Kruse Part 1 Flashcards
Blood Pressure Equation
MAP=CO x TPR
Cardiac output
- HR x SV
- the volume of blood pumped through the heart per minute
BP Drug Strategies
- reduce cardiac output and bp is reduced
- reduce total peripheral resistance and bp is reduced
- compensatory responses may include:
–reflex tachycardia (increased sympathetic activity)
–edema (increased renin activity)
4 major classes of antihypertensive agents
- diuretics
- agents that block the production or action of angiotensin
- direct vasodilators
- sympathoplegic agents (those that alter sympathetic function)
In the PCT, reabsorption of
approximately 65% of total sodium, K+ and water; 85% of NaHCO3; nearly 100% of glucose and main acids
NaHCO3–reabsorption in the PCT
-iniitated by action of the Na+/H+ exchanger (NHE3) located in luminal membrane
Na+/K+ ATP in basolateral membrane
pumps reabsorbed Na+ into the interstitium to maintain a low intracellular Na+ concentration
In the straight segment of the proximal tubule (late PT)
acid secretory systems secrete organic acids into the luminal fluid from the blood
-diuretics are delivered to the luminal side of the tubule where most of them act
Loop of Henle: H2O
-reabsorbed from the thin descending limb of the loop of Henle
Thin ascending limb of the loop of Henle
-relatively water imperbeable and is impermeable to other ions/solutes
Thick ascending limb of the loop of Henle
-reabsorbs Na+ and is impermeable to water
NaCl transport system in luminal membrane of thick ascending loop of Henle
- Na+/K+/2Cl- cotransporter
- establishes ion gradient in the interstitium
- increase in K+ concentration in the cells causes back diffusion of K+ into the tubular lumen–positive electrical potential to drive reabsorption of cations (Mg2+, Ca2+) via paracellular pathway
Inhibition of salt transport in thick ascending limb
reduces the lumen-positive potential and causes an increase in urinary excretion of divalent cations in addition to NaCl
Distal Convoluted tubule
- 10% of sodium chloride is reabsorbed
- relatively impermeable to water; NaCl reabsorption further dilutes tubular fluid
- NaCl is transported via a thiazide-sensitive Na+ and Cl- cotransporter
Ca2+ is passively reabsorbed by calcium channels (regulated by PTH)
Collecting tubule
- 2-5% of NaCl reabsorption through ENaC
- most important site of K+ secretion by the kidney and the site at which virtually all diuretic-induced changes in K+ balance occur
Diuretics that act upstream of the CCT will
increase Na+ delivery, which will enhance K+ secretion
Aldosterone
-increases the expression of both the ENaC and the basolateral Na+/K+-ATPase, leading to an increase in Na+ reabsorption and K+ secretion (which causes retention of water, an increase in blood volume, and an increase in BP)
H+ in Collecting Tubule
-secreted by proton pumps (H+-ATPases) into the lumen and increase urine acidity
ADH, vasopressin
-controls the permeability of the CCT to water by controlling the expression levles of functional aquaporin-2 water channels that insert into the apical membrane
Diuretics
- increase the rate of urine flow and sodium excretion
- used to adjust the volume and/or composition of body fluids in a variety of clinical situations including
- edematous states: heart failure, kidney disease and renal failure, liver disease (cirrhosis)
- nonedematous states: hypertension, nephrolithiasis (kidney stones), hypercalcemia, and diabetes insipidus
In the absence of ADH, the CCT (and collecting duct) is
impermeable to water and dilute urine is produced
-alcohol decreases ADH release and increases urine production
Diuretics molecular targets
- specific membrane transport proteins
- enzymes
- hormone receptors
Loop diuretics target
sodium/potassium/chloride cotransporter
Thiazide diuretics target
sodium/chloride cotransporter
K+-sparing diuretics target
sodium channels
Changes in urinary electrolytes and body pH with carbonic anhydrase inhibitors
- increased NaHCO3 in urine
- decreased body pH
Changes in urinary electrolytes and body pH with loop agents
increased NaCl in urine
increased body pH
Changes in urinary electrolytes and body pH with thiazides
- increased NaCl but not as much as loop agents
- increased body pH
Changes in urinary electrolytes and body pH with loop agents plus thiazides
- very increased NaCl in urine
- increased K+ in urine
- increased body pH
Changes in urinary electrolytes and body pH with K+ sparing agents
- K+ is lost in urine with all diuretics except these
- body pH decreased
Carbonic Anhydrase inhibitors act on
-Na/H (NHE3), carbonic anhydrase in the PCT
Loop diuretics act on
Na/K/2Cl cotransporter in thick ascending limb
Thiazides act on
Na/Cl transporter in Distal convoluted tubule
K+ sparing diuretics act on
ENaC channels in cortical collecting tubule
vasopressin antagonist act on
aquaporins in medullary collecting duct
carbonic anhydrase inhibitors include
- acetazolamide
- brinzolamide
- dorzolamide
- methazolamide
Loop diuretics include
- bumetanide
- ethacrynic acid
- furosomide
- torsemide
Thiazide diuretics include
- bendroglumethiazide
- chlorothiazide
- hydrochlorithiazide
- indapamide
- methylclothiazide
- metolazone
- polythiazide
- trichlormethiazide
K+ sparing diuretics include
- aldosterone agonists: eplerenone and spironolactone
- epithelial sodium channel inhibitors: amiloride; triamterene
Carbonic Anhydrase inhibitor MOA
- acetazolamide
- inhibits the membrane-bound and cytoplasmic forms of carbonic anhydrase
Carbonic anhydrase inhibitor actions
- decreased H+ formation inside PCT cell and decreased Na+/H+ antiport
- increased Na+ and HCO3- in lumen
- increased diuresis
- urine pH is increased and body pH is decreased
Carbonic anhydrase inhibitor clinical indications
- rarely used as antihypertensives due to low efficacy as single agents and development of metabolic acidosis
- used for glaucoma, acute mountain sickness, and metabolic alkalosis