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Flashcards in Rena Physio Deck (55):

Main cation in the ICF



Main anions in the ICF

Proteins and inorganic phosphates


Main cation in the ECF



Main anions in the ECF

Cl- and HCO3-


What percent of total body weight is water and how is the water divided up?

60% of total body water is water, 40% being intracellular and 20% being extracellular.

Of that extracellular water, 1/4 of that 20% is plasma volume and 3/4 is interstitial volume


These two conditions can cause a lower Total Body Water

Being old = more fat
Being female = more fat


Babies have a (higher/lower) TBW because...

Higher because they have less fat


The ICF has a slight ___ charge while the ECF has a slight ___ charge

ICF = negatove
ECF = Positive


Volume changes take place in the ___. ___ changes subsequently occur to equalize osmolarity between the two compartments



How do we calculate the amount of interstitial fluid?

= ECF - Plasma...think about the compartments


How do we calculate renal blood flow?

Renal plasma flow / (1 - hematocrit)


Effect of Isotonic NaCL
on ECF, ICF, plasma osmolarity and hematocrit

ECF - Up
ICF - NC (no change)
Plasma Osmolarity - NC
Hematocrit - Down


Effect of high NaCl intake
on ECF, ICF, plasma osmolarity and hematocrit

ECF - Up
ICF - Down
Plasma Osmolarity - Up
Hematocrit - Down


Effect of SIADH
on ECF, ICF, plasma osmolarity and hematocrit

ECF - Up
ICF - Up
Plasma Osmolarity - Down
Hematocrit - NC


Effect of Water Deprivation
on ECF, ICF, plasma osmolarity and hematocrit

ECF - Down
ICF - Down
Plasma Osmolarity - Up
Hematocrit - NC


Effect of Diarrhea
on ECF, ICF, plasma osmolarity and hematocrit

ECF - Down
Plasma Osmolarity - NC
Hematocrit - Up


Effect of Adrenal Insufficiency
on ECF, ICF, plasma osmolarity and hematocrit

ECF - Down
ICF - Up
Plasma Osmolarity - Down
Hematocrit - Up


Compare an SIADH patient vs/ someone who is just continually drinking a lot of water

A psychogenic polydipsia patient is jsut taking in lots of water, thus diluting their urine, but once they stop, thei urine concentration will return to normal.

In a patient with SIADH, they are constantly under the belief that they are hypovolemic and thus will retai nwater = concentrate the urine no matter what kind of water they take in.


If the clearance rate of a substance is greater than the GFR, what do we know?

The substance was filtered and secreted. The body really wants this out.


If the clearance rate of a substance is less than the GFR, what do we know?

The substance was filtered but something slowed it down on the way out = reabsorption occurred.


If the clearance rate of a substance is equal to the GFR, what do we know?

Substance filtered and then excreted with no retention or net secretion to note.


How do we know the relationship between GFR and clearence since measuring GFR is such a hassle?

We use inulin, which is neither secreted nor absorbed. It replaces GFR in the relationships described previously.


When do we consider a substance a glomerular marker?

When it is equal to the clearence rate of inulin, which is neither reabsorbed or secreted


3 layers of the glomerular filtration barrier and what is in them.

Lamina rara externa (where podocytes sit)
Lamina densa (darker on EM)
Lamina rara interna (where the endothelial capillaries are)


We use Inulin as the gold standard for GFR, but in common practice we use this instead, and why?

Creatinine, a normal by-product of muscle metabolism, is constantly released into the blood and is a good measure of how your body is filtering.
Increase in blood Creatinine = not filtering through urine fast enough = decreased GFR = pathology like renal failure


Average pressures of afferent and efferent arterioles of the glomerulus

A = 85
E = 60


Epinephrine and norepinephrine are part of the _____ and act on ___ receptors causing these effects:

Sympathetic Nervous System
alpha 1 - causes vasoconstriction of the renal arterioles, afferent more than efferent, leading to reduced RBF and GFR
Beta1 - Releases renin


Prostaglandins do this to renal arterioles leading to this.

Dilate afferent more than efferent, increases RBF and GFR


Angiotensin II is a potent ____ produced in response to ____. It overall is in charge of this general principle:

Vasoconstrictor produced in response to decrease afferent presure due to decreased renal blood flow. It constricts both afferent and efferent but preferentially acts on the efferent in order to maintain pressure in the glomerulus and keep GFR constant.


Dopamine does this to renal vessels because of:

Dopamine dilates renal vessels and suppresses sodium reabsorption in the PCT by inhibiting the Na-L-ATPase pump. Released directly by the PCT in response to an increase BP resulting in an increased RBF and GFR.


What causes a change in filtration fraction (GFR/RBF)

Not affected by constricting or dilating the afferent arteriole because GFR and RBF will fall an rise together respectively

Increased with efferent constriction because GFR goes u but RBF goes down (blood flow is reduced but that gives the Glomerulus more time to play with the material) as well as with decreased plasma protein concentration (while the RBF is not affected, the GFR goes up because we see this in nephrotic syndrome where we have holes in the membrane)

Decreased with Increased plasma protein concentration since the glomerulus has more garbage to deal with and also with constriction of the ureter or obstruction which is gonna cause back flow and a reduced GFR.


Discuss the two autoregulatory abilities of the kidney

1. Stretch mechanism - When BP goes up, the arterioles in the kidney get stretched. Afferent arteriole constricts in response to maintain the normal RBF and GFR

2. Tubuloglomerular feedback mechanism - Increased arterial pressure causes an increased RBF and GFR, increasing flow to the distal tubule which is sensed by the macula densa, which responds via vasoconstriction of the afferent arteriole, thereby attenuating RBF and GFR and closing the negative feedback loop


NSAIDs do this to the kidney

Decrease GFR and RBF by inhibiting prostaglandin synthesis.


Discuss PAH and what we use it for

para-Amino hpiiuric acid is an endogenous substance that is 90% excreted from the plasma through the kidneys via both filtration and excretion. The amount of PAH in the renal artery is approximately equal to that in the urine, therefore the clearence rate of PAH can be used to calculate the effective renal plasma flow.


Formula for ERPF?

ERPF = Clearence of PAH = (Urine concentration of PAH * urine flow rate) / Plasma PAH.


How do we calculate the True RPF?

Since PAH is only 90% cleared, meaning there is a little error in our ERPF, we can do

True RPF = ERPF / 0.9


Filtration fraction is normally 0.20. What does this mean?

20% goes through the filtration pathway and the other 80% exits via the efferent arteriole and becomes part of the peritubular cappillary system


Formula for GFR using the Starling relationships


GFR = Kf * [(PGC - PBS) - (πGC - πBS)]

PGC = hydrostatic pressure to glomerulus
PBS = Pressure exerted back by Bowman's Space
πGC = Oncotic pressure via proteins coming from the plasma to the glomerulus
πBS = Colloid force exerted back by Bowman's Space (usually 0 because not much protein actually makes it in)


Discuss glucose in the urine, when we see it, and what it indicates

Usually like 100% of the glucose is taken up immediately in the PCT. When serum levels go beyond 200, we start approaching the transport maximum and we will start missing some of the glucose that goes by (called splaying).

Now when the serum levels are 350 and above we're not splaying anymore, we are flat out pissing sugar because we've maxed out our TM and can't absorb the sugar. This is called glucosuria and is indicative of, yes you guessed it, Diabbetus.


We often don't see amino acids in the urine. They are absorbed in the ___ and unless there is a problem with ___ like we see in folks who present with ___, everything goes smoothly

Proximal tubule
Genetic abnormalities affecting transport
Cystinuria = cysteine stones from a genetic defect from not having good membrane transporters


When do we start excreting water?

Thick ascending limb


Describe what it means when water clearence (CH2O) is positive, zero, and negative.

Positive indicates we are getting rid of a lot of water and diluting too much.

Negative means we are concentrating urine and getting rid of more solutes

Zero means urine is isoosmotic to plasma


ADH does what?

ADH/Vasopressin increased permeability of the distal tubule and collecting ducts in order to make sure water gets reabsorbed in times of low volume


What happens in the PCT?

Exchange of Na for H+ which we buffer with ammonia that is put in the lumen by Cl going through. This puts sodium and Cl inside the cells of the PCT and Hydrogen and base in the lumen.

Water and CO2 are also absorbed into these cells, and via CA, turn to H+ and HCO3- (this H+ is what will be exchanged with sodium while the HCO3- will go directly into the blood)

Sodium exchanges for K via an ATPase pump to put K in the cells and sodium in the blood.


What does Digoxin do?

Stops the Na-K ATPase pump in the PCT


What activates and inhibits the Na-H exchanger in the PCT?

Angiotenisin II activates it, ANF blocks it when the atria gets stretched in order to stop the water that will accompany the Na.


Phosphate is also absorbed at the PCT. What stops it? What happens next?

Parathyroid hormone which stops the cotransport of Na-Phosphate. Stops phosphate, leading to increased cAMP excretion.


Thin descending limb does what?

Reabsorbs about 20% of the filtered water, but no solute reabsorption occurs here


This ascending limb does what?

Impermeable to water and has no significant reabsorption. What a lazy fuck.


Discuss the all-important thick ascending limb of the loop of henle

Diluting segment of the nephron. Interestingly enough, absolutely impermeable to water. It reabsorbs the ions via a Na 2Cl K transporter which is a symporter meaning it just sends all three in at once.

Once in the cells, the normal sodium potassium pump sends potasium out and sodium into the blood. K+ and Cl- just diffuse down their concentration gradient into the blood or, as per the usual due to the amount of K in the cells, the K will just exit back into the lumen.

Lastly, since the lumen is a little more positive than negative, Mg and Ca will just go through the cells into the blood.


Discuss the early distal convoluted tubule

Has an Na Cl co-transporter Which provides the basis for Na, Cl, Mg, Ca and K trafficking in and out of the lumen.


Angiotensin II and ANF act here as well to cause Na reabsorption and Na blocking respectively.

PTH acts here also to increase Ca reabsorption


Discuss the Late Distal tubule and collecting ducts

Made of two cells.

Principal cells grab Na and water and get rid of K via Na-K ATPase channels and apical ROMK channels respectively.

Alpha intercalated cells handle the acid base chemistry. They secrete H+ and reabsorb K+ and HCO3- (H-K exchanger). There are also Beta intercalated cells that absorb the H+ and secrete HCO3- which is made in the luminal cells by grabbing up water and CO2 from the lumen and turning them into carbonic acid via CA which dissociates into the H and HCO3-.


Aldosterone acts on the Distal convoluted tubule and collecting ducts. What does it do?

Stimulates Na reabsorption and K secretion in the principal cells as well as H+ secretion in the intercalated cells.


What awesome thing does ADH do?

It recruits aquaporins to attach to principal cells to make them permeable to water. Otherwise, they are impermeable.


Discuss Urea reabsorption

Only occurs in the inner medullary collecting ducts. ADH increases the urea permeability.