Overview of Renal Structure and Function Flashcards
Kidney’s job
Homeostasis
How does the kidney maintain total body content at a normal level?
Changing its rate of excretion
Where is sodium found?
**Restricted to ECF!!!!**
Hyperosmotic fluid loss means sodium depletion from:
ECF!! (so ECF would be hypoosmotic)
BP is determined by ____, which is determined by ____.
ECFV Total body Na+ content
What would you expect to see in a pt with no sodium?
Death
What is the major EC osmole? IC osmole?
Na+
K+
Hyperkalemia means excess K+ in which compartment?
EC
(don’t get confused despite K+ being major IC osmole)
Total body water most influenced by:
Osmolality of Na+, which determines majority of total body osmolality
Two major anions in ECF:
Cl- and Bicarb (HCO3-)
___% of body is water in males, ___% in females
60%
50%
Why do males have higher % TBW than females?
Males have more skeletal muscle
(Remember: 43% of TBW goes to muscle and 76% of muscle is water)
Function of HCO3-?
Maintain pH of 7.4
Major ECF buffer
Name three minerals whose levels are maintained by the kidney.
Calcium, phosphorus, magnesium
Name three waste products excreted in the urine and from which process each is produced.
Urea - protein metabolism
Creatinine - muscle metabolism
Uric acid - nucleic acid metabolism
What type of anemia is anemia of chronic kidney disease? What treats it?
Normochromic normocytic
EPO injections
What would you expect to see in a PBS of pt with EPO-secreting tumor?
Reticulocytes
(increased RBC production)
What would you expect to see in a PBS of pt with kidney necrosis?
Low reticulocyte count with a normochromic, normocytic anemia
(Less functioning kidney mass = less EPO = low RBC production = anemia)
Is anemia of chronic kidney disease reversible? How?
Yes, EPO injections
(also probably by reversing the cause of the kidney disease?)
Why might kidney disease cause bone pain, weakness, and cognitive impairment?
Vitamin D deficiency
(lack of active form of vitamin D)
What enzyme converts vitamin D to its active form, called ____?
1-alpha hydroxylase
Calcitriol
Where is renin produced?
Juxtamedullary apparatus by specialized cells in the afferent arteriole
Name four vasodilatory messengers produced by the kidney.
NO, PGI2, PGE2, bradykinin
Name the two renal functions of bradykinin.
Vasodilation and natriuresis
What role does vasodilation via PGI2 and PGE2 serve?
Autoregulation of GFR
Name a vasoconstrictor produced by the kidney. When is this produced?
Endothelin
When there is endothelial injury
Name 3 compounds for which the kidney is the sole source.
EPO, 1-alpha hydroxylase (virtually), renin
Function of angiotensin II? Aldosterone?
Vasoconstriction (systemic)
Na+ reabsorption in DT
(T/F): Kidney can cause both vasoconstriction and vasodilation systemically.
True
(Ang II/endothelin vs. NO/PGI2/PGE2/bradykinin)
Why might a person with renal medullary damage have hypertension?
Vasodilatory substances produced in the renal medulla and HTN is largely a kidney disease
Type I DM pt with poor insulin compliance and chronic kidney disease has a normal A1c. What explains this?
The kidney catabolizes insulin, so a pt with renal disease would have slower degradation of, thus less requirement for, insulin. Despite not complying with the recommended insulin schedule, his A1c is normal because more endogenous insulin is available.
Pt 1: Male lawyer with DM, poor insulin control, chronic kidney disease, and an A1c of 9.
Pt 2: Homeless man with DM, poor insulin control, chronic kidney disease, and a normal A1c.
Give two reasons for the difference in A1c.
- Pt 2 is homeless, therefore likely fasting a lot. He has chronic renal disease so is unable to produce as much glucose during fasting, as well as taking in less glucose, accounting for the normal A1c despite poor insulin compliance.
- The second pt’s renal disease also contributes to slower degradation of insulin, thus less need for exogenous injections. The first pt would have the same but not compounded by fasting.
An anorexic teenage female mentions during an office visit that she seems to never have the urge to urinate. Besides possible dehydration, what other mechanism may account for this?
During fasting, the kidney contributes to gluconeogenesis, thus pts will have a very low GFR and low urine output.
How much of gluconeogenesis is produced by the kidney during fasting?
25%-33.3%
A pt about to undergo a renal transplant should be given other antibiotics prophylactically than penicillin, cephs, or an aminoglycoside. Why?
Those are renally excreted drugs. Avoid renally excreted drugs in pts with kidney disease if possible.
Pt takes injected with 1 mg/mL inulin and excretes 0.5 mg/mL. Inulin is then in ___ balance.
Positive
(intake + production > excretion)
To be in negative balance, creatinine excretion would need to be greater than ____ mL/min.
140
(Remember: creatinine clearance ~ 140mL/min)
Too much Na+ = ___ expansion and what clinical finding?
ECFV
HTN
How can you determine if a pt’s edema is due to kidney disease?
Measure Na+ excretion in the urine; if elevated, excess Na+ not due to kidney
(too much Na+ in ECF = water follows = transudate causes edema)
How many glomeruli in the body?
Two million (one million/kidney)
What two pressures make up Starling forces and what does each pressure control?
- Hydrostatic pressure = kicks things out of cells
- Oncotic pressure = keeps things inside cells
What do Starling forces control in the kidney?
GFR, reabsorption, secretion
What kinds of cells are found in the ultrafiltrate of glomerulus?
None - ultrafiltrate is cell free and protein free
If plasma is 290 mOsm/L, glomerular filtrate will be ___ mOsm/L.
290
(iso-osmotic with plasma)
The kidneys receive how much cardiac output?
20%
(10% per kidney)
If 180L/day is filtered, ___% or ___ L/day is reabsorbed.
98-99%
178L/d
On a PET scan, which part of the kidney would be brightest? If possible to look at parts of the nephron, which part would be brightest?
Cortex
Tubules
(brightest = highest O2 consumption)
Filtrate moves from ___ into ___ in the glomerulus.
Glomerular capillaries to Bowman’s space
Main function of the tubules?
Reabsorption
What can be reabsorbed but not secreted?
Water
List one compound that is mainly removed via secretion.
K+
(Non-referred) Pain due to pyelonephritis would be felt where?
Back T12-L3
Which part of the kidney houses the glomeruli?
Cortex
Which structures in the kidney will be most affected by ischemia?
Tubules, loops of Henle, collecting ducts, vasa recta
(These are in the medulla, which only receives 10% of renal blood flow)
The renal artery, renal vein, nerves, lymphatics, renal pelvis, and ureter reside in the ___ of the kidney.
Hilum (central part)
Describe the path of urine once it’s formed.
Renal papillae –> minor calyces –> major calyces –> renal pelvis –> ureter –> retroperitoneum –> crosses pelvic brim –> trigone of bladder
What are the four possible site of urinary obstruction within the ureter?
Pelvis ureteral junction, pelvic brim, trigone, and median lobe of prostate (males)
Most common spot for urinary obstruction in males?
Median lobe of prostate
What is the advantage to males of having a longer urethra?
Less susceptibility to UTI/cystitis
What general class of bacteria causes cystitis?
Gram -
Afferent arteriole forms the ___; efferent arteriole forms the ___
Glomerular capillaries
Peritubular capillaries (cortical nephron) or vasa recta (juxtamedullary nephron)
List the path of blood flow through the kidney.
Renal artery –> segmental arteries –> lobar arteries –> interlobar arteries –> arcuate arteries –> interlobular arteries –> afferent arteriole –> glomerular capillaries –> efferent arterioles –> peritubular capillaries/vasa recta –> interlobular veins –> arcuate veins –> interlobar veins –> renal vein
Which renal arteries are end arteries? What happens if one is damaged?
Arcuate
Portion of the cortex that arcuate artery supplies is at risk for infarction
Which arteries are perpendicular branches that ascend toward the renal capsule?
Interlobular
What is unique about the renal circulation?
Which type of nephron is more numerous? Where is it found?
Cortical
Near renal capsule
What is a superficial nephron?
Another name for a cortical nephron
Why is the arterial perfusion pressure in cortical nephrons lower than in juxtamedullary nephrons? What is the significance of this?
Cortical nephrons are further from the aorta (remember: renal artery comes in at hilum, then blood has to pass through medulla to get to cortex)
Pressure inside glomerular capillaries is lower = lower GFR
Why are cortical nephrons also called short loop nephrons?
Their loops of Henle are shorter than juxtamedullary nephrons, aka long loop nephrons
Why does GFR reduce by only 75% rather than 50% after uninephrectomy?
Reserve capacity of cortical nephrons, which are never operating at 100%
When something is reabsorbed from the PT/DT/CD in the cortex, where does it go?
Into the peritubular capillaries, which surround the PT/DT/CD
Where is the larger type of nephron found?
Near the corticomedullary junction (juxtamedullary nephron)
What is a critical role of the juxtamedullary nephrons?
Concentration of the urine and renal medulla
(remember: some juxtamedullary nephrons extend down to renal papilla)
Where is the major site of Na+ transport?
Medullary thick ascending limb of Henle
What would happen if blood flow was cut off at the efferent arterioles of juxtamedullary nephrons?
The medulla would be completely infarcted as the vasa recta, formed from the efferent arterioles of juxtamedullary nephrons, is the sole blood supply to the medulla
If the plasma is 290 mOsm/L, the medullary interstitium would be:
>290 mOsm/L (hypertonic)
Why is it important for the medullary interstitium to be hypertonic?
Must be so urine can be concentrated; urine can be no more concentrated the the medullary interstitium or water would move in and dilute it
Why does the medulla only receive 10% of blood flow?
Low blood flood = won’t wash out solutes necessary to concentrate medullary interstitium
The vasa recta follow the ___ in what kind of arrangement? Why is that important?
Loops of Henle
Countercurrent
Allows oxygen and solute exchange between ascending and descending vasa recta
What happens as the vasa recta descend the medulla?
Oxygen tension decreases and medulla becomes progressively more hypoxic
Why are juxtamedullary nephrons at greater risk for hemodynamic stress than cortical nephrons?
They’re always operating at full capacity
What is Bowman’s capsule? What lines it?
Fibrous capsule surrounding the glomerulus
Parietal epithelial cells
What are visceral epithelial cells?
Podocytes - surround capillaries of glomerulus
The GBM is composed of:
Type IV collagen
What three components comprise the glomerular capillary wall?
Endothelial cell, GBM, foot processes from podocytes (visceral epithelial cels)
Which pressure is higher in glomerular capillaries than normal capillaries? Why?
Hydrostatic pressure - keeps large protein and cells inside capilaries
Besides hydrostatic pressure, what other force keeps albumin from entering glomerular capillaries?
Negative charge of slit processes
(T/F): Albumin is small enough to be filtered by the endothelial fenestrations of glomerular capillaries.
True; however, the negative charge of the foot processes of the podocytes repels albumin
Where does molecule go after it passes through the fenestrations of the endothelial cells and slit processes?
Urinary space (between glomerulus and Bowman’s capsule) which is contiguous with the PT
Mesangium consists of ___ and ___, which provides skeletal structure for:
Mesangial cells and mesangial matrix
Capillary loops
List the three functions of mesangium
- Structural support for capillary loops
- Contractile
- Phagocytic
How is the mesangium able to contract? What is the purpose of this?
Contains actin and myosin
Alter surface area available for filtration
How do mesangial cells gain access to immune complexes in order to perform macrophage functions?
Endothelial cells with large fenestrations remove mesangial cells from circulation. They then have access to immune complexes and phagocytose them.
What is common to all diseases with heavy proteinuria?
Problem with structure of visceral epithelial cells (podocytes)
Name the genetic mutation of congenital nephrotic syndrome.
Defect in podocin or nephrin
(heavy proteinuria = must be defect in visceral EC)
Name another disease associated with altered visceral EC structure.
Familial FSGS (focal segmental glomerular sclerosis)
What three parts make up juxtaglomerular apparatus?
Afferent arteriole
Efferent arteriole
Macula densa
Where is the macula densa and what does it (generally) do?
End of the cortical thick ALH
Sense how much tubular fluid is reaching it
___% (=___L) of filtrate is reabsorbed before reaching the macula densa. Thus, the distal nephron must be built for what?
90%; 160 L
Fine tuning
What is tubular glomerular feedback?
The mechanism by which each nephron feeds back on its own glomerulus to regulate its nephron filtration rate
If oncotic pressure is high in the interstitium and hydrostatic pressure is high in the capillary, which way will filtrate move?
From capillary to interstitium
If oncotic pressure if high in the capillary and hydrostatic pressure if high in the interstitium, which way will filtrate move?
Stay in capillary
What determines the net flow of fluid into or out of capillary?
Sum of Starling forces and by the filtration coefficient (Kf)
What measurement describes the permeability of a capillary?
Filtration coefficient (Kf)
GFR =
LpS(P-tau)
Lp = membrane permeability
S = surface area
P = hydrostatic pressure
tau = oncotic pressure
In a patient with nephrotic syndrome, what would you expect the oncotic pressure in Bowman’s space to be?
High - oncotic pressure in Bowman’s space is usually low because albumin is kept out; ain’t so in nephrotic syndrome
Is hydrostatic pressure in Bowman’s space high or low? Why?
Low - once filtrate is made, the PT starts reabsorbing it
What is the hydrostatic pressure along the length of the glomerular capillary? Why?
High - promotes filtration
What is the main factor determining GFR?
High glomerular capillary pressure
If cardiac output (CO) drops, what changes would you expect to see in the glomerular resistance capillaries?
Vasoconstrict afferent arteriole and/or vasodilate efferent arteriole
(less pressure in glomerulus = decreased GFR = raise blood volume = increase CO)
If you were to drink 2 L of water without any fluid loss, what changes would you expect in the glomerular resistance vessels?
Vasodilate afferent arteriole and/or vasoconstrict efferent arteriole
(raise glomerular capillary pressure = increase GFR = increase urine output)
A patient’s BP is normally 120/80. If his BP drops to 110/70, what change would occur to GFR?
None! Due to autoregulation, GFR remains constant.
A patient’s BP is normally 120/80. If his BP drops to 110/70, what changes would you expect to see in the glomerular resistance capillaries?
Vasodilate afferent arteriole and/or vasoconstrict efferent arteriole
(keep capillary pressure high = maintain GFR = autoregulation)
A patient notices over several days that he does not produce as much urine when he uses the restroom as he normally does. What can be said about his kidney function?
Nothing! Urine volume is NOT a good index of kidney function because it is not autoregulated.
A hypertensive patient produces large volumes of urine. Is his GFR greater or less than normal?
Can’t tell GFR from urine volume (increased perfusion pressure from high BP results in high urinary flow rate; when Na+ excreted, more water is excreted)
Urine flow rate is a good indicator of:
How much solute and water someone is excreting
If I just ate a bag of potato chips, and I have normal renal function, what will happen to my urinary flow rate?
Increase
What is the best indicator of overall kidney function?
GFR!!!
What is the parameter that measures the amount of substance in plasma that is filtered at the glomerulus per unit time? How is it calculated?
Filtered load
= GFR * Px
What parameter measures the amount of substance excreted into the urine per unit time? How is it calculated?
Excretion rate
ER = UF * Ux
**Remember this because it was repeated four times**
(T/F): Urinary flow rate is autoregulated.
F - UF is NOT autoregulated
Urinary flow rate is proportional to:
Perfusion pressure
Would a good marker of GFR be non- or highly protein bound?
Non protein bound
(must be freely filtered)
Two exogenous substances for measuring GFR?
Inulin, radisotopic iothalamide
___ is the best clinical estimate of GFR, thus the best clinical estimate of __ ___
Creatinine
Kidney function
Does creatinine over or underestimate GFR? Why?
Creatinine overestimates GFR because it is 10% secreted
The filtered load of inulin is equal to its __ __.
Express this as an equation.
Extraction rate (not reabsorbed or secreted)
GFR x Pin = UF * Uin
A pt is infused with inulin. How would you measure his GFR?
GFR = Uin x UF/Pin
What parameter measures the volume of plasma cleared of a substance via elimination into urine per unit time? Equation?
Renal clearance
C = UF x Ux/Px
Clearance ratio =
CR = Cx/GFR
What would be the clearance ratio of inulin?
1.0
(GFR = Cin)
What would be the clearance ratio of sodium?
<1
(reabsorbed so Cna<gfr>
</gfr>
What would be the clearance ratio of potassium?
>1
(K+ is secreted so Ck+>GFR)
What would be the clearance ratio of K+ of a pt on amiloride?
<1
(Amiloride is a K sparing diuretic, so the Ck+<gfr>
</gfr>
What would be the clearance ratio of H+ normally?
>1
(H+ is secreted so Ch+ >GFR)
What would happen to the clearance ratio of K+ of a pt with metabolic alkalosis?
Increase
(K+ would be secreted)
When would the clearance ratio of a substance be 0? Examples?
If it was completely reabsorbed
Glucose, amino acids
What is the clearance ratio of warfarin?
~0
(99% protein bound so not readily filtered)
Clearance of what is equal to RPF? Why?
PAH
It is filtered and actively secreted so it’s almost completely extracted from the urine on one pass through the kidney
