Kidney: producer, regulator, excretor Flashcards
What are the synthetic functions of the kidney?
Production of EPO, active form of vitamin D
Explain the mechanism and result of EPO production
Fall in oxygen level in renal tissues causes EPO to be secreted in kidney, stimulates RBC precursors in bone marrow
Explain the mechanism and result of vitamin D production-include chemical symbols of products
Skin+UV: cholecalciferol produces from dietary precursors (D3)
Liver: converted to 25-hydroxycholcalciferol (25-OHD3)
Kidney: converted to 1, dihydroxycholecalciferol (1,25-(OH)2D3) known as calcitriol
What cells produce EPO?
peritubular cells
What are tight junctions?
Fusion of adjacent cells to create a barrier to passage of water and dissolved particles
Describe the tight junctions in the PCT, DCT and collecting duct
PCT=loose DCT=tight CD=very tight
What is the main role of the glomerulus?
Producing filtrate
What is the mechanism of glomerulus function?
High pressure filtration of blood
Podocytes covering the ball of glomerular capillaries have very small negatively charged filtration channels
What are the properties of a marker used for GFR measurement?
Readily filtered, not metabolised, reabsorbed or secreted
What is the equation for GFR? What is the value to be found?
Filtrate flow (unknown) x filtrate concentrate (plasma concentration) = urine flow x urine concentration
What are three markers that can be used for GFR?
Creatinine: product of muscle metabolism, minor tubular secretion, results will be overestimated
Cystatin C: protein produced by mast cells
Inulin: Plant extract
If creatinine production is constant what can be used to give a GFR estimate?
Plasma creatinine concentration
What two different mechanisms of autoregulation in a broad sense?
1: Afferent arteriole dilates, improving renal blood flow at lower arterial pressure
2: Efferent arteriole constricts, improving GFR at a lower renal blood flow
What are the three tubulo-glomerular feedback mechanisms?
1) Adenosine-Produced when we are hydrated, constricts afferent arteriole, inhibits renin release, inhibited by low filtrate flow
2) Angiotensin II-RAAS system, constricts efferent
3) PGE2-Produced in DCT in response to low filtrate flow, dilates afferent arteriole, cytoprotective to tubule, antagonist to ADH
What is the main role of the proximal convoluted tubule?
Conservation of majority of useful filtrate components
What transporters are on the side of the tubule lumen in the PCT?
Na+/H+ Antiporter
Na+/Glucose symporter
What are the transporters on the side of the interstitial fluid in the PCT?
Na+/HCO3- cotransporter
Na+/K+ pump
How is H+ and HCO3- produced in the PCT?
H20 and CO2 enter cell through leaky junctions, forms H2CO3, forms H+ and HCO3-
What is the main role of the loop of henle?
Producing hypotonic tubular fluid and hypertonic interstitial fluid, and ion reabsorption
How does the loop of henle achieve it’s mechanisms?
Selective permeabilities to ions and H20 in each limb, plus countercurrent multiplier
What is reabsorbed in the descending limb of the loop of Henle? Through which channels?
H20 through AQP1 by osmosis
What is reabsorbed in the ascending limb of the loop of henle?
Ions
What transporters are on the tubular side in the ascending LoH?
K+ Na+ 2Cl- co-transporter
What is on the side of the interstitial fluid in the ascending LoH?
K+ channels, K+/Na+ active pump
What transporter do loop diuretics act on?
K+ Na+ 2Cl- co-transporter
Why is a hypertonic environment produced in the medulla?
So the collecting duct can reabsorb water
What is the main role of the DCT?
Final regulation of Na+, K+ and H+ that are secreted in urine
How does the DCT perform its main function?
1) Principal cells reabsorb, sodium secrete K+, controlled by aldosterone
2) Intercalated cells reabsorb potassium, secrete H+, ATP-ase driven
What is the sodium channel in principal cells called?
ENaC
What transporters are on the tubular side of principal cells?
Coupled Na+ and K+ channels
What transporters are on the interstitial side of principal cells?
K+ channel, Na+/K+ active pump
What does aldosterone stimulate in principal cells?
ENaC synthesis
Pump activity
What stimulates principal cells?
Mainly aldosterone, high potassium, alkalosis, high tubular flow
What transporters are on the tubular side of intercalated cells?
H+/K+ active pump
What transporters are on the interstitial side of intercalated cells?
K+ channel, Na+/K+ active pump
What stimulates intercalated cells?
Acidosis and low potassium
What is the main role of the collecting duct?
Final H20 regulation of urine concentration
What is the mechanism of the collecting duct?
Insertion of aquaporins into luminal membrane by ADH
What do aquaporin membranes contain?
Peptide helices
What significant feature is part of AQP structure?
Narrow charged channel
What receptor does ADH bind to in the CD?
V2
What effect does ADH cause in the CD?
Insertion of AQP-2 into luminal side of membrane to allow uptake of water
What are the 3 ADH receptors, location, role?
1) V1a: Peripheral circulation, vasoconstriction
2) V2: Collecting duct and endothelium, AQP-2 insertion, clotting factor release
3) V3 (V1b): CNS, ACTH release
What buffers H+?
HCO3-, HPO42-, NH3
How much HCO3- is reabsorbed?
99%
What produces NH3 in cells?
Glutamine
Where is the Juxtaglomerular apparatus located?
Between afferent arteriole and DCT
What does juxtaglomerular apparatus sense, and by which cells?
Granular: Decrease in pressure
Macula densa cells: Decrease in tubular Na+ flow
What cells release renin? What can this stimulated by?
Granular cells, sympathetic B1 stimulation
