Renal system Flashcards
What is the basic function of the renal cortex?
Where filtration and bulk processing happens
kind of the outer bit of kidney
What body cavity do nephrons drain into?
Calyx
- gives unidirectional flow
- if blocked then have back flow of urine into the kidney
What is the difference between the long and short loop of henle?
Short: mainly in the cortex
Long: dips past cortex into medulla (means urine can be concentrated)
Where does the blood flow into the kidney?
Glomelular capillaries in the renal cortex
kidney is highest perfused organ in body (or second)
Describe the route of blood flow through the kidney starting with artery and ending with vein
Artery-> afferent arteriole -> glomerulus (filtration)-> efferent arteriole -> peritubular capillary -> venule -> vein
artery-arteroile-capillary-arteriole-capillary-vein
Which has cells that have adapted to a low O2 environment: Medulla or Cortex?
Medulla
pO2 ~ 10mmHg
Why is high blood flow so important in the kidney?
High blood flow NEEDED for glomerlular filtration rate NOT metobolic purposes
What exerts colloid oncotic pressure?
net oncotic= 25 mmHg
Proteins in the blood; they PULL fluid towards them
hence why colloid oncotic pressure= pulling pressure
Are proteins filtered in Bowmans space?
No, hence the colloid oncotic pressure= 0mmHg
What DECREASES GFR?
glomelular filtration rate
angiotensin II (ANGII)
noradrenalin
endothelium-1 (ET-1)
What INCREASES GFR?
glomerular filtration rate
Nitric oxide
Prostoglandins
Protein in your urine is a sign of what?
That your filtration barrier is breaking down
What are the three filtration layers separating plasma from bowmans space?
- capillary endothelium (lets in water but not proteins, neg charge)
- basement membrane (collagen matrix- densely negative)
- Podocytes (epithelium): fine mesh
What are normal sodium and potassium levels in renal epithelial cells?
20 mM Na
110 mM K
Have about 140mM Na and 5 mMK in the blood, so this creates driving forces
What molecule is recorded from urine to calculate GFR?
Inulin: bc its excreted at same rate as its filtered by glomerulus
Creatinine: in plasma and broken down from skeltal muscles over time
How much Na, K, water, bicarbonate, phosphate, glucose, and amino acids does the PCT reabsorb?
65% of Na, K, water, bicarbonate, phosphate
100% glucose and amino acids
can do this bc it has leaky epithelial cells
The AMOUNT of Na is LARGE but the concentration is the same = as plasma => because PCT has leaky epithelial cells so water moves with the Na
Should be NO amino acids or glucose in someones urine
What transporters are found in the PCT and what are their functions?
NHE3: Na import coupled with H+ export
AQP1: water import
NaPi2: brings in P with Na
SGLT2: brings in glucose with Na (dysfunctional in T2 diabetes)
NHE3 accounts for 1/2 of the sodium that the PCT reabsorbs
Why is the thick ascending limb of the loop of henle sometimes called the ‘diluting segment’?
Because there is NO WATER reabsorption
only cations can go through
water is impermeable bc NO aquaporins = NO transcellular pathway
What transporters are found in the TAL?
thick ascending limb= TAL
NKCC2: imports K+, 2 Cl-, Na
ROMK: exports K+ (to keep NKCC2 running) and generates +10 mV in the lumen which pushes cations into the cell
Doesnt import a LOT of K because if K wasnt recycled then NKCC2 wouldnt work (bc 5mM of K in the blood so not loads)
Means that NKC22 is ELECTROGENIC
Where is the paracellular cation shunt found?
What cations does it let through into the interstital fluid?
What osmotic gradient does it generate?
- TAL
- Na+, K+, Mg2+, Ca2+
- +200 mosmol
this is generated bc of ROMK, the +10 mV in the lumen drives the cations across the apical membrane between cells
Which part of the renal system do thiazide diuretics target?
The sodium transporter in the distal convoluted tube
Thiazide diuretics used to treat high BP
What are the two cell types found in collecting duct?
Principal cell: main cell type, Na/K
Intercalated cell: intercalates between principal cells; alpha (acid) and beta (base)
also has cilila (for sensing flow)
one collecting duct for every 10 nephrons
What transporters are found in the collecting duct?
NONE there are only CHANNELS found in the collecting duct:
ENac: imports Na
ROMK: exports K
ENac and ROMK create a -40mV in the lumen
What does aldosterone act on?
Retains sodium, loses potassium
* Acts on mineralcortocoid receptors in the principal cell in the collecting duct
* Essentially behaves like a TF and generates loads of ROMK, ENac, and NaK-ATPase — inc capacity for transport
retain Na and LOSE K
Describe the angiotensin-aldosterone system (RAAS)
DECREASED blood volume makes kidney make Renin, which leads to secretion of Angiotensin which…
- stimulates brain to find more salt
- stimulates aldosterone which tells kidney to absorb more salt
- stimulates vasopressin which tells kidney to absorb more water
- stimulates arteries to vasoconstrict
all to *INCREASE blood volume *
What effect does vassopressin have on the principal cells in the collecting duct?
It puts AQP-2 in the luminal membrane so cells go from being impermeable to very permeable to water
What is countercurrent flow in the loop of Henle?
Concentrates one arm (ascending) by diluting the other (descending)
- The deeper you go into the medulla, the more concentrated = medulla is HYPERTONIC
- The longer the loop- the greater the multiplication
- Must maintain a +200 mosmol gradient between medulla interstitial and ascending thick limb
- descending is PERMEABLE to water while ascending is IMPERMEABLE to water
- law of mass action, just separating Na and water
What are the differences between interstital, plasma, and intracellular K+ concentration in the kidney? Why is this important?
Intracellular: 110-140 mM (high)
Interstital/plasma: 3.5-5 mM (low)
importrant for MEMBRANE POTENTIAL!!!
How does body maintain K balance when eating food?
Uptake of K into cells by insulin and B-adrenergic
Kidney can modify itself over time to become used to high or low K intake
when you have kidney disease you cant excrete K very well, because cannot rapidly excrete it => hyperkalemia
How much K is reabsorbed in the PT? How?
proximal tubule
750 mmol/day, 70% of K reabsorbed
Leaky epithelium, so absorbed paracellularly
Driven by the transeptihelial potential difference
What are the two routes in the collecting duct principle cell for K secretion?
- ROMK: main route, stimulated by aldosterone and high K intake
- BK: stimulated by high K intake and high flow (central cillium)
Which type of intercalated cell provides a route for K reabsorption? Alpha or beta?
Alpha : couples H+ export with K+ import
Beta has bicarbonate/Cl transporter
H-K-ATPase is important in reabsorbing K during low K diet
What is the aldosterone paradox? What is the solution?
- Paradox: Aldosterone can trigger K loss without triggering Na retention
- Soln: Na retention occurs in the DCT which has 0 K channels (bc angiotensin II is high)
- Soln: K loss occurs in PC which has loads of K channels so wld be minimizing Na reabsorption
PC= principle cell
Eg, can eat a banana which would trigger aldosterone so K is lost through urine WITHOUT aldosterone triggering Na retention which would lead to increased BP
Can eat a banana without BP going up
What is the difference between a weak and strong acid?
Weak: less dissociated, higher pKa, higher pH of soln
Strong: more dissociated, low pKa, low pH of soln
What are sources of non-volatile acid?
- Incomplete carb metabolism (lactic acid)
- Protein metabolism (H2SO4 eg cys, HCL eg arg/lys)
During diarhea, why do you become acidotic?
Because you are losing a lot of bicarbonate
Losing base = retaining acid
What are the three ways the kidney eliminates acid?
- Excretion of H+ (as NH4, H3PO4, creatine, other buffers)
- Reabsorption of bicarbonate
- Bicarbonate regeneration (via NH4 formation)
no bicarbonate should be seen in urine, BUT if you have too much base the beta intercalated cell can secrete it with its cotransporter Pendrin
Very little free H+ secreted because the max urine can be is pH 4.5, so would j be way too slow for the amt of acid in the body
Where is ammonia made?
Made in the proximal tubule, pKa of becoming ammonium is 9.0 (super ideal), exists in urine as ammonium
What stimulates aldosterone production?
- Low blood volume triggers aldosterone so Na is retained
- High plasma potassium triggers aldosterone so K is lost
