JG Apparatus

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JG Apparatus
11.

• 1) regulation of single nephron filtration rate -
• (tubuloglomerular feedback)
• Increased NaCl at macula dense, increases
  adenosine, afferent and efferent arteriole
  constriction, decreased RBF and GFR.
• 2) Regulation of renin release
• Decreased NaCl at macula densa,
• (? mechanism), increased renin.

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Macula Densa
Granular Cells
Mesangial Cells
RENIN
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Lecture 4 (Objective E)Sodium
Excretion(Chapter 34)

• 1. Describe where and how much of filtered Na
  is reabsorbed in the tubule.

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1. Intracellular and Extracellular Fluids
42 LITERS
Fig. 3-1 p.51
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Sodium Balance
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Sodium Balance

• Of all kidney functions, reabsorption of sodium
  is the most important.
• Na is the major cation in the ECF (plasma and
  interstitial fluid).
• Kidneys are responsible for making sure the body
  has the correct amount of sodium.
• To be in sodium balance you must EXCRETE the
  amount of sodium you consume each day. (i.e. if
  you ingest 150 mEq of Na, you must excrete 150
  mEq of Na)

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Sodium balance cont.

• What if you excrete less than you consume?
• You would be in POSITIVE Na balance.

Na is retained in ECF
Increased Volume of ECF
Increased BP and possible Edema
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Sodium balance cont.

• What if you excrete more than you consume?
• You would be in NEGATIVE Na balance.

Na is decreased in ECF
Decreased Volume of ECF
Decreased BP
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Sodium balance
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GFR and Na Filtration Load

• GFR 125ml/min x 1440 minutes
• 180 L/day
• In essence, your total Cardiac output (5 L) is
  filtered through the kidneys 36 times a day.
• (180 L / 5 L ) 36 cycles.
• Amount of Na filtered 180 L x Na
• 180 L x 142 mM
• 25,500 mmole/day (or, equal to 1.5 kg of salt)
• (this amount is 9 times the amount of sodium in
  the ECF)
• A typical diet is composed of only 120 mmole of
  Na/day (0.4 of filtered) (BB)
• What this means is, 99.6 of sodium filtered is
  reabsorbed, because we
• will excrete only120 mmole per day, leaving the
  remaining (25,500-120mmol) to be reabsorbed.

p. 774
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Sodium Filtration Load and Sodium Balance
INTAKE

OUTPUT

Fig. 34-1 p.775
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1.
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Sodium Handling ( reabsorption)
1.

• PCT 67 (along with water, isosmotic)
• TAL 25 (impermeable to water)
• Late DCT and Early CT 5 (no water)
• Distal CT 3 (fine tunes Na balance)

(from Fig. 34-2 p. 776)
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What if your GFR increased by 1?

• You would filter 255 mEq/day more of Na.
• (1 of 25,500 mEq)
• What if you didnt reabsorb this extra 255 mEq?
  And excreted it?
• This 255 gets subtracted from ECF compartment. A
  net loss of 255 mEq is highly significant.
• However, this doesnt happen, the nephron has a
  sophisticated way of reabsorbing sodium called
  glomerulotubular balance.

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• Describe the GENERAL mechanism for Na
  reabsorption in various parts of the nephron,
  distinguishing between the active and passive
  steps in the process.
• (see syllabus handout for succinct table of this)

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Sodium can move across the tubule cell layers
through 2 routes
1.
Fig. 34-3 p. 777
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GENERAL MECHANISMS
1. 2.
ACTIVE
Na-K PUMP
PASSIVE
All segments
Fig. 34-3 (B) p. 777
Read pages 775-776.
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Sodium excretion proximal tubule
RMP -70 mV
Na
ADPPi
ATP
Tm substances
ACTIVE
3Na
2K
Na
PASSIVE
H
Na
(various mechanisms)
Cl
Proximal cell
Interstitium
Tubular lumen
Water follows solute (lumen stays
isosmotic) Angiotensin stimulates Na/H
countertransport Site of action of osmotic
diuretics (mannitol, glucose-Tm)
Angiotensin II Acts here
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Sodium excretion thick ascending limb LOH
Na
ADPPi
ATP
K
2Cl
3Na
2K
Na
H
K
K
Proximal cell
Interstitium
Tubular lumen
Luminal side IMPERMEABLE to water. Called
diluting segment generates osmotic
gradient Site of action of loop diuretics
(furosemide, ethacrynic acid)
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Sodium excretion distal convoluted tubule
Na
ADPPi
ATP
Cl-
3Na
2K
K
Proximal cell
Interstitium
Tubular lumen
Luminal side IMPERMEABLE to water. Tubular fluid
is hypotonic Site of action of thiazide
diuretics (hydrochlorothiazide)
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Sodium reabsorption collecting duct
Na
ADPPi
ATP
3Na
2K
K
K
Aldosterone Acts here
Proximal cell
Interstitium
Tubular lumen
Luminal side permeable to water only in presence
of ADH Na reabsorption and K secretion
controlled by Aldosterone Site of action
potassium sparing diuretics (spironolactone,
triamterene)
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Sodium transport

• Most solutes and water are co-transported with Na
  in proximal tubule.
• Water does not always follow solutes
• TAL and DCT are impermeable to water
• These segments create medullary osmotic gradient
  and dilute/concentrate tubular fluid.

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Regulation of Sodium Excretion
Decreased Blood Volume
Decreased blood pressure
Increased Renin- Angiotensin-Aldosterone
Decreased pressure natriuresis
Decrease atrial Natriuretic peptide
Increased sympathetic nervous activation
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• 3. Outline the relationships between vascular
  volume, systemic blood pressure, and the
  excretion of sodium.

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Blood Volume
Atrial natriuretic peptide
Cardiac Output
(decreases renin when high)
Blood Pressure
Sympathetic NS
Renin-Angiotensin-Aldosterone System (RAA)
GFR
Na excretion
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• 4. Define the regulation of release, and
  mechanisms of action of the components of the
  renin-angiotensin-aldosterone system.

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4.
CONTROL OF RENIN SECRETION

• Renin release
• Increased by B1 adrenergic stimulation
• Increased by arteriolar pressure
• Decreased by an increase in ANP

P. 786-787
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Angiotensin-II actions
4.

• Increase aldosterone synthesis/release
• Increase vasoconstriction

Aldosterone release control

• Increased by Angiotenin II
• Increased by high plasma K why?
• Increased by ACTH
• Increased by low plasma Na

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ADRENAL GLAND
Aldosterone Synthesis
Addisons Disease lack of glucocorticoids and
mineralocorticoids -leads to severe
hyponatremia hyperkalemia -circulatory
insufficiency
Conns syndrome Hyperaldosteronism Hypertension
Fig. 49-1
p. 786
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Aldosterone actions
4.

• Increase Na channels in late DCT and CT
  (principal cells)
• Increase H secretion by primary active pump of
  late distal collecting duct.
• Increase K secretion from late distal
  collecting duct (principal cells).

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Regulation of Aldosterone

• Increased angiotensin II
• Increased plasma K
• ACTH exerts trophic effects on adrenal cortex
• Increased ANP decreases aldosterone release

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• 5. Explain how the sympathetic nervous system and
  atrial natriuretic peptide regulate the rate of
  sodium excretion.

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ANP and SNS

• ANP
• Increases Na excretion by
• Increasing GFR
• Decreasing medullary CD Na reabsorption
• Decreasing renin

• SNS
• Decreases rate of Na excretion by
• Decreasing GFR
• Increasing renin

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