D. C. MikuleckyFaculty Mentoring ProgramVirginia Commonwealth Univ.

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Water balanceElectrolyte balancePlasma volumeAcid-base balanceOsmolarity balanceExcretionHormone secretion

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KidneysBlood supply: Renal arteries and

veinsUreterUrinary bladderUrethra

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Bowman’sCapsule

Glomerulus

Proximal ConvolutedTubule

Distal ConvolutedTubule

Loop of Henle

Cortex

MedullaArtery

Vein

Peritubular Capillaries

CollectingDuct

Glomerular Filtration: Filtering of blood into tubule forming the primitive urine

Tubular Reabsorption: Absorption of substances needed by body from tubule to blood

Tubular Secretion: Secretion of substances to be eliminated from the body into the tubule from the blood

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GF

TR

TA

Urine Excreted

Efferent ArterioleAfferentArteriole

Glomerulus

KidneyTubule

Peritubular Capillary

First step in urine formation180 liters/day filteredEntire plasma volume filtered 65

times/dayProteins not filtered

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Glomerular CapillaryBlood Pressure + 55

Plasma Colloid Osmotic Pressure

-30

15

10

Bowman’s CapsuleHydrostatic Pressure

-

Net Filtration Pressure +

Water: 99% reabsorbed

Sodium: 99.5% reabsorbed

Urea: 50% reabsobed

Phenol: 0% reabsorbed

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By passive diffusion

By primary active transport: Sodium

By secondary active transport: Sugars and Amino Acids

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Lumen

Plasma

Cells

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Lumen

Plasma

Cells

PUMP: Na/K ATPase

Sodium

Potassium

Chloride

Water

Stimulates Sodium Reabsorption in distal and collecting tubules

Naturetic peptide inhibits In absence of Aldosterone, 20mg of

sodium/day may be excretedAldosterone can cause 99.5%

retention

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Fall in NaCl, extracellular fluid volume, arterial blood pressure

JuxtaglomerularApparatus

ReninLiver

Angiotensin

+

Angiotensin Angiotensin Aldosterone

Lungs

ConvertingEnzyme

AdrenalCortex

IncreasedSodiumReabsorption

HelpsCorrect

ACE Inhibitors (Angiotensin Converting Enzyme): Cause loss of salt---> water follows

Atrial Naturetic Peptide (ANP) also inhibits sodium reabsorption

Osmotic diuretics: Are not reabsorbed

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They are actively transported across the apical cell membranes of the epithelial cells

Their active transport depends on the sodium gradient across this membrane

All other steps are passive

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Renal threshold (300mg/100 ml)

Plasma Concentration of Glucose

GlucoseReabsorbedmg/min

Filtered Excreted

Reabsorbed

Protons (acid/base balance)

Potassium

Organic ions

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Lumen

Plasma

Cells

PUMP: Na/K ATPase

Sodium

Potassium

Chloride

Water

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Fall in sodium

ECF Volume

Blood Pressure

Increased PlasmaPotassium

Increased Aldosterone secretion

Increased TubularPotassium Secretion

Increased UrinaryPotassium Secretion

Increased TubularSodium Reabsorption

Fall in Urinary

Sodium Excretion

Glucose and Amino Acids67% of Filtered SodiumOther Electrolytes65% of Filtered Water50% of Filtered UreaAll Filtered Potassium

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Variable Proton secretion for acid/base regulation

Organic Ion secretion

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Variable Sodium controlled by Aldosterone

Chloride follows passively

Variable water controlled by vasopressin

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Variable Proton for acid/base regulation

Variable Potassium controlled by aldosterone

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Variable water reabsorption controlled by vasopressin

Variable Proton secretion for acid/base balance

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Medullary countercurrent system

Vasopressin

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Osmotic gradient established by long loops of Henle

Descending limb

Ascending limb

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Highly permeable to water

No active sodium transport

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Actively pumps sodium out of tubule to surrounding interstitial fluid

Impermeable to water

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300

450

600

750

900

1050

1200

1200

From ProximalTubule

To DistalTubule

Cortex

Medulla300

450

600

750

900

1050

1200

1200

100

250

400

550

700

850

1000

1000

ActiveSodiumTransport

PassiveWaterTransport

Long Loopof Henle

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From DistalTubule

Cortex

Medulla300

450

600

750

900

1050

1200

1200

300

400

550

700

850

1000

1100

1200

Interstitial Fluid

CollectingDuct

PoresOpen

Passive Water Flow

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From DistalTubule

Cortex

Medulla300

450

600

750

900

1050

1200

1200

100

100

100

100

100

100

100

100

Interstitial Fluid

CollectingDuct

PoresClosed

No Water FlowOut of Duct

Acute: Sudden onset, rapid reduction in urine output - usually reversible

Chronic: Progressive, not reversible

Up to 75% function can be lost before it is noticeable

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Gravity and peristaltic contractions propel the urine along the ureter

Parasympathetic stimulation contracts the bladder and micturition results if the sphincters (internal and external urethral sphincters) relax

The external sphincter is under voluntary control

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Bladder filling reflexively contracts the bladder

Internal Sphincter mechanically opens

Stretch receptors in bladder send inhibitory impulses to external sphincter

Voluntary signals from cortex can override the reflex or allow it to take place

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