Renal Flashcards
Osmotic diuretics (mannitol)
- mechanism of action
- site of action
Inhibit water and solute reabsorption by
increasing osmolarity of tubular fluid
Mainly proximal tubules
Loop diuretics (furosemide, bumetanide)
- mechanism of action
- site of action
Inhibit Na+/K+/Cl− co-transport in luminal
membrane
Thick ascending loop of Henle
Thiazide diuretics (hydrochlorothiazide, chlorthalidone)
- mechanism of action
- site of action
Inhibit Na+/Cl- co-transport in luminal membrane
Early distal tubule
Carbonic anhydrase inhibitor (acetazolamide)
- mechanism of action
- site of action
Inhibits H+ secretion and HCO3- reabsorption, which reduced Na+ reabsorption
Mainly proximal tubules
Aldosterone antagonists (spironolactone)
- mechanism of action
- site of action
Inhibit action of aldosterone on tubular receptor, decrease Na+ reabsorption, decrease K+ secretion
Potassium sparing
Collecting tubules
Sodium channel blockers (triamterene, amiloride)
- mechanism of action
- site of action
Block entry of Na+ into Na+ channels of luminal membrane, decrease Na+ reabsorption, decreased K+ secretion
Collecting tubules
What determines GFR (equation)
GFR = Kf x Net filtration pressure
Net filtration pressure = (Pg-Pb-COPg-COPb)
What percentage of cardiac output is supplied to the kidneys
22%
Wat are the determinants of renal blood flow (Ohm’s law)
Renal blood flow (RBF) = (renal artery pressure-renal vein pressure)/total vascular resistance
What do the macula densa cells sense and what is their action?
Macula densa cells in the distal tubule
When GFR is reduced they sense a decrease in NaCL
This causes a release of renin
Stimulates RAAS – Angiotensin II
Increase in efferent arteriolar constriction
GFR increased
Where are the macula densa cells?
Juxtaglomerular complex - consists of macula densa cells around distal tubule and near afferent/efferent arteriole.
What is the overall effect of extreme sympathetic nervous system activation on GFR?
increased vascular resistance - Decreases GFR
What is the action of Angiotensin II and its effect on GFR?
Angiotensin increases efferent arteriolar constriction -> increases GFR
Also stimulates aldosterone secretion (increasing sodium and water reabsorption)
Also directly stimulates sodium reabsorption in most segments of nephron
What is the effect of nitric oxide on GFR?
NO decreases renal vascular resistance and increases GFR
What layers make up the glomerular capillary membrane
Fenestrated endothelium of capillary
Basement membrane
Podocyte cells - separated by ‘slit pores’
Glomerular filtration rate is approximately what percentage of renal blood flow?
What equation demonstrates this?
20%
Filtration fraction = GFR/Renal plasma flow
What is the effect of prostaglandins and bradykinins on GFR
decrease vascular resistance -> increase GFR
What is the carbonic acid equilibrium equation?
What enzyme catalyses this?
CO2 + H2O <–> H2CO3 <–> H+ + HCO3-
Carbonic anhydrase
What percentage of sodium and water are reabsorbed in the proximal convoluted tubule
65%
What percentage of Lactate, glucose and amino acids are absorbed in the proximal convoluted tubule?
100%
How do lipid substances get re-absorbed in the renal tubules (e.g. urea)
diffuse through the lipid bilayer
How are small proteins reabsorbed in the renal tubule?
receptor mediated endocytosis
they are then combined with lysozymes –> hydrolysis and amino acids released into blood –> proteins recycled
What ions are reabsorbed by paracellular transport in the proximal convoluted tubule?
Cl-, K+, Mg2+, some Ca2+
How is bicarbonate absorbed in the proximal convoluted tubule?
What percentage is re-absorbed here?
Using the carbonic acid equilibrium
- Carbon Dioxide (CO2) - moves into the cell + react with water to form carbonic acid (H2CO3)
- Carbonic acid is unstable - dissociates into a proton (H+) and bicarbonate (HCO3-)
- The proton (H+) is moved out of the cell using a Sodium-Hydrogen Antiporter (secondary active transport)
- H+ combines with HCO3-outside of the cell (in tubule) to form carbonic acid
- This is again converted by carbonic anhydrase to CO2 and H2O
- Most bicarbonate (HCO3–) gets pushed back into the blood
90%
What is the vasa recta and what is its purpose
The vasa recta is a peritubular capillary network present in the deep part of the medulla
It is a counter current exchanger and maintains the medullary interstitial gradient
Aldosterone
- site of action in the nephron
- effects
DCT + CD
Increased reabsorption of: Na CL and H2O
Increase secretion of K+ and H+
Angiotensin II
- site of action in the nephron
- effects
PCT, thick ascending loop of Henle, DCT, CD
Increased reabsorption of: Na CL and H2O
Increase secretion of H+
Antidiuretic hormone (ADH)
- site of action in the nephron
- effects
DCT, CD
Increased water reabsorption
Atrial natriuretic peptide
DCT/CD
Reduced Na Cl reabsorption
Parathyroid hormone (PTH)
PCT, thick ascending loop Henle, DT
Increased calcium reabsorption
Decreased phosphate reabsorption
What are the stimuli for aldosterone release
- AT II
- Hyponatremia
- Hyperkalaemia
What are the stimuli for ADH release
- High plasma osmolarity
- AT II
Which ion transporter on the basolateral membrane of the tubular cells creates a concentration gradient for passive diffusion on the luminal membrane
Na+?K+ ATPase - 3Na+ out and 2K+ into cell
How does ADH facilitate water reabsorption in the collecting duct?
Stimulates Aquaporin II to be added to the membrane
What substance leaves in the thin descending loop of Henle
Water
Which part of the nephron is impermeable to water
Thin and thic ascending limb of the loop of Henle
How much water is reabsorbed in the thin descending loop of Henle
20%
What substances are reabsorbed in the thick ascending loop of Henle
by which transporter
and what percentage
Na+/K+/Cl-
by NKCC2 transporter
25%
As well as other ions by paracellular transport: Ca2+ Mg2+ , (also Na+ and K+)
What are the two cell types in the late distal tubule and collecting duct
Describe their action
Principle cells
- reabsorb sodium and secrete potassium under the influence of aldosterone
Intercalated cells (A and B)
- A cells secrete H+
- B cells secrete HCO3-
Which portion of the nephron contains urea transporters for facilitating urea re-absorption
What is the purpose of this?
Late collecting duct
Allows urea to contribute to the medullary concentration gradient
Clearance of which substances can be used to assess GFR
Creatinine and inulin
What nervous system pathways control the micturition reflex?
Autonomic
- SNS and PSNS
Somatic
- Pudendal nerve
What nervous pathway controls the internal urethral sphincter?
Autonomic - sympathetic
What nervous pathway controls the external urethral sphincter?
Somatic - pudendal nerve
Activation of which nervous pathway causes detrusor contraction?
parasympathetic
What is the area of the pons called that helps control the micturition reflex
pontine micturition and pontine storage centres
What triggers the voiding phase of the micturition cycle
- Bladder volume strongly activates stretch receptors.
- sends signals to the pontine micturition centre
- initiates parasympathetic activation (causing detrusor contraction)
- inhibits sympathetic and somatic pathways (causing sphincter relaxation).
What urine crystal is this?
Struvite
What urine crystal is this?
Calcium oxalate dihydrate
What urine crystal is this?
Calcium oxalate monohydrate
What urine crystal is this
Uric acid crystals
What urine crystal is this?
Bilirubin
What urine crystal is this?
Ammonium biurate
What crystal is this?
Cystine crystal
