Renal physiology

Question 1

Understand the definition and the relative size of the various body water compartments.

Answer 1

Water is 60% of body weight, approximately 40 liters Transcellular (joints, eyes, gut) 2% of weight Intracellular Extra cellular, plasma and interstitial fluid

Question 2

Know the composition and purpose of the intracellular, extracellular, and transcellular compartments

Question 3

Be able to discuss the principles of measuring the different compartments of water within the body.

Answer 3

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.

Question 4

Define active transport and the various types of diffusion.

Answer 4

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.

Question 5

Describe the various ways to effect the movement of water between intracellular and extracellular compartments.

Answer 5

Water movement in the body is always through osmosis. Following the gradient established by sodium.

Question 6

Name the condition causing the movement and be able to identify the associated clinical condition.

Answer 6

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.

Question 7

Diagram a coronal section of the urinary tract: kidney, ureter, bladder and urethra, and label its parts.

Answer 7

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

Question 8

Key levels for Na k Mg Cl Hco3 Phosphates

Answer 8

Na 142 mEq/l external, K 141 mEa/l internal Mg 58 mEq/l internal, Cl 103 external, HCO3 24 external Phosphates 75 internal

Question 9

Define The relative absorptive capabilities of the different renal tubular segments.

Answer 9

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…

Question 10

What is Tm for the kidney?

Answer 10

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.

Question 11

Describe the types of materials reabsorbed by the proximal SEGMENT (duct and tube) and their relative rates

Answer 11

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

Question 12

Describe the types of materials reabsorbed by the distal tubule and their relative rates

Answer 12

Calcium Magnesium Potassium Sodium and chloride Water

Question 13

How much plasma protein gets filtered by the nephrons

Answer 13

None, trick question. In a functioned kidney the glomeruli do not filter plasma proteins, or cells.

Question 14

How does ADH work

Answer 14

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.

Question 15

GFR

Answer 15

The glomerular filtration rate

Question 16

Renal clearance

Answer 16

Calculated as follows… Cx=(mass excreted per time/plasma concentration)

Question 17

Inulin

Answer 17

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

Question 18

Creatinine

Answer 18

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

Question 19

PAH

Answer 19

pAH is almost entirely cleared by the nephrons, allowing measurement of this value to equal the approximate Renal Perfusion Flow

Question 20

calculating renal blood flow

Answer 20

flow = RPF/(1-hematocrit)

Question 21

functional boundaries for the kidney

Answer 21

between 75 and 160 mmHg the kidneys are able to adapt resistance to maintain nearly stable flow .

Question 22

Macula densa

Answer 22

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.

Question 23

Where does hormonal control act on the nephron to preserve Na

Answer 23

The distal collecting ducts AFTER most has already been absorbed

Question 24

Apical transport of Na varying from cell to cell

Answer 24

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.

Question 25

Reflex control of Na+

Answer 25

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

Question 26

Hormonal control

Answer 26

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.

Question 27

Renin secretion

Answer 27

Involves renal sympathetic nerves.. Baroreceptors in kidneys (the juxtaglomerular cells monitor pressure in the afferent arterioles) Macula densa

Question 28

Atrial Natiuretic Factor

Answer 28

Produced bynbaroreceptors in the heart that inhibits Na reuptake.

Question 29

Management of potassium

Answer 29

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.

Question 30

Management of Ca

Answer 30

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.

Question 31

Phosphate management

Answer 31

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.

Question 32

Management of Mg

Answer 32

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.

Question 33

Counter current multiplier

Answer 33

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.

Question 34

Urea recycling

Answer 34

Unrea can be reabsorbed by the collecting duct Uta 1,2,3 are transporters in the nephron… UtaB is in the vasa recta

Question 35

effect of the vasa recta on the concentration gradient

Answer 35

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!

Question 36

ADH in the collecting tube

Answer 36

With ADH water leaves the tube on the way down and urine concentrates

Question 37

Two types of acids in the body

Answer 37

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.

Question 38

Protection against PAH change

Answer 38

three… Buffers in blood (fast acting limited response)… Lungs (relatively fast, require gradient drive) Kidneys (slowest, but most capable of restoring normality)

Question 39

Causes of acidosis

Answer 39

Tubular acidosis, failed h2co3 resorption Diarrhea, dropping h

Question 40

Anion gap

Answer 40

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

Question 41

hyponatremia

Answer 41

Electrolyte insuffincy that can present with water retention. most common cause is abnormal production of ADH, with … Common in CHF Prenancy Alcoholic cirrhosis

Question 42

List the history and physical examination clues to determine volume status.

Answer 42

Urine osmolality, urine specific gravity,

Question 43

effective arterial volume

Answer 43

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.

Question 44

volume vs hydration

Answer 44

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.

Question 45

calculating osmalality of the plasma

Answer 45

= 2x Na mEq/l + ((glucose Mg/dl)/18)+ ((BUN Mg/dl)/2.8)