4- Physiology I

omarys's version from 2017-05-23 22:40

Section 1

Question Answer
Bowman's capsule epithelium is continuous with (2)-the epithelium of the PCT + the podocytes covering the capillaries
The filtrate produced in the glumerulus is the fluid that passes the FILTRATION BARRIER made up of-the (fenestrated) endothelium >> the glomerular basement membrane >> the podocyte (with its slit diaphragm/pores)
3 structures (relevant in filtration) in increasing order of size: IMA-Inulin < myoglobin < albumin
Size selectivity is thru-the glomerular basement membrane (GBM) + the slit diaphragm (but not the endothelium)
Charge selectivity is thru-endothelium fenestrations + GBM (have negative charge)
GBM-GM bGM = גם תורם לסלקטיביות ע"ס גודל וגם ע"ס מטען
Which one drives fluid into the lumen of Bowman's capsule, the Δhydraulic pressure or Δoncotic pressure?Δhydraulic pressure
Clearance = U x V/P
Clearance has the same units as V, ml/min, which means that all other units in the formula must cancel out, i.e.U must be divided by P (both have the units of mg/dl)
1440# of minutes in a day
Clearance can includefiltration, secretion, reabsorption
Clearance = GFR whenthere's no secretion nor reabsorption (+when plasma concentration of substance is CONSTANT)

Section 2

Question Answer
Normal GFR in healthy males120±25 ml/min
Normal GFR in healthy females95±20 ml/min
GFR in L/day =135-180
IMMEDIATE observable effect of kidney removalGFR becomes half of what it was (before electrolyte imbalances etc. occur)
Elevated serum [X] (while urine [X] is constant) means that-The GFR is lower (linear relationship- if serum [X] has doubled then the GFR is half)
Perfect "X" for GFR is:inulin (ONLY FILTRATION)
Creatinine is similar to inulin, but 10% of it undergoes secretion, which means that it ______ GFR (relative to inulin).overestimates
CCT (creatinine clearance test) requires a 24-hour urine collection (bad compliance)
CCT = _____ true GFR.maximal
Damaged kidney function = secretion of creatinine _____increases (and gap bwn CCT and GFR increases, CCT>>GFR)

Section 3

Question Answer
Creatinine secretion into urine in men is 23 mg/kg (per day), and in women it is15-20 mg/kg (per day)
In a 24-hour urine collection of a 70-kg man, the how many mg of creatinine are expected?1610 mg (in all the urine collected throughout 24 hours)
eGFR estimates GFR using onlyserum [creatinine]
The lower the GFR, the ____ serum [creatinine]higher (NOT LINEAR)
A rise in serum [creatinine] from 3 to 4 mg/dl is ____ severe than a 1 to 2 mg/dl rise.less (recall the [creatinine] vs. GFR curve)
One disadvantage of eGFR is that itrelies on serum [creatinine], which might change relatively little in spite of marked decrease in GFR (leading to a sort of false negative result)
The worse the kidney function, the ____ the ____ of creatinine, and thus the greater the ______ of GFR.higher ; secretion ; overestimation (CCT or eGFR becomes >>> actual GFR)
Another disadvantage of CCT/eGFR is that creatinine levels in the serumdepend on diet (will rise in a meat rich diet)

Section 4: Alternatives to creatinine in GFR evaluation

Question Answer
What other compound may (partially) reflect GFR changes?Urea
Like creatinine, urea undergoes complete filtration in the glomerulus, but unlike creatinine, it undergoes ___ reabsorption.significant (50% compared to 10% for creatinine)
How is urea reabsorbed?Passively. It follows water-sodium reabsorption.
Can there be a significant rise in serum [urea] WITHOUT an underlying GFR change?YES! In volume depletion there is increased water-sodium reabsorption, and urea follows these guys.
Urea is produced from ____ ____ that have not been used for ____ _____ (in the liver).amino acids ; protein production
In REDUCED anabolism (less protein production) or in a protein rich diet, urea levels will _____.rise
In increased catabolism (increased breakdown)urea levels increase
Bottom line about urea is that its serum levels arevery variable
In patients with advanced renal insufficiency, what is a better way to evaluate GFR?Average of creatinine clearance and urea clearance
What serum [creatinine] characterizes advanced renal insufficiency?> 2.5 mg%
Cystatin C does not undergoreabsorption (so it would seem it is better than both creatinine and urea in this regard- "cyst/best")
Although cystatin C is not affected by diet, age, muscle mass etc., it is affected byinflammation, diabetes ("cyst/best" is a hoax)
The absolute BEST evaluation of GFR is thrua combined creatinine/cystatin evaluation (CKD-EPI-Cr-Cys equation)
In any case (whether it's urea or creatinine or cr-cys), these evaluations are reliable only whenthe body's at a steady state

Section 5

Question Answer
In the Starling GFR equation, Lp and S representcapillary permeability and surface area available
What 3 factors affect the HYDRAULIC pressure in the glomerulus?aortic pressure, afferent resistance, efferent resistance (the latter increased by AII)
The efferent arteriole's smaller diameter makes any change in it (by e.g. AII) ____ _____ in regulatingmore effective
afferent dilation and constriction cause an increase and decrease (respectively) in ____ ____ and ____.both RPF ; GFR
efferent constriction (effect of AII) causesincreased GFR and DECREASED RPF
While the hydraulic pressure _____ ____ _____ along the glomerular capillaries, the oncotic pressure in the vessels ______, which means that the GFR gradually _____ along the glomerulus.does not change ; rises ; declines
What is the filtration fraction and what is its normal value?It is GFR/RPF and its value is 20% (120 ml/min out of 600 ml/min are filtered in each kidney)
Filtration equilibrium is achieved either when the filtration fraction is ___ or when the ____ and _____ ________ are equal.20% ; hydraulic and oncotic pressures
To maintain a constant filtration fraction, when ____ rises, so will the ____. The opposite is true as well.the RPF ; GFR
Is efferent constriction guaranteed to increase the GFR?Nope. If the constriction is significant enough, then the RPF REDUCTION will be so severe that the GFR will also be reduced (due to FF balancing mechanism).

Section 6: RAAS

Question Answer
DAENA-RT (like DYNAMIC) are the factors regulating renal hemodynamics. They are:Dopamine, ANP, endothelin, NO, autoregulation, RAAS, tubuloglomerular feedback (TGF)
The juxtaglomerular apparatus is made up of 3 components:extraglomerular mesangium, macula densa, juxtaglomerular cells
Macula densa cells are parts of theTAL of the LOH
T or F- Macula densa cells secrete renin.False. JG -or granular- cells in the afferent arteriole secrete renin.
The 2 most powerful stimulants for renin release from JG cells are:increased β1 receptor activity (sympathetic) and hypoperfusion
Normal/physiological stimulant for renin release isNa+ intake
Stimulants for renin release achieve this result thru (3 mediators)baroreceptors/stretch in afferent, baroreceptors in heart/other vessels (that stimulate sympathetic system), MD cells
RAAS regulates TWO DISTINCT things:plasma [Na+] and blood pressure
Angiotensin II is a potent ______ peptide that causes arterioles to ______, resulting in ______ _____ ______ _____.vaso-active ; constrict ; increased arterial blood pressure
Aldosterone causes _____ ____ from the ____ ____ and ______ _______.Na+ absorption ; collecting duct ; K+ secretion
If the RAAS is abnormally active,blood pressure will be too high.
AII affects (raises) Na+ levels by stimulating the _________/_________ ______ in the _____.Na+/H+ exchanger ; PCT
T or F- AII constricts both the A and E arterioles, but its effect manifests as if it is only on the E.Trudat

Section 7: Autoregulation, TGF and all the other ones (of DAENA-RT)

Question Answer
Autoregulation also works in kidneys ___ ______.without innervation
Autoregulation maintains a normal ____ despite fluctuations in _____ _____.GFR ; aortic pressure
Autoregulation maintains Pgc/GFR thruconstriction or relaxation of the A arteriole
When does autoregulation NOT work?When the MAP is below 50 mmHG (but it becomes less effective already at MAP = 70 mmHg). In such a low blood pressure, the GFR = 0.
TGF regulates GFR based ontubular flow rate
What transporter do macula densa cells (of the TAL) have?Na/K/2Cl transporter
What stimulates the macula densa cells to "work"?Low [Cl-]. This will stimulate renin secretion from JG cells. ([Cl-] low e.g. because all the Cl- has been already reabsorbed in the PCT in a dehydrated person)
To prevent ischemia (in a sort of negative feedback or autoregulation kinda way), what does AII promote other than E constriction?Release of PGs, thus INHIBITING E constriction.
Dopamine and ANP (mainly) increase the ___ and ___ respectively.RPF ; GFR
Dopamine relaxesboth the A and E (so no major effect on GFR, but RPF does increase)
ANP constricts the ___ but relaxes the ____.E ; A (thus GFR will increase)
Endothelin _____ ____ the _____ and _____.constricts both E and A (both RPF and GFR will decline in this case)
Endothelin's role is played in _____ ______, such as _____ _______ _____.extreme conditions ; post-ischemic renal failure

Section 8: bye

Question Answer
Normal MAP is around93.3 mmHg
In severe hypovolemia, the (systemic) vasoconstriction will also ________________, to maintain blood flow to the brain and heart.manifest in the kidneys