Renal System Flashcards
Name 3 countercurrent systems in the body.
1) loop of Henle (nephron)
2) vasa recta (capillaries of nephron)
3) blood flow to the testes through spermatic artery and veins
What is a countercurrent system?
Inflow runs parallel to outflow for some distance; “u-shaped” tube
What is the difference in a countercurrent exchange and a countercurrent multiplier system? Which one of these does the kidney use?
Answer
What is the function of the countercurrent systems in the kidney?
Answer
What blood vessels supply the loop of Henle?
Vasa recta
The _______ regulate the volume and composition of extracellular fluid.
kidneys
The _______ is the functional unit of the kidney.
nephron
Metabolic end products are excreted by ________.
filtration; filtered into and trapped within the renal tubule
Concentration = __________
volume (in water)
Osmolality is another term for ________.
Na+ concentration
Sodium Salts are _____% of the total osmolality of the ECF.
90%
________ regulates Na+.
aldosterone
What is the normal range for osmolality?
300 mOsm/kg (range 270-310)
The kidneys maintain ECF volume by controlling _____ and ______ excretion.
salt (NaCl) and water
What are the 3 primary endocrine roles of the kidney?
1) erythropoietin–> acts on bone marrow to stimulate RBC production; chronic renal pt’s may be anemic d\t low production of erythropoietin
2) RAS—> enzyme hormone system to regulate BP, K+ excretion, and Na+ reabsorption
3) vitamin D—> starts in the skin—> liver (picks up hydroxyl group—> kidneys (picks up another hydroxyl group)—> D3 (active form)
* chronic renal pt’s may be hypocalcemic b\c vit D helps in the absorption of calcium from the intestine
Na+ concentration is another term for _______.
osmolality
Blood is delivered to the glomerulus via the _______ arteriole and exits the glomerulus via the ______ arteriole.
afferent; efferent
Kidneys get approx ______ % of cardiac output.
25% or 1.25L (based on 5L/min CO)
The kidneys rework the ECF about once every ______, thereby maintaining its composition and volume.
once every 2 hours
*dialysis machines are only capable of reworking the ECF of anephric (kidney free) pt’s once every 8-12 hours
What are the components of the renal tubule?
1) Bowman’s capsule (encapsulates the glomerulus)
2) proximal tubule
3) loop of Henle
4) distal tubule
5) collecting duct
The loop of Henle adjusts concentration of ______ and ______.
Na+ and H2O
What occurs in the descending LOH?
osmosis–> H2O reabsorbed and Na+ left behind–> becomes concentrated
What occurs in the ascending LOH?
Na+ reabsorbed and H2O stays behind
Aldosterone effects the ______ of the renal tubule, and ADH effects the _______ of the renal tubule.
aldosterone=distal tubule=Na+
ADH=collecting duct=H2O
What are the 4 primary functions of the kidney?
1) filter
2) reabsorb
3) secrete
4) excrete
Where does 2/3rds of the reabsorption of H2O, Na+, etc… take place?
proximal tubule
Where does secretion in the renal tubule take place?
proximal tubule (muscle relaxants, etc)
Where do loop diuretics work?
THICH ASCENDING LIMB (TAL) of the LOH
*inhibit the body’s ability to reabsorb Na+–> H2O follows Na+
What diuretics work on the distal tubule?
thiazide-type diuretics–> HCTZ
- inhibit Na+ chloride symporter–> retention of water in the urine, as water normally follows penetrating solutes
- The long-term anti-hypertensive action is based on the fact that thiazides decrease preload, decreasing blood pressure. On the other hand the short-term effect is due to an unknown vasodilator effect that decreases blood pressure by decreasing resistance.
What happens in the distal tubule?
“reabsorption”–> partly responsible for the regulation of potassium, sodium, calcium, and pH
- primary site for the kidneys’ hormone based regulation of calcium (Ca)
- cells of the DCT have a thiazide-sensitive Na-Cl cotransporter and are permeable to Ca, via the TRPV5 channel
- participates in calcium regulation by reabsorbing Ca2+ in response to parathyroid hormone.
- regulates pH by absorbing bicarbonate and secreting protons (H+) into the filtrate, or by absorbing protons and secreting bicarbonate into the filtrate.
What regulates Na+ absorption in the distal tubule?
Sodium absorption by the distal tubule is mediated by the hormone aldosterone.
*Aldosterone increases sodium reabsorption
What are the two types of nephrons?
1) cortical nephrons–> short LOH and glomeruli located near surface of kidney
2) juxtamedullary nephrons–> long LOH and glomeruli located deep in the cortex near cortical medullary junction
Describe the blood flow through the kidney.
afferent arterioles–> glomerular capillaries–> efferent arterioles–> peritubular capillaries–> drains into venous system
*peritubular capillaries–> rise from the efferent arteriole and engulf the renal tubule; the VASA RECTA are the peritubular capillaries of the LOOP OF HENLE of the JUXTAMEDULLARY NEPHRONS (nephrons with glomeruli adjacent to the medulla)
from the tubule to the capillary = _________
reabsorption
from the capillary to the tubule= _________
secretion
_______, _________, and __________ are found in the cortex. ______ and _______ are found in the medulla.
glomeruli, proximal tubules, and distal tubules= cortex
LOH and collecting ducts= medulla
The ______ of the outer medulla is MOST vulnerable to ischemia.
inner stripe
Name the segment of the renal tubule:
makes final adjustments on urine pH, osmolality, and ionic composition
distal tubule and collecting duct
Name the segment of the renal tubule:
reabsorbs the bulk of the filtered fluid and its dissolved constituents; coarse control mechanisms for the renal regulation of ECF and composition.
proximal tubule
Name the segment of the renal tubule:
establishes and maintains an osmotic gradient in the medulla; plays a critically important role in the regulation of water balance; handling of NaCl and water occur independently
loop of henle
The loop of henle is a __________ system.
countercurrent multiplier
A countercurrent multiplier ______ the osmotic gradient.
CREATES; LOH
A countercurrent exchange _______ the osmotic gradient.
maintains; vasa recta
The TAL of the loop of henle is impermeable to ______.
water
*has a high concentration of Na+ transporters
The deposition of Na+ in the TAL of the LOH into the medullary interstitium creates osmolality of 600 mOsm. Where does the additional 600 mOsm come from when the osmolality increases to 1200 mOsm when it reaches the tip of the medullary pyramid?
from urea
Name the end products of metabolism that are normally excreted by the kidneys.
urea, uric acid, creatinine, PO4, SO4
The reabsorption of water is under the control of ______ hormone.
ADH
The reabsorption of Na and the secretion of K+ are under the control of _________ hormone.
aldosterone
What are two BP meds that have diuretic effects?
While not classically considered potassium-sparing diuretics, ACE inhibitors (ACEi) and angiotensin receptor blockers (ARB) are anti-hypertensive drugs with diuretic effects that decrease renal excretion of potassium
Aldosterone antagonists, like ____________, help diuresis and spare _________.
spironolactone; K+
What section of the renal tubule is responsible for glucose reabsorption?
the proximal tubule–> all other sections are impermeable to glucose—> uncontrolled diabetics have glucose in the urine because they have exceeded the transport maximum for glucose in the proximal tubule
Why do untreated diabetics produce more urine?
excess glucose causes the proximal tubule to reach its transport maximum of glucose–> glucose is then trapped in the tubules causing osmotic diuresis
The rate of release of ADH into the bloodstream is directly r\t the ________.
osmolality of ECF
*severe decreases in vascular volume and other stresses such as pain also trigger ADH release
How is an increase in ECF osmolality treated?
Too much concentration–> ingest water and adding it too the ECF
How is a decrease in ECF osmolality treated?
Too diluted–> excreting water and removing it from ECF
Vasopressin (ADH) is synthesized in the ________.
hypothalamus
* in the paraventricular and supraoptic nucleus
Vasopressin (ADH) is stored in ________.
vesicles of the neurohypophysis (posterior pituitary)
What two hormones are secreted from the neurohypophysis?
ADH, oxytocin
The ______ houses the pituitary.
sella turcica of the sphenoid bone
The anterior pituitary is also called ______.
adenohypophysis
Name 6 hormones produced or stored by the adenohypophysis.
1) ACTH (stress hormone)
2) FSH
3) LH
4) TSH
5) growth hormone (GH)
6) prolactin (PRL)
What is the most powerful stimulus triggering the release of AVP (ADH)?
increase in ECF osmolality
ADH is released from ________ and when it reaches the site of the ________ and _______ it increases water reabsorption.
neurohypophysis; distal tubule and collecting duct
In the absence of ADH (AVP), the distal tubule and collecting duct are _______ in regards to water.
impermeable
What is the mechanism of action of ADH on the collecting duct?
in response to increased cAMP, aquapores open, thus retaining water
Too salty= ______ in= _______ released.
Ca+= ADH released
Not salty enough= osmolality ~______=shut down _______= decreased ________= ________ urine.
250mOsm; aquapores; ADH; diluted
What are some stresses that can trigger the release of ADH (AVP)?
1) hypovolemia
2) hypotension
3) pain
4) trauma
5) emotional
6) CPAP
7) PEEP
8 volatile agents
*promote release of ADH regardless of osmolality
Approximately ____% of filtered water is reabsorbed from the proximal tubule and ____% from the descending limb of the LOH.
67%; 13%
*the ascending LOH is impermeable to H2O
H2O moves by ______ from the tubule to higher osmolality fluid of surrounding tissue.
osmosis
When levels of AVP (ADH) are high, a _______ volume of concentrated urine is formed.
AVP HIGH=SMALL VOLUME (as low as 0.5ml/kg/hr) OF CONCENTRATED URINE (osmolality 1200-1500)
When levels of AVP (ADH) are low, a _______ volume of concentrated urine is formed.
AVP LOW=LARGE VOLUME (up to 25ml/kg/hr) OF DILUTED URINE (osmolality 50-100)
What are two causes of diabetes insipidus?
1) failure of ADH synthesis or ADH release (MOST COMMON CAUSE)
2) insensitivity of the distal tubules and collecting ducts to AVP (ADH) –> nephrogenic
What does SIADH stand for?
syndrome of inappropriate ADH
What are some causes of SIADH?
- surgery
- several pathological processes–> intracranial tumors, hypothyroidism, porphyria, and small (Oat’s) cell carcinoma of the lung
What are diagnostic indications of SIADH?
1) increased urine sodium concentration (less H2O excreted)
2) increased urine osmolality
3) hyponatremia
4) decreased plasma osmolality (retained more H2O)
* remember that SIADH and DI are the inverse of each other
State whether GFR, aldosterone, and ANP increase or decrease to achieve INCREASED Na+ Excretion.
GFR increases= Na+ excretion inc.
Aldosterone decreases= Na+ excretion inc.
ANP increases= Na excretion inc.
State whether GFR, aldosterone, and ANP increase or decrease to achieve DECREASED Na+ Excretion.
GFR decreases= Na+ excretion decreases
Aldosterone increases= Na+ excretion dec.
ANP decreases= Na excretion dec.
_______ is the MOST important hormone for regulating ECF volume.
aldosterone
*water follows Na+
Atrial natriuretic peptide (ANP) is released from the _______ and acts on the kidney to _______ sodium excretion.
right atria; increase
Aldosterone is a hormone produced in the _______ of the ________.
zona glomerulosa of the adrenal cortex
Aldosterone acts on the _____ and the _______ to alter two renal tubular functions simultaneously.
late distal tubule and the collecting duct (primarily the collecting duct)
What two functions does aldosterone alter?
1) increases the rate of Na+ reabsorption from the late distal tubule and collecting duct and thereby decreases Na+ excretion
2) increases the rate of K+ secretion into the late distal tubule and collecting duct and thereby increasing the rate of K+ excretion
The bulk of filtered Na+ is reabsorbed by the _______ (approximately ______%) and the ascending LOH (____%), but there is also a significant amount reabsorbed in the ______ and _______ (approx. _____%)
proximal tubule (approx 67%)
LOH approx 25%
late distal tubule and collecting ducts (7.2%)
*but without aldosterone the late distal tubule and collecting duct are impermeable to Na+
What are the major consequences of sodium retention?
-ECF volume expansion and increased arterial BP–> more sodium intake= increased osmolality despite normal volume= ingest water= ECF volume expands, but osmolality returns to normal despite increased volume
How does the body respond to hypervolemia?
1) GFR increases
2) renin release decreases
3) output of ANP increases
=water is excreted along with Na to keep fluid osmolality ~ 300–> this process can take several days
How does the body respond to decreased body sodium?
If normal volume, but decreased Na+ content= decreased osmolality despite a normal volume= body decreases ADH b\c it thinks the body has too much fluid= normalized ADH now that the body has pissed out more fluid= normal osmolality but a contracted fluid volume
How does the body respond to hypovolemia?
promotes Na+ retention 1) GFR decreases 2) renin release increased 3) o\p of ANP decreases =water retained along with Na+ to maintain 300mOsm
With increased aldosterone, K+ excretion is _____.
increased
Where is the bulk of K+ reabsorbed?
proximal tubule= 67%
Is there any movement of Na+ or K+ in or out of the descending LOH?
Yes, but only by passive secretion as H2O is reabsorbed
What 3 factors control K+ transport in the late distal tubule and collecting ducts?
1) aldosterone (increases rate of K+ secretion and increases Na+ reabsorption)
2) distal tubular flow rate (K+ secretion in DT is sensitive to tubular fluid flow–> increases in proportion to flow)
3) bicarbonate ion (HCO3-) concentration in tubular fluid–> when HCO3- is increased the K+ secretion rate is increased
* this is why one anecdote to hyperkalemia is administration of Na Bicarbonate–> makes the urine alkaline and induces an increase in K+ secretion; bicarbonate also alkalinizes the blood, driving H+-K+ exchange that drives K+ into the body cells
Increased secretion of K+ occurs with what type of diuretics?
high ceiling diuretics like furosemide as well as osmotic diuretics like mannitol
Name 4 loop diuretics.
1) furosemide (lasix)
2) bumetanide (bumex)
3) ethacrynic acid (edecrin)
4) torsemide (demadex)
* inhibits reabsorption of Na, K+, and Cl- in the ascending LOH–> so water follows Na+ out the collecting duct
Name 4 thiazide diuretics.
1) chlorothiazide (diuril)
2) HCTZ (esidrix, hydrodiuril)
3) chlorothalidone (hygroton)
4) metolazone (zaroxolyn)
Name 3 potassium sparing (aldosterone inhibitors) diuretics.
1) spironolactone (aldactone)
2) triamterene (dyrenium)
3) amiloride (midamor)
Why does BP decrease with the administration of furosemide?
d\t the release of prostaglandins from the kidneys–> circulating prostaglandins cause venodilation so BP begins to fall even before urine o\p increases
s\e of loop diuretics?
hypokalemia, fluid volume deficit, orthostatic hypotension, reversible deafness
*n/v/d with ethacrynic acid
What is the MOA of thiazides?
inhibit Na+ reabsorption in early distal tubule
How do potassium sparing diuretics work?
spironolactone competitively inhibits aldosterone–> inhibits Na+ reabsorption in late distal tubule and collecting duct, and decreases K+ secretion
s\e of thiazides?
hypokalemia d\t increased K+ secretion
s\e of K+ sparing diuretics?
hyperkalemia
Name a carbonic anhydrase inhibitor.
acetylzolamide (diamox)
What is the MOA of a carbonic anhydrase inhibitor?
inhibits the enzyme carbonic anhydrase in the proximal tubule of the kidney thereby inhibiting bicarbonate reabsorption–> Na+ reabsorption also diminishes–> inhibition of Na and HCO3- reabsorption promotes diuresis
What can result from giving a carbonic anhydrase inhibitor, such as diamox?
hyperchloremic metabolic acidosis–> d\t discarding of Na+ and HCO3- from less reabsorption
Why is acetylzolamide sometimes given to “eye” patients?
inhibition of carbonic anhydrase decreases the rate of formation of aqueous humor–> IOP decreases; one of the principle uses of diamox is to decreases intraocular pressure
Why is hypokalemia promoted with osmotic diuresis?
Mannitol promotes osmotic diuresis–> agent is filtered into bowmans capsule and then trapped in the tubule to exert osmotic force and hinder reabsorption of water–> increasing flow through the distal tubule and collecting duct–> increases K+ secretion
How can you differentiate pre-renal vs renal failure?
renal failure is tubular necrosis, so during this acute renal failure, the renal tubule reabsorbs sodium poorly so a large amount appears in the urine (FENa is high- fraction of excreted Na); in pre-renal, sodium is extensively reabsorbed because d\t decreased renal BF there is a lot more time for sodium reabsorption–> FENa is LOW
What is 3 causes of prerenal perioperative oliguria?
1) decreased RBF
2) hypovolemia
3) decreased CO
Name 4 causes of perioperative renal (intra) oliguria.
1) renal tubular damage
2) renal ischemia d\t prerenal causes
3) nephrotoxic drugs
4) release of hemoglobin or myoglobin
Name 3 causes of postrenal perioperative oliguria.
1) obstruction of urine flow
2) bilateral ureteral obstruction
3) extravasation d\t bladder rupture
What is the BEST test for distinguishing pre-renal failure from renal failure (acute tubular necrosis)?
fractional excretion of filtered sodium (FENa) is 90% specific and sensitive
What is the normal GFR in mL/min?
125
What is the GFR in someone with decreased renal reserve?
50-80
What is the GFR with renal insufficiency?
12-50
What is GFR in the presence of uremia?
<12
At what GFR does symptoms begin to appear?
renal insufficiency <50ml/min
What is the best test for renal reserve?
creatinine clearance (measures GFR)
What are some complications in the renal patient?
1) chronic anemia–> decreased erythropoietin–> treatment with recombinant erythropoietin until Hct reaches 30-33%
2) pruritus
3) coagulopathies–> treat with adequate dialysis and elevation of Hct–> the abnormal bleeding tendency is in despite of normal coag tests (PTT, PT, INR)
What is the cause of pruritus in renal patients?
increased levels of histamine–> this is decreased with erythropoietin administration b\c it lowers the plasma concentration of histamine
What are the 4 main electrolyte disturbances in chronic renal failure?
1) hypocalcemia
2) hyperphosphatemia
3) hyperkalemia
4) hypermagnesemia
What is the most serious electrolyte disturbance in chronic renal failure?
hyperkalemia–> d\t EKG changes (peaked T, prolonged PR interval, widened QRS, heart block, PVCs and ventricular fibrillation
Why should you avoid LR administration in renal patients?
because LR contains 4meQ/L K+
You should avoid elective surgery until K+ is < _____ in renal patients.
5.5
Name 7 strategies to decrease K levels.
1) administer calcium (fastest, but does not correct K+)
2) hyperventilation (lowers K 0.5 per 10mmHg decrease in PaCO2
3) insulin-glucose
4) B2 agonist
5) loop diuretic
6) kayexalate
7) dialysis
What is the cause of hypocalcemia in renal patients?
1) diminished renal production of the active form of vitamin D
2) hyperphosphatemia resulting from decreased GFR–> reciprocal decrease in plasma calcium concentration
Which type of NMB’s are potentiated by hypermagnesemia?
non-depolarizers and depolarizers
______ % of patients with ESRD have HTN.
80%
Acute pericardial tamponade is the life threatening complication of __________ ___________>
uremic pericarditis
________ is the MOST serious problem facing renal failure patients.
infection–> sepsis is most common cause of death in patients with renal failure
