Renal Flashcards
Function of the proximal tubule?
Isosmotic reabsorption of 70 % filtered water and NaCl, 90 % bicarb, NH3 production, reabsorption of almost all glucose and amino acids, reabsorption of potassium, phosphate, calcium, magnesium, urea and urate, secretion of organic anions and cations
Function of loop of henle?
Countercurrent multiplier, reabsorption 15-25 % filtered NaCl, active regulation of magnesium excretion
Function of distal tubule?
Small amount of NaCl absorption, active regulation of calcium excretion
Function of connecting segment/cortical collecting duct?
Aldosterone-mediated potassium secretion by principal cells, H+ secretion and potassium reabsorption by alpha intercalated cells, ADH mediated water reabsorption
Function of medullary collecting duct?
Potassium reabsorption or secretion, final NaCl reabsorption, ADH mediated water and urea reabsorption, H+ and NH3 secretion
Why is there more filtration in the glomerular capillaries than systemic?
More surface area, but not constant and can change eg with mesangial cell contraction under ATII influence
What substances constrict/relax the glomerular vessels?
Constrict afferent and efferent - norepinephrine, ATII, endothelin, thromboxane
Constrict just efferent - vasopressin
Relax both - acetylcholine, NO, dopamine, bradykinin, prostacyclin, PGI2
Relax afferent - PGE2
NE, ATII and ADH promote production of prostaglandins
What is tubuloglomerular feedback?
Local intrarenal negative feedback mechanism for individual nephrons:
Increased NaCl in the distal tubule sensed by extraglomerular mesangial cells of the juxtaglomerular apparatus, sensed by tubular cells of macular densa (transport of NaCl across them - requires Na K 2Cl transporter and ROMK potassium channel luminal, and NaKATPase basolateral)
Transcellular NaCl transport + ATII causes afferent constriction and decrease GFR to minimise NaCl loss
What transporter does furosemide inhibit?
NaK2Cl in loop of Henle, compete with Cl
What transporter do thiazides inhibit?
NaCl in distal convoluted tubule
What is sodium absorbed with in the PCT?
Glucose, amino acids, phosphate, bicarbonate
What is sodium absorbed with in the DCT/LoH?
Chloride
What transporters mediate luminal uptake of glucose in the PCT?
SGLT2 - high capacity low affinity, first and second portion
SGLT1 - low capacity high affinity, third portion
Saturatable
What mediates PCT phosphate absorption?
NaPi-IIa and IIc transporters
Low Tmax so ready excretion of phosphate at high conc cf glucose
PTH decreases Tmax and causes excretion
How is urea reabsorbed?
Passive (decreased with high tubular flow rates)
Facilitated transporters - UTA1/A3 in inner medulla collecting duct, ADH dependent, urea concentrates in interstitium
Can reenter thin descending LoH via UTA2, and reabsorbed to enter vasa recta (venous) and then arterial (have UTB) - countercurrent exchange
Impermeable to urea - DCT, cortical collecting duct, outer medullary collecting duct
What are the urinary concentrating mechanisms?
NaCl transport without water in ascending LoH causes hyper osmotic medullary interstitium
ADH increases water permeability of the collecting duct, tubular fluid equilibrates with hyper osmotic interstitium
What controls inner medullary collecting duct urea absorption?
ADH
What effect does aldosterone have in cortical collecting duct?
Sodium and chloride absorption and therefore water absorption
How is urine concentrated without ADH?
GFR decreased by dehydration, PCT reabsorbs more sodium and water
What is the vasa recta for?
Gains solute as moves distally, gains water as moves proximally. Interstitial osmolality increases as move distally (ascending LoH solute absorption) and decreases as move proximally
Where is renin from and what stimulates its release?
Juxtaglomerular apparatus, vascular endothelium, adrenal gland, brain.
Decreased renal perfusion sensed by afferent arterioles of granular cells of JGA, hypotension stimulation cardiac/arterial baroreceptors with SNS activity and catecholamines (beta 1 adrenergic receptors), decreased distal tubular flow or NaCl depletion (macula densa)
Inhibited by ATII
What are the effects of ATII?
Arteriolar vasoconstriction (most sensitive renal splanchnic cutaneous)
Facilitates NE release from adrenal medulla and sympathetic nerves
Increases PCT sodium absorption d/t NaH antiporter luminal membrane
Increases aldosterone secretion
TXA2 mediated glomerular vasoconstriction (efferent > afferent)
Increased sodium and water reabsorption
Mesangial contraction, decrease surface area
Release of vasodilatory PGE2 and I2
What inhibits 1alphahydroxylase?
Calcium, vitamin D, decreased PTH, increased phosphate
Definition of CKD?
> 2-3 m permanent irreversible loss of functioning nephrons