Renal Flashcards
8 core functions of the kidneys
- excretion of waste and foreign substances
- water/electrolyte balance
- extracellular fluid volume
- plasma osmolality
- RBC production (EPO)
- vascular resistance
- acid base
- vitamin D production
2 parallel circuits of blood flow in kidneys
both start with glomerular capillaries
- peritubular capillaries - cortex, 90%
- vasa recta capillaries- medulla, 10% (most in outer medulla)
from renal capsule to bladder
capsule –> cortex –> medulla –> minor calyx –> major calyx –> ureter –> bladder
pathway through the nephron
blood enters via afferent arteriole- bownman’s capsule/renal corpuscle - proximal convoluted tubule- HENLE (straight proximal tubule- descending thin limb- ascending thin limb- ascending thick limb)- macula densa- distal convoluted tubule- cortical collecting duct- medullary collecting duct- papillary duct
3 layers of the filtration barrier for capillaries in the glomerulus
- endothelium of capillaries
- capillary basement membrane
- interdigitated podocytes
proximal tubule vs loop of henle vs distal tubule
PT: high volume, low gradient reabsorption; brush border; lots of mitochondria
LH: makes interstitial osmolarity, poorly developed cell surfaces
DT: low volume, high gradient reabsorption; lots of folds; lots of mitochondria
what is clearance?
the volume of plasma completely cleared of any substance in 1 min; mL/min
two equations for excretion
- excretion= filtered + secreted- reabsorbed
2. excretion= U(concentration)*V(flow)
conservation of mass for kidney
PaRPFa= PvRPFv + U*V
formula for clearance
UV= PC
what does inulin measure? creatinine? BUN? PAH?
1) inulin, creatinine, BUN all measure GFR (what you clear is exactly what was filtered)
- creatinine is overestimate b/c there is some secretion (BUN= creatinine x 10)
2) PAH measures renal plasma flow b/c it is all excreted; have some in venous blood so actually multiply by 1.1
calculate renal blood flow from renal plasma flow? what is more and how do they relate to GFR? what is GFR?
RBF= RFP/1-hct
RBF>RPF>GFR>V
RBF= 25% CO
GFR= measure of overall renal function
what is the filtration fraction?
FF= GFR/RPF or 125/660
Inulin clearance/PAH clearance (normal= 20%)
Glomerular capillaries are +/- charged, so it inhibits the passage of +/- charged substances such as __
negatively charged for both, albumin
polycationic molecules are filtered freely
what is the equation for GFR? how is it regulated?
GFR= Kf * (Hydrog - Hydrob - oncoticg + oncoticb)
- regulated by changes in afferent/efferent arteriolar resistance
what happens to GFR, Pgc, and RBF when you constrict the efferent arteriole?
GFR and PGC increase
but constriction ALWAYS decreases renal blood flow
ways intrinsic autoregulation occurs to regulate GFR and RBF
1) smooth muscle myogenic theory
2) tubuloglomerular feedback theory- more Na in macula densa causes afferent arteriole to constrict
3) intrinsic vasodilators and vasoconstrictors
what is the take away from Fick’s principle in the kidney?
if blood flow is restricted to the kidney, the kidney requires less oxygen
what are Tm and RPT? which is reached first and why?
Tm- transport maximum
RPT- renal plasma threshold (mg/ml)
- RPT reached first because of splay
how do you calculate the Tm for glucose? PAH?
- glucose is actively reabsorbed: Tm= PaGFR-UV
- PAH is actively secreted:
Tm= UV-Pa*GFR
what percent of water/Na/Cl/K is reabsorbed in the proximal tubule?
what percent of glucose/aa’s is reabsorbed in the proximal tubule?
2/3rds or 67% of water/Na/Cl/K reabsorbed in PT
100% glucose/AAs reabsorbed in PT
how is Na+ transported in the loop of henle? what is the percent reabsorbed? which segment is impermeable to sodium?
- Na/K/2Cl symporter
- 25%
- thin descending loop
how is Na+ transported in the distal tubule? what is the percent reabsorbed? collecting duct?
- NaCl symporter early
- Na+ channels late
~5 % - collecting duct is 3%, Na channels only
where is no water reabsorbed?
- thin ascending & thick ascending limbs of Henle
- distal tubule
what is a positive water balance?
intake > loss ; make hypoosmotic urine
what is the threshold for change in plasma osmolarity to secrete ADH? threshold for baroreceptors?
- greater than 280 mosms
OR - decreased in bp by 10%
- bp makes you more sensitive to osmolarity *
challenges to homeostasis : drink sea water blood transfusion saline transfusion water deprivation/sweating bleeding concentrated urine
1) drink sea water- hyper expansion
2) blood transfusion- iso expansion
3) saline transfusion- hypo expansion
4) water deprivation/sweating- hyper contraction
5) bleeding- iso contraction
6) concentrated urine- hypo contraction
what is the equation for the anion gap? what is it for vomiting/diabetes?
[Na]- ([Cl]+[HCO3-])= ~15 meq/L
vomiting= 15 diabetes= 35
what contributes to the hyperosmotic gradient from cortex to medulla?
urea- 50%- 600 osmol
Na- 25%- 300 osmol
Cl- 25%- 300 osmol
3 mechanisms that generate hyperosmotic gradient from from cotex to medulla?
- countercurrent multiplier- permeability differences for Na and H20
- urea cycle- leaking out in collecting duct & only participating in right loop
- countercurrent exchanger- slow vasa recta flow (permeable to everything) allows time for Na to move in and H20 to move out
5 requirements for hyperosmolarity
1) long loops of Henle
2) blood & urine flowing in opposite direction
3) active salt pumping (in basolateral membrane of cells near TAL/DT/CD)
4) differential permeabilities
5) destruction takes days to re-establish
what are the 4 ways of regulating renal salt excretion via afferent sensors?
a- venous (increased atrial stretch, increased ANP, natriuresis)
b- arterial (increased barros, decreased symp, decreased ADH)
c- hepatic sensors (increased liver p, decreased symp)
d- CNS sensors (increased Na in CSF, decreased symp)
what is the sympathetic pathway for water/Na reabsorption
increased sympathetics decreases GFR by constricting afferent arteriole, which increases renin (RAAS) and increases Na reabsorption
what are the 3 things that stimulate renin secretion?
1) afferent arteriole- perfusion pressure sensed by baroreceptors
2) afferent arteriole- sympathetic nerves that innervate
3) macula densa- tubuloglomerular feedback senses decreased NaCl
what does reabsorption depend on in 3 parts of kidney?
1- proximal- filtered load
2- TAL- Na delivery rate
3- DT/CD- Na load remaining
what are 3 things that cause K+ release from the cell? what percent is reabsorbed vs excreted?
1) epinephrine acting on alpha receptors
2) cell lysis (burns, surgery)
3) hyperosmolarity
85-95% is reabsorbed (decreases with more in diet)
15-80% is excreted (increased with more in diet)
what are 5 things that cause K+ uptake by the cell?
1) epinephrine activating B2 receptors, especially during exercise
2) increased extracellular K+ stimulating the Na/K ATPase
3) insulin (especially following a meal)
4) aldosterone
5) hyposmolarity
glomerulotubular balance vs. tubuloglomerular feedback
GT balance- 67% of what’s put in is reabsorbed
vs
TG feedback- Na sensed by macula densa controls afferent arteriole and GFR
what is a non-volatile acid? what is a volatile acid?
not derived from CO2 (H2CO3 is the ONLY volatile acid- can be excreted as gas by lungs)
what is the compensation for metabolic acidosis?
- dec pH
- dec Co2
COMP: decrease CO2 more
what is the compensation for respiratory alkalosis?
- inc pH
- dec Co2
COMP: decrease HCO3-
principle cell vs intercalated cell
principle cell: secretes K+ in exchange for Na (K+ balance), has AQP2 (water balance); few mits
intercalated cell: acid-base balance; reabsorbs K+ in exchange for H+ (can be used for NH4+ excretion), facilitates HCO3- reabsorption; lots of mits; only cells w/o cilia
NaCl transport vs water transport % reabsorption in different compartments
NaCL: 67-25-5-3
water: 67-15-0-10/15
menomic for evaluating acid base status
ROME- respiratory opposite, metabolic equal
same direction of change for pH & PaCO2
normal pH, PaCO2, HCO3, H+
pH: 7.35-7.45
PaCO2: 35-45
HCO3-: 22-28
H+: 35-45
what propels urine to the bladder?
walls of the calyces, pelvis, and ureter contract rhythmically and propel the urine along by peristalsis; ATP from myocardium
what makes up the JG apparatus?
- macula densa of thick ascending limb
- extraglomerular mesangial cells
- renin/ATII producing cells of the afferent arteriole
T/F Cl- reabsorption in the PT exceeds water, while Pi absorption is slower
false- opposite is true (and Na parallels water)
division of water
2/3 ICF 1/3 ECF
of the ICF 3/4 interstitial, 1/4 plasma
Infusing saline is a hypo/iso/hyperosmotic fluid expansion?
hypo-osmotic; plasma has a higher osmolarity than saline
what is CH20
free water clearance- the amount of pure water the kidney adds to the urine
