbaroreceptors in the heart that inhibits Na reuptake.
Management of potassium
After a big meal you can pull in as much as 50 mEq of K which must be taken up quickly. 756 mEq is filtered per day… 65% goes back in proximal limb… 27% goes back in distal…. 4% is secreted out in the upper collecting duct … So about 12% makes it out into urine… Major control is aldosterone Increases Na channels on the lumin side of principle cells in the collecting duct and enhances Na/K pump. Both bring more Na to the interstitial side and move K into the cell. Because there are K channels that drain into the lumen side of these cells, K is allowed to flow out.
Management of Ca
Only about 10% gets into the gut.. Hypocalcemia = increased muscle contraction… Ca is reabsorbed on the way up the loop, of henly and the collecting duct, altered by parathyroid hormone.
Phosphate management
85% of filtered phosphate is reabsorbed… In the proximal 70% is reabsorbed following Na… 20% or so makes it back In the terminal distal tube… Controlled by parathyroid hormone. Increasing hormone causes bone breakdown meaning more phosphate in blood and slows reabsorption by transport proteins in kidneys.
Management of Mg
It is a critical cofactor in cells, particularly in the Na/K pump.. Only 1% is in blood… Filtered Mg is reabsorbed across tight junctions. 20% in proximal tube 60% in the think ascending limb.
Counter current multiplier
Occurs in the thick ascending limb of the kidney. Pumping sodium into the interstitium without allowing H2O to follow. The juxtamedullary nephrons, using urea, sodium and chloride can use their pumps on the acending limb to push the gradient (WITHIN THE HAIRPIN) in the medulla to 1200 milli equivalents. This is a feedback loop in that the gradient that is established in the ascending limb bleeds into the defending limb, which does a second pass into the ascending limb and is acted on AGAIN by the ascending limb. Kinda cool.
Urea recycling
Unrea can be reabsorbed by the collecting duct Uta 1,2,3 are transporters in the nephron… UtaB is in the vasa recta
effect of the vasa recta on the concentration gradient
because the vasa recta doesn’t have different permeabilities for solutes and it leaves by heading back up to the cortex, the net effect is that the blood flow into the medulla becomes hypertonic as it descends BUT GIVES BACK NEARLY ALL OF ITS HYPERTONICITY ON THE WAY BACK UP!
ADH in the collecting tube
With ADH water leaves the tube on the way down and urine concentrates
Two types of acids in the body
Volatile, can be blown off. (Majority) Nonvolatile , phosphoric and sulfuric for GI MUST BE REMOVED BY KIDNEY… MUST URINATE 500 ml per day or BECOME ACIDOTIC.
Protection against PAH change
three… Buffers in blood (fast acting limited response)… Lungs (relatively fast, require gradient drive) Kidneys (slowest, but most capable of restoring normality)
Causes of acidosis
Tubular acidosis, failed h2co3 resorption Diarrhea, dropping h
Anion gap
Na+-HCO3–Cl- = 12 If the number is greater than 16 it suggests an anion gap, therefor acidosis. There is no real gap butnthenlab always measures these three values… A gap suggests diabetes mellitus Lactic acidosis Chronic renal failure As prune Methanol Ethylene glycol
hyponatremia
Electrolyte insuffincy that can present with water retention. most common cause is abnormal production of ADH, with … Common in CHF Prenancy Alcoholic cirrhosis
List the history and physical examination clues to determine volume status.
Urine osmolality, urine specific gravity,
effective arterial volume
the body carefully monitors the total volume of the arterial system, which is a very small portion of the body mass, but is critical for determining how much fluid you retain.
volume vs hydration
saying someone is hypovolemic == dehydrated. Volemia, hypo or hyper relates to salt levels, is the amount of properly osmolaric fluid in the body. Euvolemic is proper sodium with extra water = well hydrated.
calculating osmalality of the plasma
= 2x Na mEq/l + ((glucose Mg/dl)/18)+ ((BUN Mg/dl)/2.8)
