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Renal Handling of Organic

Substances Glucose

Amino acids

Ascorbic acids

Uric acid / Urea

Creatine / Creatinine

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Renal Handling of Inorganic

Substances Sodium : RAAS / other factors

Potassium

Magnesium

Hydrogen

Chloride Bicarbonate

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NEPHRON

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Parts of the Nephron

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PROXIMAL TUBULE

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RENAL THRESHOLD

(Tm / GFR)

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Ultrafiltration is used to transportsubstances from ic to blood utilizing

osmotic or hydrostatic pressure

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PASSIVE TRANSPORTDiffusionFacilitated diffusionOsmosisSolvent drag

ACTIVE TRANSPORTPrimary activeSecondary active

cotransportcountertransport

Endocytosis

EnergyCarrier

Permeability of the membraneElectrochemical gradient

Equilibrium

Saturationenergycarrier

RENAL THRESHOLD

(Tm / GFR)

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Glucose filtration rate = 100 mg/min (Pcx GFR) reabsorption rate = 100 mg/min

site = early portion of the proximal tubule

It is freely filtered, absorbed by secondary active transport co-

transport, the energy is received by Na+s movement into thecell along the gradient. The gradient of sodium is low in the cellbecause of the Na+ K+ pump.

secretion rate = 0 mg/min

excretion rate = 0 mg / min

Tm = 375 mg/min ideal renal threshold = 300 mg/dL (tm / GFR)

actual renal threshold = 200 mg /dL (arterial)

180 mg/dL (venous)

splay

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SGLT 2

PHLORHIZIN

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GLUCOSE

100 % REABSORBED

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Amino Acids

filtration rate --- small amount

reabsorption ---- 100 %

site -- early portion of the proximal tubule

secretion ---- 0

excretion ----- 0

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amino acids

amino acids

amino acids

SIMPLE OR FACILITATED DIFFUSION

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AMINO ACIDS

100 % REABSORBED

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Proteins

peptide hormones, small proteins andsmall amount of albumin

filtration rate = 7.2 g/day (GFR x proteinin the ultrafiltrate)

reabsorption rate = 7.2 g/day

site --- early portion of the proximal tubule secretion rate = 0

excretion rate = 0

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PROTEINS

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PROTEINS

100 % REABSORBED

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Urea filtration rate = 870 mmol/day

reabsorption rate = 460 mmol/day

site -- mainly in the medullary collecting duct

secretion rate = 0

excretion rate = 410 mmol/day (53%)

45/ reabsorbed by diffusion at PT

Its not reabsorbed at thin des and asc LH but secreted

Its is then reabsorbed back at collecting duct through urea transporter a1.

Uta1 is enhanced by ADH

This is called the urea cycle. Urea undergoes this cycle about 6 times before

being excreted.

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UREA

UREA

MAIN SITE OF UREA

REABSORPTION

DIFFUSION

ADH

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Uric acid

filtration rate = 50 mmol/day

reabsorption rate = 49 mmol/day (98%)

secretion rate = 4 mmol/day

excretion rate = 5 mmol/day

Primarily reabsorbed at PT

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Creatinine / Creatine

filtration rate = 12 mmol/day

reabsorption rate = 1 (0) mmol/day (98

secretion rate = 1 (0) mmol/day

excretion rate = 12 mmol/day

Excretion = Filtration Tm = 16 mg/min

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Ascorbic acid excretion rate is regulated by

glomerular filtration

tubular reabsorption

proximal tubule

tubular secretion

distal tubule ( promoted by adrenal steroid and

increased filtered load of sodium)

Tm

- 2 mg/min

Primarily absorbed at PT co-transported with sodium.

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Primarily secreted at PT are bile salts,

catecholamines, urate, oxalate, drugs.

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Potassium Major cation in the cell.

Has to be highly regulated. Regulated by secretion

ECF K+concentration (N = 3.5 - 5.5 meq/L)

ICF - 98%, ECF - 2%

excretion

kidneys - 90 - 95% feces - 5 - 10%

Hyperkalemiacardiac arrest during systole

Hypokalemiaca during diastole

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ICF K+concentration

140 mEq/L X 28 L

3920 mEq

ECF K+

concentration

4.2 mEq/L

X 14 L

59 mEq

K+intake

100 mEq/day

K+output

Urine = 92 mEq/day

Feces = 8 mEq/day

NORMAL K+INTAKE, DISTRIBUTION OF K+IN THE BODY FLUIDS AND OUTPUT FROM THE BODY

Guyton, Medical Physiology, 2006

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filtration rate = 756 mEq/day

reabsorption rate = 644 mEq/day (87.8%)

site -- proximal tubule (65%) and thick ascendong loop of Henle (35%)

Proximal tubule - absorbance by negative chrge

Thick asc LH absorbs by co-transporter.

Secreted at collecting duct and distal tubule in exchange with sodium

by principle cell and reabsorbed in exchange with hydrogen by the

intercalated cell which is stimulated by aldosterone

Potassium sparing drug will inhibit p cell.

secretion rate = 31 mEq/day

excretion rate = 92 mEq/ day

ASCENDING LOOP

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Na+

K+K+ K+

Na+

K+K+

PROXIAML TUBULE

DISTAL TUBULE

COLLECTING DUCT

LUMEN PRINCIPAL CELL INSTERTITIUM

INTERCALATED CELL

NaK+pump

Electrochemical gradient

Permeability of the membrane

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65%

POTASSIUM25 -30%

4%

12%

Increased ECF potassium concentration

Increased aldosterone

Increased tubular flow rate

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Calcium

filtration rate = 540 mEq/day (50%)

reabsorption rate = 530 mEq/day

(98.2%)

site -- proximal tubule



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65%

CALCIUM25 -30%

4 - 9% regulated by PTH

12%

PTH

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CALCIUM or PHOSPHATE

PTH VITAMIN D3

ACTIVATION

CALCIUM RELEASE

FROM BONES

RENAL CALCIUM

REABSORPTION

INTESTINAL

CALCIUM ABSORPTION

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Phosphate

excretion is controlled primarily by an

overflow mechanism

Tm - 0.1 mM/min (renal threshold - 0.8

mM/min) --- decreased by PTH

GFR > Tm ------- excretion of excess PO4-

GFR < Tm ------- complete reabsorption

of PO4-

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Magnesium

involved in many biochemical processes,

activation of enzymes

Primarily reabsorbed at thick ascending

LH

stored in the bones

99 % - ICF, 1% - ECF

50% - bound to proteins

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25%

MAGNESIUM65%

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Hydrogen

secretion of hydrogen is necessary for

both HCO3-reabsorption and formation

of new HCO3-. involves in the regulation of acid - base

balance

Its never reabsorbed but only secreted.

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Bicarbonate

filtration rate = 4320 mEq/day

reabsorption rate = 4318 mEq/day

(99.9%)

site -- proximal tubule, loop of Henle and

distal tubules



REABSORPTION OF BICABONATE

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PROXIMAL TUBULE REABSORPTION1.Active transport of Na+ creates

an intracellular (-) allowing passive

diffusion of Na+

2. H+ is secreted into the lumen by

the Na+ - H+ exchanger

3. H+ combines with the filtered

HCO3- to form H2CO3 and then

CO2 and H2O

4. CO2 diffuses into the cell to

combine with H2O to form H2CO3

then H+ + HCO3-

5. HCO3- returns to the

circulation by a Na+ - 3 HCO3-

cotransporter

REABSORPTION OF BICABONATE

H+ SECRETION

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EXCRETION OF URINARY BUFFERS

H+ secreted combines withnonbicarbonate buffers in the

lumen and is excreted.

H+SECRETION

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SECRETION OF H+ AT THE - INTERCALATED CELL

AT THE CORTICAL COLLECTING DUCT

1. Intracellular H20 and CO2 in the

presence of carbonic anhydrase form

H+ and HCO3-

2. H+ is secreted into the lumen by

an active H+ - ATPase pump.

3. HCO3- returns to the circulation

via a Cl- - HCO3- exchanger.

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85%

BICARBONATE10%

4.9%

1 %

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FATES OF SECRETED H+

1. 90% TITRATES FILTERED BICARBONATE

IN A RECLAMATION PROCESS (H2CO3----- CO2+ H2O)

2. 1% IS BUFFERED BY NH3TO FORM NH4+

3. 1 % IS BUFFERED BY OTHER TUBULAR BUFFERS

MOSTLY HPO4=TO FORM TITRATABLE ACIDITY

4. A VERY MINUTE AMOUNT OF H+ REMAINS FREE

IN THE FINAL URINE

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Sodium

filtration rate = 25,560 mEq/day

reabsorption rate = 25,410 mEq/day

(99.4%)

site -- proximal tubule, loop of Henle, distal

tubules and collecting duct.

secretion rate = 0 mEq/day excretion rate = 150 mEq/ day

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EARLY SEMENT OF PROXIMAL TUBULES

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Overview of Sodium Chloride and WaterTransport: The Loop of Henle

TAL reabsorbsapproximately 25% -30% of filtered NaCl, K,Ca++ and HCO3-

Descending thin limbreabsorbs approx. 15%

of filtered water

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Volume regulation andOsmoregulation

Osmoregulation is achieved by changesin water balance, volume regulationprimarily by changes in sodium balance.

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Volume regulation andOsmoregulation In summary, regulation of plasma osmolality

or osmoregulation is governed byosmoreceptors influencing the release of ADHand thirst.

Changes in effective circulating volume issensed by multiple volume receptors whichactivate effectors such as aldosterone.

ADH increases water reabsorption and

therefore increases urine osmolality but doesnot affect Na+ transport.

Aldosterone enhances Na+ reabsorption butnot directly that of water.

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LATE SEGMENT

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65%

SODIUM25%

9%

1 %

aldosterone

5%

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The proximal tubule

The proximaltubule reabsorbsapproximately67% of the

filtered water, Na,Cl, K and othersolutes.

100% of the

filtered glucose,amino acids

Also secretesorganic cations

and anions.

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RENAL IV

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